SIO20 - Midterm Examination 2 v1 Winter Section A. Circle the letter corresponding to the best answer. (1 point each)

Transcription

1 NAME: Section A. Circle the letter corresponding to the best answer. (1 point each) 1. Rainbows result from: a. refraction and reflection of sunlight by water droplets b. reflection of sunlight by oceans and large lakes c. selective scattering of visible light by air molecules d. optical illusion resulting from the limitations of human eyesight 2. At sunset in the middle latitudes, look for a rainbow toward the: a. north b. south c. east d. west 3. If the earth did not have an atmosphere, the sky would appear during the day. a. white b. black c. red d. blue The sky is normally blue because molecules in the atmosphere scatter blue light the most. If there were no atmosphere, there would be no molecules to scatter light and the sky would be black. 4. In the Northern Hemisphere, the wind around a high pressure flows: a. clockwise b. counterclockwise c. northerly d. southerly 5. The force that would cause a stationary parcel of air to begin to move horizontally is called the: a. Coriolis force b. Pressure gradient force c. Centripetal force d. Frictional force 6. On average, the height of the 500 mb level generally as one goes from the equator to the poles. a. increases b. decreases c. stays the same 7. The net force acting on air which is moving parallel to straight isobars at constant speed is: a. in the direction of motion b. to the right of the wind s motion in the Northern Hemisphere 1/5

2 c. zero d. in a direction opposite the wind s motion 8. We learned that there are many types of atmospheric circulations. In general, as the size of atmospheric circulations increase, their time scale (i.e., lifetimes): a. increases b. decreases c. stays the same d. varies without relation to the spatial scale 9. A wind blowing at a constant speed parallel to straight line isobars is a geostrophic wind. This wind is produced by a balance between: a. the gravitational force and the pressure gradient force b. the gravitational force and the Coriolis force c. the Coriolis force and the pressure gradient force d. the pressure gradient force and the frictional force 10. Suppose you observe clouds 4 km above the surface moving from north to south. Assuming that the winds at cloud level are geostrophic, low pressure is located a. to the north b. to the south c. to the east d. to the west 11. A sea-breeze circulation results from: a. the unequal heating rates of land and water b. rotation of the earth c. planetary scale pressure patterns d. offshore ocean currents 12. The main reason Santa Ana winds tend to be warm is because: a. latent heat is released in rising air b. sinking air warms by compression c. condensation occurs d. solar heating warms the air 13. In a sea-breeze circulation, the wind near the surface is directed: a. from the land towards the ocean b. from the ocean towards the land c. from north to south d. offshore 14. The summer monsoon in eastern and southern Asia is characterized by: a. wet weather and surface winds blowing from land to sea b. dry weather and surface winds blowing from land to sea c. wet weather and surface winds blowing from sea to land 2/5

3 d. dry weather and surface winds blowing from sea to land 15. The intertropical convergence zone (ITCZ) is a region where: a. the polar front meets the subtropical high b. northeasterly tradewinds meet southeasterly tradewinds c. the Ferrel cell converges with the Hadley cell d. surface winds are diverging 16. The surface pressure at the bases of warm and cold columns of air are equal. Air pressure in the warm column of air will with increasing height than in the cold column. a. decrease, more rapidly b. decrease, more slowly c. increase, more rapidly d. increase, more slowly 17. In its normal position, the Pacific High is responsible for: a. the advection of cool moist surface air over the southeastern U.S. b. the advection of cool moist surface air over the southwestern U.S. c. the advection of warm moist surface air over the southwestern U.S. d. the spawning of many Pacific Ocean hurricanes 18. In the Northern Hemisphere, the tradewinds are located: a. between the equator and 30 N b. between 30 N and 60 N c. between 60 N and the North Pole d. only beneath the polar front 19. Ocean currents: a. are primarily driven by the atmospheric circulation b. are the primary driving force for atmospheric circulation c. have no relation to the atmospheric circulation 20. The surface winds in the tropics (~0 to 30 ) are: a. generally from west to east b. generally from east to west c. from ocean to land d. from land to ocean 21. Much of the effect of El Nino on the winter climate of California can be attributed to: a. an increase in the tropopause height over Southern California b. a decrease in the solar radiation absorbed at the surface due to increased cloudiness over California c. an intensification and shifting of the subtropical jetstream d. an increase in surface temperature over much of the continental U.S. 3/5

4 Section B. Define the following in a few words. (2 points each) Refraction The bending of light (as it passes through substances with different density). Onshore wind Wind that blows from the water towards the land Westerly wind Wind that blows from the west to the east Wind Shear Wind speed changes with height (or along a horizontal direction). Isobar A line of equal pressure. Section C. Briefly answer the following questions in a few sentences. (3 points each) 1. Most of the deserts on Earth are located close to 30 latitude. What feature(s) of the general atmospheric circulation is (are) primarily responsible for this? Why? At 30, the flow in the Hadley and Ferrel cells converges aloft. This convergence of air creates a surface high pressure at 30. High pressures are typically very stable with little of no precipitation. Additionally, the air above 30 is sinking toward the surface. Sinking air compresses which increases the temperature of the air. This also decreases the relative humidity. Both of these effects are responsible for the vast majority of the world s deserts being located near 30 latitude. 4/5

5 2. Why is the sky blue during midday? Why does the sky often turn a reddish/orange color at sunrise and sunset? The atmosphere (primarily N2 and O2 molecules) is a selective scatterer, that is the amount of light scattered by the atmosphere depends on the wavelength. The atmosphere primarily scatters the shorter blue wavelengths and a much smaller amount of the longer orange/red wavelengths of incoming sunlight. The more times light is scattered the better chance there is for that light ray to be absorbed or bounced back to space. During the middle of the day, the light must pass through a relatively thin layer of atmosphere and not too much of the scattered blue light is lost. This is why the sky appears blue during the midday. A small amount of the longer visible wavelengths of orange and red are also scattered, but the blue light dominates since much more of it was scattered. At sunrise and sunset, the light must pass through a much thicker layer of atmosphere. Consequently, there is much more scattering of the blue wavelengths and now most of the blue light rays are lost (either absorbed or bounced back to space) before reaching the surface. The majority of visible light reaching the surface at sunrise and sunset is the longer wavelengths of orange and red. The atmosphere (as well as some larger aerosols and pollutants) does still scatter a little bit of the orange and red wavelengths and this is why the sky appears reddish at sunrise and sunset. 3. Explain how the polar jet forms. In what season does the polar jet stream reach its maximum intensity? Why then? The polar front separates the cold air in the Polar cell from the warmer air in the Ferrel cell. The cold air is denser than the warmer air. This difference in density will lead to a pressure gradient force (PGF) aloft pointed towards the pole. The air aloft will begin to move toward the pole in response to the PGF, but the Coriolis force will act deflecting the air to the right (in the NH). This forms the polar jet stream which is a fast current of air moving from west-to-east in the upper levels of the atmosphere usually directly above the polar front. The polar jet stream reaches it's maximum intensity during the winter season since this is when the temperature difference across the polar front is at a maximum. 5/5