Modelling wet deposition in simulations of volcanic ash dispersion from hypothetical eruptions of Merapi, Indonesia

• Published in: Atmospheric environment (1994) Vol. 143; pp. 190 - 201
• Main Authors: Dare, Richard A., Potts, Rodney J., Wain, Alan G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2016
• Subjects: Dispersion modelling; HYSPLIT; Indonesia; Merapi; Volcanic ash; Wet deposition; Indonesia; Merapi; Volcanic ash; Wet deposition; Dispersion modelling; HYSPLIT; Indonesia
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2016.08.022

The statistical impact of including the process of wet deposition in dispersion model predictions of the movement of volcanic ash is assessed. Based on hypothetical eruptions of Merapi, Indonesia, sets of dispersion model simulations were generated, each containing four simulations per day over a period of three years, to provide results based on a wide range of atmospheric conditions. While on average dry sedimentation removes approximately 10% of the volcanic ash from the atmosphere during the first 24 h, wet deposition removes an additional 30% during seasons with highest rainfall (December and January) but only an additional 1% during August and September. The majority of the wet removal is due to in-cloud rather than below-cloud collection of volcanic ash particles. The largest uncertainties in the amount of volcanic ash removed by the process of wet deposition result from the choice of user-defined parameters used to compute the scavenging coefficient, and from the definition of the cloud top height. Errors in the precipitation field provided by the numerical weather prediction model utilised here have relatively less impact. [Display omitted] •Dispersion model simulations based on hypothetical eruptions of Merapi, Indonesia.•Four 24-h simulations per day over a period of three years.•Dry sedimentation removes a mean of 10% of the total released volcanic ash mass.•Wet deposition removes an addition 30% of the total mass during the wet season.•Results are most sensitive to the coefficient in the bulk wet deposition formulation.