Showing papers by "Warner L. Ecklund published in 2000"

Doppler Radar Profilers as Calibration Tools for Scanning Radars

Abstract: The National Oceanic and Atmospheric Administration’s Aeronomy Laboratory has modified a standard 915MHz profiler for use as a precipitation profiler in support of Tropical Rainfall Measuring Mission ground validation field campaigns. This profiler was modified to look vertically with a fixed dish antenna. It was operated during the Texas and Florida Underflights Experiment (TEFLUN) A in south Texas in April‐May 1998 and during TEFLUN B in central Florida in August‐September 1998. Collocated with the profiler was a Distromet, Inc., RD-69 Joss‐Waldvogel disdrometer in Texas and Florida and a two-dimensional video disdrometer in Florida. The disdrometers are used to calibrate the profiler at the lowest range gates. At higher altitudes, the calibrated profiler reflectivities are compared with observations made by scanning radars such as the Weather Surveillance Radar-1988 Doppler in Dickinson, Texas, and Melbourne, Florida, and the S-band Doppler dualpolarization radar in Florida. The authors conclude that it is possible to use profilers as transfer standards to calibrate and to validate the reflectivities measured by the scanning radars.

Cluster Analysis Techniques to Separate Air Motion and Hydrometeors in Vertical Incident Profiler Observations

Abstract: Profilers operating in the UHF range are sensitive to both Bragg scattering from radio refractive index structure and to Rayleigh scattering from small point targets. Identification of the scattering process is critical for proper interpretation of these observations, especially the data collected from the vertical incident beam. This study evaluates the performance of Doppler velocity thresholds as a means to separate air motions from hydrometeor motions in vertical incident profiler observations. This evaluation consists of three different steps. First, using two collocated profilers operating at different frequencies, the observations are unambiguously identified as Bragg or Rayleigh scattering processes. Second, the observations are separated into either air or hydrometeor motion using only the data from one profiler. The third step quantitatively evaluates the performance of the single profiler separation techniques by counting the number of correct classifications and adjusting the count by...

On the nature of 150-km radar echoes over the magnetic dip equator

Abstract: We present new experimental findings that provide insight into the nature of 150-km echoes. A finding, using data obtained with a 49.92-MHz radar on Pohnpei (6.96°N, 158.19°E, 0.5° magnetic dip angle), is an unusual east-west asymmetry in which the altitude profile of echo occurrence depends on viewing direction. The other is the narrowness of Doppler spectral widths associated with these echoes. When considered with other known properties of 150-km echoes, a scenario for 150-km echoes emerges in which 3-m-scale field-aligned irregularities (FAI) are imbedded in tilted, sheetlike structures in plasma density. These meter-scale FAI are envisioned to have narrow Doppler spectral widths if excited directly by a linear plasma instability, and they would consist of a narrow angular spectrum of plane plasma waves if the instability is weak. The latter could produce the observed east-west viewing asymmetry.

A dual‐wavelength radar technique for measuring the turbulent energy dissipation rate ε

Abstract: We used the ratio of simultaneous observations of radar reflectivity by S- and UHF-band radars together with Hill's model of refractivity fluctuations due to turbulence to infer e, the rate of viscous dissipation of turbulent kinetic energy per unit mass. Observations were made for 25 days from November 13 to December 7, 1995, at 11.4°S, 130.4°E (about 100 km northwest of Darwin, Australia) during the Maritime Continent Thunderstorm Experiment (MCTEX). The 500 m pulse length data covered the height range 872 to 3032 m MSL. The observed distribution of e has a strong diurnal variation, with mean daytime and nighttime values of e of the order of 10−3 and 10−5 m²s−3, respectively. With the dual-wavelength technique most non-turbulent echoes (including particulate echoes) are identified and filtered out, since the ensemble of turbulent observations is identified by its conformity to Hill's model. The technique is self-calibrating, requiring only the relative calibration of the two radars using observations during rain, and does not require precise absolute calibration of either radar.

Radar measurements of electric fields in the topside of the equatorial electrojet: First results

Abstract: We show that the vertical polarization electric field (Ep) in the topside of the equatorial electrojet can be determined from the Doppler spectra of type-2 echoes obtained with a radar that is appropriately displaced in latitude from the magnetic dip equator. Using a 49.92 MHz radar on Christmas Island (2.9° magnetic dip latitude), we found unexpectedly large Ep at altitudes at least as high as 120 km over the dip equator. Another new and related finding is the transient appearance of type-1 echoes at 99 km over Christmas Island, which likely was produced by an Ep of at least 11 mV/m that must have appeared at 114 km altitude over the dip equator. Elevated electron temperatures inferred from the type-1 Doppler spectra are consistent with the presence of anomalous energetics.