Suppose one wanted to modulate the power of a hypothetical, powerful ion thruster on the ISS to continuously compensate the atmospheric drag force in order to achieve near-perfect free-fall conditions (near-zero microgravity) for the station's experiments, at least between other maneuvers.
What is the time dependence of the drag force on the ISS? Is it fairly constant, say within 10% over a given orbit? Or is there a large day/night variation due to interaction of solar radiation and solar wind with the ionosphere?
Are there other effects that can cause significant changes in drag force on the ISS within the timeframe of a given orbit as well?
note: This is a Gedankenexperiment to explore the nature of the drag force on the ISS at its orbital altitude, not a proposal for a practical way to minimize microgravity, as there are several other considerations, so there's no need to start a list of these in comments. This question has its origins from comments below this answer.