This paper presents direct observation of the impact of the lithium releases on the ionospheric electron density during the WIND (wind measurement for ionized and neutral atmospheric dynamics study) campaign conducted on 2 September 2007 in Japan. The direct observation is unique in that the electron density enhancement was observed by using the NEI (number density of electrons by impedance probe) which can measure accurately the absolute value of the electron density, and the distance between the NEI and the LES (lithium ejection system) was very close (several tens of meters). Data analyses of the NEI on-board the sounding rocket S-520-23, which was launched from Uchinoura (31.3°N, 131.1°E) at 19:20 JST (JST = UT + 9 h), clarifies that lithium releases performed in the descending phase increased the electron density up to approximately 7 x 105 cm-3. A simple model calculation performed under the assumption that the increased electron density equals the photoionized lithium ion density indicates that the observed electron density enhancements cannot be explained by considering each lithium release as an instantaneous one, but rather by considering a convolution of very short-time intermittent releases. The model calculation is verified by comparison with the observation of the lithium resonance scattering light from the ground.
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