The research team, led by Professor Chi Wang, Academician of Chinese Academy of Sciences, along with Professors Qinghe Zhang, Bingxian Luo, Yanhong Chen, Ercha Aa, Wengeng Huang, Hui Li, Dr. Tianjiao Yuan, Hua Shen, Heng Xu, Siwei Liu, Xin Wang from the Chinese Academy of Sciences' National Space Science Center, and Professor Shunrong Zhang from Massachusetts Institute of Technology, Professor Xinan Yue from the Chinese Academy of Sciences' Institute of Geology and Geophysics, used data from the Chinese Meridian Project (CMP) monitoring network and other multi-instrument ground- and space-based measurements to analyze the ionospheric response during the May 10-12, 2024 super geomagnetic storm, the strongest in last two decades and known as the Mother's Day magnetic storm. Their findings revealed a dramatic storm-time depletion of ionospheric electron density, with a maximum reduction of 98% over China and across the entire Northern Hemisphere for more than two days. The largest TEC depletion reached 100 TEC units in low-latitude regions over East Asian sector, accompanied by the suppression and eventual disappearance of the northern crest of the equatorial ionization anomaly (EIA). Furthermore, this extensive depletion led to a complete loss of ionospheric backscatter echoes in multiple ionosondes within the CMP network for an extended period. Analysis of vertical plasma drift and ΣO/N₂ ratios indicated that the extreme depletion was primarily driven by neutral composition disturbances propagating from high to low latitudes, combined with the effects of a westward electric field caused by overshielding penetration and disturbance dynamo electric fields at low latitudes.
In addition to extreme depletion in the Northern Hemisphere, the research team also observed another pronounced phenomenon, the significant hemispheric asymmetry in the global ionosphere. The mid- to low-latitude ionosphere in the Southern Hemisphere exhibited considerable electron density enhancements, showing a striking contrast to the Northern Hemisphere's depletion. By combining multi-instrument observations with Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) simulations, the team demonstrated that this hemispheric asymmetry was driven by summer-to-winter neutral winds and differences in ΣO/N₂ ratios between the two hemispheres.
"The magnitude and extent of the reduction in ionospheric electron density are very unusual, and we have also observed interruptions in HF radio signals, resulting from critically low electron density that prevents effective signal reflection." explains Yanhong Chen, the first author of the study. "The observations from CMP, multi-satellites data, and numerical modeling help us to know about the physical process causing these ionospheric changes, enhancing our understanding of ionospheric response mechanisms during super geomagnetic storms."
This study not only advances the understanding of the magnetosphere-ionosphere-thermosphere coupling system, but also verifies the effects of space weather on radio-technological systems.
