Enhancing Volcanic Emission Forecasting Through Data Fusion and Trajectory Analysis: A Case Study of 2022 Hunga Tonga Eruption

A large eruption of Hunga Tonga - Hunga Ha’apai volcano located in the South Pacific occurred in January 2022. The eruption released a substantial amount of SO₂ into the atmosphere, reaching as high as the stratosphere, resulting in an SO­­­­₂ cloud that expanded to over 600 km in diameter within a few hours of the eruption. The Darwin Volcanic Ash Advisory Center (VAAC) issued volcanic ash advisories for aviation in response to the eruption. Modeling of such events is often performed with a Lagrangian atmospheric transport and dispersion model such as HYSPLIT. Data fusion techniques which incorporate satellite observations into the modeling system have been developed at NOAA ARL. These techniques encompass an inversion algorithm to estimate emissions at the source as well as a data insertion method which initializes mass in the model at a downwind location. For this case, the extensive umbrella cloud, generated by the latest explosion and perturbing plume posed unique challenges to the typical setup of the inversion algorithm. To address this, we implemented a back trajectory analysis to improve both the performance of the inversion algorithm and the data insertion. We used daily composites of VOLcanic Cloud Analysis Toolkit (VOLCAT) Satellite retrievals, including cloud top height and column mass loading of SO₂ derived from the NOAA-20 Cross-track Infrared Sounder. Back trajectories were run from the observed latitudes and longitudes and utilized to get a rough estimate of the emissions as a function of time and height near the vent, as well as to obtain estimates of the vertical profile of mass at the observed location. These estimated plume characteristics, resulting from trajectories, showed the effectiveness of our algorithm and highlighted the capacity of trajectory analysis in understanding the thickness of emitted clouds. The estimates of the vertical mass profiles at the observed locations were then used for the data insertion. HYSPLIT forecasts using the data insertion were then run forward and compared to both satellite data that had not been used in the data fusion as well as measurements at Reunion Island. Our analysis also benefited from the inclusion of retrievals available over an extended period that enabled us to explore the dynamics of long-range transport of volcanic emissions within the upper troposphere. We find that the application of the back trajectory analysis is relatively fast and can improve the forecasting of volcanic emissions. This integrated framework is also applicable to understanding volcanic ash dispersion, and is relevant towards helping VAACs meet new requirements for producing quantitative ash forecasts.