LOW LATITUDE MAGNETOMETER CHAIN IN CHINA IN THE FRAME OF THE MERIDIAN PROJECT



K. Schwingenschuh1, W. Magnes1, T. L. Zhang1, G. Berghofer1, W. Koren1, W. Riedler1, K. Mocnik1, H. Ottacher1, M. Stachel1, A. Scherr1, H. Zhao2, G.C. Zhou2, D.J. Wang2, S.W. Chen2, G. Le3, J. Means3, W. Greer3, D. Pierce3, B. Snare3 and C.T. Russell3



1 Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften (IWF/ÖAW), Graz, AUSTRIA
2Center for Space Science and Applied Research, Chinese Academy of Sciences (CSSAR/CAS), Beijing, CHINA
3Institute of Geophysics and Planetary Physics (IGPP/UCLA), Los Angeles, USA



Originally published in: Adv. Space Res., 25(7/8), 1353-1356, 2000.

ABSTRACT

MERIDIAN is a 120° east ground based multi-station and multi-instrument project proposed in China. IWF/ÖAW in Graz, Austria in cooperation with IGPP/UCLA in Los Angeles, USA and CSSAR/CAS in Beijing, China has developed variometers for magnetic field observations along this MERIDIAN chain. The variometer (CHIMAG) is a fluxgate magnetometer especially for Earth field variation and pulsation measurements. Three variometer stations have been installed in Beijing (40° N), Hainan (19° N) and Wuhan (30.5° N), respectively. Two more will be installed in 1999. In this paper we will present the design and the scientific objectives of the CHIMAG as well as the results of the first observations.

 

THE MERIDIAN PROJECT

The planned Meridian project will consist of a chain of observatories with ground-based multi-instruments for Solar-Terrestrial environment studies including magnetometers, ionosondes, whistler monitoring instruments, HF and VHF radar.

The chain is located in the neighborhood of the 120o E meridian, and is thus named the MERIDIAN Project.

The scientific objectives are:

- advance theoretical understanding and numerical modeling of physical and chemical processes in regional and global space environment (magnetic and electric field, energetic particles, solar radiation)
- provide accurate and reliable data for space weather forecasts
- provide data for seismic research and the investigation of electromagnetic pollution

 

THE CHIMAG PROJECT: GROUND STATION MAGNETOMETERS TO INVESTIGATE GEOMAGNETIC VARIATIONS AND PULSATIONS IN CHINA

Geomagnetic pulsations are the manifestation of ultra-low-frequency (ULF) plasma waves in the Earth’s magnetosphere. The pulsations have frequencies ranging from approximately 1 mHz to more than 10 Hz and appear as quasi-sinusoidal oscillations in magnetometer data recorded at the Earth’s surface, in the ionosphere and in the magnetosphere (see Table 1). The first observations of ULF fluctuations (with periods ranging from seconds to minutes) of magnetic fields were made on the ground by Steward in 1861, almost one century before their links to plasmas in near-Earth space were established. Dungey (1954) was the first to suggest that MHD waves in the outer atmosphere were the sources of the oscillating or pulsating magnetic field observed on the surface.

 

 

Continuous Pulsations

Pc 1

Pc 2

Pc 3

Pc 4

Pc 5

Period [s]

0.2-5

5-10

10-45

45-150

150-600

Frequency

0.2-5 Hz

0.1-0.2 Hz

22-100 mHz

7-22 mHz

2-7 mHz

 

 

Irregular Pulsations

 

Pi 1

Pi 2

Period [s]

1-40

40-150

Frequency

0.025-1 Hz

2-25 mHz

Table 1. Frequency ranges of ULF continuous (Pc) and irregular (Pi) magnetic pulsations.

Scientific Objectives

Magnetic field measurements are essential for correlative satellite-ground based studies of various phenomena (Schwingenschuh et al., 1996). The CHIMAG (CHInese MAGnetometer chain) results combined with the measurements aboard the ISTP satellites already in orbit or being launched in the near future (e.g., CLUSTER-2, DOUBLE-STAR) provide the unique opportunity to study the following technical and scientific objectives:

- Install a state-of-the-art fluxgate magnetometer chain in the low latitude area
- Perform remote sensing of magnetospheric phenomena
- Determine how Pi 2s are produced by substorms
- Determine how Pc 3 - 4 magnetic pulsation energy enters the magnetosphere and propagates along magnetic field lines to low latitudes
- Investigate higher frequency magnetic field fluctuations (the sampling frequency of CHIMAG is up to 64 Hz) for space weather and electromagnetic pollution studies

Fig. 1 depicts the location of the five CHIMAG stations. CHIMAG-1 in Beijing (40.30°N/116.19°E geographic latitude/longitude and 29.1°/186.2° geomagnetic lat./lon.) is operating since mid 1997, CHIMAG-2 in Wuhan (30.51°N/114.51°E geographic latitude/longitude and 19.5°/185.0° geomagnetic lat./lon.) and CHIMAG-3 in Hainan (19.53°N/109.13°E geographic latitude/longitude and 7.8°/179.4° geomagnetic lat./lon.) provide data since May 1998. In 1999 CHIMAG-4 and CHIMAG-5 will be installed in Mohe (53.5°N/120.0°E geographic latitude/longitude and 42.7°/190.7° geomagnetic lat./lon.) and Kashi (39.5°N/76.0°E geographic latitude/longitude and 30.1°/150.9° geomagnetic lat./lon.), respectively.

China map

Fig. 1: The location of the five CHIMAG variometer stations in China

Main Features and Parameters

The CHIMAG magnetometer was jointly developed by IWF/ÖAW in Graz, Austria, IGPP/UCLA in Los Angeles, USA and CSSAR/CAS in Beijing, China.. It is a three component fluxgate variometer measuring in a small range with high resolution by compensation of the Earth’s magnetic field. It comprises three main parts: the sensor assembly, the electronics box and a portable host PC. The CHIMAG design is based on the development of the magnetic field experiment MAREMF-OS (Magnes et al., 1998) for the ill fated MARS-96 mission. The main instrument features and parameters are:

- absolute time via GPS receiver (UTC better than 10 ms) and active auto compensation
- daily file generation and magneto optical (MO) backup system
- 0.01 nT resolution (instrumental noise level) in Earth field
- range:+/- 512 nT
- compensation range: X- and Z-axis: 0 ... 60000 nT , Y-axis: -30000 ... 30000 nT
- maximum / nominal data rate:64 vectors/second/ 1 vectors/second

Tests and First Results

Each of the CHIMAG instruments had to pass various tests before delivery to China. Much effort was done to test and improve the temperature stability of the variometer. The instruments were operating at stations in Austria (Wolfgruben) and Hungary (Nagycenk) for several months in order to measure the long term variations of the parameters. After delivery to Beijing the magnetometers were tested and the results compared with the station variometer (Shi-Shan-Ling Geomagnetic Observatory).

After the installation of CHIMAG-2 and CHIMAG-3 at observatories in Wuhan and Hainan island, respectively, comparative pulsation studies began. Fig. 2 shows the first results of these simultaneous observations in Beijing and Wuhan.

The data from CHIMAG-1 have been compared with those observed at the Bai-Jia-Tuan geomagnetic observatory, which is about 30 km away from Shi-Shan-Ling. Diurnal variations of these 2 data sets coincided very well.

SUMMARY AND FUTURE PLANS

The three variometers installed in Beijing, Wuhan and Hainan are providing excellent data sets. CHIMAG-4 and 5 will be delivered and installed in 1999. The comparison with the IGPP/UCLA SMALL (Le and Russell, 1996) variometers will begin in September 1998. The CHIMAG data sets will be made available to all researchers by the end of 1999 via the data centers at IWF/ÖAW in Graz/Austria and at CSSAR/CAS in Beijing/China.. The data will also be provided to the CLUSTER-2 ground-based data center at RAL/England. A problem is still the long time delay between the measurements in China and the data processing and analysis in Austria (up to 6 months). This will be improved until the CLUSTER-2 launch in 2000.

REFERENCES

Dungey, J.W., The propagation of Alfvén waves through the ionosphere,
Pennsylvania State University Ionosphere Research Laboratory Science report, 57, (1954).

Magnes, W., G. Berghofer, K. Mocnik, W. Koren, K. Schwingenschuh, W. Riedler, C. T. Russell, J. Means, D. Pierce, B. Snare, A. Balogh and T. J. Beek, A Spaceborne Magnetometer Tested Under Extended Temperature Conditions (Experiment MAREMF-OS / MARS-96), Meas. Sci. Technol., in press, (1998)..

Schwingenschuh, K., W. Riedler, H. Zhao, T.L. Zhang, G. Berghofer, W. Magnes, R. Trautner, W. Koren, K. Mocnik, J. Means, D. Pierce, W. Greer, A. Snare and C.T. Russell, Design of a Ground Station Magnetometer (CHIMAG) to Investigate Geomagnetic Pulsations in China during the CLUSTER Project, IWF-9601, Space Research Institute, Austrian Academy of Sciences, (1996).

Le, G. and C.T. Russell, Sino-Magnetic Array at Low Latitudes (SMALL), IGPP/UCLA internal report, (1996)

 

Pulsation PI2

Fig. 2: Nightside Pi 2 pulsations observed simultaneously by CHIMAG-1 in Beijing and CHIMAG-2 in Wuhan.

 


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