Kernel‐Based Estimation of Stratospheric Aerosol Radiative Effects From Volcanic and Wildfire Events

Abstract To facilitate the quantification of the stratospheric aerosol direct radiative effect (ARE), this study develops a suite of aerosol kernels based on Modern‐Era Retrospective Analysis for Research and Applications, Version 2 reanalysis data. The kernels comprise a five‐dimensional data set that includes latitude, longitude, time, wavelength, and radiative forcing scenarios. They quantify the sensitivity of top‐of‐atmosphere (TOA) radiative fluxes to changes in stratospheric aerosol optical depth (AOD), and distinguish between scattering and absorbing aerosols. Band‐by‐band radiative kernels are developed to capture the spectral dependence of ARE, while adjusted kernels account for stratospheric temperature responses. Additionally, an analytical kernel is introduced, enabling the estimation of broadband radiative kernel values from boundary conditions such as TOA insolation, reflectance, and stratospheric AOD. Using these kernels, the stratosphere AREs of the 2022 Hunga volcanic eruption and the 2020 Australian wildfire are estimated. The Hunga eruption resulted in a global mean cooling effect of approximately −0.4 W/m 2 throughout 2022. In contrast, the Australian wildfire induced a global mean instantaneous ARE of +0.3 W/m 2 and a stratosphere‐adjusted ARE of −0.04 W/m 2 . Validation against radiative transfer model calculations confirms the accuracy of our kernel‐based estimates. The results demonstrate the significance of spectral dependencies in stratospheric ARE and highlight the distinct radiative sensitivities of stratospheric aerosols compared to their tropospheric counterparts. The developed radiative kernels provide an efficient and versatile tool for assessing the climatic impacts of stratospheric aerosols.