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- ItemTropospheric and stratospheric wildfire smoke profiling with lidar: mass, surface area, CCN, and INP retrieval(Katlenburg-Lindau : European Geosciences Union, 2021) Ansmann, Albert; Ohneiser, Kevin; Mamouri, Rodanthi-Elisavet; Knopf, Daniel A.; Veselovskii, Igor; Baars, Holger; Engelmann, Ronny; Foth, Andreas; Jimenez, Cristofer; Seifert, Patric; Barja, BorisWe present retrievals of tropospheric and stratospheric height profiles of particle mass, volume, surface area, and number concentrations in the case of wildfire smoke layers as well as estimates of smoke-related cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations from backscatter lidar measurements on the ground and in space. Conversion factors used to convert the optical measurements into microphysical properties play a central role in the data analysis, in addition to estimates of the smoke extinction-to-backscatter ratios required to obtain smoke extinction coefficients. The set of needed conversion parameters for wildfire smoke is derived from AERONET observations of major smoke events, e.g., in western Canada in August 2017, California in September 2020, and southeastern Australia in January-February 2020 as well as from AERONET long-term observations of smoke in the Amazon region, southern Africa, and Southeast Asia. The new smoke analysis scheme is applied to CALIPSO observations of tropospheric smoke plumes over the United States in September 2020 and to ground-based lidar observation in Punta Arenas, in southern Chile, in aged Australian smoke layers in the stratosphere in January 2020. These case studies show the potential of spaceborne and ground-based lidars to document large-scale and long-lasting wildfire smoke events in detail and thus to provide valuable information for climate, cloud, and air chemistry modeling efforts performed to investigate the role of wildfire smoke in the atmospheric system. © 2021 Albert Ansmann et al.
- ItemHow the extreme 2019-2020 Australian wildfires affected global circulation and adjustments(Katlenburg-Lindau : EGU, 2023) Senf, Fabian; Heinold, Bernd; Kubin, Anne; Müller, Jason; Schrödner, Roland; Tegen, InaWildfires are a significant source of absorbing aerosols in the atmosphere. Extreme fires in particular, such as those during the 2019-2020 Australian wildfire season (Black Summer fires), can have considerable large-scale effects. In this context, the climate impact of extreme wildfires unfolds not only because of the emitted carbon dioxide but also due to smoke aerosol released up to an altitude of 17ĝ€¯km. The overall aerosol effects depend on a variety of factors, such as the amount emitted, the injection height, and the composition of the burned material, and is therefore subject to considerable uncertainty. In the present study, we address the global impact caused by the exceptionally strong and high-reaching smoke emissions from the Australian wildfires using simulations with a global aerosol-climate model. We show that the absorption of solar radiation by the black carbon contained in the emitted smoke led to a shortwave radiative forcing of more than +5ĝ€¯Wm-2 in the southern mid-latitudes of the lower stratosphere. Subsequent adjustment processes in the stratosphere slowed down the diabatically driven meridional circulation, thus redistributing the heating perturbation on a global scale. As a result of these stratospheric adjustments, a positive temperature perturbation developed in both hemispheres, leading to additional longwave radiation emitted back to space. According to the model results, this adjustment occurred in the stratosphere within the first 2 months after the event. At the top of the atmosphere (TOA), the net effective radiative forcing (ERF) averaged over the Southern Hemisphere was initially dominated by the instantaneous positive radiative forcing of about +0.5ĝ€¯Wm-2, for which the positive sign resulted mainly from the presence of clouds above the Southern Ocean. The longwave adjustments led to a compensation of the initially net positive TOA ERF, which is seen in the Southern Hemisphere, the tropics, and the northern mid-latitudes. The simulated changes in the lower stratosphere also affected the upper troposphere through a thermodynamic downward coupling. Subsequently, increased temperatures were also obtained in the upper troposphere, causing a global decrease in relative humidity, cirrus amount, and the ice water path of about 0.2ĝ€¯%. As a result, surface precipitation also decreased by a similar amount, which was accompanied by a weakening of the tropospheric circulation due to the given energetic constraints. In general, it appears that the radiative effects of smoke from single extreme wildfire events can lead to global impacts that affect the interplay of tropospheric and stratospheric budgets in complex ways. This emphasizes that future changes in extreme wildfires need to be included in projections of aerosol radiative forcing.
- ItemIs the near-spherical shape the "new black" for smoke?(Katlenburg-Lindau : EGU, 2020) Gialitaki, Anna; Tsekeri, Alexandra; Amiridis, Vassilis; Ceolato, Romain; Paulien, Lucas; Kampouri, Anna; Gkikas, Antonis; Solomos, Stavros; Marinou, Eleni; Haarig, Moritz; Baars, Holger; Ansmann, Albert; Lapyonok, Tatyana; Lopatin, Anton; Dubovik, Oleg; Groß, Silke; Wirth, Martin; Tsichla, Maria; Tsikoudi, Ioanna; Balis, DimitrisWe examine the capability of near-sphericalshaped particles to reproduce the triple-wavelength particle linear depolarization ratio (PLDR) and lidar ratio (LR) values measured over Europe for stratospheric smoke originating from Canadian wildfires. The smoke layers were detected both in the troposphere and the stratosphere, though in the latter case the particles presented PLDR values of almost 18% at 532 nm as well as a strong spectral dependence from the UV to the near-IR wavelength. Although recent simulation studies of rather complicated smoke particle morphologies have shown that heavily coated smoke aggregates can produce large PLDR, herein we propose a much simpler model of compact near-spherical smoke particles. This assumption allows for the reproduction of the observed intensive optical properties of stratospheric smoke, as well as their spectral dependence. We further examine whether an extension of the current Aerosol Robotic Network (AERONET) scattering model to include the near-spherical shapes could be of benefit to the AERONET retrieval for stratospheric smoke cases associated with enhanced PLDR. Results of our study illustrate the fact that triple-wavelength PLDR and LR lidar measurements can provide us with additional insight when it comes to particle characterization. © 2020 Author(s).