Ocean dynamical processes associated with the tropical Pacific cold tongue mode

Abstract

AbstractThe cold tongue mode (CTM) is the second EOF mode of sea surface temperature anomaly (SSTA) variability over the tropical Pacific and represents the out‐of‐phase relationship in SSTA variability between the Pacific cold tongue region and elsewhere in the tropical Pacific. A positive CTM is characterized by cold SSTA in the Pacific cold tongue region and warm SSTA in the rest of the tropical Pacific, with conditions reversed for a negative CTM. The CTM is a coupled air‐sea mode, and its long‐term variability is most probably induced by ocean dynamical processes in response to global warming [Zhang et al., 2010]. This study focuses on the specific ocean dynamical processes associated with the CTM and its possible relationship with global warming. A heat budget diagnosis of ocean temperature in the eastern equatorial Pacific shows that the net heat flux plays a damping role and the four ocean advection terms ( , , , and ) contribute to the temperature change associated with the CTM. Among them, the vertical advection of the anomalous temperature by the mean upwelling ( ) makes a dominant contribution to the long‐term change in the CTM. The long‐term change of the term is controlled mainly by the decreasing vertical gradient of the ocean temperature anomaly ( ). The other three advection terms make a minor contribution to the long‐term change in the CTM.