Volcanic Aerosol Impacts on Big Island Precipitation Development

Kilauea Volcano on the Big Island of Hawaii has been erupting nearly continuously since 1983. The sulfur dioxide gas (SO₂) released from the effusive volcano reacts with oxides and atmospheric moisture to produce acidic sulfate aerosols, which are locally referred to as “vog”, short for volcanic smog. Vog pollutants create hazardous air quality conditions to Hawaiian communities, a topic with a rich history of research. In addition, prior research using remote sensing methods have shown that vog also has impacts on marine cloud properties downwind of the Big Island. The impacts are found to be overall typical of the expected aerosol cloud interactions in warm clouds.

Here we investigate vog impacts on clouds, convection, and precipitation over the Big Island itself using the Weather Research and Forecasting (WRF) model with the aerosol-aware Thompson microphysics scheme. Simulations are run with and without island aerosol sources, and with and without volcanic aerosol sources. Simulations with volcanic aerosol sources have large point sources of sulfate-like aerosol from the Kilauea vent locations. The added aerosols mix into the orographic convection where they modify the properties of the warm clouds; they increase the cloud droplet number concentration, reduce cloud droplet sizes, and increase cloud water content. The volcanic aerosols also delay precipitation production, and modify the spatial distribution of rain. The impacts on cloud properties and precipitation are not surprising, but the modification of precipitation on an island has far reaching consequences. For this reason we work to quantify the sensitivity of the orographic precipitation to volcanic aerosols, create an aerosol budget to understand volcanic aerosol sinks, and move beyond the observation of relationships to the understanding of processes.