Coupled feedback between the Tropical and Subtropical Indian Ocean Dipoles
Anila Sebastian*, Dr. C Gnanaseelan
Indian Institute of Tropical Meteorology, MOES, Pune
Short Term Climate Variability and Prediction, IITM Pune, Maharastra, India Pincode: 411008 Mobile: 9400473715 E-mail: firstname.lastname@example.org
The feedback between the tropical Indian Ocean dipole (IOD) and subtropical Indian Ocean dipole (SIOD) in the interannual time scale is investigated. The positive SIOD, which peaks during January-February-March (JFM) leads to the generation or amplification of a positive IOD, which peaks during the September-October-November (SON) months and in turn the positive IOD triggers a negative SIOD in the following months. The SIOD can be generated either by the influence of the tropical Indian Ocean (IO) or Southern IO high-latitudes or the tropical Pacific Ocean. The anticyclonic circulation in the surface winds associated with positive SIOD over the subtropical IO leads to the development of positive tropical IOD. An anticyclonic circulation generated over the eastern tropical IO due to the eastern pole of positive tropical IOD during SON induces Rossby wave response in the subtropical south IO and which generates a cyclonic circulation in the subtropical region. This cyclonic circulation gives rise to the development of a negative SIOD in the following months and which peaks during JFM. These feedback and triggering mechanisms can be independent of ENSO forcing and it explains the formation of SIOD and IOD during the non-ENSO years. It is important that this feedback between SIOD and IOD has strengthened in recent years.