Chapter 1Chapter 1

Introduction to the Atmosphere

Introduction to the Atmosphere

Weather

• Weather is the condition of the atmosphere at a particular location and moment

• These atmospheric conditions include, among others, temperature, relative humidity, dew point, pressure, wind speed and direction, cloud cover, and precipitation

• What causes weather? Ultimately, the sun

Figure 01: Satellite image of North America

Courtesy of NOAA/NESDIS and SSEC, University of Wisconsin-Madison.

Definitions

• Meteorology is the study of weather variables—temperature, humidity, pressure, wind speed and direction, cloud cover, precipitation, the processes that cause weather, and the interaction of the atmosphere with the Earth’s surface, ocean, and life.

Climate

• The climate of a region is the condition of the atmosphere over many years

• Described by long-term averages of atmospheric conditions such as temperature and precipitation

• Includes extremes as well as averages• Climatology is the study of climate• Climatologists also study changes of climate in

the past and for the future• How oceans, landforms, living organisms affect

the atmosphere

Figure 02A: Polar stereographic map of the Northern Hemisphere

Figure 02B: Polar stereographic map of the Southern Hemisphere

Meteorology and Atmospheric Science

• Usually used interchangeably• Atmospheric science includes not only

meteorology but some other topics as well– Charged particles and electricity in the ionosphere,

parts of the upper atmosphere– Atmospheres of other planets– Includes the study and simulation of climate– Includes the study of climate change

What is the atmosphere?

• A fluid• A thin layer surrounding the Earth• Mainly a mixture of invisible gas with some solid

and liquid particles that stays in place on account of the force of gravity

Figure CO: Chapter 1, Introduction to the Atmosphere--Clouds over Indian Ocean

Courtesy of NASA Headquarters—Greatest Images of NASA (NASA-HQ-GRIN)

What’s in the atmosphere?

• Invisible gases – Some are permanent gases, some variable– Some are abundant, some not (trace gases)– Some are greenhouse gases, some not– Some pollutants, some not

• Liquids– Water: cloud droplets, raindrops, haze, fog– Pollutants

• Solids– Water: ice crystals in clouds, snow– Soil, sand, acid, pollen, other substances

Figure T01: Composition of the Atmosphere

Gases in the atmosphere

• Nitrogen: most abundant (78%), not very reactive, permanent, not a greenhouse gas, emitted from volcanoes

• Oxygen (O2: 2nd most abundant (21%), essential for combustion, respiration, a greenhouse gas only in the stratosphere and above (not near the surface), permanent, comes from plants as a product of photosynthesis

Other gases in the atmosphere

• Argon (1%), permanent, not reactive• Water vapor, highly variable (0-4%), extremely

important to the weather and essential to life, most abundant of the greenhouse gases, comes from volcanoes and maybe comets, hugely important to climate, invisible, makes air lighter – Part of a cycle called the hydrologic cycle– Has a whole chapter, Chapter 4

Figure 05: Hydrologic cycle

Still another gas in the atmosphere

• Carbon dioxide, the 2nd most abundant greenhouse gas, variable with concentrations increasing every year and higher now than ever before in Earth’s history, important for climate change and global warming– Has a cycle of sources and sinks called the Carbon

Dioxide (CO2) Cycle– Photosynthesis is a sink for carbon dioxide– Burning fossil fuels is an important source of carbon

dioxide– The oceans are a sink for carbon dioxide

Figure 03: Carbon dioxide cycle

Figure 04: Carbon dioxide measurements at Mauna Loa

Another gas: Methane

– Is another important greenhouse gas– Concentrations are increasing– Comes from human activities, including the cultivation

of rice, burning of forests, coal mining, and cattle raising (digestive processes of domestic animals)

– Also comes from termites

Figure 07: Atmospheric methane measurements

Source: NOAA/ESRL Global Monitoring Division - THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI). (n.d.). . Retrieved from http://www.esrl.noaa.gov/gmd/aggi/

Ozone (O3)

Is another important greenhouse gas

Forms naturally in the stratosphere from oxygen, and warms the stratosphere

Allowed life to develop over land

Gets depleted over Antarctica in winter—known as the “ozone hole”

Is a dangerous pollutant near Earth’s surface

Chlorofluorocarbons (CFCs)

• Are yet more greenhouse gases, and very powerful

• Do not occur naturally• Are chemically stable near the surface• Are broken down in the stratosphere

– Loose chlorine atoms destroy stratospheric ozone

• Are decreasing in emissions rapidly• Are decreasing in concentrations slowly

Figure 09: CFC concentrations

Source: NOAA/ESRL Global Monitoring Division - THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI). (n.d.). . Retrieved from http://www.esrl.noaa.gov/gmd/aggi/

Particles of liquid and solid in the atmosphere

• Are together known as aerosols [ai(e)rborne solutions]

• Vary in size with the type of substance• Are measured in units of microns (1/1,000,000 of

a meter or 1/1,000 of a mm)• Most are invisible because they are so small• Are more abundant over deserts, less over

oceans• Sources include wind erosion, volcanoes, fires

and human activity

Figure 10: Aerosol sizes

Figure 06: Global satellite picture of cloud distributions

Courtesy of SSEC, University of Wisconsin-Madison

Particulates

• Are needed to form clouds• Can influence climate• Can be pollutants• Are anthropogenic when caused by human

activity

Figure 11: Satellite picture of smoke from Santa Ana fires

Courtesy of NASA/MODIS Rapid Response

Pressure and density in the atmosphere

• Pressure is force per unit area• Pressure always decreases upward• Pressure is related to the weight of air in a

column above a particular location• Density is mass per unit volume• Density always decreases upward• Density is related to pressure by the gas law:

pressure = constant x density x temperature

Figure 12: Atmospheric pressure and the density of air

Adapted from Rauber, R.M., Walsh, J.E. and Charlevoix, D.J. Severe & Hazardous Weather: An Introduction to High Impact Meteorology, Third edition. Kendall/Hunt, 2008.

Barometric Pressure and Sea-Level Pressure

• The greater the atmospheric pressure, the greater the height of the mercury in the tube of a mercury barometer– This measures barometric pressure or station

pressure

• Station pressure depends both on weather highs and lows and on altitude– Without a correction for altitude a weather map would

look like a topographic map– Sea-level pressure has been corrected for altitude

Figure 13: Atmospheric pressure summary

Layers of the Atmosphere

• Temperature divides the atmosphere into four layers

• Closest to the earth, where the temperature generally decreases upward, is the troposphere– 80% of the mass of the atmosphere is here– Most of this book is devoted to the troposphere– The top of the troposphere is the tropopause

• An upper lid on weather patterns

• Higher in the tropics than at the poles

Figure 14: Layers of the atmosphere

Adapted from Rauber, R.M., Walsh, J.E. and Charlevoix, D.J. Severe & Hazardous Weather: An Introduction to High Impact Meteorology, Third edition. Kendall/Hunt, 2008.

The Upper Atmosphere

• Above the tropopause is the stratosphere, where temperature increases with altitude– Here ozone is absorbing solar energy– Here there is a lack of both mixing and turbulence

• Above the stratosphere is the stratopause• Above the stratopause is the mesosphere,

where temperature decreases with altitude• The mesopause separates the mesosphere from

the thermosphere, where temperature increases with altitude again

Figure 15: Satellite picture of aurora

Courtesy of Mark D. Conner and Air Force Weather Agency, Offutt AFB/U.S. Air Force

An Introduction to Weather Maps

• The surface chart depicts weather at the Earth’s surface

• Fronts, or boundaries between air masses, shown using lines with triangles and semicircles

• Isotherms connect observations of the same temperature

• Isobars connect observations of the same pressure

• Data from specific locations coded using the station model

Figure 16: Fronts: cold, warm, stationary, and occluded.

The Station Model

• Is a compressed graphical weather report• Is coded to display

– Weather conditions at a specific place and time• Plus cloud cover• Wind speed and direction• Temperature• Dew point temperature, atmospheric pressure adjusted

to sea level• Change in pressure over the last 3 hours• Visibility• Precipitation amounts

Figure 17: The station model

Figure 18: Surface weather map

Adapted from Plymouth State University Weather Center, [http://vortex.plymouth.edu/make.html.]. Accessed June 10, 2010

Coordinated Universal Time (UTC)

• Is the reference clock adopted by weather organizations around the world

• Greenwich, England is the reference time zone for UTC

• Meteorology also uses a 24-hour military-style clock

• UTC EST CST MST PST• 1200(noon) 0700 0600 0500 0400• 0000(midnight)1900 1800 1700 1600

Figure 19: Time zone conversion map

Courtesy of The World Factbook, 2009.

Watches, Warnings

• Issued by the National Weather Service• Watches inform that current atmospheric

conditions are favorable for hazardous weather– Often issued for large regions– You should be aware that a weather hazard may

develop in your area

• Warnings inform that hazardous weather will soon occur in an area– The hazard is developing in your area– Take immediate action

Figure T02: Typical National Weather Service Criteria for Issuing Selected Weather Watches and Warnings

Advisories

• A less urgent statement to bring to the public’s attention a situation that may cause some inconvenience or difficulty for people who have to be outdoors or to travelers

Figure 20: Watches and warnings

Courtesy of SSEC, University of Wisconsin-Madison