Impact of solar cycle variation of UV radiation in the Northern Hemisphere winter polar troposphere

Solar cycle (SC) induces variations in the UV radiation. The UV variations change the ozone production rate in the middle atmosphere. Responses to the SC-induced variations occur mainly in the equatorial upper stratosphere and the lower mesosphere. It has been reported that zonal mean temperature difference is 1--2 K between solar maximum and minimum. The temperature variation in the equatorial upper stratosphere modifies the meridional temperature gradient between the equatorial region and winter polar region. Change in the temperature gradient induces difference in the strength of the stratospheric polar vortex, which accompanies change in poleward meridional mass circulations and as a result change in the horizontal distribution of the sea-level pressure (SLP) in the winter polar region. In the present study, this mechanism of SC-induced SLP variations in the Northern Hemisphere (NH) winter polar regions is examined using an idealized whole-atmosphere general circulation model. This global model covers from the ground to the lower thermosphere and includes gravity wave drag parameterization and realistic topography. This idealized model is driven by the zonally-averaged radiative equilibrium temperature, but it nevertheless simulates quite realistically atmospheric variabilities such as sudden stratospheric warmings and quasi-biennial oscillations. Perpetual January simulations for solar maximum and minimum show that this idealized model can reproduce the negative SLP anomaly in the NH polar regions in solar maximum, but the magnitude of the anomaly is weak compared with reanalysis studies. Mechanisms of this SLP anomaly are examined through planetary wave dynamics and gravity-wave processes.