Hydrography and circulation in the Northern Gulf of California during winter of 1994–1995

Hydrographic and current measurements in the Northern Gulf of California from December 1994 through March 1995 show conditions that are markedly different from those accepted as typical for winter. A rapid subsurface warm water intrusion (∼0.5 °C warmer) was observed, which reduced the stratification and stopped, and eventually reversed the typical anticyclonic winter circulation. An empirical orthogonal function analysis of the mean vertical structure of temperature and salinity of historical hydrographic data reveals that similar conditions occurred during March 1973 (warm water intrusion and weakening of stratification). In this study, it is proposed that these anomalous conditions are due to a combination of local and remote forcings: extensive water-mass formation in the Upper Gulf of California and the arrival of an intraseasonal downwelling coastally trapped wave to the Northern Gulf of California.