Interannual Variability in Pacific SST Deviations


Jun Yu



We study variability of Pacific sea surface temperature (SST) utilizing the data of Advanced Very High-Resolution Radiometer (AVHRR) from 1985 to 1997. First, we model, and then remove from the AVHRR SST data, the seasonal cycle by using an intercept, a trend and first five harmonics of the annual cycle to fit the data at each grid point in the least squares sense. We then apply a low-pass filter defined by a Gaussian smoother to the data to suppress any variability at frequency higher than seasonal cycle. The resulting Pacific SST deviations are similar to the SST anomalies derived by removing monthly and zonally averaged temperatures. We show Hoffmueller diagrams for the SST deviations along paths in different regions in the Pacific. These paths include latitude lines at 35, 45, and 50 degree north, latitude line at 40 degree south, and paths in north Pacific and along the equator. Both 1987 and 1997-98 El Niņo events as well as the 1984-85, 1989 and 1996 La Niņa events are clearly depicted. We demonstrate spatial propagation of SST waves over interannual scale. Finally, we compare our current results with those from an earlier study using the NASA data of scanning multichannel microwave radiometer.