WELCOME BACK: Procedure continued from STUDY GUIDE.
Activity 1A dealt with the hand-twist model for relating wind directions to centers of high or low air pressure. This activity demonstrates how the air pressure patterns can be determined and the high and low pressure centers found.
The Image 1 map acquired from the DataStreme homepage (identified across the top as "Pressures") displays atmospheric pressure values in whole millibars at the time of ______ Z on __________________. This is the field of atmospheric pressure values as measured at stations across the country at the same time as the map used in Activity 1A.
The lowest reported air pressure on the map is _______ mb. This was located in [(south central Canada) (New England)].
The highest reported pressure is _______ mb. This was located in [(south central Canada) (New England)].
The isobars in the conventional series that will be needed to complete the pressure analysis on this map are: 996, _____, _____, 1008, _____, and _____. More than one isobar of the same value may need to be drawn if pressure values are located in several sections of the map area with values above and below the isobar's number.
Follow the steps below to draw these isobars on this map to determine the pressure pattern that existed at the time the observations were made. Consider each pressure to be located in the center of the reported number.
Let us start by choosing to draw the 1016-mb isobar. Let us begin where the pressure is "1016", such as Wilmington, North Carolina. Starting slightly offshore, the 1016-mb isobar will go through the center of this number. Then extend the line to the next "1016" at Greensboro, NC, and on around into Canada, keeping values higher than 1016 mb on one side of the line, and lower values on the other side. That isobar will curve around the stations with the highest pressure value you identified above. Extend the end of the 1016-mb isobar to the edge of the reported pressures. Place the isobar value, 1016, as a label, at the ends of the isobar line. Other pressure values in Georgia and Florida require another 1016-mb isobar to be drawn there.
NOTE: For helpful hints, refer to Tips on Drawing Isobars on page 1B-3 of the STUDY GUIDE, Part B: Applications.
Next, draw the 1012-mb isobar to separate lower and higher pressure values. First note that air pressures decrease to the west and south of the 1016-mb isobar you drew. Starting somewhere along the 1016-mb isobar, scan towards lower pressure until you locate a pressure of 1012 mb or less. Begin drawing the 1012-mb isobar through the location where 1012 mb would occur. This isobar line will also cross the area of map data to the boundary of plotted numbers, following the pattern of the initial 1016-mb isobar. Also label this isobar line at its ends with its value, 1012.
Complete the pressure analysis across the eastern two-thirds of the map (including the 1008-mb isobar from southeastern Arizona to Saskatchewan) for the remaining isobar values listed in question number 13 above. Be sure to label each isobar with its value at the end where it reaches a data boundary. Completion of the isobar lines to show the pressure pattern in the western one-third of the US is optional.
Compare your "Pressures" map at 00Z 03 SEP 2001 to the map of Activity 1A, also of 00Z 03 SEP 2001. The Activity 1A map had isobars drawn by computer. They were based on many more observations than were shown on that map or on the map you just analyzed. Compare the placement of the isobars you have drawn with those done by computer on the Activity 1A map. They should be in the same general locations!
Place a bold L on the map you analyzed where the lowest pressure value is. Also, place a bold H on the map where each of the highest pressure values are. The Activity 1A map [(did) (did not)] show the pressure centers in approximately the same locations as you have placed them based on the isobar pattern.
At map time, the high pressure area in New England, marked by the Hs, was associated with the large region of fair weather there over the Labor Day weekend. The low pressure in Canada was associated with some storminess in that region that preceded a change to cooler weather.
The DataStreme Homepage routinely delivers unanalyzed ("Pressures") and analyzed ("Isobars & Pressures") surface pressure maps. Practice drawing isobars by calling up the unanalyzed version. Use the DataStreme analyzed map as your "answer key". If appropriate, try having your students make a pressure analysis. You might share with your teacher colleagues this "detective scheme" of analyzing surface air pressures to find storms or broad-scale air masses that are mentioned in the news.
Record your responses to items in Activities 1A and 1B on the
Activity Response Form for transmission to your
course mentor.
Faxing Instructions:
After completing this week's applications, fax the following pages to your LIT
mentor by Monday, 10 September 2001, or as coordinated with your mentor:
Notice for Local Implementation Team (LIT) members - recall that the week's answer key will be available to mentors each Friday after 12 noon, Eastern time. Check with your LIT Manual or your LIT leader for answer key.
Return to DataStreme Homepage
URL: datastreme/learn/b_act.html
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