Seasonal Anomalies of the Thermal Upwelling Index in the Eastern Pacific Ocean

Seasonal anomalies of the thermal upwelling index are considered using the example of the Pacific upwellings (Chilean, Peruvian, and California), which are part of the eastern boundary upwelling system. It is shown that, for the northern and southern parts of the Pacific upwellings, the peak of the maximum area of the positive ocean surface temperature anomaly in the upwelling zone coincides (with an accuracy of up to one month) with the maximum absolute value of the thermal index. The statement is also true for the negative temperature anomaly, with the exception of the northern part of the Chilean upwelling. In most cases, positive temperature anomalies over the occupied area are significantly larger than negative ones. Temperature anomalies in the upwelling zone are mainly caused by changes in the intensity of upwellings, which, in turn, are associated with variations in the surface wind field. A comparison of the seasonal variability of the thermal index for two twenty-year periods (1982–2001, 2002–2021), as well as a comparison of areas with anomalously increased surface ocean temperatures, showed a slight increase in the northern and southern parts of all Pacific upwellings, with the exception of the southern part of California, which weakened slightly.