Semiannual variability of the C alifornia U ndercurrent along the S outhern C alifornia C urrent S ystem: A tropical generated phenomenon

We used a high‐resolution numerical model implementation to analyze the California Undercurrent (CU) dynamics along the Southern California Current System. In agreement with reported observations, the modeled CU was stronger during June–July and December–January, when it flowed continuously along Baja California and Southern California reaching long‐term averages up to 6 cm s −1 . Previous research has associated the biannual CU intensification to the local dynamics off Southern California. Our results evidenced, however, that the passage of remote Semiannual Coastal‐Trapped Waves (SCTW) primarily explained the semiannual CU variability. The CU was stronger 2–3 months after the passage of the upwelling SCTW phase, when the offshore propagation of Rossby waves, brought about by the SCTW transit, induced an energetic cross‐shore pressure gradient that strengthened the subsurface poleward circulation along the continental slope. The SCTW were independent of the local wind; they corresponded to the northward extension of semiannual equatorial Kelvin waves that have been observed along the northeastern tropical Pacific.