HR: 17:00h
AN: SA54A-03 INVITED     [Abstracts]
TI: Giant Dipole Moments of Submicron Ice Crystallites Nucleated on Dust Particles Cause Polarization Catastrophe, Sprites
AU: * Handel, P H
EM: handel@umsl.edu
AF: University of Missouri St. Louis, Physics-Astronomy Dept, Ctr. Molec. Electronics, St. Louis, MO 63131, United States
AB: Supersaturation of water vapor in the atmosphere is known to be low, limited to just a few percent, because the nucleation processes of water aggregates and ice crystallites are heterogeneous. Nucleation is on dust particles, known as aerosol particles. Ice nuclei are often sub-micron SiO2 particles. The ice crystallite formed on such a nucleus is different from bulk ice, which has a hindered ferroelectric transition at 78 K, according to Hentschel's calculation and to other, Japanese studies. At this transition temperature the free energy difference between the ordered and disordered states is zero, DF=0. However, the thin ice layer deposited on the nucleus has a preferential direction, the radial direction, roughly perpendicular to the surface. This spoils in the crystallite the isotropy characterizing bulk ice. Therefore, in the free energy difference DF=DU- TDS, between the entropy difference DS that tries to lower the transition temperature, and the internal energy difference DU, the entropy term looses much of its importance. Therefore, the ferroelectric transition temperature of a sub-micron, heterogeneously nucleated, ice crystallite will be much higher, close to the melting temperature of bulk ice. For temperatures below 253 K this could remain valid even for slightly larger crystallites, almost up to 10 microns. The present paper is focused on this collective ordering effect. The ferroelectric transition is never observed in bulk ice, because the activation energy needed to achieve ferroelectric ordering is prohibitive, and causes the transition time to be infinite. On the other hand, at the much higher temperature estimated for the small, defect ridden, ice crystallites, the transition time is finite and the crystallites grow from the beginning with a ferroelectric saturation polarization. This causes each crystallite to have a giant dipole moment, and causes the whole cloud of crystallites to lapse into a Clausius-Mossotti type polarization catastrophe or self-alignment transition that lowers the free energy of the cloud. The criterion for this to happen is satisfied by almost all clouds, but the polarization is continuously compensated by masking charges. Finally, when the PC breaks down, lightning, sprites, elves, blue jets, P-H pulses result from the masking charges of cumulo-nimbus clouds.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 6020 Ices
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly