Influence of Kuroshio Extension Variability on the North Pacific Atmosphere and Pacific Decadal Precession

Abstract

Abstract Recent research has revealed links between a quasi-decadal mode of climate variability over the North Pacific – the Pacific Decadal Precession (PDP) – and the North Pacific’s western boundary currents extension – the Kuroshio Extension (KE). It is suggested that on decadal time scales the PDP both responds to and influences the KE variability. A question yet to be answered is whether it is the large-scale or the mesoscale variations of the KE region that influence the overlying and downstream atmosphere and hence the PDP evolution. Using high-resolution sea surface temperature data (1981-2018) from the global ocean Operational Sea Surface Temperature (SST) and Sea Ice Analysis, low resolution Extended Reconstructed SST (ERSST) version 3b data (1949-2018), geopotential height reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) we find that it is the large-scale variations in the KE region that correlate best with the overlying and downstream atmosphere instead of the mesoscale variations. In particular, the second mode of the large-scale KE region, which is characterized by warming (cooling) of the ocean south (north) of the KE, sets up a PDP-like north-south atmospheric pressure dipole over the North Pacific Ocean by altering the large-scale baroclinicity of the atmosphere and zonal intensification of a straight jet. In turn, there is a reduction in the zonal propagation of stationary wave energy and an enhancement of the climatological zonal wave heights over North America, which results in a downstream response over the North American continent and the formation of a subsequent east-west pressure dipole over the North Pacific and North American continent. As a result, there is a strong correlation between large-scale variations in the KE region and the evolution of the PDP over the next three years.