Stratospheric impact of the Chisholm pyrocumulonimbus eruption: 1. Earth-viewing satellite perspective

[1] The pyrocumulonimbus storm near Chisholm, Alberta, on 28 May 2001 has been studied in depth. However, the impact of this eruption on the lower stratosphere has not been characterized. Here and in a companion paper we explore this topic. This paper focuses on the “young” Chisholm smoke plume, from the age of ∼3 h to 1 week, as observed by Earth-viewing satellite instruments. (The companion paper presents strictly profile data.) GOES visible and infrared image loops reveal the pyroconvective life cycle and initial transport of the smoke cloud. MISR stereographic heights are the first of their kind for a stratospheric cloud, showing smoke up to 5 km above the tropopause on 29 May. MODIS IR and visible images are analyzed to give constraints on plume height, thickness, and particle size. Infrared brightness temperature analyses reveal unique aspects of the “day-after” Chisholm plume. Particle sizes are 1/3 to 1/2 compared to normal cirrus crystals. The daytime 29 May plume is optically thick at tropopause temperatures yet smoky brown. A transition from deep anvil blow off to “dry” smoke is still occurring after ∼1.5 d. TOMS aerosol index is used as a proxy for areas of particularly high smoke plume altitude. The Chisholm smoke in the upper troposphere and lower stratosphere is traced with AI for 1 week as the plume blows across North America to western Europe. First estimates are made of stratospheric smoke mass in relation to emissions during pyroconvection. The 29 May stratospheric Chisholm pyroCb plume contains a mass between ∼1.39 × 104 and 1.09 × 105 t. This represents between ∼10% and 121% of total particle mass emitted from the fire on 28 May, calling into question some frequently assumed values for smoke single scatter albedo and/or emission estimates. Strictly in terms of mass, the stratospheric Chisholm plume amounted to ∼15% of background Northern Hemispheric stratospheric sulfate aerosol. Overall, the young pyroCb plume is seen to be a peculiar mixture of smoke aerosols and water-ice that confounds operational cloud/aerosol detection routines and exhibits extreme, and still mysterious, composition and life cycle features.