10:15 AM - 10:30 AM
[MIS13-06] Cloud-Scientific Study of Volcano Eruption -perspective-
★Invited Papers
Keywords:cloud science, volcanic eruption
This presentation aims to emphasize how cooperative observation and modeling of volcanic eruption clouds will result in mutual benefit.
Many numerical models can simulate atmospheric convective clouds if initial and environmental conditions (CCN, IN, vertical profiles of temperature, humidity, and winds, etc.) are given. However, it is almost impossible to observe these conditions, because natural clouds develop sporadically, move fast, and change rapidly. Indeed, strictly speaking, there are no numerical models verified by field observations. If we know where a cloud develops, we will be able to verify and improve the formula and parameters assumed in these cloud models.
Volcanic eruption clouds, on the other hand, develop at the same place. Therefore, observation of volcanic eruption clouds has the potential to validate numerical models. For example, using marine radars, we succeeded in estimating the high-temporal (2 sec.) and spatial (5 m) change of height, volume, and ascending speed of Sakurajima volcanic clouds (Maki et al., 2020). These data will be useful to study the dynamics of convection in the air. We also observed a small rain cloud originated from the volcanic eruption (Fig. 1). A small eruption occurred at 09:46 JST on 18 Sep. 2019, and the ash cloud reached 1800 m a.s.l.. A small cloud (condensation) began to develop at 9:50 JST, precipitation occurred at 09:51 JST, and raindrops reached the ground surface at 09:55 JST. These high-temporal and spatial data are also useful to validate microphysical processes used in cloud models.
On 5 Nov. 2019, rising volcanic ash began to fall rapidly (Fig. 2). A small eruption occurred at 12:41 JST, and the ash cloud reached 1900 m a.s.l.. The radar echo indicates that the ash cloud began to dissipate in its middle part at 12:45 JST. The lower part of the ash cloud went down to the ground very fast like a downburst. The upper air sounding data suggests that this downburst-like phenomenon was caused by dry air intrusion at the middle part level. This case clearly shows that vertical atmospheric stratification strongly affects volcanic ash transport and dispersion. We also compared electric potential gradient changes with the temporal change of radar echoes of eruption clouds. These surface and in-situ data will be useful to study the charging, charge separation, and lightning mechanisms of volcanic clouds as well as the electrification of natural clouds.
Modeling eruption clouds is challenging for meteorological researchers, although almost the same physical processes are involved both in eruption clouds and atmospheric clouds. For example, turbulence and updraft within eruption clouds are much stronger than those in atmospheric clouds. Components within eruption clouds are more complicated than those in atmospheric clouds. A larger size range of particles is included in eruption clouds than those in atmospheric clouds. Vertical profiles of temperature and updraft within eruption clouds are opposite to those within atmospheric clouds. Some volcanic ejecta is formed by fragmentation and solidification of liquid state lava. On the other hand, raindrops (liquid) are formed by melting and fragmenting snow particles (solid-state). Figure 3 shows 2DVD (2-Dimensional Video Distrometer) images of melting snow particles. It is quite interesting that these melting particles have almost the same shape as those of volcanic bombs (aggregates, spindle-shaped, ribbon-shaped, Peles’s tear, etc.).
Reference
Maki, M., et al., 2020: Monitoring of Sakurajima Volcanic Eruption Columns with Marine Radar - Results of Observations in 2018 -, Disaster Prevention Research Institute Annuals. B, 2020, 63.B: 136-148.
Many numerical models can simulate atmospheric convective clouds if initial and environmental conditions (CCN, IN, vertical profiles of temperature, humidity, and winds, etc.) are given. However, it is almost impossible to observe these conditions, because natural clouds develop sporadically, move fast, and change rapidly. Indeed, strictly speaking, there are no numerical models verified by field observations. If we know where a cloud develops, we will be able to verify and improve the formula and parameters assumed in these cloud models.
Volcanic eruption clouds, on the other hand, develop at the same place. Therefore, observation of volcanic eruption clouds has the potential to validate numerical models. For example, using marine radars, we succeeded in estimating the high-temporal (2 sec.) and spatial (5 m) change of height, volume, and ascending speed of Sakurajima volcanic clouds (Maki et al., 2020). These data will be useful to study the dynamics of convection in the air. We also observed a small rain cloud originated from the volcanic eruption (Fig. 1). A small eruption occurred at 09:46 JST on 18 Sep. 2019, and the ash cloud reached 1800 m a.s.l.. A small cloud (condensation) began to develop at 9:50 JST, precipitation occurred at 09:51 JST, and raindrops reached the ground surface at 09:55 JST. These high-temporal and spatial data are also useful to validate microphysical processes used in cloud models.
On 5 Nov. 2019, rising volcanic ash began to fall rapidly (Fig. 2). A small eruption occurred at 12:41 JST, and the ash cloud reached 1900 m a.s.l.. The radar echo indicates that the ash cloud began to dissipate in its middle part at 12:45 JST. The lower part of the ash cloud went down to the ground very fast like a downburst. The upper air sounding data suggests that this downburst-like phenomenon was caused by dry air intrusion at the middle part level. This case clearly shows that vertical atmospheric stratification strongly affects volcanic ash transport and dispersion. We also compared electric potential gradient changes with the temporal change of radar echoes of eruption clouds. These surface and in-situ data will be useful to study the charging, charge separation, and lightning mechanisms of volcanic clouds as well as the electrification of natural clouds.
Modeling eruption clouds is challenging for meteorological researchers, although almost the same physical processes are involved both in eruption clouds and atmospheric clouds. For example, turbulence and updraft within eruption clouds are much stronger than those in atmospheric clouds. Components within eruption clouds are more complicated than those in atmospheric clouds. A larger size range of particles is included in eruption clouds than those in atmospheric clouds. Vertical profiles of temperature and updraft within eruption clouds are opposite to those within atmospheric clouds. Some volcanic ejecta is formed by fragmentation and solidification of liquid state lava. On the other hand, raindrops (liquid) are formed by melting and fragmenting snow particles (solid-state). Figure 3 shows 2DVD (2-Dimensional Video Distrometer) images of melting snow particles. It is quite interesting that these melting particles have almost the same shape as those of volcanic bombs (aggregates, spindle-shaped, ribbon-shaped, Peles’s tear, etc.).
Reference
Maki, M., et al., 2020: Monitoring of Sakurajima Volcanic Eruption Columns with Marine Radar - Results of Observations in 2018 -, Disaster Prevention Research Institute Annuals. B, 2020, 63.B: 136-148.