Asian Monsoon System and its Sub-Systems

1. Outstanding Scientific Challenge for the Proposed Asian Monsoon Year Study and the Scientific Strategy for its implementationDevraj Sikka40 Mausam Vihar, New Delhi, India

2. Asian Monsoon System and its Sub-Systems • The Asian Summer Monsoon is a Key Element of General Circulation • Comes with remarkable regularity • Exhibits substantial variability on data of arrival (7-12 days in different components), temporal scale of synoptic, medium Intra seasonal rainfall variability (3-7 days 10-20 days and 30-60 days). Quantum of inter annual variability, varying from 10-50 percent in different sub-regions, with profound economic consequences • Influence extends on large horizontal scale and even on global climate • Large system which comprises of South Asian Summer Monsoon (SASM) East Asian Summer Monsoon (EASM), South China Sea Summer Monsoon (SCSM) and Western North Pacific Summer Monsoon (WNPSM) • All these regional monsoon have their respective sub-regional characteristics

5. Somali Coast, Indonesian and Western Pacific Channels are prominent in Lower Troposphere

6. Synoptic Disturbances of Asian Monsoon

7. Regional Monsoon Experiments in India since MONEX and over South China Sea • MONTBLEX and LASPEX (1989-96), BOBMEX (1998-99) and ARMEX (2002-03) in India and South China Sea Monsoon Experiment (SCSMEX 1996-2001), GEWEX Asian Monsoon Experiment (GAME 1995 onwards) etc in East Asian region. • As a result of research through field progammes great understanding of Regional Monsoon Systems, their fluctuations role of land-ocean processes, ISV and IAV achieved. • Understanding not resulted in high improvement in prediction of extreme weather (meso-scale) and extreme climate events (Intra-annual Scale) some key elements perhaps missing • Integration of processes not achieved due to attention mainly focused on sub-regional processes on Grand Asian Scale.

8. Equatorial Cloud Clusters Locked to Madden Julian Oscillation

10. Need for Comprehensive Study of All Component of Asian Summer Monsoon System • Asian Summer Monsoon System evolves almost simultaneously during May-September • Undergoes onset, peak and withdrawal periods at different phases of the system • Processes in one component influence the other particularly with respect to major sub-seasonal oscillations produced by low frequency modes (10-20 days and 30-60 days) which encompass synoptic variability. • The trough (ridge) of the two modes lying in phase enhance (suppress) convection with same phase lag over different regions as the 10-20 days mode moves westward from West Pacific toward Bay of Bengal and 30 day mode moves east wind from India to West Pacific. • These two modes are therefore the connecting links between the two major regions. Hence modulations of different sub-regional components need deeper study.

11. Sub-Seasonal Variability, Role of Land Surface and Aerosols – New Facets • Sub-seasonal variability of the monsoon in each region controlled by meso-scale and synoptic scale disturbances which distribute rainfall. • Knowledge, particularly on meso-scale, needs considerable improvement by analyzing these disturbances with respect to land surface hetrogenities, heating and cooling of land surface under dry and moist episodes. • Incursion of dry and dusty air (which may even be anthropogenically charged with soot particles) into the Gangetic Valley, Yangtze Valley and North China under prolonged dry spells. Indirect Aerosol effect likely to dominate in mid-season breaks • Current great interest to understand role of aerosols in spring heating of the upper troposphere along the foot hills of Himalayas and Tibet which might impact on the rainfall in early monsoon season.

12. Role of Remote SST Forcing (ENSO) and Regional SST Forcing (IOD) and KUROSHIO (on Asian monsoon)

13. Need for Targeted Observations over Specific Areas • Gangetic Plain and Yangtze Valley (meso-scale) • South China Sea on Tropical Disturbances and their WNW Passage (large scale) • East Tibetan Area – for influence on Meiyu season (meso-scale) • Tracking of LLJ over West Arabian Sea, South of Sri Lanka, Central B.B. (Large Scale) • Indo-China, Yangtze Valley (Large Scale) • Inter play of Monsoon active-break over India with Meiyu and N.China Sea Systems (Large Scale) • Passage of MJO and bifurcating meridionally propagating convective episodes (Large Scale) • Passage of westerly troughs north of Tibet and Western Sector of India (Large Scale) • Air-sea interactions B.B & SCS regions (medium and large scales) • Build up of EQUINO and role of ISO on it • These would help in diagnosing interactions between different components of sectoral monsoon components

14. Strategy for Implementation of AMY • Co-ordination with CTCZ (India), MAIRS, West Pacific Mahasri and other initiatives. • Co-ordination for Field Phase Regional Managements to implement overall objectives • Modelling for Better Prediction on meso, synoptic and Extended Range Scales. • Information and Data Exchange and Co-ordinated Research. • AMY would contribute to WMO/CLIVAR, THORPEX, CEOP, GEWEX, TMRP • International co-ordination necessary to achieve objectives for Integrated Asian Monsoon Studies on multi-year basis (2008-2011).

15. AMY to be a Multi-Year Programme • Hence active exchange of ideas through scientific workshops – one or two each year needed in different participating countries to keep focus on major research objectives • Primary goal of better Predictability through Modelling Framework • Success of Program to depend on Societal Impacts through better predictability and Water Resource Management

16. THANK YOU VERY MUCH