Comment on “Thermal infrared observations of a western United States biomass burning aerosol plume” by Sorenson et al. (2024)

Abstract

Sorenson et al. (2024) studied fresh smoke plumes from the proximal Dixie fire in northern California and concluded that the smoke cooled the air and Earth surface below the smoke by shielding of incoming solar radiation. The so-attributed cooling was immediate, sudden and on par with diurnal temperature variations. This comment takes issue with their conclusions, reasoning, and method. By examining the same case and others, it is shown that the observed cooling within the smoke plume is caused by plume particulates sufficiently large to intercept and thereby alter upwelling thermal infrared radiation. The evidence presented is the same satellite and radar data employed by Sorenson et al. (2024), but expanded with temporal animations. A key element of the new analysis is the demonstration of smoke-associated cooling at nighttime, a circumstance decoupled from the solar-shielding explanation. The refutation of the proposed solar-shield-cooling in fresh smokes is an essential refinement of the constraints on the radiative cause-effect in such conditions.