Synoptic and surface climatology interactions in the central Canadian subarctic: Normal and El Nino seasons

An objective hybrid classification of daily surface weather maps for Church ill, Manitoba, was used to determine the dominant synoptic conditions durin g the snowmelt and snow-free periods for the Canadian central subarctic. Th is classification yielded different dominant synoptic types for the two nor mal and one El Nine (EN) seasons. The analysis produced seven dominant syno ptic types for the study location during the pre-growing and growing period s (April 20 to September 7), accounting for approximately 90% of the days i n the study period, during the normal seasons (1996 and 1997). However, dur ing the EN season (1998), the classification yielded eight dominant synopti c types, also accounting for approximately 90% of the days in the study per iod. The effects of source regions were used to explain the observed air ma ss characteristics, and their influence on the study location. Cooler, drie r air masses were the most frequent at the study location during the normal seasons. Arctic high pressure systems approaching from the northwest and s tationary high pressure systems to the south brought the coolest and warmes t 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 c hange in source region characteristics caused by the EN influence proved to be important to the influx of moisture to the region during the pre-growin g period. These synoptic regimes and source region interactions exerted str ong controls on the precipitation and evaporation components of the water b alance during the normal and EN seasons as observed in terms of cloud cover , radiation, and precipitation and evaporation efficiencies.