Preprints
https://doi.org/10.5194/acp-2022-343
https://doi.org/10.5194/acp-2022-343
 
01 Jun 2022
01 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Self-lofting of wildfire smoke in the troposphere and stratosphere caused by radiative heating: simulations vs space lidar observations

Kevin Ohneiser1, Albert Ansmann1, Jonas Witthuhn1, Hartwig Deneke1, Alexandra Chudnovsky2, and Gregor Walter1 Kevin Ohneiser et al.
  • 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 2Tel Aviv University, Porter School of Earth Sciences and Environment, Tel Aviv, Israel

Abstract. Wildfire smoke is known as a highly absorptive aerosol type in the shortwave wavelength range. The absorption of Sun light by optically thick smoke layers results in heating of the ambient air. This heating is translated into self-lofting of the smoke up to more than 1 km in altitude per day. This study aims for a detailed analysis of tropospheric and stratospheric smoke lofting rate simulations as well as comparisons between modeled and observed smoke lofting rates. One of the main goals is to demonstrate that self-lofting processes can explain observed smoke lofting in the free middle and upper troposphere up to the tropopause and into the lower stratosphere without the need for pyrocumulonimbus convection. Simulations are conducted by using the ECRAD (European Centre for Medium-RangeWeather Forecasts Radiation) scheme. As input parameters thermodynamic profiles from CAMS (Copernicus Atmosphere Monitoring Service) reanalysis data, aerosol profiles from ground-based lidar observations, radiosonde potential temperature profiles, CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) aerosol measurements, and MODIS (Moderate Resolution Imaging pectroradiometer) aerosol optical depth retrievals were used. The uncertainty analysis revealed that the lofting rate sensitively depends on the aerosol optical thickness (AOT), layer thickness, layer height, and the black carbon to organic carbon fraction. We also looked at the influence of different meteorological parameters such as cloudiness, relative humidity, and potential temperature gradient. Largest sensitivities between 30 % and 50 % were found for variation of AOT, black carbon fraction, and cloudiness. Uncertainty in the self-lofting estimations grows with longevity of the smoke layers. In recent years, several major wildfire events occurred and injected smoke into the upper troposphere and lower stratosphere. Self-lofting processes led to the ascend of these smoke plumes. CALIPSO measurements show that in 2017, Canadian wildfire smoke plumes ascended by about 10 km in one month. In 2020, Australian wildfire smoke layers were lofted by around 20 km in two months. In 2019 and 2021, significant self-lofting of tropospheric smoke was observed in Siberia. Smoke was injected to around 4 km height and reached the tropopause within less than a week. These four examples, observed with CALIOP, are presented in this study. The observed CALIOP ascent rates are compared to the calculated ascent rates using the ECRAD model heating rate simulations.

Kevin Ohneiser et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-343', Michael Fromm, 09 Jun 2022
  • RC2: 'Review of “Self-lofting of wildfire smoke in the troposphere and stratosphere caused by radiative heating: simulations vs space lidar observations” by Ohneiser et al. (2022)', Anonymous Referee #2, 25 Aug 2022

Kevin Ohneiser et al.

Kevin Ohneiser et al.

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Short summary
This study shows that smoke layers can reach the tropopause via the self-lofting effect within 3–7 days in the absence of pyroCB convection if the AOT is larger than approximately 2 for a longer time period. In the stratosphere it can further self-loft if the AOT is larger than 0.01. When reaching the stratosphere, wildfire smoke can sensitively influence the stratospheric composition on a hemispheric scale and thus can affect the Earth’s climate and the ozone layer.
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