(It was mentioned at the beginning of Chapter 2b. I'll add the info in the Seasonal Activities topic from now on, to be sure we don't miss it.)
After a bit of experimenting with collecting the flares to harvest the raw vis they contain, Ludovicus comes to a number of conclusions. First is that a Rego Auram spell can indeed be used to bring the flares closer, although an Ignem requisite is needed (Base 2 works, no additional magnitude needed for the requisite). It isn't even particularly tricky (no magnitude for precision needed), but the spell needs to be maintained for some time before one can bring it close enough for the vis to be harvested at touch range. Maintaining the first spell while trying to cast the second one had been a difficult challenge and he'd needed several attempts to achieve it. Finally, he'd also learned that whatever item they enchanted with to harvest the vis at tough range, it would need to be proof against fire. The flares were hot, as the small burns he'd collected proved.
(As for frequency, so far there has been only a few occasion when the magus on watch has been called more than five times in a day and night. Sometimes several days can go by without any flare, then a close succession in the same day.)
"As a member of the covenant, you certainly have the right to attend the council meeting. We should be back within a week of the equinox, so the loss of vis should be minimal if Renatus," he nods to the Bjornaer magus, "is unable to collect the few flares that happen during that period."