I would assume the weather would be based on the element of the avatars. Like during thhunderstorms Ramuh would have the -3 effect. Or as SE likes to do, it could be the opposing element that gets the -3. So in thunder storms titian would get it. The 2nd would make more sence to me simply because why would i want shiva out in xarc. I dunno, I do want this though. But still got a ways to got on my summoner!
actually, its the first set of af the lvl 50 ones that get upgraded from sea, the afv2 gets upgraded from dynamis, from the CoP ones (valkurm tavnazia qufim buburimu) which you need to have beaten diabolos to access. what you want to drop is the -1 of what your trying to upgrade, (in this case a summoner horn -1) and with a few extra items and dynamis currency you can pay to have the afv2 made into +1
it's how much mp you need to keep the summoned critter out there. it reduces the cost of using it. for example. if ramuh takes 6mp/sec to be summoned and in the field, with the horn +1, it will only cost 3mp/second. couple that with the other gear a summoner can have and it's own mp regen, it might not cost anything to keep certain critters summoned.