LEC 1: THE ATMOSPHERE

The Earth’s Atmosphere

• life-giving blanket of air that surrounds the fragile earth

• shields the surface from the sun’s ultraviolet radiant energy, as well as material from interplanetary space

• a complex fluid system — a system that generates chaotic motions we call weather

Composition of the Atmosphere

• Nitrogen

  • Destruction through:

    • Soil bacteria’s biological processes

    • Planktons converting it to nutrients

  • Production through:

    • Decaying of plant and animal matter

• Oxygen

  • Destruction through:

    • Decaying of organic matter

    • Combination with other substances

    • Respiration

  • Production through:

    • Photosynthesis

• Water (H2O) Vapor

  • Amount in the atmosphere is affected by processes in the hydrologic cycle: evaporation, condensation, and precipitation

  • Extremely important gas in the earth’s heat-energy balance

    • Forms clouds and falls as precipitation

    • Important source of atmospheric energy, releases large amount during condensation

    • Potent greenhouse gas — strongly absorbs portion of earth’s outgoing energy

• Carbon Dioxide (CO2)

  • Oceans are huge reservoir of CO2: hold >50x the total atmospheric CO2 content

  • Greenhouse gas: increasing in concentration —> increasing earth’s ave surface temp

• Ozone (O3)

  • Primary component of photochemical smog which irritates eyes and throat and damages vegetation

  • Majority is found in the stratosphere, where it’s formed naturally

  • Shields plants, animals, and humans from harmful UV rays

  • Nemesis: Chlorofluorocarbons (CFCs) — releases ozone-destroying chlorine

Vertical Structure of the Atmosphere

• Air Density: W = mg

  • Gravity

    • Gravity is the reason why most of the atmosphere is crowded near the Earth’s surface

    • As it pull down on the air above, it compresses air molecules together —> the more air above, the greater squeezing effect

  • Mass

    • Mass is the quantity of matter in the object

  • Density: ρ = m/V - tells us how much matter in a given space

  • mass of air in a given volume

  • greatest at the Earth’s surface and decreases as we go up the atmosphere

• Air Pressure: P = F/A

  • aka atmospheric pressure

  • The “push” force divided y the area on which the air molecules pushes

  • Measured in terms of the total mass of air above any point

    • atmospheric pressure always decreases with increasing height

  • a column of air 1 in² in cross-section extending from sea level to the “top” would weigh nearly 14.7 lbs/in² (or psi)

Layers of the Atmosphere

• Troposphere

  • Region from the surface up to ~11 km where temperature normally decreases

  • Lapse Rate - rate at which air temperature decreases with height

  • Atmosphere is kept well stirred by rising and descending air currents

  • Contains all of the weather we are familiar with on Earth

  • Why does air temperature decrease with height?

    • As sunlight warms the earth’s surface, and the surface, in turn, warms the air above it

• Stratosphere

  • Above 11km, there is a region where lapse rate is zero —> isothermal zone

  • Tropopause - boundary separating troposphere and stratosphere

  • Air temperature begins to increase with height (temperature inversion)

  • The inversion reduces the amount of vertical motion —> layer is not well mixed; hence, it is stratified

  • Why is there an inversion?

    • Mainly caused by ozone heating layer using its absorbed UV energy

    • Air is less dense above 25km —> easier to raise the temperature

    • Energy transfer downward from above 25km is slow due to low air density

• Mesosphere

  • Stratopause - boundary separating stratosphere and mesosphere

  • Humans will become O2-straved and blood will boil at normal body temp

  • Temperature decreases with height. Why?

    • There is little ozone to absorb radiation

    • Molecules lose more energy than they absorb

  • Lowest temperature is reached at the top of this layer

• Thermosphere

  • Mesopause - boundary separating mesosphere and thermosphere

  • Oxygen molecules absorb energetic solar rays, warming the air

  • Relatively few molecules —> small amount of solar energy can cause large increase in temperature

  • Air molecules will move very far (>1km on ave) before colliding with another molecule compared at the surface (<1×10^-6 cm)

• Exosphere

  • Upper limit of the atmosphere

  • Region where atoms and molecules shoot off into space

• Ionosphere

  • Not really a “layer”, but an electrified region within the upper atmosphere

  • Large concentrations of ions and electrons exist here

  • 60 km above Earth’s surface to the “top” of the atmosphere

  • Plays a major role in AM radio communications

Introduction to Weather and Climate

• Weather

  • Condition of the atmosphere at any particular time and place

  • Always changing

  • Comprised of weather elements: air temperature, air pressure, humidity, clouds, precipitation, visibility, wind

• Climate

  • “average weather” obtained by measuring weather elements of a region over many years

  • Accumulation of daily and seasonal weather events over a long period of time

  • Includes weather extremes in a region

• Meteorology

  • the study of the atmosphere and its phenomena: liquid mechanics, physics, and chemistry

  • “meteoros” (Greek) - meaning high in the air