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The Mechanics of Falling Hailstones and Hailswaths Kevin Vermeesch and Ernest Agee

The Mechanics of Falling Hailstones and Hailswaths Kevin Vermeesch and Ernest Agee Department of Earth and Atmospheric Sciences, Purdue University. Objectives

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The Mechanics of Falling Hailstones and Hailswaths Kevin Vermeesch and Ernest Agee

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  1. The Mechanics of Falling Hailstones and Hailswaths Kevin Vermeesch and Ernest Agee Department of Earth and Atmospheric Sciences, Purdue University • Objectives • Develop a set of mechanical equations for calculating hailstone fall velocities and characteristics for a variety of thunderstorm and atmospheric conditions • Plot hailswaths for real atmospheric events and compare with model results • Physical Properties in the Model Equations • Density profile of atmosphere • Diameter and mass of spheroidal hailstones • Drag coefficient for subcritical Reynolds number flow • Translational speed of supercell thunderstorm • Updraft velocity profile of the supercell thunderstorm • Rotational velocity profile of embedded mesocyclone • Spherical vs. non-spherical hailstone and related Re and CD Cases and Model Results Cases Testing Fall Speeds Re < Rec Re > Rec Hailswaths In a size-sorted hailswath, the largest hail lands closest to the mesocyclone (or tornado track if present). The dimensions of the swath are a function of the thunderstorm’s rotational velocity (vθ), translational velocity (u), and mesocyclone radius. The image on the right shows a portion of the mesocyclone and underlying wall cloud, flanked by a spectacular hailshaft that produces the hailswath. Knight and Knight (2005), Figure 9 Hailstone shapes range from being nearly spherical and smooth to very irregular, containing knobs, lobes, or spikes on their surface. The smooth stones fall under conditions of subcritical Reynolds flow, while the irregular shapes may achieve supercritical flow conditions. Size-sorted hailswath produced by model Graphical verification of model terminal velocity with Knight and Knight (2001) References Knight, C.A. and N.C. Knight, 2001: Hailstorms. Severe Convective Storms,Meteor. Monogr., No. 50, Amer. Meteor. Soc., 223-249. Knight, C.A. and N.C. Knight, 2005: Very large hailstones from Aurora, Nebraska. Bull. Amer. Meteor. Soc., 86, 1773-1781. 3 April 1974 tornado tracks and hailswath in Indiana Knight and Knight (2001), Figure 6.2

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