Biomass-burning aerosol effects on convective cloud properties and in the detrained UTLS environment: a pyroCb case study

Abstract:

On 5 August 2014 at approximately 1800 UTC, a wildfire complex (14WB-025) south of Great Slave Lake (GSL) in the North West Territories of Canada began producing a large pyrocumulonimbus (pyroCb). The phenomena was captured at multiple times and viewing geometries from a large assortment of geostationary (GOES) and polar-orbiting (A-Train and Suomi-NPP) satellites. Between 1945 and 2000 UTC, a large anvil had formed atop the intensifying pyroCb, and at approximately 2020 UTC, the A-Train passed directly over the active pyroCb column. This overpass allowed for a rare penetration into the internal structure of this type of convection with nadir-viewing instruments: the CloudSat radar (94 GHz) and the CALIOP lidar (1064 and 532 nm). Thermal infrared (10.8 um) brightness temperatures from MODIS at the time of the A-Train overpass were lower than -60 C, which, in combination with the ~13.5 km height of the overshooting top observed by CALIOP, indicated penetration into the lower stratosphere.

This presentation compares the aerosol-laden GSL pyroCb with a concurrent meteorological cumulonimbus (pristine environment, classical Cb) that developed within the same region. The large-scale synoptic conditions which preface the pyroCb and Cb formation are similar, but CloudSat and CALIOP indicate two very different internal convective structures, much of which may be attributable to aerosol loading. Many interesting aspects of this case study will be discussed, including: i) insights gained by the observations of the external morphology and internal convective structure by passive and active sensors, ii) the impact of the heavy smoke loading on pyroCb microphysics, iii) the long lifetime of the detrained pyroCb ice anvil compared to pristine environment Cb and iv) the increase in stratospheric water vapor from the detrained anvil.