Abstract
Abstract. 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.
Highlights
The climatological wind over the northwestern United States blows from west to east, bringing moisture from the Pacific to the western United States
Many observations and simulations have shown that Arctic stratospheric ozone (ASO) variations have a significant impact on Northern Hemisphere tropospheric climate, but few studies have focused on regional characteristics
Reanalysis datasets and Whole Atmosphere Community Climate Model version 4 (WACCM4), we have shown that the March ASO changes have a significant effect on April precipitation in the northwestern United States, with a lead of 1–2 months
Summary
Stratospheric circulation anomalies can affect tropospheric climate via chemical–radiative–dynamical feedback processes (Baldwin and Dunkerton, 2001; Graf and Walter, 2005; Cagnazzo and Manzini, 2009; Ineson and Scaife, 2009; Thompson et al, 2011; Reichler et al, 2012; Karpechko et al, 2014; Kidston et al, 2015; Li et al, 2016; Zhang et al, 2016; Wang et al, 2017). Smith and Polvani (2014) used an atmospheric global climate model to reveal a significant influence of ASO changes on tropospheric circulation, surface temperature and precipitation when the amplitudes of the forcing ASO anomaly in the model are larger than those historically observed. Ivy et al (2017) presented observational evidence for the relationship between ASO and tropospheric climate, revealing that the maximum daily surface temperature anomalies in spring (March–April) in some regions of the Northern Hemisphere occurred during years with low ASO in March. Xie et al (2016, 2017a, b) demonstrated that the tropical climate can be affected by ASO They pointed out that stratospheric circulation anomalies caused by March ASO changes can rapidly extend to the lower troposphere and propagate horizontally to the North Pacific in about 1 month, influencing the North Pacific sea surface temperature (SST) in April.
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