1. W. D. Cramer1, J. Raeder1, F. R. Toffoletto2, M. Gilson1,3, B. Hu2,4
Plasma Sheet Injections into the Inner Magnetosphere: Two-Way Coupled OpenGGCM-RCM Model Results*
W. D. Cramer1, J. Raeder1, F. R. Toffoletto2, M. Gilson1,3, B. Hu2,4
1Space Science Center, University of New Hampshire, 2Department of Physics and Astronomy, Rice University, 3Pattern Technologies Inc., 4CG Services
September 27, 2017
*also see Cramer et al., 2017

2. Magnetospheric Convection
Dungey cycle [Dungey, 1961]
Reconnection at dayside magnetopause connects IMF to Earth’s magnetic field, which gets dragged into tail
Return flow sunward from tail to inner magnetosphere back to dayside
Main source of inner magnetosphere plasma, some becomes trapped
Steady convection when dayside, tail reconnection rates match
Steady adiabatic convection not possible, however [Erickson and Wolf, 1980]
Adiabatic condition: PV5/3 (“flux tube entropy”) is conserved along drift paths (V=flux tube volume)
Pressure increase of inward drift too large for observed magnetic fields (“pressure balance inconsistency”), would stop convection

3. Plasma Sheet “Bubbles”
Possible resolutions of pressure balance inconsistency: plasma sheet bubbles, gradient/curvature drift
“Bubbles”: depleted flux tubes (low relative pressure, density, and flux tube entropy)
Interchange unstable with neighboring flux tubes
Move inward until flux tube entropy matches background
Brake and oscillate around equilibrium
Likely cause of depletion: transient/local reconnection
Reduces flux tube volume
Plasma sheet entropy profile Xing and Wolf, 2007

4. Plasma Sheet Injections
Narrow (1-3 RE) channels of earthward-moving plasma
Flow Bursts
Short-duration (1-2 min) high-speed flows (generally V>400 km/s)
Bursty Bulk Flows (BBFs)
Segments of moderate-speed flows (generally V>100 km/s) with flow burst(s)
Usually accompanied by dipolarization front
Primary means of plasma transport into inner magnetosphere during active times
Yang et al., 2011

5. Model Components OpenGGCM CTIM (Coupled Thermosphere-Ionosphere Model)
3-D stretched cartesian grid
Solves semi-conservative MHD equations for single fluid
Plasma energy, not total energy, conserved
Solves ionosphere potential on 2-D spherical grid using conductances, field- aligned currents
Main inputs: solar wind plasma parameters, interplanetary magnetic field
CTIM (Coupled Thermosphere-Ionosphere Model)
Models chemical and photo-chemical reactions
Determines conductances
Main inputs: FACs, auroral precipitation, solar EUV
RCM (Rice Convection Model)
2-D ionosphere grid representing footpoints of flux tubes
Solves motion of flux tubes due to potential, magnetic induction and drift
Main inputs: outer boundary conditions, ionosphere potential

6. Model Coupling Methodology
OpenGGCM -> Ionosphere
Sends MHD density, pressure, auroral precipitation, FAC
Receives Ionosphere Potential
RCM -> Ionosphere
Sends RCM FACs, auroral precipitation
Blends with MHD values
RCM -> OpenGGCM
Convert flux tube content to pressure and density (and vice-versa)
Receives MHD pressure, density at boundary
Flux tube volume-weighted averages along field line
Sends RCM pressure, density
Nudge MHD P, n values (RCM influence greater in inner region)
RCM feedback slowly ramped up after MHD initialization period

7. Storm, Quiet SimulationsID
Solar wind Driver
Date
Minimum Dst* Q1
---
1/19/2014 I1
CIR
8/5/2013
-41 I2
6/6/1998
-46 I3
5/2/2010
-71 I4
2/27/1997
-86 M1
CME
5/1/2013
-54 M2
5/29/2010
-60 M3
7/15/2012
-105 M4
10/28/2001
-137

8. Injections in Simulation Data
Calculation of radial velocity on current sheet at boundary
Field lines traced from near-Earth points
Current sheet marked as farthest field line distance
Calculate flux tube volume
MHD quantities (v, n, P, B) interpolated to current sheet crossings
Values interpolated to spherical boundaries
LLBL filtered out using T/n (as in Tsyganenko and Mukai [2003]), v(azimuthal), and proximity to boundary

9. Snapshot of Injections at R=10
Inward injections (velocity maxima) frequently associated with entropy minima (bubbles)

10. Bubbles and Injections (Storm M.P.)

11. Bubbles and Injections (Detail)

12. Bubbles and Injections (Quiet Period)

13. Injections collocated with bubbles
Storm-times: ~70-80% of injections at R>8
Quiet-time: significantly lower % between R=6-10

14. Plasma Transport by Bubbles
Storm-times: ~80% of transport at R>8
Quiet-time: significantly lower % below R=8

15. Discrete Injections Identify individual injection time series
Only BBFs shown (w/ time of peak velocity)
R-dependent flow burst cutoff speed

16. Injection Peak Velocity
Average peak injection velocity vs. R (all injections)

17. BBF profile vs. Theory/Data
Superposed epoch of BBFs relative to peak velocity
BZ: similar dipolarization profile
Flux tube entropy: observation of bubble
Peak velocity occurs at dipolarization front
Yang et al., 2011

18. Discussion/Conclusions
Storm-time injections (fast or otherwise) are usually associated with bubbles beyond 8 RE
Quiet-time: less frequent association below 10 RE
Bubbles responsible for ~80% of storm-time plasma transport across 8 RE
Quiet-time: % transport much lower below 8 RE
Peak inward velocity of discrete injections decreases approx. linearly from 12 to 6 RE
Model reproduces BZ, PV5/3 profile for BBFs
Peak velocity coincides with dipolarization front