Climatological study of turbulence structure constant over two tropical stations, Mumbai and Guwahati in India

Wind profiling radars operating at VHF and UHF bands are highly sensitive to radio-refractive index variation associated with small-scale atmospheric turbulence. The measurement of atmospheric turbulence at these radar stations may be used to estimate the range of the radar that can be achieved based on its sensitivity. Turbulence structure constant (C-n(2)) is one of the basic parameters to measure turbulence. In the present study, climatological (2000-2011) variation of C-n(2) from 1 to 20 km height over Mumbai (72 degrees 51'E, 19 degrees 6'N) and Guwahati (91 degrees 34'E, 26 degrees 6'N) regions using radiosonde data has been analysed. It has been observed that the mean a values over the two stations are in the range 10(-18) to 10(-12) m(-2/3). The C-n(2) values are higher in the lower troposphere where both temperature and humidity gradients contribute to refractive index variation, and lower in the middle and upper troposphere where moisture gradient is negligible. The lowest values of C-n(2) are observed just below the tropopause region between 10 and 16 km over Guwahati and 10 and 13 km over Mumbai region. As a coastal station, Mumbai shows higher values of C-n(2) (two orders of magnitude) at the surface and lower troposphere compared to Guwahati. It has been observed that over the two stations, in the lower troposphere the C-n(2) values of summer (March-May) and southwest monsoon period (June-September) are higher than post-monsoon (October-November) and winter (December-February) period.