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Lecture.1.Introduction.Pdf Lecture 1: Introduction to the Climate System Earth’s Climate System Solar forcing T mass (& radiation) The ultimate driving T & mass relation in vertical mass (& energy, weather..) Atmosphere force to Earth’s climate system is the heating from Energy T vertical stability vertical motion thunderstorm the Sun. Ocean Land The solar energy drives What are included in Earth’s climate system? Solid Earth three major cycles (energy, water, and biogeochemisty) What are the general properties of the Atmosphere? Energy, Water, and in the climate system. How about the ocean, cryosphere, and land surface? Biogeochemistry Cycles ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Thickness of the Atmosphere (from Meteorology Today) The thickness of the atmosphere is only about 2% 90% of Earth’s thickness (Earth’s 70% radius = ~6400km). Most of the atmospheric mass is confined in the lowest 100 km above the sea level. tmosphere Because of the shallowness of the atmosphere, its motions over large A areas are primarily horizontal. Typically, horizontal wind speeds are a thousands time greater than vertical wind speeds. (But the small vertical displacements of air have an important impact on ESS200 the state of the atmosphere.) ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 1 Vertical Structure of the Atmosphere Composition of the Atmosphere (inside the DRY homosphere) composition temperature electricity Water vapor (0-0.25%) 80km (from Meteorology Today) ESS200 (from The Blue Planet) ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Origins of the Atmosphere What Happened to H2O? When the Earth was formed 4.6 billion years ago, Earth’s atmosphere was probably mostly hydrogen (H) and helium (He) plus hydrogen The atmosphere can only hold small fraction of the mass of compounds, such as methane (CH4) and ammonia (NH3). water vapor that has been Those gases eventually escaped to the space. injected into it during volcanic eruption, most of the water vapor was condensed into The release of gases from rock through volcanic eruption (so-called clouds and rains and gave rise to outgassing) was the principal source of atmospheric gases. rivers, lakes, and oceans. The primeval atmosphere produced by the outgassing was mostly carbon dioxide (CO2) with some Nitrogen (N2) and water vapor (H2O), The concentration of water and trace amounts of other gases. vapor in the atmosphere was (from Atmospheric Sciences: An Introductory Survey) substantially reduced. ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 2 What Happened to N ? What happened to CO2? 2 Chemical weather is the primary Nitrogen (N2): process to remove CO2 from the atmosphere. (1) is inert chemically, In this process, CO2 dissolves in (2) has molecular speeds too slow to escape to space, rainwater producing weak (3) is not very soluble in water. carbonic acid that reacts chemically with bedrock and produces carbonate compounds. The amount of nitrogen being cycled out of the atmosphere was limited. This biogeochemical process reduced CO2 in the atmosphere Nitrogen became the most abundant gas in the atmosphere. (from Earth’s Climate: Past and Future) and locked carbon in rocks and mineral. ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Where Did O Come from? 2 Where Did Argon Come from? Photosynthesis was the primary process to increase the amount of oxygen in the atmosphere. Radioactive decay in the planet’s bedrock Primitive forms of life in oceans began to produce oxygen through added argon (Ar) to the evolving atmosphere. photosynthesis probably 2.5 billion years ago. Argon became the third abundant gas in the With the concurrent decline of CO2, atmosphere. oxygen became the second most abundant atmospheric as after nitrogen. (from Earth’s Climate: Past and Future) ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 3 Composition of the Atmosphere Key Atmospheric Properties important for physical climate ! T P q U, V, ω Water vapor (0-0.25%) (from The Blue Planet) ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Units of Air Temperature Fahrenheit (ºF) Celsius (ºC) ºC = (ºF-32)/1.8 Temperature Kelvin (K): a SI unit K= ºC+273 1 K = 1 ºC > 1 ºF ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 4 Vertical Thermal Structure Stratosphere Troposphere (“overturning” sphere) . contains 80% of the mass Standard Atmosphere . surface heated by solar radiation Standard Atmosphere The reasons for the inversion in . strong vertical motion the stratosphere is due to the ozone . where most weather events occur absorption of ultraviolet solar Stratosphere (“layer” sphere) middle energy. weak vertical motions atmosphere . dominated by radiative processes Although maximum ozone . heated by ozone absorption of solar concentration occurs at 25km, the ultraviolet (UV) radiation lower air density at 50km allows . warmest (coldest) temperatures at summer (winter) pole solar energy to heat up temperature Mesosphere there at a much greater degree. heated by solar radiation at the base . heat dispersed upward by vertical motion Also, much solar energy is absorbed in the upper stratosphere (from Understanding Weather & Climate) Thermosphere (from Understanding Weather & Climate) . very little mass and can not reach the level of lapse rate = 6.5 C/km lapse rate = 6.5 C/km ozone maximum. ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Mesosphere Thermosphere Standard Atmosphere Standard Atmosphere There is little ozone to absorb In thermosphere, oxygen solar energy in the mesosphere, and molecules absorb solar rays and therefore, the air temperature in the warms the air. mesosphere decreases with height. Because this layer has a low air Also, air molecules are able to density, the absorption of small lose more energy than they absorb. amount of solar energy can cause This cooling effect is particularly large temperature increase. large near the top of the The air temperature in the mesosphere. thermosphere is affected greatly by solar activity. (from Understanding Weather & Climate) (from Understanding Weather & Climate) lapse rate = 6.5 C/km lapse rate = 6.5 C/km ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 5 Vertical Cross-Section of Atmospheric Temperatures (from Global Physical Climatology) The global average temperature at Sudden Warming the surface of Earth is about 288 K, 15°C, or 59°F. Every other year or so the In Southern Hemisphere winter, the normal winter pattern of a polar stratosphere is colder than 180 cold polar stratosphere with K, and is the coldest place in the a westerly vortex is atmosphere, even colder than the interrupted in the middle tropical tropopause. winter. The polar vortex can The Northern Hemisphere completely disappear for a stratosphere does not get as cold, on period of a few weeks. average, because planetary Rossby waves generated by surface During the sudden topography and east–west surface warming period, the temperature variations transport heat stratospheric temperatures to the pole during sudden can rise as much as 40°K in stratospheric warming events. a few days! ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Why Sudden Warming? Why No Ozone Hole in Artic? Planetary-scale waves propagating from the troposphere (produced by big mountains) into the stratosphere. Those waves interact with the polar vortex to break down the polar vortex. There are no big mountains in the Southern Hemisphere to produce planetary-scale waves. Less (?) sudden warming in the southern polar vortex. (from WMO Report 2003) ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 6 The 1997 Ozone Hole Antarctic Ozone Hole Mean Total Ozone Over Antarctic in October The decrease in ozone near the South Pole is most striking near the spring time (October). During the rest of the year, ozone levels have remained close to normal in the region. (from The Earth System) ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu Polar Stratospheric Clouds (PSCs) Ozone Hole Depletion In winter the polar stratosphere is so Long Antarctic winter (May through September) cold (-80°C or below) that certain The stratosphere is cold enough to form PSCs trace atmospheric constituents can PSCs deplete odd nitrogen (NO) condense. Help convert unreactive forms of chlorine (ClONO2 and HCl) into These clouds are called “polar more reactive forms (such as Cl2). stratospheric clouds” (PSCs). The reactive chlorine remains bound to the surface of clouds particles. The particles that form typically Sunlight returns in springtime (September) consist of a mixture of water and nitric acid (HNO3). The sunlight releases reactive chlorine from the particle surface. The PSCs alter the chemistry of the The chlorine destroy ozone in October. lower stratosphere in two ways: Ozone hole appears. (1) by coupling between the odd At the end of winter, the polar vortex breaks down. nitrogen and chlorine cycles Allow fresh ozone and odd nitrogen to be brought in from low (Sweden, January 2000; from NASA website) (2) by providing surfaces on which latitudes. heterogeneous reactions can occur. The ozone hole recovers (disappears) until next October. ESS200 ESS200 Prof. Jin-Yi Yu Prof. Jin-Yi Yu 7 Lapse Rates Dry Adiabatic Lapse Rate (from Meteorology: Understanding the Atmosphere) • An important feature of the temperature distribution is the decline of temperature Standard Atmosphere with height above the surface in the lowest 10–15 km of the atmosphere. • This rate of decline, called the lapse rate, is defined by • A lapse rate is the rate at which temperature decreases (lapses) with increasing altitude. • Three different lapse rates we need to consider: (1) dry adiabatic lapse rate (from Understanding Weather & Climate) (2) moist adiabatic lapse rate • Air parcels that do not contain cloud (are not saturated) cool at (3) environmental lapse rate lapse rate = 6.5 C/km the dry adiabatic lapse rate as they rise through the atmosphere. ESS200 ESS200 Prof.
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