Characteristics of energy dissipation rate and effect of humidity on turbulence echo power revealed by MU radar-RASS Measurements

We carried out an MU radar-RASS campaign during August 2-6, 1995, and colle cted both radar echoes and virtual temperatures with good time resolution. We first investigated the accuracy of the Brunt-Vaisala frequency squared f rom the RASS temperature profiles, comparing them with radiosonde results l aunched from the radar site. We then evaluated the turbulence energy dissip ation rate (epsilon) by two radar methods: the Doppler spectral width and t he radar echo power. Meteorological conditions were very calm throughout th e campaign, which is ideal for deriving epsilon by the spectral width metho d. Under calm conditions, the variation of epsilon from spectral width is m ainly influenced by the Doppler spectral width and is less dependent on the Brunt-Vaisala frequency. On the other hand, epsilon from echo power is mai nly determined by the echo power intensity. Though epsilon values from both methods are roughly on the same order, their characteristics differ signif icantly. epsilon with spectral width did riot show large variations with ti me and height, while epsilon with echo power showed significant fluctuation s. We suspect that epsilon from echo power is inaccurate because the refrac tive-index gradient in the calculation of epsilon is mainly controlled by t he humidity gradient in moist regions. (C) 2001 Elsevier Science Ltd. All r ights reserved.