Quantifying the impact of the Madden-Julian Oscillation on the state of the Arctic
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 and snow cover extent 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, variability of sea ice and snow cover extent 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.
In this study, anomalies in daily change in sea ice concentration and snow cover extent were isolated for all phases of the Real-time Multivariate MJO index during both summer (May-July) and winter (November-January) months. Principal findings of the relationship between sea ice concentration and the MJO included the following: 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. This variability is supported by corresponding anomalies in surface wind and temperature. 3) The MJO modulates Arctic sea ice regionally, often resulting in dipole-shaped patterns of variability between anomaly centers.
The seasonality of the MJO-snow extent relationship is also explored using snow fields from multiple data records. Use of multiple snow variables within cutting-edge reanalysis datasets was necessary due to the nature of snow “memory”, in that snow that falls and accumulates during one MJO phase may remain for several subsequent MJO phases. These results provide an important first look at intraseasonal variability of snow cover extent in the Arctic.