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Abstract

We modified the regional WRF-Chem model to study the evolution and radiative forcing of the January 2022 HTHH eruption. We use the Single Moment 5-class cloud microphysics scheme to handle the water in the troposphere and stratosphere. The Rapid Radiative Transfer Model (RRTMG) for shortwave (SW) and longwave (LW) radiation is used for radiative transfer calculations. We simultaneously inject SO₂ and water vapor at 35 km and conduct simulations in the (50S-10N) latitude belt for three months with 25 km spatial resolution. Initially, the volcanic cloud cools by thermal radiation and descends. The instantaneous radiative forcing was calculated by double call at the same meteorological fields. We found that in a month, the water vapor radiative forcing averaged over the latitude belt at the top of the atmosphere (TOA) reaches -0.016 W/m². The water vapor solar forcing is positive but two orders of magnitude smaller than LW forcing. Sulfate aerosol develops almost immediately after the injection. In two months, the sulfate SW forcing at TOA reaches -0.3 W/m². The sulfate LW forcing at TOA is positive but does not exceed 0.07 W/m² averaged over the domain. The volcanic cloud is cooling from the top at 0.1 K/day and warms from the bottom at 0.06 K/day. Thus, in our calculations, water vapor, nonuniformly distributed in the upper and middle stratosphere, cools the planet, although it is a greenhouse gas. However, the radiative effect of water vapor is 20 times smaller than sulfate aerosols.