I recorded this video from an airplane window while it was decreasing its elevation. What is the explanation for this optical distortion? This distortion appeared only in a certain range of elevation. Does it have anything to do with the temperature differences in different elevations?
Jello is caused by a combination of vibration and the use of a high shutter speed that is many times greater than the capture frame rate of the video recording.
To greatly reduce or eliminate a video's "jello" effect you need to use ND filters to reduce the incoming light and force the camera to use a much slower shutter speed. Ideally, you want to target using a shutter speed of about twice the video capture frame rate.
At very high shutter speeds, the video image being captured can shift left/right many times as the whole frame is captured. Thus, slight shifts in the image caused by vibrations are captured and horizontal bands of the captured image appear to jiggle slightly.
Using ND filters enables the use of lower shutter speeds which greatly reduces/eliminates the subtle left-right shifts in the video image that are captured in a single frame of video greatly reducing the "jello" effect.
When recording video at ~30 FPS use a 1/60th of a second shutter, similarly for 60 FPS you would prefer 1/120th of a second. That is called the 180° rule. To leave the shutter open that long on a sunny day you'll need to use ND filters.
Here is a screenshot halfway through the video, where the jello is quite bad:
Notice that the image appears OK. It is because the preceding and following frames are shifted that it appears to wobble. The image stabilization algorithm of some cameras combined with a shakey hand can cause the same effect as aircraft vibration; it's frequency specific, and a function of the rolling shutter, stabilization (if used), vibration and shutter speed.
The camera does not shoot each whole frame at the same time. It scans from top to bottom so scanlines are recorded at different times. If the camera is vibrating a few times per frame (as BenRW comments), the result is the "jello" effect.
It is a recording artifact most likely caused by vibrations affecting the camera. This effect would be strong if any part of the camera was touching the inside pane of the window or its frame.