Predictability of North Atlantic Subtropical High and its Impact on the Climate over the United States

The North Atlantic Subtropical High (NASH) is a prime circulation system exerting a large influence on North American climate, but the sources of its predictability have not been established. In this study, we investigate the summer NASH predictability using the NCEP/NCAR Reanalysis data and the Extended Reconstructed Sea Surface Temperature (ERSST) data version 5 during 1948-2020. We find that the winter SSTs over the tropical North Atlantic Ocean can be a predictor for the summer NASH. For the period of 1948-2020, the correlations between both intensity and western ridge of the summer NASH and winter SSTs over the tropical North Atlantic Ocean are statistically significant at the 95% confidence level. It has been noticed for decades that Nino3.4 SST index can be used to predict the winter SSTs over the tropical North Atlantic Ocean with lead time up to 6 months. Although the lead-lag correlation between Nino3.4 SST Index and the summer NASH is not significant, Nino3.4 SST index is also an important source of the summer NASH predictability. The NASH has profound effects on the climate over the United States. The impacts on characteristics of summer rainfall, temperature, and tropical cyclones are examined and the results will be discussed at the meeting. This study demonstrates that the NASH can provide a source of climate predictability that extends ENSO impacts to midlatitudes and to the ENSO transition phases when ENSO forcing is weak or absent.