Abstract
AbstractThe Arctic winter seasonal sea ice (WSSI) concentration from 1979 to 2019 is derived from passive microwave data. Based on Empirical Orthogonal Function (EOF) analysis, the WSSI time series includes regionally different trends, abrupt shifts and interannual variations. The time series of the first EOF mode (PC1) mainly represents the WSSI trend, which is characterized by an increase, particularly in the Pacific sector. PC1 confirms two abrupt shifts in WSSI in 1989 and 2007, with a variance of 31%. After 2007, the large-scale atmospheric circulation anomaly shows a strengthened wavenumber 3 structure at high latitudes associated with a mid-tropospheric low-pressure anomaly in central and western Siberia and a high-pressure anomaly in eastern Siberia in summer and autumn. These patterns have promoted the increased transport of moist static energy to the central Arctic and contributed to increased near-surface air temperatures that may enhance ice melting in summer and reduce ice growth in autumn and winter. The changes in ice melt and growth have had opposite effects in the Pacific and Atlantic sectors: WSSI has increased in the Pacific sector due to the replacement of multi-year ice by WSSI, and decreased in the Atlantic sector due to the replacement of WSSI by open water.
Highlights
Sea ice plays a key role in the climate system through its substantial impact on energy budgets and atmospheric and oceanic circulations (Guemas and others, 2016)
The winter seasonal sea ice (WSSI) extent and total September sea-ice extent trends are determined to assess how WSSI increases as the sea ice decreases in the Arctic
The decrease in the total sea-ice extent in September by 0.05 million square kilometers per year is accompanied by an increase in the WSSI extent by 0.02 million square kilometers per year in the wintertime (Fig. 2)
Summary
Sea ice plays a key role in the climate system through its substantial impact on energy budgets and atmospheric and oceanic circulations (Guemas and others, 2016). The changes in the sea-ice extent have mainly occurred in the marginal ice zone of the central Arctic since 2007 (Comiso and Hall, 2014); this area is a transition area between MYI and seasonal ice. Related to the strong sea-ice decline in summer, since the start of the observational record in 1979, seasonal ice (first-year ice) that has formed since the previous summer melt season has become the dominant ice type in the Arctic Ocean. We focus on the interannual variability of WSSI from 1979 to 2019 and on the associated atmospheric circulation patterns, especially over the marginal ice zone of the central Arctic, which is a key area of sea-ice decline in the summertime.
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