WELCOME BACK: Procedure continued from STUDY GUIDE.
In the Monday, Activity A Image of this week, evidence of the three storm systems can be seen that were described as affecting the eastern, central, and western US. High pressure was situated over the northeastern US. The Wednesday, Activity B Image 1 is the 500-mb, constant-pressure map for Sunday morning, 12Z 29 OCT 2000. This upper-air map depicts the atmospheric conditions found at the 500-mb pressure level over the coterminous US at the same time as the conditions shown on the Activity A surface map. These mid-tropospheric conditions were associated with the surface storm systems and high pressure shown on the surface map. Weather systems extend from the surface well into the troposphere, hence the need to examine upper-air maps to describe them more fully.
On an upper-air map the observational data from the rawinsonde reports at that pressure are plotted around each station location in an upper-air station model format, as discussed earlier in this activity and the User's Guide, linked from the Extras section of the DataStreme homepage.
The plotted report for Bismarck, North Dakota, on the Image 1 map shows that at 500 mb over the station, the conditions were:
temperature (°C): | [(-13) (-15)] |
dewpoint (°C): | [(-15) (-26)] |
wind direction: | [(south-southwest) (northeast)] |
wind speed (kt)*: | about [(20) (50)] |
height (m):* | [(5690) (5810)] |
*[ Note: A pennant is used on the station's wind shaft to signify a 50-knot increment in speed. Also, the altitudes of the constant-pressure surfaces on upper air charts are given in coded values (as is the case with the air pressures on surface maps). On 500-mb maps, the height is plotted in tens of meters. Decoding requires adding a 0 to the plotted number. That is, a plotted 500-mb height value of 556 is actually 5560 m. Contour lines are labelled on the map with the full height value.]
The following is an excerpt from a rawinsonde text report for the same time as the Image 1, 500-mb map (DataStreme Homepage: "Upper Air Data - Text"). Using the values reported at the 500-mb level, plot an upper air station model for 500 mb using the station circle to the right of the data table. Round temperature and dewpoint to the nearest whole degree and wind speed to the nearest 5 knots. Be sure your plotted height value is the coded number, that is, in tens of meters.
Date: 1200Z 29 OCT 2000 ----------------------------------------------- LEVL PRES HGHT TMPC DEWP RELH DIR SPED mb m C C % deg knt ----------------------------------------------- Station SFC 993 196 18.0 17.0 94 190 8 10 850 1525 14.4 10.4 77 270 17 21 700 3142 4.2 -0.6 71 245 35 O 32 500 5800 -12.3 -17.3 66 240 45 39 400 7470 -22.7 -26.0 74 250 51 |
Compare your station model plot to the 500-mb map. The station you have
plotted is
[(Cape Hatteras, NC) (Dallas, TX)].
Generally, wind speeds on the 500-mb map are faster where the height
contour lines are
[(closer together) (farther apart)].
This spacing relationship between wind speeds and contours at 500 mb is
[(similar to) (the opposite of)] the
spacing relationship on surface weather maps between wind speeds and isobars.
On Northern Hemisphere surface maps, the wind circulation about Lows is counterclockwise and [(inward ) (outward)] while that about Highs is clockwise and [(inward ) (outward)]. This across-isobar flow is due to the presence of friction near the Earth's surface. At 500 mb, above the influence of surface friction, wind directions are generally [("parallel to the contours") (across the contours toward lower heights)].
Compare the 500-mb temperatures and heights in Oregon and Washington State with those along the Gulf of Mexico coast. The temperatures at 500 mb over the Northwest are [(colder) (warmer)] than those over the Gulf coast and the heights of the 500-mb surface are [(higher) (lower)] over the Northwest. Recalling the Activity 5B pressure blocks, the atmospheric column associated with lower heights of pressure levels would be [(colder) (warmer)] than the column with higher heights.
Image 2 is the 500-mb map for Tuesday evening, 00Z 01 NOV 2000, two and one-half days following the Image 1, 500-mb map. This Image 2 upper-air map depicts the 500-mb atmospheric conditions at that time. The 500-mb west-to-east pattern of trough-ridge-trough seen on Image 1 at 12Z 29 OCT generally [(has reversed positions) (remained the same)] on Image 2 at 00Z 01 NOV.
Compare the Image 1 and 2 maps of this portion of the activity to the 500-mb map in the printed portion of the Activity on page 8B-2. The 500-mb map on page 8B-2 for 00Z 04 APR 2000 has positions of the trough and ridge pattern over the US generally [(reversed from) (the same as)] the Image 1 and 2 map patterns.
As noted in the Wednesday, 1 November, Daily Weather Summary, the weather systems have moved very little from their positions at the beginning of the week. The unusally persistent, large north-south air movements at 500 mb, a level noted for the "steering" of weather systems, has retarded the west-to-east progression of the weather systems. Also, the "spreading" of the 500-mb air flow seen from Texas across the central US in Image 2 at 00Z 01 NOV gave evidence of the lifting that aided the development of severe thunderstorms in that region.
You or your students can make a height-contour analysis by printing an unanalyzed 500-mb map ("500 mb - Data") from the DataStreme Homepage. You can then compare the hand-analyzed pattern to the computer-analyzed map with contours. Also, compare upper-air maps to the weather conditions you experience locally.
After completing this week's applications, fax the following pages to your LIT mentor by Monday, 6 November 2000:
Return to DataStreme Homepage
URL: datastreme/learn/b_act.html
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