New insights into volcanic eruption cloud dynamics from DSCOVR/EPIC

Abstract:

The Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) has been making unique, high-cadence observations of volcanic sulfur dioxide (SO₂) and ash emissions from the first Earth-Sun Lagrange point (L1) since 2015. On June 21, 2019, the largest volcanic eruption of the DSCOVR mission to date, and one of the largest eruptions of the past decade, occurred at Raikoke volcano (Kuril Islands, Russia). The timing and location of the Raikoke eruption, which began around sunrise at a mid-latitude volcano near the summer solstice, and continued until sunset, were optimal for EPIC observations. Here, we report the first comparisons between UV EPIC observations and geostationary IR SO₂ retrievals from the Advanced Himawari Imager (AHI) on the Japanese Himawari-8 satellite. The high cadence of both EPIC and AHI permits comparison of near-coincident (within a few minutes) UV and IR retrievals over several hours of volcanic cloud evolution for the first time. We find excellent spatial agreement between EPIC and AHI SO­₂ observations but a notable difference in SO₂ sensitivity in the presence of volcanic ash, with EPIC detecting higher SO₂ amounts, although both instruments underestimate the total SO₂ loading in the young volcanic cloud. This result provides new evidence for the higher sensitivity of UV instruments to SO₂ in optically thick volcanic clouds, likely due to UV penetration into the upper region of the cloud. To explore this further, we will attempt the first UV EPIC retrievals of aerosol optical depth and volcanic ash mass loading in the Raikoke volcanic cloud, following recent work to quantify smoke mass in stratospheric wildfire plumes. Ash mass retrievals could provide new insight into the evolution of volcanic ash and SO₂ loading in a young, stratospheric volcanic eruption cloud, with implications for the impact of explosive volcanic eruptions on the atmosphere, climate and aviation. We also report new EPIC observations of volcanic eruptions since the return of DSCOVR from safehold in March 2020, including the eruption of Nishinoshima volcano (Japan), which has produced widespread tropospheric SO₂ emissions over the Pacific Ocean in June-July 2020.