Metastable states and coalescence of charged water drops inside clouds and fog

The free energy of the charged drops of water and of light ions inside drop-ionic plasma of clouds and fog was calculated on the basis of the Poisson-Boltzmann equation. It is shown that when the charge is greater than several tens of elementary charge units, the positively and negatively charged drops can have metastable states which are characterized by the space-ordered arrangement of the drops. In general, the drop-ionic plasma has no metastable state. But, in the case that the average charges of positively and negatively charged drops differ in absolute value by less than 10-20%, drop-ionic plasma can have a metastable state as a whole. This state was thought to be responsible for the long confinement of drops in a compact volume and for their subsequent coalescence. It is shown that the electrostatic attraction of drops and their coalescence are capable of explaining the rapid growth of water drops up to rain size inside clouds. (C) 2015 Elsevier Ltd. All rights reserved.