Variability in surface inversion characteristics over India in winter during the recent decades

The variation in surface inversions during the recent decades over 20 stations in the Indian region is documented. Radiosonde data at 00UTC for the period 1971–2000 has been used to compute the inversion frequency. The depth and strength of the inversions as well as the wind speed through the inversion layer have also been computed. The frequency of inversions at stations north of 20°N is ~20–60% higher than stations located south of 20°N. Moreover, all the stations show frequencies increasing from the 1st to the 3rd decade. Most of the stations show decreasing depth and increasing strength significant at 99% level. With the exception of Nagpur and Hyderabad which show high frequency of very deep inversions increasing from the 1st to the 3rd decade, the decadal variations of inversion depth at most of the other stations show that shallow and moderate inversions occur more frequently than deep or very deep inversions. Decadal variations in inversion strength show weak inversion frequencies decreasing from the 1st to the 3rd decade while moderate/strong inversions occur more frequently at most stations. Frequencies of very strong inversions are low or are absent. Wind speeds are either weak or moderate with frequencies increasing from the 1st to the 3rd decade. Low frequency of strong winds and negligible frequency of very strong winds are observed.