Using a Plume Box Model to Resolve the Transition Between the Volcanic Plume and the Model Grid of WACCM/CARMA

Current practices of volcano-climate modeling are inhibited by the conundrum of how and when to begin the simulation of the volcanic emissions. The particle size, concentration, composition, and altitude of the initially injected material all significantly influence the lifespan of a volcanic cloud and the burden of sulfur dioxide due to important dynamical processes occurring during early stages. Limited by their grid size, global climate models are far too coarse to simulate the event as the plume erupts from the volcanic caldera, rises in altitude, injects material into the atmosphere, and forms an umbrella cloud. Global models such as WACCM/CARMA typically begin by injecting volcanic material as a single grid cell into model grid boxes with an assumed size distribution. However, sedimentation processes of the umbrella cloud have an influence on the starting point of what should go into the global model. Here, we reconcile the disconnect between the volcanic plume and the model grid of WACCM/CARMA by adding a plume box model modified from [Carazzo, Jellinek 2013]. To our knowledge, this is the first time that a global climate model will include the sedimentation process of diffusive particle convection, which is necessary for matching observations of the residence time of volcanic particles in the umbrella cloud. By providing more accurate simulations of the concentration and size distribution of non-volatile particulates available for ash scavenging of sulfur dioxide, this addition to WACCM/CARMA will allow for better constraints on adding the impacts of volcanic ash and ice to the sulfur burden.