Numerical Study on the Earthward Propagating Plasmoids

Abstract

The correlation between plasmoids and geomagnetic substorms has been demonstrated by satellite observations. In addition to the tailward propagating plasmoids with N‐S bipolar signatures, earthward propagating plasmoids are found, which are characterized by plasma sheet S‐N bipolar events and lobe S‐N bipolar signatures. The occurrence rate of the S‐N bipolar events is much lower than that of the N‐S events. The S‐N bipolar events occur primarily during quiet geomagnetic and IMF Bz north period, and they are correlated with small, isolated geomagnetic substorms. A 2.5 dimensional MHD simulation on the earthward propagating plasmoids has been carried out, on base of the specific distribution of the cross‐tail electric fields Ey during geomagnetically quiet times (IMF Bz is northward and | By |≥ Bz). The simulation results of the two cases showed the major features of the flux rope magnetic structures and plasmoids with complex closed magnetic field lines. The similar signatures to tailward propagating plasmoids could be consistent with IMP 8 observations about the earthward propagating plasma sheet S‐N bipolar events. The results displayed a similar configuration to the schema given by Schindler which may explain the low occurrence frequency of the S‐N events, and also showed that the dynamic growth of the magnetic reconnection becomes considerably suppressed for a strong cross‐tail magnetic field By. From this simulation it could be concluded that the magnetic reconnection can be the genetic mechanism of the plasma acceleration and heating in the magnetotail in both geomagnetically active and quiet time, namely, under both southward and northward (with | By |≥ Bz) IMF conditions.

Ongoing Asthenospheric Upwelling and Delamination‐Style Down‐Welling Beneath Northeast China: Evidence From High‐Resolution Magnetotelluric Profiles

“…Deep reflection seismic data were collected on the Manzhouli-Suifenhe geoscience transect (Figure 1b, dashed green line), which crossed the whole of the Northeast China in NW-SE direction (Yang et al, 1996). The 3-5 km Moho offset between the Songliao basin (shallow Moho) in the east and the Greater Xing'an Range (deeper Moho) in the west, has been proposed to be the cause of the north-south trending gravity lineament (Yang et al, 1996). Guo et al (2014) also observed a 4 km Moho offset across the north-south trending gravity lineament with a change from 33 km beneath the Songliao basin to 37 km beneath the Greater Xing'an Range using P wave and S wave receiver function.…”

“…In the interpretation presented below, estimates of Moho depth from published seismic studies are used. Deep reflection seismic data were collected on the Manzhouli‐Suifenhe geoscience transect (Figure 1b, dashed green line), which crossed the whole of the Northeast China in NW‐SE direction (Yang et al., 1996). The 3–5 km Moho offset between the Songliao basin (shallow Moho) in the east and the Greater Xing'an Range (deeper Moho) in the west, has been proposed to be the cause of the north‐south trending gravity lineament (Yang et al., 1996).…”