Linear separation of orthogonal merging component and viscous interactions in solar wind‐geospace coupling

Abstract

The general view is that the response of the magnetosphere-ionosphere system to a complex, variable solar wind input will be a complicated and nonlinear function of that input. We investigate this question using a global MHD code to simulate the interaction and determine the responses of the system to isolated aspects of the solar wind input. We present evidence from the simulations that the solar wind-geospace interaction can be linearly decomposed into component merging interactions for interplanetary magnetic field (IMF) B y separate from B z and a separate viscous interaction. One can run the global simulation (in our case, the Lyon-Fedder-Mobarry code) using just the solar wind plasma and B z time series, do a second simulation using just the solar wind plasma and B y time series, add the results of the two simulation outputs, then subtract the output from a simulation done with only the plasma input and no magnetic field, since the sum of the B y and B z runs has two viscous interactions (one for each run), and get an output that is very close to the result of a single run using the entire IMF merging field (B y and B z ) along with the plasma time series. This demonstrates that the components of merging and viscous interactions between the solar wind and geospace are linearly separable to a very large degree.

Study of Variation of Polar Cap Potential During Geomagnetic Storm Events of 24 November 2001 and 24 August 2005 as Observed From LFM and BATS‐R‐US Simulation

“…Both events were simulated for a constant ionospheric conductivity of 5 mhos. During both events we found that variation pattern of PCP was consistent with behavior of PCP observed in previous research by Bhattarai et al (), Lopez et al ( and ), Bruntz, Lopez, Bhattarai, et al, and Bruntz, Lopez, Wiltberger, & Lyon, ), and Mitchell et al (), although most of these previous works dealt with steady state IMF conditions.…”

“…Lopez et al () found that one can reproduce PCP with a complex input by using PCP values obtained from LFM simulation to generate partial responses to individual IMF components using simple linear superposition. In Figure , since full IMF is always higher than purely B z and B y IMF during periods of southward IMF (9:00–11:00 hours), the linear superposition hypothesis seems to work well.…”

“…In Figure 6, since full IMF is always higher than purely B z and B y IMF during periods of southward IMF (9:00-11:00 hours), the linear superposition hypothesis seems to work well. However, in Figure 7 where we are comparing PCP during different IMF condition in BATS-R-US simulation, during periods of southward IMF and between 9:00 and 10:00 hours we see that PCP due to purely B z component (blue line) gets higher than PCP due to full IMF (red line), suggesting that BATS-R-US might not obey linear superposition of orthogonal merging concept introduced by Lopez et al (2014). Gordeev et al (2011), Figure 2 therein) performed BATS-R-US simulation for ideal solar wind condition with purely B z component that switch from northward to southward at regular time interval.…”

Plasma Sheet Pressure Variations in the Near‐Earth Magnetotail During Substorm Growth Phase: THEMIS Observations

“…This location is in agreement with the statistical substorm onset locations at MLT ~ 21:00 to ~ 01:00 (e.g., Frey et al, ; Liou et al, ). Since the variations of P eq are suggested to be closely related to enhanced electric fields associated with dayside magnetopause reconnection transmitting through different paths, P eq variations in the tail plasma sheet should depend on the solar wind condition and ionospheric conductance distribution in the polar region (e.g., Kan, ; Lopez et al, ). Simulation results have shown that plasma sheet evolution in the near‐tail region should depend on the competition between the depletion of closed magnetic flux and addition of open flux but with the open flux being added more uniformly to the magnetotail (Hsieh & Otto, ).…”