Study on the Response of the Polar Ionosphere to Solar Storms
Members of the Meridian Project team from the China Polar Research Center conducted a study on the instantaneous observation characteristics of the magnetosphere-polar ionosphere coupling system's response to solar storms, utilizing combined observation data from the Antarctic Zhongshan Station's coherent scatter radar, digital ionosonde, and fluxgate magnetometer. By using the Meridian Project's autonomous polar space environment stereoscopic observation system to investigate the solar-terrestrial energy coupling process, the research revealed the dynamic characteristics of ionospheric irregularities influenced by energy particle precipitation. The study obtained instantaneous response characteristics of the upper polar atmosphere to solar storms and provided insights into the driving changes of field-aligned currents and ionospheric electric fields. The related work was published in the authoritative academic journal "JGR: Space Physics." The authors, Jianjun Liu, Shibaji Chakraborty, and Xiangcai Chen, were recognized with the 2023 Outstanding Achievement Award of the Meridian Project.
The polar regions serve as natural windows to outer space, where nearly vertical converging magnetic field lines connect with space plasma, and the funnel-shaped magnetic geometry facilitates the solar wind-magnetosphere coupling and the projection focusing of magnetospheric dynamics in the polar areas. As a result, the polar ionosphere acts as a display screen for changes in the solar-terrestrial environment. Solar activity events propagate through interplanetary space to Earth, manifesting in the polar sky as colorful auroras, ionospheric, and geomagnetic disturbances. Polar research stations have become vital observation platforms for understanding space physics processes and the impact of space environments. The polar space environment is influenced not only by solar illumination and seasonal effects but also by intense impacts from typical solar storms, such as coronal mass ejections, solar flares, and interplanetary shocks, which can even trigger hazardous space weather events. These extreme space weather events directly affect satellite payload safety, the orbital altitude of polar-orbiting meteorological and resource satellites, over-the-horizon and shortwave radio communications, among other things. Therefore, studying the effects of solar storms on the polar space environment is of great practical significance.
In response to the polar ionosphere effects triggered by solar storms impacting Earth's space, the Polar Atmosphere and Space Physics Research Team at the China Polar Research Center utilized cosmic noise absorption, geomagnetic field, and ionosphere observation data from the Antarctic Zhongshan Station and the Arctic Huanghe Station, combining satellite data on solar wind plasma and interplanetary magnetic fields to analyze in detail the ionospheric response characteristics caused by interplanetary shock waves hitting Earth’s space. Figure 1 illustrates the schematic of the Zhongshan Station at different times relative to the auroral oval position. At the moment the interplanetary shock wave impacts Earth, Zhongshan Station is positioned at magnetic noon. The ionosonde observed an increase in the low ionosphere electron density, a brief downward movement of the ionosphere, and a negative geomagnetic disturbance. The McMurdo coherent scatter radar covering Zhongshan Station detected a reversal of the ionospheric plasma convection from anti-sunward to sunward (south to north), while the Zhongshan coherent scatter radar detected a change in the plasma convection direction from westward into the polar gap region to eastward out of the gap (west to east, as shown in Figure 2). The near-magnetic conjugate observation pair formed by Zhongshan Station and Huanghe Station revealed significant high-energy particle precipitation after the shock wave hit Earth's space, based on a comparison of cosmic noise absorption data from Huanghe Station. Joint observations from multiple Meridian Project space physics instruments indicate that the dawn-dusk convection electric fields in solar-terrestrial interactions played a crucial role. It is the enhanced convection electric fields and high-energy particle precipitation that drove the extreme space environment changes observed in the polar gap region, providing first-hand monitoring and warning signals for mitigating hazardous space weather events caused by solar storms.
Figure 1: Schematic diagram of the daily 24-hour positional changes of Zhongshan Station relative to the auroral oval in the magnetic latitude/magnetic local time coordinate system. The shaded diagonal area approximately indicates the region of auroral activity， the black dots representing Zhongshan Station's position relative to the auroral oval throughout the day, and the red circle denotes the field of view of the auroral imager at Zhongshan Station. "12" indicates magnetic local noon, and "18" indicates dusk.
Figure 2: Ionospheric echo conditions observed by the ionosonde, high-frequency coherent scatter radar, and McMurdo radar at Zhongshan Station on June 16, 2012. The vertical line indicates the time when the interplanetary shock wave reached Earth's space.
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