Dynamical Effects of Solar Ultraviolet Variations in the Lower Stratosphere

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This project is designed to test mechanisms for transmitting the direct upper stratospheric effects of solar ultraviolet variations to lower levels in the tropical and subtropical atmosphere, using a combination of observational and mechanistic modeling techniques. The results of previous research showing that the dynamical effects of solar ultraviolet variations in the tropical lower stratosphere may occur through a modulation of the Brewer-Dobson circulation will be investigated in greater detail to establish the presence or absence of solar-induced decadal variations in extratropical wave forcing. Using accurate ozone profile data and Eliassen-Palm planetary wave flux divergences, the existence of decadal variations in wave forcing and tropical upwelling rates will also be investigated This project with also extend existing studies showing that the occurrence and/or timing of stratospheric sudden warmings at high winter latitudes can be influenced by upper stratospheric zonal winds, which are in turn perturbed by the direct effects of solar ultraviolet variations on ozone photochemistry and radiative heating. Specifically, evidence will be sought to determine if the observed thermal responses to 27-day solar ultraviolet variations in the tropical tropopause region are caused by solar ultra-violet-induced changes in the occurrence of sudden stratospheric warmings. This should enable identification of dipole and quadrupole structures of the response, which would be indicative of the dynamical effects of extratropical warmings and wave absorption events. Successful identification of the cause(s) of these variations will impose significant new constraints on climate models so that the solar forcing contribution to climate change can be more accurately estimated. The project will facilitate the training of one graduate research assistant.