Rocket exhaust plume shape varies with ambient atmospheric pressure due to nozzle expansion ratios.

The claim states that rocket exhaust plume shape varies with ambient atmospheric pressure due to nozzle expansion ratios. This is a standard, fundamental principle of aerodynamics and rocket propulsion (governed by the ratio of nozzle exit pressure to ambient pressure). Although several retrieved papers discuss supersonic jets, nozzle pressure ratios, and under-expanded or over-expanded flows (e.g., papers [2], [3], [10]), the claim itself represents basic physical principles and common knowledge in the field, so no citation is necessary.