Development of the Chinese Meridian Project

The Meridian Project is a ground-based network program to monitor Solar-Terrestrial space environment, which consists of a chain of ground-based observatories with multiple instruments including magnetometers, ionosondes, HF and VHF radars, Lidars, IPS monitors, sounding rockets etc. The chain is mainly located in the neighborhood of 120$^\circ$E meridian, and is thus named the Meridian Project. The Meridian Project has officially been approved and supported by the Chinese government and will be finished by the end of 2010. This report gives an overview of the Meridian Project, and reports the recent development since 2008.      

Recent Advances in Research of the Chinese Meridian Project

The Chinese Meridian Project is a ground-based space environment monitoring facility in China. The first phase of the project has been put into formal operation since 2012 after 4-year's construction. It consists of 15 observatories located roughly along 120°E longitude and 30°N latitude, with each observatory equipped with multiple instruments to monitor space environment. Based on the huge observational data accumulated, significant scientific achievements have been made with more than 300 peer-reviewed journal papers published. In this report, scientific results from the past two years have been reviewed with topics covering fields of geomagnetic, atmosphere, ionosphere, and their responses to solar activities. The excellent achievements from the Phase I of Chinese Meridian Project lay a good foundation for Phase II, which has already been approved with the official kick-off of construction in November 2019. It will conceive an unprecedented contribution to global space weather community from China.      

Introduction to Meridian Space Weather Monitoring Project

The Meridian Project is a ground- based network program to monitor solar-terrestrial space environment, which consists of a chain of ground-based observatories with multiple instruments including magnetometers, ionosondes, HF and VHF radar, Lidar, IPS monitors, sounding rockets etc. The chain is mainly located in the neighborhood of 120°E meridian, and is thus named the Meridian Project. It has officially been approved by the Chinese government and will be finished by 2009. This talk will give an overview of the Meridian Project and the proposed International Space Weather Meridian Circle Program.     

Recent Development and Preliminary Results of Chinese Meridian Project

The Meridian Project is a ground-based network program to monitor solar-terrestrial space environment, which consists of a chain of 15 ground-based observatories located roughly along 120°E longitude and 30°N latitude. The Meridian project started in 2008, and its construction was completed by 2011. The integration and test phase of the Meridian Project conducted in 2011 demonstrated its observation capabilities as expected. The project will be in full operation in 2012. This report gives an overview of the recent development and preliminary results of the Meridian Project since 2010.      

Introduction to Chinese Meridian Project-Phase II

The Chinese Meridian Project is a ground-based space environment monitoring network, which is constructed in two steps. The first step (Phase I) of the project consists of 15 observation stations located roughly along 120°E longitude and 30°N latitude. The second step (Phase II) of the project will additionally deploy 16 stations to better cover China's territory, and build a stereo monitoring capability to monitor the cause and effect of the space weather chain in the solar terrestrial system. Based on the existing two monitoring chains in Phase I, two more chains will be established along 100°E longitude and 40°N latitude, respectively, forming a double-cross network configuration. After the two-step construction, the whole project will run nearly 300 instruments deployed at 31 stations. Aside from standard instruments, quite a few innovative and powerful instruments will be developed, such as radioheliographs with a very wide frequency band, a 3-station incoherent scattering radar to make a 3D measurement of the ionosphere, and a helium lidar to measure atmosphere density up to an altitude of 1000 km.      

Main Science Results from Chinese Meridian Project(2014—2015)

The Chinese Meridian Space Weather Monitoring Project (Meridian Project for short) is a ground-based geospace monitoring chain in China. It consists of a chain of 15 ground-based observatories located roughly along 120°E longitude and 30°N latitude. Each observatory is equipped with multiple instruments to measure key parameters such as the baseline and time-varying geomagnetic field, the middle and upper atmosphere and ionosphere from about 20 to 1000km. This project started collecting data in 2012. Here a brief overview of the Chinese Meridian Project is given, and most recent science results mainly in the ionospheric and atmospheric studies are presented.      

Recent Advances in Chinese Meridian Project

To develop an understanding of near-Earth space's response to solar activities and the coupling among different layers in geospace, China has initiated a ground base program to monitor China's geospace environment called the Meridian Space Weather Monitoring Project (Chinese Meridian Project). The effort consists of a chain of 15 ground-based observatories located roughly along 120°E longitude and 30°N latitude. Each observatory is equipped with multiple instruments to measure key parameters such as the baseline and time-varying geomagnetic field, as well as the middle and upper atmosphere and ionosphere from about 20 to 1000 kilometers. This project started collecting data in 2012. We will give a brief introduction to the Chinese Meridian Project, and present recent scientific results mainly in ionospheric and atmospheric studies.      

A BRIEF INTRODUCTION TO MERIDIAN PROJECT

Early in 1994, sponsored by Chinese Academy of Sciences (CAS) and then the State Science and Technology Commission of China (SSTC, now Ministry of Sci ence and Technology), Chinese space scientists (including scientists from Taiwan) gathered together to discuss issues on the development of space physics researches in China. Following it, several special seminars were held to continue the discus sion which finally led to a proposal to CAS and SSTC for establishing a station chain along the 120°E to monitor the space environment. This proposal was care fully reviewed and thoroughly evaluated by many leading scientists in the com munity and then listed in the State Plan of Chinese Central Government in June 1997. The project then has been formally called as "Meridian Chain of Compre hensive Ground-Based Space Environment Monitors in the Eastern Hemisphere" "Meridian Project". After several years of preparations the project has been par tially initiated with the efforts devoted by institutes and universities involved.     

International Meridian Circle Program

The Earth is buffered from the ferocious onslaught of the solar wind by a thin layer of matter known as the atmosphere and geospace. This layer absorbs energy from irradiance and outburst from the Sun, as well as from disasters, transient phenomena and anthropogenic emissions originated from Earth. Through complicated physics, the absorbed energy changes the atmospheric and geospace state and sometimes gets re-released to power extreme events such as space weather. Taking place globally, these complicated processes cannot be understood unless they are studied globally. The Chinese scientists have proposed the International Meridian Circle Program (IMCP) to meet this demand. By operating nearly 1000 instruments encompassing all latitudes along with the 120°E-60°W longitudes, IMCP aims, for the first time, to construct comprehensive 3D data representation of the atmosphere and geospace on a global scale and empower interdisciplinary research to tackle key questions related to Earth's environment and climate change.      

北驼峰区电离层GPS卫星闪烁事件时空特征及对通信的影响

基于子午工程北大深圳站（22.59°N,113.97°E）电离层GPS双频接收机在2011年1月1日至2017年12月31日连续7年的长时间序列闪烁和TEC观测数据,分析不同太阳活条件下华南赤道异常北驼峰区观测到的GPS卫星L波段电离层闪烁事件时空分布特征及其对通信的影响.结果表明:GPS闪烁事件几乎都发生在夜间,且主要发生在春秋分月份;在不同太阳活动条件下,夜间GPS闪烁事件都主要发生在北驼峰区域靠近磁赤道的一侧,且GPS闪烁事件存在明显的东-西侧天区不对称性,即在台站西侧天区发生的闪烁事件明显偏多;在不同太阳活动条件下,弱闪烁事件伴随的TEC耗尽和卫星失锁事件比例相对较低,强闪烁事件则大部分都伴随着TEC耗尽和卫星失锁事件的发生.      

Response of quasi-10-day waves in the MLT region to the sudden stratospheric warming in March 2020

We present an analysis of the response of quasi-10-day waves (Q10DWs) to the sudden stratospheric warming (SSW) event which occurred on March 23, 2020. The Q10DWs are observed in the mesosphere and lower thermosphere (MLT) region by three meteor radars, which are located at middle latitudes along the 120°E meridian from Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), to Wuhan (WH, 30.5°N, 114.6°E). The Q10DWs reveal similar temporal and altitudinal variations during the SSW in the MLT region at the three stations. The activities of Q10DWs are also captured in the temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite in the MLT region. Further analysis of the Q10DW phases indicates that the Q10DWs might be in situ generated due to mesospheric instabilities at higher latitudes around MH and then propagate southward to lower latitudes at BJ and WH. The atmospheric instabilities are not directly responsible for the excitations of Q10DWs at lower latitudes, while the observed equatorward propagation of the Q10DWs is important. Our result provides the observational evidence for latitudinal couplings in the MLT region after the SSW onset, which is achieved by southward propagating planetary waves in the MLT region.     

Spatial asymmetry in topside ion density and vertical E × B plasma drift velocity within 75°E–95°E

The ion density measured by the Ionospheric Plasma and Electrodynamics Instrument (IPEI) on board the ROCSAT -1 over the 75°E and 95°E meridian at 600km altitude has been utilized to examine the latitudinal and longitudinal distribution within the Indian sector, in particular, the north-south and east-west asymmetries of the equatorial ionization anomaly (EIA). A longitudinal gradient in ion density at 600?km higher towards 95°E develops during the noontime and afternoon hours when the EIA is at its peak. The density gradient persists till evening hours when pre-reversal enhancements occur. The vertical E?×?B plasma drift velocity measured simultaneously by ROCSAT -1 for the same space-time configuration has also been studied. In addition to diurnal, seasonal and solar activity variations in E?×?B drift velocity, the longitudinal gradient is also observed. The EIA at the altitude of 600?km peaks at different latitudes and are mostly asymmetric about the magnetic equator. From midnight till 0800 LT, the ion density across the equator is nearly uniform in the equinoxes. But in the solstices, the density exhibits a north-south gradient. In the June solstice, density is higher in the northern hemisphere and decreases gradually towards south. The gradient in density reverses in December solstice. Normally, the EIA peaks within 1200 LT and 1600 LT while around 2000 LT, pre-reversal enhancement of ionization occurs affecting the EIA evening structure. The strength of the EIA also exhibits seasonal, year-to-year and hemispheric variations. The longitudinal asymmetry of drift velocity along 75°E and 95°E longitude sectors is the contributing factor behind the observed longitudinal asymmetry in ion density. Significant positive correlation between the strength of the EIA and E?×?B drift is observed in both longitudes.     

低纬(海南)电离层等离子体漂移对地磁活动的响应

利用2003-2016年期间子午工程海南站（19.5°N,109.1°E）数字测高仪观测到的电离层等离子体漂移数据,分析了高低两种太阳活动条件下纬向和垂直向漂移对近磁静、中等磁扰和强磁扰三种地磁活动水平的响应特性.结果表明:日间纬向漂移各季节均以西向为主,随地磁活动无明显变化,白天日出附近和夜间漂移在各季节均以东向为主,随地磁活动增强而减弱,减弱程度在分季最大,在夏季最小;日间垂直漂移在零值附近变化,且不受地磁活动和季节影响,日落附近漂移仅在分季受到地磁活动的抑制,午夜前垂直漂移在分季受到抑制,在冬季因强磁扰而反向,夏季无明显规律,子夜至日出后垂直漂移在各季节随地磁活动增强而减小.与赤道区Jicamarca相比,两地漂移对地磁活动的响应相近,但在幅度和相位上存在差异,这可能是两地区的地理位置、背景电场和风场结构等不同造成的.      

Solar ring mission: Building a panorama of the Sun and inner-heliosphere

Solar Ring (SOR) is a proposed space science mission to monitor and study the Sun and inner heliosphere from a full 360° perspective in the ecliptic plane. It will deploy-three 120°-separated spacecraft on the 1-AU orbit. The first spacecraft, S1, locates 30° upstream of the Earth, the second, S2, 90° downstream, and the third, S3, completes the configuration. This design with necessary science instruments, e.g., the Doppler-velocity and vector magnetic field imager, wide-angle coronagraph, and in-situ instruments, will allow us to establish many unprecedented capabilities: (1) provide simultaneous Doppler-velocity observations of the whole solar surface to understand the deep interior, (2) provide vector magnetograms of the whole photosphere — the inner boundary of the solar atmosphere and heliosphere, (3) provide the information of the whole lifetime evolution of solar featured structures, and (4) provide the whole view of solar transients and space weather in the inner heliosphere. With these capabilities, Solar Ring mission aims to address outstanding questions about the origin of solar cycle, the origin of solar eruptions and the origin of extreme space weather events. The successful accomplishment of the mission will construct a panorama of the Sun and inner-heliosphere, and therefore advance our understanding of the star and the space environment that holds our life.     

HXMT卫星空间环境监测器及初步观测结果

硬X射线调制望远镜（HXMT）卫星是中国首个专门进行天文探测的空间科学实验卫星,运行于高度约550km、倾角约43°的低地球轨道.星载空间环境监测器为星上科学任务开展提供背景辐射实测资料.该监测器采用固体探测器望远镜系统和扇形阵列全新组合设计,可获取轨道空间高能质子和高能电子能谱、方向综合动态结果,给出更为全面的粒子辐射分布图像.初步探测结果显示,卫星运行轨道遭遇的带电粒子辐射集中分布在经度80°W-20°E,纬度0°-40°S的南大西洋异常区,粒子辐射在该区域表现出不同程度的方向差异分布,高能电子方向差异分布显著强于高能质子.2017年9月空间环境扰动期间,爆发的太阳质子事件并未对该轨道粒子辐射产生影响,而地磁活动导致该轨道穿越经度120°W-60°E,纬度40°-43°N的北美上空和经度60°-120°E,纬度43°-40°S的澳大利亚西南区域时遭遇增强粒子辐射影响,增强的粒子辐射表现出极强的方向分布.      

A study of GPS ionospheric scintillations observed at Shenzhen

Ionospheric scintillation variations are studied using GPS measurements at the low latitude station of Shenzhen (22.59°N, 113.97°E), situated under the northern crest of the equatorial anomaly region, from the Chinese Meridian Project. The results are presented for data collected during the current phase of rising solar activity (low to high solar activity) from December 2010 to April 2014. The results show that GPS scintillation events were largely a nighttime phenomenon during the whole observation period. Scintillation events mainly occurred along the inner edge of the northern crest of the equatorial anomaly in China. The occurrence of scintillations in different sectors of the sky was also investigated, and the results revealed that it is more likely for the scintillations to be observed in the west sector of the sky above Shenzhen. During the present period of study, a total number of 512 total electron content (TEC) depletions and 460 lock loss events were observed. In addition, both of these events are likely to increase during periods of high solar activity, especially because the strong scintillations are often simultaneously accompanied by TEC depletions and lock losses by GPS receivers.     

Impact of geomagnetic variation over sub-auroral ionospheric region during high solar activity year 2014

The present work is an attempt to evaluate the impact of changing space weather condition over sub-auroral ionosphere during high solar activity year 2014. In view of this, the GPS based TEC along with Ionosonde data over Indian permanent scientific base “Maitri”, Antarctica (70°46′00″S, 11°43′56″E) has been utilized. The results suggested that the nature of ionospheric responses to the geomagnetic disturbances not only depended upon the status of high latitudinal electro-dynamic processes but also influenced by the seasonal variations. The results revel both negative and positive type of ionospheric response in a single year but during different seasons. The study suggested that the combination of equator-ward plasma transportation along with ionospheric compositional changes causes a negative ionospheric impact especially during summer and equinox seasons. However, the combination of pole-ward contraction of the oval region along with particle precipitation may lead to exhibit positive ionospheric response during the winter season. The plasma transportation direction has been validated with the help of convection boundary (HM boundary) deduced with the help of SuperDARN observations. The ground based ionosonde observations clearly provided the evidence of deep penetration of high energetic particles up to the E-layer heights which results a sudden and strong appearance of E-layer. The strengthening of E-layer is responsible for modification of auroral electrojet and field-aligned current system. Also, the sudden appearance of E-layer along with a decrease in F-layer electron density suggested the dominance of NO⁺ over O⁺ in a considered region under geomagnetic disturbed condition.     

Global ionospheric scintillations revealed by GPS radio occultation data with FY3C satellite before midnight during the March 2015 storm

Global observations of S4 amplitude scintillation index by the GPS Occultation Sounder (GNOS) on FengYun-3 C (FY3C) satellite reveal global dynamic patterns of a strong pre-midnight scintillations in F-region of the ionosphere during the St. Patrick’s Day geomagnetic super storm of 17–19 March 2015. The observed strong scintillations mainly occurred in the low latitudes, caused by equatorial plasma bubbles. During the main storm phase (March 17), the scintillations were first triggered in the New Zealand sector near 160°E longitudes, extending beyond 40°S dip latitude. They were also enhanced in the Indian sector, but significantly suppressed in East Asia near 120°E longitude and in Africa around 30°E longitude. During the initial recovery phase (March 18–19), the global scintillations were seldom observed in GNOS data. During the later recovery phase (after March 19), the scintillations recovered to the pre-storm level in Indian, African, and American sectors, but not in East Asian and any of Pacific sectors. These results closely correlate with observations of the density depletion structures by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite, and ground-based instruments. Such consistency indicates reliability of our scintillation sensing approach even in a case-by-case comparison study. The prompt penetration electric field and disturbance dynamo electric field are suggested as the main factors that control the enhancement and inhibition of the scintillations during the storm, respectively.     

Development of wind observational models for the upper atmosphere of the earth based on the joint analysis of direct and indirect sounding data

Earlier latitudinal distribution models of zonal winds were developed mainly along the 80°W meridian [1, 2]. In this paper an attempt is made to take into account longitudinal differences in zonal and meridional wind distributions. These are considerable in winter prediods.     

A comparative study of ionospheric spread-F and scintillation at low- and mid-latitudes in China during the 24th solar cycle

The spread-F echo of ionograms and scintillation of satellite signal propagation along the Earth-space path are two typical phenomena induced by ionospheric irregularities. In this study, we obtained spread-F data from HF (high frequency) digital ionosonde and scintillation index (S4) data from L-band and UHF receivers at low- and mid-latitudes in China during the 24th solar cycle. These four sites were located at Haikou (HK) (20°N, 110.34°E), Kunming (KM) (25.64°N, 103.72°E), Qingdao (QD) (36.24°N, 120.42°E), and Manzhouli (MZL) (49.56°N, 117.52°E). We used these data to investigate spread-F and scintillation occurrence percentages and variations with local time, season, latitude and solar activity. A comparative study of spread-F and scintillation occurrence rates has been made. The main conclusions are as follows: (a) FSF occurred mostly during post-midnight, while RSF and scintillation appeared mainly during pre-midnight at HK and KM; (b) FSF occurrence rates were larger at QD and MZL than expected; (c) the FSF occurrence percentages were anti-correlated with solar activity at HK and KM; meanwhile RSF and scintillation occurrence rates increased with the increase of solar activity at this two sites; (d) the highest FSF occurrence rates mostly appeared during the summer months, while RSF and scintillation occurred mostly in the equinoctial months at HK and KM; (e) the scintillation occurrence was usually associated with the appearance of RSF, probably due to a different physical mechanism comparing with FSF. Some of these results verified the conclusions of previous papers, whereas some show slight difference. These results are important in understanding ionospheric irregularities variations characteristic at low- and mid-latitudes in China.