Analysis of Cell Merging from New Cells to Multicell Formation with Dual Doppler and Vorticity Analysis

Abstract

The investigation of merging cells from new cells to multicell in thunderstorms using vertical vorticity analysis will be proposed. The vertical vorticity analysis using pseudovorticity that used only one single radar and Dual Doppler analysis (DDA) vorticity were applied to the rainfall event on 10th September 2014 with the condition of an unstable atmospheric environment with the weak vertical shear. The core pair vorticity was identified by selecting the maximum quantitative vorticity intensity at each boundary of the new cell and multicell. The comparison of time series core pair vorticity was established before, during, and after the merging cells. It was found that at the early stage of merging cells, new cell B indicated the largest intensity with cell A (older cell), whereas other new cells showed lower strength compared with the multicell after the later stage of multicell formation. This signature pattern was identical for the pseudo-vorticity and DDA vorticity analysis. By employing vertical velocity analysis, the core of the updraft was located between the pair of vorticities which influenced the construction of vertical vortex tubes with the existence of weak wind shear. The supportive mechanism that resulting in the intensification of core pair vorticity was established by examining the convergence, stretching, and tilting of the vortex tube. The convergence plays the main role in the intensification of core vorticity which influenced the stretched of vortex tube to rotate rapidly that generated the increment of core vorticity, meanwhile tilting was less affected to this increment pattern. In conclusion, the signature pattern of merging cells could be observed on the strength of core pair vorticity during the merging cells.