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North Pacific Atmospheric and SST Anomalies in 1997: Links to ENSO?




In the summer of 1997, positive sea surface temperature anomalies (SSTA) extended across the Gulf of Alaska (GOA) and into the eastern Bering Sea (EBS). The SSTA in the EBS are at least in part due to atmospheric causes. Anomalously high 925 mb temperatures and 700 mb geopotential heights and low 925 mb relative humidities, and hence decreased low cloud cover, occurred over the region during April to August. This resulted in enhanced warming of the GOA and EBS owing to increased insolation. The anomalous solar heating was particularly great in the EBS from mid-May to mid-July. The pattern of positive 700 mb height anomalies for April to August 1997 is similar to its counterpart formed by compositing the April to August anomalies that occurred during previous El Niños. The positive equatorial SSTA for 1997 was one of the strongest on record for summer months. The existence of an equatorial/high-latitude connection and the strength of the summer equatorial SSTA in 1997 suggest an El Niño/Southern Oscillation (ENSO) influence in the GOA and EBS. The warming in the Bering Sea and North Pacific during summer 1997 appears to be due in part to the confluence of three meteorological factors which favoured clear skies. There was not only an El Niño influence, but also a decadal trend toward higher 700 mb geopotential heights and a particularly strong blocking ridge weather pattern over the Gulf of Alaska in May.