Summary of Abstract Submission

Abstract Submission No. IO50-05-0027PresentationPoster

ACTIVE-BREAK CYCLES OF THE INDIAN SUMMER MONSOON IN A COUPLED GCM: RESPONSE OF THE INDIAN OCEAN

PRATAP KUMAR MOHANTY*1

1 DEPARTMENT OF MARINE SCIENCES, BERHAMPUR UNIVERSITY, INDIA

ABSTRACT :

Active-break cycle is an important component of the Indian Summer Monsoon (ISM). Understanding and prediction of active and break phases, therefore, are of fundamental importance for agricultural planning, water management, and thus for the economic development of the country. The active-break cycle is investigated using a 100-year simulation of the atmosphere-ocean coupled global climate model (HadCM3) and compared with observed data. The criterion to define the active-break monsoon conditions is based on a composite monsoon active-break structure of outgoing long wave radiation (OLR), which shows a dipole between the Indian subcontinent and equatorial Indian Ocean. Active-break cycles with characteristics time scales of 10-20 days and 30-60 days are examined by applying a Lanczos filter to the daily anomaly fields. Northward and eastward propagation of the 30-60 day mode and westward propagation of the 10-20 day mode are examined in HadCM3 and compared with observations. Both the temporal and spatial structure of the intraseasonal mode and their link with northward and eastward movement of the convection and the underlying oceanic response are well depicted in HadCM3. Response of the Indian Ocean to the active-break cycle is examined considering ocean surface fields such as SST, wind stress, latent and sensible heat fluxes, and net shortwave radiation. Dynamic-thermodynamic feedback is also examined by studying the mixed layer depth, depth of 20 o isotherms, vertical column of salinity and temperature, zonal and meridional currents. The spatial and temporal coherence evident in the active-break cycles of the above fields suggest the role of ocean-atmosphere coupling in monsoon intraseasonal oscillations and the ability of the model to depict the same.