The Development of Volcanic Ash Cloud Layers over Hours to Days Due to Atmospheric Turbulence Layering

• Published in: Atmosphere Vol. 12; no. 2; p. 285
• Main Authors: Bursik, Marcus, Yang, Qingyuan, Bear-Crozier, Adele, Pavolonis, Michael, Tupper, Andrew
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-02-2021
• Subjects: Air safety; Aircraft accidents & safety; Altitude; ash cloud; ash layer; Atmosphere; Atmospheric models; Atmospheric turbulence; Aviation; Clouds; Diffusion; Diffusion layers; Dispersion models; Eddy diffusion; eddy diffusivity; Free atmosphere; Humidity; Layering; Moisture content; Particle motion; Photography; Pinatubo; Regions; Stratosphere; Temperature; turbulence; Turbulence intensity; Turbulent diffusion; Vertical motion; Volcanic ash; volcanic cloud; Volcanoes
• ISSN: 2073-4433; 2073-4433
• DOI: 10.3390/atmos12020285

Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for the development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore dispersion models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for the development of multilayered ash clouds by modulating vertical particle motion. The largest particles, generally μ>100 μm, are little affected by turbulence. For particles in which both settling and turbulent diffusion are important to vertical motion, mostly in the range of 10–100 μμm, the greater turbulence intensity and more rapid turbulent diffusion in some layers causes these particles to spend greater time in the more turbulent layers, leading to a layering of concentration. The results may have important implications for ash cloud forecasting and aviation safety.