A satellite multi-sensor view of the Mount Redoubt eruption to aid in assessments of volcanic aerosol radiative forcing

Mount Redoubt is a stratovolcano located in the Aleutian Range of Alaska, USA. Since March 22, 2009, the volcano has erupted many times, spewing ash as high as 20 km into the atmosphere. Such violent eruptions inject gaseous and particulate species into the stratosphere, where they may remain over the sufficiently long time to influence climate. The overall radiative effects of a volcanic eruption are ultimately determined by many factors. The goal of this study is to characterize the initial conditions of the plume and its evolution over time using NASA A-Train multi-sensor data. The synergy of the A-Train satellites provides an excellent opportunity to determine amounts, trajectories, and entrainment rates of plume constituents. Here we focus on sulfur dioxide and ash particles. It is well known that sulfur dioxide emitted by volcanoes leads to the production of sulfate aerosol, which causes cooling in the troposphere and warming in the stratosphere. However, the concentrations, dynamics, and radiative properties of ash particles are less understood. Therefore, our investigation is also focused on using ash samples collected from the April 4, 2009 eruption of Mount Redoubt to discern the physical and chemical characteristics of the ash. This information will be useful in radiative transfer models, which have previously assumed that volcanic ash is similar to mineral dust. In addition, we will present the results of three-dimensional, multiphase modeling of the Redoubt eruptions using an Eulerian-Eulerian-Lagrangian (EEL) approach to supplement the satellite observations. Both the multi-sensor investigation and numerical modeling demonstrate the dynamic size segregation of ash particles in eruption plumes. The effects of the composition and size distribution of ash particles in assessments of radiative forcing of climate will be addressed.