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Studies of the hydrology, influence and variability of the Asian summer monsoon.

Deliverables

Summary: In collaboration with the EU programme on Seasonal Prediction (PROVOST), the predictability of the Indian Summer Monsoon has been investigated by using the summer ensemble of ECMWF seasonal forecasts. The results suggest that the current level of predictability is low, certainly much lower than that suggested by statistical methods. However, the model displays considerable systematic errors in its basic simulation of the predictability is continually reassessed as models improve.
Summary: Using reanalyzes from ECMWF and NCEP, a comprehensive description of the mean monsoon and its variability has been developed. This has shown the complex behaviour of monsoon variability on the regional and large scale, as well as the importance of the interaction between the interseasonal and interannual timescales. The results have been compiled in an atlas which is available electronically from the SHIVA website. This provides the most comprehensive diagnosis of monsoon behaviour currently available.
Summary: Several groups have shown that the geographical distribution of monsoon precipitation is extremely sensitive to the physical parametrizations, particularly those for convective and boundary layer transports, as well as land and surface processes. Because of this sensitivity to even minor changes in the parametrization, improvements in the physics of the parametrization schemes do not lead automatically to a better simulation of all features of the monsoon resolution have shown that systematic biases are evident at all resolutions from which it can be concluded that the major systematic errors are most likely associated with physical parametrizations.
Summary: The Asian Summer Monsoon displays substantial interannual variability which has profound social and economic consequences for the people of India and South East Asia. An understanding of the causes of this interannual variability is central to future success in seasonal and longer term prediction. Various mechanisms have been proposed to explain the interannual variability of the monsoon. Whilst the SHIVA results confirm the importance of ENSO, they have also provided evidence that the Indian Ocean, the Eurasian continent and the stratospheric Quasi-Biennial (QBO) may play crucial roles. During the season the monsoon fluctuates between active (wet) and break (dry) spells which may significantly influence the seasonal mean rainfall amounts. A key question is whether the low frequency forcing (e.g. ENSO) can alter these fluctuations in a predictable manner. Preliminary results from reanalyses and model integrations suggest that the behaviour of active/break cycles may be chaotic and therefore inherently unpredictable. The physical mechanisms involved in the phenomenology of active/break cycles have been investigated using sensitivity experiments with the GCMs. Results suggest that the coupling between the atmosphere and the land surface hydrology may be important by influencing the timescale of the oscillations rather than by altering their basic structure.
Summary: SHIVA has supported the development of websites which provide important links between scientists within the SHIVA project, as well as those working on monsoon research throughout the world. Up-to-date information on current monsoon behavior, basic information on the monsoon and its predicability are covered. The sites have become a major source of monsoon information and are heavily used by the international community. SHIVA is the focus of monsoon research within CLIVAR See http://www.met.rdg.ac.uk/shiva/shiva.html http://www.met.rdg.ac.uk/~daves/Monsoon/Main.html

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