Diurnal warming in the tropical Pacific and its interannual variability

Analyses of satellite-derived diurnal sea surface warming of the equatorial Pacific basin from 1996 through 2000 indicate that there is, in addition to seasonal changes, an east-west dipole. For roughly half the year, the western ( eastern) Pacific experiences enhanced ( decreased) diurnal warming: the opposite is true for the other six months. La Nina conditions in 1998 through 1999 affected the strength ( but not the overall sign) of the dipole. Simple analyses using a comprehensive turbulent model indicate it is important to account for diurnal warming since the SST change over a day depends on the upper ocean changes due to diurnal warming. Since the tropical Pacific SST and east-west SST gradient is of interest to ENSO processes, ocean models that do not incorporate diurnal warming may overestimate mixing-induced cooling and the east-west SST gradient.