Total mass estimate of the January 23, 2018, phreatic eruption of Kusatsu-Shirane Volcano, central Japan

On January 23, 2018, a small phreatic eruption (VEI = 1) occurred at the Motoshirane Pyroclastic Cone Group in the southern part of Kusatsu-Shirane Volcano in central Japan. The eruption ejected ash, lapillus, and volcanic blocks from three newly opened craters: the main crater (MC), west crater (WC), and south crater (SC). Volcanic blocks were deposited up to 0.5 km from each crater. In contrast, the ash released during this eruption fell up to 25 km ENE of the volcano. The total mass of the fall deposit generated by the eruption was estimated using two methods, yielding total masses of 3.4 × 104 t (segment integration method) and 2.4 × 104 t (Weibull fitting method). The calculations indicate that approximately 70% of the fall deposit was located within 0.5 km of the craters, which was mainly attributed to the low height of the eruption plume.

Kusatsu-Shirane volcano eruption on January 23, 2018, observed using JMA operational weather radars

A phreatic eruption suddenly occurred at Motoshirane (Kusatsu-Shirane volcano, Japan) at 10:02 JST on January 23, 2018. A member of the Japan Self-Defense Force was killed by volcanic blocks during training in Motoshirane, and 11 people were injured by volcanic blocks or fragments of broken glass. According to a field survey, ash fall was confirmed in Minakami, about 40 km east-northeast from Motoshirane. Although the eruption was not captured by a distant camera, the eruption plume/cloud was captured by three of the Japan Meteorological Agency’s operational weather radars. These radars observed the echo propagated to the northeast in the lower troposphere, and to the east in the middle troposphere. This is generally consistent with the observed ash fall distribution. Using the modified probabilistic estimation method, the maximum plume height was estimated to be about 5580 ± 506 m (1σ) above sea level. Estimates of the erupted mass based on the range of plume heights from radar observations and the duration of volcanic tremor during the eruption (about 8 min) do not match that obtained from a field survey (3.0–5.0 × 107 kg). This discrepancy confirms that estimates of erupted mass based on plume heights must account for eruption style parametrically, which can only be constrained by case studies of varied eruption styles.

Modelling new particle formation in a passive volcanic plume using a new parameterisation in WRF-Chem - effects on climate-relevant variables at the regional scale

<p>New particle formation (NPF) is an important source of aerosol particles at  global scale, including, in particular, cloud condensation nuclei (CCN). NPF has been observed worldwide in a broad variety of environments, but some specific conditions, such as those encountered in volcanic plumes, remain poorly documented in the literature. Yet, these conditions could promote the occurrence of the process, as recently evidenced in the volcanic eruption plume of the Piton de la Fournaise (Rose at al. 2019); a dominant fraction of the volcanic particles was moreover found to be of secondary origin in the plume, further highlighting the importance of the particle formation and growth processes associated to the volcanic plume eruption. A deeper comprehension of such natural processes is thus essential to assess their climate-related effects at present days but also to better define pre-industrial conditions and their variability in climate model simulations.</p><p>Sulfuric acid (SA) is commonly accepted as one of the main precursors for atmospheric NPF, and its role could be even more important in volcanic plume conditions, as recently evidenced by the airborne measurements conducted in the passive volcanic plumes of Etna and Stromboli (Sahyoun et al., 2019). Indeed, the flights performed in the frame of the STRAP campaign have allowed direct measurement of SA in such conditions for the first time, and have highlighted a strong connection between the cluster formation rate and SA concentration. Following these observations, the objective of the present work was to further quantify the formation of new particles in a volcanic plume and assess the effects of the process at a regional scale. For that purpose, the new parameterisation of nucleation derived by Sahyoun et al. (2019) was introduced in the model WRF-Chem, further optimized for the description of NPF. The flight ETNA13 described in detail in Sahyoun et al. (2019) was used as a case study to evaluate the effect of the new parameterisation on the cluster formation rate and particle number concentration in various size ranges, including CCN (i.e. climate-relevant) sizes.</p><p><strong>References: </strong></p><p>Sahyoun, M., Freney, E., Brito, J., Duplissy, J., Gouhier, M., Colomb, A., Dupuy, R., Bourianne, T., Nowak, J. B., Yan, C., Petäjä, T., Kulmala, M., Schwarzenboeck, A., Planche, C., and Sellegri, K.: Evidence of new particle formation within Etna and Stromboli volcanic plumes and its parameterization from airborne in-situ measurements, J. Geophys. Res.-Atmos., 124, 5650–5668, https://doi.org/10.1029/2018JD028882, 2019.</p><p>Rose, C., Foucart, B., Picard, D., Colomb, A., Metzger, J.-M., Tulet, P., and Sellegri, K.: New particle formation in the volcanic eruption plume of the Piton de la Fournaise: specific features from a long-term dataset, Atmos. Chem. Phys., 19, 13243–13265, https://doi.org/10.5194/acp-19-13243-2019, 2019.</p>

Analysis of properties of the 19 February 2018 volcanic eruption of Mount Sinabung in S5P/TROPOMI and Himawari satellite data

This study presents an analysis of TROPOMI cloud heights as a proxy for volcanic plume heights in the presence of absorbing aerosols and sulfur dioxide for the 19 February 2018 eruption plume of the Sinabung volcano on Sumatra, Indonesia. Comparison with CALIPSO satellite data shows that all three TROPOMI cloud height data products based on oxygen absorption which are considered here (FRESCO, ROCINN, O22CLD) provide volcanic ash heights comparable to heights measured by CALIPSO for optically thick volcanic ash clouds. FRESCO and ROCINN heights are very similar with only differences for FRESCO cloud top heights above 14 km altitude. O22CLD cloud top heights unsurprisingly fall below those of FRESCO and ROCINN, as the O22CLD retrieval is less sensitive to cloud top heights above 10 km altitude. For optically thin volcanic ash clouds, i.e. when Earth’s surface or clouds at lower altitudes shine through the volcanic ash cloud, retrieved heights fall below the volcanic ash heights derived from CALIPSO data. Evaluation of corresponding Himawari geostationary volcanic ash height retrievals based on InfraRed (IR) brightness temperature differences (ΔBT) reveals that for this particular eruption the ΔBT volcanic ash signature – widely used for detection of volcanic ash in geostationary satellite data – changes to a ΔBT ice crystal signature for the part of the ash plume reaching the upper troposphere beyond 10 km altitude several hours after the start of the eruption and which TROPOMI clearly characterizes as volcanic (SO2 > 1 DU and AAI > 4 or more conservatively SO2 > 10). The presence of ice in volcanic ash clouds is known to prevent the detection of volcanic ash based on broadband geostationary satellite data. TROPOMI does not suffer from this effect, and can provide valuable and accurate information about volcanic ash clouds and ash top heights in cases where commonly used geostationary IR measurements of volcanic ash fail.