Experimental Evaluation of Theoretical Formulations for the Correction of Spectral Widths of MST Radar Spectra

The turbulent kinetic energy (TKE) per unit mass estimated from the spectral width of very high frequency/ultra high frequency (VHF/UHF) radars often produce unrealistic negative values, particularly in the presence of strong winds, due to excess correction of nonturbulent factors. An experiment has been conducted with the newly acquired capabilities of the Advanced Indian MST Radar (AIR), in which several antenna configurations, providing different beam-widths, have been employed to evaluate various existing theoretical formulations for the estimation of nonturbulent factors. These formulations include traditional single-beamwidth, symmetric dual-beamwidth, and asymmetric beamwidth methods. The large variation is seen in the observed spectral widths with different antenna apertures with broader beams showing larger biases due to beam and shear broadening even in moderate winds. Wind-driven biases in spectral width are found to be larger for beams pointed perpendicular to the wind direction than those pointed parallel, particularly at heights of strong wind. After employing the above -mentioned correction methods, all profiles of mean spectral widths obtained with different antenna configurations converge and produce nearly equal values, indicating that the corrected spectral width (sigma(2)urb) values may represent realistic estimates of turbulence intensity. Comparison of estimated using east and south beams indicates that the turbulence (on average) is isotropic. Among all the correction methods, the sigma(2)urb obtained by employing the asymmetric dual-beamwidth method has relatively larger bias than other methods. The sigma(2)urb values are used to estimate the vertical eddy diffusion coefficients and eddy dissipation rates to have direct comparisons with those available in the literature.

Automated summary

An experiment was conducted to evaluate various theoretical formulations for estimating nonturbulent factors using different antenna configurations. The corrected spectral width values obtained from different antenna configurations converge, indicating realistic estimates of turbulence intensity. The sigma(2)urb obtained by employing the asymmetric dual-beamwidth method has relatively larger bias but can still be used for estimating vertical eddy diffusion coefficients and eddy dissipation rates.