Summary of Abstract Submission

Abstract Submission No. IO50-05-0003PresentationPoster

BEHAVIOUR OF THE ASIAN SUMMER MONSOON INTRASEASONAL OSCILLATION IN INITIALIZED MET OFFICE COUPLED MODEL

A. Jayakumar*1, Andrew Turner2, S. J. Bush2, Saji Mohandas1, A.K.Mitra1, E.N. Rajagopal1

1 NCMRWF, India
2 UoR, UK

ABSTRACT :

Boreal summer sub-seasonal variability in the Asian monsoon otherwise known as monsoon intra-seasonal oscillation (MISO) is one of the dominant modes of climate variability in the tropics, which has large impacts on rainfall and thus India¿s agricultural production. However our understanding of the mechanisms involved in MISO and its simulation in various numerical models is not perfect. In this study we focus on an objective evaluation of the fidelity of MISO simulation in the Met Office Global Seasonal forecast system version 5 (GloSea5), an initialized coupled model. The analysis focuses on the time-mean background state, air-sea interaction processes and monsoon dynamics, which help to diagnose the main sources of error at this time scale. Low-level wind variability in GloSea5 modulates the monsoon environment of the model through physical processes associated with air-sea interaction and tropical atmospheric dynamics and thermodynamics. We find that simulated air-sea interactions in the central Indian Ocean are not supportive of MISO initiation in that region, likely a result of the low surface wind variance there. As a consequence, the near-quadrature phase relationship between SST and convection is not represented properly over the central equatorial Indian Ocean, and northward propagation from the equator is poorly simulated. From the dynamical perspective, we find that the Rossby wave response, associated with active/break variations in monsoon diabatic heating in GloSea5, strengthens the west equatorial Indian Ocean convective variability through anomalous potential vorticity forcing from the middle atmosphere to lower levels. This may help reinforce the equatorial mean bias suffered in this GCM in comparison to observed and reanalysis estimates.