Evidence of the cloud lifetime effect from wildfire-induced thunderstorms

A case study is presented of pyro-cumulonimbi (pyroCbs) forming over Canadian forest fires. Cloud-top ice effective radius values of these pyroCbs are significantly smaller than are those within surrounding convection. The smoke provides a massive source of cloud condensation nuclei (CCN), resulting in smaller cloud droplets which freeze homogeneously at temperatures around -40 degrees C and produce very small ice crystals. It is also shown that the pyroCb anvils persist 6-12 hours longer than convectively-generated cirrus anvils from nearby convection. This provides evidence for the so-called cloud lifetime effect, an aerosol indirect effect identified by the most recent Intergovernmental Panel on Climate Change (IPCC) report. Citation: Lindsey, D. T., and M. Fromm (2008), Evidence of the cloud lifetime effect from wildfire-induced thunderstorms, Geophys. Res. Lett., 35, L22809, doi:10.1029/2008GL035680.