Annual and seasonal variability of net heat flux in the Northern Indian Ocean

ABSTRACT

We investigate the spatial and temporal variability of the net ocean–atmosphere heat flux (Q_net) over the Indian Ocean (north of 30 S) for the period 2005–2008, as estimated from remotely sensed observations. Net heat flux data are based on turbulent fluxes from the Institut Français pour la Recherche et l’Exploitation de la MER (IFREMER) and radiative fluxes, both shortwave (SW) and longwave (LW) as produced at the University of Maryland (UMD). Special attention is given to the Arabian Sea (AS) and the Bay of Bengal (BoB). The estimates are evaluated against the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA). Results are also compared to several widely used atmospheric re-analyses products such as the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis-Interim (ERA-I), the ERA5, the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2), and the Climate Forecast System Reanalysis (CFSR). It is demonstrated that satellite-based estimates of heat flux components are in better agreement with in-situ buoy observations than re-analysis-based products. As such, the satellite products can be instrumental in diagnosing model performance and utilized for addressing research issues related to atmospheric and oceanic dynamics in the Indian Monsoon. It was found that the mean Q_net is higher in the AS than in the BoB, yet the phase of their monthly time series is well correlated with ocean heat gain/loss extremes. We have also investigated the relationship between Q_net and Sea Surface Temperature (SST) (mixed layer temperature proxy) with respect to their consistency. It was found that over most of the open Indian Ocean, at least half of the seasonal SST magnitude is explained by the seasonal Q_net. Given the small ($\le 1$ month) delay between an annual maximum of the seasonal mixed layer heat content rate of change and the seasonal Q_net, it is concluded that Q_net data presented in this paper are generally consistent with independently observed SST.

Acknowledgements

The work benefited from support under the National Aeronautics and Space Administration (NASA) grant NNX13AC12G, the Energy and Water Cycle Study (NEWS) program and NASA grant NNX08AN40A from the Science Mission Directorate- Division of Earth Science to Princeton University under the MEaSUREs program. It also benefited from the ESA Ocean Heat Flux (OHF) project support (https://wwz.ifremer.fr/oceanheatflux/). Thanks are due to the NASA Goddard Earth Sciences Data and Information Services Center (https://ladsweb.modaps.eosdis.nasa.gov/search/) for the MODIS data, and to the various MODIS teams that produced data used in this study. We acknowledge the TAO Project Office of NOAA/Pacific Marine Environmental Laboratory (PMEL) for providing data from the RAMA buoys and the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) that were used in this study. A. Bentamy wishes to thank F. Paul, D. Croize-Fillon, J. F. Piolle, and IFREMER/CERSAT for data processing support and is grateful to ECMWF, EUMETSAT, CERSAT, JPL, ISRO, NOAA, NOCS, Meteo-France, NDBC, PMEL, and UK Met Office for providing numerical, satellite, and in-situ data. We thank the anonymous Reviewers for their very helpful comments and the Editor for his effort in the disposition of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors

Supplementary material

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Additional information

Funding

The work benefited from support under NASA grant NNX13AC12G, the Energy and Water Cycle Study (NEWS) program and NASA grant NNX08AN40A from the Science Mission Directorate- Division of Earth Science; NASA [NNX08AN40A, NNX13AC12G]. We wish to acknowledge the European Space Agency (ESA) for supporting the Ocean Heat Flux project (https://wwz.ifremer.fr/oceanheatflux/).