资源环境科技发展态势分析平台

In early August 2018, a record‐setting marine heatwave (MHW) occurred along the coast of Southern and Baja California. Water temperature at Scripps Pier rose to 26.4°C, the highest in 102 years of measurements. This paper investigates the large‐scale ocean‐atmospheric conditions for this Southern California MHW event. This intense and sustained event is the result of the superposition of “weather” timescale warming by a coastal wind relaxation and intraseasonal warming by coastally trapped waves. For weather‐scale warming, climatological upwelling was weakened by a wind relaxation, due to anomalous offshore low pressure associated with passing tropical cyclones John and Kristy. For intraseasonal warming, the upwelling was inhibited and the thermocline was deepened by poleward‐propagating coastally trapped waves, which provided a slow warming background. The mixed layer heat budget analysis indicates that the reduced upwelling and deepened thermocline are the major cause of the MHW.