1. Data-Model Comparisons
Yanhua Liu
University of New Hampshire
GEM Workshop 2013

2. Models in Space Science
Plasma can be described by Vlasov equation in (r, v, t) space:
It is either not easy to be solved, or not easy to be compared with observations.
More realistic models can help:
More comparable equations --- Test of plasma frozen in E+VxB=0 …
Empirical Models Tsyganenko Model, Shue 97/98 Model …
MHD Models --- OpenGGCM, RCM, Resistive MHD Reconnection …
Hybrid/Kinetic Models --- Hybrid global simulation, Hybrid or PIC reconnection simulations
Models provide global observables:
Electric and magnetic field data
Moments : density, velocity, temperature, pressure, entropy…
Plasma Distribution Functions ( Hybrid/Kinetic Model)

3. Data in Space Science Magnetosphere In-situ Observation:
Take Cluster Mission as an example, four spacecraft carry identical sets of 11 scientific instruments:
FGM – magnetic field data
EDI – electric field data via electron drift
EFW – electric field data (spin plane)
PEACE – electron distribution function, moments data (~26 KeV)
CIS – ion distribution function, moments data (~ 40 KeV)
RAPID – highest energy electron/ion data (~MeV)
STAFF, Whisper, DWP, WBD, WEC and EFW– wave package
Cluster
CODIF in CIS Package

4. Dst index as an indication of phase of magnetic storm
Data in Space Science
Ground based data:
Aurora Images
Geomagnetic Indices:Dst, Kp, Ae, Al…
Solar wind data:
Solar wind IMF, density, velocity, pressure from the observation around L1 orbit (ACE, GEOTAIL, WIND)
Auroral Image
Dst index as an indication of phase of magnetic storm

5. Limitations of Models and Data
Many assumptions, eg:
OpenGGCM:
MHD model, artificial resistivity in reconnection. Maxwellian distribution function is assumed ….
PIC/Hybrid:
Not real mass ratio: mi/me ~50,100…
Boundary condition matters: open boundary/ periodic boundary
2 Limitations of Data:
Reliable measurement: quality of data sometimes is limitted, eg: sun contamination
Limitation of instrument: The instruments have their measurement range. Eg: Cluster/CODIF measures 40-40,000 eV. Cluster/EFW measures spin plane electric field and Ez comes from E.B=0 …
Spatial and Time Resolution: only single or few measurements in the space and we can not tell if the change come from space/time evolution (MVA, timing, curlometer techniques)

6. Comparisons Model-Data-Model Comparison: Data-Model-Data Comparison:
Motivated by model result
Check with data
Compare with other model predictions
Data-Model-Data Comparison:
Motivated by observation
Use model to reproduce observation

7. Model-Data-Model
PIC simulation predicts the electron distributions in the reconnection inflow region, sepratrix and exhaust region. (Chen et al, 2008)
Cluster observation of electron distribution agrees with the simulation result

8. Model-Data-Model
Utilizing the electron distribution functions, they are able to predict the spacecraft trajectory in reconnection frame. (Chen et al, 2008)

9. Model-Data-Model Comparison
E&M fields measured by Cluster
Illustration of multiple x line
Going back to model and combining with the derived trajectory, they are able to derive out the multi-island reconnection scenario.

10. Data-Model-Data Comparison
06:40
07:47
SNAP
SNAP
FSIM
FSIM
FSMI
FSMI
GILL
GILL
GILL
06:30
Ge et al, 2011
08:30
The major breakup of aurora is at ~ 07:47 UT
From 07:47 UT, aurora brightening region starts to expand/move poleward

11. Auroral Breakups 07:47 at GILL & FSMI
Data-Model-Data
07:48
07:47
FSMI
Auroral Breakups 07:47 at GILL & FSMI
OpenGGCM Solar Wind Input

12. Data-Model-Data
The propagation of dipolarization front and the correlation between BBF is studied in detail.
Reproduction of THEMISC observation from OpenGGCM

13. Summary Model and Data both have their power and limitation.
Performing data-model comparisons should be cautious of model and data limitations.
Data-Model Comparisons can be motivated by model or data, but will finally return to a detailed physics question.

14. More Examples
Model-Data-Model: Counter streaming heavy ions in reconnection Wednesday, reconnection section.
Data-Model-Data: Cluster encounter of the reconnection hall plane, Thursday, poster# 36
Empirical Model: The thickness of O+ mediated reconnecting current sheet, Wednesday, the ionospheric source of magnetospheric plasma section.