Rainboe, I think for a 'typical jet' rate of turn of 2 degrees per second, the average groundspeed change from 'into wind' to 'downwind' would be 400kts / 90 secs, which equals just over 4kts per second.
That is an average for the 180 degree turn, so the groundspeed would be changing at a slower rate at the begining and end of the turn, and at a faster rate during the middle part of the turn.
One would imagine that this faster rate of change of groundspeed would result in some noticeable effect on the airspeed. I have flown in a 150kt jetstream and have changed heading such that the groundspeed changed by 50kts in 20 seconds or so, but I have to say I have never seen any airspeed change as a result.
We need a physicist to help! Anyone out there?
Eck