"...The pain seems to appear sporadically, and I'm at a lost on how to predict or prevent it. Taking a decongestant 1-2 hours before landing seems to work -- but I can't be sure since the pain is unpredictable in the first place.

Any ideas?"

Yes! I SWEAR by using Vicks vaporub in both ear canals- I swipe a goodly amount in each, and under the nasal passages (just use enough to swab, not clog!) it works WONDERS! NO more headaches. NO more earaches. I think it has something to do with opening the stuck canals, I am not sure. A girl gave me this tip years ago and I tell you it WORKS. Another wonderful tip: works on screaming babies on flights. I think their screaming is a result of earaches. I have saved many person's sanity and peace of mind with this tip. I also get earaches from the wind- beats me but the Vicks trick works in about 4-5 minutes after application. Please try it and let us know if it works for you, I can't see why it wouldn't. I never fly without a small travel size tin of Vicks (yes they sell them, I find them in convenience stores all the time where they display those tiny OTC meds) good luck