Proceedings with Extended Abstracts (single PDF file) - Radio ...

NEW MST RADAR METHODS FOR MEASURING THE TURBULENTKINETIC ENERGY DENSITYT.E. VanZandt * , G.D. Nastrom + , J.-I. Furumoto # , W. L. Clark * , and T. Tsuda #* Aeronomy Laboratory, NOAA, Boulder, Colorado+ St. Cloud State University, St. Cloud, Minnesota# RASC, Kyoto University, Kyoto, Japan1. IntroductionClear-air wind profiler Doppler radars offer the capability to estimate the intensity ofsmall-scale turbulent kinetic energy per unit mass (TKE) over a broad range of altitudes in thetroposphere and lower stratosphere from the width of the observed Doppler spectrum. TheTKE is related to the eddy dissipation rate and the eddy diffusivity. However, the observedspectral widths contain contributions related to the interaction of the radar beam with thelarge-scale wind which must be removed. These corrections are usually significant,sometimes being larger than the turbulence contribution to the observed spectral width. Muchof the theory used to estimate the corrections was developed decades ago. An experiment totest the corrections applied to the spectral width was conducted at the highly versatile MUradar in Japan. Essentially simultaneous observations were made using two differentbeamwidths and two different zenith angles with oblique beams directed at the four cardinalcompass points during a two-day period of relatively strong winds (peak winds over 50 ms -1 ).Theoretical predictions of changes in spectral width with respect to wind speed, azimuth, andaltitude are compared with the observations.2. The Experiment‣ Observations were made at the MU Radar (46.5 MHz, λ=6.45 m) from 1700 JST 15March to 1900 JST 17 March 2002‣ Pulse length: 2 µs (300 m range)‣ Zenith angles: 0º, 10º and 20º‣ Azimuths: N, E, S, W‣ Beamwidths: 3.46º and 1.87º (ratio 1.85)‣ Observations at each zenith angle/beamwidth/azimuth took ~55 s, and a full cycle tookabout 4 minutes‣ Altitude range: 5-22 km (5-12 km used in the present study)‣ The median peak wind speed was about 55 m/s‣ Spectral widths were determined by Gaussian fitting3. AnalysisThe traditional theory of the interaction between the beam shape and thebackground winds predicts anisotropy between the spectral widths observed on the zonal (U)2and meridional (V) beams. The observed spectral widths ( σUandσ 2 V) are the sums of theatmospheric turbulence and the effects of beam-, shear-, and wave-broadening. As discussedby VanZandt et al. (2002), σ andσ are given by Eqs. (1) and (2), respectively, where θ is2U2 V208