Possible teleconnections between North Pacific sea surface temperatures and extended dry spells and droughts on the Canadian Praries

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

Teleconnections between ENSO events and growing season precipitation on the Canadian Prairies

Teleconnections between ENSO events and growing-season precipitation variations on the Canadian Prairies are examined. Correlation and composite analyses indicate that between 1948 and 1991, El Nino events were associated with more frequent extended dry spells. Conversely, La Nina events coincided with fewer extended dry spells. Both relationships occurred during the third growing season following the onset of the ENSO events (i.e. approximately a 10-season or 30-month lag). A series of atmosphere - ocean teleconnections over the Pacific Ocean including Pacific North America (PNA) circulation patterns, North Pacific sea-surface temperature anomalies and upper-atmospheric circulation anomalies were found to result in growing-season precipitation variations over the Canadian Prairies. Results of this analysis are incorporated into a conceptual model which may form the basis of a long-range forecasting technique of growing-season precipitation variations on the Canadian Prairies