The Impact of ENSO on the North Pacific Ocean-Atmosphere System During Summer

Most previous studies of ENSO teleconnections to the Northern extratropics have focused on the winter, since the atmospheric circulation anomalies are largest during December-February. While the ENSO-related circulation anomalies are much weaker in summer, changes in low-level surface winds, temperature, moisture and clouds associated with ENSO can still drive changes in the extratropical oceans. This ��atmospheric bridge�� between the tropical and extratropical Pacific Ocean can create substantial summertime SST anomalies, since anomalies in solar radiation at the surface can be large in summer and because the mixed layer is shallow, so anomalous surface forcing is spread over a much thinner layer than in winter. Indeed, composite analyses shows that the magnitude of the El Ni�o La Ni�a SST difference exceeds 2�C along 40�N in the western North Pacific during July and September, which is more than twice the amplitude of the North Pacific SST anomalies in winter. Here we use GCM simulations, NCEP reanalysis, solar radiation estimates from satellites and subsurface ocean temperature data to diagnose 1) the extratropical atmospheric response to ENSO 2) what causes the ENSO-related SST anomalies to form in summer and 3) the extent to which these SST anomalies feedback on the atmosphere