Wind events in a subtropical coastal upwelling region as detected by admittance analysis

Wind dominates the ocean surface circulation in the subtropical coastal upwelling regions. Although the wind events in these regions are mostly favorable for upwelling, other types of wind events are occasionally dominant. The typical patterns and statistics of wind events over the waters off northern Baja California are described. The identification of wind events was carried out using a systematic technique based on both the admittance magnitude and phase. This technique proved useful and has some of the crucial characteristics expected from a classification standpoint. This technique is applied to 29 years (1990–2018) of cross-calibrated multiplatform (CCMP) 10-m wind data. Equatorward along the coast (upwelling-favorable), offshore (Santa Ana), onshore, poleward along the coast (downwelling-favorable), and relaxation events are identified. The wind stress and wind stress curl mean fields and the statistics of occurrence are described on a year-to-year and month-to-month basis for each wind type. The upwelling-favorable and relaxation events are the most frequent and occur throughout the year; the typical duration is 4 and 1.5 days, respectively. The offshore (Santa Ana), onshore, and poleward wind events are sporadic and occur only during autumn-winter. The year-to-year variation of the frequency of occurrence of the equatorward wind events shows no trend during the study period.