Observations of Boreal Forest Fire Smoke in the Stratosphere

A substantial increase in stratospheric aerosol was recorded between May and October 1998 at high northern latitudes. This phenomenon was recorded in the absence of any reported volcanic eruptions with stratospheric impact potential. The Polar Ozone and Aerosol Measurement III (POAM III) and the Stratospheric Aerosol and Gas Experiment II (SAGE II) satellite-based solar occultation instruments made numerous measurements of aerosol extinction substantially higher than background values three to five km above the tropopause. In addition to these satellite-based vertical profiles, several other detailed measurements by ground-based lidar and balloon-based backscattersonde observed this unusual summer of stratospheric aerosol increase. A comparison of these observations with aerosol index data from NASA's Total Ozone Mapping Spectrometer (TOMS) and forest fire data reveals a strong link between these stratospheric aerosol and forest fire smoke. Our analysis leads us to conclude that smoke from boreal forest fires was lofted across the tropopause in substantial amounts in several episodes occurring in Canada and eastern Russia. The vertical transport of the smoke through the troposphere is accomplished by convection in severe (most likely) supercell thunderstorms. Observations throughout the northern hemisphere summer of 1998 reveal a broad zonal increase in stratospheric aerosol that persisted for at least three months. These observations indicate that there were several episodes of intense boreal forest fire blowups combined with deep convection in 1998.

Boreal forest fires are a routine, natural occurrence that peaks in mid summer. In Canada alone, there are on the order of 30,000 forest fires annually. In some years, a small subset of these fires may develop into the huge wildfires that combine with severe thunderstorms to produce prodigious amounts of smoke and other emissions high in the troposphere and lower stratosphere. In late August 1992 the Upper Atmosphere Research Satellite's (UARS) Cryogenic Limb Array Etalon Spectrometer (CLAES) and Microwave Limb Sounder (MLS) instrument detected anomalous enhancements of stratospheric aerosols and methyl cyanide, respectively. These observations have been traced back to historically intense forest fires near Boise Idaho on August 21 and 22. These and other events in recent history, such as a reported incursion of Canadian forest fire smoke over England in 1950, give a strong indication that long-range, high-altitude, and long-lasting residuals from boreal forest fires are a very real, recurring, and perhaps important phenomenon worthy of continued exploration.

On June 25 2004, in the area of Alaska/Yukon/British Columbia, forest fires erupted into pyro-convective storms that lofted smoke and carbon monoxide to the upper troposphere and lower stratosphere. On several days in late June of 2004 abundant fire, smoke, and convection was found in this region. A stunning photograph of a pyroCb taken from an airliner on June 27, 2004 is displayed below. The photographer, a passenger on a Japan Airlines flight over British Columbia, saw what he initially thought was a volcanic plume, the top of which was at flight level in the UTLS. The pyroCb potential in June 2004 was watched closely because the fire and meteorological conditions were suspected in advance to be ripe for extreme blowup.

Figure 1.   Photograph of a pyro-convective cloud taken by Mr. Noriyuki Todo of Japan Airlines International Corporation. This photo is reproduced here with his permission. Details of the circumstances are: Flight Data ID : JAL009 B747-400 Flying Course : NCA11 Cruising Flight Level : FL340 ( 34,000 feet) Actual Time of Over BINGA (N57 42.1 W125 00.0) at 20hr 48min 27sec UTC on 27JUN2004

Figure 2.   Selected aerosol extinction and backscatter ratio profiles showing stratospheric enhancements between July 9 and 18, 1998. Tropopause height collocated with each profile is shown by a matching color-coded horizontal bar.

Figure 3.   Orthographic projection with isentropic back trajectories from the aerosol layers, as color coded in Figure 1. Each trajectory ends on June 27, 1998. Filled diamonds mark observation points. The trajectories were run on the potential temperature surface of the peak backscatter or extinction ratio. The gray shaded portion of each trajectory shows is parcel location between 12 UTC July 4 and 7. The filled triangle marks Korovin volcano, which erupted on June 30 but did not affect the stratosphere.
Figure 4.   Longitude/time series analysis of POAM III 1 micron aerosol optical depth in a 5-km thick column relative to and starting 2 km above the tropopause. The period is May through October 1998. POAM measurement latitude, which changes gradually, is annotated along the right side. The white bar is a 5-day data gap.
Figure 5.   Lidar backscatter ratio profiles taken by Jeff Thayer, SRI International, on August 23, 1998 near Sondrestromfjord, Greenland (67 N, 51 W). The vertical resolution of the lidar is 100 m. Note the three distinct aerosol layers between 13 and 15 km altitude.
Figure 6.   POAM III extinction ratio profile for August 23, 1998, at 63 N, 51 W, which is approximately 450 km south of the Sondrestromfjord lidar observation shown above. Note the aerosol enhancement between 12 and 15 km altitude, in approximate agreement with the lidar-observed layers. POAM's vertical resolution is 1 km. The local tropopause was at approximately 9 km.
Figure 7.   Profiles of balloon measurements taken by James Rosen, Univ of Wyoming, on Aug 23, 1998 near Saskatoon, Saskatchewan, Canada (52 N, 107 W). The ozone and aerosol remote sensing was by backscattersonde. Note the enhancements of aerosol and ozone between 10.5 and 14.5 km altitude. The collocated temperature profile indicates that the local tropopause was at approximately 10 km.

Selected, Relevant References

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Fromm, M. D., J. Alfred, K. Hoppel, J. Hornstein, R. Bevilacqua, E. Shettle, R. Servranckx, Z. Li, B. Stocks, Observations of boreal forest fire smoke in the stratosphere by POAMIII, SAGE II, and lidar in 1998, Geophys. Res. Lett., 27, 1407-1410, 2000.

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Fromm, M. and R. Servranckx, Transport of forest fire smoke above the tropopause by supercell convection, Geophys. Res. Lett., 30, doi: 10.1029/2002GL016820, 2003.

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Jost, H., K. Drdla, A. Stohl, L.Pfister, M. Loewenstein, J. Lopez, P. Hudson, D. Murphy, D. Cziczo, M. Fromm, T. Bui, J. Dean-Day, M. Mahoney, E. Richard, N. Spichtinger, J. Vellovic, E. Weinstock, J. Wilson, S. Wofsy, In-situ observations of mid-latitude forest fire plumes deep in the stratosphere, Geophys. Res. Lett., 31, L11101, doi:10.1029/2003GL019253, 2004.

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Li, Z., A. Khananian, R. Fraser, J. Cihlar, 2001, Detecting smoke from boreal forest fires using neural network and threshold approaches applied to AVHRR imagery, IEEE Tran. Geosci. & Rem. Sen., 39, 1859-1870.

Livesey, N., M. Fromm, J. Waters, G. Manney, M. Santee, and W. Read, Enhancements in lower stratospheric CH3CN observed by UARS MLS following boreal forest fires, J. Geophys. Res., 109, D06308, doi:10.1029/2003JD004055, 2004.

Siebert, J., C. Timmis, G. Vaughan, K. Fricke, A strange cloud in the Arctic summer 1998 above Esrange (68N), Sweden, Annales Geophysicae, vol.18, 505-509, 2000. Wang, P.K., Plumes above anvils--a newly discovered stratospheric-tropospheric chemical exchange process due to deep convective clouds, Talk A61A-08, Spring Meeting of the American Geophysical Union, May 30-June, 2000.

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