The earth revolves around the sun in an elliptic orbit. Before the sun's energy reaches the surface it must pass through the atmosphere. (You should know what Latitude and Longitudes are).
Air takes up space - it consists of billions of air molecules. Our atmosphere has evolved over 100's of millions of years.
ATMOSPHERIC COMPOSITION
Atmosphere is a gaseous envelope - N2 - 78%, O2 21% trace gases - H2O, CO2, O3, CFC and Methane - Clouds and Aerosols .
Earth first atmosphere-helium and hydrogen - very light gases.
Second Atmosphere - Outgasing of volcanoes: 85% water vapor, 10% CO2 and a few percent N2. N2 is not chemically active so after millions of years it is now the largest composition. H2O formed oceans, large amounts of CO2 are dissolved in the oceans.
Where did O2 come from? Photosynthesis: Plants combine CO2 and H2O in the presence of sunlight to produce O2.
CO2 enters mainly from the decay of vegetation, also from volcanoes, animal life and the burning of fossil fuels. Removal of CO2 occurs during photosynthesis, CO2 stored in the plant. Oceans are a large reservoir of CO2. 50 times the amount in atmosphere. Would you expect a seasonal cycle in the CO2 atmospheric concentration?
O2 is removed when organic matter decays and when O2 combines with other substances, producing oxides, also breathing. Addition of O2 occurs during photosynthesis.
N2 removed by biological processes returned through the decay of plant and animal matter.
Water Vapor is very variable, it occurs as a gas, liquid and solid state. Change of state, or phase change, is very important in the energy balance of the atmosphere. Hydrologic cycle - circulation of water in the atmosphere.
Ozone, very important because it absorbs UV solar energy. Level of maximum O3 occurs at about 25 km - 12 O3 per million molecules. O3 is formed by combining O and O2, it is destroyed when it absorbs UV, or by combining with ) or O2. Delicate balance between the production and destruction of O3.
Bad O3, pollution at the ground, smog.
CFC (Chlorofluorocarbon) safe in the troposphere in stratosphere they absorb UV generate a C1 (Chlorine), which then destroys an O3 molecule. CFC last in the stratosphere for 100 years. O3 hole occurs over Antarctica in Sept. and Oct.
Gravity keeps the gases from going out to space. Gravity weakens as you get farther away from surface, so the number of molecules decreases with altitude.
DENSITY tells us how much matter is in a given space. Density decreases with altitude.
PRESSURE - Even though we can't feel the constant bombardment of air, the push of tiny molecules, we can detect rapid changes. Ears popping - air collisions outside the ear drum lessen. Ear popping, occurs as the molecules on the inside and outside equalize.
Pressure is force per unit area. The pressure at any level in the atmosphere may be measured in terms of the total weight of the air above any point - atmospheric pressure. Pressure always decreases with altitude.
Blow up a balloon - the number of molecules, and the speed, colliding against the sides determines the air pressure inside. I had to work to blow up the balloon. Which brings us to the definition of energy, which is the ability or capacity to do work on some form of matter. Work is done on matter when matter is either pushed, pulled or lifted over some distance. Energy must be conserved, but it can be converted between different forms. Kinetic energy - energy associated with motion.
TEMPERATURE is a measure of the average speed of molecules. Vertical distribution of temperature
Troposphere Stratosphere Mesosphere
10 km 50 km 85 km
Weather occurs in the troposphere and is the focus of this course. The stratosphere is important particularly with respect to O3. There are interactions between the stratosphere and troposphere even though an inversion exists.
Back to kinetic energy and the movement of molecules. Pressure, density and temperature are related via the ideal gas law.
Hold pressure fixed - increase temperature, density decreases
decrease temperature, density increases
Cold air is more dense than warm air.
At the surface a parcel has the same temperature as air around it. When we raise the parcel the air pressure is lower; molecules push on "sides" to expand parcel - this is work; less energy (kinetic energy) cooler temperature. Rising parcels of air always cool due to expansion. Sinking or subsiding air always warms by compression. I cannot overstate the importance of these last statements.