Say I operate a satellite in LEO, and I think I have instruments on board that will be sensitive to space weather events. If I keep an eye on space weather activity levels, when do I start turning off these sensitive instruments? How often should I expect to take action like this? Finally, how dependent is all of this on my orbit altitude?
To boil this down to a simple answer is difficult, but here's some of the factors that are required to make this assessment.
First of all, the question comes, what is your satellite is specified to. When you build a satellite, you specify a level of radiation tolerance you desire. If you have more than that level of radiation, then you have to start taking special precautions. That level depends very much if you are in LEO, GEO, or worse, an elliptical orbit. The requirement should take care of you for your day to day operations, but probably won't take care of you for the really extreme stuff (Unless you are willing to pay for it).
So, what are some typical requirements for different orbits? One example of the typical radiation levels can be found from ESA, which has several graphs like the following:
Suffice to say, if you have anything much larger than the normal levels, you will start to worry about it. You can take a look at space weather today from NOAA, and see how the radiation events look. Or look at some of the archives.
In reality, this is often somewhat of a trial and error. If you notice something bad starting to happen during one solar storm, then you might look at the parameters and set limits based off of that. Or you might simply end up ultra conservative. Look through historical data, and decide how often it is acceptable to be off the air. For many communications, defence, and other uses, it's just simply not acceptable to be off the air ever, some, like special telescopes, limited outage might be preferred to the added expense of shielding.
There are also metrics which show that you aren't having a problem yet, but you might be experiencing higher levels of radiation than is healthy for your system. The best indicator is some idea as to the number of times your Error Detection and Correction algorithms are firing off. If you see a spike in them, it might indicate that you have a radiation problem that you need to deal with.
A number I've often found to be useful is looking at the proton flux, and stating if it's over 10 cm-2s-2sr-1, for LEO. I'm not very familiar with eclipse/ GEO, but I do know the satellites experience more radiation overall. Thus, they probably have more protection, and overall are better off.