MPV-Q⁎ view of vorticity development in a saturated atmosphere

Abstract

Based on the three-dimensional moist potential vorticity (MPV) equation and diabatic heating excluding latent heating (Q*), a Lagrangian vertical vorticity equation is deduced for a saturated atmosphere. The convective stability and water vapor are considered in this equation, and the impacts of sensible heating and radiative heating on the vertical vorticity development are focused. This MPV-Q* theory is then applied to a vortex case over the Yangtze-Huaihe River valley of China in 2016. The contributions of the convective stability, MPV and the horizontal component of MPV (MPV2) to the development of vertical vorticity are investigated, and the influence of nonuniform spatial distribution of Q* on the movement of the vortex is expounded.Theoretical deduction and case analysis show that, the more convectively neutral the atmosphere tends to be, the more favorable it is for the vortex development. Q⁎ affects the development of vertical vorticity by affecting MPV. Considering the convective stability, the effect of Q* on vortices can be divided into four scenarios. When the atmosphere is convectively unstable (stable), the increase (decrease) in MPV2 will lead to an increase in vertical vorticity. Furthermore, the case analysis reveals that the maximum Q* corresponds coincidentally to the high-level clouds, implying the possible effect of cloud radiation.