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• What you should bring for exam: 2B pencil, pencil/pen, your photo ID • Exam Length: 50 minutes Date and Time: Feb 13th:Monday,11:00-11:50 am • Location: our lecture room, Franz 1178 AOS 3 Mid-term Review • Exam Layout: Winter 2012 by Yang Cao Review Time : Feb 10th Friday Location : Franz Hall 1178 1) around 36 Multiple-choice questions 2) around 20 Filling-blank questions 5:00 – 6:50 PM • Coverage: 1 From the beginning through the end of Chapter 4: Atmospheric Pressure. 2 Atmosphere is a relatively thin layer. Earth Viewed from space, it appears to hug the ground. 3 4 Nitrogen (78.08%) Permanent Gases Oxygen (20.95%) more abundant (Fixed Gases, Non-variable Gases) Most abundant variable gas Argon (0.93%) …… Atmosphere Water Vapor Variable Gases Minor constitutes are also very important. Carbon Dioxide Ozone Methane …… Greenhouse gases (absorb Infrared Radiation) • Ozone also absorbs Ultraviolet radiation 5 6 • being cycled in Produced by • Ozone in the stratosphere (97% of the total atmospheric ozone) : ‘Good Ozone’ • Stratospheric Ozone absorbs harmful Ultraviolet (UV) radiation— ‘earth’s natural Sun scream’ Removed by 7 20 -40 km • Ozone in the stratosphere screens UV radiation. • Human exposure to UV increases the risk of skin cancer. • If there’s less Ozone in the stratosphere, more UV radiation gets to the earth; • If there’s more Ozone in the stratosphere, less UV radiation gets to the earth. 9 Weight of air Air is compressible, water can be treated as uncompressible. " Pressure goes down with increasing altitude simply because the weight of the air above some point decreases as we travel upward; " Pressure and density decreases exponentially (extremely quickly) with height, due to the compressibility of air. 11 Ozone near the surface: ‘Bad Ozone’ (eat rubber; damage plants, contribute to smog) earth 8 Why Ozone Hole at South Pole? -- South Pole is much colder than the North Pole, and the reaction between Chlorofluorocarbon and Ozone needs a very cold environment. Ozone hole at the South Pole A chemical released from refrigeration and air conditioning, manufacture of plastic foams, solvents. !reduction of the stratosphere ozone 10 over Antarctica. • The most important direct source of energy for the atmosphere is not downward-moving solar radiation but rather energy emanating upward from Earth’s surface. • The reason is that the atmosphere is relatively transparent (absorb Ultraviolet radiation) to most types of radiant energy emitted by the Sun and opaque to outgoingTerrestrial Radiation. (80% of the atmospheric mass) 12 *The ionosphere influences the distance to which AM radio waves can be transmitted. D, E layer(exist only daytime): absorptive;F layer: reflective Gas constitutes uniformly distributed expect Ozone and Water Vapor • During the day, the Dlayer absorbs the radio waves, the D-and Elayer break up at night, allowing the waves to reach the F-layer. • The F-layer reflects the radio waves back towards Earth’s surface. Lighter gases (Hydrogen, Helium) increase with height Earth • Repeated reflections between the F-layer and Earth’s surface enable the waves to be picked up by receivers at greater distances at night. 13 14 15 16 17 18 Representing Weather elements on the map 19 20 Macroscopic KE Microscopic KE 21 22 Converting Celsius to Kelvin: Heat ~ ! Energy (cumulative ) T ~ Energy (average) Converting Fahrenheit to Celsius: Converting Celsius to Fahrenheit: 23 24 Conduction (slowest) Heat transfer: Convection (moderate) 1) Radiation (fastest) 25 2) 3) 27 29 28 • Ozone absorbs Ultraviolet radiation • Solar radiation is mainly shortwave radiation (visible light takes up to 50%) • Terrestrial radiation (from the earth) is mainly longwave (Infrared radiation) • Greenhouse gases (water vapor, carbon dioxide, ozone, methane) absorb infrared radiation 30 E emitted= E absorbed Intensity of radiation If Ta: Tb=2:1. Then Ea:Eb=16:1. ‘Plank curve’ 31 32 (µm) constant=2900 This is shortwave radiation! (1 µm =10 -6 m) 33 34 r r This is longwave radiation! E ~ 1 / r2 35 36 E received on a planet ~ 1 / r2 (r = distance away from the Sun) depending on ( Depending on solar altitude (angle): 0~90° ) ( Duration of daylight ) Solar altitude 37 38 tilting angle A common misunderstanding is the seasons are determined by the distance of the Earth from the Sun. The actual reason is the tilt of the Earth’s axis of rotation. Ecliptic Plane shortest distance longest distance 39 40 41 42 Equator Always so for Equator 43 44 June 21 December 21 30°N 30°S 45 Solar altitude Solar altitude 47 46 Inverse square law E ~ 1 / r2 49 50 (shorter wavelength) (during daytime) A higher solar altitude (angle) allows sunlight to pass through the atmosphere with a relatively short path. 51 52 53 54 (red setting sun) At sunset • At sunrise or sunset, the sunlight passes through longer path of the atmosphere. • This increase in atmospheric length results in a depletion of mostly preferential scattering light—bluish light. • Blue light has been depleted through transmitting the longer path of atmosphere during sunset, leaving mostly red lights reaching our eyes. latitude dominates Clouds dominate: more humid at the East Coast=> more clouds=> less radiation 55 56 57 58 59 60 Net lost SH+LH= 29 units! Net gain 61 62 63 64 * Solar radiation can be treated as shortwave radiation. * Terrestrial radiation can be treated as longwave radiation. * The atmosphere is almost transparent to solar radiation (does NOT absorb solar radiation). But atmosphere is a good absorber of longwave terrestrial radiation emitting from the earth surface . Without Greenhouse Effect With Greenhouse Effect 65 66 This figure shows the balance between incoming and outgoing radiation varies with latitude on an annual basis. The Earth is spherical, the poles receive less intense sunlight than the tropics. This imbalance is alleviated by transport or circulation of heat poleward by the 67 atmosphere and oceans. Slope aspect is one of the local factors affecting temperature: • In the north hemisphere: north-facing slopes typically receive less intense daytime heating=> lower temperature=> retards the rate of surface evaporation=> more water available for plants. 68 Maximum daily temp: mid-to-late afternoon; daily temp curve Minimum daily temp: just after sunrise. Red curve: depending on earth’s temperature 69 Effect of Cloudy condition on Daily Temperature Range 1.Clouds can REDUCE daily temperature range: Reason: 1) During the day: clouds can shade the earth surface, reduce the incoming solar radiation received at the surface=> decrease max temp; 70 Effect of Windy condition on Daily Temperature Range 2. Reason: Higher wind speeds promote greater forced turbulence ! the enhanced vertical movement causes any small parcel of air immediately in contact with the ground to be quickly displaced upward and replaced by another parcel ! enhance air mixing! !make the vertical temperature profile much more uniform (homogeneous) ! reduce daily temperature ranges (shown in figures). Calm height height Windy 2) During the night: clouds absorb the outgoing LW radiation emitting from the earth=> increase min temp. Temperature 71 Temperature Inversion phenomenon: temperature increases 72 with height near the ground, very common during the night. When heated or cooled Measure maximum temperature only: contain mercury, has within a small constriction that only allows the mercury to move outward from the bulb. Measure minimum temperature only: contain dyed alcohol, has within a small dumbbell-shape index. Surface tension pulls the index toward the bulb when temperature is decreasing.73 All metal have different rates of expansion and contraction with temperature, one undergoes a greater change in length than the other. A thermistor is a particular type of resistance thermometer that uses a ceramic semiconductor instead of a metallic wire for a filament. 74 Located 1.5 meter above the ground 75 76 77 78 (Fundamental force to drive winds) different associated with Friction 80 Pressure decreases exponentially (extremely quickly) with height, due to the compressibility of air. 81 82 83 84 Barometric pressure is often expressed as the height of the column of mercury in a barometer. Mercury is adopted because it is extremely heavy, and allows the instrument to be of a manageable size. The atmosphere presses on the chamber and compresses it by an amount proportional to the air pressure. Means “without liquid” An aneroid barometer and its working. Isobars on weather map are usually at 4mb intervals. 1 mb (millibar=100 pascal) 85 86 500mb height contour map weaker pressure gradient greater pressure gradient The contour labels tell how high you must go upward from the surface to find a pressure of 500 mb. 87 88 89 90 Arise due to the rotation of the earth Pressure gradient force (PGF): the fundamental force to drive winds 91 92 This is the vertical plane: 93 94 Gradient wind This is the horizontal plane! Subgeostrophic wind PGF Supergeostrophic wind PGF Geostrophic flow occurs only in the upper atmosphere where friction is absent and only the Coriolis and PGF apply. 95 96 wind Angle between winds and the isobars: 15~30 degree wind PGF (The angle is greater at higher latitudes and over smooth surfaces.) PGF 97 98 Surface Weather Map Wind direction We have friction Converging wind around the Low at the surface Diverging wind around the High at the surface Cyclone Anticyclone 99 100 Difference between (anti)cyclone and Trough/Ridge 850 mb (~1.5 km) Ridge: elongated areas around the High Pressure 700 mb (~3 km) Trough: elongated areas around the Low Pressure 500 mb (~5.5 km) 101 300 mb (~9 km) Many low- and high- pressure systems occur not as closed cells, but rather as troughs (low p) and ridges (high p). E.g.,there is a tendency for pressure to be distributed as cyclones and anticyclones at the surface gradually give way 102 to ridges and troughs in the upper atmosphere. Aerovane: measure both speed and direction 103