The long-term transport and radiative impacts of the 2017 British Columbia pyrocumulonimbus smoke aerosols in the stratosphere

Abstract

Abstract. Interactions of meteorology with wildfires in British Columbia,\nCanada, during August\xa02017 led to three major pyrocumulonimbus (pyroCb)\nevents that resulted in the injection of large amounts of smoke aerosols and\nother combustion products at the local upper troposphere and lower\nstratosphere (UTLS). These plumes of UTLS smoke with elevated values of\naerosol extinction and backscatter compared to the background state were\nreadily tracked by multiple satellite-based instruments as they spread\nacross the Northern Hemisphere (NH). The plumes were observed in the lower\nstratosphere for about 8–10\xa0months following the fire injections, with a\nstratospheric aerosol e-folding time of about 5 months. To investigate the\nradiative impacts of these events on the Earth system, we performed a number\nof simulations with the Goddard Earth Observing System (GEOS) atmospheric\ngeneral circulation model (AGCM). Observations from multiple remote-sensing\ninstruments were used to calibrate the injection parameters (location,\namount, composition and heights) and optical properties of the smoke\naerosols in the model. The resulting simulations of three-dimensional smoke\ntransport were evaluated for a year from the day of injections using daily\nobservations from OMPS-LP (Ozone Mapping Profiler Suite Limb Profiler). The\nmodel-simulated rate of ascent, hemispheric spread and residence time (or\ne-folding time) of the smoke aerosols in the stratosphere are in close\nagreement with OMPS-LP observations. We found that both aerosol self-lofting\nand the large-scale atmospheric motion play important roles in lifting the\nsmoke plumes from near the tropopause altitudes (∼\u200912\u2009km) to\nabout 22–23\u2009km into the atmosphere. Further, our estimations of the\nradiative impacts of the pyroCb-emitted smoke aerosols showed that the smoke\ncaused an additional warming of the atmosphere by about 0.6–1\u2009W/m2\n(zonal mean) that persisted for about 2–3 months after the injections in\nregions north of 40∘\u2009N. The surface experienced a comparable magnitude\nof cooling. The atmospheric warming is mainly located in the stratosphere,\ncoincident with the location of the smoke plumes, leading to an increase in\nzonal mean shortwave (SW) heating rates of 0.02–0.04\u2009K/d during September\n2017.\n