Using observations and reanalysis, we find that changes in April precipitation variations in the northwestern US are strongly linked to March Arctic stratospheric ozone (ASO). An increase in ASO can result in enhanced westerlies in the high and low latitudes of the North Pacific but weakened westerlies in the midlatitudes. The anomalous circulation over the North Pacific can extend eastward to western North America, decreasing the water vapor concentration in the air over the northwestern United States and enhancing downwelling in the northwestern US, which results in decreased precipitation there and vice versa for the decrease in ASO. Model simulations using the Whole Atmosphere Community Climate Model version 4 (WACCM4) support the statistical analysis of observations and reanalysis data and further reveal that the ASO influences circulation anomalies over the northwestern US in two ways. Stratospheric circulation anomalies caused by the ASO changes can propagate downward to the troposphere in the North Pacific and then eastward to influence the strength of the circulation anomalies over the northwestern US. In addition, sea surface temperature anomalies over the North Pacific, which may be related to the ASO changes, would cooperate with the ASO changes to modify the circulation anomalies over the northwestern US. Our results suggest that ASO variations could be a useful predictor of spring precipitation changes in the northwestern?US.
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