The Meridian Project Shandong University team conducted a series of studies on the formation and evolution of polar cap irregularities using multiple ground-based observation devices and the PPMLR-MHD numerical model. The research uncovered events of near-complete closure of the Earth's magnetosphere (the minimum open magnetic flux event known in academia), proposed a mechanism for auroras in the throat region generating polar cap plasma clouds, and revealed the physical mechanisms behind the transition between cold and hot cloud blocks. These findings were published in authoritative journals including Communications Earth & Environment, Geophysical Research Letters, and JGR: Space Physics. The first authors are PhD students Wang Xiangyu and Zhang Duan, and postdoctoral researcher Ma Yuzhang, with Professor Zhang Qinghe as the corresponding author. These results have been selected as Outstanding Achievements of the Meridian Project for 2023.
"In the small building,I listen to the spring rain all night.
In the deep alley,tomorrow morning they will sell apricot blossoms."
With changing winds and clouds,alternating temperatures,the cycle of day and night,and the shifting of the seasons,the weather and climate of the lower atmosphere continue to profoundly impact people's daily lives and production activities. As humanity's exploration extends further into the vast reaches of space,the impact of weather changes in the cosmos on human activities can no longer be ignored.
The Earth's polar regions serveas a natural gateway tospace, being one of the mostdirect and active areas for observing space weather changes. Here, high-energy charged particles from the solar windcan precipitate into the polar ionosphere, creating vibrant auroras. The interaction between the solar wind and theEarth's magnetosphere can also drive high-speed convection in the upper polar atmosphere, causing the ionosphere’s plasma to sometimes coalesce into clouds and sometimes dissolve into the background space. These structures, which stand out from the background mainly due to density or electromagnetic differences, are known as irregularities. These irregularities can significantly impact human communications, navigation, power infrastructure, and space systems, and even pose threats to human safety.
Thus,understanding the mechanisms and evolution of polar ionospheric irregularities,as well as their related solar-terrestrial energy coupling processes,can deepen our knowledge of space weather. This understanding is crucial for space weather modeling and forecasting,ensuring that space weather can better serve daily human activities.
Members of the Meridian Project team, specifically the Polar Ionosphere-Magnetosphere Coupling ResearchGroup from Shandong University's "Solar Eruptions and Their Impact on Planetary Space Environments" innovation team, have conducted a systematic study on the formation mechanisms and evolution characteristics of two typical types of polar ionosphere irregularities. This study utilized observational data from the SuperDARN radar network at Zhongshan Station and the all-sky aurora imager at Huanghe Station, combined with high-resolution MHD simulations from the Space Center's PPMLR model.
Research Findings:
1. Under prolonged strong northward conditions of the interplanetary magnetic field (IMF), the interaction between the solar wind and the magnetosphere causes the inner boundary of the auroral oval to contract sharply toward higher latitudes and merge, forming a "yoke-shaped" aurora and causing the polar cap region to nearly disappear. This indicates that the Earth's magnetosphere is nearly closed (with the open magnetic field lines of the Earth's magnetosphere almost completely eroded, forming a quasi-dipolar magnetosphere, and the magnetotail extending only 28 Earth radii, see Figure 1);
2. In the auroras appearing in the throat auroral zone,the numerous fine structures within are continuously moving toward higher latitudes. As a result,the high-density plasma produced by particle precipitation is transported from the sub-auroral zone to the auroral zone and polar cap region,leading to the formation of plasma blobs (new mechanism for plasma blob formation,see Figure 2);
3. Due to the magnetic reconnection at the dayside magnetopause,auroral structures with polar motion are formed,and the accompanying particle precipitation locally heats the high-density plasma clouds in the corresponding regions,creating hot plasma clouds. These hot plasma clouds are then convected into the polar cap region,where their electron temperature decreases due to reduced particle precipitation,gradually transforming into cold plasma clouds (Figure 3).
These research results not only deepen our understanding of polar dynamics under different solar wind and interplanetary magnetic field conditions,providing physical bases for polar space weather modeling and forecasting,but also effectively demonstrate the Meridian Project's multi-station,multi-device,and global collaborative monitoring capabilities. This indicates significant scientific value and application prospects for space weather research,modeling,and forecasting.
Figure 1: Magnetosphere Anomalous Contraction and Reshaping Under Strong Northward IMF Conditions
Figure 2: New Mechanism for Plasma Cloud Formation Induced by Throat Auroras
Figure 3: Formation and Evolution Process of Cold and Hot Plasma Clouds
Download link for the original article:
1.https://doi.org/10.1038/s43247-023-00700-0
2.https://doi.org/10.1029/2022GL102263
3.https://doi.org/10.1029/2022JA031166
