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Geophysical Research Letters

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Results are presented of the first measurements of detailed structure of electron density within striated vapor releases in the ionospheric F-region. Six rocket probes penetrated ion clouds in three separate barium release events (two in each case) and showed considerable enhancement in F-region electron density over the normal background ionization. In four traversals the electron density exceeded 10 cm- 3 with the maximum of 5 x 106cm- 3 observed in one case. Two showed dramatic structure in the electron density profiles associated with the passage through striated portions of the cloud. These structures had spatial extent as measured by the rocket.probe normal to the terrestrial magnetic field of hundreds of meters with the density changing factors in the range from 2 to 10 as the probe passed into and out of the structures. The change of density on some of the features had particularly fast drop off corresponding to less than 20 meters travel normal to the magnetic field. The spectral power distribution of the irregularity amplitudes versus wavenumber scale size could be roughly described as a power law with a spectral index of from-2 to -3 within the striated regions. These results are in good agreement with predictions of the ExB gradient drift instability mechanism as depicted by the simulation studies of Scannapieco, et al. [1976] in the late time nonlinear regime. Introduction