Dynamical perturbation of the stratosphere by a pyrocumulonimbus injection of carbonaceous aerosols

Abstract

The Pacific Northwest Pyrocumulonimbus Event (PNE) took place in British Columbia during the evening and nighttime hours between 12 and 13 August 2017. Several pyroconvective clouds erupted on this occasion, and released in the upper troposphere and lower stratosphere unprecedented amounts of carbonaceous aerosols (300 ktn). Only a few years later, an even larger pyrocumulonimbus (pyroCb) injection took place over Australia. This event, named “the Australian New Year (ANY) event”, injected up to 1100 ktn of aerosol between 29 December 2019 and 4 January 2020. Such large injections of carbonaceous aerosol modify the stratospheric radiative budgets, locally perturbing stratospheric temperatures and winds. In this study, we use the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to study the perturbations on the stratospheric meteorology induced by an aerosol injection of the magnitude of the PNE. Our simulations include the radiative interactions of aerosols, so that their impact on temperatures and winds are explicitly simulated. We show how the presence of the carbonaceous aerosols from the pyroCb causes the formation and maintenance of a synoptic-scale stratospheric anticyclone. We follow this disturbance considering the potential vorticity anomaly and the brown carbon aerosol loading and we describe its dynamical and thermodynamical structure and its evolution in time. The analysis presented here shows that the simulated anticyclone undergoes daily expansion–compression cycles governed by the radiative heating, which are directly related to the vertical motion of the plume, and that the aerosol radiative heating is essential in maintaining the anticyclone itself.