Influence of the Meridional Shifts of the Kuroshio and the Oyashio Extensions on the Atmospheric Circulation

Abstract

The meridional shifts of the Oyashio Extension (OE) and of the Kuroshio Extension (KE), as derived from high-resolution monthly sea surface temperature (SST) anomalies in 1982-2008 and historical temperature profiles in 1979-2007, respectively, are shown based on lagged regression analysis to significantly influence the large-scale atmospheric circulation. The signals are independent from the ENSO teleconnections, which were removed by seasonally varying, asymmetric regression onto the first three principal components of the tropical Pacific SST anomalies. The response to the meridional shifts of the OE front is equivalent barotropic and broadly resembles the North Pacific Oscillation/western Pacific pattern in a positive phase for a northward frontal displacement. The response may reach 35 m at 250 hPa for a typical OE shift, a strong sensitivity since the associated SST anomaly is 0.5 K. However, the amplitude, but not the pattern or statistical significance, strongly depends on the lag and an assumed 2-month atmospheric response time. The response is stronger during fall and winter and when the front is displaced southward. The response to the northward KE shifts primarily consists of a high centered in the northwestern North Pacific and hemispheric teleconnections. The response is also equivalent barotropic, except near Kamchatka, where it tilts slightly westward with height. The typical amplitude is half as large as that associated with OE shifts.

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

“…The remote atmospheric response to oceanic fronts and eddies, in comparison to the local response, is generally more difficult to identify using direct observations (Frankignoul et al 2011;O'Reilly and Czaja 2015); hence, most existing studies are based on high-resolution model experiments. A particularly useful experimental strategy for this type of study is a set of twin atmospheric model simulations, one of which is forced by observed SSTs and the other by spatially smoothed SSTs (Xie et al 2002;Minobe et al 2008;Kuwano-Yoshida et al 2010;Small et al 2014b;Piazza et al 2016;X.…”

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“…24). The reason for examining the unfiltered regressions is to separate the relatively fast (order several weeks; Deser et al 2007;Ferreira andFrankignoul 2005, 2008) atmospheric response from the relatively slow atmospheric forcing of the ocean (order several years due to midlatitude Rossby wave adjustment processes; Frankignoul et al 1997). We further isolate the response to North Pacific SST anomalies by removing covariability with the first 3 EOFs of tropical Indo-Pacific SST anomalies through multiple linear regression (Frankignoul et al 2011).…”

“…The reason for examining the unfiltered regressions is to separate the relatively fast (order several weeks; Deser et al 2007;Ferreira andFrankignoul 2005, 2008) atmospheric response from the relatively slow atmospheric forcing of the ocean (order several years due to midlatitude Rossby wave adjustment processes; Frankignoul et al 1997). We further isolate the response to North Pacific SST anomalies by removing covariability with the first 3 EOFs of tropical Indo-Pacific SST anomalies through multiple linear regression (Frankignoul et al 2011). The results show that the atmospheric circulation anomalies undergo a rapid change in sign between 11-and 21-yr lag, such that the spatially extensive positive SLP and negative wind stress curl regressions when the atmosphere leads the subsurface ocean by 1 yr are replaced by statistically significant regressions of the opposite sign localized to the region of positive SST anomalies along the KOE when the atmosphere lags the subsurface ocean by 1 yr (Fig.…”

“Hot Spots” in the climate system—new developments in the extratropical ocean–atmosphere interaction research: a short review and an introduction

“…The frontal SST gradient is, nevertheless, maintained despite the differential heat release into the atmosphere, owing to the deep-ocean mixed layer under the strong surface westerlies with storminess and the differential thermal advection by the confluent warm and cool currents. It has been pointed out that variability of the subarctic frontal zone in the Kuroshio-Oyashio Extension (KOE), a prominent oceanic frontal zone in the North Pacific, generates pronounced decadal SST variability that can force basin-scale atmospheric anomalies, manifested as the anomalous surface Aleutian Low, by modulating stormtrack activity (Frankignoul et al 2011;Taguchi et al 2012). It has been also pointed out that an oceanic frontal zone is important for maintaining the annular-mode variability, which is manifested as variability of the eddy-driven jet (Nakamura et al 2008).…”