Observational Analysis of Extratropical Cyclone Interactions with North Pacific Sea Surface Temperature Anomalies

In 2013, a large upper-ocean thermal anomaly formed in the Gulf of Alaska (GOA) causing surface temperatures to reach 4 degrees C above the climatological norm. Formation of the anomaly has been associated with a persistent ridge in the GOA which produced a lull in storm activity during the boreal winter of 2013 (Bond et al. 2015; Hartmann 2015). This resulted in a suppression of winter ocean heat loss to the atmosphere, leading to a warmer, more stratified water column and an anomalous warm pool, colloquially named the blob. While storm activity was anomalously low during these winters, we show cases where storms nonetheless significantly shaped the evolution of the SST anomaly. This research seeks to understand how the thermal anomaly began in 2013 with respects to surface fluxes as well as the response of the warm anomaly to high-frequency atmospheric forcings and to test the hypothesis that it was the interactions between the thermal anomaly and fall storms that was the primary mechanism for dissipating heat in the mixed layer. Discussion of whether this was a normal mode of oscillation within the area is still being debated as this warm anomaly is not unprecedented (Liang, et al. 2017). During the almost three years that the anomaly resided in the GOA, it interacted with synoptic-scale cyclones which eroded the surface signature and manipulated the spatial structure. Not all storms, however, affected the thermal anomaly equally. We show case studies of early fall storms that produced the largest fluxes of turbulent heat and the greatest differential in the SST anomaly. Although surface fluxes alone can't explain subsurface cooling down to 100m it does account for at least 40% between ARGO profiles during large falls storms.