A Seasonal Heat Budget across the Extent of the California Current

Abstract

Abstract A seasonal heat budget is based on observations that span the broad California Current (CC) region. Budget terms are estimated from satellite data (oceanic heat advection), repeat ship transects (heat storage rate), and the Comprehensive Ocean–Atmosphere Data Set (COADS) (surface heat flux). The balance between terms differs with distance from shore. Offshore, a local balance between the heat storage rate and net heat flux (Q0) holds; the latter is dominated by its shortwave component QSW. Shoreward of ∼500 km, oceanic heat advection shifts the phase of the heat storage rate to earlier in the year and partially offsets an increase in Q0 due to cloud clearing. During the summer maximum of Q0, the ∼500-km-wide CC region loses heat to alongshore geostrophic transport, offshore Ekman transport, and, to a lesser degree, cross-shore geostrophic transport and eddy transport. The advective heat loss is neither uniform in space nor temporal phase; instead, the region of geostrophic and eddy heat loss expands cross shore with the annual widening of the California Current to ∼500 km. This expansion begins in spring with the onset of equatorward winds. A region of relatively positive wind stress curl widens at the same gradual rate as the CC, suggesting a coupling mechanism between the two.