Effect of Pacific warm and cold events on the sea ice behavior in the Indian sector of the Southern Ocean

The teleconnections between sea ice area (SIA) in the Indian Ocean Sector (IOS) of the Southern Ocean (20–90°E) and the El Niño Southern Oscillation (ENSO) for the period 1982–2009 are studied. The ENSO years are divided into La Niña, El Niño and El Niño Modoki years. The sea surface temperature anomalies averaged over the Niño 3.4 (SST3.4A) region (120–170°W, 5°N–5°S) are used as proxy for ENSO. A significantly stronger negative correlation between SST3.4A and SIA anomalies is found at a positive lag of 6–12 months in 50–80°E region than elsewhere in the IOS. Variations in sea level pressure anomalies over the Antarctic continent and the subpolar regions play an important role in shaping the surface wind. Variation in the surface wind along with the changes in sea surface temperature (SST), sea ice drift and surface air temperature (SAT) shape the sea ice cover over the region. Composites show that the winters following La Niña years are associated with more SIA compared to that of ENSO-neutral years. This is attributed to the increase in sea level pressure gradient between the Antarctic land mass and the subpolar region, which enhances the southerly wind and results in a reduction in SAT. Also, anomalous northward advection of sea ice increases the SIC over the outer margin of the sea ice cover. The in-phase relation among SAT, SST and sea ice advection results in an increase in SIA. Also, a weaker Regional Ferrel Cell (RFC) during this period results in the reduction of poleward heat transport and contributes to the increase in SIA. During the winters following El Niño years, interaction among anomalous easterlies, wind-induced sea ice motion, SAT anomalies and heat transport by the RFC increases (decreases) the SIA in the western (eastern) part of the high correlation region. During El Niño Modoki years, an increase in SST and presence of warmer surface air over the high correlation region reduce SIA during summer as well as the winter following it. The study also highlights the contrasting signals in SIA observed during El Niño and El Niño Modoki years. Our study found that, in general, the variation in SAT determines the sea ice condition over the Antarctic during austral winters. The variations in both SST and SAT play significant roles in modifying the SIA during El Niño and El Niño Modoki years. The study found that the ENSO induced variabilities of SIA in the IOS are mainly controlled by (1) the thermodynamics of the region (SAT and SST changes d