Earth’s Atmosphere: A Brief Intro(and Ocean Circulation Patterns) Dr. Mark A. McGinley Honors College and Department of Biological Sciences Texas Tech University
Atmosphere• An atmosphere is a layer of gases that may surround a material body of sufficient mass and that is held in place by the gravity of the body.• An atmosphere may be retained for a longer duration, if the gravity is high and the atmospheres temperature is low.• Some planets consist mainly of various gases, but only their outer layer is their atmosphere• Wikipedia
Earth’s Atmosphere• The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earths gravity.• The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.
The Earth’s Atmosphere– The atmosphere has a mass of about 5×1018 kg • three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface.– An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft.– The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.
The Layers of Earth’s Atmosphere• We will talk about the layers of earth’s atmosphere in more detail later on.• The layer closest to the earth is known as the troposphere – We live in the troposphere – Factors that affect climate and weather occur in the troposphere
Composition of dry atmosphere, by volumeppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume(thermodynamics))Gas VolumeNitrogen (N2) 780,840 ppmv (78.084%)Oxygen (O2) 209,460 ppmv (20.946%)Argon (Ar) 9,340 ppmv (0.9340%)Carbon dioxide (CO2) 394.45 ppmv (0.039445%)Neon (Ne) 18.18 ppmv (0.001818%)Helium (He) 5.24 ppmv (0.000524%)Methane (CH4) 1.79 ppmv (0.000179%)Krypton (Kr) 1.14 ppmv (0.000114%)Hydrogen (H2) 0.55 ppmv (0.000055%)Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)Carbon monoxide (CO) 0.1 ppmv (0.00001%)Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)Ammonia (NH3) traceNot included in above dry atmosphere:Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface
Gases of the Atmosphere• Nitrogen gas is the most common gas in the atmosphere – N2 – Two atoms of Nitrogen held together by a triple bond • Second strongest bond in nature (I think)• Thus, nitrogen gas is fairly non-reactive – We are surrounded by Nitrogen, but we can not use atmospheric nitrogen to help make proteins, nucleic acids, etc.
Gases of the Atmosphere• Oxygen gas is the second most common gas in the atmosphere. O2• Oxygen is required for aerobic respiration – Break down sugar to release energy that can be used by our bodies • This process is much more efficient in the the presence of oxygen• O2 can be converted to O3 (ozone) in the atmosphere – We will talk about the importance of ozone later on
Gases of the Atmosphere• Carbon dioxide (CO2)• Terrestrial plants convert carbon dioxide into sugar during the process of photosynthesis – Energy stored in sugar is required to power most life on earth• Carbon dioxide is a “greenhouse gas”
Wind• Wind can be defined simply as air in motion. This motion can be in any direction, but in most cases the horizontal component of wind flow greatly exceeds the flow that occurs vertically.• Wind develops as a result of spatial differences in atmospheric pressure. Generally, these differences occur because of uneven absorption of solar radiation at the Earths surface.
Unequal Distribution of Solar Energy Across the Earth • Solar radiation more concentrated at the equator than at the poles – Because of the curvature of the earth • Thus, warmer near the equator than at the poles
Effect of Increasing Temperature on Gasses• When gasses are heated the molecules start to “move” more which results in a lower density of gas molecules – Fewer molecules per volume• As the density decreases, the mass of the gas decreases
Hot Air Rises• As air warms its density decreases which causes the warmer air to become lighter than the cooler air surrounding it• Thus, the more dense, cooler air replaces the warmer, lighter air near the surface of the ground• HOT AIR RISES
Hadley Cells• Warm air at the equator rises and is replaced by cooler air moving from higher latitudes – From North to South in Northern Hemisphere – From South to North in the Southern Hemisphere• As air rises it cools. – In the Northern Hemisphere high altitude winds blow from South to North – In the Southern Hemisphere high altitude winds blow from North to South
Hadley Cells• As the air cools at high altitudes it becomes heavier• Falls to the earth at approximately 30o latitude N and S
Importance of Hadley Cells• Influence global wind patterns• Also have profound effects of global patterns of precipitation – We will talk much more about this later on