Seasonal Variability of Salinity and Salt Transport in the Northern Indian Ocean

D’Addezio, Joseph M.; Subrahmanyam, Bulusu; Nyadjro, Ebenezer S.; Murty, V. S. N.

doi:10.1175/jpo-d-14-0210.1

Cited by 33 publications

(19 citation statements)

References 48 publications

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“…This SODA product is obtained from the University of Maryland at https://www.atmos.umd.edu/~ocean/index_files/soda3.12.2_mn_down-load_b.htm. Previous versions of SODA have been used in multiple studies in the Indian Ocean, and the reanalysis is found to have superior mixed layer dynamics (D' Addezio et al, 2015;Grunseich et al, 2011;Karmakar et al, 2018;Li et al, 2018;Zhou & Murtugudde, 2013).…”

Section: Data 211 Reanalysis Productsmentioning

confidence: 99%

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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: Data 211 Reanalysis Productsmentioning

confidence: 99%

“…S is salinity in units of kg/kg (10 −3 psu). H is the water depth (45 m in this study), z 0 is the ocean surface, and L is the meridional (zonal) distance of the box considered (D' Addezio et al, 2015;Nyadjro et al, 2011;Wijffels et al, 1992).…”

Section: 1029/2019jc015592mentioning

confidence: 99%

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

2020

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“…Models used for transport calculations typically close the Palk Strait due to its negligible flow, so leaving it open provides an opportunity for HYCOM and SODA to overestimate its flow (Kurian & Vinayachandran, 2007;Rao et al, 2011). However, despite opening the Palk Strait, HYCOM and SODA are both commonly used for transport calculations in the Indian Ocean (Carton & Giese, 2008;D'Addezio et al, 2015;Grunseich et al, 2011;Nyadjro et al, 2011;Nyadjro et al, 2013;Trenary & Han, 2008). Additionally, the first layer of each model (1-m depth in HYCOM and 5-m depth in SODA) is adequate for resolving the SSS (Cahyarini et al, 2008;Grunseich et al, 2011;Melzer & Subrahmanyam, 2015;Nyadjro et al, 2013;Yuhong et al, 2013).…”

Section: Hycom Model and Reanalysis Datamentioning

confidence: 99%

Large‐Scale Fresh and Salt Water Exchanges in the Indian Ocean

et al. 2019

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Upper‐ocean dynamics in the Northern Indian Ocean (NIO) depend on changes in the magnitude and location of the high salinity waters of the Arabian Sea and low salinity waters of the Bay of Bengal. The large sea surface salinity (SSS) differences between these two basins are related to the surface freshwater flux (evaporation minus precipitation), which is positive (negative) in the Arabian Sea (Bay of Bengal). To quantify large‐scale salinity changes on decadal time scale over the whole water column and to study trends in salinity and volume transport, we have analyzed Simple Ocean Data Assimilation (SODA) reanalysis product, HYbrid Coordinate Ocean Model (HYCOM) simulations, European Centre for Medium‐Range Weather Forecasting's ERA‐Interim reanalysis product, and riverine streamflow data from the National Centers for Atmospheric Research's Global River Flow and Continental Discharge Dataset for the NIO. We find increased freshening conditions in the Bay of Bengal and salinification conditions in the Arabian Sea that would support a stronger zonal SSS difference in the NIO but that it is partially compensated by positive (negative) salt transports into the Bay of Bengal (BoB) (Arabian Sea). Empirical orthogonal function analysis of SODA SSS indicates that the main factors of SSS variability are Indian Ocean Dipole and El Niño‐Southern Oscillation and seasonal currents. The trends in the volume transport reveal decadal changes in zonal equatorial currents in HYCOM and Somali Current in SODA.

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“…In the long-term mean, in situ and satellite fields agree relatively well with a strong east-west gradient of surface salinity: SSS varies from less than 32.4 in the Bay of Bengal to more than 36.6 in the Arabian Sea, although RSS/JPL products slightly under-/overestimated in situ SSS as measured by Argo in the Arabian Sea. Broadly speaking, the Indian Ocean salinity pattern is controlled by four major processes [37][38][39][40][41][42][43]: net-air sea fluxes (evaporation minus precipitation), runoff from large rivers in the Bay of Bengal, inflow of relatively fresh waters from the Pacific Ocean through Indonesian throughflow straits, and inflow of saltier waters from the Red Sea and the Arabian/Persian Gulf. The wide salinity range and a variety of processes controlling SSS make the North Indian Ocean especially attractive to assess spaceborne SSS measurements.…”

Section: Introductionmentioning

confidence: 99%

Statistical Assessment of Sea-Surface Salinity from SMAP: Arabian Sea, Bay of Bengal and a Promising Red Sea Application

Menezes

2020

Remote Sensing

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Sea-surface salinity (SSS) is an essential climate variable connected to Earth's hydrological cycle and a dynamical component of ocean circulation, but its variability is not well-understood. Thanks to Argo floats, and the first decade of salinity remote sensing, this is changing. While satellites can retrieve salinity with some confidence, accuracy is regionally dependent and challenging within 500-1000 km offshore. The present work assesses the first four years of the National Aeronautics and Space Administration's Soil Moisture Active Passive (SMAP) satellite in the North Indian Ocean. SMAP's improved spatial resolution, better mitigation for radio-frequency interference, and land contamination make it particularly attractive to study coastal areas. Here, regions of interest are the Bay of Bengal, the Arabian Sea, and the extremely salty Red Sea (the last of which has not yet received attention). Six SMAP products, which include Levels 2 and 3 data, were statistically evaluated against in situ measurements collected by a variety of instruments. SMAP reproduced SSS well in both the Arabian Sea and the Bay of Bengal, and surprisingly well in the Red Sea. Correlations there were 0.81-0.93, and the root-mean-square difference was 0.38-0.67 for Level 3 data.

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Seasonal Variability of Salinity and Salt Transport in the Northern Indian Ocean

Cited by 33 publications

References 48 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 Fresh and Salt Water Exchanges in the Indian Ocean

Statistical Assessment of Sea-Surface Salinity from SMAP: Arabian Sea, Bay of Bengal and a Promising Red Sea Application

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