Solar Influence on Troposphere through Stratospheric Dynamical Processes

Kunihiko Kodera [kodera@mri-jma.go.jp], Meteorological Research Institute, Tsukuba, Japan.

    Traditionally the solar influence on climate is considered in term of the variation of the total solar irradiance (TSI). This is particularly true for a longer time variation such as the Maunder minimum. Observed TSI variation, however, shows little variation. Also, the regional aspects of the solar influence are better characterized as dynamical rather than radiative. In the present study the solar influence through a solar spectrum change is discussed.

            The change in the ozone heating rate produces small zonal wind anomalies in the subtropics of the winter hemisphere. This initial solar effect in the stratopause region is amplified through interaction with planetary waves propagating from the troposphere. The solar effects can be dynamically transmitted to the troposphere by two processes: (i) poleward and downward shift of the westerly jet through interaction with the planetary waves, and the wave reflection. (ii) modulation of the mean meridional circulation. For example, solar influence on North Atlantic Oscillation or AO is produced by first process, while that of monsoon rainfall and the El Nino can be explained by the second one. These processes should work for centennial scale variation as well as the 11-year cycle.