From the wind direction data, I was pointed to a problem with this sonic, and photos show that it is upside down. This time, I think the "cassette" was incorrectly positioned – probably a year ago, but we hadn't noticed it. It would be a 5-min fix to remount, especially since it is low on the tower, but Chris and I decided to come home, rather than add over an hour of driving with a loaded pickup over the rutted road. We'll need to address this in our next site visit.
This also brings up the question of whether we should have sealed the cassette mounts as Campbell had advised last spring. We'll need to consider this in the coming weeks.
In the meantime, I changed the cal_file to "flipped", so the data now appear to be correct.