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Recent Temperature Changes in the Western Arctic during Spring

James E. Overland1, Muyin Wang2, and Nicholas A. Bond2

1Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington, 98115
2Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, 98195

Journal of Climate, 15(13), 1702–1716, (2002).
Copyright ©2002 by American Meteorological Society. Further electronic distribution is not allowed.

1. Introduction

Much of the recent work on Arctic climate variability has focused on the winter period (e.g., Thompson and Wallace 1998; Monahan et al. 2000; Shindell et al. 2001). But at least in the western Arctic, here defined as the region extending from eastern Siberia across Alaska to northern Canada, many striking changes in surface conditions have occurred in the spring. Stabeno and Overland (2001) note an early and rapid ice melt in the Bering Sea in the 1990s compared to the 1980s. The duration of open water in Resolute Bay, Canada, is over 50 days longer in the 1990s than earlier decades (Canadian Ice Service 2000, personal communication). Stone (1997) found a prominent, long-term warming trend in springtime surface temperature records at Barrow, Alaska. Native communities report that recent springs have featured earlier retreat of ice and a faster rate of breakup, increased depth of the active permafrost layer, and less predictable weather (Riedlinger and Berkes 2001).

Spring may be a critical season with respect to climate change because the return of the sun at high latitudes initiates potential positive feedbacks. These include effects related to interactions between atmospheric dynamics and chemistry in the stratosphere, and between albedo and the melt of snow and sea ice. Regarding the stratosphere, Pawson and Naujokat (1999) found that the 1990s included years that had stratospheric temperatures cold enough to support polar stratospheric clouds, which had not been characteristic of the Arctic. The presence of these clouds tends to exacerbate the destruction of stratospheric ozone in the spring, which in turn tends to reduce the local absorption of UV radiation, and hence promotes cold anomalies. Regarding surface albedo effects, an 8-day advancement of the timing of snowmelt in the Barrow region has occurred since the 1960s. This absence of snow cover has caused the net radiative heat flux at the surface to increase by more than 100 W mto the minus 2 locally over that 8-day period (Stone et al. 2002).

In this paper we conduct a diagnostic study of changes that have occurred in the western Arctic near the surface and in the lower stratosphere. A primary aspect of this study is to examine whether the characteristic signature of the Arctic Oscillation (AO) carries over into spring. Special attention is devoted to comparing the 1980s with the 1990s, and how this decadal change was manifested in individual years. We pursue the dynamics behind the observed changes through analysis of the principal contributions to the low-level thermodynamic energy budget.

We begin by discussing the data sets used in our analysis, the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis and the Television Infrared Observational Satellite (TIROS-N) Operational Vertical Sounder (TOVS) Polar Pathfinder (Path-P) product. We illustrate decadal and monthly variability in the western Arctic using time series at Barrow, Alaska, and Eureka, Canada. These time series show striking differences during spring between the 1990s and the previous four decades. We then explore the hemispheric patterns of temperature differences between these decades as a function of season, both aloft and near the surface. Finally, we document the mechanisms responsible for the anomalous lower-tropospheric warming observed in the western Arctic during spring in the 1990s.

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