Search Results

You are looking at 1 - 2 of 2 items for :

  • Author or Editor: W. L. Ecklund x
  • Monthly Weather Review x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
O. D. Nastrom
,
W. L. Ecklund
, and
K. S. Gage

Abstract

Radars that can make wind measurements in the clear air are expected to play an increasing role in meteorological observing systems in the future, especially for horizontal wind measurements. This paper considers the prospects for using these radars, which are sometimes called wind profilers, to also measure the large‐scale vertical velocity. Unfortunately, all radars for which vertical velocity data are available at this time are located in or near mountains, where standing lee‐wave effects often make the data representative of only small‐scale features. Confining attention to those times when lee wave effects are not expected, case‐study comparisons of the existing radar data with indirectly computed synoptic‐scale motions suggest that time averaged radar data are representative of large‐scale features smaller than the synoptic scale, perhaps more aptly termed subsynoptic‐scale features. Results from a three‐station radar network in France show that the time‐averaged vertical velocities are usually nearly the same at all stations, although there are some differences, and suggest that the spatial scale of the flow features they represent is greater than 50 km. Over a long-term average, the net influence of lee wave effects at mountain sites is small, and radar measurements appear to be useful for climatological studies of vertical velocity in large‐scale circulation systems.

Full access
W. L. Ecklund
,
K. S. Gage
,
B. B. Balsley
,
R. G. Strauch
, and
J. L. Green

Abstract

During March 1981 the Sunset and Platteville VHF clear-air radars located in Colorado to the east of the continental divide observed vertical winds continuously over a three-week period. The vertical winds at these locations contain fluctuations with periods from a few minutes to several hours and with magnitudes ranging up to a few meters per second. The Sunset radar, which is located in the foothills, observed systematically larger vertical velocities than the vertical velocities observed by the Platteville radar, which is located on the plains, some 60 km to the east. Although periods of enhanced vertical wind activity were observed to occur at the same time at both sites, attempts to correlate vertical wind structures over the two sites in detail were generally not successful.

The magnitude of vertical velocity fluctuations seen by both radars show large day-to-day variations with “active” periods alternating with “quiet” periods. An examination of upper level maps reveals that the occurrence of active and quiet periods are linked to the large-scale wind field. During the March experiment the magnitude of the vertical velocity variance was well correlated with the 500 mb zonal (west) wind.

Full access