Abstract
Abstract. This paper analyzes the effects of the solar rotational (27-day) irradiance variations on the chemical composition and temperature of the stratosphere, mesosphere and lower thermosphere as simulated by the three-dimensional chemistry-climate model HAMMONIA. Different methods are used to analyze the model results, including high resolution spectral and cross-spectral techniques. To force the simulations, an idealized irradiance variation with a constant period of 27 days (apparent solar rotation period) and with constant amplitude is used. While the calculated thermal and chemical responses are very distinct and permanent in the upper atmosphere, the responses in the stratosphere and mesosphere vary considerably in time despite the constant forcing. The responses produced by the model exhibit a non-linear behavior: in general, the response sensitivities (not amplitudes) decrease with increasing amplitude of the forcing. In the extratropics the responses are, in general, seasonally dependent with frequently stronger sensitivities in winter than in summer. Amplitude and phase lag of the ozone response in the tropical stratosphere and lower mesosphere are in satisfactory agreement with available observations. The agreement between the calculated and observed temperature response is generally worse than in the case of ozone.
Highlights
The variation of solar radiation reaching the Earth atmosphere with a period of approximately 27 days is caused by the longitudinally inhomogeneous distribution of magnetic field structures on the surface of the rotating Sun
We have presented a first modeling study of the atmospheric effect of the 27-day solar rotational variation, using a 3dimensional chemistry climate model that covers the atmosphere from the surface to the thermosphere
To analyze the atmospheric response to the 27-day solar forcing, we used a variety of spectral and cross-spectral analysis techniques, in addition to the linear correlation and regression methods used in most previous observational and modeling studies
Summary
The variation of solar radiation reaching the Earth atmosphere with a period of approximately 27 days is caused by the longitudinally inhomogeneous distribution of magnetic field structures on the surface of the rotating Sun. A 27-day solar induced signal is clearly identifiable in the middle and upper atmosphere. The unambiguous identification of the response to solar variations on the 11-year and longer time scales requires the analysis of very long timeseries. Knowledge on amplitude and phase characteristics of the response of the atmospheric thermal structure and chemical composition to the 27-day solar forcing is easier to derive and is useful for better understanding atmospheric photochemical processes. Because the periods of the 27-solar variation and of its harmonics are close to the typical periods of wave-like disturbances occurring in the middle atmosphere, the possible interaction of the solar and planetary wave signals is an interesting issue
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