Association of the sea-ice in southern Indian Ocean with ENSO

S.S Dugam

doi:10.17485/ijst/2008/v1i4.7

Abstract

In this paper the wavelet analysis of monthly mean satellite-derived Sea-Ice Extent (SIE) anomalies in the southern Indian Ocean and in the Antarctica region have been carried out for 22 years (1979-2000) of data. The study reveals that prior to major El Nino events, 2 to 4 and 6 to 8 modes in the SIE anomalies during winter (December-January- February) and spring (MarchApril-May) seasons are quite dominant and significant in both regions (southern Indian Ocean and Antarctica). The lag lead relationship between SIE and sea surface temperature (SST) anomalies over different Nino regions are also investigated and it is observed that winter time SIE anomaly in southern Indian Ocean shows a significant relationship with the succeeding year SST anomalies in Nino4 and Nino3.4 regions. The analysis of the zonal flow at 850hPa level (i.e. U anomaly field) over the three regions: east, west and central equatorial Pacific Ocean are also investigated. The study reveals that there is a strong inverse relationship between the SIE in southern Indian Ocean and U anomaly over west and central equatorial Pacific Ocean during winter and spring seasons. Key words: Indian Ocean sea ice, Antarctic sea ice, ENSO

Highlights

For many decades the role of sea-ice in climate variability have been the subject of considerable speculation since the radiation balance and the ocean atmosphere heat transfer change significantly from ice free to ice covered regions of the ocean
Chiu (1983) used early and spare data to show that relationship existed between the SOI and Antarctic sea ice, changes in the sea ice leading those in the SOI (Consistent with Walker, 1923 Premise)
Peng and wang (1989) use a model to suggest that the observed correlation between the Antarctic sea ice area extent and strength of the northwest Pacific subtropical high is due to a large scale teleconnection where by an anomalously large sea ice area and extent leads to colder westerlies and underlying ocean currents, leading to a sequence of colder current progressively equator ward and the walker circulation is strengthened and the Hadley circulation is weekend, leading to a weaker Northwest pacific high

Summary

The cross correlation analysis of the SIE anomalies with the Southern

Oscillation Index (SOI), on the seasonal scale, is carried out (Fig.[4]). It reveals that the winter and spring SIE anomaly over southern Indian Ocean shows a positive association with winter and spring SOI (significant 5% level). The effect of SIE anomaly of the southern Indian Ocean with the circulation feature over the different regions of equatorial Pacific viz. East, Antarctica region, it is seen that almost all the El Nino events are followed after the significant modes in SIE of the previous year It suggests that previous year SIE anomaly have some association with the occurrence of El Nino event. In order to see the relationship of SIE anomaly with the SST field over different regions (viz. Nino 1+2, Nino 3, Nino 4, and Nino3.4), the lag lead correlation analysis have been carried out on seasonal scale. For this we consider the four seasons as mentioned above.

Following conclusions are drawn

Seasons of Nino regions

Findings

Seasonal SOI