A comparison of two kinds of eastward-moving mesoscale vortices during the mei-yu period of 2010

Abstract

During the mei-yu period, the east edge of the Tibetan Plateau and the Dabie Mountain are two main sources of eastward-moving mesoscale vortices along the mei-yu front (MYF). In this study, an eastward-moving southwest vortex (SWV) and an eastward-moving Dabie vortex (DBV) during the mei-yu period of 2010 have been investigated to clarify the main similarities and differences between them. The synoptic analyses reveal that the SWV and DBV were both located at the lower troposphere; however, the SWV developed in a “from top down” trend, whereas the DBV developed in an opposite way. There were obvious surface closed low centers corresponding to the DBV during its life span, whereas for the SWV, the closed low center only appeared at the mature stage. Cold and warm air intersected intensely after the formation of both the vortices, and the cold advection in the SWV case was stronger than that in the DBV case, whereas the warm advection in the DBV case was more intense than that in the SWV case. The Bay of Bengal and the South China Sea were main moisture sources for the SWV, whereas for the DBV, in addition to the above two moisture sources, the East China Sea was also an important moisture source. The vorticity budget indicates that the convergence was the most important common factor conducive to the formation, development, and maintenance of the SWV and DBV, whereas the conversion from the vertical vorticity to the horizontal one (tilting) was the most important common factor caused the dissipation of both of the vortices. The kinetic energy (KE) budget reveals that the KE generation by the rotational wind was the dominant factor for the enhancement of KE associated with the SWV, whereas for the DBV, the KE transport by the rotational wind was more important than the KE generation. The KE associated with the SWV and the DBV weakened with different mechanisms during the decaying stage. Furthermore, the characteristics of baroclinic and barotropic energy conversions during the life spans of both vortices indicate that the SWV and DBV both belong to the kind of subtropical mesoscale vortices.