Cyclone‐induced mixing does not cool SST in the post‐monsoon north Bay of Bengal

Sengupta, Debasis; Goddalehundi, Bharath Raj; Anitha, D. S.

doi:10.1002/asl.162

Cited by 146 publications

(134 citation statements)

References 25 publications

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“…Past studies have suggested a potential role of BLs in TC-induced SST cooling (19) and TC intensification (20)(21)(22). However, the impact of BLs on TC intensification has not been definitively demonstrated or quantified.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Ocean barrier layers’ effect on tropical cyclone intensification

Balaguru

Chang

Saravanan

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

246

221

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Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are "quasi-permanent" features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Ocean barrier layers’ effect on tropical cyclone intensification

Balaguru

Chang

Saravanan

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

246

221

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“…Water advected by these currents was associated with fresher surface waters (Figure 2e), the development of a barrier layer (Thadathil et al, 2007), and a change in sign of T z . 2006-2008 , respectively (Girishkumar et al, 2013. Strong atmospheric heating during the transition (Figure 2c) was the principal reason for greatly increased nearsurface stratification and the nearly complete isolation of the ocean at 15 m depth from weak surface forcing.…”

Section: Monsoon Mixing Cyclesmentioning

confidence: 99%

“…This warming comes from the fact that the pre-storm temperature structure was negatively stratified, supported by stable salinity stratification. This is not uncommon; subsurface mixing during post-SW monsoon cyclones in the northern BoB have been observed to contribute to SST warming due to the presence of a barrier layer (Sengupta et al, 2008;Neetu et al, 2012). Once mixing eroded through the subsurface warm layer, cooling by turbulent mixing dominated atmospheric cooling during the subsequent 30 hours: J q t = -390 W m -2 compared to J q 0 = -176 W m -2 .…”

Section: Tropical Storm Hudhudmentioning

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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“…easterly waves and tropical wave activity, including Rossby-gravity waves, equatorial Rossby waves, Madden Julian Oscillation (MJO) play an important role in the TC formations (Bessafi and Wheeler 2006;Frank and Roundy 2006). The favorable hydrographic conditions such as formation of stably stratified thick barrier layer in & Yashvant Das yashvantdas@rediffmail.com 1 the upper ocean that acts as barrier to vertical mixing and entrainment cooling induced by TC's leading to an increase in heat fluxes from the ocean into the atmosphere play a dominant role for the enhanced TC activity over BoB during post monsoon seasons (Sprintall and Tomczak 1992;Sengupta et al 2008;Balaguru et al 2012). TC activity in BoB is strongly modulated by the tropical intraseasonal oscillation (ISO) (Yanase et al 2010(Yanase et al , 2012.…”

Section: Introductionmentioning

confidence: 99%

Development of tropical cyclone wind field for simulation of storm surge/sea surface height using numerical ocean model

Das

Mohanty

Indu

2015

Model. Earth Syst. Environ.

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Coupled ocean-atmospheric phenomenon such as tropical cyclones (TC's) is governed by geophysical fluid dynamics. TC associated strong wind stress transfer momentum energy to the ocean surface that acts as the prime mechanism in modulating the sea surface and in generating the storm surge. A primitive equation, Princeton ocean model (POM) with free surface, sigma (terrain-following) coordinates and realistic bottom topography is configured in Bay of Bengal (BoB) to simulate the storm surge/sea surface height (SSH) and surface currents during a super cyclone TC05B 1999. TC wind fields are developed by adopting a suitable formulation based on partial conservation of angular momentum. Modeled TC wind fields are superimposed with QuikSCAT Satellite/National Centre for Environmental Prediction (QSCAT/NCEP) blended ocean surface winds to drive the three-dimensional ocean model. Model simulated storm surge and SSH are compared with limited available surge estimates/observations and multi-satellite observed AVISO (Archive, Validation and Interpolation of Satellite Oceanography) SSH, respectively to evaluate its performance.

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Cyclone‐induced mixing does not cool SST in the post‐monsoon north Bay of Bengal

Cited by 146 publications

References 25 publications

Ocean barrier layers’ effect on tropical cyclone intensification

Ocean barrier layers’ effect on tropical cyclone intensification

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

Development of tropical cyclone wind field for simulation of storm surge/sea surface height using numerical ocean model

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