Trends in sea level pressure across western Canada

Abstract

This paper examines recent trends in sea level pressure (SLP) in western Canada. Time series of mean monthly SLP from each of 51 stations from 1956 to 1993 were analyzed for temporal and spatial trends using a number of analytical techniques, such as simple regression and correlation, trend surface analyzes, and geographical information system. Over the period, annual SLP declined at an average rate of 0.4 hPa/100 yr. Seasonal trends were clearly marked. In winter (December, January, February) and spring (March, April, May), SLP decreased at an average rate of 1.6 hPa/100 yr and 3.3 hPa/100 yr, respectively. The opposite trend was measured in the summer (+1.1 hPa/100 yr) and the fall (+2.3 hPa/100 yr). Trends in January and March were strongly negative (−9.7 hPa/100 yr and −4.3 hPa/100 yr, respectively). Equivalent values for July and October were +0.30 hPa/100 yr and +5.9 hPa/100 yr, respectively. All trends and their statistical significance levels amplified poleward. In general, trends were larger and more consistent in the Arctic and sub‐Arctic, and least in British Columbia and the southern prairies. These observations suggest a weakening of the Arctic High in the winter and spring which, if correct, is in agreement with recent mild winters in the Canadian Prairies and the Arctic.