Diurnal and seasonal variability of turbulence parameters observed with Indian mesosphere-stratosphere-troposphere radar

Abstract

Seasonal and diurnal variation of turbulence parameters such as refractivity structure constant C_n² and eddy dissipation rate ε is presented using the data collected with the Indian mesosphere-stratosphere-troposphere (MST) radar over 3 years. The log C_n² values estimated from signal-to-noise ratio (SNR) are found to be in the range of -17 to -19 m^-2/3 in the height range of 7.5-21 km. Monthly mean values of log C_n² show a maximum variation below 12 km with a magnitude of 12-15 dB during the course of annual cycle. A maximum variability of ~7-10 dB is observed below 12 km in seasonal mean values of log C_n². The diurnal variation of log C_n² at different heights is also given. C_n² is found to be more in the region of strong shears, generally observed in the boundaries of jet streams. Different methods for the estimation of eddy dissipation rate and their limitations are discussed. For the present study, spectral width method is used after correcting the observed spectral width from beam and shear broadening effects. The observed median log ε is on the order of -3 to -4 m² s^-3. Monthly variation of log ε is found to be ~5-7 dB. Below 10 km the magnitude of ε is more in the postmonsoon than that observed in other seasons. The interannual variation of ε is less in winter than in other seasons. The diurnal variation of log ε is found to be small in postmonsoon at most of the heights. To facilitate a comparison with the other results, we have estimated the eddy diffusivity K and the inner and outer scales of turbulence. The observed values of C_n², ε, K, and the inner and outer scales of turbulence are largely consistent with the results available in the literature.