Electrification in mesoscale updrafts of deep stratiform and anvil clouds in Florida

Size distributions with numerous small- and intermediate-sized ice crystals (mostly aggregates) and large aggregates were observed in these regions. We infer that the uniform electric field, radar reflectivity, and broad particle size distributions were the result of mesoscale updrafts, confirmed by high-resolution images of particles showing diffusional growth and no riming.

No measurable supercooled liquid water was found in these regions from -10 to -45 degrees C. Calculated particle collision rates from observed distributions were >5x10(3) collisions per cubic meter per second in this volume. Laboratory results show that weak charge separation occurs when ice particles collide and separate even in the absence of supercooled water. We infer that charge separation occurred in the mesoscale updrafts via a noninductive mechanism in which ice particles growing by diffusion collide and transfer charge without supercooled water being present.