Ekman dynamics variability along the southern coast of Java revealed by satellite data

ABSTRACT

It has been widely known that the coastal upwelling along the southern coast of Java is generated by southeasterly wind which induces offshore Ekman Mass Transport (EMT) during southeast monsoon. However, the variability of EMT has not been fully described in previous studies. The present study investigated the variability of Ekman dynamics which consist of EMT and Ekman Pumping Velocity (EPV) along the southern coast of Java, based on remotely sensed data. We demonstrated the incongruity between the distribution of southeasterly wind speed and sea surface temperature (SST) during southeast monsoon which is related to the distribution of Ekman dynamics. Offshore EMT at the western region of the southern coast of Java is stronger than offshore EMT at the eastern region. However, stronger offshore EMT at the western part is inhibited by downwelling EPV while weaker offshore EMT at the eastern part is accelerated by upwelling EPV. Consequently, SSTs at the eastern parts are lower than those at the western parts. Thus, the changes of offshore EMT intensity from eastern to western parts are balanced by their EPV distributions which explain the incongruity between the distribution of wind speed and SST during southeast monsoon. On an interannual timescale, the combination of La Niña and negative Indian Ocean Dipole (IOD) events tends to weaken offshore EMT and EPV which reduce the intensity of Chl-a bloom and SST cooling during southeast monsoon season. Furthermore, ENSO has a less significant impact on the Ekman dynamics variability than IOD.

Acknowledgements

MODIS SST and Chl-a data are obtained from PO.DAAC Drive. The description about PO.DAAC Drive can be seen at https://podaac.jpl.nasa.gov/dataaccess. ASCAT data and Ocean reanalysis data can be downloaded at http://marine.copernicus.eu/services-portfolio/access-to-products/. Argo floats data were collected and made freely available by the International Argo Program and the national programs that contribute to it. (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System. This research is partially funded by non-APBN DPA LPPM 2019, Universitas Diponegoro Contract No: 329-121/UN7.P4.3/PP/2019 and the Indonesian Ministry of Research, Technology and Higher Education under WCU Program managed by Institut Teknologi Bandung. Anindya Wirasatriya thanks to World Class Professor program managed by Indonesian Ministry of Research, Technology and Higher Education, contract number : T/49/D2.3/KK.04.05/2019. He also thanks to Firman Ramadhan from Department of Oceanography, Diponegoro University for assisting Argo float data processing. R. Dwi Susanto is supported by the US National Aeronautics and Space Administration (NASA) through University of Maryland grants # 80NSSC18K0777 and NNX14AI81G. Riza Setiawan acknowledged a research support of PDUPT (2633/UN1.DITLIT/DIT-LIT/LT/2019).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Indonesian Ministry of Research, Technology and Higher Education under WCU Program managed by Institut Teknologi Bandung [1534/C5/KB.07.02/2019]; the US National Aeronautics and Space Administration [80NSSC18K0777, NNX14AI81G]; non-APBN DPA LPPM 2019, Universitas Diponegoro [329-121/UN7.P4.3/PP/2019]; the Indonesian Ministry of Research, Technology and Higher Education under World Class Professor Program [T/49/D2.43/KK.04.05/2019]; the Indonesian Ministry of Research, Technology and Higher Education under PDUPT scheme [2633/UN1.DITLIT/DIT-LIT/LT/2019].