Seasonality and Buoyancy Suppression of Turbulence in the Bay of Bengal

Thakur, Ritabrata; Govindarajan, Rama; Farrar, J. Thomas; Weller, Robert A.; Moum, James N.

doi:10.1029/2018gl081577

Cited by 20 publications

(19 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Within the north-central Bay of Bengal, substantial freshwater from precipitation and rivers creates a shallow low-salinity layer and sharp pycnocline, which modifies the upper ocean's response to atmospheric forcing (Jaeger and Mahadevan 2018;Thakur et al 2019;Chaudhuri et al 2019) and allows for development of subsurface warm layers and heat storage (e.g., Sengupta et al 2008;Thadathil et al 2016;Shroyer et al 2016;Lucas et al 2016). Coupled models tend to show biases in ocean mixed layer depth and SST in this region (Goswami et al 2016, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Tandon

Sengupta

Fernando

et al. 2021

Bulletin of the American Meteorological Society

Self Cite

View full text Add to dashboard Cite

In the Bay of Bengal, the warm, dry boreal spring concludes with the onset of the summer monsoon and accompanying southwesterly winds, heavy rains, and variable air-sea fluxes. Here, we summarize the 2018 monsoon onset using observations collected through the multinational Monsoon Intraseasonal Oscillations in the Bay of Bengal (MISO-BoB) program between the US, India, and Sri Lanka. MISO-BoB aims to improve understanding of monsoon intraseasonal variability, and the 2018 field effort captured the coupled air-sea response during a transition from active-to-break conditions in the central BoB. The active phase of the ~20-day research cruise was characterized by warm sea surface temperature (SST > 30°C), cold atmospheric outflows with intermittent heavy rainfall, and increasing winds (from 2 to 15 m s−1). Accumulated rainfall exceeded 200 mm with 90% of precipitation occurring during the first week. The following break period was both dry and clear, with persistent 10−12 m s−1 wind and evaporation of 0.2 mm h−1. The evolving environmental state included a deepening ocean mixed layer (from ~20 to 50 m), cooling SST (by ~ 1°C), and warming/drying of the lower to mid-troposphere. Local atmospheric development was consistent with phasing of the large-scale intraseasonal oscillation. The upper ocean stores significant heat in the BoB, enough to maintain SST above 29°C despite cooling by surface fluxes and ocean mixing. Comparison with reanalysis indicates biases in air-sea fluxes, which may be related to overly cool prescribed SST. Resolution of such biases offers a path toward improved forecasting of transition periods in the monsoon.

show abstract

Section: Introductionmentioning

confidence: 99%

Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Tandon

Sengupta

Fernando

et al. 2021

Bulletin of the American Meteorological Society

Self Cite

View full text Add to dashboard Cite

show abstract

“…This discrepancy may arise from using the seasonal median of K T instead of time‐varying K T to estimate vertical diffusive heat flux. As demonstrated by W16 and Thakur et al (2019) K T has significant subseasonal variations in response to surface forcing and stratification. Nevertheless, the above analysis highlights the importance of accurately representing diffusive heat fluxes at the base on ML to determine the seasonal evolution of SST.…”

Section: Resultsmentioning

confidence: 76%

Estimation of Vertical Heat Diffusivity at the Base of the Mixed Layer in the Bay of Bengal

et al. 2020

View full text Add to dashboard Cite

One approach to estimating vertical heat diffusivity (K T) is to compute it from the residual of the mixed layer (ML) heat budget. Based on this approach, we use moored buoy data at 15°N, 12°N, and 8°N along 90°E over the period of 2007-2018 to estimate the seasonal average of K T at the base of the mixed layer in the Bay of Bengal (BoB). We find that K T is lower during spring and higher during winter compared to summer and fall at the mooring locations. Moreover, K T is generally higher in the southern BoB compared to the northern BoB. The present study also shows that the seasonal and spatial variability of K T is modulated both by stratification at the base of ML and by seasonal and spatial heterogeneity in atmospheric forcing, most notably wind stress and buoyancy flux. The availability of information on the spatial and seasonal variability of K T in the BoB will facilitate evaluation and validation of turbulent mixing parameterization schemes incorporated into ocean models.

show abstract

“…The seasonality of turbulent mixing in the upper ocean, both in coastal and open-ocean regions, remains poorly assessed due to the limited number of microstructure observations spanning entire annual cycles, such that the limited present knowledge derived mostly from indirect methods (Whalen et al, 2012;Warner et al, 2016;Inoue et al, 2017;Evans et al, 2018;Thakur et al, 2019;Cherian et al, 2020). Previous studies carried out in this region provided information about the variability of turbulent diffusivity on short-time scales during specific seasons (Barton et al, 2016;Villamaña et al, 2017;Fernández-Castro et al, 2018;Broullón et al, 2020) or along seasonal scales with coarser temporal resolution (Cermeño et al, 2016;Moreira-Coello et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Mixing and Phytoplankton Growth in an Upwelling System

et al. 2021

View full text Add to dashboard Cite

Previous studies focused on understanding the role of physical drivers on phytoplankton bloom formation mainly used indirect estimates of turbulent mixing. Here we use weekly observations of microstructure turbulence, dissolved inorganic nutrients, chlorophyll a concentration and primary production carried out in the Ría de Vigo (NW Iberian upwelling system) between March 2017 and May 2018 to investigate the relationship between turbulent mixing and phytoplankton growth at different temporal scales. In order to interpret our results, we used the theoretical framework described by the Critical Turbulent Hypothesis (CTH). According to this conceptual model if turbulence is low enough, the depth of the layer where mixing is active can be shallower than the mixed-layer depth, and phytoplankton may receive enough light to bloom. Our results showed that the coupling between turbulent mixing and phytoplankton growth in this system occurs at seasonal, but also at shorter time scales. In agreement with the CTH, higher phytoplankton growth rates were observed when mixing was low during spring-summer transitional and upwelling periods, whereas low values were described during periods of high mixing (fall-winter transitional and downwelling). However, low mixing conditions were not enough to ensure phytoplankton growth, as low phytoplankton growth was also found under these circumstances. Wavelet spectral analysis revealed that turbulent mixing and phytoplankton growth were also related at shorter time scales. The higher coherence between both variables was found in spring-summer at the ~16–30 d period and in fall-winter at the ~16–90 d period. These results suggest that mixing could act as a control factor on phytoplankton growth over the seasonal cycle, and could be also involved in the formation of occasional short-lived phytoplankton blooms.

show abstract

Seasonality and Buoyancy Suppression of Turbulence in the Bay of Bengal

Cited by 20 publications

References 46 publications

Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Estimation of Vertical Heat Diffusivity at the Base of the Mixed Layer in the Bay of Bengal

Mixing and Phytoplankton Growth in an Upwelling System

Contact Info

Product

Resources

About