Australia: The Land Where Time Began

A biography of the Australian continent 

Wyrtki Jets - Impact of IOD & ENSO Wind-Forcing

In this paper the authors¹ report their study of the interannual variability of the Wyrtki Jets in the context of the Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) wind-forcing by use of a 3-D numerical ocean model and observations. The Wyrtki Jet is affected more significantly in the boreal autumn, October-November, than in the boreal spring (April-May) Wyrtki Jet as there is a tendency for the IOD and ENSO to peak at the end of the calendar year. The authors¹ used various statistical techniques as they attempted to separate out the impacts on the jets of the IOD and ENSO, with emphasis on the autumn jet. The first 2 modes of an Empirical Orthogonal Function (EOF) decomposition accounts for about 90 % and 85 % of variability in zonal currents and wind stress respectively along the Equator in the Indian Ocean, though EOF analysis does not separate out cleanly IOD and ENSO forcing and response. IOD and wind-forcing and zonal equatorial current response are on average stronger than for ENSO and extend further to the west  across the basin as revealed by partial correlation analysis. A complementary definition of the relative contributions of the these 2 phenomena on the variability of the Wyrtki jet is provided by composite analysis of IOD only, ENSO only, and combined IOD and ENSO years, and in general is consistent with the results of the partial correlation analysis.

Sources & Further reading

1. Gnanaseelan, C., Aditi Deshpande, and Michael J. McPhaden. "Impact of Indian Ocean Dipole and El Niño/Southern Oscillation Wind-Forcing on the Wyrtki Jets." Journal of Geophysical Research: Oceans 117, no. C8 (2012): C08005.