Space physics and astronomy research from Chinese polar stations:current and future directions

ZONG Qiugang, HU Zejun, LIU Jianjun, JIANG Peng, DU Yang & ZHANG Wei

Review

Space physics and astronomy research from Chinese polar stations:current and future directions

ZONG Qiugang1,2*, HU Zejun1, LIU Jianjun1, JIANG Peng1, DU Yang3& ZHANG Wei3

1Key Laboratory of Polar Science, MNR, Polar Research Institute of China, Shanghai 200136, China;2Institute of Space Physics and Applied Technology, Peking University, Beijing 100871, China;3Shanghai Institute of Satellite Engineering, Shanghai 201109, China

Space weather has a remarkable effect on modern human activities, e.g., communication, navigation, space exploration etc. Space physics study from polar stations is as an important part of the entire solar-terrestrial space, and conducts quantitative research from the perspective of overall space plasma behavior. One of the most important issues is to identify the dominant processes that transfer plasma and momentum from the solar wind to Earth’s magnetosphere. Thus, it is necessary to carry out research for combination the observations from polar ground stations and spacecraft observations in the space. Observations at polar regions can be as a window to the space for satellite traffic controls. The operation of the observation chain―Zhongshan-Taishan-Kunlun Station could monitor polar space debris in a large area with high temporal and spatial resolution. Also, night-time measurements of astronomical seeing at Dome A in Antarctica make it less challenging to locate a telescope above it, thereby giving greater access to the free atmosphere because of a thinner boundary layer.

Great Wall Station, Zhongshan Station, Yellow River Station, Kjell Henriksen Observatory, China-Iceland Arctic Science Observatory, Dome A

1 Introduction to the polar regions

It has been almost 40 years since the first Chinese National Antarctic Research Expedition (CHINARE) took place in 1984. Space physics observation, survey and research conducted/merged during CHINARE program first began at Great Wall Station (GWS, 1985) and then at Zhongshan Station (ZHS, 1989) in Antarctica, and later in the Arctic at Yellow River Station (YRS, 2003), Kjell Henriksen Observatory (KHO, 2011) on Svalbard, and at the China-Iceland Arctic Science Observatory (CIAO, 2018) in Iceland. The ZHS is located at a unique geographical site that is well suited to take measurements on the magnetospheric cusp where solar wind could entry directly into the Earth’s magnetosphere. Also, together with YRS, it provides excellent opportunity to perform conjugated space weather observations for both northern and southern hemispheres. Along this line, conjugated observations can be offered by these unique geomagnetic conjugate locations: GWS (with Millstone Hill), ZHS (with YRS), and the CIAO station in Iceland (with Syowa Station).

The polar regions serve as natural windows for Earth’s connection to space. The Earth’s magnetic field lines converge and extend almost vertically outward in the polar regions, reaching into the magnetosphere and interplanetary space. This makes the polar regions the entry point for solar wind particles and energy into Earth’s space environment and a crucial area for direct coupling between the solar wind, magnetosphere, ionosphere/thermosphere, and middle-upper atmosphere. The energy and particles from the solar wind entering Earth’s space generate phenomena such as auroras and ionospheric disturbances, leading to hazardous space weather that can affect advanced technology systems like satellites, communication, navigation, and positioning. Therefore, the polar regions are one of the most intense areas of space environment disturbances on Earth and an ideal ground-based platform for monitoring space weather, addressing urgent demands for space weather monitoring and applications.

The polar regions exhibit the most direct, intense, and sensitive response to space weather. The U.S. National Science Foundation’s “2016–2025 Key Capabilities in Earth and Space Sciences” and “Investments in the Critical Capabilities for Geospace Science, 2016–2025” report (Baker et al., 2016) explicitly states that understanding the dynamics and coupling processes of the Earth’s magnetosphere, ionosphere, and atmosphere and their responses to solar inputs is one of the three key scientific objectives and capabilities in Earth’s space sciences for the next decade. The polar regions are critical for understanding the solar-terrestrial energy coupling processes, as highlighted in the U.S. National Science Foundation’s report “Solar-Terrestrial Research in Polar Research: Past, Present, and Future” (Lessard et al., 2014). Therefore, conducting ground-based observations of elements such as auroras, ionosphere, convection, and geomagnetism in polar observation stations, combined with localized satellite exploration of the magnetosphere and ionosphere, as well as evaluations using magnetohydrodynamic models, is crucial for achieving the objective of understanding the dynamics and coupling processes of the Earth’s magnetosphere, ionosphere, and atmosphere and their responses to solar inputs.

The polar regions have strategic significance for global governance and the construction of a human community with shared future. They are also a strategic frontier for China. For example, the strategic position of the Arctic region is of great importance as it provides a strategic “high ground” overlooking the northern hemisphere and an ideal area for implementing strategic deterrence. Enhancing data acquisition capabilities in the marine space environment of the Arctic region can provide robust data support for China’s transition from a strategy of coastal defense to oceanic defense and global defense. Moreover, major space missions spanning the Arctic, such as polar orbiting space activities, polar aviation, and the Arctic shipping route, have special requirements for monitoring, researching, and forecasting space weather in the polar regions.

2 Solar eruption activity and space weather

Solar eruption activity, also known as “solar storms” in a figurative sense, is the most spectacular astronomical phenomenon in the solar system. During an eruption in the solar atmosphere, a tremendous amount of magnetized plasma is ejected into interplanetary space, forming solar winds that can reach speeds of several hundred kilometers per second. These solar winds dominate the changes in the entire space environment of the solar system. Earth has a strong intrinsic magnetic field, which forms a “protective shield” called the magnetosphere around it, capable of blocking direct impacts of solar winds on the Earth’s surface. However, when solar winds collide with the Earth’s magnetosphere, it still causes dramatic changes in the Earth’s space environment, including significant disturbances in the magnetic field, a sharp increase in energetic particles, the formation of irregularities in the ionosphere, and a rapid rise in upper atmospheric density. These events lead to hazardous space weather phenomena, severely impacting China’s aerospace, navigation and communication systems, deep space exploration, and ground-based networks.

The peak year of the 25th solar activity cycle is approaching, and China is striving to build a three-dimensional monitoring system covering the Sun, interplanetary space, Earth’s magnetosphere, and ionosphere. This system aims to provide safeguarding measures for China’s growing space industry as well as related technological and economic activities.

As shown in Figure 1, McIntosh et al. (2020, 2023) predicted the variation in sunspot numbers for the solar activity cycle. The light green line represents the actual observed daily sunspot numbers, the black line represents the monthly average sunspot numbers, and the blue line represents the sunspot numbers predicted by the National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center for the 25th solar activity cycle. It is evident that there is a significant deviation between the predicted values and the actual observations. The green line represents the average cycle of solar activity since 1750, and the red line represents the predicted sunspot numbers for the 25th solar activity cycle based on McIntosh et al. (2020, 2023), which aligns more closely with the actual observations.

Figure 1 Variations in observed and predicted sunspot numbers for the 25th solar activity cycle.

The Sun is a star composed of hot plasma, and it possesses a strong magnetic field within its interior. The Sun’s magnetic field arises from the interaction between magnetohydrodynamic effects and self-generated magnetic fields. Within the Sun, there exist large regions of intense magnetic fields called sunspots. Sunspots are areas with lower temperatures compared to their surroundings, and their activity is enhanced due to the high intensity of magnetic fields. The activity in sunspot regions involves the twisting and reconnection of magnetic field lines, which releases a significant amount of energy and magnetized plasma. This energy release leads to solar flares and eruptions. Solar flares are intense explosions that release immense energy and electromagnetic radiation. Eruptions involve the ejection and expulsion of material from the solar atmosphere, forming solar winds. The frequency and intensity of solar eruption activity are related to the solar activity cycle. The solar activity cycle has a duration of approximately 11 years, during which the number and activity of sunspots exhibit periodic variations. The formation of solar eruption activity is a result of the twisting and reconnection of the Sun’s internal magnetic field, leading to the release of energy. The energy and material released during these activities have an impact on the planets and the space environment within the solar system.

Active regions where sunspots are present are prone to explosive events such as solar flares and coronal mass ejections (CMEs). Solar flares are sudden releases of energy in the Sun’s atmosphere, often accompanied by intense electromagnetic radiation and the generation of high-energy particles. The energy released during intense flare events can reach the equivalent of billions of hydrogen bomb explosions or millions of violent volcanic eruptions. The enormous energy released during solar flares has significant implications for Earth and human society. The occurrence rate of flares is closely related to solar activity, with a significant increase during years of high solar activity, leading to a more pronounced impact on space weather and the Earth’s space environment. In addition to flares, CMEs can also occur in active regions. CMEs are large-scale ejections of magnetized plasma from the Sun’s corona into interplanetary space. They are the largest eruptive phenomena in the solar system and can expel billions of tons of material, releasing energy equivalent to millions or even billions of atomic bombs. The violent release of such immense energy has a profound effect on the space environment of the solar system and serves as the primary driving force directly impacting space weather. Similar to solar flares and sunspots, CMEs are highly correlated with the solar activity cycle. Therefore, accurate predictions of the solar activity cycle and solar activity are helpful in forecasting specific solar eruptive phenomena such as flares and CMEs and their resulting space weather effects.

Based on historical data of solar activity cycles since 1750, McIntosh et al. (2020, 2023) used an empirical model to predict the trend of sunspot numbers for the 25th solar activity cycle (as shown in Figure 1). In contrast to previous predictions for most solar activity cycles that significantly deviated from actual observations, this prediction aligns more closely with the observed data. Based on this prediction, the solar activity is expected to reach its peak around 2025 during the 25th solar activity cycle, with activity levels surpassing or approaching those of the 23rd solar activity cycle. This forecast will help estimate future changes in solar activity and contribute to the prediction of solar eruptive events and space weather forecasts.

Space weather is the variation in Earth’s and other planetary space environments caused by solar activity, which can have varying degrees of impact and hazards on human spacecraft, communication systems, navigation systems, power grids, as well as astronaut health and safety. The source of space weather is solar activity, as the Sun continuously emits electromagnetic radiation and charged particles that interact with Earth and other planets, resulting in various solar phenomena, including sunspots and more intense events such as solar flares and CMEs.

3 Solar storm and its impacts on the Earth’s space environment

In interplanetary space, including the space between the Sun and the Earth, intense solar activities and rapid changes in solar wind are manifested through two phenomena: Interplanetary Coronal Mass Ejections (ICMEs) and Co-rotating Interaction Regions (CIRs). Strong ICMEs and CIRs, when directed towards the Earth, can trigger geomagnetic storms. Regarding ICMEs, the strongest event since 2000 was the Carrington-class ICME that occurred on 23 July, 2012. The speed of this interplanetary CME exceeded 2000 km·s?1with a magnetic field intensity of 90 nT. If this ICME event had been directed towards the Earth, it could have caused severe geomagnetic storms with potentially catastrophic consequences for power grids and other technological infrastructure.

As for CIR events, a notable one occurred in late October 2003, causing a severe geomagnetic storm. It reached a G5 intensity level on the NOAA Space Weather Scales, which is the highest possible level. The space storm between the Sun and the Earth disrupted power grids, satellite communications, and GPS signals, and even made auroras visible at much lower latitudes than usual.

Therefore, exploring and understanding the physical processes of ICMEs and CIRs, which occur in interplanetary space, is an important step in understanding the causal chain of space weather between the Sun and the Earth. Unlocking the characteristics, patterns, and mysteries of ICMEs and CIRs requires a multidimensional, multisource, comprehensive approach involving remote sensing, in-situ measurements, and analysis and interpretation of large-scale data. Additionally, high-precision numerical simulations and theoretical analyses driven by boundary data from the inner solar atmosphere are needed.

A geomagnetic storm occurs when high-speed plasma generated by solar eruptions reaches the Earth, causing global-scale changes in the Earth’s magnetic field. These storms typically last for about a day and are characterized by a rapid decrease in the horizontal component of the geomagnetic field followed by a gradual recovery over several days. During periods of intense solar activity, a large number of charged particles from the Sun enter the Earth’s space through magnetic reconnection and are captured by the Earth’s magnetic field, resulting in the formation of ring currents. The gradient and curvature drifts of the geomagnetic field cause the electrons and ions to move in opposite directions around the Earth, forming the ring currents. The enhanced influx of particles into the Earth’s magnetosphere during heightened solar activity leads to an amplification of the ring currents. The magnetic field generated by these ring currents combines (in the opposite direction) with the Earth’s magnetic field, resulting in significant variations in the horizontal component of the geomagnetic field. The intensity of geomagnetic storms is described by the Dst index, which is measured in nanoteslas (nT) and can range from several tens of positive nanoteslas to negative several thousand nanoteslas (Gonzalez et al., 1994). As pointed out by Yokoyama and Kamide (1997), based on the magnitude of the Dst index, geomagnetic storms can be classified as weak storms (–50 nT ≤ Dst < –30 nT), moderate storms (–100 nT ≤ Dst < –50 nT), strong storms (–300 nT ≤ Dst < –100 nT), and super storms (Dst < –300 nT).

Another impact of solar eruptive activities is triggering substorms in the magnetosphere. Substorms are transient disturbances in the geomagnetic field that last from minutes to a couple of hours and result from the sudden release of solar wind energy stored in the magnetotail. On average, 4 to 5 substorms occur per day, each releasing energy equivalent to a moderate earthquake. When the southward interplanetary magnetic field reconnects with the dayside geomagnetic field, energy propagates from the solar wind to the magnetotail, causing the tail to elongate and the neutral sheet to thin. Subsequent magnetic reconnection across the neutral sheet leads to dipolarization of the magnetic field, accelerating particles that penetrate the inner magnetosphere and ionosphere and collide with gas molecules and atoms in the upper atmosphere, producing auroras. The intensity of substorms is described by the auroral electrojet (AE) index. Depending on the magnitude of the AE index, substorms can be classified as weak substorms (300 nT ≤ AE < 500 nT), moderate substorms (500 nT ≤ AE < 1000 nT), strong substorms (1000 nT ≤ AE < 2500 nT), and super substorms (AE ≥ 2500 nT) (Zong et al., 2021). During periods of super substorms, energetic particles can directly enter the region of ring currents, significantly affecting the ring currents and potentially causing or intensifying geomagnetic storms, leading to stronger space weather effects.

In order to mitigate the impact of geomagnetic storms and superstorm/substorms on human activities, scientists and government institutions worldwide are monitoring geomagnetic storms and substorms and issuing warnings and alerts when necessary to mitigate their potential effects on society. These measures aim to protect communication systems, navigation systems, power grids, and other critical infrastructure from the adverse effects of space weather events. By closely monitoring solar activity, analyzing data, and developing predictive models, scientists and policymakers can better understand the characteristics and behavior of geomagnetic storms and substorms, allowing for improved preparedness and response strategies. Additionally, ongoing research and technological advancements contribute to the development of more resilient systems that can withstand the effects of space weather events. By fostering international collaboration and information sharing, efforts are being made to enhance our understanding of space weather phenomena and their impacts on Earth’s space environment, ultimately ensuring the safety and well-being of individuals and the stability of technological systems.

The intensity of geomagnetic storms and substorms depends on factors such as solar wind velocity, density, and magnetic field orientation. These two space weather phenomena can potentially affect human activities such as communication, navigation, and power systems, and even pose threats to spacecraft and astronauts’ health. Figure 2 shows a strong geomagnetic storm event that occurred around 24 March, 2023, with the Dst index reaching its minimum value of ?184 nT at 3:00 on 24 March. The storm onset was rapid, starting around 5:00 on 23 March, and entered the main phase at around 10:00 on 23 March. The main phase lasted for approximately 17–18 h, followed by the recovery phase. As of 27 March, the magnetic field intensity had not fully returned to a calm state. Significant substorm activity was also observed from 23 March to 25 March. From 8:00 on 23 March to 7:00 on 24 March, there were approximately 13 strong substorm events (AE > 1000 nT).

Figure 2 Dst index variation (Data resource: https://wdc.kugi. kyoto-u.ac.jp/dst_ realtime/202303/index.html).

To mitigate the impact of geomagnetic storms and superstorm/substorms on human activities, scientists and government institutions worldwide monitor geomagnetic storms and substorms and issue warnings and alerts when necessary to mitigate their potential effects on society.

Geomagnetic storms and superstorm/substorms are directly influenced and controlled by solar activity, and most changes in the Earth’s space environment can be traced back to variations in solar activity (Figure 3). During peak solar activity years, solar activity becomes more intense, resulting in enhanced particle radiation and electromagnetic radiation. When geomagnetic storms or substorms occur, the flux of relativistic electrons in the outer radiation belt, with energies ranging from hundreds of keV to MeV, can increase by two to three orders of magnitude. This increase is a major cause of radiation damage to spacecraft materials, devices, and human bodies.

Figure 3 The model of substorm current wedge for moderate substorms and intense substorms is depicted. a, The substorm current wedge during a normal substorm. b, An additional current wedge observed during an intense substorm, in addition to the normal nightside substorm current wedge. The red arrows represent magnetospheric currents (e.g., the ring current or the tail current). Adopted from Fu et al. (2021).

Due to the higher flux of high-energy electrons, they can penetrate the shielding layers of spacecraft and deposit within dielectric materials, such as coaxial cables or electronic circuit boards. The electric fields generated by these charges may exceed the breakdown threshold of the dielectric, leading to electrostatic discharge and damage to certain components of the spacecraft, ultimately resulting in complete spacecraft failure. In recent years, several spacecraft failures have been attributed to electrostatic charging and discharge caused by high-energy electrons within the spacecraft. Therefore, high-energy electrons are often referred to as “killer” electrons for satellites.

During solar activity peak years, the ionosphere and the middle and upper atmosphere also undergo significant changes. Anomalous abrupt variations in electron density in the ionosphere can disrupt critical infrastructure such as power grids, navigation systems, and communication systems. Protective measures, such as adding shielding and backups, can help mitigate the risk of damage or interruption. Solar eruptive activities also heat the middle and upper atmosphere, leading to an increase in atmospheric temperature, enhanced convection, and expansion of the lower atmosphere, resulting in a substantial increase in density in the middle and upper atmosphere. This increased density can increase drag on low Earth orbit satellites and alter their orbits. Solar activity peak years can also cause an increase in radiation reaching the Earth, posing potential health concerns for astronauts and personnel in the aviation or other industries.

4 The Earth’s space environment and vertical panoramic observations

Strengthening real-time monitoring and research on the Earth’s space environment is an important measure to cope with solar activity peak years. Now, it is in real-time monitoring of the Earth’s space environment, particularly in particle radiation and electromagnetic radiation monitoring. Currently, a number of space weather monitoring instruments have been successfully developed and deployed in orbit, including instruments for monitoring high-energy particle radiation, medium-energy electron radiation, satellite charging effects (Figure 4), and space magnetic field detection. The satellites are carrying these instruments including the China-Brazil Earth Resources Satellite series, the BeiDou Navigation Satellite System series, and the Fengyun series. The operational orbits cover Sun-Synchronous Orbit (SSO), Geostationary Orbit (GEO), and Medium Earth Orbit (MEO). However, the overall number of instruments is relatively small, and further efforts are needed to strengthen the development of space environment monitoring instruments in preparation for the upcoming solar activity peak years.

Figure 4 The classification and statistics of satellite failures from 1973 to 1997 internationally. The statistical results indicate that out of a total of 299 failures, 162 cases, accounting for 54 % of the total anomalies, were caused by charging and discharge-related abnormalities. ESD: electrostatic discharge; SEU: single event upset (Source data: Koons et al., 2000).

On 3–4 February, 2022, two consecutive CMEs from solar flareactivities impacted the Earth’s magnetosphere, resulting in magnetic storms and increased density in the nearby space atmosphere. As a result, out of the 49 Starlink satellites launched by SpaceX on 3 February, 38 were destroyed on 7 March, causing direct economic losses of over 500 million US dollars. This event sparked a new wave of research on catastrophic space weather events (Dang et al., 2022; Fang et al., 2022; Hapgood et al., 2022; Kataoka et al., 2022; Tsurutani et al., 2022; Zhang et al., 2022; Lockwood et al., 2023). In this catastrophic space weather event, the SYM-H index, which characterizes the intensity of magnetic storms, was less than 80 nT, indicating a minor storm. On the other hand, the SML index, which characterizes the substorm intensity, reached 1250 nT, indicating a strong substorm. This highlights the significant role of substorms in this space weather event, which may have been severely underestimated in its impact. Conducting research on the response of the polar ionosphere and the adjacent space atmosphere to strong substorms, utilizing observation data from China’s polar research stations and satellite observations, is of great scientific value in understanding the coupling between the magnetosphere, polar ionosphere, and adjacent space atmosphere (Liu and Yang, 2012; He et al., 2016; Huang et al., 2016). It also holds important application value for spaceweather monitoring andforecasting (Hu et al., 2005; Liu et al., 2019, 2023).

The “vertical panoramic” study of the coupling process between solar wind, magnetosphere, ionosphere, middle and upper atmosphere, and lower atmosphere is one of the current forefront research areas in international polar studies (Figure 5). Understanding how the injection of matter and energy resulting from the Sun-Earth coupling affects the various atmospheric layers in polar regions and the connection between polar atmospheric variations and global climate change is a crucial scientific question of global interest. China’s Zhongshan Station in Antarctica is located within the Earth’s polar gap during daylight periods and possesses unique geographical conditions (Liu and Yang, 2012; Huang et al., 2016; He et al., 2016). It also has a solid observational foundation but lacks direct observations of the upper atmosphere’s top region. Therefore, it is necessary to develop advanced incoherent scatter radar technology and conduct research on polar plasma detection based on the existing comprehensive observation system for the upper atmosphere in polar regions. Establishing an internationally leading vertical panoramic comprehensive detection system for Sun-Earth coupling in polar regions will provide an observational basis for studying the interaction between Sun-Earth coupling and the polar atmospheric layers.

As the most powerful probing device in the ground-based space environment, incoherent scatter radars can detect electron density, electron/ion temperature, and ion line-of-sight velocity in the intermediate region to the topside ionosphere (altitude of approximately 90–800 km). Currently, there are only 14 incoherent scatter radars worldwide, mainly distributed in North America, Europe, and other regions. China, led by the Institute of Geology and Geophysics of the Chinese Academy of Sciences, started the development of the “Sanya Incoherent Scatter Radar” in 2015, and it was accepted and put into operation in 2021. This is China’s first (and currently the only) large phased array radar used for space environment monitoring.

Compared to traditional incoherent scatter radars, phased array detection technology can also retrieve three-dimensional flow velocities, electric fields, and currents (such as Pedersen/Hall currents) of the ionosphere and other plasma regions in the area. Additionally, the equipment is easy to maintain due to modular design. The development and operation of the Sanya phased array radar have also provided favorable guarantees for China’s independent research and development of incoherent scatter technology.

Looking globally, the vast Antarctic region still lacks such powerful space environment monitoring equipment. This is partly due to the harsh climate conditions and inconvenient maintenance and supply in Antarctica. On the other hand, it is also due to the non-indigenous nature of detection technology. The Polar Research Institute of China (PRIC), through years of continuous Antarctic expeditions and the operation of research stations throughout the year, has accumulated rich experience in logistics and supply. Meanwhile, the independent research and development of the Sanya phased array technology has overcome the current technological bottlenecks and the technological blockade imposed by Europe and the United States. Conducting strong ionosphere detection device observations in the Antarctic region also holds the promise of providing more convincing observations and answers to scientific questions such as debris in near-Earth space, asymmetry in ionospheric and auroral activities between the northern and southern hemispheres, and anomalies in regional space environments (such as the Weddell Sea anomaly).

5 Strategic planning for polar based space weather study

Various space weather phenomena in polar regions are caused by the dynamic processes in the coupled system of solar wind, magnetosphere, ionosphere/atmosphere. The solar wind-magnetosphere-ionosphere/atmosphere system is a complex coupled system with interactions ranging from macroscopic scales (such as magnetospheric convection driven by solar wind, polar vortex variations, planetary waves) to microscopic scales (such as wave-particle interactions, cosmic dust). These interactions can result in global effects from the energy input by the Sun and solar wind. Due to the complexity of these interactions, addressing fundamental and unresolved issues requires a multidisciplinary approach involving multiple ground-based instrument arrays, coordinated studies with spacecraft, and various theoretical tools and modeling techniques.

Figure 5 The “vertical panoramic” carton of the coupling process between solar wind, magnetosphere, ionosphere, middle and upper atmosphere, and lower atmosphere.

Inhomogeneities in the polar ionosphere result in scintillation of radio signals passing through the ionosphere, affecting wireless communication and navigation. For example, the plasma patches in auroral regions can cause strong signal outages of the Global Positioning System (GPS) receivers on board Swarm satellites (Xiong et al., 2019). Density variations in the polar ionosphere/upper atmosphere can impact the damping of polar orbiting satellites, causing changes in their orbits and potentially reducing their operational lifetimes or leading to premature re-entry. The study has shown that the increase in atmospheric density leads to an increase in atmospheric drag, which in turn affects the orbit of satellites and even causes satellite crashes, as was the case with the crash of 38 Starlink satellites on 4 February, 2022 (Dang et al., 2022). Monitoring very low-frequency (VLF) signals in the Arctic region enables the detection of space environment variations and can be used for navigation, earthquake monitoring, nuclear explosion detection, and communication assessment (e.g., for sub-surface communications).

The ionosphere, thermosphere, and middle-upper atmosphere over China are highly susceptible to adverse space weather events originating from the polar regions. This is because the rapid changes in the polar space environment can affect the lower-latitude ionosphere, thermosphere, and neutral atmosphere through related dynamical processes. Therefore, establishing a comprehensive observation system for the polar space environment, acquiring high-quality observational data, understanding the response of the polar space environment to solar wind energy and its terrestrial effects, conducting monitoring of polar space environment changes, obtaining source information for space weather in China, developing models for space weather in China, and improving China’s capability for space environment perception and establishing prediction and warning systems are of utmost importance.

Auroras contain essential information about the coupling between the solar wind and Earth’s magnetosphere, so the study of auroras often focuses on the details of their generation mechanisms (to understand specific plasma processes) and the morphology of auroras (Figure 6), which reveals key information about the driving processes. Although research on substorm auroras started early, new observational phenomena have led to new questions. For example, it has been observed that the enhancement of auroras during substorm bursts is driven by waves, fast-moving plasma flows (originating from Earth’s magnetotail), and their connection to the auroras in the north-south direction.

Figure 6 Satellite launch-view from Antarctic Zhongshan Station. On 5 October, 2019, at 2:51 AM, China successfully launched the Gaofen-10 satellite into orbit using the Long March-4B carrier rocket at the Taiyuan Satellite Launch Center (Credit: Wentao Huang from PRIC).

Dayside auroral ovals are the ionospheric projections of various magnetospheric boundary layers on the dayside. Clear structured discrete auroras appear predominantly on the dayside auroral oval, along with diffuse auroras resembling veils on the low-latitude side of the discrete auroras. The morphology, spectra, intensity, and motion characteristics of dayside auroras are closely related to various dynamic processes in the dayside magnetospheric boundary layers and reflect the feedback processes between the polar ionosphere and the magnetosphere. However, the particle precipitation mechanisms for dayside auroras are still not well understood, for example, the connection between different types of discrete auroras and quasi-static acceleration and Alfvénic acceleration, as well as the relationship between diffuse auroras and dayside magnetospheric plasma waves. These precipitation mechanisms highlight the complexity of wave-particle interactions.

Pulsating auroras are a type of aurora with relatively dim intensity and wave-like fluctuations with periods of only a few seconds. Recent research has clearly linked their driving factors to the Earth’s equatorial magnetosphere. In recent years, some milestone research results on pulsating auroras have shown that they provide an important pathway for energy transfer from the magnetosphere to the ionosphere and thermosphere (Nishimura et al., 2010, 2020; Kasahara et al., 2018). The significance of pulsating auroras is also manifested in their connection to diffuse auroras and their impact on the thermosphere and lower atmospheric regions, as theory suggests that pulsating auroras can lead to ozone depletion.

Proton auroras differ significantly from electron auroras because proton scattering from high-altitude regions often depends on mass and is not directly linked to electron precipitation. Observations of proton auroras have been used to aid in understanding the evolution of substorms on the nightside. However, recent studies have discovered a connection between proton precipitation and electromagnetic ion cyclotron (EMIC) waves near the cusp region on the dayside of Earth (Usanova et al., 2010;Engebretson et al., 2013; Xiao et al., 2013). Theoretical explanations have been developed in previous radiation belt studies to elucidate how EMIC waves scatter high-energy magnetospheric protons into the ionosphere. Yet, the observation of such an effect in the high-latitude cusp region is somewhat surprising and requires further investigation to understand the conditions under which this occurs.

The relationship between auroras and upward ions remains undetermined. Observations have shown that atomic oxygen ions can be lifted out of the ionosphere, escaping Earth’s gravity and reaching the magnetosphere. This process is common in the nighttime auroral zone and near the cusp region. The ultimate result is a significant increase in the mass density of the magnetosphere, leading to a substantial alteration of its dynamic response. Auroras also generate various types of non-thermal radio emissions in the kilohertz to megahertz frequency range. These include auroral “sizzling” sounds in multiple modes, observations of ground-based kilometer radiation from auroras, electron cyclotron harmonic radiation reaching up to the fifth harmonic, intense burst emissions during auroral substorms, and complex emissions just above the electron cyclotron frequency (recently discovered at Antarctic stations). Many of these phenomena can only be observed in Antarctica because they occur within the frequency range dominated by artificial broadcasting in the auroral positions of the northern hemisphere. Some of these auroral radio emissions and associated plasma waves play important roles in controlling the energy flow between plasma populations through wave-particle interactions. Some of the auroral radio emissions and plasma waves provide effective methods for remote sensing of ionospheric plasma conditions and processes, and some exhibit similarities to important wave processes in planetary magnetospheres or stellar atmospheres that are not easily studied through detailed experimental measurements like those conducted in Earth’s auroral ionosphere.

6 Development of polar space weather monitoring technology and equipment

The polar regions provide a vast platform for conducting comprehensive observations of the Sun-wind-magnetosphere-ionosphere/atmosphere coupling system and offer a unique observational window for studying many important physical mechanisms. For example, the Antarctic region has advantages in optical observations of dayside auroral phenomena. This is because the magnetic pole in the south is offset from the geographic pole by nearly 10 degrees, making the high geographic latitudes of the Antarctic region ideal for studying dayside auroras as they can remain in darkness for extended periods (e.g., the Antarctic experiences 3 months of complete darkness in winter). In winter, the surface temperatures on the Antarctic plateau are the coldest in the world (<195 K), and in summer, the natural temperatures in the middle mesosphere region (around 5 km) at both poles are the coldest anywhere on Earth (<130 K). These low temperatures contribute to the formation of polar stratospheric clouds (PSCs) in winter and middle clouds (MCs) in summer. PSCs play a crucial role in springtime stratospheric ozone depletion. Additionally, the Antarctic region is relatively free from artificial electromagnetic noise and interference, providing a unique platform for measuring all types of electromagnetic radiation (critical for space science research) with minimal contamination.

Therefore, the development of three-dimensional observation and monitoring technology and equipment for polar space weather should focus on the research and development of autonomous polar space environment monitoring satellites, onboard sensors, ground-based space environment automatic monitoring platforms and sensors, polar ionospheric/thermospheric active probing radars, high spatiotemporal resolution aurora imaging observation devices and spectroscopic observation devices, and ultra-high-frequency geomagnetic/plasma wave monitoring devices. This will enable a complete chain of observations of the Sun-wind-magnetosphere-ionosphere/atmosphere coupling system.

Due to Antarctica being a continent covered by deep ice and snow, it provides an opportunity to conduct ground-based observations of day-to-geospace processes at very high latitudes. Therefore, establishing a distributed ground-based space weather unmanned monitoring array in Antarctica can achieve near-global coverage in high geomagnetic latitude regions and observe the high-latitude global effects of space weather. As the Earth’s magnetic field connects with the solar wind magnetic field over the polar regions, the polar regions serve as the gateway for solar wind particles and energy to enter Earth’s space environment. They also represent the most direct and important region for the coupling of solar wind-magnetosphere-ionosphere/thermosphere-middle-upperatmosphere. Many global effects influenced by solar activity are first detected in the polar regions. Therefore, the establishment of polar space weather forecasting and warning models is of significant importance for global space weather forecasting. It can enable early prediction of their global impacts.

7 Space debris and astronomy

The development of a monitoring system for space debris in Antarctica (Figure 7) is being carried out, enabling to achieve highly reliable energy assurance, real-time communication support, unmanned and fully automatic operation, intelligent diagnosis and recovery of faults, and other key technologies to ensure stable operation and efficient application of equipment systems in extreme environments. Addressing the characteristics of dense distribution of space debris in the polar region, the focus is on polar multi-site network scheduling, rapid identification of space debris clusters, high-precision orbit determination, and collision risk assessment, aiming to break through key technologies such as rapid and accurate perception of polar space debris. Combining the requirements for satellite on-orbit flight safety assurance in China, flexible network layout and rapid scheduling monitoring system design, and equipment development are conducted in the high-cold and high-altitude environment of Antarctica, aiming to achieve large-area, high-efficiency, multi-dimensional, and high-precision technology for space debris monitoring in the polar region, supporting the enhancement of China’s capability to respond to the threat of space debris.

Figure 7 Low Earth orbit is crowded with satellites and space debris, only 3.6% largest objects are tracked.

The research work is carried out by a national-level innovation team jointly established by the Chinese Arctic and Antarctic Administration, PRIC, the Space Debris Monitoring and Application Center of the China National Space Administration, and the Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences. The applicant is directly responsible for the overall planning of on-site equipment, deployment and implementation of observations, and the development of support and assurance technologies for the Antarctic platform.

In 2023, the first manned experimental observation telescope has been installed and operated at the Zhongshan Station in Antarctica. During the 14th Five-Year Plan period, it is planned to deploy medium and small telescope arrays at Chinese Antarctic research stations such as Zhongshan Station, Taishan Station, and Kunlun Station, to establish an Antarctic observation chain for space debris search and observation. At the same time, collaborative observations with multiple domestic and international sites will be conducted, significantly expanding the spatiotemporal baseline for space debris monitoring in China.

The terahertz wavelength range covers fine structure spectral lines of highly abundant elements such as C, N, O, as well as rotational level transition spectral lines of important molecules. It serves as an important probe for tracing the origin and evolution of stellar and planetary systems, stellar formation processes in galaxies, and the coevolution of supermassive black holes and galaxies, among other fundamental astrophysical processes. Due to the scarcity of sites that meet the long-term atmospheric observation window conditions, terahertz becomes the only “window” for ground-based astronomical observations across the entire electromagnetic spectrum.

Dome A in Antarctica is an excellent site for terahertz astronomical observations. In 2010, a research team from the Purple Mountain Observatory, Chinese Academy of Sciences, used an ultra-wideband Fourier spectrometer for monitoring at the Kunlun Station and successfully obtained 19 months of observation data covering a frequency range of 0.75 to 15 THz, demonstrating the year-round long-duration terahertz observation window at Dome A. The results were published in the journal(Shi et al., 2017). The applicant’s team plans to collaborate with the research team from the Purple Mountain Observatory, Chinese Academy of Sciences to carry out key technology research, aiming to complete on-site environmental adaptability tests for terahertz terminals and manned summer observations with terahertz telescopes within five years. This will promote the construction of an unmanned, year-round terahertz telescope at the Kunlun Station and facilitate multi-band observational studies on forefront topics such as supermassive black holes and the coevolution of galaxies.

8 Planetary polar research

Planetary polar research involves the study of the polar regions on planets, moons, and other celestial bodies within our solar system and beyond. These regions are of particular interest because they often exhibit unique geological features, atmospheric and space physical conditions, and potential for the existence of water ice. It’s important to note that conducting planetary studies at polar stations may require international collaboration and coordination due to the limited number of suitable locations and the significance of planetary research for global scientific understanding. To conduct planetary polar research, it is typically employed a combination of remote sensing techniques and in situ measurements. Here are some key aspects and methods involved in such research. Spacecraft equipped with various instruments, such as cameras, spectrometers, and radar, are used to gather data from orbit around the target planet or moon. Remote sensing provides valuable information about the surface composition, topography, and the presence of ice and other materials. Robotic landers or rovers are sent to the planetary polar regions to directly study the environment. These missions can provide detailed measurements of the atmosphere, temperature, ice properties, and collect samples for analysis. Examples of such missions include NASA’s Mars rovers, Curiosity and Perseverance.Becerra et al. (2021) gives an overview on the current status of Mars Polar Science, highlights the important advances, presents the key open questions, and shows the direction for Mars within the larger context of planetary science and exploration.

Determining the distribution, composition, and physical properties of ice is a major focus of polar research. Techniques like ground-penetrating radar, thermal sensors, and spectrometers help to identify the presence of ice, to study its structure, and to analyze its composition. Understanding the climate dynamics and weather patterns in polar regions is crucial for planetary scientists. Studying atmospheric circulation, temperature variations, and seasonal changes provides insights into the overall climate system and its impact on the polar regions.

Polar regions often exhibit unique geological formations, including polar caps, valleys, and impact craters. Analyzing these features helps scientists unravel the planet’s history, geologic processes, and the potential for past or present habitability. Polar regions can harbor conditions suitable for the existence of microbial life. Studying the habitability of these environments involves assessing factors like the availability of water, chemical composition, energy sources, and the presence of organic compounds.

It is particularly interesting to study giant planetary system and comparative planetary science by using polar stations on the Earth, e.g., to set up radio receivers capable of detecting and analyzing radio emissions from giant planetary magnetosphere. These emissions, such as decametric and kilometric radiations, provide insights into the plasma processes and auroral activity within the magnetosphere. Equipping the polar station with high-resolution imaging instruments, such as cameras or spectrographs, aims to capture images or spectra of giant planetary auroras. These observations can reveal the structure, dynamics, and energy deposition processes within the giant planetary magnetosphere.

Comparing polar regions across different celestial bodies allows scientists to understand the similarities and differences in their geology, climate, and habitability. This approach helps broaden our knowledge of planetary processes and the potential for life beyond Earth. Planetary polar research is a multi-disciplinary field that involves scientists from various backgrounds, including planetary science, geology, atmospheric science, and astrobiology. The data collected from these research efforts contributes to our understanding of the solar system’s history, the potential for habitability, and informs future exploration missions. Collaborative efforts and international cooperation are essential for advancing our understanding of this complex and dynamic environment.

9 Perspective

As the key area of solar terrestrial mass and electromagnetic coupling processes, the polar region is of great significance to the study of the physical and dynamic processes of solar terrestrial coupling, especially on the solar wind energy injection process, the wave particle interaction in the energy coupling process, the cross-scale coupling of space plasma dynamics, and the north-south asymmetries. Polar observation is key to fulfill this goal, and especially we need to:

(1)Develop and construct ground-based/space-borne auroral imagers with high temporal and spatial resolution, particle detectors with high temporal resolution and geomagnetic/electric field detectors for research on solar wind-magnetosphere-ionosphere coupling (from space to ground).

(2)Build a high spatio-temporal resolution geomagnetic, and ionospheric integrated detection array (including Incoherent Scatter Radar) in key coupling areas of the polar region, to establish a comprehensive spatial environment monitoring network covering the entire polar region through international cooperation to conduct cross-scale coupling research.

(3)Develop high-precision monitoring technology for space debris in the polar region, enhancing the China’s capability to respond to the threat of space debris.

Having constructed a comprehensive monitoring network for the space environment of the North and South Poles, and combining it with the space environment monitoring satellites of polar region, we can carry out comprehensive studies on the physical and dynamic processes of solar terrestrial coupling, especially on the north-south asymmetries in solar wind-magnetosphere-ionosphere coupling, solar wind energy injection process, the wave particle interaction in the energy coupling process, the cross-scale coupling of space plasma dynamics, etc.

This work was supported by the National Natural Science Foundation of China (Grant nos. 42242406, 42230202), and Innovation Fund from Joint Innovation Center of Space Science (Aerospace Shanghai). We appreciate two anonymous reviewers and Associate Editor Dr. Akira Kadokura for constructive comments that helped us improve the manuscript.

Baker D N, Chau J, Cohen C, et al. 2016. Investments in critical capabilities for Geospace Science 2016 to 2025. (2016-04-14) [(2023-07-08)]. https:// www.nsf.gov/geo/adgeo/geospace-review/geospace-portfolio-review-final-rpt-2016.pdf.

Becerra P, Smith I B, Hibbard S, et al. 2021. Past, present, and future of Mars polar science: Outcomes and outlook from the 7th International Conference on Mars Polar Science and Exploration. Planet Sci J, 2(5): 209, doi:10.3847/psj/ac19a5.

Dang T, Li X L, Luo B X, et al. 2022. Unveiling the space weather during the Starlink satellites destruction event on 4 February 2022. Space Weather, 20(8): e2022SW003152, doi:10.1029/2022sw003152.

Engebretson M J, Yeoman T K, Oksavik K, et al. 2013. Multi-instrument observations from Svalbard of a traveling convection vortex, electromagnetic ion cyclotron wave burst, and proton precipitation associated with a bow shock instability. J Geophys Res: Space Phys 118(6): 2975-2997, doi:10.1002/jgra.50291.

Fang T W, Kubaryk A, Goldstein D, et al. 2022. Space weather environment during the SpaceX Starlink satellite loss in February 2022. Space Weather, 20(11): e2022SW003193. https://doi.org/10. 1029/2022sw003193

Fu H B, Yue C, Zong Q G, et al. 2021. Statistical characteristics of substorms with different intensity. J Geophys Res: Space Phys, 126(8): e2021JA029318, doi:10.1029/2021ja029318.

Gonzalez W D, Joselyn J A, Kamide Y, et al. 1994. What is a geomagnetic storm? J Geophys Res, 99(A4): 5771-5792, doi:10.1029/93ja02867.

Hapgood M, Liu H X, Lugaz N. 2022. SpaceX—sailing close to the space weather? Space Weather, 20(3): e2022SW003074, doi:10.1029/ 2022sw003074.

He F, Hu H Q, Yang H G, et al. 2016. Recent progress in Chinese polar upper-atmospheric physics research: review of research advances supported by the Chinese Arctic and Antarctic expeditions. Adv Polar Sci, 27(4): 219-232, doi:10.13679/j.advps.2016.4.00219.

Hu Z J, Yang H G, Ai Y, et al. 2005. Multiple wavelengths observation of dayside auroras in visible range—A preliminary result of the first wintering aurora observation in Chinese Arctic Station at Ny-?lesund. Chin J Polar Res, 17(2): 107-114 (in Chinese with English abstract).

Huang D H, Hu H Q, Liu R Y, et al. 2016. The polar space environment observation system at Zhongshan Station, Antarctica. Chin J Polar Res, 28(1): 1-10, doi: 10.13679/j.jdyj.2016.1.001 (in Chinese with English abstract).

Kasahara S, Miyoshi Y, Yokota S, et al. 2018. Pulsating aurora from electron scattering by chorus waves. Nature, 554(7692): 337-340, doi:10.1038/nature25505.

Kataoka R, Shiota D, Fujiwara H, et al. 2022. Unexpected space weather causing the reentry of 38 Starlink satellites in February 2022. J Space Weather Space Clim, 12: 41, doi:10.1051/swsc/2022034.

Koons H C, Majur J E, Selesnick R S, et al. 2000. The impact of the space environment on space systems. Proceedings of 6th Spacecraft Charging Technology Conference, September, 2000.

Lessard M R, Gerrard A J, Weatherwax A T. 2014. Solar-terrestrial research in polar regions: past, present, and future. Proceedings of the Polar Research Meeting, 12–13 November, 2012, University of New Hampshire, USA.

Liu J J, Hu H Q, Han D S, et al. 2019. Interplanetary shock-associated aurora. Adv Polar Sci, 30(1): 11-23, doi:10.13679/j.advps.2019.1. 00011.

Liu J J, Chen X C, Wang Z Q, et al. 2023. Effect of interplanetary shock on an ongoing substorm: simultaneous satellite-ground auroral observations. Sci China Technol Sci, 66(3): 654-662, doi:10.1007/ s11431-022-2244-0.

Liu R Y, Yang H G. 2012. Progress in polar upper atmospheric physics research in China. Adv Polar Sci, 23(2):55-71, doi:10.3724/sp.j.1085. 2012.00055.

Lockwood M, Owens M J, Barnard L A. 2023. Universal time variations in the magnetosphere and the effect of CME arrival time: analysis of the February 2022 event that led to the loss of Starlink satellites. J Geophys Res: Space Phys, 128(3): e2022JA031177, doi:10.1029/2022ja031177.

McIntosh S W, Chapman S, Leamon R J, et al. 2020. Overlapping magnetic activity cycles and the sunspot number: forecasting sunspot cycle 25 amplitude. Sol Phys, 295(12): 1-14, doi:10.1007/s11207- 020-01723-y.

McIntosh S W, Leamon R J, Egeland R. 2023. Deciphering solar magnetic activity: the (solar) hale cycle terminator of 2021. Front Astron Space Sci, 10: 1050523, doi:10.3389/fspas.2023.1050523.

Shi S C, Paine S, Yao Q J, et al. 2017. Terahertz and far-infrared windows opened at Dome A in Antarctica. Nat Astron, 1: 0001, doi:10.1038/ s41550-016-0001.

Nishimura Y, Bortnik J, Li W, et al. 2010. Identifying the driver of pulsating aurora. Science, 33(81): 81-84, doi:10.1126/science.1193186.

Nishimura Y, Lessard M R, Katoh Y, et al. 2020. Diffuse and pulsating aurora. Space Sci Rev, 216(1): 4, doi:10.1007/s11214-019-0629-3.

Tsurutani B T, Green J, Hajra R. 2022. The possible cause of the 40 SpaceX Starlink satellite losses in February 2022: prompt penetrating electric fields and the dayside equatorial and midlatitude ionospheric convective uplift [Submitted on 14 Oct 2022 (v1), last revised 2 Nov 2022 (this version, v2)]. arXiv: 2210.07902. https://arxiv.org/abs/ 2210.07902.pdf.

Usanova M E, Mann I R, Kale Z C, et al. 2010. Conjugate ground and multisatellite observations of compression-related EMIC Pc1 waves and associated proton precipitation. J Geophys Res, 115(A7): A07208, doi:10.1029/2009ja014935.

Xiao F L, Zong Q G, Su Z P, et al. 2013. Determining the mechanism of cusp proton aurora. Sci Rep, 3: 1654, doi:10.1038/srep01654.

Xiong C, Yin F, Luo X M, et al. 2019. Plasma patches inside the polar cap and auroral oval: the impact on the spaceborne GPS receiver. J Space Weather Space Clim, 9: A25, doi:10.1051/swsc/2019028.

Yokoyama N, Kamide Y. 1997. Statistical nature of geomagnetic storms. J Geophys Res, 102(A7): 14215-14222, doi:10.1029/97ja00903.

Zhang Y L, Paxton L J, Schaefer R, et al. 2022. Thermospheric conditions associated with the loss of 40 Starlink satellites. Space Weather, 20(10): e2022SW003168, doi:10.1029/2022sw003168.

Zong Q G, Yue C, Fu S Y. 2021. Shock induced strong substorms and super substorms: preconditions and associated oxygen ion dynamics. Space Sci Rev, 217(2): 33, doi:10.1007/s11214-021-00806-x.

: Zong Q G, Hu Z J, Liu J J, et al. Space physics and astronomy research from Chinese polar stations: current and future directions. Adv Polar Sci, 2023, 34(4): 239-250,doi:10.12429/j.advps.2023.0016

10.12429/j.advps.2023.0016

, ORCID: 0000-0002-6414-3794, E-mail: qgzong@pku.edu.cn

8 August 2023;

21 October 2023;

30 December 2023