1. Ionospheric impacts on LoFAR
Ian McCrea
Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Oxfordshire, UK
On behalf of…
Mike Hapgood (RAL), Lilli Cander (RAL), Cathryn Mitchell (Univ. of Bath)

2. Imaging (MIDAS) Imaging software uses mainly GPS data
Produces 3D time-evolving electron-density maps over a wide area
Resolution over North America and Europe is typically 15 minutes and tens to hundreds of km
Recent capability added to image continuously from mid-to-high latitudes across the polar cap ionosphere

3. Space weather & the ionosphere
SW momentum, E-field, energy, mass
Gravity waves, winds, composition changes
EUV, X-rays
SW momentum, E-field, energy, mass

4. Ionospheric effects on phase
Total electron content
Daily, seasonal and solar cycle patterns – easy stuff
Perturbations - gravity waves (TIDs), storm effects
Metal ion layers (sporadic-E)
Evanescent propagation?
Ionospheric turbulence (spread-F)
Small-scale TEC changes, phase scintillation
Underlying physics is plasma turbulence
Low frequency effects (near plasma freq.) ?
Propagation strongly modified, polarisation significant (hybrid mode effects)
Plasmasphere is also important

5. Ground-based GPS
Space-based GPS
Thanks to Dr Cathyrn Mitchell

6. Vertical TEC Electron density 2D Electron density 3D
Thanks to Dr Cathyrn Mitchell

7. Storm day (30th ) October 2003 in terms of iso-contours of electron density
Thanks to Dr Cathyrn Mitchell

8. Thanks to Dr Cathyrn Mitchell

9. Thanks to Dr Cathyrn Mitchell

10. Thanks to Dr Cathyrn Mitchell

11. Thanks to Dr Cathyrn Mitchell

12. Thanks to Dr Cathyrn Mitchell

13. Over the USA the quiet day and storm day are almost identical at 12 UT
Enhancement in TEC/density over South-East USA has started by 13 UT (just after sunrise)
Enhancement in TEC/density evolves into longitudinally limited structure
Thanks to Dr Cathyrn Mitchell

14. 2. Uplifts in the F-region at mid-latitudes

15. 15th July 2000
Europe (15 E) USA (70 W)
Thanks to Dr Cathyrn Mitchell

16. F-region uplift characteristics for three storms  - July 2000, October 2003 and November 2003
Dramatic elevation of the F-region over Europe and the USA
All three storms show an east-west time delay in the peak height elevation: European sector, then east coast of the USA, then west coast of the USA
The F-region elevations move from high latitudes to lower latitudes for the Nov 2003 storm but for the other two storms the elevation is simultaneous across all latitudes
The uplifts in the USA sector are always accompanied by increasing TEC/electron density but those in the European sector are accompanied by decreasing TEC/electron densities

17. Ionospheric effects on phase
Total electron content
Daily, seasonal and solar cycle patterns
Perturbations - gravity waves (TIDs), storm effects
Metal ion layers (sporadic-E)
Evanescent propagation?
Ionospheric turbulence (spread-F)
Small-scale TEC changes, phase scintillation
Underlying physics is plasma turbulence
Low frequency effects (near plasma freq.) ?
Propagation strongly modified, polarisation significant (hybrid mode effects)
Plasmasphere is also important

18. Metal ion layers (Sporadic-E)
Thin layers of metal ions (e.g. Na+) around 100 km
Common in summer
Focused by upper atmosphere winds
Evanescent propagation through layers at higher freqs
Can easily extend > 10 MHz

19. Ionospheric turbulence
Mid-latitude ionosphere can become filamented (along B)
Km-scale structure seen in radar images from Aricebo (top) & Illinois (bottom) (Mathews, 2001)
Filamentation present down to HF/VHF wavelengths
Seen in MHz radars as spreading of echo

20. Ionospheric diagnostics
HF radar monitoring of ionosphere (ionosonde)
Gives vertical resolution
Absolute technique for Ne
Images show conditions
See 18 Nov examples

21. Off-vertical observations
Ray at elevation e cuts ionosphere at angle  to local normal where sin() = (R/(R+h)) sin (90+e).
Simple model: ionosphere reflects frequencies below ~ fp sec  where fp is the local plasma frequency
So minimum elevation at which external signals of frequency f penetrate ionosphere is
emin(f) = 90 - asin(X*sin()), where  = acos(fp/f), X = (R+h)/R and asin returns values between 0 and 90 degrees.

22. Ionospheric blocking
 Chilton, SolarMin
Chilton, Solar Max. 

23. Ionospheric blocking
 Chilton, Spring 2000
Chilton, Summer 2000 

24. Plasmasphere Extension of ionosphere
Plasmasphere imaged by resonant fluorescence - from spacecraft above pole
Extension of ionosphere
tenuous plasma co-rotating with Earth
to ~20000 km altitude
Significant TEC
major impact on signal phase (~50% nighttime ionosphere)
Can change abruptly due to space weather.
Dayside
Aurora
Earth shadow
Image: NASA

25. Blackout example – 5 Dec 2006

26. Tropospheric effects on ionosphere
Important open area, not well-understood
Gravity waves from convective activity
Electrical coupling, e.g. sprites

27. Summary of effects Sporadic-E E/F region:
D region – absorption,
X-ray flares, protons
Sporadic-E
Reflection, evanescent propagation?
E/F region:
phase delay/refraction,
scintillation
magnetic storms/aurora, plasma turbulence

28. What can we contribute? Diagnostic approach Adding value
Can identify ionospheric state: normal (for season), absorbing, storm, turbulent, auroral, metal ion layers
Can this help customise the calibration?
Also any value for operations?
Adding value
Use know-how to add constraints on to current methods, e.g. properties of gravity waves/TIDs?
Provide access to additional data inputs, e.g. GPS/TEC, vertical profiles
Knowledge of ionospheric methods?

30. Programmatic stuff

31. RAL/SSTD interests Space Environment Group (SP Div)
Ionospheric observations and science
Space weather expertise – full SpW chain from Sun, deeply involved in European SpW activities
Radio Communications Research Unit
Propagation expertise
TEC expertise

32. Link to LOFAR calibration
Approach as space weather application?
Understand user needs
Post-event analysis?
Need to understand radio astronomers approach ionospheric issues
Compare terminology, language
Self-calibration? Inverse problem?
Then can see how our expertise and data can contribute
Some thoughts to follow

33. Alan Alyward’s modelling?
Other:
Alan Alyward’s modelling?
Bath?

34. Aurora and space weather
Thermosphere (neutral) temperatures
waves from aurora
Propagate globally
Impacts
Atmospheric density => spacecraft drag
Ionospheric density => comms, GPS, space radar, …
Image: courtesy UCL

35. Alan Alyward’s modelling?
Other:
Alan Alyward’s modelling?
Bath?

36. Introduce the imaging method
Outline
Introduce the imaging method
Describe physical results
1. October differences from a quiet day in terms of TEC
2. Uplifts in F-region plasma height – several storms
3. High latitude to polar cap imaging
What can the imaging do in its own? Where next?

37. Comparison between a quiet day (23rd) and storm day (30th ) October 2003 in terms of TEC

38. QUIET DAY

39. STORM DAY

40. QUIET DAY

41. STORM DAY

42. 3. Imaging into the polar cap

43. Specific problems for imaging the polar-cap
MIDAS – polar cap
Specific problems for imaging the polar-cap
Limited ground-based data
Severe gradients, localized features
Fast moving structures
Incorporate Wiemer model of the convection to compensate
for missing data

44. MIDAS – mid and low latitude
Low resolution global image using spherical grid centred on geographic pole

45. MIDAS – mid and high latitude
Spherical grid rotated equator and centred on geomagnetic pole
Acknowledgement: Wiemer electric field model

47. MIDAS – mid and high latitude
Thanks to Dr Cathyrn Mitchell

48. MIDAS – comparison to EISCAT
Electron density as a function of height and universal time from the EISCAT radar (69oN,19oE), above, and MIDAS below, 30th October 2003
Acknowledgement: EISCAT Scientific Association, in particular Ian McCrea at CCLRC

49. Can we reproduce the imaging results using a physical model?
Summary and questions
Enhancement in TEC/density on 30th October 2003 starts just after sunrise and grows into a longitudinally limited feature – why?
For three storms the uplifts in the F-region start in Europe and then appear in the USA about 1 hour later – why?
Evidence that for similar local times (different storms) the uplift occurs during decreasing TEC in Europe but increasing TEC in USA – significant?
Polar-cap imaging shows the polar cap plasma convecting but does not provide evidence of a continuous TOI from mid-latitudes into the polar cap
Future work
Can we reproduce the imaging results using a physical model?

50. Ionospheric effects on phase
Total electron content
Daily, seasonal and solar cycle patterns – easy stuff
Perturbations - gravity waves (TIDs), storm effects
Metal ion layers (sporadic-E)
Evanescent propagation?
Ionospheric turbulence (spread-F)
Small-scale TEC changes, phase scintillation
Underlying physics is plasma turbulence
Low frequency effects (near plasma freq.) ?
Propagation strongly modified, polarisation significant (hybrid mode effects)
Plasmasphere is also important

56. Cause
Effect
Effect