Abstract
Abstract. At 18:00 UTC on 21 June 2019 the Raikoke volcano in the Kuril islands began a large-magnitude explosive eruption, sending a plume of ash and sulfur dioxide into the stratosphere. A Raman lidar system at Capel Dewi Atmospheric Observatory, UK, was deployed to measure the vertical extent and optical depth of the volcanic aerosol cloud following the eruption. The elastic channel at 355 nm allowed measurements up to 25 km, but the Raman channel was only sensitive to the troposphere. Therefore, retrievals of backscatter ratio profiles from the raw backscatter measurements required aerosol-free profiles derived from nearby radiosondes and allowance for aerosol extinction using a lidar ratio of 40–50 sr. Small amounts of aerosol were measured prior to the arrival of the volcanic cloud (27 June–5 July 2019), from pyroconvection over Canada. Model simulations by de Leeuw et al. (2020) and Kloss et al. (2020) show that volcanic ash may have reached Europe from 1 July onwards and was certainly present over the UK after 10 July. The lidar detected a thin layer at an altitude of 14 km late on 3 July, with the first detection of the main aerosol cloud on 13 July. In this initial period the aerosol was confined below 16 km, but eventually the cloud extended to 20.5 km. A sustained period of clearly enhanced stratospheric aerosol optical depths began in early August, with a maximum value (at 355 nm) around 0.05 in mid-August and remaining above 0.02 until early November. Thereafter, optical depths decayed to around 0.01 by the end of 2019 and remained around that level until May 2020. The altitude of peak backscatter varied considerably (between 14 and 18 km) but was generally around 15 km. However, on one notable occasion on 25 August 2019, a layer around 300 m thick with peak lidar backscatter ratio around 1.5 was observed as high as 21 km.
Highlights
From 18:05 UTC on June 2019 to 05:40 UTC on June the Raikoke volcano in the Kuril Islands (48.29◦ N, 153.25◦ E) erupted, sending plumes of ash and sulfur dioxide into the stratosphere (Crafford and Venzke, 2019)
Sulfur dioxide was measured from 11 to 20 km by the TROPOMI instrument on the Sentinel-5 satellite on 24 June, with ash detected by the CALIOP spaceborne lidar on the CALIPSO satellite at 17 km on 22 June and around 13 km on 23 and 24 June (Hedelt et al, 2019)
Two aerosol layers are shown in this figure – one around 12 km, just above the tropopause, which seems from its optical properties to have been smoke and another between 13 and 14 km where a lidar ratio of 40 sr sufficed
Summary
From 18:05 UTC on June 2019 to 05:40 UTC on June the Raikoke volcano in the Kuril Islands (48.29◦ N, 153.25◦ E) erupted, sending plumes of ash and sulfur dioxide into the stratosphere (Crafford and Venzke, 2019). Maximum average stratospheric aerosol optical depths at 449 nm (derived from SAGE-III/ISS data) reached 0.045 north of 55◦ N and 0.030 between 40 and 55◦ N in the early months after the eruption (Kloss et al, 2020). During the months following the initial eruption the aerosol evolved in height, depth and optical thickness (Kloss et al, 2020). It merged with aerosol from the smaller eruptions of Ulawun in Papua New Guinea (5.05◦ S, 151.3◦ E) that occurred on 26 June and 3–4 August 2019, which reached 19 km altitude and injected around. Lidar measurements of the volcanic aerosol cloud at 355 and 532 nm from four Russian stations were presented for the second half of 2019 by Grebennikov et al (2020). All the measurements were taken during the hours of darkness when there was no cloud cover over the site; in all there were 34 nights of measurements between 27 June 2019 and 30 May 2020
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