Long Island Sound temperature variability and its associations with the ridge-trough dipole and tropical modes of sea surface temperature variability

Possible mechanisms behind the longevity of intense Long Island Sound (LIS) water temperature events are examined using an event-based approach. By decomposing an LIS surface water temperature time series into negative and positive events, it is revealed that the most intense LIS water temperature event in the 1979-2013 period occurred around 2012, coinciding with the 2012 ocean heat wave across the Mid-Atlantic Bight. The LIS events are related to a ridge-trough dipole pattern whose strength and evolution can be determined using a dipole index. The dipole index was shown to be strongly correlated with LIS water temperature anomalies, explaining close to 64 % of cool-season LIS water temperature variability. Consistently, a major dipole pattern event coincided with the intense 2012 LIS warm event. A composite analysis revealed that long-lived intense LIS water temperature events are associated with tropical sea surface temperature (SST) patterns. The onset and mature phases of LIS cold events were shown to coincide with central Pacific El Niño events, whereas the termination of LIS cold events was shown to possibly coincide with canonical El Niño events or El Niño events that are a mixture of eastern and central Pacific El Niño flavors. The mature phase of LIS warm events was shown to be associated with negative SST anomalies across the central equatorial Pacific, though the results were not found to be robust. The dipole pattern was also shown to be related to tropical SST patterns, and fluctuations in central Pacific SST anomalies were shown to evolve coherently with the dipole pattern and the strongly related East Pacific-North Pacific pattern on decadal timescales. The results from this study have important implications for seasonal and decadal prediction of the LIS thermal system.