We thank Jianhua Sun, Benjamin Green, Matthew Parker, and Rich Rotunno for discussions that benefited this study. The radar mosaics were made available by Chinese National Meteorological Center. This study was partially completed when ZM spent her sabbatical visit at the Penn State University. Computing provided by the Texas Advanced Computing Center (TACC) is acknowledged. ZM is supported by Grants NSFC41075031, NSFC40921160380, and GYHY200906025 from China and FZ is supported by NSF Grant ATM-084065.
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Strictly speaking, it is the shear over the depth of the control volume; the top of the control volume used by Rotunno et al. (1988) was chosen here to be the height at which the control volume–relative wind vanished at the top rear and top forward corners of the volume. This altitude is slightly higher than the mean height of the cold pool.