Meridian Project Research Articles

Derivation of global ionospheric Sporadic E critical frequency (f o Es) data from the amplitude variations in GPS/GNSS radio occultations.

The ionospheric sporadic E (Es) layer has a significant impact on the global positioning system (GPS)/global navigation satellite system (GNSS) signals. These influences on the GPS/GNSS signals can also be used to study the occurrence and characteristics of the Es layer on a global scale. In this paper, 5.8 million radio occultation (RO) profiles from the FORMOSAT-3/COSMIC satellite mission and ground-based observations of Es layers recorded by 25 ionospheric monitoring stations and held at the UK Solar System Data Centre at the Rutherford Appleton Laboratory and the Chinese Meridian Project were used to derive the hourly Es critical frequency (foEs) data. The global distribution of foEs with a high spatial resolution shows a strong seasonal variation in foEs with a summer maximum exceeding 4.0 MHz and a winter minimum between 2.0 and 2.5 MHz. The GPS/GNSS RO technique is an important tool that can provide global estimates of Es layers, augmenting the limited coverage and low-frequency detection threshold of ground-based instruments. Attention should be paid to small foEs values from ionosondes near the instrumental detection limits corresponding to minimum frequencies in the range 1.28–1.60 MHz.

Optical observation of plasma bubbles and comparative study of multiple methods of observing the ionosphere over China

Ionospheric plasma bubbles and scintillation phenomena often occur at low latitudes in China. The all-sky airglow imager located at Fuke station in Hainan (19.5°N, 109.2°E) is part of the Meridian project in China. In this work, we used mainly the observation data obtained by the imager and a digisonde to study plasma bubbles. Optical image processing—including image enhancement, azimuth correction and image projection—was performed on the original airglow observation images, and clear high-resolution images of the bubbles were obtained. Based on these, the morphological features, spatial and temporal variations, spatial scale, drift velocity of the plasma bubbles in the F region of the ionosphere were investigated and analyzed. The plasma bubbles appeared as long, dark stripes on the bright airglow emission background. Their large-scale structures often bifurcated vertically, and were usually tilted westward with north-south extension along the magnetic field lines. The east-west scale of the plasma bubbles was usually greater than 200 km and these increased gradually with time. Moreover, the distance between the adjacent plasma bubbles also increased over time, and was in the 100–400 km range. Plasma bubbles generally drifted eastward with an average drift velocity of approximately 90 m/s. The occurrence and duration of the plasma bubbles were compared with digisonde observations, and it was shown that plasma bubbles lasted for nearly four hours. Additionally, the main characteristics of the plasma bubbles were obtained using both optical and radio observations and the study of which can be beneficial for monitoring and predicting ionospheric scintillations.

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.

Features and Source Current of Long‐Period Induced Geoelectric Field During Magnetic Storms: A Case Study

AbstractWe present a case study on the long‐period ( s) induced geoelectric field disturbance during magnetic storms. A set of continuous 33‐day measurements of the geoelectric field, geomagnetic field, geomagnetic indices, and interplanetary magnetic field are analyzed. In the studied 33 days, two magnetic storms occurred after 10 geomagnetic quiet days. To exclude the effects from the different underground electrical structures, geomagnetic and geoelectric field measurements from the same ground observatory enrolled in Chinese Meridian Project are studied. Besides, Space Weather Modeling Framework is adopted to calculate the global geomagnetic field disturbances and the contribution from different current systems. The wavelet power spectra analysis reveals that the long‐period geoelectric field disturbance appears only during magnetic storms. Especially, stronger magnetic storm generates weaker geoelectric disturbances at the same observatory. The opposite‐direction eastward geomagnetic field disturbance, which is generated mainly by the field‐aligned current at different magnetic local time, significantly changes the magnitude and direction of the induced geoelectric field via the underground impedance tensor. Therefore, both the effects caused by ring current and field‐aligned current should be considered in analyzing the ground induced geoelectric field. Excluding the effect from the geospace current source, the more accurate electrical conductivity in the upper mantle would be obtained in future.

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.

Сравнение результатов моделирования сложенной и развернутой логопериодической антенны, используемой для наблюдений Солнца

There are two antenna arrays located in Mingantu Spectral Radio Heliograph (MUSER). MUSER-I and MUSER-II cover the frequency band ranging from 0.4 to 2 GHz and from 2 to 15 GHz respectively. A third antenna array covering 30–240 MHz will be established in the coming years. A log-periodic antenna is one of the choices for MUSER low frequency band; it radiates structures capable of maintaining consistent impedance characteristics over a wide bandwidth. Due to the ability of achieving high gain, it is widely used in many broadband applications. In this program, folded and unfolded log-periodic antennas are simulated for the Meridian project. In order to improve its return loss, this antenna is optimized with the width of each pole and the height of the substrate. This optimized process has been implemented in the simulated software HFSS.

Comparing simulated results of folded and unfolded log-periodic antenna used for observing the Sun

There are two antenna arrays located in Mingantu Spectral Radio Heliograph (MUSER). MUSER-I and MUSER-II cover the frequency band ranging from 0.4 to 2 GHz and from 2 to 15 GHz respectively. A third antenna array covering 30–240 MHz will be established in the coming years. A log-periodic antenna is one of the choices for MUSER low frequency band; it radiates structures capable of maintaining consistent impedance characteristics over a wide bandwidth. Due to the ability of achieving high gain, it is widely used in many broadband applications. In this program, folded and unfolded log-periodic antennas are simulated for the Meridian project. In order to improve its return loss, this antenna is optimized with the width of each pole and the height of the substrate. This optimized process has been implemented in the simulated software HFSS.

Scaling-laws of Radio Spike Bursts and Their Constraints on New Solar Radio Telescopestwo

Radio observation is one of important methods in solar physics and space science. Sometimes, it is almost the sole approach to observe the physical processes such as the acceleration, emission, and propagation of non-thermal energetic particles, etc. So far, more than 100 solar radio telescopes have been built in the world, including solar radiometers, dynamic spectrometers, and radioheliographs. Some of them have been closed after the fulfillment of their primary scientific objectives, or for their malfunctions, and thus replaced by other advanced instruments. At the same time, based on some new technologies and scientific ideas, various kinds of new and much more complicated solar radio telescopes are being constructed by solar radio astronomers and space scientists, such as the American E-OVSA and the solar radio observing system under the framework of Chinese Meridian Project II, etc. When we plan to develop a new solar radio telescope, it is crucial to design the most suitable technical parameters, e.g., the observing frequency range and bandwidth, temporal resolution, frequency resolution, spatial resolution, polarization degree, and dynamic range. Then, how do we select a rational set of these parameters? The long-term observation and study revealed that a large strong solar radio burst is frequently composed of a series of small bursts with different time scales. Among them, the radio spike burst is the smallest one with the shortest lifetime, the narrowest bandwidth, and the smallest source region. Solar radio spikes are considered to be related to a single magnetic energy release process, and can be regarded as an elementary burst in solar flares. It is a basic requirement for the new solar radio telescope to observe and discriminate these solar radio spike bursts, even though the temporal and spatial scales of radio spike bursts actually vary with the observing frequency. This paper presents the scaling laws of the lifetime and bandwidth of solar radio spike bursts with respect to the observing frequency, which provide some constraints for the new solar radio telescopes, and help us to select the rational telescope parameters. Besides, we propose a spectrum-image combination mode as the best observation mode for the next-generation solar radio telescopes with high temporal, spectral, and spatial resolutions, which may have an important significance for revealing the physical essence of the various non-thermal processes in violent solar eruptions.

Global Statistical Study of Ionospheric Waves Based on COSMIC GPS Radio Occultation Data**Supported by the National Natural Science Foundation of China under Grant Nos 41774158, 41474129 and 41704148, the Chinese Meridian Project, and the Youth Innovation Promotion Association of the Chinese Academy of Sciences under Grant No 2011324.

Extracting and parameterizing ionospheric waves globally and statistically is a longstanding problem. Based on the multichannel maximum entropy method (MMEM) used for studying ionospheric waves by previous work, we calculate the parameters of ionospheric waves by applying the MMEM to numerously temporally approximate and spatially close global-positioning-system radio occultation total electron content profile triples provided by the unique clustered satellites flight between years 2006 and 2007 right after the constellation observing system for meteorology, ionosphere, and climate (COSMIC) mission launch. The results show that the amplitude of ionospheric waves increases at the low and high latitudes (∼0.15 TECU) and decreases in the mid-latitudes (∼0.05 TECU). The vertical wavelength of the ionospheric waves increases in the mid-latitudes (e.g., ∼50 km at altitudes of 200–250 km) and decreases at the low and high latitudes (e.g., ∼35 km at altitudes of 200–250 km). The horizontal wavelength shows a similar result (e.g., ∼1400 km in the mid-latitudes and ∼800 km at the low and high latitudes).

Recent Advances in Observation and Research of the Chinese Meridian Project

The Chinese Meridian Space Weather Monitoring Project (Meridian Project) is a ground-based geospace monitoring chain in China. It consists of 15 ground-based observation stations located roughly along 120°E longitude and 30°N latitude. In recent two years, using data from the Meridian Project, significant progress has been made in space weather and space physics research. These advances are mainly in four aspects:regional characteristics of space environment above China or along 120°E meridian line, coupling between space spheres at different heights and different physical processes, space weather disturbance and its propagation along the meridian chain, and space weather effects on ground technical facilities.

Hainan Coherent Scatter Phased Array Radar (HCOPAR): System Design and Ionospheric Irregularity Observations

The Hainan coherent scatter phased array radar (HCOPAR) is one of the most important radio systems of the Chinese Meridian Space Weather Monitoring Project (Meridian Project). The radar is located at Fuke station (19.5°N, 109.1°E, dip latitude 8.1°N), Hainan island, China, to observe the field-aligned irregularities in ionospheric $E$ - and $F$ -regions. It is operated with a peak power of 54 kW and uses the Barker codes for good sensitivity. Its antenna array is composed of $18 \times 4$ five-element Yagi antennas and is used for both transmitting and receiving. The Yagi antennas are arranged in a rectangular grid 100 m long and 20 m wide, covering an area of 2000 m2. This antenna arrangement forms seven radar beams from −22.5° to 22.5° in azimuth with an angle step of 7.5°. The central beam points to due geographic north. A brief description of the radar system, data processing, and signal characteristics is also provided. The intensity, Doppler velocities, and spectral widths of the quasi-periodic echoes measured in the nighttime of June 23, 2013 are presented as typical data of type II irregularities in the $E$ -region. The data recorded by the HCOPAR in the fan-beam mode on September 15, 2013 are displayed as the typical $F$ -region plasma bubbles.

MST Radars of Chinese Meridian Project: System Description and Atmospheric Wind Measurement

Based on the construction of the Chinese Meridian Project, two mesosphere, stratosphere, and troposphere (MST) radars were designed and located in Beijing and Chongyang, Hubei province, China, to investigate the atmospheric dynamics in the troposphere, stratosphere, and mesosphere. The official names of the two radio systems are Beijing MST radar and Wuhan MST radar. They are the monostatic radars with an active phased antenna array consisting of 576 Yagi antennas and operated by a 53.8-MHz frequency. The three-element Yagi antennas are arranged in a square grid of 96-m side length to form the aperture of 9216 m2. This antenna array arrangement forms the five symmetric radar beams of vertex, east, west, south, and north. The beamwidth is 3.2°, the maximum directive gain is 34.8 dB, and the total transmitting peak power is ∼172 kW. The zenith angle of the oblique beams is adjustable between 0 and 20° with a 1° step. The average power aperture product of the radars is $3.2\times 10^{8} \text{Wm}^{2}$ . There are three operating modes of the MST radars, including the low, middle, and high modes, applied to observe the troposphere, stratosphere, and mesosphere, respectively. Thus, these two coherent pulse Doppler MST radars have the ability to study the features of the midlatitude atmospheric turbulence and wind field vector from the troposphere to the lower thermosphere with high spatiotemporal resolution. In this paper, the antenna array, system hardware, and signal processing methods, as well as the typical observation results of the troposphere, stratosphere, and mesosphere, are introduced.

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.

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.

First scanning Fabry–Perot interferometer developed in China

A scanning Fabry-Perot interferometer (SFPI) was first developed and deployed at the Langfang near Space Environment Field Scientific Observation Station (39.38 N, 116.65°E) of the National Space Science Center, CAS. The instrument is designed to measure the mesospheric and thermospheric wind velocities using the atomic oxygen 557.7-nm and 630.0-nm emissions. Data from February 28 to March 3 and February 28 to March 15 in 2011 were chosen for case study and mean value study, respectively. The errors of the meridional and zonal winds are 6.5 and 7.5 m/s at 557.7-nm and at 630.0-nm, they are 7.1 and 6.6 m/s, respectively. During the whole experiment, the instrument has performed in good condition and provided high-quality data. The mean neutral wind data were consistent with that predicted by HWM07. Good agreement has been found in between the SFPI and a neighbor Meridian Project Fabry-Perot interferometer (MP FPI), with a corresponding coefficient ( r 2) larger than 80%. In general, the scanning FPI meets the design goal, and it is a useful ground-based instrument for measuring mesospheric and thermospheric winds at middle latitudes and is able to provide high-quality data for future scientific studies.

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.

Nighttime and Seasonal variations of the Sodium Layer Measured by Lidar at Different Latitudes in China

AbstractThis study is based on long‐term observations of the sodium layer by lidars at Beijing (40.47°N, 115.97°E), Hefei (31.87°N, 117.23°E) and Hainan (19.99°N, 110.34°E), which are part of the Meridian Project of China. The purpose is to reveal characteristics of nighttime and seasonal variations of the background sodium layer over China along 120°E. The observations from three lidar stations on Dec. 17, 2010 show that, the nighttime variations of the sodium layer are not correlated to each other. The fitted long‐term variations with annual plus semiannual changes reveal that the column abundance of the sodium layer over Beijing and Hefei varied annually, while that over Hainan changed semiannually. The seasonal variations of centroid heights and RMS widths of the sodium layer present apparent semiannual variation tendency, excluding the long‐term change of RMS width for Hainan. Statistics illustrate that the seasonal variations of column density of background sodium layer is correlated with the change of temperature near the mesopause. It has the maximum in winter and minimum in summer, respectively. With the growth of the latitude, the column abundance increases and the annual variation tendency becomes more obvious. There is no clear latitude dependence on the centroid height of the sodium layer, and it changes semiannually with seasons at three locations. The RMS width of the sodium layer is the largest at Beijing (middle and upper latitude) and the least at Hefei (middle latitude) in every month of one year, and it is the medium at Hainan (lower latitude).

Plasma transport between the ionosphere and plasmasphere in response to solar wind dynamic pressure pulsation

The plasma transport between the plasmasphere and the ionosphere in response to the interplanetary conditions is still not fully understood until now. Simultaneous observations of the plasmasphere and ionosphere from the newly developed Chinese Meridian Project provide a new opportunity for understanding the characteristic of the plasma transport and the coupling mechanism between these two regions. We investigate the response of the plasmasphere (L≈2) and ionosphere to the solar wind dynamic pressure pulse during geomagnetically quiet period of 21–27 March 2011. The response of the plasmasphere shows a significant depletion. The plasmaspheric density nearly decreases by half in response to the solar wind dynamic pressure pulse, and subsequently recovers to the original level in 1–2 d. Meanwhile, the maximum electron density of the ionospheric F2 layer (NmF2) and the total electron content (TEC) increase by 13% and 21%, respectively, and then gradually recover, which is opposite to the behavior during magnetic storms. Preliminary analysis shows that the plasmaspheric depletion may be mainly caused by the southward interplanetary magnetic field and changing dawn-dusk electric field. The plasmaspheric density variations seem to be controlled by both the IMF and ionospheric conditions.

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.

Simultaneous observations of plasmaspheric and ionospheric variations during magnetic storms in 2011: First result from Chinese Meridian Project

AbstractThe plasma transport between the plasmasphere and ionosphere during magnetic storms is a long‐standing problem and is still not fully understood. Simultaneous observations of the plasmasphere and ionosphere are vital to understand the coupling between the two regions. In this study, using the measurements from the newly developed Chinese ground‐based space weather monitoring network (Meridian Project), we investigate the plasmaspheric density at L ≃ 2 inferred from ground magnetometers and the ionospheric electron density inferred by digital ionosondes and GPS signals during magnetic storms in 2011. Five moderate magnetic storms with minimum Dst index between −47 and −103 nT during this period have been investigated. The observations show that the plasmaspheric density drops significantly by more than half of the prestorm value. The ionospheric F2 layer electron density NmF2 and the total electron content (TEC) show ~20–50% decreases, and the NmF2 and TEC reductions take place before the plasmaspheric density reaches its minimum. These findings suggest that the plasmaspheric depletion is very likely due to the reduced plasma supply from the ionosphere for the five moderate magnetic storms in 2011. Therefore, the plasmasphere dynamics seems to be controlled by the ionosphere during magnetic storms.