Volcanic Ash Forecast Verification Using HYSPLIT and Satellite Ash Observations Identified by VOLCAT

Volcanic activity has a profound impact on aviation operations and air quality for people living near, and in some cases well downwind, of a volcanic eruption. Due to the remote location and relatively unpredictable behavior of volcanic eruptions, Volcanic Ash Advisory Center (VAAC) forecasters rely heavily upon a variety of tools and instruments including space-based satellite observations to forecast ash for ongoing eruptions; a vital service to the aviation community. The VOLcanic Cloud Analysis Toolkit (VOLCAT) developed by NOAA/NESDIS in collaboration with the University of Wisconsin uses automated algorithms to identify volcanic clouds from various satellite observations and issues alerts for any detected volcanic activity. In addition to observations, forecasters use computer models like HYSPLIT, a Lagrangian trajectory and dispersion model, to forecast ash movement. In this study we use satellite observations processed by VOLCAT, and modeled ash dispersion results from HYSPLIT, to calculate verification statistics for multiple volcanic eruptions including the recent eruption of Raikoke in the Kuril Islands in the northwest Pacific Ocean. We explore different verification techniques for volcanic ash forecasts and provide thorough discussion of the information garnered from each statistical method. Development of an automated process to compare HYSPLIT ash dispersion forecasts and VOLCAT satellite observations is discussed, and approaches to improve HYSPLIT forecasts are recommended.