GAFD Seminar: Colleen Golja (Imperial College London)

The stratosphere is a region uniquely characterized by a temperature inversion, resulting in a radiatively nonconvective region. Air parcels in the stratosphere are instead driven away from radiative equilibrium by mechanical wave forcing from breaking atmospheric waves. Thus, the circulation is driven by complex wave-mean flow interactions which remain challenging to directly observe and, in turn, represent, in climate models. At present, models have significant differences in their representation of the stratospheric circulation. Never-the-less, these models are our primary tools for understanding the climate impacts of largescale stratospheric perturbations, including proposals to intentionally intervene in the Earth’s radiative budget; technologies often referred to as geoengineering or climate intervention proposals.

The introduction of aerosol or aerosol precursors to create an artificial reflective stratospheric aerosol layer, known as stratospheric aerosol injection (SAI), has been suggested as a strategy to reduced global average surface temperature to combat the effects of climate change. While SAI would reduce incoming shortwave radiation, it would also increase lower stratospheric heating, with substantial consequences for the overturning circulation and vortex formation; features which are highly coupled to surface climate features, such as the NAO. Recognizing substantial inter-model differences in stratospheric representation, this study employs a small model intercomparison to quantify and elucidate how variations in the response to an idealized lower‑stratospheric heating contribute to the total uncertainty in the stratospheric response to SAI.