Linking interannual variations of California precipitation and Arctic sea ice through circulation patterns

Abstract Cycles of drought and deluge in California impact the lives of millions of people. It is important to understand the causes of large interannual variations of precipitation in California (Pca) and help the stakeholders prepare for the future. The Pacific sea surface temperature (SST) is known to influence Pca, but seasonal forecasts of Pca based on the SST have been unreliable. Previously model simulations have shown a decrease of Pca in response to a reduction of sea ice cover (SIC) in the Arctic, which has not been supported using observations. This study attempts to fill this gap, and link the interannual variations of Pca and the rapidly changing Arctic sea ice through atmospheric circulation patterns. The circulation patterns were identified based on empirical orthogonal function (EOF) analysis of the daily fields of geopotential height at 500 hPa (z500) in winters during 1979–2019. First it is found that Pca changes from high to low SIC conditions depended on Pacific SST conditions (~10% decrease for La Niña-like, ~10% increase for El Niño-like conditions). Secondly, the impact of Pacific SST anomalies on Pca was found to be small in winters following high SIC in the Nordic seas in autumn, but large following low SIC. This occurred because of changes in the number of rainy days in association with the phase shifts of circulation patterns in the Pacific-North America (PNA) sector. Possible mechanisms for the phase shifts in response to changes of SST and SIC are proposed for further investigation.