Research on the interannual variability of the great whirl and the related mechanisms
Based on AVISO (archiving, validation and interpretation of satellite data in oceanography) data from 1993 to 2010, QuikSCAT (Quick Scatterometer) data from 2000 to 2008, and Argo data from 2003 to 2008, the interannual variability of the Great Whirl (GW) and related mechanisms are studied. It shows that the origin and termination times of the GW, as well as its location and intensity, have significant interannual variability. The GW appeared earliest (latest) in 2004 (2008) and vanished earliest (latest) in 2006 (2001), with the shortest (longest) duration in 2008 (2001). Its center was most southward (northward) in 2007 (1995), while the minimum (maximum) amplitude and area occurred in 2003 and 2002 (1997 and 2007), respectively. The GW was weaker and disappeared earlier with its location tending to be in the southwest in 2003, while in 2005 it was stronger, vanished later and tended to be in northeast. The abnormal years were often not the same among different characters of the GW, and were not all coincident with ENSO (El Niño-Southern Oscillation) or IOD (Indian Ocean Dipole) events, indicating the very complex nature of GW variations. Mechanism investigations shows that the interannual variability of intraseasonal wind stress curl in GW region results in that of the GW. The generation of the GW is coincident with the arrival of Rossby waves at the Somali coast in spring; the intensity of the GW is also influenced by Rossby waves. The termination of the GW corresponds well to the second one of the top two peaks in the baroclinic energy conversion rate in GW region, and the intensity and the position of the GW are also closely related to the top two baroclinic energy conversion rates.
Key wordsthe Great Whirl interannual variability wind stress Rossby wave baroclinic instability
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