Abstract
Arctic sea ice responds to atmospheric forcing in primarily a top-down manner, whereby near-surface air circulation and temperature govern motion, formation, melting, and accretion. As a result, concentrations of sea ice vary with phases of many of the major modes of atmospheric variability, including the North Atlantic Oscillation, the Arctic Oscillation, and the El Niño-Southern Oscillation. However, until this present study, variability of sea ice by phase of the leading mode of atmospheric intraseasonal variability, the Madden–Julian Oscillation (MJO), which has been found to modify Arctic circulation and temperature, remained largely unstudied. Anomalies in daily change in sea ice concentration were isolated for all phases of the real-time multivariate MJO index during both summer (May–July) and winter (November–January) months. The three principal findings of the current study were as follows. (1) The MJO projects onto the Arctic atmosphere, as evidenced by statistically significant wavy patterns and consistent anomaly sign changes in composites of surface and mid-tropospheric atmospheric fields. (2) The MJO modulates Arctic sea ice in both summer and winter seasons, with the region of greatest variability shifting with the migration of the ice margin poleward (equatorward) during the summer (winter) period. Active regions of coherent ice concentration variability were identified in the Atlantic sector on days when the MJO was in phases 4 and 7 and the Pacific sector on days when the MJO was in phases 2 and 6, all supported by corresponding anomalies in surface wind and temperature. During July, similar variability in sea ice concentration was found in the North Atlantic sector during MJO phases 2 and 6 and Siberian sector during MJO phases 1 and 5, also supported by corresponding anomalies in surface wind. (3) The MJO modulates Arctic sea ice regionally, often resulting in dipole-shaped patterns of variability between anomaly centers. These results provide an important first look at intraseasonal variability of sea ice in the Arctic.
Highlights
Arctic sea ice is a complex component of the Earth climate system
(1) The Madden–Julian Oscillation (MJO) projects onto the Arctic atmosphere, as evidenced by statistically significant wavy patterns and consistent anomaly sign changes in composites of surface and mid-tropospheric atmospheric fields
In MJO phase 1, negative height anomalies were found over northern Russia, Alaska, and the north Atlantic, and positive height anomalies were found over northern Europe and North America
Summary
Arctic sea ice is a complex component of the Earth climate system. Part of its complexity comes from its sensitivity to the atmosphere on a range of spatial and temporal scales. Sea ice tends to organize—via motion, formation, melting, and accretion—in accordance with large-scale patterns of atmospheric circulation (Walsh and Johnson 1979; Overland and Pease 1982; Fang and Wallace 1994; Slonosky et al 1997; Prinsenberg et al 1997; Overland and Wang 2010). Because of these responses to the atmosphere, concentrations of sea ice have been found to be correlated with several of the major modes of atmospheric variability, including the North Atlantic Oscillation (NAO) (Deser et al 2000; Kwok 2000; Parkinson 2000; Partington et al 2003), the Arctic Oscillation (AO) (Wang and Ikeda 2000; Rigor et al 2002; Belchansky et al 2004) (the NAO and AO are often referred to as part of the Northern Hemisphere annular mode; Wallace 2000), the El Nino-Southern Oscillation (ENSO) (Liu et al 2004), and longer-period oscillations (Polyakov et al 2003).
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