Statistical study of the properties of the magnetic field and plasma in the earth’s magnetotail near lunar orbit

Abstract

Based on the magnetic field and plasma data obtained by GEOTAIL in 1992–1995 and WIND in1994–2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the superposed epoch analysis. The results showed that near the 0° sector the plasma density was negatively correlated with Dst index while the temperature was positively correlated with Dst index. The plasma velocity and magnetic field strength had little correlation with Dst index. Around the current sheet near the lunar orbit, the Bx varied between −15-15 nT, the plasma density was less than 0.4 cm−3, the median of plasma density for all events was less than 0.1 cm−3, the temperature varied from 0.016 to 8.98 keV, the median of the plasma temperature for all the events was ∼3 keV, the median of speed was about 200 km/s and the maximum speed was up to 1500 km/s. The tailward and earthward flows could be observed accompanied with the current sheet. For the current sheet cases with tailward flow, the Bx varied from −15 to 15 nT, the upper quartile of plasma velocity was more than 400 km/s, the maximum speed was up to 1500 km/s. For the current sheet cases with tailward flow, the Bx varied from −10 to 10 nT, the upper quartile of plasma velocity was less than 400 km/s, the maximum speed was up to 1200 km/s. The median of plasma density, temperature and velocity were similar for the two categories. This paper discussed the relationship between above results and magnetic reconnection at magnetic tail, compared the above results with the observation in the far magnetotail. We fitted the statistical results according to the Harris current sheet model, and the observation was consistent with Harris current sheet model. The above results can provide useful information for the design and protection of lunar-orbiting spacecraft and can be used as the background magnetic field and plasma parameters in the numerical simulation of mid-magnetotail reconnection.