Synoptic moisture pathways associated with mean and extreme precipitation over Canada for summer and fall

摘要

Large-scale meteorological patterns (LSMPs), especially vertically integrated water vapor transport (IVT) patterns were identified using the self-organizing map algorithm, and LSMPs were related to seasonal precipitation totals and widespread precipitation extremes for summer and fall seasons over Canada West and East, using the JRA-55 reanalysis and the ANUSPLIN precipitation dataset (1958-2013). Changes in the frequency of occurrences, persistence and maximum duration of each LSMP were detected. Trends in seasonal precipitation totals and extreme precipitation events associated with each LSMP were also detected. Our results show that synoptic settings of precipitation that have occurred over Canada exhibit a variety of spatial clusters of IVT anomalies, pressure highs and lows, troughs and ridges over North America, North Pacific, North Atlantic and Arctic. Extremely high IVT magnitude anomaly (|IVT|) over central Canada West are associated with the Aleutian low and Gulf cyclone across Canada West and Alaska, which force moisture from North Pacific to Canada West. Widespread positive |IVT| over Canada East are related to a strengthened and southwest-shifted trough across Canada East. Annually, only 19.4% of the occurrence characteristics of LSMPs show statistically significant changes. More statistically significant changes in the daily precipitation and occurrences of extreme precipitation related to each LSMP, than changes in the occurrence of LSMPs, have resulted in changes to seasonal precipitation totals and the occurrence of extreme precipitation across Canada. LSMPs associated with a dry climate and less frequent extreme precipitation events over Canada West in summer and fall tend to occur during the negative phase of PNA. LSMPs associated with a wet climate and frequent occurrence of extreme precipitation events over the south (north) of Canada East are more likely to occur during the positive (negative) phase of NAO.