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Thickness of the Atmosphere (from Meteorology Today) Lecture 1: A Brief Survey of the Atmosphere The thickness of the atmosphere is only about 2% 90% of Earth’s thickness (Earth’s 70% Origins of the atmosphere radius = ~6400km). Vertical structures of the atmosphere Most of the atmospheric mass is confined in the lowest 100 Weather maps km above the sea level. Because of the shallowness of the atmosphere, its motions over large areas are primarily horizontal. ÎTypically, horizontal wind speeds are a thousands time greater than vertical wind speeds. (But the small vertical displacements of air have an important impact on ESS55 the state of the atmosphere.) ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu Vertical Structure of the Atmosphere Vertical Structure of Composition up to ~500km composition Dominated by lighter gases Heterosphere wihiith increas ing a liltitud e, such as hydrogen and helium. temperature ~80km This part of the atmosphere electricity continually circulates, so that the principal atmospheric Homosphere gases are well mixed. 80km Î For most purpose, we consider the homosphere virtually the entire atmosphere. (from Meteorology Today) ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 1 Composition of the Atmosphere Origins of the Atmosphere (inside the DRY homosphere) When the Earth was formed 4.6 billion years ago, Earth’s atmosphere was probably mostly hydrogen (H) and helium (He) plus hydrogen compounds, such as methane (CH4) and ammonia (NH3). Î Those gases eventually escaped to the space. The release of gases from rock through volcanic eruption (so-called outgassing) was the principal source of atmospheric gases. Water vapor (0 -0. 25%) Î The primeval atmosphere produced by the outgassing was mostly water vapor (H2O), with some Nitrogen (N2) and Carbon dioxide (CO2), and trace amounts of other gases. (from The Blue Planet) ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu What Happened to H2O? Saturation Vapor Pressure Saturation vapor pressure describes how much water vapor is needed to make the The atmosphere can only hold air saturated at any given temperature. small fraction of the mass of water vapor that has been Saturation vapor pressure depends primarily on the air temperature in the injected into it during volcanic following way: eruption, most of the water The vapor was condensed into Clausius-Clapeyron clouds and rains and gave rise to Equation rivers, lakes, and oceans. Î Î The concentration of water vapor in the atmosphere was (from Atmospheric Sciences: An Introductory Survey) substantially reduced. Saturation pressure increases exponentially with air temperature. ESS55 ESS55 Prof. Jin-Jin-YiYi Yu L: latent heat of evaporation; α: specific volume of vapor and liquid Prof. Jin-Jin-YiYi Yu 2 Carbon Inventory What happened to CO2? Chemical weather is the primary process to remove CO2 from the atmosphere. Î In this process, CO2 dissolves in rainwater producing weak carbonic acid that reacts chemically with bedrock and produces carbonate compounds. This biogeochemical process reduced CO2 in the atmosphere (from Earth’s Climate: Past and Future) and locked carbon in rocks and mineral. (from Atmospheric Sciences: An Introductory Survey) ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu What Happened to N2? Where Did O2 Come from? Photosynthesis was the primary Nitrogen (N2): process to increase the amount of (1) is iner t c hem ica lly, oxygen ithtin the atmosp here. (2) has molecular speeds too slow to escape to space, Î Primitive forms of life in oceans (3) is not very soluble in water. began to produce oxygen through photosynthesis probably 2.5 billion ÎThe amount of nitrogen being cycled out of the atmosphere years ago. was limited. Î With the concurrent decline of CO2, oxygen became the second most ÎNitrogen became the most abundant gas in the atmosphere. abundant atmospheric as after nitrogen. (from Earth’s Climate: Past and Future) ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 3 Permanent and Variable Gases Where Did Argon Come from? Those gases that form a constant portion of the atmospheric mass . Radioactive decay in the planet’s bedrock added argon (Ar) to the evolving atmosphere. Î Argon became the third abundant gas in the atmosphere. Those gases whose concentrations changes from time to time and from place to place, and are important to weather and climate. ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu Carbon Dioxide (CO2) Water Vapor (H2O) (Mauna Loa, Hawaii) current Early spring maximum: takes less CO2 due to Water vapor is supplied to the atmosphere by evaporation from level slow plant growth in winter plus CO2 the surface and is removed from the atmosphere by proddfduced from tree leave condensation (clouds and rains). decomposing. Late summer minimum: The concentration of water vapor is maximum near the surface summer growth removes (from CO2 from the and the tropics (~ 0.25% of the atmosphere) and decreases Understanding atmosphere. rapidly toward higher altitudes and latitudes (~ 0% of the Weather atmosphere). & Climate) Carbon dioxide is supplied into the atmosphere by plant and Water vapor is important to climate because it is a greenhouse animal respiration, the decay of organic material, volcanic gas that can absorb thermal energy emitted by Earth, and can eruptions, and natural and anthropogenic combustion. release “latent heat” to fuel weather phenomena. Carbon dioxide is removed from the atmosphere by photosynthesis. ESS55 ESS55 Prof. Jin-Jin-YiYi Yu CO2 is an important greenhouse gas. Prof. Jin-Jin-YiYi Yu 4 Formation of Ozone (O3) Ozone (O3) With oxygen emerging as a major component of the “good” ozone atmosphere, the concentration ~ 15ppm of ozone increased in the atmosphere through a photodissociation process. “bad” ozone ~ 0.15ppm ESS55 (from WMO Report 2003) ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu (from WMO Report 2003) Other Atmospheric Constituents Air Pressure Can Be Explained As: Aerosols: small solid particles and liquid droplets in the air. They serve as condensation nuclei for cloud formation. weight of the air motion of Air Pollutant: a gas or aerosol produce by human air molecules activity whose concentration threatens living organisms or the environmentenvironment. The weight of air above a surface The bombardment of air molecules (due to Earth’s gravity) on a surface (due to motion) ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 5 Air Pressure and Air Density How Soon Pressure Drops With Height? Weight = mass x gravity Ocean Atmosphere Density = mass / volume Pressure = force / area = weight / area (from Is The Temperature Rising?) In the ocean, which has an essentially constant density, pressure increases linearly with depth. In the atmosphere, both pressure and density decrease exponentially with elevation. ESS55 ESS55 (from Meteorology Today) Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu One Atmospheric Pressure The average air pressure at sea level is equ iva le nt to t he pressure produced by a column of water about 10 meters (or about 76 cm of mercury column). This standard atmosphere pressure is often expressed as 1013 mb (millibars), which means a pressure of about 1 kilogram per square centimeter. (from The Blue Planet) ESS55 ESS55 (from The Atmosphere) Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 6 Units of Atmospheric Pressure Air Mass and Pressure Pascal (Pa): a SI (Systeme Internationale) unit for air pressure. Atmospheric pressure 1 Pa = a force of 1 newton acting on a surface of one square meter tells you how much 1 hectopascal (hPa) = 1 millibar (mb) [hecto = one hundred =100] atmospheric mass is Bar: a more popular unit for air pressure. above a particular 1 bar = a force of 100,000 newtons acting on a surface of one altitude. square meter = 100,000 Pa Atmospheric pressure = 1000 hPa dbbtdecreases by about = 1000 mb 10mb for every 100 meters increase in One atmospheric pressure = standard value of atmospheric pressure elevation. at lea level = 1013.25 mb = 1013.25 hPa. ESS55 (from Meteorology Today) ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu Units of Air Temperature “Absolute Zero” Temperature Fahrenheit (ºF) Celsius (ºC) Î ºC = (ºF-32)/1.8 (from Is The Temperature Rising?) The absolute zero temperature is the temperature that the molecules do not move at all. Kelvin (K) : a SI unit Î K= ºC+273 This temperature occurs at –273°C. The Kelvin Scale (K) is a new temperature scale that has 1 K = 1 ºC > 1 ºF its “zero” temperature at this absolute temperature: ESS55 K = °C + 273 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 7 Vertical Thermal Structure Variations in Tropopause Height Troposphere (“overturning” sphere) contains 80% of the mass Standard Atmosphere surface heated by solar radiation strong vertical motion where most weather events occur Stratosphere (“layer” sphere) middle weak vertical motions atmosphere dominated by radiative processes heated by ozone absorption of solar ultraviolet (UV) radiation warmest (coldest) temperatures at summer (winter) pole Mesosphere heated by solar radiation at the base heat dispersed upward by vertical motion Thermosphere (from Understanding Weather & Climate) (from The Atmosphere) very little mass lapse rate = 6.5 C/km ESS55 ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu Dry Adiabatic Lapse Rate Moist Adiabatic Lapse Rate (from Meteorology: Understanding the Atmosphere) ESS55 (from Meteorology: Understanding the Atmosphere) ESS55 Prof. Jin-Jin-YiYi Yu Prof. Jin-Jin-YiYi Yu 8 Stratosphere Ozone Distribution Standard Atmosphere The reasons for the inversion in the stratosphere is due to the ozone AtAntarc tic absorption of ultraviolet solar Ozone energy. Hole Although maximum ozone concentration occurs at 25km, much solar energy is absorbed in (from The Earth System) the upper stratosphere and can not The greatest production of ozone occurs in the tropics, where the solar UV reachhh the leve l o f ozone max imum.
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