[RH77]

I'm guessing: first, additional throttle is required to maintain speed in a corner, and secondly -- perhaps a change in wind-speed and direction.

On the off-ramp, you're changing direction and increasing throughput of air past the sensor as the frictional loss requires more throttle to maintain speed. I get the same condition because very little throttle is used until the tight off-ramp corner and merge acceleration. The throttle opens wider and more air is allowed to flow past the sensor as the frictional loss from the tires biting into the corner requires more power. This equals more airflow and many times, lower IATs.

It's entirely normal -- more air generally means lower IATs (or at least a change).

RH77

EDIT: If the ambient temp is hotter than IAT norms, the opposite might be true.