1. First validation of Level 2 CAT-2 products: FAC/IBI/TEC
Jaeheung Park1, Jan Rauberg1, Patricia Ritter1, Max Noja2, Claudia Stolle1, and Hermann Lühr1
1Helmholtz Centre Potsdam, GFZ, German Research Centre for Geosciences, Telegrafenberg, Potsdam, Germany
2TomTom Telematics, Berlin, Germany
3rd International Swarm Science Meeting and topical Cal/Val team workshop, Copenhagen, Denmark, 10:00-10:30 on 18 June 2014

2. Chapter 1: FAC

3. Introduction to FAC
FAC and radial current density in the high-/low-latitude ionosphere

4. inter-comparison between prototype and operational FAC data

5. FACsingle-sat/operational vs. FACsingle-sat/prototype
Time [msec]
FACsingle-sat/operational -FACsingle-sat/prototype
The difference is smaller than the product uncertainty specified as follows: “70 nA/m2 … for latitudes below 80°, gradually degrading between 80° to 86°, no values beyond 86° ”
The maximum difference (~0.06) is about 0.2% of the maximum FAC (~25) in the figure.
Time [msec]

6. MLAT vs. (FACdual-sat/operational -FACdual-sat/prototype)
The difference is smaller than the product uncertainty specified as follows: “50 nA/m2 … for latitudes below 80°, gradually degrading between 80° to 86°, no values beyond 86°”

7. cross-correlation between FACAlpha/OP and FACCharlie /OP (scientific validation 1)

8. During a sample period from to (5 days) Swarm-A was behind Swarm-C by about 9 seconds.
If we cross-correlate single-sat FAC(Alpha) and FAC(Charlie), we get the highest correlation coefficient for the very time delay of 9-10 seconds (although the correlation coefficient is not so high: R=0.2~0.3).
Cross-correlation between single-sat FAC(Alpha) and dual-sat FAC also shows similar results.
Swarm-C
Swarm-A
~9 seconds

9. Comparison of FAC/OP with previously published single-sat FAC data (scientific validation 2)

10. MLAT vs. | FACsingle-sat |
The maximum FAC amplitude is around 1 μA/m2
the FAC between 65o-80oMLAT is generally stronger than that at lower and higher latitudes.
High-latitude region
strong FAC (~1 μA/m2)
High-latitude region
strong FAC (~1 μA/m2)

11. Comparison with previous studies 1
peak FAC amplitude is around 1 μA/m2
the FAC between 65o-78oMLAT is generally stronger than that at lower and higher latitudes.
Data source: CHAMP magnetic field
FAC calculation method: single-sat method
[He et al., 2012, Figure 3]

12. Comparison with previous studies 2
peak FAC amplitude is around 1 μA/m2
the FAC between 65o-80oMLAT is generally stronger than that at lower and higher latitudes.
Data source: CHAMP magnetic field
FAC calculation method: single-sat method
[Wang et al., 2010, Figure 2]

13. discussion: single-sat FAC vs. dual-sat FAC
FACdual is low-pass filtered considering inter-satellite distance.  lower amplitude + smoother variation
FACdual is suitable for detecting medium-to-large-scale currents [Ritter et al., 2013].

14. Chapter 2: IBI

15. Introduction to IBI
Plasma irregularities, so-called bubbles, perturb geomagnetic field, and may cause radio wave scintillations.
The IBI processor detects such magnetic fluctuations and gives appropriate flags.
B residual
Plasma bubble
Plasma density
Stolle et al. [JGR, 2006]

16. Introduction to IBI (EFI/MAG correlation)
High-pass filtered signals
Anti-correlation between b and ne
An event is considered as bubble when the anti-correlation is strong enough (e.g. R<-0.6)

17. Comparison of IBI/PP with previously published data (scientific validation)

18. Visual inspection of an example
Swarm-A on 31-DEC-2013 (LT~23)
L1b-MAG’
B-field perturbation
L1b-EFI
Plasma bubble
L2-IBI
(prototype)
Flags

19. Bubble distribution (from mid-DEC 2013 to mid-MAY 2014, Swarm-A)
High occurrence rate near Africa and the Pacific Ocean
High occurrence rate near Brazil

20. early commissioning phase of Swarm
Comparison with a previous study
Pacific Ocean
Africa
near Brazil
early commissioning phase of Swarm
Stolle et al. [JGR, 2006]

21. The equinoctial bubble distribution in the Swarm data suffers from poor statistics so far, because:
both March and September data are crucial to construct bubble climatology (for about 131 days) while the latter is missing.
the Swarm satellites were in the post-midnight LT (where bubbles hardly occur) around the March equinox ( LT in March).
Other seasons show reasonable results.

22. Stolle et al. [JGR, 2006]

23. Chapter 3: TEC

24. Introduction to TEC
The TEC processor estimates total electron content in the ionosphere/plasmasphere.
GPS signals are delayed in the ionosphere due to high total electron content. The delays in two different frequencies (L1 and L2) are used to estimate the total electron content.

25. inter-comparison between prototype and operational TEC data

26. The agreement is generally good.
The difference is generally within the nominal uncertainty (2 TECU)

27. Comparison of TEC/PP with the Swarm/LP data and with previously published data (scientific validation)

28. Does the TEC product reproduce some well-known features?
(double-hump) equatorial anomaly
polar patch
High-latitude region
Low-latitude region LT
Noja et al.
[Radio Sci., 2013] ne
latitude

29. TEC vs. plasma density
The two profiles from the two independent payloads (GPS antenna and Langmuir probe onboard Swarm) exhibit similar latitude dependence.

30. TEC vs. plasma density (in shorter scales)

31. Up to now we have seen that the ‘relative’ variation of TEC is similar to that of ne, which is a qualitative validation of the Swarm L2 TEC.
However, is the ‘absolute’ TEC level also on the right order of magnitude?

32. We may conduct an order-of-magnitude estimation.
The topside ionospheric plasma density is often assumed to exhibit exponential height profile.

33. When the elevation angle is very high, STEC approximates to VTEC.

34. The scale height of about 200 km has the order of magnitude consistent with that from previous studies.
Liu et al. [JGR, 2008]

35. Chapter 4: Summary

36. The FAC/IBI/TEC prototype processors work properly with real Swarm L1b data. The results are consistent with previous studies and/or with independent payload data onboard Swarm.
As for FAC and TEC, the operational and prototype processors produce consistent results.

37. First validation of Level 2 CAT-2 products: FAC/IBI/TEC
Jaeheung Park, Jan Rauberg, Patricia Ritter, Max Noja,
Claudia Stolle, and Hermann Lühr
GFZ, German Research Centre for Geosciences, Potsdam, Germany
10:00-10:30 on 18 June 2014
3rd International Swarm Science Meeting and topical Cal/Val team workshop
Copenhagen, Denmark

38. discussion 2: possible application
The main application is certainly the auroral FAC.
Atmospheric wind dynamo produces vertical (radial) current near the equator.
This current density can also be estimated by the dual-sat method of the L2 FAC processor.
Lühr and Maus [GRL, 2006]