HR: 11:40h
AN: SH11E-05 INVITED     [PDF]
TI: Effects of Solar Ultraviolet Variability on the Stratosphere: A Sun-Climate Connection
AU: * Hood, L L
EM: lon@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AB: Solar ultraviolet radiation at wavelengths near 200 nm is responsible for photodissociation of molecular oxygen and ozone production in the stratosphere. On the time scale of the 27-day solar rotation period, previous work has documented the response of the upper stratosphere and lower mesosphere to solar UV variations. This response is largely a result of direct photochemical and radiative forcing. Recent work, however, indicates an additional response to 27-day UV forcing in the lower stratosphere, including the tropical tropopause region. The thermal response maximizes near the 100 hPa level and amounts to 0.24 +/- 0.07 Kelvin for a 4% change in the solar UV flux near 200 nm (typical of UV variations occurring on this time scale under solar maximum conditions). The phase lag is 2 +/- 2 days. Parallel analyses using other solar-correlated variables (total solar irradiance, Galactic cosmic ray flux, etc.) verify that the solar UV flux is the most probable forcing mechanism. 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 in the upper stratosphere. On the time scale of the 11-year solar cycle, stratospheric total column ozone and lower stratospheric temperature are also observed to vary approximately in phase with the solar UV flux during the period since 1979 when continuous global satellite measurements began. Most of the column ozone variation occurs in the lower stratosphere (85% below 16 hPa), a result that contrasts with most prior model predictions. At low latitudes, there is evidence that the observed ozone and temperature variation is caused by changes in upwelling rates that are, in turn, probably due to observed decadal changes in extratropical wave forcing. The latter may be modulated by the direct effects of solar UV variations in the upper stratosphere. These observed lower stratospheric dynamical effects of solar UV variations and their secondary tropospheric consequences must be understood to allow more accurate model simulations of solar-induced climate change.
DE: 1650 Solar variability
DE: 7549 Ultraviolet emissions
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting