Glaciation temperatures of convective clouds ingesting desert dust, air pollution and smoke from forest fires

Abstract

] Heavy aerosol loads have been observed to suppresswarm rain by reducing cloud drop size and slowing dropcoalescence. The ice forming nuclei (IFN) activity of thesame aerosols glaciate the clouds and create ice precipitationinstead of the suppressed warm rain. Satellite observationsshow that desert dust and heavy air pollution over East Asiahave similar ability to glaciate the tops of growing convec-tive clouds at glaciation temperature of Tg <∼−20°C,whereas similarly heavy smoke from forest fires in Siberiawithout dust or industrial pollution glaciated clouds atTg ≤−33°C. The observation that both smoke and air pollu-tion have same effect on reducing cloud drop size impliesthat the difference in Tg is due to the IFN activity. Thisdependence of Tg on aerosol types appears only for cloudswith r