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Ocean Science An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/os-2017-67
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Sep 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Ocean Science (OS).
Importance of vertical mixing and barrier layer variation on seasonal mixed layer heat balance in the Bay of Bengal
Ullala Pathiranage Gayan Pathirana1,2, Gengxin Chen1, Tilak Priyadarshana2, and Dongxiao Wang1 1State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China
2Faculty of Fisheries and Marine Sciences & Technology, University of Ruhuna, Matara, Sri Lanka
Abstract. Time series measurements from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15° N, 90° E; 12° N, 90° E; 8° N, 90° E; 4° N, 90° E; 1.5° N, 90° E; 0° N, 90° E are used to investigate the seasonal mixed-layer heat balance and the importance of barrier layer thickness (BLT) and vertical mixing (Qh) in the Bay of Bengal (BoB). It is found that the BLT, Qh and mixed-layer heat balance all have a strong seasonality in the central BoB. Sea surface temperature (SST), salinity and wind are important for the observed strongest seasonal cycle of BLT in the central BoB, and wind is more important than the SST in the southern BoB. The heat storage rate (HSR) is primarily driven by latent heat flux and shortwave radiation (QSW and QL). Seasonal variations and the magnitudes of longwave radiation (QLW), sensible heat flux (QS), and horizontal mixed-layer heat advection are much weaker compared to those of QSW and QL. Qh follows a pronounced seasonal cycle in the central BoB and is significantly positively correlated with the seasonal cycle of BLT at each mooring location. The seasonal variability of the stability favors the Qh during winter and summer monsoon and suppress Qh during monsoon transition periods. We found that Qh plays the secondary role in the seasonal mixed-layer heat balance in the BoB. It is evident from the analysis that Qh associated with temperature inversion (∆T) warms the mixed layer during winter and cools the mixed layer during summer. The warming tendency during winter is strong in the central BoB and weakens towards the equator, indicating a cooling tendency around the year. Our analysis further indicates the weakening of Qh during monsoon transition periods favors the existence of warmer SST in the BoB, associated with thermal and salinity stratification in the central BoB.

Citation: Gayan Pathirana, U. P., Chen, G., Priyadarshana, T., and Wang, D.: Importance of vertical mixing and barrier layer variation on seasonal mixed layer heat balance in the Bay of Bengal, Ocean Sci. Discuss., https://doi.org/10.5194/os-2017-67, in review, 2017.
Ullala Pathiranage Gayan Pathirana et al.
Ullala Pathiranage Gayan Pathirana et al.
Ullala Pathiranage Gayan Pathirana et al.

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Short summary
Seasonal changes of the mixed layer heat storage in the BoB significantly contribute to the regional weather and climate by inducing air-sea interactions. Seasonality associated with vertical mixing and barrier layer indicates the seasonal response from the ocean in the BoB. This study will provide a significant contribution to further studies on air-sea interactions in the BoB, especially the role of vertical mixing and barrier layer variation during cyclone formation and intensification.
Seasonal changes of the mixed layer heat storage in the BoB significantly contribute to the...
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