Roles of vertical distributions of atmospheric transient eddy dynamical forcing and diabatic heating in midlatitude unstable air–sea interaction

Abstract

Atmospheric transient eddy dynamical forcing (TEDF)-driven midlatitude unstable air–sea interaction has recently been recognized as a crucial positive feedback for the maintenance of the extratropical decadal variabilities. Our recent theoretical work (Chen et al., Clim Dyn 10.1007/s00382-020-05405-0, 2020) has characterized such an interaction through building an analytical midlatitude barotropic atmospheric model coupled to a simplified upper oceanic model. This study extends the analytical model to including a two-layer quasi-geostrophic baroclinic atmospheric model and then identifies the roles of vertical distributions of atmospheric TEDF and diabatic heating in midlatitude unstable air–sea interaction. It is found that midlatitude air–sea coupling with more realistic vertical profiles of atmospheric TEDF and diabatic heating destabilizes oceanic Rossby wave modes over the entire range of zonal wavelengths, in which the most unstable coupled mode features an equivalent barotropic atmospheric low (high) pressure over a cold (warm) oceanic surface. Spatial structure and period of the most unstable mode are more consistent with the observation than those from in previous model. Although either TEDF or diabatic heating alone can lead to a destabilized coupled mode, the former makes a dominant contribution to the instability. The increase of low-layer TEDF stimulates the instability more effectively if the TEDF in upper layer is larger than in lower layer, while the TEDF in either high or low layers can individually cause the instability. The surface heating always destabilizes the air–sea interaction, while the mid-level heating always decays the coupled mode. The results of this study further confirm the TEDF-driven positive feedback mechanism in midlatitude air–sea interaction proposed by recent observational and numerical experiment studies.

Effect of Oceanic Stochastic Forcing on Wintertime Atmospheric Decadal Variability Over Midlatitude North Pacific

“…As revealed by previous studies, midlatitude SST anomalies can influence atmospheric circulations through both diabatic heating and transient eddy forcing, in which the diabatic heating may act as the triggering factor whereas the transient eddy forcing plays an essential role in generating and maintaining a barotropic structure of “cold trough” or “warm high” response (Fang et al., 2021; Fang & Yang, 2016; Inatsu et al., 2003; Kushnir et al., 2002; Xuguang Sun et al., 2018; Tao et al., 2019). Therefore, the roles of diabatic heating and transient eddy forcing in the influence of stochastic SSTAs on atmospheric circulations are diagnosed.…”

“…Processes of oceanic impact on atmospheric circulations in midlatitudes are more complicated than those in the tropics. Different from the moisture condensation latent heat release‐driven processes in the tropics (Gill, 1980; Hoskins & Karoly, 1981; Jin & Hoskins, 1995; Matsuno, 1966; Sardeshmukh & Hoskins, 1988), the midlatitude SSTAs can influence the mid‐to‐high level atmospheric circulation primarily through the atmospheric transient eddy forcing (Chen et al., 2020; Fang et al., 2021; Fang & Yang, 2011; Tao et al., 2022). The atmospheric transient eddy activity called “storm track” is most active over the midlatitude oceans (Blackmon et al., 1977), and it can efficiently redistribute heat and momentum throughout the troposphere (Holopainen et al., 1982; Hoskins et al., 1983; Lee & Kim, 2003).…”

Midwinter Reversal of the Atmospheric Anomalies Caused by the North Pacific Mode‐Related Air‐Sea Coupling

“…Previous studies provide a clue that oceanic thermal conditions can affect the atmosphere in two possible ways: Direct thermal forcing by diabatic heating and indirect thermal and dynamical forcing by atmospheric transient eddies. Especially the involvement of atmospheric transient eddies makes the processes of ocean influencing atmospheric circulation more complicated (L Chen et al, 2020;Fang et al, 2021;Kushnir et al, 2002;Li & Conil, 2003;S-L Peng et al, 1997;Tao et al, 2019).…”

Cross‐Season Effect of Spring Kuroshio‐Oyashio Extension SST Anomalies on Following Summer Atmospheric Circulation

“…From a thermodynamic perspective, surface heat fluxes from ocean to atmosphere related to the midlatitude SSTAs can directly influence the low‐level air temperature, which is further adjusted by the temperature advection, thus, the atmospheric response initially occurs in the lower troposphere (Brian J. Hoskins & Karoly, 1981; Sun et al., 2018; Tao et al., 2022). Subsequently, changes in low‐level air temperature can influence the atmospheric baroclinicity, leading to anomalous atmospheric transient eddy activities in upper troposphere (L. Chen et al., 2020; Fang et al., 2021; Kushnir et al., 2002; Z. X. Li & Conil, 2003; Peng et al., 1997; Sein et al., 2018). Therefore, a comprehensive understanding of how the midlatitude SSTAs affect the atmosphere requires considering both the roles of diabatic heat forcing and atmospheric transient eddy forcing (L. Chen et al., 2020; Fang et al., 2021; Tao et al., 2023, 2020).…”