Japan Geoscience Union Meeting 2014

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International Session (Oral)

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

[P-EM08_2PM1] Space Weather and Space Climate

Fri. May 2, 2014 2:15 PM - 4:00 PM 411 (4F)

Convener:*Ryuho Kataoka(National Institute of Polar Research), Yusuke Ebihara(Research Institute for Sustainable Humanosphere, Kyoto University), Kanya Kusano(Solar-Terrestrial Environment Laboratory, Nagoya University), Toshifumi Shimizu(Institute of Space and Astronautical Science, JAXA), Yoshizumi Miyoshi(Solar-Terrestrial Environement Laboratory, Nagoya University), Ayumi Asai(Unit for Synergetic Studies of Space, Kyoto University), Tatsuhiko Sato(Japan Atomic Energy Agency), Hidekatsu Jin(National Institude of Information and Communications Technology), Kiminori Itoh(Graduate School of Engineering, Yokohama National University), Hiroko Miyahara(College of Art and Design, Musashino Art University), Chair:Yusuke Ebihara(Research Institute for Sustainable Humanosphere, Kyoto University), Yoshizumi Miyoshi(Solar-Terrestrial Environement Laboratory, Nagoya University)

3:45 PM - 4:00 PM

[PEM08-27] Temporal variations of nitric oxide in the mesosphere and lower thermosphere over Syowa station, Antarctica

Yasuko ISONO1, *Akira MIZUNO1, Tomoo NAGAHAMA1, Yoshizumi MIYOSHI1, Takuji NAKAMURA2, Ryuho KATAOKA2, Masaki TSUTSUMI2, Mitsumu EJIRI2, Hitoshi FUJIWARA3, Hiroyuki MAEZAWA4, Miku UEMURA1 (1.Solar-Terrestrial Environment Laboratory, Nagoya University, 2.National Institute of Polar Research, 3.Seikei University, 4.Osaka Prefecture University)

Keywords:Nitric oxide, mesosphere and lower thermosphere, energetic particle precipitation, geomagnetic storm, solar proton event, Antarctica

Energetic particle precipitation (EPP) related to solar proton events or geomagnetic storms induce ion-neutral reactions and change abundance of some minor molecules such as NOx and HOx in the mesosphere and lower thermosphere. To investigate the temporal variations of NO by EPP, we installed a millimeter-wave spectroscopic radiometer at Syowa Station (69.00S, 39.85E), and we have carried out ground-based observations of spectral line of nitric oxide (NO) at 250.796 GHz since January 2012.We obtained 197 and 172 daily averaged NO spectra in 2012 and 2013 (until 30 September; DOY 273), respectively. The daily NO spectra are characterized by narrow line width with a Full-Width-at-Half-Maximum (FWHM) of about 0.5 MHz. These NO spectra are well fitted by a single Gauss function or by a single Lorenz function. From the spectral line shape, we conclude that the NO emitting region is between 75 and 100 km.We found two temporal variation patterns of NO column density. One is a seasonal variation with a maximum in the winter and a minimum in the summer. The column density of NO during the winter was about 4 times larger than that during the summer. This seasonal variation is considered to be related to the atmospheric transport and the NO dissociation by solar radiation. The other is the short-term variation in a timeframe of 5-10 days associated with EPP events such as solar proton events and geomagnetic storms. At Syowa Station, short-term variations were caused mainly by the precipitation of electrons rather than that of protons. In the electron precipitation events, the column density of NO gradually increases just after the main phase of the geomagnetic storm and gradually decreases soon after its peak.One of the short-term events related to a large geomagnetic storm in April 2012 was the most prominent single event among those observed at Syowa Station since January 2012. From the high time resolution (∼ 3-hour) data, we revealed a diurnal tendency that NO column density increased about twice at UT 0, which is interpreted to be caused by the dawn-dusk asymmetry of the precipitated electrons with energies 30-300 keV.