DataStreme Activity 9A:

WESTERLIES AND THE JET STREAM

Do Now:

  1. Print this file.
  2. Print the Monday Image 1, Image 2 and Image 3 Files.
  3. Print (when available) the Tuesday, 6 November 2001, Daily Summary File.

To Do Activity:

  1. Read Chapter 9 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 9A.
  3. Return here (Monday Activity A File) when told to do so.

Go To STUDY GUIDE - Activity 9A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. As noted in the Monday, 5 November 2001, Daily Weather Summary, most of the coterminous US experienced relatively mild and tranquil weather over the weekend. The exceptions were scattered showers in the Southwest and Northeast, and Florida's brush with Hurricane Michelle.

    Image 1 is the surface weather map for 00Z 05 NOV 2001, Sunday evening. At that time an area of low pressure was producing scattered showers in the Southwest. Two major frontal systems were crossing the country. One low-pressure center was located in northeastern New York with an occluded front trailing to Pennsylvania where it became a cold front continuing around to Illinois. From Illinois to southeastern South Dakota it is shown as a stationary front and then warm front extending to Saskatchewan. These frontal depictions depended upon its local movements. A second cold front was entering the Pacific Northwest. Finally an area of extensive rainfall in southern Florida was associated with Hurricane Michelle. Temperatures at map time showed the coldest surface air to be located to the [(south) (north)] of the two fronts draped across the northern states and southern Canada.

    The wind directions at Key West, Miami, and Nassau in the Bahamas implied the intense low-pressure center of Michelle was located to the [(south) (north)] of those stations at map time.

  2. Image 2 is the 500-mb constant-pressure map for 00Z 05 NOV 2001, the same time as the surface map. This level represents conditions in the middle troposphere above the surface systems of Image 1. The 500-mb map had a contour pattern that showed a [(trough) (ridge)] over the northeastern portion of the country. There was a broad [(trough) (ridge)] over the north-central portion. (For the purposes of this activity, ignore the closed contours over North and South Dakota. The data reported for Aberdeen appears inaccurate, probably due to instrument or reporting errors.)

  3. The wind speeds reported on the 05 NOV 2001 500-mb map are generally faster where the contour lines are relatively [(far apart) (close together)]. And where the wind speeds are greater than about 25 knots, the wind directions are generally [("parallel") (perpendicular)] to the contour lines.

  4. Image 3 is the 300-mb constant-pressure map for 05 NOV 2001, the same time as the surface and 500-mb maps. This level represents conditions in the upper troposphere. The plotted heights on both the 500- and 300-mb maps are in 10's of meters. The heights at which 500 mb of pressure occurred over the US at map time were within several hundred meters of [(5500) (9000) (12,500)] meters, while the heights of the 300-mb pressure level were within several hundred meters of [(5500) (9000) (12,500)] meters.

    Compare the heights of the 300-mb constant pressure surface at stations across the US. In general, the heights of the 300-mb pressure level were [(higher) (lower)] across the northern tier of states than heights across the southern states. Stations across the northern US were also reporting temperatures at this pressure level that were [(warmer) (cooler)] than those of the southern US. (Again, ignore the anomalous South Dakota report.) This relationship of atmospheric temperatures to heights of pressure surfaces should be familiar from Activity 5B.

  5. Compare the flow patterns of the air at the 500-mb and 300-mb pressure levels. The location of troughs and ridges at the two levels are in [(similar) (opposite)] parts of the country.

  6. Comparing the 05 NOV 2001 maps, the wind speeds generally [(increase) (remain the same) (decrease)] with increasing height above the Earth's surface.

  7. Using the conventional threshold of 70 knots wind speed for the existence of a jet stream, there [(is) (is not)] evidence for a jet stream on the 300-mb constant-pressure map. One band of high wind speeds at 300 mb, some 100 knots or higher, exists across Washington State. Another higher wind speed region is found around the [(trough) (ridge)] from western Ontario, Canada around to Maine.

    The 300-mb jet stream, as denoted by the highest wind speeds, generally flows eastward across the region where surface temperatures were colder to the [(north) (south)] of the jet stream and warmer temperatures were to the [(north) (south)].

  8. Commercial aircraft routinely fly at heights near the 300-mb level. If one were to be flying from Detroit, Michigan, to Boston, Massachusetts, about 00Z on 05 NOV 2001 at the 300-mb level, the aircraft's speed relative to the ground ("ground speed") would be around 80 knots [(faster) (slower)] than its speed relative to the air through which it is moving ("air speed").

    The dashed lines on the 300-mb map are isotachs that encircle regions of particular wind speeds. For example, a 90-knot isotach from Lake Superior across lower Michigan shows a "jet streak" or locally faster region of wind speeds within the general flow. Another jet streak is evidenced by the 110-kt isotach across lower British Columbia in western Canada. These jet streaks and troughs were located to the west of their surface low-pressure centers, providing the steering of the systems and associated fronts. This upper-level flow also provided the divergence above the surface Low's counterclockwise and inward convergence.


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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