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Abstract The 2022 Hunga volcanic eruption injected a significant quantity of water vapor into the stratosphere while releasing only limited sulfur dioxide. It has been proposed that this excess water vapor could have contributed to global warming, potentially pushing temperatures beyond the 1.5 °C threshold of the Paris Climate Accord. However, given the cooling effects of sulfate aerosols and the contrasting impacts of ozone loss (cooling) versus gain (warming), assessing the eruption’s net radiative effect is essential. Here, we quantify the Hunga-induced perturbations in stratospheric water vapor, sulfate aerosols, and ozone using satellite observations and radiative transfer simulations. Our analysis shows that these components induce clear-sky instantaneous net radiative energy losses at both the top of the atmosphere and near the tropopause. In 2022, the Southern Hemisphere experienced a radiative forcing of −0.55 ± 0.05 W m⁻² at the top of the atmosphere and −0.52 ± 0.05 W m⁻² near the tropopause. By 2023, these values decreased to −0.26 ± 0.04 W m⁻² and −0.25 ± 0.04 W m⁻², respectively. Employing a two-layer energy balance model, we estimate that these losses resulted in cooling of about −0.10 ± 0.02 K in the Southern Hemisphere by the end of 2022 and 2023. Thus, we conclude that the Hunga eruption cooled rather than warmed the Southern Hemisphere during this period. 

Abstract The wind‐blown flux of sand generates dunes, wind erosion, and mineral dust aerosols. Existing models predict sand flux using the wind friction velocity that characterizes near‐surface turbulent momentum fluxes. However, these models struggle to accurately predict sand fluxes. Here we analyze root causes of these model discrepancies using high‐frequency field measurements of winds and sand fluxes. We find that friction velocity is only predictive of sand fluxes on long timescales, when it correlates with horizontal wind speed. On shorter timescales, and for non‐ideal surface conditions, friction velocity is much less predictive, likely because the near‐surface wind momentum budget is dominated by other, less predictable terms. We furthermore find that variability in 30‐min averaged sand fluxes at a given friction velocity is not driven by changes in turbulence but by changes in surface conditions, raising a challenge for models. These findings can improve sand flux models and clarify their limitations. 

Abstract Measurements of dust aerosol size usually obtain the optical or projected area‐equivalent diameters, whereas model calculations of dust impacts use the geometric or aerodynamic diameters. Accurate conversions between the four diameter types are thus critical. However, most current conversions assume dust is spherical, even though numerous studies show that dust is highly aspherical. Here, we obtain conversions between different diameter types that account for dust asphericity. Our conversions indicate that optical particle counters have underestimated dust geometric diameter (D_geo) at coarse sizes. We further use the diameter conversions to obtain a consistent observational constraint on the size distribution of emitted dust. This observational constraint is coarser than parameterizations used in global aerosol models, which underestimate the mass of emitted dust within 10 ≤ D_geo ≤ 20 μm by a factor of ∼2 and usually do not account for the substantial dust emissions withD_geo ≥ 20 μm. Our findings suggest that models substantially underestimate coarse dust emission.