MLT Plasmapause Characteristics: Comparison Between THEMIS Observations and Numerical Simulations

Abstract

We perform a statistical comparison of the global behavior of the THEMIS observed and simulated plasmapause in the geomagnetic equatorial plane. Simulation is based on the interchange instability mechanism. Analyzing plasmapause positions (LPPs) from the period July 2008 to December 2012, we derived formation and propagation characteristics of the main plasmapause, which reflect the most probable global plasmapause behavior. The results suggest a global eastward azimuthal plasmapause propagation and a radial plasmapause motion limited to the 21–07 MLT sector. The formation of the plasmapause takes place with the highest probability at postmidnight. It is likely that the erosion occurs in a range of MLTs simultaneously. On the dayside, the plasmapause moves almost entirely azimuthally. We suggest that the plasmapause propagates azimuthally with a mean angular velocity close to the corotation speed at all MLTs, at least during periods of lower geomagnetic activity. The results also show that the experimental plasmapause characteristics are in accordance with the interchange instability mechanism. Along with the proposed suggestions for future works, this study contributes to making a further step toward resolving some of the long‐lasting, unresolved issues related to plasmapause dynamics.

Relationship Between Global Plasmapause Characteristics and Plasmapause Structures in the Frame of Interchange Instability Mechanism

“…The simulation outputs for all investigated cases clearly show that the initial plasmapause radial motion (erosion or expansion) occurs at the nightside, more intense around postmidnight. This is in accordance with the strongest E5D field in these MLT sectors, lower conductivity, but may be influenced with the simulation starts at 02 MLT (as discussed in detail in Verbanac et al, 2018). For different changes in the E-Field (different Kp jumps: e.g., Kp increase and Kp decrease), the formation of the new plasmapause Journal of Geophysical Research: Space Physics 10.1029/2019JA026768 can be noted in slightly different night MLT sectors (this will be noted below when describing main plasmapause with specific structures).…”

“…Thus, the width of T lag values affected by the changes in the correlation reflects the azimuthal extension of the structure. On the other side, the results by Verbanac et al (2018) suggested that the T lag belts reflect the MLT range of the plasmapause formation. Since both results seem to be physically plausible, and not necessarily exclusive, we suggest that this issue has to be further investigated.…”

“…Time of the structure passages through this MLT sector is estimated to be 9-14 UT, 13-14 UT, and 9-17 UT for plume, shoulder, and notch, respectively. Assuming that the plasmapause at all MLTs azimuthally propagates with the mean angular velocity close to corotation (as suggested by Verbanac et al, 2018), this is equivalent to the azimuthal extension of these structures that account for MLT = 5, MLT = 1, and MLT = 8 for plume, shoulder, and notch, respectively. Figure 4), we find that the correlation maximums are placed within T lag intervals that correspond to the mentioned UT intervals.…”

“…The aim of the present study is to 1. analyze in detail the plasmapause characteristics as obtained in Verbanac et al (2018). Since the plasmapause dynamics derived from experimental and modeled plasmapause are in accordance, we focus here on the modeled plasmapause.…”

“…These works did not follow the formation and time evolution of any plasmapause structures, and the obtained results represent the most probable global plasmapause characteristics. The study by Verbanac et al (2018) has also performed a statistical comparison of the global behavior of the large statistical plasmapause sample derived from THEMIS satellite observations in the period 2008-2012 and plasmapause that was modeled using the simulation based on interchange instability mechanism (Lemaire & Gringauz, 1998;Pierrard & Stegen, 2008). The response of both the experimental and simulated plasmapause to various solar wind/geomagnetic activity indices (thereafter PP indicators) at different magnetic local times (thereafter MLTs) was investigated by applying the cross-correlation analysis that is shown to be a powerful tool to derive global plasmapause characteristics statistically (Bandić et al, 2017;Verbanac et al, 2015Verbanac et al, , 2018.…”