Observed features of monsoon low-level jet and its relationship with rainfall activity over a high-altitude site in Western Ghats, India

In the present work, monsoon low-level jet (MLLJ) characteristics and its relationship with rainfall activity have been studied using three years (2016–2018) of radiosonde observations taken from a high altitude site (Mahabaleshwar, 1348 m AMSL) in Western Ghats, India. Initial analysis of zonal and meridional winds showed an apparent monthly variation with respect to altitude with robust features in zonal winds compared to meridional winds. Analyzed zonal wind and vertical shear in zonal wind during south west monsoon showed clear intra seasonal variation with respect to altitude especially below 5 km. Derived MLLJ characteristics, such as core speed, core height, and westerly wind depth, also exhibited apparent intra-seasonal variation where core height was comparatively invariant. Strong zonal wind and vertical shear in the zonal wind including higher core speed and westerly wind depth was noticed during July and August compared to June and September. Further, MLLJ association with rainfall activity has been analyzed. An increase in core speed and westerly wind depth was noted during the active period of monsoon compared to the break period. Later, the evolution of MLLJ characteristics before, during, and after heavy and high rainfall has been analyzed which showed strengthening of zonal wind, vertical shear in zonal wind, core speed, and westerly wind depth before and during the rainfall events categorized. Abundant moisture transport from the Arabian Sea to the Indian land mass prior to the event was noticed in the analysis of zonal water vapor flux. Intensification of few MLLJ characteristics mostly brings copious moisture, possibly leading to heavy or high rainfall over the study region.