Evolution of the Climate Forcing During the Two Years after the Hunga
Tonga-Hunga Ha'apai Eruption
Abstract
We calculate the climate forcing for the two years after the January 15,
2022, Hunga Tonga-Hunga Ha’apai (Hunga) eruption. We use satellite
observations of stratospheric aerosols, trace gases and temperatures to
compute the tropopause radiative flux changes relative to climatology.
Overall, the net downward radiative flux decreased compared to
climatology. Although the Hunga stratospheric water vapor anomaly
increases the downward infrared radiative flux, the solar flux reduction
due to Hunga aerosol shroud dominates the net flux over most of the
two-year period. Decreases in temperature produced by the Hunga
stratospheric circulation changes contributes to the decrease in
downward flux; however, the Hunga induced decrease in ozone increases
the net short-wave downward flux creating small sub-tropical net flux
increase in late 2022. Coincident with the aerosols settling out, the
water vapor anomaly disperses, and circulation changes disappear so that
the contrasting forcings all decrease together. By the end of 2023, most
of the Hunga induced radiative forcing changes have disappeared. There
is some disagreement in the satellite stratospheric aerosol optical
depth (SAOD) which we view as a measure of the uncertainty; however,
SAOD uncertainty does not alter our conclusion that, overall, aerosols
dominate the radiative flux changes followed by temperature and ozone.