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ATMO 1300-006 Class #2

Monday, August 31, 2009

Chapter 1

Introduction to the Atmosphere

Definitions

• Meteorology is the study of weather variables—temperature, humidity, pressure, wind speed and direction, cloud cover, precipitation

• Climate is the condition of the atmosphere over many years, including averages, seasonal changes and records of extremes

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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

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What’s in the atmosphere?

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

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Abundance of gases in the atmosphere

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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

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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

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The Hydrologic Cycle: sources and sinks

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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

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Carbon dioxide measurements at Mauna Loa, Hawaii

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The carbon dioxide cycle

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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

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Increasing concentrations of methane

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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

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Layers of the Atmosphere

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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

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Global use of CFCs

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Concentration of CFCs

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Particles of liquid and solid in the atmosphere

• Are together known as aerosols [ai(e)rborne solutions]• Varies 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• Are less abundant over the oceans• Are needed to form clouds• Can influence climate• Can be pollutants• Are anthropogenic when caused by human activity

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Particles in the atmosphere

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Smoke from fires in Southern California viewed by satellite

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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

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How pressure and density decrease upward

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Surface pressure corrected to sea level

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Pressure in the different layers of the atmosphere