Aspects of potential vorticity circulation in the Northern Hemisphere: climatology and variation

Abstract

This study revisits the concept of potential vorticity (PV) circulation (PVC) and presents new findings. Results suggest that PVC can cross the isentropic surface. The gross PV in the Northern Hemisphere (NH) depends solely on the total flux of PVC crossing the atmospheric upper boundary, bottom, and cross-section along the equator. In terms of climate, the cross-upper boundary PVC flux is critical for forming the positive basic state of the gross PV in the NH. In terms of variation, a cancelation intrinsically rooted in the PV dynamics between the cross-upper boundary PVC flux and cross-equator PVC flux means that the NH’s gross PV anomaly is largely determined by the cross-bottom PVC flux. Further analysis sheds light on a seminal atmospheric process in which anomalous PVC inflowing from the NH’s upper boundary outflows from the cross-section along the equator and vice versa. An analysis of the quasi-biennial oscillation verifies the process. All results imply that the PVC is a novel tool for examining the interaction between the upper and lower levels of the atmosphere and the interaction between hemispheres.