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R. G. Strauch

Abstract

A modulation waveform for meteorological Doppler radars that obtain estimates of radar reflectivity, mean velocity, and Doppler width with dwell time much shorter than that used with conventional meteorological Doppler radars is described. The transmitted signal is a sequence of three identical chirp pulses; signal parameters can be estimated from the radar echoes of a single sequence with standard deviation similar to that of conventional meteorological radars that use dwell times more than an order of magnitude longer. This waveform would be particularly useful for radars with electronically steered antennas where the antenna scan rate is not limited by mechanical constraints and there is no spectral broadening caused by antenna motion.

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R. G. Strauch and R. Frehlich

Abstract

Simulations of weather radar echoes were used to determine whether single-pulse estimates of velocity could be made with sufficient accuracy to measure the velocity aliasing that is inherent with pulse Doppler weather radars. The results indicated that this type of velocity measurement can be made, but such a large number of single-pulse estimates need to be averaged to determine the velocity aliasing that the concept is not compatible with the spatial and temporal resolution requirements of the WSR-88D (NEXRAD).

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A. S. Frisch and R. G. Strauch

Abstract

In this paper we report the results of measurements of turbulent kinetic energy dissipation rates within a convective storm. The measurements were obtained with two Doppler radars, one scanning the storm from a distance at low elevation angles and the other pointing vertically with the storm passing overhead. With the scanning radar we measured the wind shear in the radial velocity field and the turbulent kinetic energy dissipation rates within the storm. These dissipation rates showed good agreement with those measured by the zenith-pointing radar data; dissipation rates ranged from 30 cm2 s−3 to greater than 3500 cm2 s−3 in the region between the updraft and downdraft.

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R. G. Strauch and F. H. Merrem

Abstract

Two X-hand Doppler radars observed a hailstorm that passed directly over one of the radars during the 1973 National Hail Research Experiment (NHRE). While one of the radars scanned the storm at low elevation angles the other radar, which operated simultaneously in a zenith–pointing mode, measured part of an updraft. Observations by other NHRE participants assisted in interpreting the radial velocity fields so that inflow and outflow could be identified from the scanning radar measurements. The peak updrafts occurred just ahead of. the highest reflectivity while the strongest downdrafts were found only 6 km behind the updraft. Strong turbulence was generated in the transition region between updraft and downdraft as evidenced by large velocity variances. A substantial part of the downdraft appeared to have been led by air that had ascended in the updraft. Low–level velocity fields were in general agreement with surface measurements and showed the outflow toward the front of the storm in the gust front as well as outflow opposite the echo motion behind the storm. There was strong outflow opposite the direction of echo motion at the top of the storm which agreed with photographs of the anvil overhang.

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K. P. Moran and R. G. Strauch

Abstract

Temperature measurements made with a 50-MHz wind profiler equipped with a radio acoustic sounding system (RASS) are compared with radiosonde observations (raobs) during a 5-week period in the fall of 1991. The accuracy of the RASS temperature measurements corrected for vertical air motion is reported. Measurements made during a period when vertical air motion was observed showed a mean improvement of 0.7°C after correction. The rms differences between the RASS observations and the raobs showed improvement at all the measurement heights when the correction for vertical air motion was made. The accuracy for all the observations is reported to be 0.9°C. The remaining differences in the temperature are compared with a model of RASS errors induced by horizontal winds and turbulence.

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R. B. Chadwick, K. P. Moran, R. G. Strauch, G. E. Morrison, and W. C. Campbell

A new radar technique for measuring winds in the lower atmosphere is discussed. It is an extension of the well-known FM-CW technique and has the same advantages of relatively low cost and high flexibility for a clear-air radar. Two different types of wind data from clear-air returns are presented. The first is horizontal wind data by the FM-CW radar; these are compared with winds obtained from a tethered balloon. The second is radial velocities associated with convection cells drifting past the radar. Also, two types of data processing are illustrated. The first is off-line processing of recorded digital data, and the second is real-time processing using a commercial spectrum analyzer.

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R. M. Hardesty, P. A. Mandics, D. W. Beran, and R. G. Strauch

Wind shear has been recognized as a major aviation hazard in the airport environment. A dual, acoustic Doppler–microwave Doppler radar system has been installed at Dulles International Airport near Washington, D.C., to measure the vertical profile of wind from the surface to 510 m in 30 m height increments. The acoustic system gathers data under clear-air conditions, and the microwave radar takes over automatically when precipitation is present. System performance is being assessed by comparing its output with National Weather Service radiosondes and with balloon-borne anemometers and by intercomparing the acoustic- and microwave-measured winds under light precipitation conditions. The dual-sensor system has been operating for several months, registering the passage of fronts, some with potentially hazardous wind shears.

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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.

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A. S. Frisch, B. L. Weber, D. B. Wuertz, R. G. Strauch, and D. A. Merritt

Abstract

We computed the monthly average backscattered power over a five-year period for the Fleming 50 MHz wind profiler, which is proportional to CN 2. We found that in addition to seasonal cycle in CN 2 below the tropopause, there was a year-to-year variation as well. Above the tropopause, the seasonal variations were almost gone; however, there were significant changes with periods longer than one year. We examined a shorter back-scattered power record from the Stapleton wind profiler and found similar longer-term trends. These long-term trends will affect the performance of wind profilers.

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K. P. Moran, D. B. Wuertz, R. G. Strauch, N. L. Abshire, and D. C. Law

Abstract

A network of 31 radar wind profilers is being installed in the central United States by the National Oceanic and Atmospheric Administration (NOAA). The radars are expected to measure the vertical profile of horizontal and vertical wind starting at 500 m above the surface (AGL) and extending to about 16 km AGL. These 404.37-MHz radars can also be adapted to measure virtual temperature profiles in the lower troposphere by the radio acoustic sounding system (RASS) technique. RASS experiments were conducted using the prototype radar of the NOAA network, and results showed that virtual temperature profiles can be measured starting at 500 m AGL (the lowest height observed with this radar) and extending to 3.5–5.2 km AGL.

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