DataStreme Activity 1A:

AIR PRESSURE AND WIND


Do Now:

  1. Print this file.
  2. Print the Monday Image 1 File.
  3. Print (when available) the Tuesday, 4 September 2001 Daily Summary File.

Welcome to DataStreme. We hope the use of current weather information will become a pleasant and anticipated daily experience. We encourage your exploration of the DataStreme weather products from the homepage and the use of that material in your classroom or school.

To Do Activity:

  1. Read Chapter 1 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 1A.
  3. Return here (Monday Activity A File) when told to do so.

Go to Study Guide - Activity 1A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. The Image 1 "Isobars, Fronts, Radar & Data" map acquired from the DataStreme homepage is the depiction of weather conditions at stations across the contiguous US at 00Z 03 SEP 2001. (00Z 03 SEP is 4 hours ahead of Eastern Daylight Time, so the map depicts conditions at 8 PM 2 SEP EDT, the evening before.)

    The Image 1, 00Z 03 SEP 2001, map shows an area of high pressure (marked by two Hs) centered in New England. The area of high pressure was associated with a large mass of relatively cool and dry air that provided a wonderful Labor Day weekend to the northeastern US. There is also a low pressure center (L) in south central Canada which gave focus to changeable weather conditions. The highest pressure associated with the New England High was 1020 millibars as shown by the bold number beneath the eastern H while the lowest pressure with the Canadian Low was 992 millibars.

  2. Weather data at individual locations are plotted in a coded format called the "station model". The wind directions at reporting stations on the map are shown by the line (which can be thought of as an arrow shaft) which depicts the air flow into circles representing station locations. Wind at a station is named by the direction from which the air flows, i.e., air coming towards the station from the south is a south wind. The wind direction at St. Louis was from the [(east) (south)], so it was a(n) [(east) (south)] wind.

    The wind speed is given by a combination of long and short "feathers" on the direction shaft. [The station model will be explained in Activity 2A or further details for deciphering station data can be found in your Homepage User's Guide (linked from the DataStreme Homepage).] At map time, St. Louis, MO, had a 10-knot wind (single, long feather). [A double circle without a direction shaft signifies calm winds, such as Atlanta, GA, and a shaft without feathers denotes 1-2 knots. A knot is a nautical mile per hour. A nautical mile is about 1.2 land miles.]

  3. Apply the hand-twist model of a High to infer the wind directions in the broad high-pressure area centered in the northeastern US. Wind directions at stations from North Carolina to Maine show that, as seen from above, the air spiraled generally [(clockwise) (counterclockwise)] around the high-pressure center.

  4. The wind directions around the high-pressure area also indicated that the air also generally spiraled [(inward toward) (outward from)] the high-pressure center. This pattern is [(consistent with) (contrary to)] the hand-twist model of a High.

  5. The wind at Detroit, Michigan, (at the western end of Lake Erie) was from the [(northwest) (southeast)] at 5 knots (one-half feather). This direction is [(outward from) (inward toward)] the New England Hs.

  6. The low-pressure center in Canada has wind directions surrounding it that show the air spiraling generally [(clockwise) (counterclockwise)] and inward. This pattern [(is) (is not)] consistent with the hand-twist model of a Low.

When the centers of fair weather Highs or stormy Lows are near your location, you might try having students fit your local wind direction (as shown by the school flag, for example) with map circulations and the hand-twist model of weather systems. (One note: the hand-twist model must be applied cautiously. Mountainous terrain in the western US can be a predominant factor affecting wind directions as can low wind speeds. The numerous Hs and Ls in the western US result from an objective computer analysis of a greater number of pressure values than you used in Activity 1A and reflects this variable pressure and wind pattern.)


Hold this activity until you have completed all applications for this week. Instructions for faxing your LIT mentor will appear at the end of this week's Wednesday Activity B. (If possible, take this activity to your first course group meeting.)


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©Copyright, 2001, American Meteorological Society