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Intraseasonal perturbations in the 20-100 day band, including the Madden-Julian oscillation (MJO), are large-scale convective and dynamical disturbances in the tropics. These disturbances give some weather predictability at medium range (10-15 days) and extended range (15-30 days). Moreover, these perturbations affect the mean tropical climate and its variability at seasonal and interannual time scales. These perturbations have an important impact on the tropical variability, especially for: the frequency and intensity of cyclones; the initiation and modulation of Asian, Australian and African monsoons and; the onset and evolution of El NiƱo. Major international programs such as CLIVAR and THORPEX recognize the importance of intraseasonal perturbations in weather and global climate. Recent studies show however that most Atmospheric General Circulation Models (A-GCMs), forced or coupled to the ocean, give a poor representation of this essential tropical variability.

The international CINDY (Japan)-DYNAMO (USA) field experiment in the equatorial Indian Ocean will give a unique framework to study the physical sources of the intraseasonal perturbations. This experiment extends over a period of 6 months between October 2011 and March 2012. During this period, atmospheric and oceanic measurements will be performed from research vessels and from islands (radar and aircraft measurements) and using a reinforced network of buoys and radiosondes over the whole Indian Ocean. Forecast and hindcast at different time scales from synoptic to seasonal will be done for the field experiment period by many international centres with either operational or research models. Conventional single column models (SCMs) and cloud resolving models (CRMs) forced at the boundaries by the quadrilateral CINDY-DYNAMO sounding array will provide a very valuable source of new information for parameterization development. Comparison between CRMs output and the field experiment dataset will be especially valuable for the investigation of detailed sub-grid scale process (cumulus mass fluxes, entrainment, mesoscale organization, etc.) that may explain the organisation of the convection in the MJO envelop. Idealized and large-scale models will be also used to investigate the role of different processes (convective parameterization, air-sea interaction, etc.) in the initiation and the propagation of these intraseasonal perturbations.

Last Updated on Friday, 20 May 2011 09:20
 
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