Effects of solar cycle variability on the lower stratosphere anti the troposphere

The effects of solar irradiance variability on the lower stratosphere and t he troposphere are investigated using observed and general circulation mode l (GCM)generated 30 and 100 mbar geopotential heights. The GCM includes cha nges in UV input (+ or -5% at wavelengths below 0.3 micron and no ozone pho tochemistry and transport) to roughly approximate the combined effects of U V and ozone changes associated with the solar variability. The annual and s easonal averages of the height differences between solar maximum and solar minimum conditions are evaluated. In the subtropics, observations indicate statistically highly significant increased geopotential heights during sola r maximum, compared to solar minimum, in composite annual and seasonal aver ages. The model simulates this feature reasonably well, although the magnit ude and statistical significance of the differences are often weaker than i n observations, especially in summer. Both the observations and the model r esults show a strong dipole pattern of height differences when the data are partitioned according to the phase of the quasi-biennial oscillation (QBO) , with the pattern reversing itself with the change in the phase of the QBO . The connection between solar variability and lower atmospheric charges ar e interpreted as follows: The solar changes directly affect the stratospher e by changing the vertical gradients of temperature and zonal wind. This le ads to changes in propagation conditions for planetary waves resulting in c hanges of E-P flux divergence and then by the downward control principle, a ffecting the circulation in the lower stratosphere and the troposphere.