Upper-atmospheric models are simulations of the Earth's atmosphere between 20 and 100 km (65,000 and 328,000 feet) that comprises the stratosphere, mesosphere, and the lower thermosphere. Whereas most climate models simulate a region of the Earth's atmosphere from the surface to the stratopause,[citation needed] there also exist numerical models which simulate the wind, temperature and composition of the Earth's tenuous upper atmosphere, from the mesosphere to the exosphere, including the ionosphere.[citation needed] This region is affected strongly by the 11 year Solar cycle through variations in solar UV/EUV/Xray radiation and solar wind leading to high latitude particle precipitation and aurora. It has been proposed[who?] that these phenomena may have an effect on the lower atmosphere, and should therefore be included in simulations of climate change. For this reason there has been a drive in recent years to create whole atmosphere models to investigate whether or not this is the case.