Dominant Factors Responsible for Interannual Variability of the Summer Monsoon in the Southwestern United States

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Abstract
Interannual variability of the summer monsoon in the southwestern United States is controlled by various ocean- and land-based conditions (e.g., SST, soil moisture, and snow cover) that provide sources of memory of antecedent climate anomalies such as ENSO. It is hypothesized that this interannual variability is also modulated by decade-scale fluctuations in the North Pacific SSTs. The following observations have been made in support of this hypothesis. First, the summer precipitation regime is dominated by a continental-scale precipitation pattern characterized by an out-of-phase relationship between precipitation in the southwestern United States and that in the Great Plains of the United States. Second, interannual fluctuations in the onset date of the monsoon in the southwestern United States are significantly correlated with interannual fluctuations in the intensity of summer rainfall in this region such that early monsoons are often very wet and late monsoons tend to be dry. Third, wet (dry... Abstract Interannual variability of the summer monsoon in the southwestern United States is controlled by various ocean- and land-based conditions (e.g., SST, soil moisture, and snow cover) that provide sources of memory of antecedent climate anomalies such as ENSO. It is hypothesized that this interannual variability is also modulated by decade-scale fluctuations in the North Pacific SSTs. The following observations have been made in support of this hypothesis. First, the summer precipitation regime is dominated by a continental-scale precipitation pattern characterized by an out-of-phase relationship between precipitation in the southwestern United States and that in the Great Plains of the United States. Second, interannual fluctuations in the onset date of the monsoon in the southwestern United States are significantly correlated with interannual fluctuations in the intensity of summer rainfall in this region such that early monsoons are often very wet and late monsoons tend to be dry. Third, wet (dry...

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