The Asymmetric Atmospheric Response to the Midlatitude North Pacific SST Anomalies

Abstract

Forced by Pacific Decadal Oscillation‐related sea surface temperature (SST) anomalies with the same pattern but opposite signs in the western‐central North Pacific, nonlinear wintertime atmospheric responses are produced by a state‐of‐the‐art atmospheric general circulation model (GFDL AM2.1); that is, an obvious equivalent barotropic geopotential low appears over the cold SST forcing (“CSST”), whereas a weak baroclinic structure shows up corresponding to the warm SST forcing (“WSST”), and both of them have similar characteristics in the lower troposphere. Specifically, because of the relatively dry environment in the central North Pacific, nonlinear responses of moisture process including latent heat flux and low‐level atmosphere moisture advection induce asymmetric diabatic heating (Qd): in WSST, Qd tends to increase in the middle‐lower troposphere but decrease in the middle‐upper level, whereas it always increases in the whole troposphere in CSST. Thus, Qd has the same low‐level positive vertical gradient in both CSST and WSST, which produces similar atmospheric circulation anomalies in the lower troposphere. In turn, the asymmetric responses of low‐level temperature advection further modify air temperature meridional gradient as well as atmospheric baroclinicity in the lower troposphere, significantly shifting the transient eddy activities southward in CSST and greatly weakening their intensity in WSST, respectively. Accordingly, the transient eddy vorticity forcing primarily determines the upper‐level atmospheric responses in CSST, but it has unsystematic effects in WSST that are overtaken by Qd. Therefore, the dominance of diabatic heating in WSST and transient eddy forcing in CSST over the central North Pacific lead to the asymmetric atmospheric responses among which the asymmetry of moisture plays an essential role.

PDO-Related Wintertime Atmospheric Anomalies over the Midlatitude North Pacific: Local versus Remote SST Forcing

“…3c,d), but the amplitude is greatly reduced. A simplified modeling study presented similar evidence that PDO-like cold SST anomalies in the midlatitude North Pacific can trigger a significant dipole mode of westerly jet response (Tao et al 2019).…”

Prolonged Periodicity and Eastward Shift of the January North Pacific Oscillation Since the Mid‐1990s and Its Linkage With Sea Ice Anomalies in the Barents Sea

“…Figures 3f and 16). Therefore, probably by extratropical air‐sea interaction (Kushnir et al, 2002; Peng & Whitaker, 1998; Tao et al, 2019), the horseshoe SST anomalies in the preceding October may play a role in the changes of properties of the January NPO around the mid‐1990s.…”

Midlatitude unstable air-sea interaction with atmospheric transient eddy dynamical forcing in an analytical coupled model

“…Changes in SST, particularly in the midlatitude oceanic frontal zones, have the potential to influence the activities of storm tracks and the intensity change or meridional shift of eddy-driven jet (Nakamura et al 2008;Small et al 2014;Xiao et al 2016;Wang et al 2017). The possible dynamical processes in which the midlatitude SST anomalies affect the seasonal-mean atmospheric circulation include the direct diabatic heating (Tanimoto et al 2003;Gulev et al 2013;Zhang and Stone 2011;Woollings et al 2016) and the indirect transient eddy thermal and dynamical forcing (Lau and Holopainen 1984;Fang and Yang 2016;Yao et al 2016;Wang et al 2017;Tao et al 2019Tao et al , 2020. There are indications that the midlatitude oceanic thermal anomaly can significantly affect atmospheric transient eddy activities through changing the lower-level atmospheric baroclinicity (Brayshaw et al 2011;Gan and Wu 2015), and then the nonlinear transport of heat and momentum by transient eddies can feedback to the time-mean flow.…”