Decadal and Multi-decadal Contributions to the Anomalous Zonal Tropical Pacific Temperature Gradient and the Associated Global Impacts

A strengthening of the anomalous zonal tropical Pacific sea surface temperature (SST) gradient (hereafter referred to as the gradient) during La Niņa events has been linked with global climatic extremes, most notably the historical dry years over areas such as East Africa and Western Asia during the last decade. Here, we examine the decadal and multi-decadal variations of the gradient and its impacts on previously identified continental areas sensitive to SST gradients across the Pacific.

Long-term changes to the gradient result from the synchronous behavior of Pacific decadal variability (PDV) and the trend in Pacific SST. PDV is primarily responsible for the semi-regular SST changes over the central and eastern tropical Pacific Ocean while the trend is primarily responsible for the warming (cooling) of SST over the west Pacific (central Pacific). The warming of the west Pacific Ocean has resulted in a stronger gradient during the negative phase of PDV and a weaker gradient during the positive phase of PDV.

Successive negative PDV events since the early 20th century have been associated with stronger gradients due to the continued warming of the west Pacific Ocean. The stronger gradients during successive PDV events throughout the 20th century have been linked to an intensification of the anomalous circulations and drying across much of the Northern Hemisphere, including North America, the Middle East, Africa, and Western Asia.