Abstract
Both large-scale atmospheric circulation and moisture content in the atmosphere govern regional precipitation. We partition recent changes in mean, heavy, and extreme precipitation for all seasons over Canada to changes in synoptic circulation patterns (dynamic changes) and in atmospheric moisture conditions (thermodynamic changes) using 500-hPa geopotential height and precipitation data over 1979-2014. Using the self-organizing map (SOM) cluster analysis, we identify statistically significant trends in occurrences of certain synoptic circulation patterns over the Canadian landmass, which have dynamically contributed to observed changes in precipitation totals and occurrence of heavy and extreme precipitation events over Canada. Occurrences of circulation patterns such as westerlies and ridges over western North America and the North Pacific have considerably affected regional precipitation over Canada. Precipitation intensity and occurrences of precipitation extremes associated with each SOM circulation pattern also showed statistically significant trends resulting from thermodynamic changes in the atmospheric moisture supply for precipitation events.A partition analysis based on the thermodynamic-dynamic partition method indicates that most (∼90%) changes in mean and extreme precipitation over Canada resulted from changes in precipitation regimes occurring under each synoptic circulation pattern (thermodynamic changes). Other regional precipitation changes resulted from changes in occurrences of synoptic circulation patterns (dynamic changes). Because of the high spatial variability of precipitation response to changes in thermodynamic and dynamic conditions, dynamic contributions could offset thermodynamic contributions to precipitation changes over some regions if thermodynamic and dynamic contributions are in opposition to each other (negative or positive), which would result in minimal changes in precipitation intensity and occurrences of heavy and extreme precipitation events.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 7105-7126 |
| Number of pages | 22 |
| Journal | Journal of Climate |
| Volume | 32 |
| Issue number | 21 |
| DOIs | |
| State | Published - Nov 1 2019 |
Funding
Acknowledgments. The analysis was financially supported by the National Natural Science Foundation of China (NSFC) (Grants 51809295, 91547108, and 51779279), the Outstanding Youth Science Foundation of NSFC (51822908), and the National Key Research and Development Program of China (Grants 2017YFC0405900 and 2016YFC0401300). All analyses were conducted using the R language (package ‘‘kohonen’’ for the SOM analysis) and R code is available upon reasonable request from the corresponding author or the github website (https://github.com/tanxuezhi/SOM-based-partition). Thanks to Daniel W. McKenney and Pia Papadopol from the Canadian Forest Service, Natural Resources Canada for providing ANUSPLIN precipitation data. NCEP–DOE Reanalysis 2 and NCEP–NARR reanalysis data were downloaded from ftp://ftp.cdc.noaa.gov/. ECMWF ERA-Interim data were downloaded from http://www.ecmwf.int/. JRA-55 data were downloaded from http://jra.kishou.go.jp/JRA-55/index_en.html; CFSR reanalysis data were downloaded from http://cfs.ncep. noaa.gov/cfsr/, and MERRA-2 reanalysis data were downloaded from https://gmao.gsfc.nasa.gov/reanalysis/ MERRA-2/. The authors thank three anonymous reviewers for their thoughtful comments and recommendations, which helped to improve the manuscript a lot. Author contributions: X.T. and T.Y.G. and S.C. conceived the study. X.T. and S.C. conducted the analysis and wrote the manuscript. D.E.H. provided the analysis code. X.C., B.L., and K.L. helped to write the manuscript.
ASJC Scopus subject areas
- Atmospheric Science