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

The effects of solar irradiance variability on the lower stratosphere and the troposphere are investigated using observed and general circulation model (GCM)‐generated 30 and 100 mbar geopotential heights. The GCM includes changes in UV input (+ or −5% at wavelengths below 0.3 micron and no ozone photochemistry and transport) to roughly approximate the combined effects of UV and ozone changes associated with the solar variability. The annual and seasonal 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 solar maximum, compared to solar minimum, in composite annual and seasonal averages. The model simulates this feature reasonably well, although the magnitude and statistical significance of the differences are often weaker than in observations, especially in summer. Both the observations and the model results 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 changes are interpreted as follows: The solar changes directly affect the stratosphere by changing the vertical gradients of temperature and zonal wind. This leads to changes in propagation conditions for planetary waves resulting in changes of E‐P flux divergence and then by the downward control principle, affecting the circulation in the lower stratosphere and the troposphere.