Composition, Structure, & Heat Budget The Atmosphere Composition, Structure, & Heat Budget

Atmospheric Composition Reported on a dry basis, water vapor excluded since it’s so variable. Only 2 gases comprise 99% Water vapor normally <1 - 4% Minor gases exert influence far greater than their abundance would suggest, e.g. greenhouse effect, UV protection, photosynthesis, etc.

Atmospheric Pressure A measure of the mass per unit area of air. Increases as the density of air increases because a volume of air with high density has more gas molecules than a volume with a lower density. Decreases with altitude.

Dynamic Equilibrium of Atmospheric Water Vapor Atmospheric water vapor varies immensely with place and time. For Earth as a whole, evaporation equals precipitation. For ocean as a whole, evaporation exceeds precipitation. Latent heat of vaporization supplies much of the heat to drive convection.

Air Parcel Size and Temperature Rising and cooling triggers condensation which forms clouds and rain. Latent heat released at condensation further warms air and forces more rising.

Layers of the Atmosphere The inner most layer is the troposphere. It is mostly nitrogen and oxygen. Chemical cycling occurs in this layer. Responsible for the planet’s weather and climate. The second layer is the stratosphere. Contains less matter than the troposphere. Ozone concentration is high, water concentration is very low. The third layer is the mesosphere. This gives way to the thermosphere. The exosphere is the last layer and it tails off into space and meets the solar wind. The ionosphere straddles several layers. The ionosphere reflects radio waves & hosts the aurora borealis & aurora australis.

TROPOSPHERE

Structure & Temperature Profile of Lower Atmosphere Virtually all weather occurs in troposphere. Earth’s surface heats troposphere from bottom; favors vertical mixing. Stratosphere heated most at middle & top because of UV ray absorption by ozone; limits vertical convective mixing there. strongest heating by UV-absorbing ozone heating from below

Sun Angle Controls Sunlight Intensity At low angles, sunlight spreads over much larger areas & thus heats less effectively. At low angles, sunlight reflects from water & ice more efficiently.

Variation of Solar Radiation with Latitude (also with Seasons and with Time of Day) noon radiation intensity (cal/cm2/min.) at given latitude on equinox days: @40o = 1.53 @66.5o = 0.80 @89.5o = 0.02 At winter solstice (N.H.) the most intense radiation is at Tropic of Capricorn @ noon.

Absorbed Visible Light Converted to IR, Sensible & Latent Heat Global Heat Budget These numbers indicate global averages. Locally the energy fluxes vary with season, time of day, cloud cover, snow cover, vegetation patterns, etc. Greenhouse Effect = + X 5% X 39% X 16% Absorbed Visible Light Converted to IR, Sensible & Latent Heat

Latitudinal Variations in Radiation Budget Garrison, 2005 Excess heat lost near poles must be carried from tropics to poles by ocean currents & winds. Surplus must equal deficits to maintain heat budget.

Poleward Heat Transport to Balance Unequal Heating Equator would be hotter & poles would be much colder without this transport. Transport by winds & ocean currents. Garrison, 2005