Thermal response of the tropical tropopause region to solar ultraviolet variations

Correlative and linear regression analyses of National Centers for Environmental Prediction (NCEP) temperature data in the tropical lower stratosphere and upper troposphere confirm the existence of a thermal response to solar ultraviolet variations occurring on the time scale of the solar rotation period. The maximum response occurs near the 100 hPa level (approximately 16 km altitude) at a phase lag of 2 ± 2 days with an amplitude of 0.24 ± 0.07 Kelvin for a change in the Mg II core-to-wing ratio of 0.01 (approximately equivalent to a 4% change in solar UV flux at a wavelength near 200 nm). It is suggested that the observed thermal response near the tropical tropopause is caused by changes in upwelling rates induced by the direct effects of solar UV forcing on photochemistry, radiative heating, and dynamics in the upper stratosphere.