Synoptic Climatology of the Canadian High Arctic

ABSTRACT

An objective classification of daily weather maps for the Canadian High Arctic was developed with a view to identifying those synoptic situations which greatly affect ablation season temperatures and annual precipitation totals. This classification was used to catalog synoptic types for the period January, 1946 to August, 1974. 22 basic types were recognized, accounting for ∼ 96 % of days in the period. Most types have distinct seasonal maxima. Using data from Alert, Isachsen and Thule, monthly mean temperature characteristics of the types were obtained, enabling them to be ranked, warmest to coldest. Although “warm” and “cold” types were different for each station, the circulation characteristics of cold types, and of warm types, were similar. Stepwise multiple regression analysis was used to indicate the synoptic types which are closely related to inter-annual variations of mean monthly maximum temperatures. Generally, the maximum reduction of variance in the temperature record was achieved with a minimum number of synoptic types in the months April-August, suggesting greater “control” on temperature by a few types in spring and summer months. Ablation season climatic data were used to identify synoptic types which were “cool and wet”, “warm and dry”, “cool and dry” or “warm and wet”. Cool, wet types have increased in frequency over the last 10–15 years whereas warm, dry types were slightly less frequent. Such changes are not sufficient to account for the deterioration in summer climate of the area in the 1960s; within-type changes are probably significant factors in this deterioration.

Stratification of precipitation data by synoptic type indicates a small number of types account for most of the annual precipitation at each station, though this is really a function of type frequency. Other, less frequent, types are more efficient precipitation-bearing situations, in terms of precipitation per day of type occurrence. In many of these situations, low pressure close to the station dominates the circulation; these may be North Atlantic depressions regenerated along the Siberian coastline. Even small changes in the frequency of these systems would have important consequences for High Arctic precipitation.