Middle atmosphere response to different descriptions of the 11-yr solar cycle in spectral irradiance in a chemistry-climate model

摘要

The 11-yr solar cycle in solar spectral irradiance (SSI) inferred frommeasurements by the SOlar Radiation & Climate Experiment (SORCE) suggests amuch larger variation in the ultraviolet than previously accepted. We presentmiddle atmosphere ozone and temperature responses to the solar cycles inSORCE SSI and the ubiquitous Naval Research Laboratory (NRL) SSIreconstruction using the Goddard Earth Observing System chemistry-climatemodel (GEOSCCM). The results are largely consistent with other recentmodeling studies. The modeled ozone response is positive throughout thestratosphere and lower mesosphere using the NRL SSI, while the SORCE SSIproduces a response that is larger in the lower stratosphere but out of phasewith respect to total solar irradiance above 45 km. The modeled responses intotal ozone are similar to those derived from satellite and ground-basedmeasurements, 3–6 Dobson Units per 100 units of 10.7-cm radio flux() in the tropics. The peak zonal mean tropical temperatureresponse using the SORCE SSI is nearly 2 K per 100 units – 3times larger than the simulation using the NRL SSI. The GEOSCCM and theGoddard Space Flight Center (GSFC) 2-D coupled model are used to examine howthe SSI solar cycle affects the atmosphere through direct solar heating andphotolysis processes individually. Middle atmosphere ozone is affected almostentirely through photolysis, whereas the solar cycle in temperature is causedboth through direct heating and photolysis feedbacks, processes that aremostly linearly separable.This is important in that it means that chemistry-transport models shouldsimulate the solar cycle in ozone well, while general circulation models withoutcoupled chemistry will underestimate the temperature response to the solar cyclesignificantly in the middle atmosphere.Further, the net ozone response results from thebalance of ozone production at wavelengths less than 242 nm and destructionat longer wavelengths, coincidentally corresponding to the wavelength regimesof the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) and SpectralIrradiance Monitor (SIM) on SORCE, respectively. A higherwavelength-resolution analysis of the spectral response could allow for abetter prediction of the atmospheric response to arbitrary SSI variations.