Understanding UTLS Dynamics in the Tropics during Deep Convection: Insights from 205 MHz ST Radar 

Abstract

Deep convection plays a crucial role in transporting atmospheric components, including mass, momentum flux, heat, and moisture, across various layers of the atmosphere. This transport gains particular significance in the Upper Troposphere and Lower Stratosphere (UTLS) region, an area that remains relatively unexplored but holds considerable importance in the context of the changing climate scenario. In response to the identified scientific gap, a dedicated initiative was launched to investigate the impact of thunderstorms in the UTLS over Kochi,India. This region is Situated in the tropical coastal zone and recognized as the gateway to the Indian monsoon, It exhibits distinctive features, including frequent deep convective activities. Utilizing the capabilities of the 205 MHz ST Radar at Cochin University of Science and Technology (CUSAT), renowned for its high spatio-temporal resolution, this campaign sought a comprehensive understanding of the impact of thunderstorms on the less-explored UTLS region. An experiment, conducted at ACARR from November 3 to November 10, 2022, involved a 24-hour observation period using the ST radar along with other instruments, including microwave radiometer, Disdrometer, AWS observation, ceilometer, and MRR, enabling multiplatform observation of dynamic and thermodynamic states during post-monsoon thunderstorms. These events exhibited characteristics of deep convection, showcasing unique signatures in the upper troposphere and lower stratosphere. The radar captured robust updrafts, reaching maximum speeds of 4-5 m/s and extending from the mid-troposphere to the lower stratosphere. Hodographs constructed during convective activities unveiled strongly'veered' winds extending into the upper troposphere. This observation highlighted the complexity of convective processes in this tropical region. A pivotal aspect of the study centered on calculating vertical and horizontal momentum flux during thunderstorm events in the UTLS region. This analysis provided valuable insights into the intricate momentum exchange between different atmospheric layers, offering a deeper understanding of the convective systems' dynamics in the UTLS region. We have observed 5-6 times enhancement in the vertical momentum flux during convective activity in the UTLS and 4-5 times in the mid-troposphere. We also estimated turbulence in the UTLS region during this period using the spectral width method. We also tried to understand the existence of any periodic wind behavior in the tropopause region using a periodogram. Detailed statistics are presented in this paper.