Heliospheric studies with LOFAR and EISCAT-3D Andy Breen, Mario Bisi & Richard Fallows

Solar System Physics GroupSolar System Physics Group

Heliospheric studies with LOFAR and EISCAT-3D

Andy Breen, Mario Bisi & Richard Fallows

Aberystwyth University


Solar wind• Continuous supersonic expansion of the solar atmosphere

• Fills interplanetary space• Driver for all solar-terrestrial disturbances

McComus et al., 2008 ESA/NASA SOHO|LASCO


Solar wind is primarily bimodal

• Fast (~600-800 km s-1), low-density streams above large regions of open field on Sun

• Relatively uniform

• Slow (~250-400 km s-1), higher-density streams above bright coronal streamers

• Highly structured• Many transient structures

• Large transient structures released by solar eruptions or destabilisation of coronal loops

• “Coronal mass ejections”

ESA/NASA SOHO|LASCO

NASA STEREO|SECCHI (RAL)


Large solar eruption

• Release of stored magnetic energy

• Burst of radiation • Ejection of

matter/magnetic field (Coronal Mass Ejection – “CME”)

Potentially highly geoeffective…

… depending on whether the mass ejection passes over Earth and what the orientation of its magnetic field is.

ESA/NASA SOHO EIT & LASCO


Significant evolution in solar wind structure between Sun and 1 AU

• Interaction between streams with different speeds• Forms regions of compression and rarefaction

• “Stream interaction regions” or “Co-rotating interaction regions”• Shocks form on stream boundaries by 1 AU – can be geoeffective

• Interaction between solar wind transients and background wind• Transients (including CMEs) slowed or accelerated by interaction

with solar wind• Changes path of transient

• Smaller transients entrained by stream interaction regions• Larger ones (esp. CMEs) disrupt stream interaction regions

• Structure of large transients changes through interaction with background wind

• Over-expansion into faster wind• Magnetic field orientation can change

Andy Breen

Higher density - about 2.5-4x fast wind density

Andy Breen

Also get interaction between CMEs - changes trajectory and structure


Smaller transients conspicuous in interplanetary observations

• Appear to be associated with short-period magnetic field rotations (Dorrian et al., 2009)

• May be capable of perturbing comet tails(?)

Andy Breen

With referees, Solar Physics, May 2010 - but they seem happy with the results

Andy Breen

Interpretation advanced by Dorrian et al. - other workers favour instabilities on stream boundaries as driver of perturbations

Andy Breen

comet (P-encke, enters from LH) has tail torn off by CME, but tail activitiy contrinues after regrowth - associated with solar wind transientsIPS observatins by Dorrian et al 2009 suggest B field rotations in transients may play a role


Science questions

Evolution of large-scale solar wind structure• Interaction between CMEs and background wind

• How rapidly are events accelerated/decelerated?• Interaction between CMEs and stream interaction regionsAll influence CME trajectory – will it hit the Earth?

• Rate of over-expansion of CMEs into fast wind• Distortion of CME structure by interaction with background wind, stream interaction regions, other CMEs, smaller transientsAll influence CME structure and magnetic field orientation – will it be goeeffective if it hits the Earth?

• Smaller transients – are they ubiquitous in the slow wind?• Origin/evolution?• Interaction with Earth’s magnetic field?


Requirements

• Comparison of data and modelling needed to get at the underlying physics• Better data covering fine 3D structure of inner heliosphere needed to constrain models

Potential data sources

In-situ measurements (e.g. Messenger, Venus Express, ACE..Measure primary physical parameters (e.g. velocity, density, magnetic field)Very limited spatial coverage

Optical remote sensing (e.g.STEREO imagers, Solar Mass Ejection Imager)

Radio remote sensing (radio bursts, radio scintillation)

Andy Breen

Also in-situ instruemtns on STEREO, SOHO, many other nearer-Earth spacecraft)

Andy Breen

But usually excellent time resolution

Andy Breen

which is not covered in this talk!


Remote sensing of the solar wind

White-light imaging• Visible-wavelength light from Sun scattered from electrons in solar wind

• Thomson scatter• Intensity of scattered light from a volume proportional to Ne • Scattered intensity varies with viewing geometry

• Distant scattering events appear fainter than nearer ones

Radio scintillation observations (IPS)• Radio waves from distant astronomical sources scattered by density irregularities (few 10s to few 100s km scale) in solar wind

• Phase variations in scattered waves converted to amplitude variation by interference

• Variation in intensity (scintillation) roughly proportional to Ne2

• Scattering events nearer observer less clearly observed than further ones

Andy Breen

as interference will have converted less of the phase variation to amplitude variation


White-light imaging and radio observationsor, why do we need radio observations now we've got STEREO?

Temporal resolution• STEREO HI cameras return images every 40 minutes (inner field, HI-

1) or 2 hours (outer field, HI-2). • Radio scintillation (IPS) measurements can give density-proxy and

bulk velocity estimates on < 10 minute cadences• IPS can reveal transient events better

Different sensitivity to electron density• White light imagers – linear sensitivity to Ne

• IPS – ~ Ne2 sensitivity

• IPS better able to resolve faint structures

Multi-site IPS measurements can detect other solar wind properties e.g. magnetic field rotation in CMEs/transients....

White-light imagery extremely good at giving context for eventsComplimentary techniques!


Some current IPS facilities – what they can doSome current IPS facilities – what they can doOotacamund: single antenna, 560m x 30m, observes ~ >1000 sources/day at distances of 20-250 RSun

• Can produce near-real time images of Ne proxy, bulk flow speed• Used as input to 3D tomographic reconstruction, yields 3D Ne proxy and velocity distributions with ~10° angular resolution

Ootacamund radio telescope (P.K. Manoharan)

Nagoya (STELab): 106m x 41m antenna, 100m x 20 m antenna, 74m x 27 m antenna, observes ~ 50 sources/day, inc. ~20-40 2-site observations at distances of 30-200 RSun

• Can produce daily maps of Ne proxy, velocity• Good monthly maps of Ne proxy, velocity• Used as input to 3D tomography, ~20° angular resolution

Fuji radio telescope (M. Tokumaru)

EISCAT: 3 32m dishes, makes ~5 2-site observations /day at distances of ~15-100 RSun • Accurate measurements of velocity• Can detect other solar wind parameters e.g. field rotation• Even small number of long-baseline measurements greatly

improve accuracy of tomographic reconstructions


Some limiting factors with IPS

• Solar wind irregularities are “better” at producing scintillation when the radio waves are low frequency

• Can get useful solar wind data from weaker radio sources at lower frequencies

• Can get useful solar wind data further from Sun at lower frequencies (with same sources)

• Many astronomical radio sources stronger at lower frequencies• Moving to lower frequencies can improve spatial coverage &

resolution of measurements..• .. particularly at distances from Sun where white-light

imaging more difficult

• Lower frequency observations harder to interpret closer to Sun• White-light imaging can help with these regions

• As can IPS at higher frequencies

LOFAR Hi-Band (~100-220 MHz) will give good inner heliospheric converage – as will EISCAT-3D


3D velocity reconstruction from EISCAT IPS data (B.V. Jackson and M.M. Bisi)

To study:• Internal structure of CMEs• CME/solar wind interaction• CME/SIR interaction• Evolution of mesoscale structure• Interaction of mesoscale structure with CMEs and SIRs• Interaction of solar wind structures with comets and planetary environments• Cometary and planetary tails

Need at least as good spatial resolution (sources/day..) as Ootacamund, many more long-baseline 2-site observations/day than STELab or EISCAT


LOFARLOFARLOFAR should provide all these things!

Ample collecting areaPlenty of combinations of 2-site observations

Should be able to match Ootacamund’s number of source-observations/day, exceed 100 2-site observations/day (currently being verified!)

~5°angular resolution in tomographic reconstructions looks achievable with LOFAR data

MWA will match (and probably exceed) number of source-observations/day, but won’t offer 2-site measurements

Won’t be able to study physical parameters (turbulence, flow direction) that LOFAR will be able to detect


What’s neededWhat’s neededIPS requires:• Rapid sampling rate (>50 Hz, ideally >100 Hz)• Wide receiver pass-band (> 10 MHz)Only total received power measurements are required• Want to observe as many sources/day as possible, on as many days as possible• Want to make many 2-site measurements

Experiment should run on “remote” (non-core) sites, ideally in background mode

Need to safeguard non-core observing time for solar and heliospheric experiments

IPS experiment for LOFAR needs buildingInitial input – data stream produced by generic solar/heliosphere mode running at each remote station?

Need format for this data stream, sample data – and to start taking real data as soon as possible


What about EISCAT-3D?What about EISCAT-3D?To operate on frequency close to LOFAR Hi-Band maximum (224 MHz)

• Gives good potential for observing scintillation• Siting in northern Scandinavia provides excellent IPS baselines for

high-resolution observations in conjunction with LOFAR sites

Potential problems with ionospheric scintillation, particularly when looking at sources to the south (close to field line)

Combination of LOFAR and EISCAT-3D could provide the best heliospheric observatory for the next 10+ years (certainly until SKA)

Opportunities for significant science gain

If interested, get in touch:[email protected]

mailto:[email protected]

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Heliospheric studies with LOFAR and EISCAT-3D Andy Breen, Mario Bisi & Richard Fallows