The role of low-frequency intraseasonal oscillations in the anomalous Indian summer monsoon rainfall of 2002

Surendran, Sajani; Beegum, S. Naseema; Moorthy, K. Krishna

doi:10.1007/s12040-007-0015-5

Cited by 10 publications

(5 citation statements)

References 35 publications

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“…The dominant intraseasonal oscillation in 2002 was on low-frequency intraseasonal time scales, and the most pronounced mode was the northward propagating intraseasonal oscillations (Sajani et al 2007). This intraseasonal mode is characterised by successive 30-40 day time scale northward propagations of organized convection over the Indian sector in summer (Sikka and Gadgil 1980;Yasunari 1979Yasunari , 1981.…”

Section: Low-frequency Intraseasonal Oscillationmentioning

confidence: 99%

Ensemble Simulation of Indian Summer Monsoon Rainfall by an Atmospheric General Circulation Model

Surendran

Nakazawa²,

Rajendran

2007

Journal of the Meteorological Society of Japan

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This study examines the fidelity of the Meteorological Research Institute (MRI) atmospheric general circulation model (AGCM), ensemble runs forced with observed sea surface temperature (SST), in simulating Indian summer monsoon rainfall (ISMR), and its interannual variation. Despite the simple ensemble mean (SEM) capturing essential features of climatological ISMR pattern and its extreme ISMR anomalies, it still shows certain systematic bias in simulating mean seasonal variation of rainfall over the Asia-Pacific region. Concurrently, the ISMR interannual variability throughout the analysis period is not adequately represented.A bias-correction is applied to remove this bias by deriving weights for the member simulations for each Julian day separately at every grid point through multiple linear regression of their daily rainfall, against corresponding observation over a 23-year 'training phase' (out of the total 24-year analysis period). Thereafter, at every grid point, for each Julian day of the remaining 1-year 'forecast phase', the bias-removed ensemble mean (BREM) is computed as an optimal linear combination of weighted member simulations. In cross validation, each year in the analysis period is treated successively as the 'forecast phase', with the remaining 23 years included in the corresponding training phase. The methodology minimises the systematic bias in mean seasonal variation of rainfall, and BREM consequently improves upon SEM in simulating the mean ISMR pattern, and its interannual variability over the entire analysis period.The skill of BREM in forecasting the ISMR, and its intraseasonal variability is validated, for the severe monsoon drought of 2002. The effective removal of climatological bias brings out the realistic precipitation response in BREM to fluctuations in SST boundary forcing. As a result, BREM captures the seasonal rainfall anomaly pattern of 2002, and markedly improves its intraseasonal evolution. Apart from the basic skill of the AGCM ensemble system, pronounced equatorial SST impact in modulating the monsoon circulation during 2002, played a seminal role in the success of the methodology. The analysis also underlines the importance of mean seasonal variation, not only for capturing ISMR climatology, and its interannual variation but for improving its intraseasonal variability as well. With the aid of realistic SST forecasts, this methodology has the application potential for dynamical prediction of ISMR.

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Section: Low-frequency Intraseasonal Oscillationmentioning

confidence: 99%

Ensemble Simulation of Indian Summer Monsoon Rainfall by an Atmospheric General Circulation Model

Surendran

Nakazawa²,

Rajendran

2007

Journal of the Meteorological Society of Japan

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“…The study concluded that Tibetan Plateau moisture and its transport could be greatly affected by the SASM evolution, through the adjustments in the moisture spatial distribution and transport . The active and break spells of convection and rainfall over the monsoon region are important for sowing, harvesting of crops, and water management (Sajani et al, 2007;Zhou et al, 2012). Over South Asia, the maxima and minima values in precipitation are associated with the active and break spells of the SASM (Webster et al, 1998;Krishnamurthy and Shukla, 2000;Ding and Sikka, 2006).…”

Section: Relationship Between Precipitation Extremes and Atmospheric mentioning

confidence: 99%

Changes in precipitation extremes in Southeastern Tibet, China

Zhang

Shen

Wang

2015

Quaternary International

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“…The boreal summer ISV associated with the 30-50 day mode is represented by the co-existence of poleward propagation of convection over the Indian and tropical Western Pacific longitudes and eastward propagation along the equator (Annamalai and Sperber 2005). Although the above investigations give some insight into the liaison between MJO and ISM, only a few researchers (e.g., Saith and Slingo 2006;Sajani et al 2007) relate the monsoon droughts with MJO. These are, however, case studies.…”

Section: Introductionmentioning

confidence: 99%

Eastward propagating MJO during boreal summer and Indian monsoon droughts

2008

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Improved understanding of underlying mechanism responsible for Indian summer monsoon (ISM) droughts is important due to their profound socio-economic impact over the region. While some droughts are associated with 'external forcing' such as the El-Niño and Southern Oscillation (ENSO), many ISM droughts are not related to any known 'external forcing'. Here, we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics. We show that most ISM droughts are associated with at least one very long break (VLB; breaks with duration of more than 10 days) and that the processes responsible for VLBs may also be the mechanism responsible for ISM droughts. Our analysis also reveals that all extended monsoon breaks (whether co-occurred with El-Niño or not) are associated with an eastward propagating Madden-Julian Oscillation (MJO) in the equatorial Indian Ocean and western Pacific extending to the dateline and westward propagating Rossby waves between 10°and 25°N. The divergent Rossby wave associated with the dry phase of equatorial convection propagates westward towards Indian land, couple with the northward propagating dry phase and leads to the sustenance of breaks. Thus, the propensity of eastward propagating MJO during boreal summer is largely the cause of monsoon droughts. While short breaks are not accompanied by westerly wind events (WWE) over equatorial western Pacific favorable for initiating air-sea interaction, all VLBs are accompanied by sustained WWE. The WWEs associated with all VLB during 1975-2005 initiate air-sea interaction on intraseasonal time scale, extend the warm pool eastward allowing the convectively coupled MJO to propagate further eastward and thereby sustaining the divergent circulation over India and the monsoon break. The ocean-atmosphere coupling on interannual time scale (such as El-Niño) can also produce VLB, but not necessary.

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The role of low-frequency intraseasonal oscillations in the anomalous Indian summer monsoon rainfall of 2002

Cited by 10 publications

References 35 publications

Ensemble Simulation of Indian Summer Monsoon Rainfall by an Atmospheric General Circulation Model

Ensemble Simulation of Indian Summer Monsoon Rainfall by an Atmospheric General Circulation Model

Changes in precipitation extremes in Southeastern Tibet, China

Eastward propagating MJO during boreal summer and Indian monsoon droughts

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