Seasonal Characteristics of Atmospheric Boundary Layer and its Associated Dynamics over Central India

Abstract

Atmospheric boundary-layer studies have applications in lower tropospheric processes, air pollution meteorology, weather prediction and climate monitoring. Despite this, very few studies are available over tropics, especially over central India. Here, we analyse, high resolution vertical profiles of meteorological parameters corresponding to fully developed mixed layer obtained using balloon borne radiosonde to study characteristics of atmospheric boundary layer over Nagpur (21.15 °N, 79.15 °E). Study reveals that, within the mixed layer, variation in RH is very less (within 20%) while above mixed layer, large variations are seen. Back trajectory analysis confirms that the moist days (dry days) are associated with the transport of air masses from the Arabian Sea (from arid locations). Mixed layer heights derived through gradients in Virtual Potential Temperature (VPT) showed highest values during Pre monsoon (2564 ± 867 m) and lowest (788 ± 477 m) in Monsoon season. Specific Humidity varies in the range from 0 to 10 g/kg during pre-monsoon and 0–20 g/kg during monsoon season. D-theta exhibits lowest values in monsoon and highest values during pre-monsoon season while Parcel saturation pressure difference exhibits highest values in monsoon and lowest values during pre-monsoon season. During the monsoon and early post monsoon there is a presence of high moist static energy (Theta-e ~ 365 K) at the surface and moderate during mid-winter. We have examined, for the first time, the spatial (vertical) coherence of VPT using a novel technique of auto correlation analysis. Coherence length scales, derived with this method are found to be Maximum (1129 ± 48 m) in winter and minimum (694 ± 281 m) in Pre monsoon season.