Climate Change and Monsoon Variability (CCMV): Troposphere and Stratosphere Interactions

Extensive research has been carried out to predict summer monsoon rainfall variability on various time scales, namely, the interannaul, the intraseasonal, the super synoptic time scales, etc. However, monsoon is also viewed as discrete rain events throughout the season and the current scenario suggests an increasing trend in extreme rain events over India. The intense rainfall associated with these extreme events results in landslides, flash floods, and crops damage. Thus a diagnosis of ‘Preferred Regions’ of occurrence of the Extreme/Intense Rain Events (ERE/IRE) of the Indian Summer Monsoon over both the land and the oceans is the need of the hour. Also, it is absolutely imperative to unravel the factors responsible for this increasing tend although several attempts related the increasing trend in EREs to warming trend of Indian Ocean in JJAS SST, increase in the number of Indian Ocean Dipole years in recent decades, etc.

The Indian summer monsoon variability is a manifestation of the deep cloud systems originating over the Indian seas and propagating northwards to cover the entire Indian continent. These deep cloud systems are the agents to transport water vapor, Ozone and trace gases to stratospheric heights. Radiative warming and cooling of the atmosphere is significantly sensitive to these variations in water vapour and trace gases at stratospheric heights. Hence, the links between the Indian summer monsoon and the Global warming is complex and is required to be well understood to diagnose the Climate change of the present times. On the other hand, the changing rainfall pattern of the Indian summer monsoon with increasing trend in EREs is attributed to the unequivocal warming of the environment. The mutual interaction between stratospheric processes and Indian summer monsoon is unambiguous. SPARC, a core programme of WCRP, addresses the role of stratospheric processes on Earth’s climate and the related significant issues with three primary themes, 1. Atmospheric Dynamics and Predictability, 2. Climate and Chemistry, 2. Long-term Records for Climate Understanding.

Southwest Monsoon is the major atmospheric phenomena of the country (extending to Asian region) and is global in influences, therefore, studying Stratosphere-Troposphere impact on Indian summer monsoon would be a new perspective. Thus the project goals here are:

  • How does Indian monsoon influence the stratosphere region and get influenced?
  • What processes and interactions are important in Upper troposphere and Lower Stratosphere (UTLS) region to be identified, understood and parameterized for realistic representation in monsoon climate models?
  • The influence of monsoon variability on intraseasonal timescales, and the northward movement of the Oceanic TCZ on UTLS temperature distribution over the monsoon region remains to be investigated.
  • To examine influence of potential changes in the strength and variability of the monsoon circulation linked to increased convection and rainfall on transport pathways.
  • To parameterize variations in cosmic ray intensity with the low cloud cover, considering the time scales of variations, for realistic representation in global climate models.
  • Numerical modelling of troposphere-stratosphere coupling and its implication on monsoon variability using WACCM3, a coupled 3-d chemistry-climate model.