Diagnosing diathermal velocities in the eastern tropical Pacific
Diapycnal mixing, eddy driven vertical transport from tropical instability waves, wind-driven horizontal transport, and remotely forced thermocline heave all contribute to local changes in diathermal velocity. We approach this from two different perspectives, a kinematic approach that includes locally-driven isopycnal layer thickness changes and horizontal divergence, and a thermodynamic approach in which mixing, solar heating, eddy transports and local temperature tendency are calculated. Controls on the seasonal cycle and ENSO evolution are identified, describing the balance among vertical mixing, upwelling, and eddy fluxes. We connect the mechanisms controlling diathermal velocities to SST variability and the impact on the tropical climate.