DataStreme Activity 5A:

AIR PRESSURE CHANGE

Do Now:

  1. Print this file.
  2. Print the Monday Image 1, Image 2, and Image 3 Files.
  3. Print (when available) the 10 October 2000 Tuesday Daily Summary File.

To Do Activity:

  1. Read Chapter 5 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 5A.
  3. Return here (Monday Activity A File) when told to do so.

Go To STUDY GUIDE - Activity 5A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. Highs (Hs) and Lows (Ls), the pressure systems routinely plotted on surface weather maps, identify local values of atmospheric pressure that are relatively the highest or lowest in a region. These systems generally move from west to east across our midlatitude portion of the globe so that pressure values fall as a Low approaches or a High departs, and pressures rise with approaching Highs or departing Lows.

    The major weather maker for the eastern two-thirds of the nation over this past weekend was a massive high pressure system that brought record or near record setting low temperatures (for this time of year) to much of the country. Toward the end of last week a cold front moved southeastward from the Canadian border as the leading edge of this cold air mass.

    Image 1 is the meteogram for Rapid City, South Dakota (RAP) for the 24-hour period from 1300Z 04 OCT 2000 to 1200Z 05 OCT 2000. Central Daylight Time is 5 hours behind UTC, thus 1300Z is 0800 (8 AM CDT). Label the time line of the meteogram in local time along the bottom starting at 8 AM, 04 OCT.

  2. The bottom panel on the graph is the atmospheric pressure (PRESS) in millibars, corrected to sea level. Rapid City, SD, is at an elevation of 1051 m (3448 feet) above sea level. (To eliminate the effects of elevation in comparing pressure readings at various stations, the equivalent pressure of an air column of local temperature and humidity characteristics and of height equal to the elevation of the station is added to the observed barometric pressure to provided the "corrected sea-level pressure".)

    The atmospheric pressure value at 13Z was approximately [(1015) (1020) (1028)] mb. The lowest pressure during this 24-hour period was about ______ mb which occurred at ____ Z. From 13Z to 22Z, the pressure was [(rising) (steady) (falling)].

  3. From 13Z to 20Z, the winds (second panel) were from the [(southeast) (northwest)], and the temperature (top panel) was generally [(rising) (falling)] until 22Z. (The steady day-long temperature increase under cloudy skies probably included warm air advection as well as solar effects.)

  4. After 22Z the pressure was[(rising) (steady) (falling)]. Temperatures fell slightly from 22Z until 06Z (1 AM 05 OCT). From 06Z to 12Z the temperature decreased about [(5) (13) (26)] F° while the dewpoint fell about [(6) (17)] F°. During this period winds were generally from the [(north) (east)] with speeds of 25 knots from 07 to 09Z.

  5. The strong northerly winds and rapidly falling temperatures with rising pressure would suggest [(cold) (warm)] air advection following the passage of the [(warm) (cold)] front at Rapid City near 22Z on 04 OCT.

  6. Image 2 is the surface weather map for 12Z 07 OCT 2000. At map time the cold front had advanced southeastward past Texas, into Florida and off the East Coast. The front stretching from Alberta, Canada to New Mexico was shown as a [(cold) (stationary) (warm)] front. Where the cold air was prevented from advancing westward by the Rocky Mountains, the air mass showed little movement. Rapid City was located near the center of the air mass marked by the bold Hs where the pressure was 1042 mb. The wind directions in the several state area surrounding the center of the High were generally [(counterclockwise and inward) (clockwise and outward)]. (At Rapid City, near the Black Hills, winds were influenced by downslope flow from the west.)

  7. Image 3 is the meteogram for Rapid City (RAP) for the 24-hour period from 0100Z 07 OCT 2000 to 0000Z 08 OCT 2000. At 12Z, the same time as the surface map of Image 2, the Rapid City wind, temperature and dewpoint values on the meteogram were [(the same as) (different from)] the conditions shown on the map.

    At 15Z the pressure was about _______ mb. From 01Z until 15Z on 07 OCT, the pressure was [(rising) (steady) (falling)]. The wind directions from 01Z to 15Z were either calm (small circle) or light from the [(northeast or northwest) (southeast or southwest)].

  8. Following 17Z pressures generally [(increased) (decreased)] as the center of the High moved away from Rapid City. Wind directions after 15Z were generally light from the [(northeast or northwest) (southeast or southwest)]. These wind directions would be expected to occur on the [(west) (east)] side of the center of a High.

This past week has provided an example of a passing cold front, the leading edge of a cooler air mass, and the wind and pressure changes accompanying the travel of that cool air mass across many of the stations in the central and eastern US.

When weather changes or passing storm systems influence your weather, print out meteograms for a city near you. If you have local recording instruments, or have plotted local weather conditions such as those reported hourly by NOAA Weather Radio, have your students compare their values with those of the meteograms. (A blank meteogram for plotting purposes may be printed from the DataStreme homepage.) Also relate the view of weather conditions from meteograms with those of a sequence of weather maps. Post these meteograms and maps in your classroom.


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 Activity B.


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