Lab G - Atmosphere and Climate. Lab I Temperature and Pressure - Presssure Portion

LAB G - ATMOSPHERE AND CLIMATE LAB I TEMPERATURE AND PRESSURE – PRESSURE PORTION Introduction This lab will provide the student with the opportunity to become familiar with the concepts introduced in Chapter 5. Students will review the element of pressure and its effect on global circulation and weather patterns. Materials needed: textbook, atlas, pencil, calculator, colored pencils, and World Map (last page) Part II. Atmospheric Pressure and Wind The atmosphere (air) does weigh something and this weight exerts force or pressure on all surfaces. At Sea Level air presses down at an average of 14.7 lbs. per square inch. At Phoenix (1,092 ft. above Sea Level) the atmospheric pressure, or weight of the air, is less than 14.7 lbs. per square inch because there is 1,092 fewer feet of atmosphere above the city. Around the globe, air is either rising (warm air) or sinking (cool air), in response to temperature variations. If air is sinking, the weight of the atmosphere above is increased and the atmospheric pressure is said to be high (high pressure). Conversely, if the surrounding air is rising, the weight of the atmosphere above is decreased and the atmospheric pressure is low (low pressure). If air is rising in some places and sinking in others, the sinking air must flow back to places where the air is rising in order to balance global atmospheric pressure. Thus, air always flows from areas of high pressure (sinking air) to areas of low pressure (rising air). This horizontal movement of air is known as advection, or wind. Atmospheric pressure, also known as barometric pressure, is measured with a barometer. Different types of barometers are used and they measure pressure in different units. Some barometers measure pressure in lbs. per square inch or in inches of mercury, as differing weights of air will push mercury up a glass tube to differing heights. Other barometers measure the pressure of the atmosphere in SI units called millibars (mb). The average atmospheric pressure at Sea Level on earth is 14.7 lbs. per square inch, 29.92 inches of mercury or 1013.25 millibars (mb). Image source: Christopherson, R.W., 1994: Geosystems: An Introduction to Physical Geography G-1 A. Using the graph paper below, plot the data from Table G-1. These data are pressures in relationship to altitude for a “Standard Atmosphere”. Connect your points with a line. The curve you will draw shows how pressure changes as altitude increases. Table G-1 Standard Barometric Pressures at specified heights above sea level Height (km) Pressure (mb) 0 1013.25 1 899 3 701 5 540 7 411 10 264 20 55 30 12 40 3 50 1 1. Using your own words, describe what you see in terms of the relationship between height and pressure. Be sure to comment on the rate of change with altitude. _____________________ ___________________________________________________________________________ ___________________________________________________________________________ 2. Using the following locations and what you learned above, answer the following. a. Which location would have the lowest standard barometric pressure? ________________ b. Which location would have the highest standard barometric pressure? _______________ Lewis Hills, Newfoundland (2,672 ft) Mt. Hood, Oregon (2.13 miles) Humphrey’s Peak, Arizona (12,633 ft) Cheyenne, Wyoming (6,100 ft) Mt. McKinley, Alaska (20,320 ft) Mt. Mitchell, North Carolina (2,040 meters) G-2 B. Air flows from areas of high pressure to areas of low pressure. The direction of this flow is influenced by three variables: Pressure Gradient, Coriolis Effect and Friction. Remember that pressure gradient is the force that causes air to move from areas of high pressure to areas of low pressure. Once the air is moving, Coriolis will then act upon it causing it to be deflected from its path of motion. Pressure gradient is related to wind speed. In regions where the pressure gradient is weak (small change in pressure over distance = wide spacing between isobars), the winds are weak; where the pressure gradient is steep (large change in pressure over distance = closely spaced isobars), the winds are strong. This relationship is depicted in Figure G-4. Figure G-4 Using the diagrams below, indicate with an arrow, the direction of movement of a parcel of air in the Northern Hemisphere under the following conditions (variables): Fig G-5: influenced by Pressure Gradient only and Fig G-6: influenced by Pressure Gradient and Coriolis Effect. Figure G-5: Pressure Gradient only Figure G-6: Pressure Gradient and Coriolis Effect* * Use one arrow that represents the “end result” for a wind when PGF and Coriolis are the only two forces present. C. Using Figure G-5, examine the pressure gradient between 1004 mb and 998 mb and the pressure gradient between 998 mb and 990 mb. Describe the difference between these two regions. Hint: Review the relationship between isobar spacing, pressure gradient and wind speed. G-3 D. How does air flow if pressure gradient is the only force? (across the isobars at a right angle, parallel to the isobars, across the isobars at a 45° angle). Circle the correct answer. Diagram wind direction associated with the following pressure cells influenced by pressure gradient only. (NO Coriolis Effect and NO Friction). Northern Hemisphere Southern Hemisphere E. How does air flow if pressure gradient and coriolis are the only forces? (across the isobars at a right angle, parallel to the isobars, across the isobars at a 45° angle). Circle your answer. Diagram wind direction associated with the following pressure cells influenced by pressure gradient and Coriolis effect (NO Friction). Northern Hemisphere Southern Hemisphere F. How does air flow if pressure gradient, coriolis, and friction are the forces? (across the isobars at a right angle, parallel to the isobars, across the isobars at a 45° angle). Diagram wind direction associated with the following pressure cells influenced by pressure gradient, coriolis effect and friction. Northern Hemisphere Southern Hemisphere G-4 G. Why is friction so important in determining wind direction? _______________________ ________________________________________________________________________ H. Which low pressure cell has the steeper (stronger) gradient? (left or right picture) _______ I. Which low pressure cell would have the stronger/faster winds? Why? ________________ __________________________________________________________________________ Part III. Global Pressure and Wind Systems The following questions refer to the World Map (attached – see last page). Use this map to construct a generalized global circulation model for an Equinox. Then answer the associated questions. A. Draw in the Intertropical Convergence Zone (ITCZ). 1. Is this a high pressure or low pressure zone? 2. Why? 3. Is the air rising or sinking? B. Draw in the Subtropical High (STH) pressure zones and their five main cells of high pressure. 1. Why is the air sinking here? 2. Examine the “Pressure and Predominant Wind” maps in Goode’s World Atlas. Starting with the Southern Hemisphere, at which time of year are the STH cells more distinct and in which season are they more “belt-like”? Is this behavior also apparent in the Northern Hemisphere STH cells? 3. What causes these observed changes in the STH from appearing ‘belt-like’ to more defined cells? G-5 C. Draw in the Trade Winds. From which global pressure system do the Trade Winds in the Northern Hemisphere originate? C. Draw in the Westerlies. 1. Describe the general flow pattern of the Westerlies. 2. Describe the difference between surface air patterns and those in the upper atmosphere in the zone of the Westerlies? E. Mark the location of the Subpolar Lows. Why is air rising here? F. Draw in the Polar Easterlies. What is the relative temperature of these winds? G. Mark the location of the Polar Highs. Why is there high pressure here? Is the air sinking or rising here? __________________ H. Draw arrows on the world map denoting the general direction of the major ocean currents. Draw warm currents in red and cold currents in blue. I. Using the 3-cell model (with no seasonal shifting) for the general circulation of the atmosphere, give the prevailing wind direction for the following locations. Use the atlas to determine the latitude and longitude for each location, then answer the question. 1. 2. 3. 4. 5. Skjálfandafljót River, Iceland (______°N, _____°W) = ______________________ Yozgat, Turkey (______°N, _____°E) = _________________________________ Kimba, Australia (______°S, ______°E) = __________________________ Goundam, Mali (_____°N, ______°W) = _____________________________ Molepolole, Botswana (_____°S, ______°E) = ___________________________ G-6 J. Name five countries dominated by the Westerlies. K. Name five countries dominated by the Trade Winds. L. Name three countries that are influenced by the ITCZ in June but not in December. M. Why do the global pressure zones and wind systems shift north and south during the year? N. Phoenix, Arizona is located at approximately 33° N near the west coast of our continent. a. Describe the typical weather conditions you would experience here in June. ________ b. Which pressure system or global wind belt dominates the region at this time and creates these conditions? ____________________________________ c. Describe the typical weather conditions you would experience here in January. ________ d. Which pressure system or global wind belt dominates the region at this time and creates these conditions? ____________________________________ O. Using the circulation diagram for the month of June (below), diagram the corresponding situation for the month of December and an Equinox date. Show the shift of the ITCZ and the new locations of the subtropical high pressure zones. EQUINOX 60ºN_____________30ºN________________0º________________30ºS______________60ºS DECEMBER 60ºN______________30ºN________________0º________________30ºS______________60ºS G-7