Investigation of atmospheric turbulence and scale lengths using radiosonde measurements of GVAX-campaign over central Himalayan region

Abstract

The atmospheric turbulence characteristics such as energy dissipation rate (ε), eddy diffusivity (K), and refractive index structure parameter (Cn2), which are inevitable to understand the vertical mixing and transport of pollutants, momentum, and energy, are least explored over the Himalayan region owing to the unavailability of observations. Here, we investigate the characteristics of turbulence in the troposphere (TS) and lower stratosphere (LS) using Thorpe's method for intense radiosonde measurements made during July 2011 to March 2012, from a central Himalayan site Manora Peak (79.5°E, 29.4°N, and 1936 m AMSL). Findings reveal that the energy dissipation rate (log ε), and eddy diffusivity (log K), are right-skewed with central mean values about −3.90 (−3.30) m2s−3 and -0.19 (−0.24) m2s−1, in the TS (LS) region. However, Cn2 follows the right (left) -skewed distribution with the mean value of −16.9 (−19) m−2/3, in the TS (LS). The mean values of inner scale (lo) and buoyancy scale (LB) are 0.051 (0.104) m and 84.62 (8.34) m in the TS (LS). The monthly and seasonal variations of these parameters were also examined and presented. The mean profiles of log ε show the lowest dissipation rate (−4.5 m2s-3) during the post-monsoon season and constant dissipation rate (∼−4 m2s-3) below 5 km in winter, however, mixing coefficient log K shows a constant variation (∼−0.01 m2s-1) above 8 km. Larger buoyancy scales (>100 m) are observed in the altitude range of 8–14 km during moist and lighter monsoon circulations. This study extricates the effect of orography-induced local circulations that controls turbulence intensity in the lower troposphere, especially in the weak mean flow conditions. This study essentially provides the quantified vertical distribution of the atmospheric parameters associated with turbulence and to be utilized for understanding the related physical processes.