An objective hybrid classification of daily surface weather maps for Churchill, Manitoba, was used to determine the dominant synoptic conditions during the snowmelt and snow-free periods for the Canadian central subarctic. This classification yielded different dominant synoptic types for the two normal and one El Niño (EN) seasons. The analysis produced seven dominant synoptic types for the study location during the pre-growing and growing periods (April 20 to September 7), accounting for approximately 90% of the days in the study period, during the normal seasons (1996 and 1997). However, during the EN season (1998), the classification yielded eight dominant synoptic types, also accounting for approximately 90% of the days in the study period. The effects of source regions were used to explain the observed air mass characteristics, and their influence on the study location. Cooler, drier air masses were the most frequent at the study location during the normal seasons. Arctic high pressure systems approaching from the northwest and stationary high pressure systems to the south brought the coolest and warmest conditions, respectively. During the EN season, there was a change in the frequency distribution of the dominant synoptic types over the pre-growing and growing periods. This frequency distribution in conjunction with the change in source region characteristics caused by the EN influence proved to be important to the influx of moisture to the region during the pre-growing period. These synoptic regimes and source region interactions exerted strong controls on the precipitation and evaporation components of the water balance during the normal and EN seasons as observed in terms of cloud cover, radiation, and precipitation and evaporation efficiencies.
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Acknowledgments: Financial support for this research has been provided by the Natural Science and Engineering Research Council of Canada and by student northern training grants from the Canada Department of Indian and Northern Affairs. The authors would like to thank Bob Kochtubajda for his assistance in obtaining the surface synoptic maps, and the Churchill Northern Studies Centre for their hospitality and assistance in the field. Assistance in the reduction of the surface synoptic data was provided by Paula Rotenberg, Claire Oswald, Merrin Macrae, and Peter Brown. Finally, the authors gratefully acknowledge improvements and corrections suggested by the reviewers.
- El Niño (EN)
- Synoptic climatology