Midlatitude unstable air-sea interaction with atmospheric transient eddy dynamical forcing in an analytical coupled mode
- PDF / 4,449,050 Bytes
- 21 Pages / 595.276 x 790.866 pts Page_size
- 6 Downloads / 179 Views
Midlatitude unstable air‑sea interaction with atmospheric transient eddy dynamical forcing in an analytical coupled model Lilan Chen1 · Jiabei Fang1 · Xiu‑Qun Yang1 Received: 13 April 2020 / Accepted: 29 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract While recent observational studies have shown the critical role of atmospheric transient eddy (TE) activities in midlatitude unstable air-sea interaction, there is still a lack of a theoretical framework characterizing such an interaction. In this study, an analytical coupled air-sea model with inclusion of the TE dynamical forcing is developed to investigate the role of such a forcing in midlatitude unstable air-sea interaction. In this model, the atmosphere is governed by a barotropic quasi-geostrophic potential vorticity equation forced by surface diabatic heating and TE vorticity forcing. The ocean is governed by a baroclinic Rossby wave equation driven by wind stress. Sea surface temperature (SST) is determined by mixing layer physics. Based on detailed observational analyses, a parameterized linear relationship between TE vorticity forcing and meridional second-order derivative of SST is proposed to close the equations. Analytical solutions of the coupled model show that the midlatitude air-sea interaction with atmospheric TE dynamical forcing can destabilize the oceanic Rossby wave within a wide range of wavelengths. For the most unstable growing mode, characteristic atmospheric streamfunction anomalies are nearly in phase with their oceanic counterparts and both have a northeastward phase shift relative to SST anomalies, as the observed. Although both surface diabatic heating and TE vorticity forcing can lead to unstable air-sea interaction, the latter has a dominant contribution to the unstable growth. Sensitivity analyses further show that the growth rate of the unstable coupled mode is also influenced by the background zonal wind and the air–sea coupling strength. Such an unstable air-sea interaction provides a key positive feedback mechanism for midlatitude coupled climate variabilities. Keywords Midlatitude air-sea interaction · Atmospheric transient eddy vorticity forcing · Parameterization · North Pacific
1 Introduction The air-sea interaction in the midlatitudes is believed to be crucial to understand the mechanisms responsible for the decadal-to-interdecadal climate variability (Latif and Barnett 1996; Miller and Schneider 2000). Many early studies suggested that the sea surface temperature (SST) variability in the midlatitudes is a passive response to the atmospheric forcing (Hasselmann 1976; Frankignoul et al. 1997; Saravanan and McWilliams 1998; Neelin and Weng 1999). Recent study shows that the atmospheric forcing causing * Xiu‑Qun Yang [email protected] Jiabei Fang [email protected] 1
CMA‑NJU Joint Laboratory for Climate Prediction Studies, School of Atmospheric Sciences, Nanjing University, Nanjing, China
midlatitude SST variability is non-stochastic, but associated with some persistent atmospheric anomal
Data Loading...
