Ph.D. Geography, 1989
Director, National Snow and Ice Data Center (NSIDC)
Professor, Dept. of Geography
- Arctic climate variability and change
- High latitude atmospheric circulation
- Numerical weather prediction in high latitudes
- Arctic atmosphere-ocean-ice interactions
- The hydrologic cycle
Current Research: Winds of Change in the Arctic
Part of my work over the past year has focused on understanding how seasonal and spatial characteristics of recent Arctic air temperature anomalies in the lower troposphere (the 925- hPa level) are related to wind patterns, and how relationships with winds are being modulated by changes in sea-ice concentration, sea-surface temperature, and snow cover. The focus is on the period 1979-2009 in contrast with the most recent decade (2000-2009), during which the Arctic has undergone strong warming and sea ice loss. The primary objective is to provide a better understanding of why the Arctic is warming at a much faster rate than the rest of the northern hemisphere, a process known as Arctic amplification. While much of this work has involved analysis of gridded fields of atmospheric data, it has also meshed with other projects including fieldwork in the Arctic to assess changing snow and sea-ice conditions.
Along with the expected pattern of opposing temperature anomalies for northerly and southerly winds (winds blowing from the north and south, respectively), there are prominent temperature anomaly signals linked to onshore versus offshore flow. For example, northerlies in summer, blowing off the cold Arctic Ocean, yield cold anomalies over northern Eurasia that can extend several hundred kilometers inland from the coast. While onshore westerlies yield above-average temperatures over northwestern Eurasia and the Barents and Kara seas, continental easterlies yield an opposing anomaly pattern.
Positive temperature anomalies (e.g., warming trends) for the decade 2000-2009 encompass most of the Arctic and are present for all wind directions. That is, northerlies, southerlies, easterlies, and westerlies are all warmer than they used to be. While this general warming points to the effects of radiative forcing linked to rising greenhouse gas concentrations, influences of recent shifts in atmospheric circulation, reduced sea-ice extent, and rising sea-surface temperature are also prominent. For example, reduced winter ice extent between Svalbard and Novaya Zemlya (islands on the Atlantic side of the Arctic), while likely maintained in part by anomalous southerly winds, provides for a surface heat source that leads to positive 925- hPa temperature anomalies (again, meaning warming) for all wind directions. Influences of ice loss and sea-surface temperature change are especially noticeable in autumn. Part of the spring signal of warming appears to be linked to reductions in snow cover over land.
Temperature anomalies with respect to wind direction are further contrasted for years with high and low September sea-ice extent. Results suggest that through transports by the atmosphere, temperature anomalies linked to anomalous open water areas can influence much of the Arctic Ocean and penetrate far into the Eurasian continent.