The origins of the anomalous warming in the California coastal ocean and San Francisco Bay during 2014–2016. Issue 9 (18th September 2017) - Chao, Yi
Abstract: During 2014 exceptionally warm water temperatures developed across a wide area off the California coast and within San Francisco Bay (SFB) and persisted into 2016. Observations and numerical model output are used to document this warming and determine its origins. The coastal warming was mostly confined to the upper 100 m of the ocean and was manifested strongly in the two leading modes of upper ocean (0–100 m) temperature variability in the extratropical eastern Pacific. Observations suggest that the coastal warming in 2014 propagated into nearshore regions from the west while later indicating a warming influence that propagated from south to north into the region associated with the 2015–2016 El Niño event. An analysis of the upper ocean (0–100 m) heat budget in a Regional Ocean Modeling System (ROMS) simulation confirmed this scenario. The results from a set of sensitivity runs with the model in which the lateral boundary conditions varied supported the conclusions drawn from the heat budget analysis. Concerning the warming in the SFB, an examination of the observations and the heat budget in an unstructured‐grid numerical model simulation suggested that the warming during the second half of 2014 and early 2016 originated in the adjacent California coastal ocean and propagated through the Golden Gate into the Bay. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance. Plain Language Summary: The origins of the exceptionally warm water temperatures that developed off the California coast and in San Francisco Bay were studied using observations and computer model experiments. The coastal warming was mostly confined to the upper ocean. The coastal warming in 2014 was found to have moved into coastal waters from further offshore in the northeastern Pacific. Warming persisted into 2015‐2016 as a warming influence from the south associated with the 2015‐16 El Niño event in the tropical Pacific Ocean. The model experiments suggested confirmed that propagation of the warming signals from the west and north into the California coastal ocean and suggested that the warming in San Francisco Bay was found to have originated primarily in the adjacent California coastal ocean. The finding that the coastal and Bay warming are due to the relatively slow propagation of signals from remote sources raises the possibility that such warming events may be predictable many months or even several seasons in advance. Key Points: Observations and model heat budget analyses show warming to be a result of propagation of signals from the west (Blob) and south (El Niño) Results from model sensitivity experiments support the conclusions drawn from the heat budget analyses The relatively slow propagation of the remote signals means that such warming events may be predictable months in advance