A251-12
The Climate Response to Megafires: Uncertainty Quantification for the 2017 British Columbia Stratospheric Mass Injection Event

Thursday, 17 December 2020: 04:33
Virtual
Steve Guimond, University of Maryland Baltimore County, Department of Physics, Baltimore, MD, United States, Gennaro D'Angelo, Los Alamos National Laboratory, Theoretical Division, Los Alamos, NM, United States, Manvendra Krishna Dubey, Los Alamos National Laboratory, Los Alamos, NM, United States and Jon M Reisner, Los Alamos National Laboratory, XCP-4, Los Alamos, NM, United States
Abstract:
Recent observations of megafires in California, British Columbia and Australia have sparked new questions about the two-way couplings between the troposphere and stratosphere that impact climate. Specifically, the August 2017 British Columbia Pyrocumulonimbus (PyroCb) event injected 0.1 – 0.3 Tg of smoke into the lower stratosphere where it projected quickly onto climate scales. The observed stratospheric mass removal time scale was estimated at ~ 4 – 6 months. We perform global simulations of the atmospheric response to the 2017 PyroCB event with the NASA GEOS-5 and NCAR CESM models to quantify the impact of key uncertainties: stratospheric injection height, black carbon (BC) mass fraction, particle size and resolution (e.g. sub-grid-scale effects). A parallel abstract in this session (Reisner et al.) models the convective injection of smoke into the stratosphere from fire sources at the ground to establish the coupling to the climate model.

The NASA GEOS-5 is a general circulation model with reanalysis wind fields, fully coupled radiation and resolved BC and organic carbon aerosols. Simulations are performed at 2.0-degree and 1.0-degree resolutions with 72 vertical levels and no chemistry model is employed. NCAR’s CESM is a global Earth System Model that can be used to simulate climate scales. Simulations are performed in a fully coupled and fully prognostic configuration, at about a 2.0-degree horizontal resolution and up to an altitude of about 140 km. A simple smoke flux profile is inserted into each model for a 5 h time period to approximate the observed PyroCb event.

The results show that both modeling systems produce stratospheric mass removal time scales within the margin of observational error with the following settings: 2% BC by mass, 300-350 nm mean particle radius, ~ 13 km injection height with 0.2 Tg of smoke. With these settings, the peak height of the plume was estimated to be 18 – 19 km; in agreement with recent studies. However, lower peak height values have been documented and are being examined further. Our simulated removal time scale is solely driven by plume dynamics (smoke self-lofting from radiative effects, transport and sedimentation) and may not require a chemical sink.

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