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METEOROLOGICAL TARGETS
TO DETECT STORMS AND OTHER WEATHER PHENOMENA
SEVERE STORM AND TORNADO WARNINGS, HURRICANE OBSERVATIONS, FLOOD WARNINGS AND WINDSHEAR WARNINGS SAVING OF LIVES AND POPERTY
CLOUDSCLOUDS
not precipitating cloud: Small particles, new cloud
Clouds Water droplets + ice crystals or both, Temp. and others
Liquid droplets 0 °C Supercooled : 0 °C - (-40) °C
Size distribution
Kind
age
height
Geographic location
The farther from cloud base The larger the droplets are
As a cloud gets older Droplets get larger
Maritime clouds Continental clouds
Droplets sizes : 5 – 100 m
The mean droplet size distributions for various cloud types.
(Fletcher, 1966)
Cu
St
As
z : generally quite weak 6ii DNz
Diameter (m)
Number ND6 (mm6/m3)
5 100 1.56.10-6
10 100 1.00.10-4
15 50 5.69.10-6
20 25 1.60.10-3
25 10 2.44.10-3
30 5 9.19.10-3
35 1 4.01.10-3
Total: 1Total: 1.80.10.80.10-2-2=-17.4 dBz=-17.4 dBz
RAINRAINEasly detectable Raindrop size dist. 30-40 years
One technique Raindrop camera
From these distributions
Rainrate (mm/h)
Liquid water content (g/m3)
Radar reflectivity (mm6/m3)
Marshall and Palmer drop-size distributions compared with the results of Laws and Parsons.
The Marshall-Palmer relationsihip is given by
Dod eNN .
ND : approximate size distribution (number of drops)
No : 8000/m3mm
D : droplet diameter (mm)
: wavelength
21.01.4 R R : rainrate in mm/h
Using these,,,,, obtain : the number of drops per unit volume
Z-R RELEATIONSHIP
By plotting
rainrate
reflectivity
Correlate statisticallay Z-R rel.
Emprical relationship: bRAz .R : rainrate in mm/hZ : rad. ref. Factor (mm6/m3)A, b : emprical constants
Battan (1973) : 60 experiments for Z-R
Most commonly used Z-R : 6.1.200 Rz
(Marshall and Palmer)
Z for rain :Z for rain :From 20 dBZ (100 mmFrom 20 dBZ (100 mm66/m/m33) ) to 50 dBZ (100 000 mmto 50 dBZ (100 000 mm66/m/m33) )
Z for storms :Z for storms : 75 dBZ75 dBZ
Z for hail :Z for hail : 55 dBZ55 dBZ
NWS’s results for rainrate and reflectivitiy :NWS’s results for rainrate and reflectivitiy :
Rainrate (in/h)Rainrate (in/h) Reflectivity (dBZ)Reflectivity (dBZ)0.1 29.5
0.25 39.5
0.5 40.7
1.25 47.0
2.5 51.9
4.0 55.1
SNOWSNOW Easily detectable
Snow and Rain differences
1.1. Precipitation rate for snow is usually mucc less than it is for rain. “water equivalent” precipitation rate
MOISTURE --- TEMPERATURE :
at warm temp. more water vapor at cold temp.
heaviest snows : above the melting temp. of ice, 33 ° to 36 °F
2.2. DECice DECwater DEC : the dielectric constant
2K term in the radar equation :
0.93 for water
0.197 for ice
The primary reason snow is not detectable by radar is the shallow height of typical snow storms.
Snow storms are usually much lower than most rain storms.
Snow storms are often very widespread in area, but they may only extend a few thousand meters above the surface.
SNOW IS LESS EASILY DETECTABLE THAN RAIN..
HAIL
HAIL : A precipitation in the form of ice.
Diameter : 5 mm (at least)
thunderstorms Lightning and thunder
85 % of thunderstorms contain hail (at least during part of their lives)
Diameter : ranges from 5 mm to 10 cm
World’s record hailstoneCoeffeville, Kansas,14 September 197214 cm (longest dimension)
Terminal Velocity of Hail
Hailstone diameter Shape of the hail Density of the air
Measurements and calculations for Vt :5.0.DAVt
D : hailstone diameter (usually in cm)
Vt : terminal velocity (in m/s)
A : an emprical constant. Measurements for A ; 11.45 (Matson and Huggins, 1979)
Z from hail depends upon wether the outside surface is WET or DRY.
Dry hail has a lower reflectivity than wet hail of the same size.
HAILSTONES MIE REGION
For =3 cm and 5 cm radars MIE REGION
For =10 cm radars RAYLEIGH REGION
DISCUSSIONS
Besides those already discussed ; there are certainly other targets of meteorological interest. Among those are: TORNADOES, HURRICANES, MCC’s and various WIND PHENOMENA
Tornadoes : prevalent within USA, to detect ---- WSR-88D radars
NEXRAD algorithms are being used specifically for the detection of mesocyclones and tornedoes themselves.
Hurricanes generally form hundreds or thousands of kilometers away from land. Ground-based radars have detectable ranges on the order of 400 km or so. Consequently, hurricanes are not detected until they have moved close enough to land to already be a problem. But Doppler radars have been used in stduying H.
MCC’s are complexes of numerous storms. As such, the various components are just as detectable as they would be if they occured individually.
MCC’s are sometimes so large, however, that a single radardoes not have the ability to cover the entire event; they are justtoo extensive.
DATA from more than one radar are rouitnely combined, fortunately, so that entire events can be monitored by ground-based radar networks.
The NEXRAD network will add velocity measurements to the reflectivity measurements already available and should provide even more useful information to study this events.
Both technological comfort and scientific researches can be presented for people using by radars in developed countries especially.
Some natural disasters (meteorologically) such as avalanche, flood, tornado have occured in many regions of the world and they have caused to the death of huming beings and bringing greate ecenomic losses.
Therefore, radars have a great importance in determining of the natural disasters and its early warning systems.
National Weather Service Doppler Radars
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Turkish State Meteorological Service Radars
SELECTED TOPICS FOR NEXT SELECTED TOPICS FOR NEXT SEMINAR ARE:SEMINAR ARE:
Clear-Air Return
Doppler, NEXRAD and TDWR radars
Advanced uses of Meteorological Radars
Radar Maps and Interpretations
R E F E R E N C E S (selected)R E F E R E N C E S (selected) Atlas, D., 1990: Radar in Meteorology, Boston, Amer. Meteor. Soc., 806 pp. Battan, L. J., 1973: Radar Observation of the Atmosphere, Chicago, University of Chicago
Press, 324 pp., [Reprinted by: TechBooks, 2600 Seskey Glen Court, Herndon, VA 22071].
Buderi, R., 1996: The Invention That Changed the World, Simon & Schuster, New York, 575 pp.
Doviak, R. J. and D. S. Zrnic, , 1993: Doppler Radar and Weather Observations, Second
Edition, San Diego, AcademicPress, Inc., 562 pp. Marshall, J. S. and W. McK. Palmer, 1948: The Distribution of Raindrops with Size, J.
Meteor., 5, 165-166. Matson, R. and A. W. Huggins, 1979: Field Observations of the Kinematics of Hailstorms,
NCAR/CSD, Boulder, NCAR /TN-139+STR, 68 pp. Rinehart, R. E., 2001: Radar for Meteorologists, Rinehart Publicatipns, Columbia, MO, 427
pp.
THANKSTHANKS
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