Climate variability inferred from a layered model of the ventilated thermocline

Climate variability of a layered model of the ventilated thermocline is studied. Assuming the Ekman pumping is unchanged, cooling (heating) causes a southward (northward) shift of the outcrop line and thus induces a baroclinic response in the ventilated thermocline. The perturbations propagate within a characteristic cone downstream from the cooling (heating) region, defined by the two outermost characteristics streaming from the edge of the cooling (heating) region. Changes in Ekman pumping rate induce a barotropic response that propagates westward, which is a classic result obtained from the Sverdrup relation. However, if the outcrop line is nonzonal, there can be an additional baroclinic response, which propagates within the characteristic cone downstream from the source region of an Ekman pumping anomaly.