Recently an episode of intensified coastal warming off California has been detected in satellite sea surface temperature (SST) imagery along many portions of central-to-southern California and down to Baja California. This is an ongoing and highly unusual event during a seasonal period that is typically associated with strong coastal upwelling of cool subsurface water that chills the coastal zone. Upwelling along central-to-southern California (and Baja) during the spring-summer period provides a seasonal ecological environment beneficial to the marine ecosystems from phytoplankton to fisheries.
The animation shows both the extent and regional intensity of the SST anomalies (deviation of SST from a 10 year averaged seasonal reference). From July to August, large SST anomalies up to 4-5ºC were observed in the coastal waters. The magnitude of this warming is the largest in the past decade. But what caused the warming? Blame it on the winds, and perhaps also on a positive feedback loop involving regional ocean and weather patterns. A recent study by Yuan and Yamagata (2014) explained the nature of interannual variation of summertime SST off southern and Baja California through an intrinsic air-sea coupling mechanism that is characterized by a positive feedback between wind and SST. For example, the initial weakening of the equatorward along-shore wind weakens the upwelling and induces a positive SST anomaly. The latter lowers the atmospheric pressure near the coast and results in a cross-shelf atmospheric pressure gradient. This pressure gradient weakens the along-shore wind further and enhances the positive SST anomaly. Yuan and Yamagata (2014) coined this phenomenon the California Niño/Niña because the positive feedback mechanism is akin to that associated with the tropical El Niño/La Niña phenomenon that impacts global weather patterns.
Scientists and many others interested in our ocean are paying close attention to this warming because of its importance to marine life. For instance, warming of the upper ocean usually comes with changes in the plankton and fish community that you find along the California coast. There have been many reports of warm water species being caught in Southern California this summer, where the ocean has been especially warm since late winter.