Wind relaxation and poleward flow events in the upwelling region off Baja California, Mexico

Abstract

Wind relaxation events are commonly observed in eastern boundary upwelling ecosystems. The wind fields over the southern part of the California Current System were separated into upwelling-favorable winds and wind relaxations by using a technique based on complex correlation analysis. Using vessel-mounted Acoustic Doppler Current Profiler and conductivity-temperature-depth observations from 4 consecutive Mexican Investigations of the California Current (IMECOCAL) cruises carried out during 2001–2002, a description of the ocean state associated with these stages of the wind field was elaborated for the northern Baja California (Mexico) upwelling region. Relaxation events occurred during each cruise. A coastal poleward flow event was conspicuous when a relaxation event followed a long upwelling favorable wind event. This pattern was also correlated with a negative or close to zero wind curl at the coast. A coastal equatorial jet and an upper-ocean offshore poleward flow were observed during spring, representing a typical upwelling pattern that is correlated with a large positive wind stress curl near the coast. In winter, a surface poleward flow was inhibited by a strong northwest wind event, which generated a shallow equatorward flow. The circulation patterns described here are consistent with theories that explain surface poleward flows through wind relaxation and negative wind curl. Key words: winds, upwelling regions, poleward flows, wind relaxation events, IMECOCAL.