[P-EM10] Space Weather and Space Climate

[PEM10-21] Low-latitude auroral appearance associated with compressed magnetosphere as revealed by citizen science

*Tomohiro M. Nakayama^1,2, Ryuho Kataoka^3,4 (1.Arctic Research Center, Hokkaido University , 2.Graduate School of Environmental Science, Hokkaido University, 3.National Institute of Polar Research, 4.SOKENDAI)

Keywords:aurora, magnetic storm, solar wind density

We report four low-latitude auroral events observed from Hokkaido, Japan, on June 28, August 4, September 12, and November 9, 2024. These events are identified through citizen science efforts. The interesting point is that these four events occurred during moderately strong magnetic storms of Dst ~ -100 nT, associated with significant magnetopause compression. We estimate the emission altitude of these auroras from the multiple points datasets. The estimated altitudes are unusually high at ~600 km, indicating the strong enhancement of Joule heat in subauroral latitudes at that time. During the appearance of red auroras, the ASYM-H index was enhanced 1.5 times larger than the SYM-H index in all cases. The asymmetric tendency can be interpreted by the fact that an intense magnetopause compression can cause the flow-out of ring current particles, leading to the relatively small SYM-H and Dst indices than the actual ring current evolution. In this talk we emphasize the potential importance of solar wind density rather than the simple dynamic-pressure driven compression effects.