TRMM observed first direct evidence of smoke from forest fires inhibiting rainfall

Although it has been known that smoke from biomass burning suppresses warm rain processes, it was not known to what extent this occurs. The satellite observations of the Tropical‐Rainfall‐Measuring‐Mission (TRMM), presented here, show that warm rain processes in convective tropical clouds infected by heavy smoke from forest fires are practically shut off. The tops of the smoke‐infected clouds must exceed the freezing level, i.e., grow to altitudes colder than about −10°C, for the clouds to start precipitating. In contrast, adjacent tropical clouds in the cleaner air precipitate most of their water before ever freezing. There are indications that rain suppression due to air pollution prevails also in the extra‐tropics.