Abstract Submesoscale eddies (1-10 km diameter) were identified using surface velocity observations obtained from a high-frequency radar system (HFR) operated in Todos Santos Bay (TSB), Baja California, Mexico. Eddies were detected through a special case of the Okubo-Weiss parameter for divergent flows in the form of eigenvalues of the Jacobian matrix. The detection method, applied for a surface velocity grid, shows encouraging results in the recognition and tracking of submesoscale features in TSB. The detection method is rapid and efficient. Results show the formation and persistence of an eddy structure inside the Bay in December 6, 2010, displaying a trajectory from NE to SW until disappearing at the center of the Bay. The eddy is approximately 4 km in diameter with a frequency of ~0.1f (f is the Coriolis parameter). The real part of the Okubo-Weiss parameter ranged between − 4 × 10 − 9 to − 1 × 10 − 9 s − 2, and outlined the eddy for approximately 9 hours. Although it is difficult to identify the origin of the detected submesoscale eddy, its appearance coincided with a drop in relative atmospheric humidity suggesting land-ocean Santa Ana winds as a possible generating mechanism.

ABSTRACT The influence of easterly and northeasterly dry and warm Santa Ana winds (SAw) on the surface circulation of Todos Santos Bay, Mexico, is studied from surface currents and wind data measured during the most extreme periods of activity (autumn-winter season). Sea surface currents were measured using a system of coastally-based HF radar stations between 2009 and 2015. Winter-mean surface circulation showed a cyclonic tendency. Atmospheric variables allowed the grouping of ~122 SAw events, 23% of which caused a noticeable change in the background circulation. Event-mean current patterns showed dissimilar responses to the acting winds, with some SAw events driving weak offshore currents, another that developed an eddy-pair circulation inside the bay, and one rather intense (winds of 8-10 m s-1) that developed a clockwise circulation overturning the cyclonic long-term winter-mean. In general, changes in the circulation were related to an offshore transport of surface waters into the open ocean.

RESUMEN Se utilizan datos de vientos y corrientes superficiales para estudiar la influencia de vientos de Santa Ana (SAw), relativamente secos y cálidos del este y noreste, sobre la circulación superficial de la Bahía de Todos Santos, México. El análisis se realiza para periodos de vientos intensos en la época de otoño-invierno. Las corrientes superficiales fueron medidas entre 2009 y 2015 usando un sistema de estaciones de radar HF sobre la costa. La circulación superficial promedio durante el invierno mostró una tendencia ciclónica. Las variables atmosféricas permitieron identificar ~122 eventos SAw, de los cuales 23% causó un cambio notable en la circulación media. Los patrones de circulación promedio durante los eventos cálidos mostraron respuestas diferentes a los vientos forzantes. En algunos eventos la influencia de los vientos generó corrientes débiles hacia afuera de la costa, mientras que en otros se desarrolló una circulación de dos remolinos ciclónicos dentro de la bahía. Un evento intenso (8-10 ms-1) desarrolló una circulación anticiclónica, opuesta a la circulación ciclónica promedio de invierno. En general, los cambios en la circulación mostraron relación con un transporte en la misma dirección del viento hacia el océano abierto.