Time scale of FAC variations estimated by SWARM and a comparison with ground based geomagnetic and micro-barometric observations

Wednesday, 16 December 2015: 16:45
300 (Moscone South)
Toshihiko Iyemori1, Kunihito Nakanishi1, Tadashi Aoyama1, Hermann Luhr2, Yoko Odagi1, Yoshihiro Yokoyama1, Masato Iguchi3, Shigeo Sugitani4, Hiroyuki Hashiguchi5, Mitsuru Utsugi6, Toshimitsu Ono7 and Yasuharu Sanoo8, (1)Kyoto University, Graduate School of Science, Kyoto, Japan, (2)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (3)Sakurajima Volcanic Observatory, Kagoshima, Japan, (4)NICT National Institute of Information and Communications Technology, Onna, Okinawa, Japan, (5)University of Kyoto Gokasho, Kyoto, Japan, (6)Kyoto Univ., Kumamoto, Japan, (7)Committee for Education, Niyodo-cho, Japan, (8)Asahi University, Hozumi, Japan
The low altitude magnetic satellites such as Oersted, CHAMP or SWARM observed small scale magnetic fluctuations having period about 10 to 30 sec along their orbits in middle or low latitudes. The amplitude is usually less than a few nT and they were observed almost always on the dayside. Most of them are interpreted as the spatial structure of small scale FACs probably generated by atmospheric gravity waves (Nakanishi et al., 2014). From a statistical analysis of correlation coefficients between a pair of the SWARM satellites, Iyemori et al. (2015) estimated the temporal scale of FAC variation to be roughly about 200 secs for meridional magnetic components and about 340 secs for longitudinal, i.e., east-west component. Based on a spectral analysis of ground geomagnetic and micro-barometric observations, we found that the spectral peaks with similar periods, i.e., 200sec or 320-350sec tend to appear statistically. This tendency supports the idea that the source of the FACs is mainly the acoustic mode of gravity waves. We discuss the characteristics of the power spectra, in particular, those of micro-barometric observations.