Radiative impacts of the Australian bushfires 2019-2020 - Part 1: Large-scale radiative forcing

International audienceAs a consequence of extreme heat and drought, record-breaking wildfires developed and ravaged south-eastern Australia during the fire season 2019-2020. The fire strength reached its paroxysmal phase at the turn of the year 2019-2020. During this phase, pyrocumulonimbus clouds (pyroCb) developed and injected biomass burning aerosols and gases into the upper troposphere and lower stratosphere (UTLS). The UTLS aerosol layer was massively perturbed by these fires, with aerosol extinction increased by a factor of 3 in the visible spectral range in the Southern Hemisphere, with respect to a background atmosphere, and stratospheric aerosol optical depth reaching values as large as 0.015 in February 2020. Using the best available description of this event by observations, we estimate the radiative forcing (RF) of such perturbations of the Southern Hemispheric aerosol layer. We use offline radiative transfer modelling driven by observed information of the aerosol extinction perturbation and its spectral variability obtained from limb satellite measurements. Based on hypotheses on the absorptivity and the angular scattering properties of the aerosol layer, the regional (at three latitude bands in the Southern Hemisphere) clear-sky TOA (top-of-atmosphere) RF is found varying from small positive values to relatively large negative values (up to -2.0 W m-2), and the regional clear-sky surface RF is found to be consistently negative and reaching large values (up to -4.5 W m-2). We argue that clear-sky positive values are unlikely for this event, if the ageing/mixing of the biomass burning plume is mirrored by the evolution of its optical properties. Our best estimate for the area-weighted global-equivalent clear-sky RF is -0.35±0.21 (TOA RF) and -0.94±0.26 W m-2 (surface RF), thus the strongest documented for a fire event and of comparable magnitude with the strongest volcanic eruptions of the post-Pinatubo era. The surplus of RF at the surface, with respect to TOA, is due to absorption within the plume that has contributed to the generation of ascending smoke vortices in the stratosphere. Highly reflective underlying surfaces, like clouds, can nevertheless swap negative to positive TOA RF, with global average RF as high as +1.0 W m-2 assuming highly absorbing particles

Observation of the Aerosol Plume From the 2022 Hunga Tonga - Hunga Ha'apai Eruption With SAGE III/ISS

International audienceThe Tonga eruption of 15 January 2022 has released a long-lived stratospheric plume of sulfate aerosols.More than 17 months after, we focus on the high quality data series of SAGE III (Stratospheric Aerosol and Gas Experiment) on board the International Space Station (ISS) to determine the mean radius and size distribution of the aerosols and their total mass.The persisting volcanic aerosols -- with a mode width of 1.25 and an effective radius of 0.4 µm -- differ from the significantly smaller background aerosols and from those measured during recent stratospheric eruptions. The sulfuric acid mass between 50°S and 30°N is estimated to be very stable in spite of considerable redistribution in latitude at a value of 0.66 ± 0.1 Tg, corresponding to an initial sulfur dioxide emission of 0.44 Tg. Such properties are expected to facilitate the persistence of a climate warming due to the volcanic water vapour

The Hunga Tonga-Hunga Ha'apai stratospheric eruption of 15th January 2022: a global warming volcanic plume?

International audienceThe underwater Hunga Tonga-Hunga Ha'apai volcano erupted in the early hours of 15th January 2022 and injected volcanic gases and aerosols to over 50 km altitude. In this talk, we synthesise satellite, ground-based, in situ and radiosonde observations of the eruption to investigate the emissions, the horizontal and vertical dispersion, and the strength of the stratospheric aerosol and water vapour perturbations in the initial six months after the eruption. The aerosol plume was initially formed of two clouds at 30 and 28 km, mostly composed of submicron-sized sulfate particles, without ash, which is washed out within the first day following the eruption. The large amount of injected water vapour led to a fast conversion of SO2 to sulphate aerosols. We find that the Hunga Tonga-Hunga Ha'apai eruption produced the largest global perturbation of stratospheric aerosols since the Pinatubo eruption in 1991 and the largest perturbation of stratospheric water vapour observed in the satellite era. Then, using offline radiative transfer calculations driven by aerosol and water vapour observations, we quantify the net radiative impact across the two species. Immediately after the eruption, water vapour radiative cooling dominated the local stratospheric heating/cooling rates, producing a spectacular radiatively-driven plume descent of several kilometres. At the top-of-the-atmosphere and surface, volcanic aerosol cooling dominated the radiative forcing during this first dispersion phase. However, after two weeks, due to dilution, water vapour heating started to dominate the top-of-the-atmosphere radiative forcing, leading to a net warming of the climate system. On a longer timescale, sulphate particles, undergoing hygroscopic growth and coagulation, sediment and gradually separate from the moisture anomaly entrained in the ascending branch Brewer-Dobson circulation. This is the first time a warming effect on the climate system has been linked to volcanic eruptions, which usually produce a transient cooling

The Evolution and Dynamics of Hunga Tonga-Hunga Ha'apai Stratospheric Plume over One Year and Half after the Eruption

International audienceThis study is based on the combination of data from CALIOP, OMPS-LP, IASI, MLS, SAGE-III, AHI/HIMAWARI, ATLID/AEOLUS, COSMIC2 and balloon LOAC measurements. The main stratospheric plume of the Tonga eruption, very rich in water vapour and from which ash particles have been washed out within the first hours after the eruption, underwent a fast conversion of SO2 to sulfates within the first 15 days. IASI observations show that SO2 has returned to background levels by the beginning of February 2022. The large amount of water vapour in the plume induced a radiative cooling and a descent of 4 to 6 kilometers during the first 3 weeks. Compact patches of aerosols survive until March 2022 due to the water vapour cooling and the formation of anticyclonic meso-scale structures. During the following months, sedimenting aerosols and water vapour separated vertically. The water vapour ascended within the Brewer Dobson circulation (BDC), first slowly then very rapidly (up to 150 m/day) during the winter 2022-2023 due to the successive phases of the QBO. The resulting pattern in the tropics is a strong perturbation of the tape recorder amplitude. The aerosol plume dispersed in latitude and altitude but penetrated hardly beyond 30°N in the northern hemisphere until April 2023. The vortex jet has been a barrier in the southern hemisphere until fall 2022. Due to the BDC, the aerosol sedimented in the extratropical southern hemisphere but stayed at a fairly constant level around 22 km in the tropical domain. The result is a sloping distribution descending to about 15 km at southern hemispheric high latitudes. The effective radius of the aerosols determined from SAGE III and fall rates, and in agreement with LOAC in situ observations, has been very stable in the 0.35-0.40 µm range even if a decreasing trend appears during winter 2022-2023. The width of the distribution is relatively narrow, basically twice smaller than that of the background and this is also persistent in time. The total mass of stratospheric sulphate aerosols as measured from SAGE III is about 0.66 Tg of H2SO4 corresponding to 0.44 Tg of SO2 at the source, even if considerable redistribution occurred in latitude and altitude

The Evolution and Dynamics of Hunga Tonga-Hunga Ha'apai Stratospheric Plume over One Year and Half after the Eruption

International audienceThis study is based on the combination of data from CALIOP, OMPS-LP, IASI, MLS, SAGE-III, AHI/HIMAWARI, ATLID/AEOLUS, COSMIC2 and balloon LOAC measurements. The main stratospheric plume of the Tonga eruption, very rich in water vapour and from which ash particles have been washed out within the first hours after the eruption, underwent a fast conversion of SO2 to sulfates within the first 15 days. IASI observations show that SO2 has returned to background levels by the beginning of February 2022. The large amount of water vapour in the plume induced a radiative cooling and a descent of 4 to 6 kilometers during the first 3 weeks. Compact patches of aerosols survive until March 2022 due to the water vapour cooling and the formation of anticyclonic meso-scale structures. During the following months, sedimenting aerosols and water vapour separated vertically. The water vapour ascended within the Brewer Dobson circulation (BDC), first slowly then very rapidly (up to 150 m/day) during the winter 2022-2023 due to the successive phases of the QBO. The resulting pattern in the tropics is a strong perturbation of the tape recorder amplitude. The aerosol plume dispersed in latitude and altitude but penetrated hardly beyond 30°N in the northern hemisphere until April 2023. The vortex jet has been a barrier in the southern hemisphere until fall 2022. Due to the BDC, the aerosol sedimented in the extratropical southern hemisphere but stayed at a fairly constant level around 22 km in the tropical domain. The result is a sloping distribution descending to about 15 km at southern hemispheric high latitudes. The effective radius of the aerosols determined from SAGE III and fall rates, and in agreement with LOAC in situ observations, has been very stable in the 0.35-0.40 µm range even if a decreasing trend appears during winter 2022-2023. The width of the distribution is relatively narrow, basically twice smaller than that of the background and this is also persistent in time. The total mass of stratospheric sulphate aerosols as measured from SAGE III is about 0.66 Tg of H2SO4 corresponding to 0.44 Tg of SO2 at the source, even if considerable redistribution occurred in latitude and altitude

The Evolution and Dynamics of Hunga Tonga-Hunga Ha'apai Stratospheric Plume over One Year and Half after the Eruption

International audienceThis study is based on the combination of data from CALIOP, OMPS-LP, IASI, MLS, SAGE-III, AHI/HIMAWARI, ATLID/AEOLUS, COSMIC2 and balloon LOAC measurements. The main stratospheric plume of the Tonga eruption, very rich in water vapour and from which ash particles have been washed out within the first hours after the eruption, underwent a fast conversion of SO2 to sulfates within the first 15 days. IASI observations show that SO2 has returned to background levels by the beginning of February 2022. The large amount of water vapour in the plume induced a radiative cooling and a descent of 4 to 6 kilometers during the first 3 weeks. Compact patches of aerosols survive until March 2022 due to the water vapour cooling and the formation of anticyclonic meso-scale structures. During the following months, sedimenting aerosols and water vapour separated vertically. The water vapour ascended within the Brewer Dobson circulation (BDC), first slowly then very rapidly (up to 150 m/day) during the winter 2022-2023 due to the successive phases of the QBO. The resulting pattern in the tropics is a strong perturbation of the tape recorder amplitude. The aerosol plume dispersed in latitude and altitude but penetrated hardly beyond 30°N in the northern hemisphere until April 2023. The vortex jet has been a barrier in the southern hemisphere until fall 2022. Due to the BDC, the aerosol sedimented in the extratropical southern hemisphere but stayed at a fairly constant level around 22 km in the tropical domain. The result is a sloping distribution descending to about 15 km at southern hemispheric high latitudes. The effective radius of the aerosols determined from SAGE III and fall rates, and in agreement with LOAC in situ observations, has been very stable in the 0.35-0.40 µm range even if a decreasing trend appears during winter 2022-2023. The width of the distribution is relatively narrow, basically twice smaller than that of the background and this is also persistent in time. The total mass of stratospheric sulphate aerosols as measured from SAGE III is about 0.66 Tg of H2SO4 corresponding to 0.44 Tg of SO2 at the source, even if considerable redistribution occurred in latitude and altitude

The Evolution and Dynamics of Hunga Tonga-Hunga Ha'apai Stratospheric Plume over One Year and Half after the Eruption

International audienceThis study is based on the combination of data from CALIOP, OMPS-LP, IASI, MLS, SAGE-III, AHI/HIMAWARI, ATLID/AEOLUS, COSMIC2 and balloon LOAC measurements. The main stratospheric plume of the Tonga eruption, very rich in water vapour and from which ash particles have been washed out within the first hours after the eruption, underwent a fast conversion of SO2 to sulfates within the first 15 days. IASI observations show that SO2 has returned to background levels by the beginning of February 2022. The large amount of water vapour in the plume induced a radiative cooling and a descent of 4 to 6 kilometers during the first 3 weeks. Compact patches of aerosols survive until March 2022 due to the water vapour cooling and the formation of anticyclonic meso-scale structures. During the following months, sedimenting aerosols and water vapour separated vertically. The water vapour ascended within the Brewer Dobson circulation (BDC), first slowly then very rapidly (up to 150 m/day) during the winter 2022-2023 due to the successive phases of the QBO. The resulting pattern in the tropics is a strong perturbation of the tape recorder amplitude. The aerosol plume dispersed in latitude and altitude but penetrated hardly beyond 30°N in the northern hemisphere until April 2023. The vortex jet has been a barrier in the southern hemisphere until fall 2022. Due to the BDC, the aerosol sedimented in the extratropical southern hemisphere but stayed at a fairly constant level around 22 km in the tropical domain. The result is a sloping distribution descending to about 15 km at southern hemispheric high latitudes. The effective radius of the aerosols determined from SAGE III and fall rates, and in agreement with LOAC in situ observations, has been very stable in the 0.35-0.40 µm range even if a decreasing trend appears during winter 2022-2023. The width of the distribution is relatively narrow, basically twice smaller than that of the background and this is also persistent in time. The total mass of stratospheric sulphate aerosols as measured from SAGE III is about 0.66 Tg of H2SO4 corresponding to 0.44 Tg of SO2 at the source, even if considerable redistribution occurred in latitude and altitude