Precipitation variability associated with the North American Monsoon in the 20th century

Abstract

An analysis of century‐long precipitation data shows that the interseasonal and continental‐scale variations of precipitation anomalies associated with interannual variations of the North American Monsoon (NAM) are notably different between the two periods of 1901–1962 and 1963–1994. In Arizona‐New Mexico (AZ‐NM), wet (dry) summers are preceded by dry (wet) winters only after 1962. Another characteristic of the NAM variability, a summer rainfall pattern of wetter (drier) AZ‐NM, and drier (wetter) Great Plains (GP), is observed only after 1962, as well. The strongest contrast in summer rainfall anomalies appears between AZ‐NM and the southeastern U.S. for 1901–1962, while it appears between AZ‐NM and the GP for 1963–1994. For the period after 1962, the precipitation variability obtained here show the same features found in earlier studies. Causes of the observed changes in the precipitation characteristics around 1960 are not clear due to a lack of large–scale atmospheric and oceanic data before 1950.