Dramatic irregularities in the plasma density of the ionosphere, first discovered by their effects on radio wave propagation in 1938, despite decades of investigation, still remain puzzling. Their deleterious effects on radio wave communication, satellite command and control, and GPS navigation strongly motivate better understanding of their nature. Many aspects of such irregularities are now understood, but the mechanism(s) of their formation and their detailed nature remain a topic of great interest. In this work, detailed time resolved measurements of lightning generated waves sometimes show dispersionless, strongly attenuated propagation with substantial propagation delays. These characteristics of the electromagnetic wave propagation in the hypothetical two-phase bubble/non-bubble lower ionosphere parallel the characteristics of acoustic wave propagation through two-phase liquid/vapor foams. This motivates the suggestion that the bottomside layer of the ionosphere may sometimes be foamy.Plain Language Summary Just as ocean waves breaking at the interface between sea and land produce copious bubbles and foam, recent satellite data suggests a similar phenomenon at the interface between neutral atmosphere and the charged plasma of the ionosphere. Lightning generated electromagnetic waves passing through the lower ionosphere observed by low altitude satellites are found to have the same characteristics as acoustic waves passing through foamy water. This hypothetical foam in the lower ionosphere apparently strongly absorbs some radio wave frequencies and seems to prevent most such waves from escaping the foam to pass through to the upper ionosphere.
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