Relationship between large-scale atmospheric circulation and interannual variability of extreme events of sea ice in the Antarctic Dipole

Abstract

The Antarctic sea ice plays an important role in the global climate system due to its high albedo, low thermal conductivity, influence on the position of the storrn tracks, forrning water masses and air masses. Some studies suggest that the Pacific-South America (PSA), pattem more directly related to the variability of the EI Nino Southem Oscillation (ENSO), has a greater influence on the sea ice in the interannual timescale on the region of the Antarctic Dipole (ADP), located in the central/eastem Pacific and South Atlantic. Thus, the objective of this study was to analyze the influence of large-scale atmospheric circulation on the interannual variability of extreme events of sea ice in the ADP region. We used the ERAInterim reanalysis (ECMWF Data Server) and the sea ice extent from the National Snow and Ice Data Center (University of Colorado) for the sectors of the Bellingshausen-Arnundsen Seas (BAS, 130° W to 60° W) and Weddell Sea (WS, 60° W to 20° E). The time series (1989- 2007) were filtered on interannual timescale (> 370 days). For the austral winter the extremes were defined using the first (q25) and third (q75) quartile ofthe distribution ofinterannual sea ice anomalies. Below the q25 were considered extremes negative of sea ice (ENSI) and above the q75 extremes positive (EPSI). Lastly composites were lagged in time for the interannual anomalies of atmospheric fields, considering 365 days prior and subsequent to ENSIIEPSI. Statistical significance was obtained with the Student's t test, at 10%. The positive anomalies of air temperature at 2 meters over the equatorial Pacific are associated with positive anomalies of SLP/geopotential at 500 hPa (GE0500) on the BAS/southeast of the South Pacific, which are part of the wave train between middle and high latitudes of the Southem Hemisphere, similar to the PSA pattem. Thus, there is an intensification of the northerly winds at low levels on the BAS, contributing to the heating/ENSI. Simultaneously, there is a weakening of northerly winds over the region of WS, leading to negative enomalies of air temperature/EPSI. This configuration is observed since the lag = 365 days. On the other hand, when there is cooling in the region of the equatorial Pacific, anomalies of SLP/GE0500 on the BAS/southeastem South Pacific are negative. Therefore, there is a weakening of the northerly winds and thus negative anomalies of air temperature/EPSI. At the sarne time, on the WS there is an intensification of the northerly winds, contributing to the positive anomalies of air temperaturelENSI. As the ENSO signal persists for about two seasons, changes in sea ice are amplified and persistent even after two to four seasons ofENSO. Thus, ENSI (EPSI) in BAS and EPSI (ENSI) in WS are associated with the wave train similar to the PSA pattem during warm (cold) ENSO. These results are in agreement with previous studies.