Interannual variations and their dynamic mechanisms of wintertime temperature inversions in the Gulf of Alaska

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Using the Simple Ocean Data Assimilation Version 2.2.4 dataset from 1950 to 2010, we analyzed the interannual variations in wintertime temperature inversions in the Gulf of Alaska (GOA), and the linkages to the Aleutian Low are also examined. The results show that the climatological wintertime temperature inversions is predominantly distributed in the northwestern GOA (NWGOA) and northern GOA (NGOA), in which it is stronger in the NWGOA than in the NGOA. Interannual variations in the temperature difference (∆T) are pronounced and are mainly controlled by the temperature minimum (Tmin) of the inversions layer. The temperature inversions layer became warmer and shallower during 1950–2010, among Tmin and the temperature maximum (Tmax) was notably warming, and the upper edge depth (Dmin) and lower edge depth (Dmax) revealed significant shoaling. ∆T decreased by 0.12 °C from 1950 to 2010 in the NWGOA but had no trend in the NGOA. The interannual variations in wintertime temperature inversions are controlled by the mixed-layer temperature anomalies and are closely correlated with the changes in the Aleutian Low. The weakened (deepened) Aleutian Low during strong (weak) ∆T winters could cause the weakening (enhancement) of the cyclone wind field in the North Pacific subarctic region, which is conducive to slowing down (spinning up) the flow of the Alaskan Gyre and the transportation of warm air into the GOA. Thus, a negative (positive) Tmin anomalies within the mixed layer is larger than Tmax anomalies, resulting in a larger (smaller) ∆T; meanwhile, the strong (weak) cooling effect leads to a deeper (shallower) Dmax. The interannual variations in the wintertime temperature inversions could be influenced by net heat flux and advection anomalies in the NWGOA, but only caused by net heat flux anomalies in the NGOA.