An assessment of Indian Summer Monsoon (ISM) characteristics observed in continuous Radiosonding from New Delhi, National Capital Region (NCR-Delhi)

Abstract

The geographical location of the New Delhi, National Capital Region (NCR) within the Northern Gangetic Plains is influenced by the Indian Summer Monsoon (ISM) and its associated weather. Monsoon weather is observed by the appearance of organised clouds, an outbreak of rainfall, and humid conditions. The current study examines pre-monsoon and monsoon weather conditions, together with intra-monsoonal variations (viz. wet, dry, and withdrawal spells) in wind structure, thermodynamic parameters, precipitation, and the structure of the Monsoon Boundary Layer (MBL). Investigations are also made into the macrophysical aspects of the monsoonal clouds/ weather systems that initiate and maintain ISM characteristics over the region. Moisture availability in the boundary layer carried by the low-level monsoon winds has a substantial role in forming monsoonal cloud mechanisms, such as shifting down the Lifting Condensation Level (LCL) closer to the Level of Free Convection (LFC) as an effect of continuous moisture supply from the lower levels and rising of Level of Neutral Buoyancy (LNB) near the tropopause region during the monsoonal period. Further influenced by the moisture in the boundary layer, the Precipitable Water (PW) is also reliant on the LCL height. Additionally, it is observed that the short-term zonal disturbances induced by extra-tropical and sub-tropical flows impacts intra-monsoonal weakening and variations. Analysis from several of the convective parameters and indices revealed that deep convective systems might occur throughout the monsoon season, while severe thunderstorms could develop during the pre-monsoon, and thunderstorms are less likely to happen during the withdrawal spell. The data presented here are the first to use continuous Radiosondes observations for quantitative assessments of the nature of the ISM over northern India.