Investigating the role of air-sea forcing on the variability of hydrography, circulation, and mixed layer depth in the Arabian Sea and Bay of Bengal

Srivastava, Atul; Dwivedi, Suneet; Mishra, Alok Kumar

doi:10.1016/j.oceano.2017.10.001

Cited by 32 publications

(22 citation statements)

References 43 publications

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“…The energy required for mixing (ERM) is a measure of the potential energy of the upper water column, which is computed as (Srivastava et al, 2018)

italicERM = \frac{1}{8} ((), ρ_{h} - ρ_{0}) g h^{2},

where ρ 0 is the density of surface water and ρ h is the density of water at depth h . Thus, the ERM surface water to the base of the mixed layer is the difference between the potential energy of a stratified column at the base of the mixed layer and that of the same column when it is unstratified (or mixed vertically) (Shenoi et al, 2002).…”

Section: Methodsmentioning

confidence: 99%

“…The energy required for mixing (ERM) is a measure of the potential energy of the upper water column, which is computed as (Srivastava et al, 2018)…”

Section: Estimation Of the Energy Required For Mixingmentioning

confidence: 99%

“…The estimation of the ERM (Shenoi et al, 2002;Srivastava et al, 2018) surface water to specific depths provides a simple diagnosis for the energy balance in the composite anticyclonic eddy. The results show an increase in the ERM in the eddies in winter (Figure 13a).…”

Section: Dynamical Mechanismsmentioning

confidence: 99%

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Anticyclonic Eddies Enhance the Winter Barrier Layer and Surface Cooling in the Bay of Bengal

Zhan

Cai

2020

JGR Oceans

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Oceanic barrier layer impedes the vertical exchanges of heat and biogeochemical substances between the mixed layer and deep ocean, playing essential roles in modulating air-sea heat flux and oceanic biogeochemical cycles. Recent studies revealed that mesoscale eddies can modify the vertical motions of the mixed layer. But their influence on the barrier layer has not been determined. By analyzing more than a decade of in situ, satellite, and reanalysis data, this study investigated the influence of eddies on barrier layer in the Bay of Bengal. The results show that the barrier layer in anticyclonic eddies is significantly thickened in winter (by 50% on average). This thickening consists of the deepening of isothermal layer by eddy downwelling and the shoaling of mixed layer by near-surface salinity restratification. The thickening of the barrier layer enlarges with latitude, in consistent with the reinforcement in salinity stratification and surface cooling. The thickened barrier layer impedes the upward supply of heat into the mixed layer from the below, promoting the winter surface cooling (by 0.7°C on average) and subsurface temperature inversion (by 0.6°C on average). The feature is contrary to the intuitive expectation that anticyclonic eddies possess high sea surface temperature in eddy interiors. As a consequence, both cyclonic and anticyclonic eddies result in negative sea surface temperature anomalies, indicative of a net decrease in the local sea surface temperature. These effects of eddies may be a common feature in salinity-stratified oceans in winter and have potential implications for the local biogeochemistry and air-sea coupled models. Plain Language Summary Oceanic barrier layer impedes the vertical exchanges of heat and biogeochemical substances between the near-surface and deep ocean, playing essential roles in modulating sea surface temperature, air-sea heat flux, and oceanic biogeochemical cycles. Here, we investigated the influence of mesoscale eddies on the barrier layer in the Bay of Bengal. We show that in such salinity-stratified oceans, anticyclonic eddies significantly thicken the barrier layer in winter. This thickening consists of the deepening of isothermal layer and the shoaling of mixed layer. The thickened barrier layer impedes the upward supply of heat into the mixed layer and retains the heat in the barrier layer, promoting the winter surface cooling and subsurface temperature inversion. As a consequence, sea surface temperature is lower in the eddies compared to the ambient, contrasting to the intuitive expectation that anticyclonic eddies possess high temperature. In addition to the low sea surface temperature in cyclonic eddies, both types of the eddies lead to surface cooling, breaking the standard symmetry of cyclonic versus anticyclonic eddies, whose effects usually cancel each other out. These results may potentially have far-reaching implications from the local biogeochemistry to climate models which, due to their coarse, non-eddy-resolving resolution, are unable to capt...

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“…The energy required for mixing (ERM) is a measure of the potential energy of the upper water column, which is computed as (Srivastava et al, 2018)

italicERM = \frac{1}{8} ((), ρ_{h} - ρ_{0}) g h^{2},

Section: Methodsmentioning

confidence: 99%

“…The energy required for mixing (ERM) is a measure of the potential energy of the upper water column, which is computed as (Srivastava et al, 2018)…”

Section: Estimation Of the Energy Required For Mixingmentioning

confidence: 99%

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Anticyclonic Eddies Enhance the Winter Barrier Layer and Surface Cooling in the Bay of Bengal

Zhan

Cai

2020

JGR Oceans

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“…ROM simulated values closely agree with observations over the homogeneous rainfall zones. We notice that the root mean square error (RMSE) between the model and observation is relatively less than the observed rainfall standard deviation for all zone except SPI, thus demonstrating our simulation's quality as a lesser RMSE of the model than observed variability (standard deviation) is good skill score to measure the quality of the model (Srivastava et al, 2016(Srivastava et al, , 2018Dwivedi et al, 2018Dwivedi et al, , 2019Mishra et al, 2020a) Noticeably, the increasing resolution results in improving the model's performance over most of the study regions except SPI where performance is found to degrade with increasing resolution. The ISM undergoes enhanced and suppressed rainfall activity over India on an intraseasonal time scale (Goswami and Ajaya Mohan, 2001;Dwivedi et al, 2006;Shahi et al, 2018).…”

Section: Spatiotemporal Variability Of Ismrmentioning

confidence: 69%

“…It is interesting to note that the LS shows greater sensitivity to horizontal resolution in comparison to CS. The strength of the Indian monsoon is significantly affected by the sea surface temperature (SST) of the IO (Srivastava et al, 2018;Mishra et al, 2020a). Therefore, the comparative skill of the ROM in representing the IO SST is worth mentioning.…”

Section: Identification Of Source Of Bias In Seasonal Mean Precipitationmentioning

confidence: 99%

Impact of horizontal resolution on monsoon precipitation for CORDEX-South Asia: A regional earth system model assessment

Mishra

Kumar

Dubey

et al. 2021

Atmospheric Research

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For the first time for CORDEX-South Asia, a high-resolution regional earth system model (ROM) is adopted to assess the impact of horizontal resolution (0.22 • and 0.11 • ) in simulating the Indian summer monsoon rainfall (ISMR) and the underlying spatiotemporal variability. ROM at both resolutions bears a close resemblance to observations in simulating the mean precipitation climatology compared to other regional climate models (RCMs) participated in CORDEX-South Asia. ROM shows substantial improvement relative to the ensemble mean of the RCMs included in CORDEX-South Asia. While comparing both simulations with observations, some systematic wet and dry bias over Central India (CI) and Northern Western Ghats is noticed. In general, the wet/dry bias over India is mainly associated with the overestimation/underestimation of the large-scale/convective component. Increasing horizontal resolution from 0.22 • to 0.11 • significantly adds value in simulating the JJAS mean precipitation by reducing the wet bias over western central India (WCI) and southern peninsular India and dry bias over eastern CI. The reduction in wet/dry bias is mainly associated with suppression/enhancement of the large scale/convective precipitation. This improvement in mean precipitation is partially due to the improved representation of the propagation of mesoscale systems such as boreal summer intraseasonal oscillation (eastward and northward). Despite the above improvements, the wet precipitation bias, particularly over WCI, persists. The weaker Findlater Jet associated with weaker land-ocean thermal contrast caused by the warm sea surface temperature (SST) bias over the western Arabian Sea (AS) suggests that AS moisture transport does not contribute to the wet bias over India. The wet bias is possibly associated with favourable atmospheric conditions (atmospheric instability).

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Regional earth system model for CORDEX‐South Asia: A comparative assessment of RESM and ESM over the tropical Indian Ocean

Kumar

Mallick

Mishra

et al. 2022

Intl Journal of Climatology

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Understanding climate variability requires good quality high resolution spatially and temporally varying ocean fields due to its decisive role in regulating the region's climate, including the Indian summer monsoon. In this regard, we employed a new high-resolution regional earth system model (RESM), namely ROM over CORDEX South Asia. We demonstrated the performance of the RESM and its added value over the global earth system model, namely MPI-ESM, in simulating the hydrographic characteristics and associated mechanism over the tropical Indian Ocean (TIO). ROM shows better skill than MPI-ESM in simulating the near-surface and subsurface characteristics of the ocean. However, larger added values are noticed for subsurface (>350 m) thermal structure. MPI-ESM's cold sea surface temperature (SST) bias is reduced in ROM which is associated with weaker winds, anomalous cyclonic wind stress curl, enhanced stratifications, and a shallower mixed layer, resulting in greater upper-ocean heating. The reduced SST bias is also consistent with improved ocean meridional heat transport (OMHT) in ROM. For example, reduced southward export of OMHT over the Arabian Sea increases the surface warming by 4%, reducing the RMSE by 0.2-0.6 C and becoming closer to observation. The anomalous cyclonic wind stress curl, in turn, caused mixed layer stratifications in the western Indian Ocean. The advective heat transfer from the south-eastern Indian Ocean to the western Indian Ocean reduced oceanic cooling by vertical processes, overcame the cooling by the net loss of surface heat fluxes, and favoured the TIO's surface warming.

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Investigating the role of air-sea forcing on the variability of hydrography, circulation, and mixed layer depth in the Arabian Sea and Bay of Bengal

Cited by 32 publications

References 43 publications

Anticyclonic Eddies Enhance the Winter Barrier Layer and Surface Cooling in the Bay of Bengal

Anticyclonic Eddies Enhance the Winter Barrier Layer and Surface Cooling in the Bay of Bengal

Impact of horizontal resolution on monsoon precipitation for CORDEX-South Asia: A regional earth system model assessment

Regional earth system model for CORDEX‐South Asia: A comparative assessment of RESM and ESM over the tropical Indian Ocean

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