CLIMATOLOGY OF UPWELLING RELATCiD PROCESSES ANDREW BAKUN AND CRAIG 5. NELSON Pacific Envimnmontd Omup Southwest Fiaheriea G n h r

Marine surface data are used to describe large scale features of upwelling and certain related processes off the west coast of Baja California. The offshore-directed component of sea surface b a n transport, computed from the wind stress distribution, is considered an index of coastal upwelling intensity. Upwelling appears to be strongest south of W N latitude, from March to June. Departures fTom randomness in the offshore Ekman transport signals include the annual and diurnal periodicities, an energetic irregular rhythm in the “event ” frequency range (several day to several week periods), and two types of persistence. A short-term persistence appears to be related to the duration of synoptic scale atmospheric disturbances, while a much longer-term persistence may be related to a feedback mechanism between the upwelling and the overlying wind stress field. The longshore current field is highly correlated seasonally with the upwelling cycle. Strong equatorward surface flow is indicated during the spring upwelling maximum; during the fall there is generally a poleward component of flow. Wind stress curl distributions indicate a tendency for the surface wind drift to be convergent (negative curl) in the offshore region. From Punta Baja to Punta Eugenia the convergent area extends to the coast. Areas of divergent surface drift (positive curl) extend several hundred kilometers off the coast north of Punta Baja and south of Punta Eugenia. From a “Sverdrup transport ” point of view, this pattern is consistent with evidence of separate cyclonic gyral circulations north of Punta Baja and south of Punta Eugenia