Current Science

Open Access Open Access  Restricted Access Subscription Access

Role of Ocean Dynamics on Mesoscale and Sub-Mesoscale Variability of Ekman Pumping for the Bay of Bengal using SCATSAT-1 Forced Ocean Model Simulations


Affiliations
1 Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, India
 

Role of ocean dynamics on vertical velocity of Ekman pumping (VVE) is analysed using simulations from very high resolution Ocean General Circulation Model (OGCM) configured for the Bay of Bengal (BoB). For this purpose, OGCM is forced with SCATSAT-1 scatterometer wind fields for 2017. Three mechanisms which modify VVE in the ocean are addressed in this study; the first results from the influence of sea surface temperature (SST) on wind field, and the other two arise from the influence of ocean surface currents (OSCs) on the wind field. Analysis for different length scales ranging from mesoscale to sub-mesoscale is also carried out. The results suggest a significant role of ocean dynamics on VVE, especially over submesoscale range (spatial scales of the order of 2– 10 km). Relative vorticity of OSC-induced Ekman pumping is found to be quite high (~3 m/day) at 2 km length scale, especially along the periphery of mesoscale eddies and along the filament structures. Impact of SST on VVE is least amongst the three factors and is observed to be significant only up to the length scales of 30 km. For length scales less than 10 km, relative vorticity-induced Ekman pumping increases drastically and the total Ekman pumping vertical velocity is predominantly controlled by the relative vorticity of OSC-induced Ekman pumping only.

Keywords

Ekman Pumping, Ocean Dynamics, Scatterometers, Vertical Velocity, Wind Field.
User
Notifications
Font Size

  • Klein, P. and Lapeyre, G., The Oceanic vertical pump induced by mesoscale and submesoscale turbulence. Annu. Rev. Mar. Sci., 2009, 1, 351–375.

  • Brannigan, L., Intense submesoscale upwelling in anticyclonic eddies. Geophys. Res. Lett., 2016, 43, 3360–3369; doi:10.1002/2016GL067926.

  • Pickett, M. H. and Paduan, J. D., Ekman transport and pumping in the California current based on the US Navy’s high resolution atmospheric model (COAMPS). J. Geophys. Res., 2003, 108(C10), 3327; doi:10.1029/2003JC001902.

  • Thushara, V. and Vinayachandran, P. N., Formation of summer phytoplankton bloom in the northwestern Bay of Bengal in a coupled physical–ecosystem model. J. Geophys. Res. Oceans, 2016, 121, 8535–8550; doi:10.1002/2016JC011987.

  • Chelton, D. B., Schlax, M. G., Freilich, M. H. and Milliff, R. F., Satellite measurements reveal persistent small-scale features in ocean winds. Science, 2004, 303, 978–983.

  • Sharma, R., Agarwal, N., Chakraborty, A., Mallick, S., Buckley, J., Shesu V. and Tandon, A., Large-scale air–sea coupling processes in the Bay of Bengal using space-borne observations. Oceanography, 2016, 29(2), 192–201; http://dx.doi.org/10.5670/oceanog.2016.51.

  • Jensen, T. G. et al., Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere– ocean–wave model of the Bay of Bengal. Ocean Dyn., 2018, 68, 391; https://doi.org/10.1007/s10236-018-1136-x.

  • Wijesekera, H. W. et al., ASIRI: an ocean–atmosphere initiative for Bay of Bengal. Bull. Am. Meteorol. Soc., 2016, 97, 1859– 1884; https://doi.org/10.1175/BAMS-D-14- 00197.1.

  • Chelton, D. B. and Xie, S., Coupled ocean–atmosphere interaction at oceanic mesoscales. Oceanogaphy, 2010, 23, 52–69; doi:10.5670/oceanog.2010.05.

  • Gaube, P., Chelton, D. B., Samelson, R. M., Schlax, M. G. and O’Neill, L. W., Satellite observations of mesoscale eddy induced Ekman pumping. J. Phys. Oceanogr., 2016, 45(104), 131; doi:10.1175/JPO-D-14-0032.1.

  • McGillicuddy Jr, D. J., Mechanisms of physical–biological– biogeochemical interaction at oceanic mesoscale. Annu. Rev. Mar. Sci., 2016, 8, 125–159.

  • Ledwell, J. R., Watson, A. J. and Law, C. S., Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment. Nature, 1993, 364, 701–703.

  • McWilliams, J. C., Submesoscale currents in the ocean. Proc. R. Soc. A: Math. Phys. Eng. Sci., 2016, 472(2189), 20160117; http://dx.doi.org/10.1098/rspa.2016.0117.

  • Mahadevan, A. and Tandon, A., An analysis of mechanisms for submesoscale vertical motion at ocean fronts. Ocean Model., 2006, 14, 241–256.

  • Wei, Y., Zhang, R.-H. and Wang, H., Mesoscale wind stress–SST coupling in the Kuroshio extension and its effect on the ocean. J. Oceanogr., 2017, 73(6), 785–758; doi:10.1007/s10872-0170432-2.

  • O’Neill, L. W., Wind speed and stability effects on coupling between surface wind stress and SST observed from buoys and satellite. J. Climate, 2012, 25, 1544–1569; doi:10.1175/JCLI-D-11-00121.1.

  • Small, R. J. et al., Air–sea interaction over ocean fronts and eddies. Dyn. Atmosp. Oceans, 2008, 45, 274–319.

  • Seo, H., Miller, A. J. and Roads, J. O., The Scripps coupled Ocean–Atmosphere Regional (SCOAR) model, with applications in the eastern Pacific sector. J. Clim., 2007, 20, 381–402.

  • Okumura, Y., Xie, S.-P., Numaguti, A. and Tanimoto, Y., Tropical Atlantic air–sea interaction and its influence on the NAO. Geophys. Res. Lett., 2001, 28, 1507–1510.

  • Agarwal, N., Sharma, R., Basu, S. K., Sarkar, A. and Agarwal, V. K., Evaluation of relative performance of QuikSCAT and NCEP re-analysis winds through simulations by an OGCM. Deep Sea Res. Part I: Oceanogr. Res. Pap., 2007, 54(8), 1311–1328.

  • Deb, S. K., Bhowmick, S. A., Kumar, R. and Sarkar, A., Intercomparison of numerical model generated surface winds with QuikSCAT winds over the Indian Ocean. Mar. Geodesy, 2009, 32(4), 391–408.

  • Jaeger, G. S. and Mahadevan, A., Submesoscale selective compensation of fronts in a salinity-stratified ocean. Sci. Adv., 2018, 4(2); doi:10.1126/sciadv.1701504.

  • Adcroft, A., Hill, C., Campin, J. M., Marshall, J. and Heimbach, P., Overview of the formulation and numerics of the MIT GCM. In Proceedings of the ECMWF Seminar Series on Numerical Methods, 2004, pp. 139–149.

  • Sindhu, B., Suresh, I., Unnikrishnan, A. S., Bhatkar, N. V., Neetu, S. and Michael, G. S., Improved bathymetric datasets for the shallow water regions in the Indian Ocean. J. Earth Syst. Sci., 2007, 116(3), 261–274.

  • Mallick, S. K., Agarwal, N., Sharma, R. and Prasad, K. V. S. R., Sensitivity of upper ocean dynamics in high-resolution tropical Indian Ocean model to different flux parameterization: case study for the Bay of Bengal (BoB). Int. Arch. Photogramm. Remote Sensing Spatial Inf. Sci., 2018, 839–847; https://doi.org/10.5194/isprs-archives-XLII-5-839-20.

  • Dee, D. et al., The era-interim reanalysis: configuration and performance of the data assimilation system. Q. J. Roy. Meteorol.Soc., 2011, 137, 553–597; doi:10.1002/qj.828.

  • Papa, F., Durand, F., Rossow, W. B., Rahman, A. and Bala, S. K., Satellite altimeter‐derived monthly discharge of the Ganga– Brahmaputra River and its seasonal to interannual variations from 1993 to 2008. J. Geophys. Res.: Oceans, 2010, 115(C12); https://doi.org/10.1029/2009/C006075.

  • Yaremchuk, M., Yu, Z. and McCreary, J., River discharge into the Bay of Bengal in an inverse ocean model. Geophys. Res. Lett., 2005, 32(16); https://doi.org/10.1029/2005GL023750.

  • Mandal, S., Sil, S., Shee, A., Swain, D. and Pandey, P. C., Comparative analysis of SCATSAT-1 gridded winds with buoys, ASCAT and ECMWF winds in the Bay of Bengal. IEEE J. Selected Top. Appl. Earth Observ. Remote Sensing, 2018, 11(3), 845–851; doi:10.1109/JSTARS.2018.2798621.

  • Stern, M., Interaction of a uniform wind stress with a geostrophic vortex. Deep–Sea Res. Oceanogr. Abstr., 1965, 12, 355–367; doi:10.1016/0011-7471(65)90007-0.

  • Chelton, D., Schilax, M. G. and Samelson, R. M., Summertime coupling between sea surface temperature and wind stress in the California current system. J. Phys. Oceanogr., 2007, 495–517.

  • Wortham, C. and Wunsch, C., A multidimensional spectral description of ocean variability. J. Phys. Oceanogr., 2014, 44, 944– 966; doi:10.1175/JPO-D-13-0113.1.

  • Biri, S., Serra, N., Scharffenberg, M. G. and Stammer, D., Atlantic sea surface height and velocity spectra inferred from satellite altimetry and a hierarchy of numerical simulations. J. Geophys. Res., 2016, 121, 4157–4177; doi:10.1002/2015JC011503.

  • Seo, H., Murtugudde, R., Jochum, M. and Miller, A. J., Modeling of mesoscale coupled ocean–atmosphere interaction and its feedback to ocean in the western Arabian Sea. Ocean Model., 2008, 25, 120–131.


Abstract Views: 359

PDF Views: 125




  • Role of Ocean Dynamics on Mesoscale and Sub-Mesoscale Variability of Ekman Pumping for the Bay of Bengal using SCATSAT-1 Forced Ocean Model Simulations

Abstract Views: 359  |  PDF Views: 125

Authors

Smitha Ratheesh
Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, India
Aditya Chaudhary
Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, India
Neeraj Agarwal
Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, India
Rashmi Sharma
Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, India

Abstract


Role of ocean dynamics on vertical velocity of Ekman pumping (VVE) is analysed using simulations from very high resolution Ocean General Circulation Model (OGCM) configured for the Bay of Bengal (BoB). For this purpose, OGCM is forced with SCATSAT-1 scatterometer wind fields for 2017. Three mechanisms which modify VVE in the ocean are addressed in this study; the first results from the influence of sea surface temperature (SST) on wind field, and the other two arise from the influence of ocean surface currents (OSCs) on the wind field. Analysis for different length scales ranging from mesoscale to sub-mesoscale is also carried out. The results suggest a significant role of ocean dynamics on VVE, especially over submesoscale range (spatial scales of the order of 2– 10 km). Relative vorticity of OSC-induced Ekman pumping is found to be quite high (~3 m/day) at 2 km length scale, especially along the periphery of mesoscale eddies and along the filament structures. Impact of SST on VVE is least amongst the three factors and is observed to be significant only up to the length scales of 30 km. For length scales less than 10 km, relative vorticity-induced Ekman pumping increases drastically and the total Ekman pumping vertical velocity is predominantly controlled by the relative vorticity of OSC-induced Ekman pumping only.

Keywords


Ekman Pumping, Ocean Dynamics, Scatterometers, Vertical Velocity, Wind Field.

References





DOI: https://doi.org/10.18520/cs%2Fv117%2Fi6%2F993-1001