Processes of 30–90 days sea surface temperature variability in the northern Indian Ocean during boreal summer

• Published in: Climate dynamics Vol. 38; no. 9-10; pp. 1901 - 1916
• Main Authors: Vialard, J., Jayakumar, A., Gnanaseelan, C., Lengaigne, M., Sengupta, D., Goswami, B. N.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.05.2012; Springer; Springer Nature B.V; Springer Verlag
• Subjects: Atmospheric circulation; Climate change; Climatology; Climatology. Bioclimatology. Climate change; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Environmental aspects; Environmental Sciences; Exact sciences and technology; External geophysics; Fluctuations; Geophysics; Geophysics/Geodesy; Global Changes; Latent heat; Marine; Meteorology; Monsoons; Ocean temperature; Ocean-atmosphere interaction; Oceanic eddies; Oceanography; Physics; Physics of the oceans; Sciences of the Universe; Sea surface temperature; Sea-air exchange processes; Summer; Surface water; Upwelling; Variability; Wind; Indian Ocean; Bay of Bengal; Arabian Sea; India; ISW, Indian Ocean; ISW, Arabian Sea; ISW, Oman; ISW, Bangladesh, Bengal Bay; Monsoon active and break phases; Heat budget; Northern Indian Ocean; Intraseasonal variability; Air–sea interactions; General circulation models; Intraseasonal variation; sensitivity analysis; heat balance; Observation data; Summer; digital simulation; Sea surface temperature; ocean-atmosphere interaction; monsoons; Ocean model; Air-sea interactions
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-011-1015-3

During summer, the northern Indian Ocean exhibits significant atmospheric intraseasonal variability associated with active and break phases of the monsoon in the 30–90 days band. In this paper, we investigate mechanisms of the Sea Surface Temperature (SST) signature of this atmospheric variability, using a combination of observational datasets and Ocean General Circulation Model sensitivity experiments. In addition to the previously-reported intraseasonal SST signature in the Bay of Bengal, observations show clear SST signals in the Arabian Sea related to the active/break cycle of the monsoon. As the atmospheric intraseasonal oscillation moves northward, SST variations appear first at the southern tip of India (day 0), then in the Somali upwelling region (day 10), northern Bay of Bengal (day 19) and finally in the Oman upwelling region (day 23). The Bay of Bengal and Oman signals are most clearly associated with the monsoon active/break index, whereas the relationship with signals near Somali upwelling and the southern tip of India is weaker. In agreement with previous studies, we find that heat flux variations drive most of the intraseasonal SST variability in the Bay of Bengal, both in our model (regression coefficient, 0.9, against ~0.25 for wind stress) and in observations (0.8 regression coefficient); ~60% of the heat flux variation is due do shortwave radiation and ~40% due to latent heat flux. On the other hand, both observations and model results indicate a prominent role of dynamical oceanic processes in the Arabian Sea. Wind-stress variations force about 70–100% of SST intraseasonal variations in the Arabian Sea, through modulation of oceanic processes (entrainment, mixing, Ekman pumping, lateral advection). Our ~100 km resolution model suggests that internal oceanic variability (i.e. eddies) contributes substantially to intraseasonal variability at small-scale in the Somali upwelling region, but does not contribute to large-scale intraseasonal SST variability due to its small spatial scale and random phase relation to the active-break monsoon cycle. The effect of oceanic eddies; however, remains to be explored at a higher spatial resolution.