How would a warp bubble interact with an atmosphere? What would happen if a warp drive entered the Earth atmosphere?
IIRC some scientists have created mathematical models that have shown that warp bubbles that don't exceed the speed of light may be physically possible. However, that left me wondering about sonic booms. The craft itself clearly wouldn't generate any sonic booms, because it'd be at rest relative to its warp bubble, right? However, how would the warp bubble itself interact with the surrounding atmosphere? Would it produce a sonic boom, if it's just expanding and contracting space? Would the expanding and contracting space have any unusual effects on the atmosphere around it?
The question was inspired by the recent US government statements on UFOs (which can be summed up as "they're real, they're not ours, and we don't know what they are") and some of the capabilities that many reports have given them: extremely high acceleration to super- or hyper-sonic speeds, extremely tight 90 degree turns at those speeds, a lack of sonic booms when operating at supersonic speeds, etc.
Edit: The related question 'What happens when some asteroid comes in the way of warp drive?' is about superluminal warp drives, while this question is about subliminal solutions.
 A: Subluminal warp bubbles have a surface, and it is made of some physical material 1. If such objects were to interact with the atmosphere, the usual intuition applies regarding how solid objects interact with gases. Subluminal and subsonic warp drives don't make sonic booms, and subluminal supersonic warp drives do make sonic booms, just like any other physical object. Depending on velocity, subluminal supersonic warp drives would be heated by the atmosphere similar to meteoroids and can produce a glowing ball.
Some further points:

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*Physical warp drives require propulsion to accelerate


*Positive-mass warp drives have to have large masses to have any interesting properties (e.g. Jupiter mass for a 10-meter craft), and hence would crush the Earth were they to enter Earth atmosphere.


*I left out of discussion warp drives based on negative energy since we don't know if such things can exist as well as superluminal warp drives as they require superluminal matter (more accurately, violate the dominant energy condition), which is also unlikely to exist 1, 2.
