First observations of turbulence parameters in the troposphere over the Bay of Bengal and the Arabian Sea using radiosonde

This paper discusses the turbulence characteristics of the free atmosphere over the Bay of Bengal and the Arabian Sea during the premonsoon season of 2006. The turbulence scaling concepts, developed over the past decades for application to oceanic mixing, are used for retrieving turbulence properties in the free atmosphere from high-resolution soundings, as described by Clayson and Kantha (2008). The variability in the vertical turbulence structure over a large spatial region is studied using this novel method for the first time. Investigations revealed the presence of a highly turbulent band at upper troposphere below the cold point tropopause (CPT) with significant enhancements in Thorpe length and eddy diffusion coefficient. This increased turbulence is studied in conjunction with the observations of the tropical tropopause layer (TTL). It is seen that the lower and upper boundaries of this turbulence band nearly coincide with the height where the potential temperature lapse rate begins to show a decrease (LRHmin) and cold point tropopause, respectively. The TTL is the transition regime from convectively dominated troposphere to radiatively dominated stratosphere, and is characterized by a decrease in the static stability. The enhanced zonal and meridional wind shear observed in this region shows that the stability in this region is further weakened because of the breaking of Kelvin-Helmholtz waves, which results in the enhancement of turbulence. The study reveals the potential of high-resolution soundings to be used in the investigations of turbulence in the free atmosphere.