Whole Atmosphere Climate Change: Dependence on Solar Activity

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Thursday, May 9, 2019

Solomon and colleagues conducted global simulations of temperature change due to emissions of trace gases due to human activity, that extended from the surface, throughout the atmosphere, to space. These simulations were done under conditions of high solar activity, in order to compare the effect of the solar cycle on global change to previous work using low solar activity.

Graph of global simulations of temperature change due to emissions of trace gases
We conducted global simulations of temperature change due to emissions of trace gases due to human activity, that extended from the surface, throughout the atmosphere, to space. These simulations were done under conditions of high solar activity, in order to compare the effect of the solar cycle on global change to previous work using low solar activity. The Whole Atmosphere Community Climate Model–eXtended was employed in this study. As in previous work, lower atmosphere warming, due to increasing emissions of greenhouse gases, is accompanied by upper atmosphere cooling, starting in the lower stratosphere, and becoming dramatic, almost 2 K per decade on average, above 100 km altitude. This upper atmosphere cooling, and consequent reduction in density, is less than the almost 3 K per decade for low solar activity conditions calculated in previous simulations. This dependence of global change on solar activity is due to solar-driven increases in other gases other that cool the thermosphere, so greenhouse gases such as carbon dioxide have less effect. An ancillary result of these and previous simulations is an estimate of the solar cycle effect on temperatures as a function of altitude. There weren’t enough repeated runs to tell if there were any solar cycle effects in the lower atmosphere, but at higher altitudes, temperature change from solar minimum to maximum increased from near-zero at about 15 km, to approximately 1 K at about 50 km, to approximately 500 K at about 400 km, commensurate with observations and previous modeling studies.

The Whole Atmosphere Community Climate Model–eXtended was employed in this study. As in previous work, lower atmosphere warming, due to increasing emissions of greenhouse gases, is accompanied by upper atmosphere cooling, starting in the lower stratosphere, and becoming dramatic, almost 2 K per decade on average, above 100 km altitude. This upper atmosphere cooling, and consequent reduction in density, is less than the almost 3 K per decade for low solar activity conditions calculated in previous simulations. This dependence of global change on solar activity is due to solar-driven increases in other gases other that cool the thermosphere, so greenhouse gases such as carbon dioxide have less effect. An ancillary result of these and previous simulations is an estimate of the solar cycle effect on temperatures as a function of altitude. There weren’t enough repeated runs to tell if there were any solar cycle effects in the lower atmosphere, but at higher altitudes, temperature change from solar minimum to maximum increased from near-zero at about 15 km, to approximately 1 K at about 50 km, to approximately 500 K at about 400 km, commensurate with observations and previous modeling studies.

Publication Name: Journal of Geophysical Research Space Physics
First HAO Author's Name: Stanley C. Solomon

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