Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM16] Physics and Chemistry in the Atmosphere and Ionosphere

Wed. May 29, 2019 10:45 AM - 12:15 PM A03 (TOKYO BAY MAKUHARI HALL)

convener:Yuichi Otsuka(Institute for Space-Earth Environmental Research, Nagoya University), Takuya Tsugawa(National Institute of Information and Communications Technology), Seiji Kawamura(National Institute of Information and Communications Technology), Chairperson:Yuichi Otsuka, Mitsumu Ejiri(国立極地研究所)

11:00 AM - 11:15 AM

[PEM16-08] Vertical fine structure and time evolution of plasma irregularities in the Es layer, observed by a high resolution Ca+ lidar

*Mitsumu K. Ejiri1,2, Takuji Nakamura1,2, Takuo T. Tsuda3, Takanori Nishiyama1,2, Makoto Abo4, Toru Takahashi1, Katsuhiko Tsuno5, Takuya Kawahara6, Takayo Ogawa5, Satoshi Wada5 (1.National Institute of Polar Research, 2.SOKENDAI (Department of Polar Science, The Graduate University for Advanced Studies), 3.The University of Electro-Communications, 4.Tokyo Metropolitan University, 5.RIKEN, RAP, 6.Shinshu University Faculty of Engineering)

Keywords:resonance scattering lidar, calcium ion density, sporadic E layer, fine structure, The mesosphere and lower thermosphere region

The vertical fine structures and the time evolution of plasma irregularities in the sporadic E (Es) 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 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 (K-H) 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 (foEs) observed by the ionosonde at Kokubunji (35.7°N, 139.5°E) simultaneously. The correlation showed a strong positive correlation with a coefficient of 0.91. These results suggest that Ca+ contributes forming the Es 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 just after the sunrise time at the conjugation point and before the local sunrise. 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 eastward winds at around 100 km, rather than the enhancement of the eastward electric field.