THE PYROCONVECTIVE PATHWAY FOR STRATOSPHERIC WATER VAPOR AND AEROSOL

A detailed analysis of pyrocumulonimbus (pyroCb) cases is presented that explores their convective dynamics, stratospheric plume characteristics and down-stream radiative effects. Satellite observations in conjunction with ground station data and radiative transfer models are used to quantify the impact that pyroCbs have on localized stratospheric aerosol and water vapor. The initial meteorological and fire conditions are explored using a cloud- and aerosol-resolving model to determine the dominant mechanics driving the convection and their effects on microphysics. Results show that intense sensible heat fluxes are the dominant convection trigger over a wildfire in an unstable atmosphere. Direct observations by cloud profiling radar of the active convective stage of a pyroCb are analyzed for the first time, and comparisons with non-pyro meteorological deep convection in the same vicinity and season show that the pyroCb has an extreme delay in the growth of precipitation-sized cloud droplets to altitudes above the homogeneous freezing level.Stratospheric aerosol plume morphology is analyzed for several cases, and an empirical heat accumulation efficiency model is developed to describe observed radiatively-induced self-lofting in the stratosphere. The model results suggest pyroCb aerosol plumes are ∼ 30% efficient at converting shortwave radiative heating into sensible heating, thereby driving buoyant uplift once injected into the stratosphere. PyroCbs directly inject H2O vapor into the stratosphere, which is shown to be significantly large for two separate cases. The cloud-resolving model confirms a previous hypothesis that uniquely small ice particle microphysics can enhance stratospheric H2O in detrained convective anvils. Satellite retrieval evidence suggests plume water vapor anomalies are a result of inefficient removal of small ice particles within the detrained pyroCb anvil. Model-injected total water—represented as the sum of all ice and absolute humidity—shows at least 30% of H2O survives the convective detrainment stage, and diminishes within the evolving plume over the observation period when using satellite observations of H2O as a benchmark. In the plumes presented herein, pyroCb H2O anomalies are as large as 4±3 ppmv above the background in the lower stratosphere. Detailed line-by-line radiative transfer simulations suggest that these anomalies produce an instantaneous longwave radiative forcing up to +1.0 W m −2 at the tropopause