Wednesday, 9 November 2016
Broadway Rooms (Hilton Portland )
The impact of various assumptions in the microphysical parameterization--such as the assumed initial cloud condensation nuclei (CCN) concentration--on simulations of supercells and associated tornadoes has been well documented by many recent studies. Most of these studies, however, have focused on supercells forming in environments of high CAPE more typical of the Great Plains of the U.S. Strong sensitivity to aspects of supercell behavior such as cold pool strength and tornadogenesis potential have been revealed by these experiments. In the case of initial CCN concentration, studies have tended to show a trend toward weaker cold pools and greater tornadogenesis potential with increasing values. However, it is unknown to what extent these sensitivities transfer to supercells evolving in environments of relatively low CAPE, weak low-level lapse rates, and deep moist layers, which are more commonly seen in the cool season in the southeastern U.S. During the 2016 VORTEX-SE field program, several targeted observations of tornadic and nontornadic supercells in relatively low CAPE environments were made, including atmospheric soundings characteristic of the inflow environment of these storms.
In this study, suitable proximity soundings for two different supercell cases from the VORTEX-SE program are used to initialize horizontally-homogeneous high-resolution (250 m grid spacing and smaller) idealized simulations that utilize a triple-moment bulk microphysics scheme. The sensitivity of 1) cold pool strength, and 2) tornadogenesis to the assumed initial CCN concentration are assessed and compared with similar simulations of tornadic supercells in high-CAPE environments from the recent VORTEX-2 field program (2009-2010). The question of the extent to which the overall sensitivity of these storm characteristics to the assumed CCN concentration differs in the aforementioned VORTEX-SE vs. VORTEX-2 environments will be discussed.
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