Modification of the Baroclinic Instability Associated with Positive and Negative Arctic Oscillation Index: A Theoretical Proof of the Positive Feedback

Abstract

The modification of the baroclinic instability associated with positive and negative Arctic Oscillation Index (AOI) is theoretically investigated using a linearized 3D spectral primitive equation model. The linear instability analysis shows that the most unstable Charney mode MC changes its structure to intensify (weaken) the polar jet by the eddy momentum flux associated with the positive (negative) AOI. More importantly, the meridionally dipole Charney mode M2 is modified into the monopole Charney mode M1 to transport eddy momentum flux northward under the positive AOI condition. It is found that this modification is essential to intensify the polar jet during the AOI positive phase. Hence, we have theoretically confirmed that there are positive feedbacks between the baroclinic instability waves and the Arctic Oscillation characterized by the intensity of the polar jet.