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

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

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

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

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

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

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

Thanks to Dr Cathyrn Mitchell

Thanks to Dr Cathyrn Mitchell

Thanks to Dr Cathyrn Mitchell

Thanks to Dr Cathyrn Mitchell

Thanks to Dr Cathyrn Mitchell

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

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

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

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

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

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

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

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

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.

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

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

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

Blackout example – 5 Dec 2006

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

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

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?

Programmatic stuff

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

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

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

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

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

Introduce the imaging method Outline Introduce the imaging method Describe physical results 1. October 2003 - 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?

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

QUIET DAY

STORM DAY

QUIET DAY

STORM DAY

3. Imaging into the polar cap

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

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

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

MIDAS – mid and high latitude Thanks to Dr Cathyrn Mitchell

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

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?

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

Cause Effect Effect