Name SOLUTIONS T.A./Section Atmospheric Science 101 Homework #6 Due Thursday, May 30 th (in class) 1. General Circulation Briefly describe where each of the following features is found in the earth s general circulation. What meteorological conditions (wind, pressure, precipitation, temperature) might you find associated with each feature? A. Horse latitudes This region is found near 30º in both hemispheres. Specifically, they are in the middle of anticyclonic gyres over the oceans where winds are light, precipitation is light, pressure is high, and temperatures are generally high. B. Polar front The Polar Front is found near 60º N and 60º S. This is where cold air from the poles meets warmer air from the midlatitudes. Air converges and storms are common. Winds are variable but average out to westerlies at the surface and aloft, with a strong jet stream near the tropopause. On average pressure is low from all the midlatitude cyclones. Precipitation is generally high. C. Trade winds The trade winds are the return surface flow of the Hadley Cell. This region, between 10º and 30º N/S, is fairly consistent winds from the northeast in the NH and from the southeast in the SH (at least over the ocean). Temperatures are high, precipitation is variable depending on the location, and pressure is moderate and consistent. D. Intertropical Convergence Zone (ITCZ) The ITCZ is found generally at the equator. It moves slightly north in the NH summer and south in the NH winter, following the location of maximum daylight. Rainfall is abundant, pressure is low, winds are light, and temperatures are high but not scorching. 1
2. Advection of Air Masses by Anticyclone Explain how a synoptic scale anticyclone initially centered over the central US can bring record-breaking low temperatures and cp air (cold, dry continental air from Canada) to the southeastern US and only a few days later bring very high temperatures and mt air (warm, humid air from the Gulf of Mexico) to the same area. Hint: remember that mid-latitude pressure systems usually move from west to east. Winds flow clockwise around a NH anticyclone. As it moves eastward, it has winds from the north ahead of it and winds from the south behind it. If you were in Oklahoma, it would bring cold, dry (cp) air from Canada when it is to your west. As it passes overhead, winds are light. When it has passed you (it is now to your east), the winds are from the south. Warm, moist air from the Gulf of Mexico (mt) will come your way. High pressure systems typically move across the country in a week, so they can bring cold air for a couple days as they approach and then bring warm air for a few more as they move away. 3. Surface Fronts A. List four types of weather data that can help identify the location of a front. 1. Winds 2. Pressure 3. Clouds 4. Dew Point 5. Temperature 2
B. Use this information to identify the location of the warm front, cold front, and surface low on the following map. Use the proper symbols to denote the cold and warm front. Use Appendix C in your book (simplified surface station model) to help interpret the symbols on the map. Note that the pressure tendency is not shown here. 3
4. Contrast clouds and precipitation from cold and warm fronts Explain why the passage of a cold front is often associated with cumulonimbus clouds and heavy rain, whereas the passage of a warm front is usually associated with stratus clouds and little or no rain. Draw a sketch for each case, to aid your explanation. Cold Front: Warm air is lifted sharply as cold air is forced to flow underneath warm air at a vertically sloping cold front. The warm air is often lifted high enough so that adiabatic cooling condenses water vapor into tall cumulonimbus clouds and raindrops grow large enough to fall. Cold Air Warm Air Warm Front: In the case of a warm front, the boundary between warm and cold air is more gradual, and the environment is more stable to vertical motion. The warm air overrunning the cold air beneath is lifted gradually--enough to form stratus clouds but usually not enough to form heavily precipitating cumulonimbus clouds. Warm Air Cold Air 4
5. Southern Hemisphere Mid-Latitude Storm Consider an extratropical (midlatitude) cyclone in the Southern Hemisphere. A. Sketch the pattern of the surface winds around the low-pressure center denoted by L below. B. Sketch the location of the warm front and the cold front relative to the low-pressure center. Think about which direction the warm air is coming from, which direction the cold air is coming from and which way the winds are going around the low. (Your answer does not have to be perfect, but you have to get the right idea and orientation of the fronts.) N L 5