Eruption of Mt. Kilauea Impacted Cloud Droplet and Radiation Budget over North Pacific

Abstract

Mount Kilauea Volcano began to erupt on 19 March 2008 and continued to release large amounts of volcanic gas until the end of 2008. The volcanic SO2 was oxidized to sulfate aerosol. The impact of the sulfate aerosol from this eruption on cloud microphysical properties was clearly observed by MODIS satellite. Mt. Kilauea is located in a clean maritime environment characterized by the steady easterly trade wind, ubiquitous cumulus clouds and without any large anthropogenic emission sources. This condition is ideal for studying the impact of aerosol on cloud physical and radiative properties. Here we report our original findings for the 2008 eruption of the Mt. Kilauea volcano and its impact on cloud properties. Figure 1 shows the MODIS AOD measurements for August 2008. A significant increase in AOD is evident in the downwind region extending from the Hawaiian Islands to the western North Pacific, with a zonal extent of 5000 km and a meridional extent of 1500 km. The volcanic aerosol layer persisted over a large area of the remote North Pacific, where cumulus clouds are ubiquitous. The effect of aerosol particles on the cloud radius (CDR) and properties is known as the Twomey effect. We examined that the CDR distribution and the difference between August of average in 2003 – 2007 and 2008. Over the study region, the average CDR was 17.6 mm in 2003 – 2007 before the eruption and decreased to 13.7 mm (~23 % decrease) during the eruption. Meanwhile, the averaged cloud fractional coverage increased from 9.1% in 2003 – 2007 to 13.4% in 2008 (a relative increase of ~37 %). The aerosol index (AI; product of AOD and the Ångström exponent) is a measure of the aerosol column number concentration. It is approximated by CDR = 10.8 AI^(-0.19) based on MODIS measurements. The CDR rapidly decreased as the volcanic aerosol number increased. This relationship between the CDR and the surrounding sulfate aerosol will provide an important foundational reference for climate change studies.