Last year I made a summary on the best conditions for a good seeing. Unfortunately there are as well other conditions that damage it. Here is a “good” example on Jupiter: the influence of the jet-stream.
What is the jetstream?
The jet-stream is a very narrow, but very fast, stream of wind that runs at high altitude over various Earth latitudes. Of course we find jet-streams on every planet possessing an atmosphere. This wind stream demarcates big air masses of different temperatures, like between poles (cold air) and tropics (warm air).
The left image is a visualization of the jet-stream thanks to a map from the Global forecast system (GFS) during the night of December 29th, 2014. This was one of my very rare observing windows recently :(.
Colors stand for wind speed (warmer = stronger, so red, orange or yellow). The stream is circulating between high pressures (A) and low pressures (D).
What’s its influence on images ?
The jet-stream generates instability and this is well visible on images. On the map above we easily see that France is located under a strong jet that circulates on the eastern flank of the high pressure. This is a highly unfavorable situation! Here is a short video taken with a red filter that clearly shows the result (movie is compressed so viewing quality is bad).
And here is a processed image (from another 2 mn video)
Bad result ;). Unfortunately, in western France during winter, this situation is often met for the observer, because the jet-stream is generally more intense and circulates at lower latitudes than during summer. The position of the high pressure is preponderant.
