Wind Waves and Weather

FEIEX

-

Rotary Drilling Series Unit V J Lesson 1

Wind, Waves, and Weather Third Edition

THE UNIVERSITY OF TEXAS AT AUSTIN PETROLEUM EXTENSION SERVICE

PETEX

ROTARY DRILLING SERIES \.'

-Unit I: The Rig and Its Maintenance

Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson 7: Lesson 8: Lesson 9: Lesson TO:

The Rotary Rig and Its Components The Bit Drill String and Drill Collars Rotary, Kelly, Swivel, Tongs, and Top Drive The Blocks and Drilling Line The Drawworks and the Compound Drilling Fluids, Mud Pumps, and Conditioning Equipment: Diesel Engines and Electric Power The Auxiliaries Safety on the Rig

Unit II: Nonnal Drilling Operations Lesson T: Lesson 2: Lesson r Lesson 4: Lesson 5:

Making Hole Drilling Fluids Drilling a Straight Hole Casing and Cementing Testing and Completing

Unit III: Nonroutine Operations Lesson T: Lesson 2: Lesson 3:

Controlled Directional Drilling Open-Hole Fishing Blowout Prevention

Unit IV: Man Management and Rig Management

Unit V: Offshore Technology Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson 7: Lesson 8: Lesson 9: Lesson 10:

Wind, Waves, and Weather Spread Mooring Systems Buoyancy, Stability, and Trim Jacking Systems and Rig Moving Procedures Diving and Equipment Vessel Inspection and Maintenance Helicopter Safety and Survival Procedures Orientation for Offshore Crane Operations Life Offshore Marine Riser Systems and Subsea Blowout Preventers

ROTARY DRILLING SERIES Unit V, Lesson 1

.-

Wind, Waves, and Weather Third Edition

By Ron Baker

Published by FETEX PETROLEUM EXTENSION SERVICE

Continuing & Extended Education The University of Texas at Austin Austin, Texas

in cooperation with

INTERNATIONAL ASSOCIATION OF DRILLING CONTRACTORS Houston, Texas

204

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\'"

Library of Congress Cataloging-in-Publication Data

Baker, Ron, 1940-Wind, waves, and weather / William R. Baker.- 3rd ed.

p. em. - (Rotary drilling series; unit 5, lesson 1) ISBN 0-88698-212-X (alk. paper) 1. Offshore oil well drilling-Environmental conditions-Safety measures. 2. Offshore gas well drilling-Environmental conditionsSafety measures. 3. Marine meteorology. 1. Title. II. Series. TN871.3.B3S 2004 622'.3 381 9-dc22 2004008111

2004 by The University of Texas at Austin All rights reserved First Edition published 1977. Second Edition 1984. Third Edition 2004. Second Impression. Printed in the United States of America This book or parts thereof may not be reproduced in any form without permission of Petroleum Extension Service, The University ofTexas at Austin.

Brand names, company names, trademarks, or other identifying symbols appearing in illustrations and!or text are used for educational purposes only and do not constitute an endorsement by the author or the publisher.

Catalog no. 2.50130 ISBN 0-88698-212-X

No state tax funds were used to publish this book. The University ofTexas at Austin is an equal opportunity employer.

Figures v Contents Preface Vll

....

Acknowledgments IX ....

Units of Measurement x ....-

Introduction I

Wind 3 Latitude and Longitude 3

Angle of the Sun's Rays 4

Insolation 5 Atmospheric Pressure 6

Coriolis Force IO

Prevailing Winds 12

Winds of the Upper Troposphere 15 Measurement 15 Reporting 17 To summarize 26

Waves and Sea States 29 Waves 29

32Currents

34Tides

37Observation

4 To summarize 48 Reporting

Weather 51 Climate versus Weather 51 Air Masses 52

Fronts 53 Northers 55 Clouds 56 Fog 62 Sea Ice 64

Cyclones 65 Waterspouts 68

Weather Observation 70

111

Reporting

To summarize

"-

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Offshore Operations

Drilling Units

Fixed Rigs 87 Regulating Agencies 89 Wind, Waves, and Weather Effects

To summarize 108

Glossary I I I

Review Questions 135

Answers 143

IV

1. Offshore operations are being carried out over a large part of the earth. Figures

2.

3. 4. 5. 6. 7. 8. 9.

10. I I.

12.

13. 14. IS. 16. 17. 18. 19. 20.

2 I.

22. 23. 24. 25. 26.

27. 28.

29 3 31. p.

33 34 35 36.

Operations in the hostile environment of Alaska 2 Radiation pattern in the earth-atmosphere system 5 T

TBasic hydrological cycle 7 TAverage atmospheric pressure at the earth's surface 9

Effect of Conolis force on masses in motion 10 Circulation of the air in the Northern Hemisphere I I Simplified general circulation of the prevailing winds 12 A cup anemometer 16 Awind rose 18 Wind warning displays on the United States coastline 2 I Weather map showing fronts and pressure patterns 22 Wind direction and speed symbols 23 Sea, fetch boundary, and swell 29 Wave description 30 Prevailing ocean currents 32 The sun-earth-moon tidal force system 36 Beaufort scale with sea characteristics 40 Beaufort numbers O-TO 41-42 Page from Worldwide Radiofacsimile Broadcast Schedules for Kodiak, Alaska 45 Satellite image of clouds in the Gulf of Mexico, Caribbean, and South Atlantic Ocean 47 National Weather Service Internet sites 47 U.S. Navy and other weather Internet sites 47 Air mass source regions 52 Cross section of froms 53 Common types of clouds organized according to their heights in the sky 56 Cirrus clouds 57 Cirrostratus clouds Cirrocumulus clouds Altostratus clouds Altocumulus clouds Mamma 59 Stratus clouds 60 Nimbostratus clouds

57 58

58 59

60 Stratocumulus clouds 61 Cumulus clouds 61

v

-Table T T T

37. Cumulonimbus clouds 62 38. Wind moves counterclockwise around a cyclonic system

in the Northern Hemisphere. 65 39. Pilot chart containing storm tracks representing average

cyclonic acti,,;ty for the month ofJuly 66 40. Waterspout over Big Pine Key, Florida 68 4l. Astandard thermometer 70 42. An aneroid barometer 7I 43. A digital hygrometer 7l 4+ Asling psychrometer 72 45. A hurricane track supplied by a contract weather service 46. A jackup drilling rig 84 47- A semisubmersible drilling rig 85 48. A drillship 86 49. A fixed platform rig 87 50. A tension-leg platform rig 88 5I. The Coast Guard icebreaker Polar Star working the ice

channel near McMurdo, Antarctica 93 52. A mobile arctic caisson rig 94 53. An iceberg floats in the North Atlantic somewhere off the

coast of Greenland 95 54. Helicopters transport personnel to and from offshore rigs. I02 55. Boats carry personnel and equipment to and from the rig. I04 56. A personnel basket transfers personnel from a rig to a boat. l04 57. A covered lifeboat l05 58. An escape capsule I06

I. Beaufort Scale with Corresponding Wind Speeds

V1

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L

78

\:" Preface-

For many years, the Rotary Drilling Series has oriented new personnel and further assisted experienced hands in the rotary drilling industry. As the industry changes, the manuals in the series are updated and revised to reflect those changes. Wind, Waves, and Weather is Lesson 1ofUnitV in the Offshore Technology section of the Rotary Drilling Series.

The purpose of this manual is to acquaint offshore personnel with the environment they will encounter as they work in the oceans, seas, and gulfs of the world. As in the Second Edition, the first part of the book covers basic meteorology and oceanography, as well as the observation and reporting of environmental conditions. The second part discusses the types of offshore rigs and platforms, regulating agencies ofrigs and equipment, the effects of the environment on offshore operations, and safety procedures that should be followed in severe weather and sea conditions.

The layout has been changed to make the information easier to take in, the study questions have been rewritten, and each major section has been summarized to provide a handy, comprehensive review for the reader.

The PETEX Advisory Board wishes to thank industry reviewers-and our readers-for invaluable assistance in the revision of the Rotary Drilling Series.

Although every effort was made to ensure accuracy, this manual is intended only as a training aid; thus, nothing in it should be construed as approval or disapproval of any specific practice or product.

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V1I

Acknowledgments-

T he United States Department ofCommerce's National Oceanic and Atmospheric Administration (NOM) provides a tremendous amount of useful and essential information about weather in the United States and the world. Moreover, the National Weather Service (NWS), which is part ofNOM, disseminates huge quantities ofweather and climate information. Anyone interested in marine and offshoreweather should be aware of these services, which are free to the public. Perhaps the best way to obtain this information is to log on to NOM's World Wide Web site at www.noaa.gov. NOM's Web site has dozens of links to other Web pages of weather-related interest. In any case, this manual owes a great deal to the information provided by NOM and its departments. PETEX is also grateful to the United States Coast Guard (USCG), which publishes and distributes a wealth of free information germane to offshore petroleum operations. Indeed, PETEX recognizes and thanks the USCG for the photo of the ice breaker and the iceberg (pp. 93, 95)' For more about the ~oast Guard, log on to their Web site at www.uscg.mil.

PETEXwould also like to thankPlymouth State University's Weather Center in Plymouth, New Hampshire, for their kind permission to use the center's excellent cloud photos (http:// vortex.plymouth.edu/clouds.html). For the pictures of the Beaufort sea states, PETEX extends thanks to the National Weather Service in Chicago. PETEX is also grateful to Weems & Plath for the photo of the aneroid barometer, to GE Protimeter for the picture of the digital hygrometer, and to Red Alert Australia's Escape Craft Training Center at Barry Beach for the photo of the escape capsule.

A special thanks goes to Thomas Payne, trainer of nautical science at Diamond Offshore Drilling, Inc., who took on the project ofreviewing this book for accuracy and pertinent information, and who did so quickly and ably.

IX

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, Units of Measurement T T T

Throughout the world, two systems of measurement domi': nate: the English system and the metric system. Today, the United States is one of only a few countries that employs the English system.

The English system uses the pound as the unit ofweight, the foot as the unit oflength, and the gallon as the unit of capacity. In the English system, for example, I foot equals I2 inches, I yard equals 36 inches, and I mile equals 5,280 feet or I,760 yards.

The metric system uses the gram as the unit of weight, th~ metre as the unit of length, and the litre as the unit of capacity. In the metric system, I metre equals ro decimetres, roo centimetres, or I ,000 millimetres. A kilometre equals I ,000 metres. The metric system, unlike the English system, uses a base of roj thus, it is easy to convert from one unit to another. To convert from one unit to another in the English system, you must memorize or look up the values.

In the late I970S, the Eleventh General Conference on Weights and Measures described and adopted the Systeme International (Sn d'Unites. Conference participants based the SI system on the metric system and designed it as an international standard of measurement.

The Rotary Drilling Series gives both English and SI units. And because the SI system employs the British spelling ofmany of the terms, the book follows those spelling rules as well. The unit oflength, for example, is metre, not meter. (Note, however, that the unit of weight is gram, not gramme.)

To aid U.S. readers in making and understanding the conversion to the SI system, we include the following table.

x

EngJish-Units-to-SI-Units Conversion Factors Quantity Multiply

or Property English Units English Units By

-

Length, depth,

or height

inches (in.)

feet (ft) yards (yd) miles (mi)

254 254 0.3048 0.9 144

169344 1.61

Hole and pipe diameters, bit size inches (in.) 254 Drilling rate feet per hour (ftlh)

Weight on bit pounds (1b) 0445 Nozzle size 3mds of an inch 0.8

barrels (bbl) 0.159

Volume

gallons per stroke (gaVstroke) ounces (oz)

cubic inches (in.J) cubic feet (ft3)

quarts (qt) gallons (gal) gallons (gal)

pounds per barrel (1bfbbl) barrels per ton (bbVtn)

159 0.0379

2957 16.387 28,3 169 0.0283 0.9464 3-7 854 0.00379 2.895 0.175

Pump output and flow rate

gallons per minute (gpm) gallons per hour (gph)

barrels per stroke (bbVstroke) barrels per minute (bbVmin)

0.00379 0379 0.159 0.159

Pressure pounds per square inch (psi) 6.895 0.006895

Temperature degrees Fahrenheit (OF) OF - 32 1.8

Thermal gradient

Mass (weight) ounces (oz) pounds (1b)

tons (tn) pounds per foot (1b/ft)

28,35 45359

0.453 6 0.97 2 1.488

Mud weight pounds per gallon (ppg) pounds per cubic foot (1b/ft3)

Pressure gradient pounds per square inch per foot (psi/ft) 22.621

Funnel viscosity seconds per quart (s/qt) 1.57

To Obtain These 51 Units millimetres (mrn) centimetres (cm)

metres (m) metres (m) metres (m)

kilometres (Ian) millimetres (mm)

metres per hour (mIh) decanewtons (dN) millimetres (mm) cubic metres (m3)

litres (1) cubic metres per stroke (m3/stroke)

millilitres (mL) cubic centimetres (cm3)

litres (1) cubic metres (m3)

litres (1) litres (L)

cubic metres (m3) kilograms per cubic metre (kg/m3)

cubic metres per tonne (m 3/t) cubic metres per minute (m3/min)

cubic metres per hour (m3/h) cubic metres per stroke (m3/stroke) cubic metres per minute (m3/min)

kilopascals (kPa) megapascals (MPa)

degrees Celsius Cc) 1C per 33 metres

grams (g) grams (g)

kilograms (kg) tannes (t)

kilograms per metre (kg/m) kilograms per cubic metre (kg/m3) kilograms per cubic metre (kg/m3)

kilopascals per metre (kPalm) seconds per litre (slL)

pascals (Pa) pascals (pa)

millimetres (mm) kilowatts (kW)

square centimetres (cm2) square metres (m2) square metres (m2)

square kilometres (km2) hectare (ha)

megajoules (M]) tonne-kilometres (telan) newton metres (Nem)

Yield point Gel strength

Filter cake thickness Power

Area

Drilling line wear

Torque

pounds per 100 square feet (lblroo ft2) pounds per 100 square feet (Iblroo ft2)

32 nds of an inch horsepower (hp)

square inches (in.2) square feet (ft2)

square yards (yd2) square miles (mi2)

acre (ac) ton-miles (tnemi)

foot-pounds (ftelb)

0.8 07 645 0.929 0.8361 259 04

14317 1.459

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- Introduction T T T

Oil companies drill for oil and gas in oceans and seas all over the world (fig. I). No matter where an offshore rig operates, weather affects it. In some places, reasonably clement weather occurs most of the time. But, even in moderate climates, severe thunderstorms and hurricanes or typhoons can occasionally wreak havoc. And, where badweather prevails, as in the North Sea, offthe east coast of Canada, and in Alaska (fig. 2), it is a constant threat. Thus, offshore oil companies and drilling contractors pay a great deal of attention to the weather and its effect on personnel and equipment.

ARCTICARCTIC OCEANOCEAN

NORTH ATLANTIC

NORTH OCEAN PACIFIC OCEAN

INDIAN OCEAN

SOUTH SOUTH PACIFIC ATLANTIC OCEAN OCEAN

Figure I. Offshore operations are being carried out over a large part ofthe earth.

I

WIND, WAVES, AND WEATHER

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Figure 2. Operations in the hostile environment ofAlaska (Courtesy ofUnited States Coast Guard)

Allover the world, 24 hours a day, meteorologists who study the weather use sophisticated instruments, computers, and satellite imagery to observe the weather. They interpret their observations and report current weather conditions to everyone. Moreover, they issue forecasts and warn ofhazardous weather. Most of these services are free. Sometimes, however, a company may pay for detailed weather forecasts for specific areas, but such services are not costly and are usually worth the expense.

When operators and contractors are ready to drill on a site, they consider many factors besides weather. However, because the local weather affects tides, currents, winds, and wave heights, the weather is a vital factor. Weather and environment playa big role in the type of rig companies choose and how to outfit it. After drilling begins, supervisorypersonnel keep aclose watch on weather forecasts to avoid surprises, which can be very costly. Adverse weather can destroy rigs and harm personnel. Thus, rig supervisors study a weather report at least once a day. When large systems or fronts threaten the rig, they check forecasts more often. Being aware of the weather and taking appropriate precautions can save time, money, and, most important, the lives of rig personnel.

The first part of this lesson covers wind, wave, and weather infonnation crucial to offshore rig operations. The second part covers rig types, regulatory agencies that govern rig design and operation, and safety procedures for severe weather.

2

.'". Wind-

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The sun radiates, or gives off, energy that strikes the earth. Much ofthis energy is in the form oflightand heat. This solar energy, however, does not affect areas ofthe earth equally. Instead, the sun heats the earth's surface unevenly. For example, the Arctic and Antarctic receive less solar energy than the equator. Because the earth's axis is tilted in relation to the sun, solar energy hits polar areas at an angle. The poles do not get as much solar energy as the equator, where the sun's energy strikes head on. Therefore, it is cold at the poles and hot in the tropics. Scientists call this temperature difference differential heating.

Another factor in differential heating is that some regions on earth absorb more heat than others. For example, because polar regions are covered with ice, they reflect a great deal of heat back into the air. On the other hand, tropical areas, with their massive amounts of dark green foliage, absorb more heat than they reflect. Thus, the sun heats the earth unequally. Consequently, the earth heats the air in its atmosphere unequally. The resultant mixture of warm and cool air in the atmosphere causes wind. Wind is the horizontal movement of air in the earth's atmosphere.

The sun showers the earth with shortwave radiation. This shortwave radiation, or energy, is visible as light, and it provides heat. As stated before, the angle at which the sun's rays strike the earth affects the amount ofheat received by areas on the earth. To understand the effect, it also helps to understand latitude and longitude.

Geographers divide the earth into imaginary lines oflatitude and longitude. Latitude is an imaginary line joining points on the earth's surface that are all of equal distance north or south of the equator. Longitude is the angular distance east or west ofthe prime meridian that stretches from the North Pole to the South Pole and passes through Greenwich, England. The prime meridian is the line of longitude that is 0 degrees (0). All other longitudes are measured either east or west of the prime meridian. For example,

Latitude and Longitude

3

WIND. WAVES. AND WEATHER

the latitude and longitude ofNewYork City is approximately400N latitude and 73E longitude. Chicago is approximately 900E lati

-tude and 4ION longitude. In short, lines of latitude nm parallel north and south of the equator, and lines oflongitude run parallel east and west of the prime meridian.

Angle of the The sun heats the earth the most where it is directly, or nearly directly, overhead. The area that receives the most heat is betweenSun's Rays the Tropic of Cancer and the Tropic of Capricorn. The Tropic of Cancer is an imaginary line around the earth at 23'So north latitude. That is, it is 23'SO north of the equator. (The equator is 0 latitude.) The Tropic of Capricorn is at 23'So south latitude, or 23. SO south of the equator. Geographers usually report latitude as a given number of degrees north of the equator or south of the equator. They abbreviate north as N and south as S. Thus, they denote the Tropic ofCancer as 23.SoN latitude, which means that it is 23'SO north of the equator. The Tropic ofCapricorn is 23.SoS latitude, or 23. SO south of the equator.

Geographers further divide degrees oflatitude and longitude into smaller units of minutes and seconds. Sixty minutes are in 1 and 60 seconds are in I minute. Therefore, when stating the latitude of the Tropic of Cancer, for example, it can be written as 23. So, or 23 0, 30 minutes, seconds. Also, geographers sometimes express longitude in degrees of are, minutes of arc, or seconds of arc. An arc is simply a section of a circle, an ellipse, or other curved figure. In the case of the earth, an arc is a section of a circle from the earth and is equivalent to longitude.

The earth rotates on an axis of 23.So in relation to the plane of its orbit. This tilt accounts for the seasons of spring, sununer, fall, and winter as the earth orbits around the sun. In the Northern Hemisphere, which is the half of the earth that is north of the equator, the sun is directly over 23. SON latitude about June 2I. Thus, June 2I is the first day ofsummer. Fall begins when the sun is directly over the equator (0). The sun assumes this position about September 2I.The sun is directly over 23.SOS latitude about December 2I; at this time, winter begins in the Northern Hemisphere. The sun is again directly over the equator (0) about March 21. March 21 marks the beginning of spring in the Northern Hemisphere.

In the Southern Hemisphere, which is the half of the earth south of the equator, summer-winter and spring-fall are reversed with respect to the Northern Hemisphere. Thus, when it is winter in Europe, for example, it is summer in South America.

4

WIND

Insolation is the technical term for the shortwave solar radiation the earth's surface receives. Simply put, insolation is sunlight. The earth may absorb, refract, or refieetinsolation depending on what the

- insolation encounters (fig. 3). For example, the atmosphere absorbs some ofthe insolation, or radiation. Clouds, water, and land absorb some of it, too. Also, clouds, air, or water refract, or bend, some of the insolation. Refraction occurs when the sun's rays travel through areas of different density. The density change causes a speed change. Finally, clouds, ice, snow, water, and land reflect some of the-insolation.

Absorption occurs when the earth retains shortwave energy. Different regions ofthe earth absorb different amounts ofenergy. As mentioned earlier, green tropical plants surround the equator. Consequently, maximum absorption of the sun's energy occurs near the equator. The oceans, which comprise about 7 I percent of the earth's surface, also absorb large quantities ofheat. In between the tropics and the poles lie temperate zones, which absorb varied amounts of energy. The poles absorb little of the sun's energy.

REFRACTED INSOLATION FROM SUN SHORTWAVE

RADIATION FROM ABSORBED REFLECTEDSUN IN ATMOSPHERE FROM EARTH \, t ~ ~ y \. ..... I \ REFLECTED FROM L

CLOUDS ' I \ \ , (I

~~N~/--./ ~

CLOUDS \\ Jg" ~ (,-- - '"'- '? 5'~ c


Light-colored areas, such as snowy polar regions, smooth-water surfaces, and cloud tops, do not absorb shortwave radiation.

-

Instead, they reflect it toward the sun in the form of long-7vave radiation. Long-wave radiation is invisible and less intense than shortwave radiation. Bodies considerably cooler than the sun that receive the sun's energy, such as the earth, emit long-wave radiation rather than shortwave radiation. About 43 percent of the insolation is reflected with no effect on the earth's atmosphere.

Atnight, the earth returns large amounts ofheat energy in the form of long-wave radiation to space. Because the earth gives back heat energy at night, surface temperatures cool. Because ofnighttime cooling, the earth does not become so hot as to make life impossible. At the same time, however, the earth's atmosphere retains some of the heat and sends it back to earth. This phenomenon that scientists call the greenhouse effect, is most pronounced when a cloud cover exists. The clouds reflect the heat and reduce night cooling. Therefore, when clouds exist at night, the temperature differences between night and day are not very great.

Two forms ofmoisture are in the atmosphere. This moisture is either water vapor or cloud layers. Both prevent our environment from being hostile. Water vapor is water in its gaseous, or vaporous, form. It is invisible. Cooling or compressing water vapor liquefies it and makes itvisible. Water vapor retains and transports a great deal of heat and energy. Meteorologists describe this retention and transport ofwater vapar as the hydrologic cycle. Water in the form of precipitation (rain, snow, sleet, etc.) falls to earth, where plants, land, and bodies of water retain it for a time. Then, the water evaporates into the atmosphere, and eventually falls again as precipitation (fig. 4)'

Atmospheric When the sun heats the earth's surface, the surface heats the air Pressure above it; however, the amount of heating varies with the surface's

characteristics. Thus, unequal heating occurs. The unequal heating of the earth unequally heats the air in the atmosphere. Land surfaces heat up and cool offfaster than water surfaces. Therefore, we experience greater daily ranges of temperatures over land than over water.

Warm air in the atmosphere expands, becomes lighter, and rises. Cool air contracts, becomes denser, and moves downward. Warm air lying over cool air eventually cools, moves downward, and replaces the cool air. The warm and cool air in the atmosphere exerts pressure over the surface of the earth. This pressure is

6

WIND

OCEAN

SURFACE RUNOFF

Figure 4. Basic hydrological cycle

atmosphericpressure, or barometricpressure, because weather observers use an instrument called a barometer to measure it.

Warm air that expands and rises in the atmosphere forms a low-pressure area. The pressure is lower in warm air than in cool air because warm air is lighter, or less dense, than cool air. Cool air that contracts and moves downward in the atmosphere forms a high-pressure area. The pressure is higher in cool air because cool air is heavier, or denser, than warm air.

The rotation ofthe earth causes these low- and high-pressure areas to move and circulate. This circulation of air creates wind and other weather phenomena. Air travels from a high-pressure area to a low-pressure area. Meteorologists call the air thatmovesthe winds-around a low-pressure area cyclonic. Winds that move around a high-pressure area are called anticyclonic.

7


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In 1857, a Dutch meteorologist named C.H.D. Buys-Ballot observed that if a person in the Northern Hemisphere stands facing the wind, the pressure to the person's right is lower than to the left. The reverse is true in the Southern Hemisphere. Meteorologists later termed this phenomenon Buys-Ballot's law, or the baric wind law.

Manufacturers usually calibrate barometers to measure the weight of a column of air above a given area. Thus, they can calibrate barometers to measure atmospheric pressure in inches of mercury, in millibars, or in kilopascals. Inches of mercury is the English, or conventional, system unit; millibars is the conventional metric system unit; and kilopascals is the SI metric unit. (SI stands for Systeme International d'Unites, a measurement system based on metric units that members attending the Eleventh General Conference on Weights and Measures described and adopted in the 1970s.)

In conventional units, standard atmospheric pressure is 29.92 inches of mercury. This statement means that, at a standard temperature, the atmospher-e presses on the end of a tube full of mercury with enough force to make it rise 29.92 inches. Standard temperature for atmospheric pressure measurement is usually 60 Fahrenheit or 15.5 Celsius. A barometric pressure of29.92 inches of mercury equals 1,013.25 millibars or 101.33 kilopascals. Normal surface pressure ranges from a low of 28.05 inches ofmercury (950 millibars or 95.0 kilopascals) to a high of 31.01 inches of mercury (1,050 millibars or 105.0 kilopascals).

In the northern Gulf of Mexico, average atmospheric pressure reaches a minimum of 29.97 inches of mercury (1,015 millibars or 101.5 kilopascals) in the summer months. In the winter months, average atmospheric pressure reaches a maximum of 30. I 5 inches of mercury (1,02 I millibars or 102. I kilopascals). Figure 5 shows average atmospheric pressure at various places in the earth's surface, in winter and in summer. For example, in the Atlantic Ocean near Iceland, aJanuary low-pressure area measures 995 milllibars. In July, this low-pressure area measures 1,010 millibars. Warm air is denser than cold air and therefore exerts higher pressure than cold air. As a rule, highs reach theirmaximum development in summer, lows in winter.

Incidentally, another way ofmeasuring atmospheric pressure in English units is in pounds per square inch. At sea level, the air puts about 14.7 pounds ofpressure on a square inch of the earth's surface. This 14.7 pounds per square inch (psi) is often referred to as I atmosphere (atm).

8

30'

60'-'----'-""--....L---l..-L-..l..----L....---J-..........L-....L---l..---'-.L..-...J....--l.._L-....L--L---L_..L-....L---l-.-J--l60 120' 150' 180' 150' 90' 60' 30' O' 30' 60' 90'

UNITS ARE MILLIBARS PLUS 1,000 JANUARY

120' 150' 180' 150' 120' 90' 60' 30' O' 30' 60' 90'

120' 150' 180' 150' 120' 60' 30' O' 30' 60' UNITS ARE MILLIBARS PLUS 1,000 JULY

Fip;ure 5. Average atmospheric pressure at the earth's suiface (millibars + 1,800)


Coriolis Force The earth's rotation deflects air and objects that are moving from north to south or south to north on the earth's surface. Scientists

-

call this rotational deflection Coriolis force-an apparent force caused by the rotation of the earth about a vertical axis. Coriolis force is named after a French civil engineer, Gustave Gaspard Coriolis, who described this phenomenon in 1835. Coriolis force affects wind direction in both the Northern and Southern hemispheres. It causes wind or water in motion to move clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere (fig. 6).

NORTH POLE

:- ---\-:-\~~~'-' \ ~- \ -'\.'._- \

, \ \. ,

~ i ,- -: -- _: --~-~~-~~--l- '\ LK ' EQUATO~ I ' -~ ...J!~~ -,c -~ - ~i-~tT \ __ \.~._\~ - - . ~ I ! " _._-';'--1~.-\~ -'_"--_\~_ - ~---y-:L----!--:'--J-

SOUTH POLE

Figure 6. Effect ofCoriolis force on masses in motion

In the Northern Hemisphere, air moves in a clockwise direction around high-pressure areas. Air moves in a counterclockwise direction around low-pressure areas (fig. 7). In the Southern Hemisphere, Coriolis force moves air counterclockwise around high-pressure areas and clockwise around low-pressure areas.

Coriolis force has no effect on wind at the equator. Its effect increases in the middle latitudes and reaches a maximum at the poles. Coriolis force increases as wind speed increases. The speed of the wind is determined by the intensity of the high pressure or low pressure. In general, the higher or lower the pressure is, the greater are the winds.

10

WIND

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A

B

Figure 7. Circulation ofthe air in the Northern Hemisphere: (A) clockwise around a high-pressure area; (B) counterclockwise around a low-pressure area

Centrifugal force and gravity also affect winds. (Centrifugal force is the force that tends to pull all matter from the center of a rotating mass. Gravity is the attraction exerted by the earth's mass on objects at its surface.) Centrifugal force and gravity work in opposition. Centrifugal force pushes objects (or mass) away from the earth's axis of rotation. This rotational force has shifted the earth's mass so that the earth is not spherical. Instead, earth is an oblate spheroid. That is, earth's diameter through the poles is less than its diameter through the equator. Because of this asymmetrical geometry, a component of gravity is directed toward the poles. Similarly, a component of the centrifugal force acts towards the equator.

II


Heating, cooling, and Coriolis force produce prevailing winds.Prevailing Winds Prevailing winds occur in the lower troposphere. The troposphere is the part of the atmosphere that extends from the surface to about

- 6to 12 miles (10 to 20 kilometres). Prevailing winds (fig. 8) are wind patterns that persist throughout the year with some seasonal modification. For example, in the southern U.S., summertime winds most often blow from the southeast. Thus, the weather observers in this area say that the prevailing winds are southeasterly.

Meteorologists classify prevailing winds as suiface winds. Surface winds are winds that a person can measure at a surface observing station. Weather reports always indicate surface wind direction as blowing, or coming, from a given direction. For example, a northeast wind blows from (or comes from) the northeast.

Reports generally give wind speeds in knots. A knot is nautical mile per hour. A nautical mile is based on the length of a minute of arc of agreat circle of the earth. (A great circle is a circle, or anear circle, that aplane passing through the center of the earth

... ~,.~~ , Trade Winds

, ..-..~""

.. '7:-'::--'' ..... j Prevailing Westerlies

....../ Polar SoutheasterIies

SOUTH POLE

Figure 8. Simplified general circulation ofthe prevailing winds

12

I

WIND

-

describes on the earth's surface.) A nautical mile is different from a statute mile. Astatute mile is what most people in the U.S. think ofwhen they think ofa mile's distance. Astatute mile equals 5,280 feet (1,69,344 metres). A nautical mile equals 6,076.II5 feet (1,852 metres). One knot equals 1.143 statute miles per hour. Note that a knot is an acceptable unit of measure in the SI system.

Starting at the North Pole and moving south, meteorologists name Common Prevailing and describe several prevail}ng winds. Winds

Arctic polar northeasterlies. These north polar winds blow from the northeast and meet prevailing westerlies near 600N latitude. The polar northeasterlies ordinarily do not blow at high speeds.

NorthTemperate Zone prevailingwesterlies. These winds blow between latitudes 300N and 600N. They blow from the southwest at speeds of about 10 to 18 knots in the summer and 25 to 30 knots in the winter.

Northeast and southeast trade winds. The northeast trade wind blows between the equator to 300N latitude. The southeast trade wind blows between the equator to 300S latitude. Early mariners named them trade winds because they used them to sail the world as they trans

ported people and supplies from continent to continent. The northeast and southeast trade winds are the most constant winds on earth. They are stronger in the winter months than in the summer months. An intertropical con

vergence zone (ITCZ) divides the trade winds into an area of low pressure that moves northward during the Northern Hemisphere's summer season and southward during the Southern Hemisphere's summer season. The ITCZ never moves farther than 15 latitude north or south. Although cyclonic storn1S (hurricanes and typhoons) usually do not travel into trade wind regions, they frequently form there.

SouthTemperate Zone prevailingwesterlies. These northwest winds circulate between latitudes 300S and 600S. They blow throughout the year at 18 to 30 knots.

Antarctic polar southeasterlies. These south polar winds meet the prevailing westerlies near 600Slatitude. The polar southeasterlies maintain a strong wind speed throughout the year. In this area, winds ofover 64 knots are common, and wind speeds can reach 200 knots.

13


Monsoons Monsoons affect prevailing winds. Monsoons are large-scale seasonal wind systems that strongly influence the climate of the area in which they occur. Monsoon winds reverse direction in the

- winter and summer months. The large temperature differences between land and sea cause them to occur. As stated earlier, land surfaces have faster rates of heating and cooling and a greater variation of temperatures than water surfaces. Because the land is cool in winter, high-pressure air dominates. Similarly, because the land is warm in summer, low-pressure air dominates.

In winter, cool, high-pressure air intensifies as it moves over land. This cool air evenhlally meets wann, low-pressure air over the warm oceans. When high-pressure air meets low-pressure air, strong winds result, frequently reaching speeds of 3S knots. These winter monsoon winds exhibit little or no rainfall. Consequently, meteorologists sometimes call them dry monsoons.

In the summer months, warm, low-pressure winds reverse and travel back over the oceans, meeting warm, low-pressure airon land. Warm air on land intensifies the low-pressure air. Summer monsoons are usually characterized by heavy rainfall. Thus, meteorologists sometimes refer to them as wet monsoons. High humidity and large differences in temperature between land and surrounding oceans may cause a monsoon fog to occur.

Monsoons have little or no effect in polar regions and in areas surrounding the equator, because temperatures of the land and water are similar in these areas. Monsoons are common in southern Asia, northern Australia, North and South America, and parts of Africa.

The greatest monsoons occur in southern and southeastern Asia. During the winter months in these areas, the northeast monsoon transports cold, dry air from the Siberian High across the Himalaya Mountains. Some air is trapped by the mountain range, but the rest of the air continues to the sea. The cold air meets the warm air over the ocean, and light rainfall may occur.

,

I I

In southern Asia's summer and early fall, the high-pressure I '-'.

winds ofthe southwestmonsoon move inland. Thesewinds extend the southeast trade winds to southern Asia while overpowering the r'1 low-pressure northeast trade winds that usually reside there. This shift in wind direction changes the direction of underlying ocean currents. The winds of the southwest monsoon become extremely warm and humid as they pass over tropical oceans toward cooler air on land. Clouds, heavy showers, and thunderstorms characterize the southwestmonsoon. For five months ofthe year, this monsoon brings constant rain to the southern slopes of the Himalaya Mountains. The annual rainfall for this area is about 400 inches (1,016 centimetres), the highest rainfall in the world. (This amount of rainfall is equal to more than 33 feet or 10 metres.)

No set boundary divides the upper and lower troposphens. However, many meteorologists accept the idea that the upper troposphere starts at an altitude of 18,000 to 19,000 feet (about 5.5 to 5.8 kilometres) and extends to about 50,000 feet (about 15 kilometres). Low- and high-pressure areas control the surface winds in the lower troposphere (especially in the middle latitudes). However, winds in the upper troposphere are less variable. From 20 north and south latitudes to 60 north and south latitudes, upper troposphere winds are strong and westerly. Weak easterly winds exist near the equator and near the poles.

Also present in the upper troposphere are narrow, long paths of high winds called jet streams. Jet streams usually lie at altitudes of35,000 to 40,000 feet(lo.5 to 12 kilometres) and travel fromwest to east. These winds may reach speeds as high as 300 knots.

Weather observers measure surface winds at a surface observing station. They make their measurements near the ground, typically at an elevation of 10 metres (32.8 feet) or above any obstructions that might affect the flow of the wind.

WIND

Winds of the Upper Troposphere

Measurement

WIND, WAYf5, AND WEATHER

-

Surface Wind Measuring Instruments

Figure 9. A cup anemometer

Upper Wind Measuring Instruments

Meteorologists usually measure surface wind speed with an anemometer. Various types of anemometers are available. The most common are the cup, vane, and hot-wire anemometers. A cup anemometer (fig. 9) consists of three or more hemispherical cups extended on horizontal arms from avertical shaft. The wind rotates the cups, and the rate at which the cups turn is transmitted to instruments that translate this information to wind speed.

A vane anemometer consists of a number of flat blades (vanes) attached to a common point. As the anemometer faces the wind, the vanes rotate, and a dial records the number ofrotations. A computer or a person with a stopwatch can then calculate the wind speed.

Used to measure both wind speed and boundary layers, a hot-wire anemometer consists of a thin platinum wire that electrical current heats to about 1,000 degrees Celsius (over 1,800 degrees Fahrenheit). A special instrument measures wind speed byexamining either the wire's change in resistance or the amount of current required to maintain the temperature of the wire when it is under the influence of wind.

Meteorologists use several measuring devices to gauge wind speed and direction at various levels in the troposphere. One is a pilot balloon with a known rate of ascent. Aperson launches the balloon and views it through an optical instrument called a theodolite. The theodolite consists of a sighting telescope through which an observer can view scales for measuring vertical and horizontal angles. The observer tracks the balloon through the telescope and reads the elevation and azimuth angles of the theodolite. (Azimuth is an arc of the horizon measured between a fixed point, such as true north, and the vertical circle passing through the center of an object.) The person using the theodolite employs the changes of elevation and azimuth angles to determine wind speed and direction.

Another device has radiosondes, which are balloon-borne instruments that simultaneously measure and transmit meteorological data. Their ascent is electronically tracked to gauge wind direction and speed.

16

WIND

L I" , 1-

In spite of modern and sophisticated instruments that accurately measure wind speed, people at sea still use a scale created by a British ship captain in r805. Captain Francis Beaufort, in command of the HMS Woolwich, realized that sailors needed a consis

Reporting Beaufort Scale

tent and uniform method of determining and reporting wind and sea states and their effect on ships. Because no instruments were available, Beaufort based his scale on direct observation ofhow the wind affected sails and the sea. Meteorologists have modified the Beaufort scale since its invention, but offshore personnel still use it to report wind speed and sea states. Persons directlyobserve the sea and estimate wind speed from its state. Thus, Beaufort scale reporting does not depend on instruments that could malfunction or be destroyed by high winds. The scale assigns Beaufort numbers to average wind speeds in knots, miles per hour, and kilometres per hour (table I).

Table 1 Beaufort Scale with Corresponding Wind Speeds

Wind Speed

Beaufort Miles Kilometres Number Knots per Hour per Hour

0 0 0 0 I I to 3 Ito 3 2to6 2 4 to 6 4 to 7 8 to II

3 7 to 10 8 to 12 13 to 19

4 I I to 16 13 to 18 21 to 29

5 17 to 2I 19 to 24 32 to 39 6 22 to 27 25 to 3I 40 to 50

7 28 to 33 32 to 38 52 to 61 8 34 to 40 39 to 46 63 to 74 9 41 to 47 47 to 54 76 to 87 10 48 to 55 55 to 63 89 to 101 II 56 to 63 64 to 73 103 to II8 12 64 to 71 74 to 83 II9 to 134


Note the short arrow with the six feathers. It is %2 of an inch (2.38 millimetres) long, which equals 4 on the wind percentage scale. Thus, on average, 4 percent of the winds blew at Beaufort

- force 6 from the west during the observation period. The last arrow is I V32 of an inch (I I.9I millimetres) long,

which equals 18 on the wind percentage scale. It has two feathers. Thus, on average, 18 percent of the winds blew at Beaufort force 2 from the northwest. As mentioned earlier, the number 29 in the middle circle indicates that 29 percent of the winds were calm, light, or variable.

Operators should use wind roses only for a broad definition ofwinds in an area. Keep in mind that the figures in wind roses are percentages of observations and not percentages of actual wind occurrence. Further, the agency that distributes wind rose maps obtains most of its information from ship reports. And, ships usually avoid areas ofheavy weather. Therefore, wind roses do not accurately reflect extreme events. Wind roses cover weather conditions for a period of time that is acceptable to the agencies preparing the maps. Pilot charts developed by NAVOCEANO, which show wind roses and other data for major oceans, can be obtained from the U.S. Government Printing Office, whose Web site address (URL) is www.gpo.gov.

Wind Warnings NWS is an office of the National Oceanic and Atmospheric Administration (NOAA). NOAA, in turn, is an agency of the u.s. Department ofCommerce (DOC). Its Web site address is www.noaa.gov. NOAA establishes national policies and manages and conserves oceanic, coastal, and atmospheric resources and provides practical services and scientific information to interested parties. NWS provides weather information and warnings to every county, parish, and major metropolitan area in the cOlmtry, as well as to marine interests. Its Web site URL is www.nws.noaa.gov.

Among many services, NWS issues forecasts and wind warnings for the United States coastline. It issues four types ofwamings: (I) small craft advisories when winds of33 knots or less are expected to cause dangerous conditions for small vessels in the open ocean; (2) gale warnings ifwinds ofbetween 34 and 47 knots are forecast; (3) storm warnings when winds of between 48 and 63 knots are expected; and (4) hurricane warnings if winds are forecast to reach or surpass 64 knots.

Until recently, the United States Coast Guard (USCG) issued wind warnings for the United States coastline. (USCG's URL is

20

WIND

www.uscg.mil.) Today, the USCG is part of the U.S. Department of Homeland Security (DOHS), which has changed the Coast Guard's mission somewhat. USCG's responsibilities include mari

-- time safety, maritime security, maritime mobility, national defense, and the protection of natural resources. USCG also carries out search and rescue missions, ice breaking, vessel traffic management, maritime law enforcement, homeland security, and antipollution enforcement. Because USCG responsibilities have increased, and because NWS is providing wind advisories and warnings as well as other weather information, USCG no longer issues them.

Before 1989, NWS was responsible for a coastal windwarning-and-display network. This network consisted of flags, pennants, and colored lights to warn mariners of storms at sea. Although the NWS notified the display stations to raise and lower the signals, volunteers or independent agencies operated the stations. NWS now prefers to use telephone recordings and NOAA Weather Radio to disseminate warnings. (NOAA Weather Radio is a nationwide network of radio stations broadcasting continuous weather information from a nearby NWS office.)

Although NWS and USCG no longer participate in the coastal warning display program, many stations continue to show them. Because such displays may still be seen, figure I I illustrates them. The warnings consist ofpennants, flags, and lights. One red pennant during the day and a red light over a white light at night

SMALL CRAFT GALE STORM HURRICANE WARNINGS WARNINGS WARNINGS WARNINGS (up to 33-knot (34- to 47-knot (48- to 53-knot (54-knot winds

winds) winds) winds) and greater)

ee o e oo e e e _BLACK o WHITE _RED

Fig;ure I I. Wind warning displays on the United States coastline. Pennants are used in daytime and lights are used at night.

1

21

WIND. WAVES. AND WEATHER

indicate a small craft warning. Two red pennants during the day and a white light over a red light at night indicate a gale warning.

-

One red flag with a black square center during the day and two red lights at night depict a storm warning. Two red flags with black square centers during the day and a white light between two red lights at night indicate a hurricane warning.

Weather Maps Weather agencies plot fronts, atmospheric pressure, wind, and other weather conditions over an area at a given time on weather maps, or surface charts (fig. r2). (A weather map, or surface chart, is a chart that indicates atmospheric conditions and circulation over an area at a given time.) Aperson can determine wind direction and speed on aweather map by looking at awind arrow (fig. r3). Ablack dot signifies the location on themap ofthe wind reading. The angle the shaft makes leaving the dot indicates wind direction. The angles relate to r6 compass points-that is, north, north northeast, northeast, east northeast, east, east southeast, southeast, south southeast, south, south southwest, southwest, west southwest, west, west northwest, northwest, and north northwest. Thus, a shaft drawn vertically upward from the dot indicates a north wind, while a shaft drawn vertically downward indicates a south wind.

Figure 12. Weather map showingfronts and pressure patterns

22

SPEED

-

I

DIRECTION

Figure 13. Wind direction and speed symbols

j


Weather Forecasting Services

Intermediate angles indicate other directions. Short angular lines (feathers) and, at the highest wind speeds, small black triangles on the shaft indicate wind speed.

Weather agencies often draw isobars on weather maps. Isobars connect points of equal atmospheric pressure. They are superimposed on conventional map projections so that both the location and intensity ofpressure patterns are evident. Most charts label the isobars in millibars of pressure. Spacing of isobars indicates wind conditions that can be expected in a given area.

Meteorologists call a change in air pressure along a horizontal distance the pressure gradient. The pressure gradient, in turn, determines the speed of wind in an area. The larger the pressure gradient, the higher is the wind speed. Isobars that are close together indicate a large pressure gradient, a low-pressure area, and high winds. Isobars that are far apart indicate a small pressure gradient, a high-pressure area, and light winds. Intervals between isobars usually range from 2.5 to 4 millibars.

The USCG; NOAA; the NWS, which is part of NOAA; and several Internet sites widely distribute marine weather information. For example, NOAA Weather Radio (NWR) continuously broadcasts coastal and marine forecasts for the United States (including Hawaii and Alaska), Puerto Rico, the Virgin Islands, Guam, and the Northern Mariana Islands. In addition, NOAA broadcasts offshore and coastal forecasts and storm warnings on 4, 12 5 kilohertz (kHz) in Alaska.

Moreover, the USCG broadcasts high seas weather maps, sea surface temperature maps, and text forecasts on high-frequency radiofax. Radiofax, also known as HF FAX, radiofacsimile, or weatherfax, transmits graphic weather maps and other images via high frequency (HF) radio. A radiofax receiver or a single sideband shortwave receiver on board the rig receives the maps and images. (A single sideband receiver is a special radio that is set up to receive sideband radio transmissions.)

WIND

The Marine and Coastal Weather Services (MCWS) of NWS disseminate a wealth of marine weather information. Besides weather broadcasts and radiofaxes mentioned earlier, interested parties can receive high-frequency text broadcasts of high seas warnings and offshore forecasts, voice broadcasts on very high frequency (VHF) radio bands, marine weather forecasts from commercial maritime coast stations and weather networks, broadcasts ofhigh seaswarnings via satellite, and real time weather radar Images.

The National Center for Environmental Prediction (NCEP), which is partoftheNWS, has an Ocean Prediction Center (OPC), which posts information on the World Wide Web at www.mpc.ncep.noaa.gov. The site displays charts with predicted wind speeds and wave heights for areas that lie within the Atlantic and Pacific Oceans.

USCG also broadcasts offshore forecasts and storm warnings on 2,670 kHz following an initial call on 2,182 kHz. Radio station WWVbroadcasts high seas and storm information for the Atlantic Ocean at frequencies of 2.5 and 20 MHz, while WWVH broadcasts high seas and storm information for the Pacific Ocean at 2.5 MHz. Web sites of interest include:

NOAA Home Page-www.noaa.gov

NWS Home Page-www.nws.noaa.gov

National Center for Environmental Prediction (NCEP)-www.ncep.noaa.gov

OceanPrediction Center (0PC)-www.mpc.ncep.noaa. gov

Marine Product Home Page-http://z05.156.54-2061 om/marine/home.htm

USCG Home Page-www.uscg.mil

Anyone interested in weather and particularly in marine weather should explore these Web sites for further information.


To summarize

- Unequal heating and cooling of the earth's surface

creates wind. Wind moves in the earth's atmosphere. Geographers divide the earth into imaginary lines of

latitude and longitude. Such division allows the locations of winds and other weather phenomena to be pinpointed.

The tilt of the earth's axis creates seasons. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere.

Insolation (solar radiation) warms the earth unequally. This unequal heating creates areas of high and low pressure, which create winds.

Warm air in the atmosphere expands, becomes lighter and rises. Cool air contracts, becomes heavier, and moves downward. Thus, warm air has low pressure and cool air has high pressure. ~

A barometer measures atmospheric pressure, usually in inches ofmercury or millibars. Sometimes, atmospheric pressure is stated in pounds persquare inch or kilopascals.

In the Northern Hemisphere, Coriolis force moves air clockwise around high-pressure areas and counterclockwise around low-pressure areas. Coriolis force has the opposite effect in the Southern Hemisphere.

Common prevailing windsArctic polar northeasterlies North Temperate Zone prevailing westerlies Northeast and southeast trade winds South Temperate Zone prevailing westerlies Antarctic polar southeasterlies

Monsoons are large seasonal wind systems that influence the climates in which they occur.

Jet streams (narrow bands ofwinds) occur at altitudes of 35,000 to 40,000 feet (10.5 to 12 kilometres) and travel from west to east.

26

WIND

Anemometers measure wind speed near the surface. Pilot balloons carrying special instruments measure the

-winds aloft.

The Beaufort scale with numbers from 0 to 12 indicate wind speeds from none at all to 64 to 7I knots.

A wind rose is a graphic representation of the winds in a particular area over a given period.

The National Weather Service (NWS) not only issues wind forecasts, but also gives out additional weather information.

T T T

I 27 j

Waves and Sea - States

Several forces form ocean waves. These forces include the frictional contact between the wind and the ocean, the tidal attraction of the sun and the moon, and the vibration of the earth.

Formed by the contactofwind with the ocean's surface, windwaves are the type of waves that affect offshore operations the most. As wind blows over an ocean, friction occurs between the wind and the ocean's surface. This friction is a form of energy and it moves the ocean's smface. \Nind energyonly affects the top ofthe water. However, the top layer ofwater imparts energy to the water directly beneath it. The water eventually absorbs this energy as depth increases. This transfer of energy through friction forms wind waves.

Wind waves develop and grow where the wind blows from the same direction for a long time. Oceanographers call this area ofwave deve1opmentfttch. Fetch is the distance over which the wind blows to generate the observed waves at a given position. A fetch may be hundreds ofmiles long. Maximum wave heights occur on the downwind boundary of the fetch. Oceanographers call waves that are still in the fetch, and under the influence of its wind, sea. They call waves that have moved out of their fetch and into weaker winds swell. Swell decreases in height and has regular movement. Sea appears choppy, while swell appears round-topped. The left part offigure 14 shows

\ WIND DIRECTION

\ \ \\\~ FETCH BOUNDARY

Waves

Wind Waves

Figure 14. Sea, fetch boundary, and swell


wind blowingover the sea's surface and creatingwaves and sea. The middle of the figure shows the fetch boundary, the area far enough away from the wind that the waves decrease in size. To the right of

-

the fetch boundary, swell occurs. Oceanographers measure wave height from the crest (the top

ofthe wave) to the trough (the lowest point ofthewater surface level between crests). Wind waves rarely exceed 55 feet (17 metres) in height, but reliable observers have reported some higher than 100 feet (30 metres). To give you an idea ofhow high a loa-foot wave is, think of a IO-stOry building. If one story equals IO feet, then imagine a wave as high as a la-story building. Figure 15 illustrates wave crest, wave trough, wave height (H), and wavelength (L). It also shows the crest length and the trough length. Further, it depicts the water depth (D) and the stillwater level, which is the mean, or average, level of the sea. The stillwater level is the level thatwould occur ifno waves existed. Note that the depth is measured from the stillwater level to the ocean bottom.

Four factors-wind speed, duration, fetch, and water depthdetermine wave height. Wind speed is the most important. The faster or stronger the wind blows, the higher the waves are. Wind speed affects wave height only to acertain point. In intense storms, the very strong winds blow the tops from waves, which restricts further growth.

DIRECTION OF WAVE TRAVEL )0

L :: Wavelength

H :: Wave Height

Figure IS. Wave description

3

-

The longer astrong wind blows, the higher the waves will be. For example, if a 3o-knot wind blows over an area of unlimited fetch for 5 hours, 7Y2-foot (2.3-metre) waves develop. If that same 3o-knot wind blows over the same area ofwater for 30 hours, the waves reach 16 feet (nearly 5 metres).

The longer the fetch is, the higher are the waves. For example, if a 35-knot wind blows across a fetch of only 1 mile (1.61 kilometres), the waves may reach only 2feet (0.6 metres) in height. On the other hand, if the same 35-knot wind blows across an area of unlimited fetch, waves at least 30 feet (9 metres) high may develop. As with wind speed, duration and fetch affect wave height only to a certain point.

Water depth is significant to wave development only in shallow seas and bays. Shallow water keeps the waves relatively small. In deep oceans, however, waves can grow to great heights.

The horizontal distance between two successive wave troughs or crests is the wavelength (see fig. 15). Wind waves have wavelengths that are usually 12 to 35 times their height. Fo! example, a wave 12 feet(3.7 metres) high may have alength offrom 144 to 420 feet (44-4 to 129.5 metres). Waves in swell have wavelengths that are 35 to 200 times their height. The wave period is the time interval between the passage oftwo successivewave troughs or crests. Most wind waves have periods of 3 to 30 seconds.

When sea and swell, or two or more swells, converge, wave interference occurs. Wave interference, in turn, creates irregular waves. When the crests of irregular waves combine, wave height usually increases. On the other hand, when crests and troughs meet, flat zones may occur. When these different wave systems cross each other at an angle, the irregular wave patterns they produce is a cross-sea.

Breakers are sea-surface waves that are too steep to be stable. Offshore breakers form when the wave height increases beyond a height-to-Iength ratio ofabout one to seven (1:7). Thewater at the crestmoves faster than the rest ofthe wave, causing the crest to fall forward. These breakers appear as whitecaps, waves with white, foamy tops. Strong winds also generate whitecaps when they blow the tops from the waves. When viewed from above, whitecaps created by wind appear as white streaks.

WAVES AND SEA STATES

31


Tide Waves The action ofthe sun and the moon on the oceans ofthe earth cause tide waves. They occur as tides rise and fall. Tide waves have the longestwave periods ofall, some lasting over 24hours. Tide waves travel at speeds of about 400 knots.

Tsunamis Submarine earthquakes or explosions produce tsunamis, or seismic waves, which many people also call tidal waves. (Do not confuse tide waves with tsunamis. Tide waves, which are also called tidal waves, occur with the rise and fall of tides and do not cause destruction when they contact a shoreline. Tsunamis often do cause destruction when they contact a shoreline.) In the case oftsunamis, seismic disruptions such as earthquakes displace great volumes of water and transfer energy from the ocean floor to the surface. This energy creates huge breakers that inundate the shoreline, destroying virtually everything in their path. Tsunamis are nearly unnoticeable in deep water. There, a tsunami's wave height is usually only a little over 3 feet (I metre). Its wavelength is hundreds of miles (kilometres) and its ~ave period is from IS to 60 minutes.

Currents An ocean current is the predominantly horizontal movement of ocean waters. Oceanographers roughly divide ocean currents into two types. The first are currents that flow on the surface of the sea. Surface currents usually travel in a cyclical pattern (fig. 16). The

60' 30' O' 30' 60' 90' 120'

Figure 16. Prevailing ocean currents

32


second type is a deep, slow-moving flow, which usually travels in a , north-south direction. (Geographers refer to this north-south !".....

travel as meridional, because the travel is parallel to the earth's I'- meridians, or lines oflongitude.) Acountercurrent often accompa

nies currents. This reverse current lies next to the current itself. Oceanographers classify ocean currents as warm or cold.

Warm and cold currents act as a heat distribution system for the earth. Cold currents from the high latitudes and warm currents from the low latitudes flow toward each other and circulate. Horizon-tal differences in temperature are equalized; thus, temperature extremes between different areas are reduced. The meetingofwarm and cold currents may cause fog or frontal activity to occur.

A current's direction of motion is its set. Acurrent's speed of motion is its drift. The speed at which acurrent moves depends on the density of the water and the speed and direction of the wind.

I. The North Equatorial Current is a warm, narrow cur Representative rent that the northeast trade winds drive. The current Currents of the flows west between IOON and 300N latitude in the Northern Atlantic Ocean and between loON and 200N latitude in Hemisphere the Pacific Ocean. In the summer, the southwest monsoon extends the southeast trade winds. The eastwardmoving monsoon current then replaces the westward-moving north equatorial current and the eastward-moving equatorial countercurrent in the Indian Ocean.

2. The GulfStream is awarm current that flows northeastward off the coast ofFlorida and up the east coast of the United States. At 400N latitude, sooW longitude, the Gulf Stream turns eastward and is called the North Atlantic Current. Because of its relatively warm temperature and relatively high drift (sometimes as fast as 6 knots), the Gulf Stream is unique.

3. The Kuroshio, or]apan, Current, is awarm current that flows northeastward along the east coast ofAsia and near the coast ofjapan as far as 3SoN latitude. The Kuroshio travels at aspeed of2 to 4knots. When it turns to the east at40ON latitude, oceanographers call it the North Pacific Current.

4- The Labrador Current is a cold current that flows southward from Baffin Bay, then southeastward past Labrador and Newfoundland. The Labrador Current

33


meets the Gulf Stream near the Grand Banks. Here, a cold wall, which is a sharp water-temperature gradient,

-divides the two currents. The Labrador Current transports much of the dangerous ice in the North Atlantic.

Representative I. The South Equatorial Current is a warm, narrow curCurrents of the rent that the southeast trade winds drive. The current

Southern flows west between the equator and zooS latitude in the Hemisphere Atlantic Ocean and between latitudes 3N and IOoS in

the Pacific Ocean. The narrow, eastward-flowing Equatorial Countercurrent divides the North and South Equatorial Currents. Along the east coast of South America, the South Equatorial Current splits into the Guiana Current, which flows northwest, and the southwest-flowing Brazil Current.

2. The Humboldt, or Peru, Current, is a cold current that flows northward along Chile and Peru. Just soutll of the equator, the current turns toward the west, joining the South Equatorial Current.

3. Prevailing westerlies, which blow toward the east, cause the Antarctic Circumpolar Current, or West Wind Drift. The current flows from west to east around the Antarctic Continent, between latitudes 400S and 50oS. The Antarctic Circumpolar Current has the greatest drift and the largest volume transport of all currents. It transports three times more water than the GulfStream. The ocean's topography, the distribution oflandmasses in the area, and the currents in nearby oceans cause the path of the Antarctic Circumpolar Current to be irregular.

Tides Tides are the periodic rising and falling of the surface of the oceans and bodies ofwater, such as gulfs and bays, connected to the oceans.

Cause The unequal gravitational attraction of the sun and the moon on the earth cause most tides. However, other forces also produce tides. For example, when the contours of an ocean bottom or a landmass near the ocean changes, tides can rise or fall accordingly. What is more, strong winds can blow seawater onto adjacent land, creating abnormally high tides. When the wind ceases, the water recedes and the tides return to normal.

34


The speed ofan ocean current can increase or decrease. This increase or decrease affects the level of the water in which the current occurs. Also, when a large river floods and empties into a

- gulf or bay, the water level in the gulf or bay rises, only to recede when the flood is over. High waves can transport great quantities ofwater, which can raise the level of the tides where they strike the shore. Finally, low-pressure centers, or depressions, can raise ocean water levels during their development.

The moon causes lunar tides and the sun causes solar tides. Lunar and solar tides are essentially the same, although the moon's impact on the earth's tides is greater. The strength ofthe forces that the moon and sun exert on the earth depends on their mass and their distance from earth. The sun is considerably more massive (or dense) than the moon-indeed, 27 million times denser. But the moon is 390 times closer to the earth. Consequently, the moon's tidal force on the earth is roughly twice that of the SlID. In other words, lunar tides are about twice the size ofsolar tides. The period between the sun's maximum tidal forces on a given area on the earth is 12 hours. The moon has a tidal force period of about 12 Y2 hours.

Certain actions affect the behavior of tides, such as the moon Behavior revolving around the earth and the sun, and the moon's planes of motion that lie at an angle to the equator. Also, Coriolis force causes most tides to move clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Tidal current is the horizontal movement of a tide as it rises, falls, and moves toward and away from the coast Oceanographers call a tidal current aflood current when it moves toward the shore. When it travels back toward the sea, they identify it as an ebb current. In open sea, tidal currents rotate continuously 3600 once or twice a day. Near coastal areas, the direction of tidal currents depends on the region's topography. Near the shore, tidal currents often reach speeds of I Y2 to 2 Y2 knots.

35


Ordinary tides are quite predictable. As long as no storms or high winds occur, the tide takes about 6 hours to rise to its high point and about 6hours to fall to its lowpoint. The tide's high point

- is high tide, and its low point is low tide. The difference in height between the high tide and the low tide is the tidal range. The positions of the moon and the sun daily affect tidal ranges (fig. 17). The range of the tide is at its highest when the moon and the sun are aligned (during new and full moons). When this moon-sun alignment occurs, the tide is aspring tide. When the moon and the sun are at right angles to each other (during first and third quarters), the tidal range is at its lowest. This tide is a neap tide. Average tidal range varies from under 2 feet (0.6 metres) in areas of theMediterranean, the Arctic, and theSouth Pacific to over50 feet (IS metres) in the Bay of Fundy, Canada. The geography of the area where the tide occurs also affects tidal ranges. For example, tides may increase in height when they move through narrow passages.

The depth, size, and shape of the oceans determine the frequency of tides. Most of the world's oceans and seas have tides with two high-water levels and two low-water levels each day. This type of tide is a semidiurnal tide. On the other hand, tides in the waters surrounding Alaska and in the GulfofMexico have only one high-water level and one low-water level per day. This type of tide

O NEW MOON POSITION

FIRST QUARTER POSITION

THIRD QUARTER POSITION

Figure 17- The sun-eanh-moon tidal force system


-

is a diurnal tide. Tides around certain islands in the Pacific Ocean have characteristics of both semidiurnal and diurnal tides. These mixed tides show discrepancies in the heights of the high tides and the low tides that occur each day.

A storm surge, or storm tide, is a high tide near the shore that is significantly higher than normal. A storm surge often results from a cyclonic storm (a hurricane or a typhoon) or a squall (a wind of 16 knots or higher, sustained for at least 2 minutes). Cyclonic storms cause tides to grow as high as 20 feet (6 metres) over their normal heights. The size and behavior of a surge depends on the atmospheric pressure at the storm's center, the storm's speed and direction, the horizontal scale, and the topography of the ocean bottom and coastline. When a cyclonic storm meets the coastline, the surge is usually greatest to the right of its path.

Observers measure wave heights either visually or by using instruments called wave height recorders. Wave height recorders s~nse, record, and store information that can be downloaded to a computer for later analysis by technicians.

To determine wave height for a particular site, oceanographers usually calculate the height of the significant waves. They develop significant wave height on a statistical basis-that is, they measure wave heights in the area over a given period. Then, they determine the significant wave height by taking the average of the highest one-third of the waves. -

Once the observers determine the significant wave height for the area, they devise synoptic wave charts. Synoptic means the display of conditions over a wide area. Thus, synoptic wave charts are charts that givewave data for aparticular, but broad, area. Weather forecasters devise synoptic wave charts from actual wave data collected from vessels and, in areas where no data exists, from computed wave heights. Synoptic wave charts provide an overall view of waves-their heights, periods, and direction-and also display atmospheric fronts, highs, and lows. Using wind estimates for an area, meteorologists can prepare prognostic wave charts. A prognostic wave chart shows predicted wave heights and directions.

Observation

Synoptic and Prognostic Wave Charts

37


Current Weather observers use several methods to measure ocean currents, '-'.

-

Measurement Measuring ocean currents and collecting data about them is important. For one thing, naval architects can apply ocean-current data to study a current's effect on both fixed and free bodies. For example, they can measure the effect of current drag on a fixed body, such as a drilling platform. To show current motion on stationary vessels, engineers often use a Pitot tube. A Pitot tube is an open-ended tube arranged to face against the current of a stream of fluid. As the fluid flows through the tube, its pressure changes. The amount of pressure change indicates the speed of the stream, which an attached instrument or gauge can display. (Henri Pitot, a French physicist, invented the device in the 1850s.)

Weather observers may use various free-body instruments to determine a current's set and drift in a given period. For example-

I. A drogue is a kind ofsea anchor. (A sea anchor is an openended parachute-shaped device that creates drag but, because water flows through it, slows the speed ofa body attached to it.) A buoy suspends and lowers the drogue to encounter currents at a specified depth. The movement of the buoy at the ocean's surface shows the effect of the current on the drogue.

2. A Swallow float is a device an observer drops into the water to travel with the current. 00hn Swallow, a British oceanographer, invented it in the 195os.) It includes a recording device to measure the current's speed. The observer can adjust it to travel at a specific depth within the current. A sound-emitting device called a pinger tracks the Swallow float's journey. Later, the observer retrieves it and reads the current's velocity.

3. Sometimes, observers use the navigation equipment on board an ocean-going vessel, such as a ship or a rig, to measure currents. Called ship drift, the on-board equipment measures the current's effect on the vessel.

4. A drift bottle, or floater, is an inefficient, but inexpensive, method of current measurement. A person simply releases a watertight bottle into the water. The bottle contains nothing but air and a card with the date and location ofthe bottle's release. Later, with luck, another person finds the bottle wherever the current has carried it. The finder writes the date and location of the bottle's recovelY on the card and returns it. Instead of a bottle,

-

aperson can use adrift card. The observer puts acard into a buoyant, waterproof envelope and sets it adrift. The drift card method is more accurate because the envelope is more buoyant than the bottle. Both methods are exceedingly inefficient because luck plays a role and the observer can only estimate the set and drift of the current.

S. An anchor or a weight moors a current meter in position on the ocean bottom. Afloat on the surface is connected to a current meter to mark its position. The current meter measures and records acurrent's speed and direction (along with temperature, salinity, pressure, and other variables, if desired) as it passes the mooring location.

Tide Measurement A tide gauge is an instrument that measures the height of the tide. Tide gauges can be uncomplicated or complex. For example, a graduated staff is a simple tide gauge. It may be graduated in feet and inches, or metres and centimetres. The observer keeps it in a sheltered location and checks the height of the tide by merely reading the graduations on the staff. On the otl1er hand, sophisticated sensors and recorders can make up tide gauges. Such gauges record data directly or via a transmitter. Scientists call one gauge that records data directly a marigraph. It makes a continuous graphic record of tide height in relation to time. Information collected by tide gauges serves as the primary means for making tide predictions.


39


Reporting

-

Beaufort Scale As with wind, observers can report wave heights and sea characteristics using the Beaufort scale (fig. 18). The scale ranges from Beaufort number 0, which indicates calm, mirror-like seas with no waves, to Beaufort number 12, which indicates wave heights of 45 feet (13-72 metres) and a sea that is completely white with blowing foam and spray. Figure 19 displays photographs of Beaufort numbers 0-10.

Beaufort Scale with Sea Characteristics

Beaufort State of Sea umber (deep water)

a Calm and mirror-like. 1 Small ripples; no crests or foam. 2 Small choppy waves; crests do

not break. 3 Large choppy waves with a few

foam crests. 4 Small, fully-developed waves,

frequent foam crests. 5 Moderate waves with many foam

crests and possibly some spray. 6 Large waves form; most have

foam crests; spray is possible. 7 Waves increase in height; foam is

blown in direction of wind. 8 Continued increase in wave height;

spindrift at edges of crests; foam blown in streaks.

9 Very high waves; dense streaks of foam along direction of wind; wave crests begin to tumble and roll.

10 Extremely high waves; sea surface is white in appearance; large patches of foam are blown; heavy tumbling in waves; visibility is reduced.

11 Small ships may be obscured by high waves; sea covered by flowing foam; visibility is reduced.

12 Sea completely white with blowing foam and spray so that visibility is very poor.

Figure T8. Beaufort scale with sea characteristics

Average Significant

Wave Height feet (metres)

a \4 (0.08) Yz (0.15)

2 (0.61)

4 (1.22)

6 (1.83)

10 (3.05)

14(4.27)

18(5.45)

23 (7.01)

29 (8.84)

37 (11.28)

45 (l3.72)

Beaufort ml71zber 0 Beaufort number I

1-

Figlln' 19. Beaz~(rm 1I1l'l77bers 0-10 (COl/rte.")' of Meteorologic Seruice ofCanada)

Beaufort number 6

Beaufort numher [0

Figure 19. Continued


Note that the Beaufort scale gives average significant wave heights. An area may experience wave heights that are higher or lower than those waves that correspond to wind speeds on the

- scale. Although it was devised almost two hundred years ago, the

Beaufort scale is still important in determining wind and sea conditions. Rig personnel should know how to recognize wind scales and equivalent sea states. Recording equipment can malfunction and sometimes gives erroneous information.

Aeronautical and navigational charts and related materials for the United States coastal waters and the Great Lakes are prepared by the NOAA's National Ocean Service (NOS). NOS conducts geodetic and oceanographic surveys; makes tide and current predictions; maintains wave-monitoring programs for scientific, environmental, and engineering projections; and operates a fleet of oceanographic and fishery research and survey ships. NOS's vVeb site is www.nos.noaa.gov.

Marine Service Charts

NWS publishes Marine Service Charts for fifteen areas of the United States, including the waters surrounding Alaska and Hawaii. The charts provide NWS telephone numbers, a listing of warning display stations for the area, and the broadcast schedules of local radio stations. You can obtain Marine Service Charts at www.nws.noaa.gov/orn!marine/pub.htrnon the World Wide Web.

SMGC Data

Surface Marine Gridded Climatology (SMGC) data for coastal and marine areas are available from the United States Navy's Fleet Numerical Meteorology and Oceanography (METOC) Detachment, which is headquartered in Asheville, North Carolina. SMGC data cover climatological data for the world, including offshore petroleum areas such as WestAfrica, SoutheastAsia, North America, and Australia. Severalvolurnes ofdata cover each area. SMGC data include information on the state of the sea, weather, wind, cloud density, precipitation, visibility, and air and sea temperature. To view and obtain SMGC data, log on to http://navy.ncdc.noaa.gov/ products/products.html, or contact: Officer in Charge, Fleet Numerical Meteorology and Oceanography Detachment, 151 Patton Avenue, Room 563, Asheville, NC 28801-5014.

Charts

43


-

Publications and Web Sites

Several branches of the United States government publish books, magazines, and informational data both as hard copies and on the World Wide Web. For example, NOM and NWS not only provide information about publications and downloadable charts and books on their Web sites, but also carry several links to other sites ofinterest. Following are some ofthe more useful publications and sites for those who work offshore.

Mariners Weather Log

The Mariners Weather Log is a publication ofNWS and contains articles, news, and information about marine weather events and phenomena, storms at sea, and weather forecasts. Much of the data in the magazine is obtained through the NWS's Voluntary Observing Ship (VOS) program, port meteorological officers (PMOs), and cooperating ships officers and their vessels.

NWS publishes the Mariners Weather Log twice ayear with a spring-summer edition and a fall-winter edition. One way to obtain copies is to download Adobe Acrobat (PDF) versions from NWS's Web site atwww.nws.noaa.gov. Or, to subscribe, write to; Mariners Weather Log, Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954.

Tide Tables

Tide tables give infonnation on tide heights and behavior for most waters ofthe world. All offshore drilling vessels should have tide tables for the areas they work in. The data given in tide tables are recorded for specfic near-shore and inshore points. Nearby locations may have significantly different values. So, modifications for specific rig sites may need to be made. Tide tables may be obtained from the National Ocean Service's (NOS's) Center for Operational Oceanographic Products and Services (CO-OPS) at http://co-ops.nos.noaa.gov.

Worldwide Marine Radiofacsimile Broadcast Schedules

Information on marine weather broadcasts can be found in the 122-pageNWS publication Worldwide Marine Radiofacsirnile Broadcast Schedules. The book covers information on marine weather broadcasts in areas where the service is provided. Consequently, it lists several radio stations ranging from Africa to Antarctica. For example, figure 20 is a page from the publication that shows Kodiak, Alaska. It gives the radio call sign (NO]); its frequencies (2,054 kilohertz, or kHz, 4,298 kHz, and so on); the times of the

44


KODIAK, ALASKA, U.S.A. 1- CALL SIGN

NOJ FREQUENCIES 2054 kHz 4298 kHz 8459 kHz

12412.5 kHz

TIMES 1000-1159,1., 1600-1748 CONTINUvUS CONTINUOUS 0400-0548,22000018

EMISSION F3C F3C F3CF3C

POWER 10KW 10KW 10KW 10KW

TIME CONTENTS OF TRANSMISSION 0400/1600 TEST PATIERN 0403/1603 SURFACE ANALYSIS 0427/1627 REBROADCAST 24HR SURFACE F'CAST 2227/10270437/1637 REBROADCAST 48HR SURFACE F'CAST 2237/10370447/1647 COASTAL MARINE FORECAST TABLES (ALASKA) 0456/1656 SEA STATE ANALYSIS/REBROADCAST0506/1706 GOES IR SATELLITE IMAGE 0517/1717 500 MB ANALYSiS 0527/1727 SYMBOLS AND CONTRACTIONS/SCHEDULE0548/1748 REQUEST FOR COMMENTS/PRODUCT NOTICE 1000/2200 TES' PATIERN 1003/2203 SURFACE ANALYSIS 1027/2227 24HR SURFACE FORECAST 1037/2237 48HR SURFACE FORECAST 1047/2247 48HR WINDNVAVE FORECAST 1057/2257 5-DAY SEA ICE FORECAST/SEA ICE ANALYSIS 1117/2317 GOES IR SATELLITE IMAGE 1128/2328 48HR WAVE PERIOD" SWELL DIRECTION 1138/2338 48HR 500 MB ANALY"IS 1148/--- SEA SURFACE TEMPERATURE ANAL YSIS 1159/--- COOK INLET SEA ICE FORECAST -----.,'2348 96HR SURFACE FORECAST -----12358 96HR WINDNVAVE FORECAST -----10008 96HR WAVE PERIOD" SWELL DIRECTION -----10018 96HR 500 MB ANALY"IS

RPMIIOC 120/576 120/576120/576 120/576120/576120/576120/576120/576120/576120/576120/576 120/576120/576120/576120/576 120/576120/576120/576120/576 120/576120/576120/576120/576120/576120/576

VALID

00/1212100 02100 LATEST 00100 00/1200/12

06/1800/1200/1200/12LATEST 00/12 00/1200/12LATEST LATEST 1200 1200 1200 1200

MAP

2 3 1

1 5 1

2 3 1 1 6 5 1 1 4 7 1 1 1 1

MAP AREAS 1. 20N-70N. 115W-135E 2, 40N - 70N, 125W -150E 3 40N - 70N. 115W -170E 4 40N - 60N. 125W - 160E 5. 05N - 60N, 11 OW - 160W 6 ICE COVERED AK WATERS 7 COOK INLET

NOTES 1 BROADCAST MAY BE PERFORMED ON FOUR FREQUENCIES SIMULTANEOUSLY WHEN RESOURSES ARE AW,ILABLE

2. CARRIER FREQUENCY IS 1.9 kHz BELOW THE ASSIGNED FREQUENCY

3 COMMENTS AND SUGGESTIONS SHOULD BE DIRECTED TO

METEOROLOGIST-iN-CHARGE N.A.TIONAL WEATHER SERVICE/NOAA

6930 SAND LAKE ROAD ANCHORAGE AK 99502-1845 PH (907) 266-~105/FAX (907) 266-5188 E-MAIL: nwsfoanC@alaska net

(EFFECTIVE DATE Oct 01 2002 2200z)(INFORMATION DATED O'c! 16. 2002)tdr http'l/weather.noaa.govlfaxlalaska.shtml

Figure 20. Page from vVorldwide Radiofacsimile Broadcast Schedules for Kodiak, Alaska (Courtesy ofNational Oceanic and Atmospheric Administration)

broadcasts (basedon the 24-hour clock); its emission type (F3C,which is oftechnical interest to radio operators and beyond the scope ofthis manual); and its power in kilowatts, or KW). It also lists the contents ofeach transmission at specific times-for example, at 1003 hours in the morning (10:03 A.M.) and at 2203 hours in the evening (10:03 P.M), the station broadcasts a smface analysis of the weather.

Worldwide Marine Radiofacsimile Broadcast Schedules is available on the Web at http://weather.noaa.govlfaxlmarine.shtml or a

45


hard copy may be ordered from the Superintendent ofDocuments, U.S. Government Printing Office, Washington, D.C. 20402. The book's order number is 3-017-540-2. On the Web, click on

-

marine radiofax charts to find the area ofinterest. In any case, NOM updates the bookyearlyand reports interim revisions in its publication LocalNotice to Mariners(LMN). LMNsare available on the Internet at www.nav.cen.uscg.gov. (Note thatLMNs are no longer available in printed form; they must be obtai