Vertical fine structure and time evolution of plasma irregularities in the Es layer observed by a high-resolution Ca+ lidar

• Published in: Earth, planets, and space planets, and space, 2019-01, Vol.71 (1), Article 3
• Main Authors: Ejiri, Mitsumu K., Nakamura, Takuji, Tsuda, Takuo T., Nishiyama, Takanori, Abo, Makoto, Takahashi, Toru, Tsuno, Katsuhiko, Kawahara, Takuya D., Ogawa, Takayo, Wada, Satoshi
• Format: Article
• Language: English
• Subjects: 2. Aeronomy; Earth and Environmental Science; Earth Sciences; Geology; Geophysics/Geodesy
• ISSN: 1880-5981; 1880-5981
• DOI: 10.1186/s40623-019-0984-z

The vertical fine structures and the time evolution of plasma irregularities in the sporadic E ( E s ) layer were observed via calcium ion (Ca + ) density measurements using a resonance scattering lidar with a high time-height resolution (5 s and 15 m) at Tachikawa (35.7°N, 139.4°E) on December 24, 2014. The observation successfully provided clearer fine structures of plasma irregularities, such as quasi-sinusoidal height variation, localized clumps, “cats-eye” structures, and twist structures, in the sporadic Ca + ( Ca + s ) layers at around 100 km altitude. These fine structures suggested that the Kelvin–Helmholtz instabilities occurred in the neutral atmosphere whose density changed temporarily or spatially. The maximum Ca + density in the Ca + s layer was two orders of magnitude smaller than the maximum electron density estimated from the critical frequency ( f o E s ) simultaneously observed by the ionosonde at Kokubunji (35.7°N, 139.5°E). A strong positive correlation with a coefficient of 0.91 suggests that Ca + contributes forming the E s layer as well as major metallic ions Fe + and Mg + in the lower thermosphere. Moreover, the formation of a new Ca + s layer at 110 km and the upward motions of the Ca + s layers at 100 km and 110 km were observed before the local sunrise and just after the sunrise time at the conjugation point. Although the presence or absence of a causal relationship with the sunrise time was not clear, a possible explanation for the formation and the upward motions of the Ca + s layers was the occurrence of strong horizontal wind, rather than the enhancement of the eastward electric field.