The solar wind is a stream of charged particles from the sun. The space formed by continuously compressing the magnetic field lines of the Earth's magnetic field is called the Earth's magnetosphere. The top of the magnetosphere is the outer boundary of the magnetosphere, with an elliptical surface on the sunny side and a cylindrical shape slightly outward on the sunny side. The cavity enclosed by the cylinder is called the magnetic tail. On the sunny side of the heliocentric line, the top of the magnetosphere is approximately 10 Earth radii away from the center of the Earth. How does the material and energy of the solar wind enter the Earth's magnetosphere? How to drive the convective motion of plasma in the magnetosphere? How is energy transported, stored, and dissipated in the magnetosphere? This series of questions is a cutting-edge scientific problem in the coupling of solar wind and magnetosphere, which has important scientific and practical value for exploring the basic physical processes of magnetosphere space and space weather forecasting.
Dai Lei, a researcher at the Key Laboratory of Solar Activity and Space Weather of the National Space Science Center of the Chinese Academy of Sciences, Wang Chi, an academician of the CAS Member, and members of the international team proposed a new model of large-scale convection in the magnetosphere directly driven by the Japan side magnetic reconnection. On January 20th, the relevant research results were published online in Nature Communications.
The global scale convection of plasma matter is a fundamental feature of the planetary (Earth) magnetosphere. Since the classic model of large-scale convective circulation in the magnetosphere was proposed in the 1960s, it has been the fundamental physical image of the coupling of solar wind and magnetosphere, playing a key role in space weather phenomena such as energy bursts in Earth's space, such as magnetic storms and substorms. However, this classic convection cycle model predicts that the plasma convection period is generally on the order of hours, and difficulties are encountered in explaining fast response convection events of 10 to 20 minutes. This study analyzed the response of the magnetosphere to the solar wind on March 11, 2016, revealing a new image of the twin convection model directly driven by the diurnal magnetic reconnection. Through numerical simulation and observation data analysis, it was found that the diurnal magnetic reconnection directly drives the diurnal convection within the magnetosphere by exciting the field oriented currents in zone 1 and zone 2, and the convection enhancement gradually extends from the diurnal side to the nighttime side within 10-20 minutes. This process occurs almost immediately after the interplanetary magnetic field turns from north to south, and the nocturnal magnetic reconnection does not affect the convective mode during this period. In the classical convection circulation model of the magnetosphere, the diurnal and nighttime magnetic reconnection drivers must operate together.
This study found that diurnal and nighttime magnetic reconnection can independently drive large-scale convection in the magnetosphere, proposing new physical images beyond the classical convection cycle model, supporting the expectations of modern extended/contracted polar cover models and direct driven substorm models. This work emphasizes the crucial role of large-scale field current and plasma convection in the coupling of solar wind and magnetosphere. The new physical images proposed by the team are expected to be further tested in the future China Europe Joint Space Science Satellite Project Smile (SMILE) mission.
The research work was supported by the National Natural Science Foundation of China and the second phase of the space science pilot project of the Chinese Academy of Sciences.
Paper link
Schematic diagram of magnetospheric convection driven by the sun
