Characteristics of low-level meso-γ-scale vortices in the warm season over East China

Abstract This work firstly studies the radar climatology of low-level meso-γ-scale vortices (MVs) occurred in the warm season of East China. Two kinds of MVs are considered which are, respectively, produced by isolated cells and mesoscale convective systems (MCSs). Results show that MVs most often occur in June and July. For MCS-type MVs, there is a high occurrence frequency in the late afternoon and early evening, while no apparent diurnal variation is found for cell-type ones. Moreover, MCS-type MVs tend to be stronger and longer-lived due to their favorable environment conditions of higher convective available potential energy (CAPE) and larger vertical wind shear. Compared to the supercell MVs in southeastern United States, the cell-type MVs in East China are much weaker and shorter-lived, indicating a lower occurrence frequency of supercells and thus prevailing of low-level MVs in East China than in the United States. The MCS-type MVs in East China mainly form in the developing and mature stages of their parent system which suggests that the cold-pool induced baroclinic vorticity plays a major role in the genesis of MV. This seems to be different from the MVs produced by quasi-linear convective systems (QLCSs) in the United States where frictional vorticity owing to surface drag contributes more significantly to MV genesis. Given their higher damaging potential, tracking of MVs within MCSs based upon the linear, least squares derivatives (LLSD) azimuthal shear used in this work would be helpful for the operational warning and forecasting of severe convective weather in East China.