Tracking CME s With LOFAR

Size: px

Start display at page:

Download "Tracking CME s With LOFAR"

Clement Garrett
5 years ago
Views:

1 Tracking CME s With LOFAR Interplanetary Scintillation Studies With a Large, Multi-beaming, Phased Interferometric Array Michael Stevens

2 What s A? WHat are All These Silly Acronyms? LOFAR- the LOw Frequency ARray CME- Coronal Mass Ejection IPS- InterPlanetary Scintillations ORT- Ooty Radio Telescope STELab- Solar-TErrestrial Laboratory EISCAT- European Incoherent SCATtering facility VLA- Very Large Array

Project Motivation Why study Coronal Mass Ejections?

Commercial Solar January storms weather 1997 and can government damage

damage storms anticipating grid, harm solar astronauts) weather

3 Project Motivation Why study Coronal Mass Ejections? Practical Goals (these Ex. Commercial Solar January storms weather 1997 and can government damage event- cause $200 geomagnetic satellites, interest million power in damage storms anticipating grid, harm solar astronauts) weather Theoretical Advancement Heliospheric- CME origins and sunspots Atmospheric- Does solar weather influence our atmosphere? How can LOFAR contribute?

Neutral plasma, speed about 400 km/s, density on order of a few protons/cm 3.

4 Solar Plasma Ejections Background Solar Wind. Periodic spiral structure, generally corotating. Neutral plasma, speed about 400 km/s, density on order of a few protons/cm 3. Coronal mass ejections (CME s). Irregular, linked to sunspots. Up to 2000 km/s, 10 billion tons of material, density jumps by several orders of magnitude.

5 What Is IPS? The measurement of interplanetary scintillations (IPS) provides line-of-sight information about a body of plasma. Lines of sight form a mesh of visibility Phase vs. amplitude scintillations

6 compact source radiating at λ IPS Concept p d ε l

7 Reconstruction Raw measurements are g-level and IPS velocity. We must interpolate f(r,θ,φ) with tomography. g = S S(ε) Line-of-sight integration means answer is not unique 1 g N e 2 Approximations: gaussian density function, empirical g-level power law (Tappin, 1986), point-p approximation (Hewish, 1964), thin-layer phase screens (Readhead, 1971) g(θ, φ) 2 0 f(r,θ, φ) β(r) ω(z) dz 0 β(r) ω(z) dz

Optimizing the Technique Discovery by Hewish in 1964 leads to work at ORT, STELab, and UCSD. Limitations are noise, elongation, observing time, myopic perspective.

8 Optimizing the Technique Discovery by Hewish in 1964 leads to work at ORT, STELab, and UCSD. Limitations are noise, elongation, observing time, myopic perspective. STELab and UCSD collaboration leads to successful tomography algorithm (Jackson, 1998). Single perspective does not offer corroboration, or localized velocities (B-fields). Single frequency prevents optimization for elongation versus collecting area. Low spatial resolution makes correlations weak. Weak signals require long integration times (10-60 min), but scintillations are transient!

9 Recent Campaigns ORT, STELab, EISCAT, VLA, Cambridge 3.6 Hec. In practice, IPS signals require long integration times. Pointing time is also a factor. ST E L ab O R T C am bridge E ISC A T V L A frequency 327 M H z M H z 81.5 M H z 224 M H z >300 M H z sensitivity* 7.35 Jy 3.35 Jy.2 Jy.16 Jy.34 Jy baselin e 207 km 530 m 200 m 232 km 36 km collecting area 1384 m m m m m 2 sam ples/day * 1 second averaging at maximum bandwidth

10 Anticipating LOFAR Performance: Inherent Improvements Sensitivity.9 resolution LOFAR baselines for velocity measurements Software steering 32, 4 MHz bandwidth Multi-beaming Modularity Flux Density (mjy) LOFAR Minimum Detectable Flux Density High Frequency Mode Low Frequency Mode Frequency (MHz)

11 LOFAR Bottom Line Comparison LOFAR vs. Contemporary Instruments STELab O RT LO FAR frequency 327 M H z M H z 240 M H z sensitivity 7.35 Jy 3.35 Jy.0031 Jy m ax baseline 207 km 530 m 400 km collecting area 1,384 m 2 8,500 m 2 100,000 m 2

12 Further Considerations Integrated solar observation with LOFAR Passive thermal and steep-spectrum emissions Solar radar? LOFAR upgradeability, post-processing possibilities, further multi-beaming, added capabilities of the VC Site selection could be a factor Seasonal availability Atmospheric, ionospheric interference

13 In Conclusion Geomagnetic storms and gaps in scientific understanding make solar weather studies important. IPS is a powerful ground-based technique for tracking disturbances once out of range by direct solar observation. Through IPS, LOFAR will have the potential to model the solar wind with unprecedented detail. Observing velocity and B-field structure Anticipating geomagnetic storms

14 Follow-up LOFAR and the STELab/UCSD IPS simulator Even large features are compromised by lowresolution data High-resolution IPS mesh should result in truer reconstructions

15 Acknowledgements and Thanks Dr. Ananthrakrishnan, Dr. Kojima, and Dr. Hewish Dr. Salah The REU program

Ooty Radio Telescope Space Weather

Ooty Radio Telescope Space Weather P.K. Manoharan Radio Astronomy Centre National Centre for Radio Astrophysics Tata Institute of Fundamental Research Ooty 643001, India mano@ncra.tifr.res.in Panel Meeting