Interannual Variability of the Upper Ocean in the Southeast Pacific Stratus Cloud Region

Persistent stratus/stratocumulus cloud decks in the southeast Pacific near the coasts of Peru and northern Chile play an important role in regional and global climate variability. Interannual variability of the upper ocean under stratus cloud decks in the southeast Pacific is investigated using ocean general circulation model (OGCM) experiments. The model was first forced with daily surface fluxes based on the NCEP–NCAR reanalysis and satellite-derived surface shortwave and longwave radiation for the period of 1979–2004. Gridded surface heat flux estimates used in the model integration agree well with those based on Woods Hole Oceanographic Institution (WHOI) Improved Meteorology (IMET) buoy measurements at 208S, 858W. Also, the OGCM is able to reproduce well the observed interannual SST and sea surface height variations in this region. The results suggest that the interannual variation of the upper ocean north of 208S is mostly associated with ENSO variability. Additional model experiments were conducted to examine the relative importance of ocean dynamics and surface heat fluxes in determining the interannual variation in SST. The results of these experiments indicate that upper-ocean dynamics play a dominant role in controlling the interannual variation of SST north of 208S in the stratus cloud region. The upper-ocean heat budget analysis shows that meridional heat advection associated with ENSO events primarily controls the interannual SST variation in the stratus cloud region north of 208S.