Numerical simulation of climate response to ultraviolet irradiation forcing

Abstract

Using the Whole Atmosphere Community Climate Model, sensitivity experiments are performed to identify the climate response to ultraviolet (UV) irradiation forcing. In the experiment, total solar irradiance (TSI) and solar spectral irradiation (SSI) are adopted as solar input from the dataset (1610–2009) reconstructed by Lean. Results show that UV variability has a strong impact on the middle atmosphere. Ozone (O3) distribution in the atmosphere is sensitive to UV irradiation variability. When UV irradiation is enhanced, the O3 content increases at altitudes from 30 km to 60 km and decreases at altitudes from 15 km to 30 km. The atmospheric temperature appears positive anomaly below the mesosphere. Anomalous warmth develops above 35 km with maximum warming anomaly apparent at the stratopause, consistent with the atmospheric distribution of O3, which indicates that the ozone heating mechanism plays an important role in warming. The O3 and temperature respond in an opposite manner when the UV irradiation is reduced. Furthermore, the stronger UV forcing leads to a change in the temperature distribution because of the O3 heating mechanism. This condition then modulates the zonal wind in the stratosphere and upper troposphere. Although the tropospheric response is weak on a global scale, a notable local response occurs over mid–high latitudes in the Northern Hemisphere (NH) during winter. Along with the enhanced zonal wind in the lower stratosphere near the North Pole, the positive phase of the Arctic Oscillation pattern appears over the NH, which causes a temperature increase over mid-latitude Asia. Finally, the behavior evident in the reanalysis data is compared with the results of the numerical experiments. The similar structure of the response fields means the results of simulation experiment is credible to some extent.