On the relative roles of El Nino and Indian Ocean Dipole events on the Monsoon Onset over Kerala

Sankar, Syam; Kumar, M. R. Ramesh; Reason, C. J. C.

doi:10.1007/s00704-010-0306-7

Cited by 41 publications

(17 citation statements)

References 37 publications

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“…They found that years with advanced MOK had persistent westerlies before MOK and enhanced convection over the SEAS and Bay of Bengal, and the opposite was true for delayed MOKs. They also found that the localized Hadley circulation associated with the monsoon was stronger during advanced MOKs compared to delayed MOKs (Sankar et al, ). Both La Niñas and negative IOD phases were found to support increased moisture over India, whereas El Niños and positive IOD phases were found to inhibit this.…”

Section: Introductionmentioning

confidence: 93%

The Role of Salinity in the Southeastern Arabian Sea in Determining Monsoon Onset and Strength

2020

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In this study, we examine the role of freshwater transported from the Bay of Bengal into the southeastern Arabian Sea (SEAS) in determining both the timing of monsoon onset and the strength of the ensuing monsoon. To do this, we use a combination of satellite-derived salinity data and reanalysis products from 1980 to 2016 in order to discuss seasonal, interannual, subdecadal, and long-term decadal variability in various atmospheric and oceanic contributors such as ocean heat content, freshwater transport, ERA5 instantaneous moisture flux, mixed layer depth, and barrier layer thickness. The salt budget in the SEAS reveals the dominance of meridional freshwater advective transport that brings in variability in salinity and thus in salinity stratification, as well as in mixed layer processes. We find that these parameters exhibit the prevalence of a long-term decadal variability (with trends of increasing/decreasing phases over a 15-year duration) over which interannual (3-year trend) and intradecadal (7-year trend) variability trends are superimposed. The patterns of both the 3-and 7-year trends follow each other closely, and relatively high amplitudes are seen in the 3-year trends. The long-term decrease in moisture flux and freshwater transport into the SEAS along with a rise in ocean heat content over a 15-year duration after 1994 contributed to a lack of strong monsoons in recent years; the prevailing interannual and intradecadal variability in these parameters associated with the Indian Ocean Dipole and El Niño Southern Oscillation events favored weaker and normal monsoons after 1994. Plain Language SummaryThe timing and intensity of the southwest monsoon is difficult to forecast and has been the subject of a great deal of research. In particular, the genesis of a monsoon onset vortex over the southeastern Arabian Sea (SEAS) encompassing the Arabian Sea Mini Warm Pool has received increased attention for the role it plays on the onset of the southwest monsoon. In our study, we examine how the low salinity waters transported from the Bay of Bengal (both along the east coast of India and from the southern Bay of Bengal) into the SEAS region influence the strength and timing of the ensuing southwest monsoon. Our finding is that this low salinity water has a significant impact on barrier layer formation in the SEAS and the vertical thermal structure of the Arabian Sea Mini Warm Pool. Further examination of subdecadal, decadal, and long-period decadal trends from 1980 to 2016 shows that instantaneous moisture fluxes and zonal winds over the SEAS have decreased substantially, and barrier layer thickness has increased since 1994 in association with the increasing trend in ocean heat content and contributed to the lack of strong southwest monsoons after 1994.

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Section: Introductionmentioning

confidence: 93%

The Role of Salinity in the Southeastern Arabian Sea in Determining Monsoon Onset and Strength

2020

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“…Since the formation and intensity of the low-pressure cell over Asia is mainly triggered by the radiative heating of the Tibetan Plateau, an enhanced snow cover during winter and spring increases the surface albedo and results in a delayed and reduced formation of the thermal low and subsequently in decreasing summer precipitation amounts. Moreover, many studies highlight the importance of the Southern Oscillation for the intensity of monsoonal precipitation (Sankar et al, 2011;Shrestha, 2000), although some studies illustrate that the correlation of the Southern Oscillation index (SOI) and the Indian and the East Asian summer monsoon precipitation weakened during recent decades (Kumar et al, 1999;Wang and He, 2012). Studies by Pokhrel et al (2012) and Sigdel and Ikeda (2012) indicate that El Niño events are accompanied by reduced moisture fluxes into South Asia.…”

Section: Large-scale Circulation Modes Pluviometric Regimes and The mentioning

confidence: 99%

Large-scale atmospheric forcing and topographic modification of precipitation rates over High Asia – a neural-network-based approach

2015

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Abstract. The heterogeneity of precipitation rates in high-mountain regions is not sufficiently captured by stateof-the-art climate reanalysis products due to their limited spatial resolution. Thus there exists a large gap between the available data sets and the demands of climate impact studies. The presented approach aims to generate spatially high resolution precipitation fields for a target area in central Asia, covering the Tibetan Plateau and the adjacent mountain ranges and lowlands. Based on the assumption that observed local-scale precipitation amounts are triggered by varying large-scale atmospheric situations and modified by local-scale topographic characteristics, the statistical downscaling approach estimates local-scale precipitation rates as a function of large-scale atmospheric conditions, derived from the ERA-Interim reanalysis and high-resolution terrain parameters. Since the relationships of the predictor variables with local-scale observations are rather unknown and highly nonlinear, an artificial neural network (ANN) was utilized for the development of adequate transfer functions. Different ANN architectures were evaluated with regard to their predictive performance.The final downscaling model was used for the cellwise estimation of monthly precipitation sums, the number of rainy days and the maximum daily precipitation amount with a spatial resolution of 1 km 2 . The model was found to sufficiently capture the temporal and spatial variations in precipitation rates in the highly structured target area and allows for a detailed analysis of the precipitation distribution. A concluding sensitivity analysis of the ANN model reveals the effect of the atmospheric and topographic predictor variables on the precipitation estimations in the climatically diverse subregions.

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“…Strong coupling between the air-sea processes is unique to the Indian Ocean; however, this coupling is not completely independent of the El Niño southern oscillation [16]. Ummenhofer et al [8] found that major droughts in southeast Australia were related to periods when the IOD remained persistently "positive" or "neutral" whilst during a negative phase of the IOD, unusually wet conditions dominated across southern regions of Australia.…”

Section: Climate Influences On Northwest Cloudbands the Indianmentioning

confidence: 99%

Influence of Northwest Cloudbands on Southwest Australian Rainfall

Telcik

Pattiaratchi

2014

Journal of Climatology

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Northwest cloudbands are tropical-extratropical feature that crosses the Australian continent originating from Australia's northwest coast and develops in a NW-SE orientation. In paper, atmospheric and oceanic reanalysis data (NCEP) and Reynolds reconstructed sea surface temperature data were used to examine northwest cloudband activity across the Australian mainland. An index that reflected the monthly, seasonal, and interannual activity of northwest cloudbands between 1950 and 1999 was then created. Outgoing longwave radiation, total cloud cover, and latent heat flux data were used to determine the number of days when a mature northwest cloudband covered part of the Australian continent between April and October. Regional indices were created for site-specific investigations, especially of cloudband-related rainfall. High and low cloudband activity can affect the distribution of cloudbands and their related rainfall. In low cloudband activity seasons, cloudbands were mostly limited to the south and west Australian coasts. In high cloudband activity seasons, cloudbands penetrated farther inland, which increased the inland rainfall. A case study of the southwest Australian region demonstrated that, in a below average rainfall year, cloudband-related rainfall was limited to the coast. In an above average rainfall year, cloudband-related rainfall occurred further inland.

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On the relative roles of El Nino and Indian Ocean Dipole events on the Monsoon Onset over Kerala

Cited by 41 publications

References 37 publications

The Role of Salinity in the Southeastern Arabian Sea in Determining Monsoon Onset and Strength

The Role of Salinity in the Southeastern Arabian Sea in Determining Monsoon Onset and Strength

Large-scale atmospheric forcing and topographic modification of precipitation rates over High Asia – a neural-network-based approach

Influence of Northwest Cloudbands on Southwest Australian Rainfall

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