35 research outputs found
On the Relationship Between North India Summer Monsoon Rainfall and East Equatorial Indian Ocean Warming
No full textGenerally, a strong north India summer-monsoon rainfall (NISR) is associated with anomalous upper troposphere ridge over northwest of India. This ridge triggers anomalous northerly winds over Tibetan Plateau and easterlies over India. The easterly anomaly over India reduces the tropospheric wind shear, while the northerly at Tibetan plateau allows frequent intrusions of high-latitude dry and cold meridional winds to interact with the lower-level relatively warm and moist easterly monsoonal flow, enhancing the NISR. The current study, using a suite of observations, reanalysis products and numerical model sensitivity experiments, explores the changes in NISR, and its association with the warming in the equatorial Indian Ocean.
In the recent two decades (1996-2017), the NISR has been exhibiting a decreasing trend with increased variability, much larger than the earlier period (1979-2000). A possible reason for this is due to the rise in warm sea surface temperature (SST) observed in the east equatorial Indian ocean, which shows a negative correlation to NISR. The current analysis indicates that the warmer SST induce strong convection and associated northward propagating off-equatorial Rossby gyres to the west of the equatorial eastern Indian ocean, spreading the tropospheric heating towards the northeast of India, thereby elevating the geopotential height. This creates upper troposphere low pressure anomaly at the northwest of India. These factors are consistent with the suppression of the NISR, resulting in the observed decreasing trend in the recent decade
Coupled Land‐Atmosphere Regional Model Reduces Dry Bias in Indian Summer Monsoon Rainfall Simulated by CFSv2
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Indian Ocean Warming: The Bigger Picture
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Indian Ocean Warming: The Bigger Picture
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Projected future changes in the contribution of Indo-Pacific sea surface height variability to the Indonesian throughflow
No full textThe Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959-2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25-30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions
Indian Ocean Warming: The Bigger Picture
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