Quantifying model uncertainty in the dynamical and radiative adjustments to stratospheric heating
Dr Colleen Golja, ImperialCambridge Fluids Network - fluids-related seminars4 November 2024 1:00pmMR3, CMSThe stratospheric circulation is driven by complex wave-mean flow interactions, and models and even reanalysis products have significant differences in their representation of the stratospheric circulation. Nevertheless, these models have been used to predict climate change due to Solar Radiation Management (SRM) strategies. The introduction of aerosol or aerosol precursors to create an artificial reflective stratospheric aerosol layer, known as stratospheric aerosol injection (SAI), leads to two major radiative effects: (1) a reduction in short wave forcing, and (2) an increase in lower stratospheric heating.
To date, very little work has been done to specifically examine the effects and uncertainties related to this lower stratospheric heating. To fill this gap, we analyze the outputs of a model intercomparison project in which a persistent, idealized heating rate is applied in the equatorial lower stratosphere of five GCMs. Despite an identical forcing, each model exhibits unique stratospheric and surface adjustments. We quantify inter-model differences in the stratospheric dynamical and radiative response to heating, providing a basis for understanding discrepancies in the corresponding tropospheric responses. We use offline radiative transfer calculations to probe the role of the baseline thermal state in a model’s sensitivity to the imposed heating tendency, providing a correction to the assumption of fixed dynamical heating. We couple this with an assessment of changes to the stratospheric overturning circulation and stratospheric water vapor to unpack key drivers of the modeled uncertainty in the response to stratospheric heating.