Possible teleconnections between North Pacific sea surface temperatures and extended dry spells and droughts on the Canadian Praries
Bonsal, Barrie Richard
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This thesis examines the possible teleconnections between North Pacific sea surface temperatures and synoptic extended dry spells and droughts on the Canadian Prairies. Dry spells are a natural occurrence on the Canadian Prairies. It is also a well known fact that extended dry spells often lead to droughts. The major synoptic cause of extended dry spells and droughts on the Canadian Prairies includes the presence of a quasi-stationary mid-tropospheric ridge over the area. What causes this ridge to become quasi-stationary is not certain. Some previous studies have shown that sea surface temperature anomalies over the North Pacific Ocean may be a significant factor in affecting upper atmospheric long wave patterns and abnormal weather conditions over North America. The main objective of this study is to determine if there is a significant statistical relationship between anomalous North Pacific sea surface temperatures and the occurrence of extended dry spells and droughts on the Canadian Prairies during the agricultural growing season (May - August) for the period 1948-1988. Individual extended dry spells are identified and then ranked in terms of their severity. Results show a significant correlation between these extended dry spells and a positive sea surface temperature anomaly gradient located in the east central North Pacific. This gradient consists of a region of anomalously cold water located in the east-central North Pacific in the area bounded by 30°N to 40°N latitude and 165°W to 135°W longitude and a region of anomalously warm water found along the west coast of North America bounded by the coordinates 45°N to 55°N latitude and 130°W to 125°W longitude. A probability model shows that the longer this gradient persists, the greater the probability of a major extended dry spell. A conceptual model is also constructed and shows a distinctive pattern in sea surface temperature anomalies and 50 kPa anomalies associated with the major extended dry spells.