THE ROTATIONAL DYNAMICS OF ATMOSPHERIC ICE: ELECTRICAL AND AERODYNAMIC TORQUES
WEINHEIMER, ANDREW JOHN
Doctor of Philosophy
The rotational motion of atmospheric ice particles is analyzed to determine the conditions under which the particles align with atmospheric electric fields. The particle shapes are approximated by prolate and oblate spheroids and may be treated as conductors or dielectrics, depending on the speed of the rotation in relation to the electric response times. At low Reynolds numbers, the electrical torque is opposed by a Stokes drag torque. The resulting equation of motion is that of a damped pendulum oscillator. At higher Reynolds numbers, the electrical torque competes with an aerodynamic torque which itself attempts to produce an alignment of the ice crystals not necessarily compatible with that for the electrical torque. This aerodynamic torque is investigated in some detail in Chapter 1. In Chapter 2, the dynamics of a spectrum of ice particle shapes and sizes in a wide range of electric fields is examined. Numerical values are obtained for the relevant characteristic times and torque ratios, and the different dynamical regimes are delineated. It is found that electric fields of at least 1 kV/m, or perhaps 10 kV/m, are required to produce significant alignment. The significance of these results and the possibilities for further research are briefly discussed.