“…Plasma bubbles were first discovered by in-situ satellite measurements [Hanson and Sanatani, 1973;McClure et al, 1977], and have since been detected by rocket [Kelley et al, 1976;Morse et al, 1977;Szuszczewicz et al, 1980] and by incoherent-scatter radar [Towle, 1980;Tsunoda, 1980a,b]. The plasma density within bubbles was found to be as much as three orders of magnitude less than the peak plasma density in the F layer (i.e., the depletion can approach 99.9 percent).…”