Monsoons to Mixing in the Bay of Bengal: Multiscale Air-Sea Interactions and Monsoon Predictability

Goswami, B. N.; Rao, Suryachandra A.; Sengupta, Debasis; Chakravorty, Soumi

doi:10.5670/oceanog.2016.35

Cited by 58 publications

(39 citation statements)

References 41 publications

(32 reference statements)

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“…This unique characteristic of the northern BoB results in high convective activity over this region which can further develop into LPS [ Goswami et al . ]. The CFSv2 CTL run simulates a cold SST bias in the northern BoB with magnitudes varying from −0.1 to −0.5 (Figure b), owing to the overestimation of southward meridional heat transport in the model (figure not shown).…”

Section: Resultsmentioning

confidence: 99%

“…Also, the northern BoB receives enormous freshwater discharge from various river basins making it one of the freshest area in the world ocean. The low salinity in this region implies a shallow mixed layer and hence can result in warm SST anomalies of the order of 1–2°C on intraseasonal time scales [ Goswami et al ., ; Sengupta and Ravichandran , ]. This unique setting might be important for LPS genesis.…”

Section: Introductionmentioning

confidence: 99%

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Structure, characteristics, and simulation of monsoon low‐pressure systems in CFSv2 coupled model

Srivastava

Rao

et al. 2017

JGR Oceans

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Indian Summer Monsoon (ISM) synoptic scale systems (low‐pressure systems, LPS) are known to produce increased rainfall over central India (CI). Fidelity of the Climate Forecast System version 2 (CFSv2) at simulating the LPS and their characteristics is evaluated in this study using a feature tracking algorithm. The model is able to reproduce the clustering of LPS by monsoon intraseasonal oscillations and the associated precipitation over eastern‐central India. It is found that mean biases in circulation and moisture stem from cold sea surface temperature (SST) bias in the model which results in weak LPS linked rainfall events over central India. Two sensitivity experiments were carried out to study the effect of coupled dynamics of tropical basins on LPS. Suppression of active dynamics of the tropical Indian Ocean in CFSv2 causes a reduction in cold SST bias and enhanced cyclogenesis in the northern Bay of Bengal. The reduced low‐level anticyclonic bias and enhanced moisture availability result in a better simulation of LPS structure, and associated precipitation over CI. Suppression of active ocean dynamics in tropical Pacific Ocean causes a perennial El‐Niño type bias which restricts LPS propagation over the Indian landmass, possibly due to time‐mean subsidence induced by remote El‐Niño forcing. Sensitivity experiments indicate the need for improvements in the representation of tropical Indian Ocean coupled dynamics as well as convective parameterization schemes in the model for subsequent improvements in the simulation of ISM at various time scales.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structure, characteristics, and simulation of monsoon low‐pressure systems in CFSv2 coupled model

Srivastava

Rao

et al. 2017

JGR Oceans

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“…Earlier studies have shown that the BoB is one of the regions in the Indo‐Pacific basin with high amplitude intraseasonal oscillations associated with the MISO (Fu & Wang, ). Hence, a better understanding about the processes that modulate the MLT balance and air‐sea interaction on MISO time scales in the BoB will enhance our knowledge on the amplification and northward propagation of MISO variability and its predictability (Goswami et al, ).…”

Section: Introductionmentioning

confidence: 99%

Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

et al. 2017

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Composite analyses of mixed layer temperature (MLT) budget terms from near‐surface meteorological and oceanic observations in the central Bay of Bengal are utilized to evaluate the modulation of air‐sea interactions and MLT processes in response to the summer monsoon intraseasonal oscillation (MISO). For this purpose, we use moored buoy data at 15°N, 12°N, and 8°N along 90°E together with TropFlux meteorological parameters and the Ocean Surface Current Analyses Real‐time (OSCAR) current product. Our analysis shows a strong cooling tendency in MLT with maximum amplitude in the central and northern BoB during the northward propagation of enhanced convective activity associated with the active phase of the MISO; conversely, warming occurs during the suppressed phase of the MISO. The surface mixed layer is generally heated during convectively inactive phases of the MISO primarily due to increased net surface heat flux into the ocean. During convectively active MISO phases, the surface mixed layer is cooled by the combined influence of net surface heat loss to the atmosphere and entrainment cooling at the base of mixed layer. The variability of net surface heat flux is primarily due to modulation of latent heat flux and shortwave radiation. Shortwave is mostly controlled by an enhancement or reduction of cloudiness during the active and inactive MISO phases and latent heat flux is mostly controlled by variations in air‐sea humidity difference.

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“…They found subsurface heat fluxes using a constant diffusivity between November and February of -23 ± 15 and -10 ± 4 W m -2 in two subsequent years. Most recently, as part of the Air-Sea Interactions Regional Initiative (ASIRI; Goswami et al, 2016, in this issue), investigations of air-sea interactions (Weller et al, 2016, in this issue) and mixed layer heat budgets (Thangaprakash et al, 2016, in this issue) were carried out. In all of these studies, subsurface fluxes were either estimated using mixing parameterizations or calculated as a residual.…”

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confidence: 99%

Monsoon Mixing Cycles in the Bay of Bengal: A Year-Long Subsurface Mixing Record

Warner¹,

Becherer²,

Pujiana³

et al. 2016

Oceanog

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salinity stratification and negative temperature gradients between the base of the mixed layer and the thermocline form periodically on both short and long time scales and large and small spatial scales (Thadathil et al., 2002(Thadathil et al., , 2007Girishkumar et al., 2011;Agarwal et al., 2012). Precipitation and riverine input are the main sources of freshwater in barrier layers, and processes such as wind, local currents (Thadathil et al., 2007), and westward-propagating Rossby waves (Girishkumar et al., 2011) can modify and dissipate barrier layers. Consequent reversing temperature gradients result in mixing upward of water that can both warm and cool the sea surface (de Boyer Montégut et al., 2007). The alternating sign of the turbulent heat flux in part distinguishes the role of subsurface fluxes to sea surface modification between alternating monsoon seasons. Because of the influence of the monsoons on local weather, particularly precipitation, accurate prediction of the monsoon is a priority for BoB rim countries. However, the South Asian monsoon is a particularly difficult phenomenon for climate models to predict accurately (Syed et al., 2014). Good estimates of surface fluxes are considered a necessity in predicting large-scale air-sea interactions that contribute to coupled systems such as the South Asian monsoons, but these values can be difficult to constrain (Schott et al., 2009). It is even more challenging to estimate subsurface fluxes and their contributions to surface properties using observations. BoB heat budgets have been computed in the past. For example, Loschnigg and Webster (2000) used a model that parameterized vertical mixing, showing that lateral transport and storage balance surface heat fluxes. Shenoi et al. (2002) used climatological temperatures and surface heat fluxes and assumed a constant diffusivity at the base of a 50 m deep mixed layer, and found diffusive fluxes ranging between -35 W m -2 and -60 W m -2 . Sengupta et al. (2002) used data collected from a mooring in the central BoB to estimate a springtime heat budget of the mixed layer. They estimated residual cooling due to vertical mixing and advection to be about -25 W m -2 .de Boyer Montégut et al. (2007) use a global ocean general circulation model to highlight the importance of barrier layers in the BoB that allow negative temperature gradients in regions of strong salinity stratification. Girishkumar et al. (2013) also highlight the importance of barrier layers in their calculation of a wintertime heat budget using mooring data. They found subsurface heat fluxes using a constant diffusivity between November and February of -23 ± 15 and -10 ± 4 W m -2 in two subsequent years. Most recently, as part of the Air-Sea Interactions Regional Initiative (ASIRI; Goswami et al., 2016, in this issue), investigations of air-sea interactions (Weller et al., 2016, in this issue) and mixed layer heat budgets (Thangaprakash et al., 2016, in this issue) were carried out. In all of these studies, subsurface fluxes were either estima...

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Monsoons to Mixing in the Bay of Bengal: Multiscale Air-Sea Interactions and Monsoon Predictability

Cited by 58 publications

References 41 publications

Structure, characteristics, and simulation of monsoon low‐pressure systems in CFSv2 coupled model

Structure, characteristics, and simulation of monsoon low‐pressure systems in CFSv2 coupled model

Mixed Layer Temperature Budget for the Northward Propagating Summer Monsoon Intraseasonal Oscillation (MISO) in the Central Bay of Bengal

Monsoon Mixing Cycles in the Bay of Bengal: A Year-Long Subsurface Mixing Record

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