Understanding Global Atmospheric Circulation and Wind Patterns

Name: Insert name here Lab 10: General Atmospheric Circulation Objective: This lab is designed to determine the global atmospheric wind patterns and pressure systems that create atmospheric motion. Distinct pressure systems, such as El Nino, will be diagnosed along with analyses concerning its effects on weather patterns across the United States. Materials needed: Calculator and Textbook Part 1: Global Pressure and Wind Belts Well-defined patterns dominate the distribution of pressure and winds across the globe. The largest-scale patterns, called the general circulation, can be considered the background against the daily wind and pressure variations. Well established pressure zones at distinct latitudes create dominant planetary wind motions. 1. Use your textbook and label the Earth’s 3-Cell model by completing the following: ✓ Label the correct locations of the pressure zones ✓ Label the correct locations of the global wind belts ✓ Label the distinct thermally driven cell circulations Polar cell Enter pressure zone. Enter wind belt. Subpolar law. Ferrel Cell Westerlies subtropical high Hadley cell . NE Trade-in Ferrel cell SE trade wind sub tropical Polar cell Sub polar law easterlies 1

Enter thermal cell. Enter pressure zone. Enter wind belt. Enter thermal cell. Enter pressure zone. Answer the following questions about the general circulation of the atmosphere. 1. List the pressure zones that would be considered cloud and precipitation producers. ITCZ and Lower pressure 2. List the pressure zones that would be considered dry and free of clouds. Subtropical highs and higher pressure 3. Which wind belt controls the circulation of the atmosphere in Crystal Lake? Westerly 4. True of False? The ITCZ changes its location based upon the seasonal variations of solar energy. TRUE 5. Which pressure belt is responsible for creating the Sahara Desert in North Africa? Subtropical high pressure 6. Which pressure zone is sometimes called the “doldrums”? ITCZ 7. Which cell is sometimes associated with the horse latitudes? Subtropical high 8. Simply by looking at a satellite image of the Earth from space, how could you detect the location of the ITCZ? There are huge bunches that you’d recognize 2

9. If these wind belts are permanently established, how come we don’t always have a west wind in Crystal Lake? They don’t actually exist Part 2: Upper Air Maps Winds in the upper atmosphere are controlled by distributions of temperatures and pressures at varying heights. These upper air circulations are discernable on maps located at standard constant pressure surfaces of 850 mb, 700 mb, 500 mb, and 250 mb. Numerous features such as low level moisture fields and jet streams, local spinning (vorticity) of the atmosphere and upper air jet streams are amongst the features discernable on these upper air maps. 850 mb maps: The 850 mb map is the lowest standard constant height chart used in meteorology for upper air analysis. The 850 mb map often displays a low level moisture and temperature field which helps in determining precipitation type, rain or snow. The low level maps also determine if a low level jet is present to advect moisture into a storm system. The blue shading indicates locations of a jet stream. 3 Solid Lines Dashed Lines

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For the 850 mb map above the solid lines represent heights in meters, so a value of 475 is equivalent to 1475 meters. The dashed lines represent temperature in degrees Celsius. The stations provide actual data points, however the pressures are given as heights of the 850 mb surface above the ground in meters. From the 850 mb map on the previous page, answer the following questions: 1. What is the date and local time (CST) of the map above? October 24, 2006 at 7 am 2. The height of this map above the ground can be represented by solid height contours. a. What is the approximate average height of this map in meters? 1500 Meters b. If there are approximately 3.28 feet in one meter, how many feet above the ground is this map representing? 5000 ft 3. Find the station for Peoria, Illinois and write down the current temperature, dew point, wind speed and 850 mb height in meters. -7 C Dewpoint: -15 C 475 MB 1475 Meters 4. Find the station for Los Angeles, California and write down the current temperature, dew point, wind speed and 850 mb height in meters. 15 C -5 Dewpoint 486 MB 1486 Meters 5. Which station has the thicker atmosphere from the ground to 850 mb? Why? LA because it has hotter temps. 4

700 mb maps: The 700 mb map is the considered the lower portion of the troposphere. The 700 mb map often displays low level moisture and temperature field which help in determining moisture available for precipitation. The blue shading indicates locations of a jet stream. For the 700 mb map above the solid lines represent heights in meters, so a value of 078 is equivalent to 3078 meters. The dashed lines represent temperature in degrees Celsius. The stations provide actual data points, however the pressures are given as heights of the 700 mb surface above the ground in meters. 1. The height of this map above the ground can be represented by solid height contours. a. What is the approximate average height of this map in meters? 3000 meters 5 Solid Lines Dashed Lines

b. If there are approximately 3.28 feet in one meter, how many feet above the ground is this map representing? 10000 ft 2. Find the station for Peoria, Illinois and write down the current temperature, dew point, wind speed, and 700 mb height in meters. -10 C -42 dewpoint 956 mb 27056 3. Find the station for Los Angeles, California and write down the current temperature, dew point, wind speed and 700 mb height in meters. 3 C 1 Dewpoint 93 mb 3093 meters 4. What’s happening to the temperature and dew point and wind speed as you increase in height over Peoria, Illinois? The higher you go, the colder it gets 500 mb maps: The 500 mb map is the considered the upper portion of the troposphere. The 500 mb map lines of constant height often indicate the general flow of storm systems, as they tend to follow the line like a road map. Many times these map will display locations of high absolute vorticity, which indicates the amount of spin in the atmosphere usually associate with short wave systems embedded within the long wave pattern. The blue shading indicates locations of a jet stream. 6

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For the 500 mb map above the solid lines represent heights in meters, so a value of 710 is equivalent to 5710 meters. The dashed lines represent temperature in degrees Celsius. The stations provide actual data points, however the pressures are given as heights of the 500 mb surface above the ground in meters. From the 500 mb map on the previous page, answer the following questions: 1. The height of this map above the ground can be represented by solid height contours. a. What is the approximate average height of this map in meters? 5500 meters b. If there are approximately 3.28 feet in one meter, how many feet above the ground is this map representing? 18000 2. Find the station for Peoria, Illinois and write down the current temperature, dew point, wind speed and 500 mb height in meters. -15 C -24 dewpoint 3060 meters 3. Find the station for Los Angeles, California and write down the current temperature, dew point, wind speed and 500 mb height in meters. -15 C 7 Solid Lines Dashed Lines

-17 dewpoint 5730 meters 4. Even at 500 mb, which is well above the surface, the winds at Los Angeles never really got strong. Why not? LA because not in the direct of the wind Part 3: Rossby Waves and Short Waves The ridges and troughs give rise to wavelike flow in the upper atmosphere of the middle latitudes. The largest of these are called long waves , or Rossby Waves. Usually, there are anywhere from three to seven Rossby waves circling the pole at any given time. As these waves migrate from west to east around the globe, they often contain smaller systems embedded within the high amplitude wave called short waves . 8

The 500 mb map on the previous page represents long waves (Rossby waves) represented on a northern hemispheric projection looking down on top of the North Pole. Complete the following tasks using the previous 500 mb map: 1. How many distinct troughs did you find on the map? 4 2. How many distinct ridges did you find on the map? 7 3. How many total distinct Rossby waves did you find on the map? 11 9

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4. What kind of temperatures would you expect for a location that is located in the middle of a large dip (trough) in the mean flow? 0 C 5. Locate Illinois on the map and place a star for the approximate location of Crystal Lake. If these Rossby waves move like waves on an ocean, and they generally propagate from west to east, would you expect over the next couple of days MCC would be situated over a trough or a ridge? Why? 6. When there are no distinct Rossby waves located on a region of the map, the 500 mb height lines tend to become fairly straight line. This establishes a wind regime often called flow. 7. When a Rossby wave trough grows too high in amplitude, what often happens to the base of the trough? Click here to enter text. The following maps represent the 500 mb mean flow over the United States. The shaded regions indicate locations of maximum absolute vorticity (spin). The long wave Rossby pattern is recognizable with short waves embedded in the mean flow distinguished by the letter “X”. The major Rossby wave axis is denoted with a heavy dashed line. 10

Day 1 Day 2 Day 3 Day 4 Use the day 1 – 4 maps on the previous page to answer the following questions. 1. Does the amplitude of the Rossby wave tend to increase or decrease between day 1 and day 4? Increase 11

2. What does this imply about the strength of any small scale storm system located within the mean long wave trough? Click here to enter text. 3. Embedded with the long wave trough is a small scale storm called a short wave. Between day 2 and day 3 does the short wave appear to strengthen or weaken? They look weak 4. What happens to this short wave between day 3 and day 4? Does this imply the storm will strengthen or weaken? Why? Smaller because it helps keep the strength of the storm not large 12

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Part 4: El Nino, La Nina, and the Southern Oscillation 13

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Use the diagrams on the previous page and answer the following questions. 1. Of the three diagrams, which 2 diagrams appear most similar? LA nina and normal 2. What appears to be the major difference between a fully developed El Nino and Normal conditions in terms of: a. atmospheric pressure? Southern b. precipitation patterns? On different sides c. ocean currents? They move on opposite sides d. ocean surface temperatures? There is none and gets colder 3. What appears to be the major difference between a fully developed La Nina and Normal conditions in terms of atmospheric pressure? a. atmospheric pressure? More concentrated b. precipitation patterns? They stay normal c. ocean currents? It changes a little d. ocean surface temperatures? It decreases 15

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The map below represents general temperature anomalies during the winter associated with an El Nino. 1. Which state should expect a much warmer than normal temperature during an El Nino winter? Click here to enter text. 2. Which state should expect a much colder than normal temperature during an El Nino winter? Click here to enter text. 3. What can we expect for winter temperatures in Crystal Lake during an El Nino winter? 16

Click here to enter text. The map below represents general precipitation anomalies during the winter associated with an El Nino. 1. Which state should expect to be much wetter than normal during an El Nino winter? Minnesota 2. Which state should expect to be much drier than normal during an El Nino winter? New Mexico 3. What can we expect for winter precipitation in Crystal Lake during an El Nino winter? Warmer 17

The map below represents general temperature anomalies during the winter associated with a La Nina. 1. Which state should expect a much warmer than normal temperature during a La Nina? Florida 2. Which state should expect a much colder than normal temperature during a La Nina winter? Washington 3. What can we expect for winter temperatures in Crystal Lake during a La Nina winter? 18

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Low precipitation The map below represents general precipitation anomalies during the winter associated with a La Nina. 1. Which state should expect to be much wetter than normal during a La Nina winter? Louisiana 2. Which state should expect to be much drier than normal during a La Nina winter? North Dakota 3. What can we expect for winter precipitation in Crystal Lake during a La Nina winter? It will be normal 19

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The chart below represents the Southern Oscillation Index. Basically, when the SOI becomes negative for a prolonged period of time, this establishes a fully developed El Nino Pattern. 1. Approximately how often does an El Nino occur? Around 4 years 2. Identify a time period of an extreme El Nino event based on the amplitude of the event. About 1990 3. The most current SOI numbers for 2006 are listed in the table below. Does it appear that the winter of 2006-2007 will be experiencing another El Nino? Why? No because the weather is normal 21

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200 6 12. 7 0.1 13. 8 15. 2 -9.8 -5. 5 -8. 9 -15. 9 -5.1 Year Jan Fe b Mar Apr Ma y Ju n Jul Aug Se p 22

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Lab10

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