Simulation of radiative and dynamical responses of the middle atmosphere to the 11-year solar cycle

Details Simulation of radiative and dynamical responses of the middle atmosphere to the 11-year solar cycle Simulation of radiative and dynamical responses of the middle atmosphere to the 11-year solar cycle

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jastp..67..125s&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 67, Issue 1-2, p. 125-143.

Physics

11

Scientific paper

This paper investigated the effect of solar irradiance variation of the 11-year cycle on the middle atmosphere with numerical models, focusing on the separate evaluation of radiative and dynamical effects. Time slice runs were made for solar maximum and minimum conditions by imposing changes in solar ultraviolet (UV) irradiance and ozone distribution. Radiative responses of the middle atmosphere to individual and combined changes were investigated with a fixed dynamical heating model (FDHM). We found solar forcing to be linearly decomposed into the forcings due to UV and ozone changes. The UV forcing is dominant and over twice as large as the ozone forcing around the stratopause and above, while the UV forcing is negligible and the ozone forcing is dominant below 5 hPa. The temperature response to the UV forcing has a vertical structure similar to that of the forcing with a maximum around the stratopause. In contrast, the temperature does not respond linearly to the ozone forcing because of the non-local response of terrestrial radiation. The ozone forcing induces a maximum warming at 10 20 hPa, while the forcing exhibits primary peak at the stratopause and secondary peak at 10 hPa. FDHM cannot reproduce the observed lower stratospheric warming in the tropics. We performed general circulation model (GCM) experiments to investigate the radiative and dynamical effects with T42L45 GCM, which is truncated triangularly at a total wavenumber of 42 in the horizontal and has 45 layers from the surface to 0.01 hPa (about 80 km) in the vertical. All the GCM experiments yield statistically significant annual mean warming between 40°S and 40°N in the stratosphere, which is quantitatively similar in amplitude to the radiative responses by FDMH. However, the responses are highly variable in high latitudes not only in the winter hemisphere but also in the summer hemisphere due to the updraft associated with the mean residual circulation. GCM results do not present realistic features of the seasonal march of zonal mean zonal wind anomalies of the polar night jet oscillation. We also investigated the effect of semi-annual oscillation in the tropical upper stratosphere on the solar signal by using Doppler-spread parameterization of gravity-wave drag instead of Rayleigh friction.

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