Studies on refractivity structure constant, eddy dissipation rate, and momentum flux at a tropical latitude

Abstract

VHF and UHF Doppler radars provide a unique database to estimate the refractivity structure constant Cn2, eddy dissipation rate ∈, and vertical flux of horizontal momentum. Using the data collected from the Indian MST radar, these parameters are studied at a tropical latitude. The refractivity turbulence structure constant is estimated from the backscattered power of the received echoes. Cn2 (radar) and Cn2 (model), derived from radiosonde observations, are compared, and a fairly good agreement is seen. Diurnal and seasonal variations of Cn2 are also presented. The eddy dissipation rate is estimated from the radar echoes employing the power and spectral width methods. A fairly good agreement is seen between the two methods. Values of ε are found to vary from 10−6 to 10−3 m2 s−3 in a height range of 4–19 km. Cn2 and ε are observed to be minimum during a moderate jet stream wind of 50–60 m s−1. Vertical flux of horizonal momentum is computed using the symmetrical two‐beam method. Significant fluxes of westward and northward momentum are observed, and the values lie in the range of −1 to +1 m2 s−2. The implied accelarations are also estimated. The results presented are largely consistent with the results available in the literature.