Simulating the Black Saturday 2009 smoke plume with an interactive composition‐climate model: Sensitivity to emissions amount, timing, and injection height

Abstract

We simulated the high‐altitude smoke plume from the early February 2009 Black Saturday bushfires in southeastern Australia using the NASA Goddard Institute for Space Studies ModelE2. To the best of our knowledge, this is the first single‐plume analysis of biomass burning emissions injected directly into the upper troposphere/lower stratosphere (UTLS) using a full‐complexity composition‐climate model. We compared simulated carbon monoxide (CO) to a new Aura Tropospheric Emission Spectrometer/Microwave Limb Sounder joint CO retrieval, focusing on the plume's initial transport eastward, anticyclonic circulation to the north of New Zealand, westward transport in the lower stratospheric easterlies, and arrival over Africa at the end of February. Our goal was to determine the sensitivity of the simulated plume to prescribed injection height, emissions amount, and emissions timing from different sources for a full‐complexity model when compared to Aura. The most realistic plumes were obtained using injection heights in the UTLS, including one drawn from ground‐based radar data. A 6 h emissions pulse or emissions tied to independent estimates of hourly fire behavior produced a more realistic plume in the lower stratosphere compared to the same emissions amount being released evenly over 12 or 24 h. Simulated CO in the plume was highly sensitive to the differences between emissions amounts estimated from the Global Fire Emissions Database and from detailed, ground‐based estimates of fire growth. The emissions amount determined not only the CO concentration of the plume but also the proportion of the plume that entered the stratosphere. We speculate that this is due to either or both nonlinear CO loss with a weakened OH sink or plume self‐lofting driven by shortwave absorption of the coemitted aerosols.

Pyroconvection Risk in Australia: Climatological Changes in Atmospheric Stability and Surface Fire Weather Conditions

“…Although the focus of this study is on climatological features, rather than individual case studies of events, it is noted that the compound event days include both of the cases observed in Australia for which the pyroconvection was strong enough to inject biomass into the stratosphere; for the Canberra fires in eastern Australia during January 2003 and Black Saturday in southeastern Australia during February 2009 (Cunningham & Reeder, 2009;Dowdy et al, 2017;Field et al, 2016;Fromm et al, 2006;McRae et al, 2013;Mills & McCaw, 2010). For the Canberra and Black Saturday events, CH values are 13.5 and 13.4, respectively, and FFDI values are 56 and 136, respectively, all of which are the highest on record at each location for the study period 1979-2016 with the exception of FFDI at Canberra (which is above the 99.8th percentile for that location).…”

“…A number of disastrous fire events associated with pyroconvection have recently occurred in Australia (Cunningham & Reeder, 2009;Dowdy et al, 2017;Field et al, 2016;Fromm et al, 2006;McRae et al, 2013;Mills & McCaw, 2010) and other regions of the world (Fromm et al, 2010;Lang & Rutledge, 2006;Lang et al, 2014;Peterson et al, 2017;Rosenfeld et al, 2007). Extreme fire events associated with pyroconvection have only been discussed relatively recently in the literature, with available reports of PyroCbs primarily occurring in recent decades (Fromm et al, 2010).…”

Radiative Forcing and Stratospheric Warming of Pyrocumulonimbus Smoke Aerosols: First Modeling Results With Multisensor (EPIC, CALIPSO, and CATS) Views from Space

“…To represent the vertical variation in the smoke plumes and to allow for direct stratospheric injection of pyroCb smoke emissions, we must incorporate injection heights with the pyroCb emission estimates from Peterson et al (2018). Altitude of emission injection has been shown in many previous studies to be significant in determining aerosol transport and residence time (Colarco et al, 2004;Field et al, 2016;Leung et al, 2007;Turquety et al, 2007;Val Martin et al, 2010). Similarly, modeled radiative forcings can also be sensitive to emission injection heights (Ban-Weiss et al, 2012;.…”

Future changes in extreme weather and pyroconvection risk factors for Australian wildfires

“…Wildfires with extreme pyroconvection have recently caused severe impacts in Australia, including the deaths of many people. Examples include the Black Saturday (February 2009) and Canberra fires (January 2003) in southern Australia which had pyroconvection strong enough to produce pyroCb that injected smoke into the stratosphere 1,6,12,13 . This volcano-like process has also been documented for extreme pyroconvection events in other regions including in North America 3,7,14–16 .…”