Japan Geoscience Union Meeting 2015

Presentation information

International Session (Oral)

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

[P-EM06] Mesosphere-Thermosphere-Ionosphere Coupling in the Earth's Atmosphere

Wed. May 27, 2015 9:00 AM - 10:45 AM A01 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Huixin Liu(Earth and Planetary Science Division, Kyushu University SERC, Kyushu University), Yuichi Otsuka(Solar-Terrestrial Environment Laboratory, Nagoya University), Libo Liu(Institute of Geology and Geophysics, Chinese Academy of Sciences), Atsuki Shinbori(Research Institute for Sustainable Humanosphere (RISH), Kyoto University), Chair:Huixin Liu(九州大学理学研究院地球惑星科学専攻)

10:15 AM - 10:30 AM

[PEM06-10] Characteristics of long-term variation of the geomagnetic solar quiet daily variation

*Atsuki SHINBORI1, Yukinobu KOYAMA2, Masahito NOSE2, Tomoaki HORI3, Yuichi OTSUKA3, Akiyo YATAGAI3 (1.Research Institute for Sustainable Humanosphere (RISH), Kyoto University, 2.World Data Center for Geomagnetism, Kyoto University, 3.Solar-Terrestrial Environment Laboratory, Nagoya University)

Keywords:Solar activity, Geomagnetic solar quiet daily variation, Ionospheric conductivity, Ionospheric dynamo, Secular variation of geomagnetic field, Thermospheric wind

Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 - 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10 - 12 year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 - 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53 % of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 - 2013, and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100 km altitude and residual Sq amplitude showed an anti-correlation for about 71 % of the geomagnetic stations. The decreasing trend of the residual Sq amplitude implies that the ionospheric Sq current intensity tends to weaken due to a decrease of the ionospheric conductivity associated with an increase of the ambient magnetic field intensity. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. The decreasing trend of the residual Sq amplitude in the equatorial region indicates movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.