Measurements of atmospheric turbulence with the dual-beamwidth method using the MST radar at Gadanki, India

摘要

A brief experiment was conducted during 24-29 April and 9-10 May 2002,using the MST radar at Gadanki, India, to test the dual-beamwidth method ofestimating the turbulence kinetic energy (TKE). Because the beamwidth can bemodified on only one polarization at a time at Gadanki, an elliptical beamwas used with a modified dual-beamwidth analysis. Estimates of the TKE fromthe dual-beamwidth method and the traditional method are very similar inregions of light winds (~10ms). In regions of stronger wind(~15ms) the traditional method often gives TKE0 becausethe beam-broadening correction is greater than the observed spectral width.It is suggested that some of the problems with the traditional method aredue to the uncertainty in the effective width of the radar beam. In all regionsthe modified dual-beamwidth method gives TKE0 on the beam parallel to theprevailing wind; on this beam the estimates depend only on the ratio of thebeamwidths, which is presumably well-known, and the observed spectralwidths. The values of TKE from the dual-beamwidth method are approximatelyconstant with height at 0.2ms from about 5 to 7.5km duringthe afternoon during both April and May (all April observations were madebetween 9:00 and 17:00 local time), and then decrease rapidly to about 0.02msby about 9km. The data from May extend over one fulldiurnal period and the diurnal range of TKE during this period is found tobe about 5dB below about 12km and from about 15 to 19km, near thetropopause, with maximum values during local afternoon.