R. Atlas

Abstract

The aim of this paper is to report extreme winter/early-spring air temperature (hereinafter temperature) anomalies in mid-latitude Europe, and to discuss the underlying forcing to these interannual fluctuations. Warm advection from the North Atlantic in late winter controls the surface-air temperature, as indicated by the substantial correlation between the speed of the surface southwesterlies over the eastern North Atlantic (quantified by a spe-cific Index Ina) and the 2-meter level air temperatures (hereinafter Ts) over Europe, 45-60°N, in winter. In mid-March and subsequently, the correlation drops drastically (quite often it is negative). This change in the relationship between Ts and Ina marks a transition in the control of the surface-air temperature: absorption of insolation replaces the warm advection as the dominant control. This forcing by maritime-air advection in winter was demonstrated in a previous publication, and is re-examined here in conjunction with extreme fluctuations of temperatures in Europe. We analyze here the interannual variability at its extreme by com-paring the warm-winter/early-spring of 1989/90 with the opposite scenario in 1995/96. For these two December-to-March periods the differences in the monthly mean air temperature in Warsaw and Torun, Poland, range above 10°C. Short-term (shorter than a month) fluctuations of air temperature are likewise very strong. We conduct pentad-by-pentad analysis of the surface-maximum air temperature (hereinafter Ттах), in a selected location, examining the dependence on Ina. The increased cloudiness and larger amounts of total precipitable water, corollary effects to the warm low-level advection in the 1989/90 winter, enhance the positive air temperature anomalies. The analysis of the ocean-surface winds is based on the Special Sensor Microwave/Imager (SSM/I) dataset; ascent rates, and over land wind data are from the European Centre for Medium-Range Weather Forecasts (ECMWF); maps of 2-m air tempera-ture, cloud cover and precipitable water are from the National Centers for Environmental Prediction (NCEP) Reanalysis.

Keywords: anomalies of air temperature in Europe, maritime-air advection, climatic fluctuations

J. Otterman, Land-Atmosphere-Ocean-Research; at Data Assimilation Office, Code 910.3, NASA GSFC, Greenbelt, MD 20771, USA;
J. Ardizzone, General Science Corp., Beltsville, MD, USA
R. Atlas, Laboratory for Atmospheres, NASA GSFC, Greenbelt, MD 20771, USA
D. Bungato, General Science Corp., Beltsville, MD, USA
J. Cierniewski, Adam Mickiewicz University, Poznan, Poland; 5 Nicholas Copernicus University, Torun, Poland
J. C. Jusem, General Science Corp., Beltsville, MD, USA
R. Przybylak, Nicholas Copernicus University, Torun, Poland
S. Schubert, Laboratory for Atmospheres, NASA GSFC, Greenbelt, MD 20771, USA
D. Starr, Laboratory for Atmospheres, NASA GSFC, Greenbelt, MD 20771, USA
J. Walczewski, Institute of Meteorology and Water Management, Branch of Cracow, Poland
Alojzy Woś, Institute of Geography, Adam Mickiewicz University, Poznari