DataStreme Activity 7B:

DOPPLER RADAR

Do Now:

  1. Print this file.
  2. Print the Wednesday Image 1, Image 2 and Image 3 Files.

    Note: You should examine the color images (Images 2 and 3) while you are "on-line".

  3. Print (when available) the Thursday, 25 October 2001, Daily Summary File.

To Do Activity:

  1. Read Chapter 7 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 7B.
  3. Return here (Wednesday Activity B File) when told to do so.

Go To STUDY GUIDE - Activity 7B Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. From 18 to 21 March 2001, a strong winter storm system traveled from northern Florida northward along the East Coast. This storm brought extensive rainfall to coastal areas and heavy snows to higher elevations in the Appalachian Mountains along its path. Image 1 is the visible satellite image on Tuesday 20 MAR 2001 at 1815Z showing the storm circulation about a large low-pressure area centered in central Georgia. The circulation pattern about the Low, as depicted by the hand-twist model is [(clockwise) (counterclockwise)] and [(outward) (inward)].

    The circulation pattern about the Low can be seen by the cloud shield which follows the hand-twist model. We will concentrate our attention in the area centered on the National Weather Service radar site near Wilmington, NC, (denoted by the "x") in a circle with a 230-km radius. The wind directions implied by the hand-twist model across North Carolina, to the northeast side of the Low centered in Georgia, would be generally from the [(northeast) (southwest)]. Actual surface observations confirm this wind direction.

  2. We will next look at radar images acquired from the Wilmington, NC, NWS Doppler radar. Image 2 is the reflectivity display for 2044Z 20 MAR 2001. In the radar display the radar is located at the center of the 230-km radius circle of shaded (color coded on-screen) echoes. The shading shows that, at the time of the image, precipitation generally [(did) (did not)] extend over the region. The most intense echoes depicting greatest rainfall rates were in the lighter-shaded areas (yellows and oranges on-screen) northwest and west of the radar with one patch to the southeast over the ocean.

  3. Image 3 is the NWS Wilmington Doppler radial velocity display for the same time as the reflectivity of Image 2. The darkest shadings within the inner circle show "Doppler wind speeds" within about 150 km of the radar, located again at the center of the image circle. On the Image 3 display, the dark shadings (reds in screen view) to the left of the "S"-shaped white curve passing through the radar site depict radial motion away from the radar and are denoted as "positive" velocities in the scale at the right. Dark shadings (greens in screen view) to the right of the "S" depict radial motion toward the radar ("negative" velocities).

    The "S"-shaped white curve running generally from north-to-south through the radar site indicates 0 "Doppler wind speed". This "zero-speed" situation occurs when the beam direction is [(perpendicular) (parallel)] to the actual wind direction.

  4. The white line of 0 Doppler speed [(is) (is not)] a straight line across Image 3 through the radar site. This occurs because the wind directions detected by the radar change with distance from the radar. The changing wind direction is due to the fact that the radar beam is actually sampling motions of the precipitation particles at higher elevations above the surface as distance from the radar increases.

  5. At the center of the image where the radar is located, draw a short arrow (about 1 cm) perpendicular to the white curve, directed from the green side to the red side. Place an arrow head on the southwest end of the line to show the motion direction. At the radar where the wind is nearest the surface (antenna height), the air motion is from the [(northeast) (southeast)]. (At 20Z Wilmington reported a wind from 70° (east-northeast) at 17 knots.)

  6. As one moves away from the radar along the "S" curve, the beam is at increasingly higher elevations. An arrow drawn perpendicular to the white curve about halfway from the center to the circle edge north of the radar shows winds there at higher levels to be more from the [(east) (north)].

In this way, Doppler radars can detect wind motions at various elevations about the radar site. The radar images in this activity were from sites located via http://www.intellicast.com/LocalWeather/World/UnitedStates/BaseReflectivity/. NOAA Weather radio and television often provide local radar information. When storm systems threaten, compare DataStreme radar products and maps with local media reports to monitor how large scale weather systems affect your local area.


Faxing Instructions:

After completing this week's applications, fax the following pages to your LIT mentor by Monday, 29 October 2001:

  1. Chapter 7 Progress Response Form
  2. 7A and 7B Activity Response Form
  3. STUDY GUIDE, Part B: Applications, page 7B-2.
    [BEFORE faxing this page, label each arrow with the letter "R" for red and "G" for green to identify the chosen color on the black and white fax copy your mentor will be viewing.]

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