Evaluating the Radiative Effects of Volcanic Ash and Sulfate from the 2015 Calbuco Eruption

After 54 years of dormancy, Calbuco Volcano (southern Chile) erupted on 22 April 2015, producing two explosive pulses and stratospheric eruption columns. This study investigates the dispersion and radiative effects of volcanic ash and sulfur dioxide (SO₂), including sulfate aerosol formation, using the updated Weather Research and Forecasting-Chemistry (WRF-Chem) v4.8 model. Simulations reproduce the observed large-scale transport of ash, sulfate, and SO₂, with generally good agreement with AERONET aerosol-loading observations and IASI/Metop-B SO₂plume observations. Remaining discrepancies in aerosol volume size distributions and plume vertical structure highlight sensitivities to eruption timing, plume intensity, vertical mixing, and chemical removal. A concentration-based 1 2 3 4 5 6 7 8 9 sampling framework identifies plume-affected grid cells, reducing background interference in radia- 10 tive forcing estimates. During 23–30 April 2015, ash dominated the short-term radiative response, 11 producing atmospheric heating of up to approximately 16 Wm⁻² and substantial surface cooling. 12 The ash-only experiment yielded near-neutral or slightly positive top-of-atmosphere (TOA) forcing, 13 whereas the combined ash–sulfate experiment produced negative TOA forcing. On 23 April, TOA 14 forcing shifted from approximately +3.8 to −3.2 Wm⁻². These findings indicate that ash controls the 15 magnitude of the short-term radiative response, while sulfate influences its net TOA sign.