ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-12-6989-2012 Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear Riemer M. 1 Montgomery M. T. 2 3 Nicholls M. E. 4 Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany Department of Meteorology, Naval Postgraduate School, Monterey, California, USA NOAA's Hurricane Research Division, Miami, Florida, USA University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, USA 07 03 2012 12 3 6989 7038 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/12/6989/2012/acpd-12-6989-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/12/6989/2012/acpd-12-6989-2012.pdf

Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, &theta;<sub>e</sub>) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we here survey and diagnose five additional numerical experiments with some modifications of the experimental setup to assess the robustness of our previous results. The modifications comprise the values of the exchange coefficients of surface heat and momentum fluxes, the inclusion of experiments with ice microphysics, and the consideration of weaker, but still mature tropical cyclones. <br><br> In all experiments, the depression of the inflow layer &theta;<sub>e</sub> values is significant and all tropical cyclones exhibit the same general structural changes when interacting with the imposed vertical wind shear. Tropical cyclones with a higher downdraft activity exhibit a more pronounced depression of inflow layer &theta;<sub>e</sub> <i>outside</i> of the eyewall in our experiments. The magnitude of the &theta;<sub>e</sub> depression <i>underneath</i> the eyewall early after shear is imposed in our experiments correlates well with the magnitude of the ensuing weakening of the respective tropical cyclone. Based on the evidence presented, it is concluded that the newly proposed framework is a robust description of intensity modification in our suite of experiments.

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