Open AccessObservations of precipitation associated with a cold front using a VHF wind profiler and a ground‐based optical rain gauge
Author(s) -
Chu YenHsyang,
Song JuneShyen
Publication year - 1998
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/98jd00206
Subject(s) - precipitation , radar , lapse rate , wind speed , atmospheric sciences , cold front , wind profiler , meteorology , intensity (physics) , weather radar , precipitation types , environmental science , clear air turbulence , geology , turbulence , optics , physics , telecommunications , computer science
In this paper the VHF radar returns from hydrometeors and refractivity fluctuations associated with a cold front are analyzed. A composite analysis of the precipitation echo intensity and the vertical air velocity indicates that the vertical air velocity plays a vital role in the formation of the bright band. The observations show that the VHF radar reflectivity from precipitation at the height around the melting layer may be enhanced in the condition of weak vertical air velocity, while the bright band may be disrupted if the upward vertical air speed is as large as 1.2 m/s. The intense updraft may also diminish the echo intensity from refractivity fluctuations through the mechanism of turbulent mixing, as first suggested by Chu and Lin [1994]. The corresponding observational evidence will be presented and discussed in this paper. Comparing the time series of the VHF precipitation echo intensity aloft with that of the surface rainfall rate indicates there is a systematic time delay in the two, which increases approximately linearly with height. The drop‐off rate of the time difference is approximately equal to the average fall velocity of the raindrop. A regression analysis of the precipitation data between range‐corrected VHF radar reflectivity P r and ground‐based rainfall rate R using the equation P r = α R β is also made. It shows that β has a tendency to decrease with height, while α is nearly height‐independent.