Smoking Pyrocumulonimbus: observations from MODIS, MISR, AVHRR, DMSP, GOES and TOMS

On 17 August 2003 in far northeastern Alberta an extreme forest fire near the town of Fort Smith NWT exploded into a pyrocumulonimbus (pyroCb for short). PyroCb have in recent years been confirmed as an agent for deep transport of biomass burning emissions deeply into the lower stratosphere. The Fort Smith pyroCb created a plume of smoke that, on 18 August, was manifested as an optically opaque smoke cloud that spread from the lower troposphere into the lower stratosphere. A remarkable distinction of this pyroCb was that it grew to convective maturity during midday, enabling three true-color sensors (SeaWiFS, Terra MODIS, and Aqua MODIS) to observe the growth and spread of the tropopause-level anvil—and the anvil was smoky in color throughout. In this paper we will give a multiple nadir-viewer description of the entire life cycle of this pyroconvection. In addition to the unique smoky composition of the mature pyroCb, we will show the fire hot spot evolution, the cloud-top changes in terms of IR brightness temperature, an analysis of the cloud top altitude, and the deposition/advection of the smoke pall during and after convection. We will discuss the similarities and differences between the Fort Smith pyroconvection and the other convection that occurred in the vicinity at that time.