W. J. Sun

Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times

An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earths high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.

Observations of kinetic-size magnetic holes in the magnetosheath

Magnetic holes (MHs), with a scale much greater than ρixa0(proton gyroradius), have been widely reported in various regions of space plasmas. On the other hand, kinetic-size magnetic holes (KSMHs), p ...

The Magnetic Field Structure of Mercury's Magnetotail

In this study, we use the magnetic field data measured by MESSENGER from 2011 to 2015 to investigate the average magnetic field morphology of Mercury’s magnetotail in the down tail 0~ 3 RM (RM = 2440 km, Mercurys radius). It is found that Mercury has a terrestrial-like magnetotail, the magnetic field structure beyond ~1.5 RM down tail is stretched significantly with the typical flaring lobe field ~50 nT. A tail current sheet separating the antiparallel field lines of lobes is present on the equatorial plane. The magnetotail width in north-south direction is ~5 RM, while the transverse width is ~ 4 RM. Thus, magnetotail is elongated along north-south direction. At current sheet center, the normal component of magnetic field (10~20 nT) is much larger than the cross-tail component. The magnetic field profile over current sheet can be well fitted by the Harris sheet model. The fitting shows that the curvature radius of field lines at sheet center usually reaches a minimum around the midnight (100 ~200 km) with stronger current density (40~50 nA/m2). While the curvature radius increases towards both flanks (400~600 km) with the decreased current density (~20 nA/m2). The typical half-thickness of current sheet around the midnight is about ~0.25 RM (~600 km), and the inner edge of current sheet is located at the down tail ~ 1.5 RM. Our results about the tail field structure does not show the evident dawn-dusk asymmetry as that found in the Earth’s magnetotail. Possible reasons are provided and discussed.

The Effect of Solar Radio Bursts on GNSS Signals

Abstract A solar radio burst (SRB) is the intense solar radio emission related to a solar flare and one of the extreme space weather events. If an SRB occurs with the enhancement in L band radio flux, it could influence the Global Navigation Satellite System (GNSS) signals through direct radio wave interferences. An SRB could result in reduction of signal-to-noise ratio (SNR) and instantaneous or long-period loss of lock (LOL) on GNSS signals. Therefore decreasing the observation quality, which subsequently will influence all the applications based on these observations such as radio occultation technique and precise GNSS positioning. An SRB will mainly affect stations located in the sunlit hemisphere during radio flux enhancement, while the strength of the influence depends on the solar incidence angle, the antenna pattern, the tracking algorithm, and some other factors. The threshold value of SRB flux value that could result in a significant effect on GNSS signals is believed to be between 1000–10,000 solar flux units (SFU; 1 SFUxa0=xa010 −xa022 xa0Wxa0m −xa02 xa0Hz −xa01 ) in L band. Significant SRBs can occur at solar minimum and maximum. During 2003–12, eight SRB events occurred that have shown degrading effects on GNSS signals in the literature, which is approximately 8.8 events per solar cycle. Although the occurrence ratio is not significantly high, we should pay sufficient attention to its side effects on modern society.