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An overview of the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project is presented with a brief description of the products to be developed. This is a Japanese inter-university research program to build the metadata database for ground-based observations of the upper atmosphere. The project also develops the software to analyze the observational data provided by various universities/institutes. These products will be of great help to researchers in efficiently finding, obtaining, and utilizing various data dispersed across the universities/institutes. This is expected to contribute significantly to the promotion of interdisciplinary research, leading to more a comprehensive understanding of the upper atmosphere.

Characteristics of seasonal variation and solar activity dependence of the X and Y components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in midlatitudes and Guam near the equator have been investigated using long‐term geomagnetic field data with 1 h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq‐X and Sq‐Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq‐X and Sq‐Y. The result of the correlation analysis between the solar F10.7 index and the Sq‐X and Sq‐Y shows an almost linear relationship, but the slope of the linear fitted line varies as a function of local time and month. This implies that the sensitivity of Sq‐X and Sq‐Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq‐Y at Guam shows good agreement with that of a magnetic field produced by interhemispheric field‐aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the prenoon to afternoon sectors. The direction of the interhemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.

The magnetic data obtained by the SWARM (the Earth's Magnetic Field and Environment Explorers) satellites in middle or low latitudes during the initial 2 months after launch were analyzed, when they flew nearly on the same orbit with variable time separation ranging from 5 to 100 s. It was confirmed that the small-scale magnetic fluctuations having period around 10-30 s are the manifestation of spatial structure of small-scale field-aligned currents along the orbits. From the statistical relation between correlation coefficients and two satellite separation in time, the typical time scale of temporal variation of the field-aligned current system is estimated to be around 200 s for meridional component and 340 s for zonal components of the magnetic fluctuations, respectively. Existence of shorter time scale around 30-50 s was also found. These results suggest that the main source of current generation is the acoustic mode of atmospheric gravity waves.