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Arctic cyclones are an extremely common, year-round phenomenon, with substantial influence on sea ice. However, few studies address the heterogeneity in the spatial patterns in the atmosphere and sea ice during Arctic cyclones. We investigate these spatial patterns by compositing on cyclones from 1985-2016 using a novel, cyclone-centered approach that reveals conditions as functions of bearing and distance from cyclone centers. An axisymmetric, cold core model for the structure of Arctic cyclones has previously been proposed, however, we show that the structure of Arctic cyclones is comparable to those in the mid-latitudes, with cyclonic surface winds, a warm, moist sector to the east of cyclones and a cold, dry sector to the west. There is no consensus on the impact of Arctic cyclones on sea ice, as some studies have shown that Arctic cyclones lead to sea ice growth and others to sea ice loss. Instead, we find that sea ice decreases to the east of Arctic cyclones and increases to the west, with the greatest changes occurring in the marginal ice zone. Using a sea ice model forced with prescribed atmospheric reanalysis, we reveal the relative importance of the dynamic and thermodynamic forcing of Arctic cyclones on sea ice. The dynamic and thermodynamic responses of sea ice concentration to cyclones are comparable in magnitude, however dynamic processes dominate the response of sea ice thickness and are the primary driver of the east-west difference in the sea ice response to cyclones.

The predictability of sea ice during extreme sea ice loss events on subseasonal (daily to weekly) time scales is explored in dynamical forecast models. These extreme sea ice loss events (defined as the 5th percentile of the 5-day change in sea ice extent) exhibit substantial regional and seasonal variability; in the central Arctic Ocean basin, most subseasonal rapid ice loss occurs in the summer, but in the marginal seas rapid sea ice loss occurs year-round. Dynamical forecast models are largely able to capture the seasonality of these extreme sea ice loss events. In most regions in the summertime, sea ice forecast skill is lower on extreme sea ice loss days than on nonextreme days, despite evidence that links these extreme events to large-scale atmospheric patterns; in the wintertime, the difference between extreme and nonextreme days is less pronounced. In a damped anomaly forecast benchmark estimate, the forecast error remains high following extreme sea ice loss events and does not return to typical error levels for many weeks; this signal is less robust in the dynamical forecast models but still present. Overall, these results suggest that sea ice forecast skill is generally lower during and after extreme sea ice loss events and also that, while dynamical forecast models are capable of simulating extreme sea ice loss events with similar characteristics to what we observe, forecast skill from dynamical models is limited by biases in mean state and variability and errors in the initialization. Significance Statement We studied weather model forecasts of changes in Arctic sea ice extent on day-to-day time scales in different regions and seasons. We were especially interested in extreme sea ice loss days, or days in which sea ice melts very quickly or is reduced due to diverging forces such as winds, ocean currents, and waves. We find that forecast models generally capture the observed timing of extreme sea ice loss days. We also find that forecasts of sea ice extent are worse on extreme sea ice loss days compared to typical days, and that forecast errors remain elevated following extreme sea ice loss events.

Recent work has emphasized the important role of midlatitude moisture fluxes in enhancing Arctic warming and sea ice loss. Conversely, less attention has been paid to the impact of Arctic warming and sea ice loss on midlatitude moisture fluxes. Analysis of an atmosphere-only general circulation model indicates that sea ice loss promotes changes in the large-scale midlatitude atmospheric circulation that have a substantial impact on moisture transport into and out of the Arctic. While poleward moisture transport into the Arctic does increase in a reduced sea ice climate, the increase in equatorward moisture transport out of the Arctic is larger, particularly in boreal winter over the North Pacific. A decomposition of the meridional moisture transport reveals that this increase in equatorward moisture transport is driven, at least in part, by changes in the background circulation. Specifically, sea ice loss drives a series of large-scale tropospheric circulation changes, including an increase in cyclonic Rossby wave breaking over the North Pacific that results in a preferential enhancement of equatorward moisture transport out of the Arctic in the days following the peak of the Rossby wave breaking event.

The effects of Arctic cyclones on sea ice are the subject of many papers, however aside from individual case studies, few address the heterogeneity in the spatial pattern of the sea ice response.We composite atmospheric conditions from ERA5 reanalysis and satellite sea ice concentrations on Arctic cyclones using a storm-centered approach to reveal the typical atmosphere and sea ice responses at different bearings and distances relative to an Arctic cyclone.Asymmetry in the pattern of the sea ice concentration response to cyclones is revealed, with increased growth/reduced melt to the west of cyclones and decreased growth/increased melt to the east.In part, this is explained by heterogeneity in the spatial patterns of atmospheric temperature and cloud fraction associated with cyclones, which result in heterogeneity in patterns of the surface energy fluxes.Using the CICE sea ice model forced with prescribed atmospheric reanalysis from the Japan Meteorological Agency, we reveal the relative importance of the dynamic and thermodynamic forcing of cyclones on sea ice, as well as the spatial patterns of each. The dynamic and thermodynamic responses of sea ice concentration to cyclones are comparable in magnitude, however dynamic processes dominate the response of sea ice thickness.These results highlight and explain important details often missed when answering “do cyclones cause an increase or decrease sea ice?”, as it appears the answer is both.

Confusion exists regarding the tropospheric circulation response to volcanic eruptions, with models and observations seeming to disagree on the sign of the response. The forced Southern Hemisphere circulation response to the eruptions of Pinatubo and El Chichon is shown to be a robust positive annular mode, using over 200 ensemble members from 38 climate models. It is demonstrated that the models and observations are not at odds, but rather, internal climate variability is large and can overwhelm the forced response. It is further argued that the state of the El Nino–Southern Oscillation can at least partially explain the sign of the observed anomalies and may account for the perceived discrepancy between model and observational studies. The eruptions of both El Chichon and Pinatubo occurred during El Nino events, and it is demonstrated that the Southern Annular Mode anomalies following volcanic eruptions are weaker during El Nino events compared to La Nina events.