Attendance Sign-Up Sheet. A L: Light Yellow-Green. M Y: Bright Orange

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1 Attendance Sign-Up Sheet Last Name A L: Light Yellow-Green M Y: Bright Orange

2 Lecture #02 January 13, 2010, Wednesday (1) Thickness of the atmosphere (2) Composition of the atmosphere (3) Thermodynamic state variables of the atmosphere Temperature, Pressure, Density these 3 variables are linked by the ideal gas law (4) Vertical Structure of the Atmosphere

3 How high is the sky? The Thickness of the Atmosphere The top of the atmosphere is NOT clearly defined. Atmospheric density decreases rapidly with height % of the atmosphere is below 100 km altitude Very thin: < 2% of Earth s radius (~6,500 km). Shallowness or thin atmosphere atmospheric motions over large areas are mainly horizontal horizontal wind speed is typically much greater than vertical wind speed Jet Stream Vertical motions can be important in major weather events Storms

4 Atmosphere (composition): a mixture of gas molecules, microscopically suspended particles of solid and liquid, falling precipitation. Gases and particles are exchanged between Earth s surface and the atmosphere through physical (e.g., volcanic), biological (e.g., photosynthesis, respiration) processes. Longer residence time Residence time (exchange rate, concentration). Shorter residence time

5 Aerosols Any solid or liquid particle, other than water, which exists in the atmosphere. Synonymous with the term particulate. Both natural (sea spray, dust, volcanic) and human (combustion) sources. Due to small size, easily remain in suspension for long periods. Contribute to precipitation processes as condensation nuclei.

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7 A constant proportion of the atmosphere (i.e., fixed concentration). However, constantly cycle through the atmosphere, and so not really a permanent resident. }Trace Gases

8 Variable Gases (Concentrations vary spatially and temporally) (0-4) }Trace Methane CH Gases Greenhouse Gases: H 2 O, CO 2, CH 4 Directly affect the atmosphere s ability to retain energy from the sun (solar radiation) or the Earth (terrestrial radiation, greenhouse effect). Human activities (fossil fuel, deforestation) have attributed to the significant variations (increases) in methane and carbon dioxide.

9 The most abundant variable gas, also a greenhouse gas, but not a trace gas. Water Vapor (H 2 O) Added or removed from atmosphere through the hydrologic cycle (short residence time). Nearly 0% over desert and polar regions to nearly 4% near tropics. Major contributor to Earth s energy balance and many important atmospheric processes (e.g., weather events).

10 Carbon Dioxide (CO 2 ) A variable gas, a greenhouse gas, and a trace gas. Sources: biologic respiration, volcanic activity, decay, natural and human-related combustion. Removed from the atmosphere through photosynthesis. Methane (CH 4 ) A variable gas, a trace gas, and a greenhouse gas. Sources: fossil fuel, livestock digestion, agriculture cultivation (especially rice).

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13 Ozone (O 3 ) Tri-atomic form of oxygen (vary seasonally and spatially). Formed when atomic oxygen (O) bonds with molecular oxygen (O 2 ). A pollutant near the surface, causing health problem when its concentration > 0.1ppm or 100 ppb, kills trees. An essential absorber of ultraviolet radiation (UV) in the stratosphere where there is highest concentration. CFCs (chlorofluorocarbons) react with O 3 in the stratosphere thus destroy the ozone layer. Ozone destruction peaks over southern hemisphere, persists through Spring (Ozone Hole).

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15 Ozone Hole The ozone hole is usually measured not in terms of ozone concentrations at these levels (which are typically of a few parts per million) but by reduction in the total column ozone, above a point on the Earth's surface, which is normally expressed in Dobson units, abbreviated as "DU". The ozone hole occurs as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this circumpolar or polar vortex, over 50% of the lower stratospheric ozone is destroyed during the Antarctic spring.

16 The Antarctic ozone hole was equal to the record single-day largest area of 11.4 million square miles (or 29.5 million square kilometres), reached on Sept. 9, Satellite instruments monitor the ozone layer. Ozone Hole Blue & purple: the least ozone Green, yellow, red: more ozone. September 24, 2006 NASA

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18 Ozone Depletion comparison in North America The Ozone depletion does not affect only the south pole.

19 Ideal Gas Law General physics for gas: pressure = density x temperature x gas constant Pressure increases (decreases) when either or both density and temperature increases (decreases). When tires are heated up but its volume is held constant, tire pressure increases.

20 Temperature Temperature measures the amount of heat energy in a substance. It reflects the speed at which molecule/atom move. The higher temperature, the faster the movement. All molecular/atomic motions stop at 0 K. Average earth surface temperature: 59 o F = 15 o C = 288 K

21 Three Temperature Scales The Celsius and Fahrenheit scales permit negative values, implying an impossible negative heat scientists use the Kelvin scale. Zero K: no molecule vibration or movement. Fahrenheit: US. Celsius: everywhere else in the world.

22 Conversion between Temperature Scales o F = 9 / 5 o C + 32 o C = 5 / 9 ( o F 32 ) K = o C o C = K Which is the smallest change in temperature, 1 o F, 1 o C or 1 K?

23 Density Mass of a substance (in kg) contained in a unit volume (in m 3 ) density=mass/volume Changing either the number of molecules or the volume of an air parcel would alter air density. Atmosphere is compressible: the density of an air parcel increases (decreases) when pressure increases (decreases), if the air temperature is held constant.

24 Density Mean free path: average distance a molecule needs to travel before colliding with another molecule greater density means shorter mean free path length. Atmospheric density is greater at a lower level: Why? greater weight (more air mass in above that are pulled down by Earth s gravity) greater atmospheric pressure greater air density.

25 Atmospheric (Barometric) Pressure Atmosphere is composed of gas molecules that are subject to gravitational attraction by the solid earth molecule weight. Atmospheric pressure at a given altitude, in part, reflects the weight of the atmosphere above. Measurement: first barometer Torricelli (1643) Mean Sea Level Pressure: mb = inch Hg = 14.7 psi

26 Mercury Barometer Mercury is used instead of water because the atmosphere only needs to support a inch column of mercury, as opposed to a 37 foot column of water

27 Atmospheric (Barometric) Pressure 500 mb elevation: fewer molecules above, thus less pressure. About half of the atmospheric mass above and below this pressure level. At sea level: atmospheric pressure is mb due to more molecules above.

28 The atmosphere is not a homogeneous fluid. Its composition and state variables vary both vertically and horizontally. Here we focus on vertical variations by averaging atmospheric variables horizontally over the globe: pressure density temperature composition Radiosondes: weather instruments carried upward on balloons

29 Pressure decreases by half about every 5.5 km increase in altitude. Most rapidly near the surface.

30 Four Thermal Layers of the Atmosphere

31 Both temperature and pressure decreases with height (or altitude) in the Troposphere. Density decreases with height

32 Greek (Tropos) meaning overturning: The atmosphere is transparent to most of solar radiation that heats the surface, which then heats the atmosphere from below. Temperature decreases with altitude: average environmental lapse rate 6.5 o C km -1. Thinnest of the 4 layers. Troposphere Contains 80% of atmosphere Contains most of atmospheric water vapor. Most clouds and weather events.

33 Tropopause Transition zone: temperature ceases to decrease. The altitude of tropopause, or the thickness of troposphere is not uniform on the Earth, km over tropics, 9-10 km at the poles, and it is a function of the temperature of the troposphere. Flat top of cumulonimbus cloud overshoots into the stratosphere driven by violent updrafts.

34 Stratosphere Latin (Layer) : little vertical motions and turbulence. Maximum ozone (O 3 ) layer: km, but actual concentration may be as low as 10ppm (trace gas). Inversion: temperature increases with height, after initial layer of constant temperature. Why inversion: absorption of ultraviolet (UV) radiation by O 3, more absorption of UV near the top of this layer even though maximum O 3 is in the lower stratosphere. Thickness: > 3 times that of the troposphere, 19.9% atmospheric mass, dry. Little weather occurs.

35 In the stratosphere: very strong horizontal winds (jet streams) leads to rapid global distribution of aerosols, e.g., from the eruption of Mount Pinatubo in the Philippines in 1991 redder sunrises & sunsets. Volcano Mt. Pinatubo, 1991 Spread of sulfur dioxide & dust aerosol plume (red & yellow areas)

36 Volcano Mt. Pinatubo, 1991 Short-term cooling, by 1992, mean global surface temperature dropped by ~ 0.5 O C

37 Mesosphere & Thermosphere These two layers contain only 0.1% of the atmospheric mass, with % in the mesosphere. Mesosphere: Coldest layer Temperature decreases with height up to ~ 80 km Thermosphere: Merges with inter-planetary space Temperature increases with altitude up to 1,500 o C due to UV absorbed by molecular oxygen (O 2 ). But sparse mass precludes actual heat content.

38 Homosphere It includes troposphere, stratosphere, mesosphere. Below 80 km, % of atmospheric mass. Gases are well mixed with a uniform composition of the permanent gases. Thermosphere. Above the homosphere. Heterosphere Gases are layered, lighter gases (hydrogen & helium) more dominant. Composition changes with altitude. Not much permanent gases.

39 Ionosphere Ionosphere: from upper mesosphere to thermosphere. Not defined by temperature but electrical properties. Abundance of electrically charged particles (ions) due to bombarding by solar energy. Aurora

40 Ionosphere Sublayers: D-, E-, F- with increasing altitude. Daytime: D-layer absorbs AM radio waves. Nighttime: no solar radiation, D-layer disappears, E-layer weakens, F-layer reflects AM radio waves as does the Earth s surface.

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42 Auroras in the Ionosphere Subatomic particles (protons & electrons) emitted from the Sun captured by Earth s magnetic field and the energy excite atmospheric gases in the ionosphere. Aurora borealis (northern lights), Aurora australis (southern lights). Closely correlated in time with solar flare activity.

43 Temperature increase due to absorption of UV by O 2, high temperature, low heat content Maximum O 3 concentration ~ 10ppm Virtually all weather Coldest Atmosphere Ionosphere Auroras Inversion caused by O 3 absorption of UV. More UV available near the top. Mean environmental lapse rate = 6.5 C km -1, vertical motion, turbulence