Actually, I'm looking for an relation between upper atmospheric density variation and solar activities. I wanna know how they were interconnected.

https://www.nasa.gov/topics/solarsystem/features/solar-effects.html

http://www.sws.bom.gov.au/Category/Educational/Space%20Weather/Space%20Weather%20Effects/SatelliteOrbitalDecayCalculations.pdf

During times of strong solar activity, the upper atmosphere (ionosphere and exosphere) is heated more strongly. Also, diatomic molecules in the upper atmosphere are more likely to be split into single atoms, halving their molecular weight. Both effects reduce the rate of decrease of upper-atmospheric density with increasing altitude. Thus both effects increase aerodynamic drag on satellites and shorten their orbital lifetimes.