Corotating Interaction Regions: Heliospheric Structure

in 3 (and 4) Dimensions

Tuesday Afternoon

SHINE 2009

In-situ Observations of CIRs on STEREO and ACE during 2007-2008

G. M. Mason, JHU/APL, Laurel, MD 20723M. I. Desai, SWRI, San Antonio, TX

U. Mall and R. Bucik, MPS, Lindau, GermanyK. Simunac, Univ. New Hampshire

R. A. Leske, Caltech, Pasadena, CA

SHINE Workshop 2009Wolfville, Nova Scotia, Aug 3-7, 2009

plot from R. Bucik, MPS

Spectograms from -A and -B in spring 2007...quite similar

plot from R. Bucik, MPS

Aug. 2008 spectograms (~5 days corotation) ... some features shifted as expected, others not seen on both S/C

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Stereo-B SECCHI 19.5nm image

Aug 7, 2007 00:06:32

(day 220)

10 degree heliographic grid overlay as seen from STEREO-B

Central meridian seen from STEREO-B is in blue; green as seen from Earth; red as seen from STEREO-A

Solar Weather Browser image

Stereo A is at 8.98° latitude; B at 3.78°; so the 5.2° difference is about one-half of a grid spacings. The hole at about E45 is probably the one seen by STEREO-B on day 224-26, and was probably missed by STEREO-A since it’s trace is about 5°‚ north of B, a size shown by the double headed arrow at E5

Summary --• many fast solar wind streams and CIRs observed in 2007-2008, but not all streams produced CIRs

• spectral forms similar to earlier surveys; much lower intensities at ~few MeV/n compared to active period

• CIRs observed sequentially from -B to -A, but not always seen; energetic particle intensity pattern did not corotate rigidly, probably due to magnetic connection effects to the CIR beyond 1 AU

• for 1994-2008 the most intense CIRs were during solar active periods, but cannot pinpoint simple cause for this

Summary --• many fast solar wind streams and CIRs observed in 2007-2008, but not all streams produced CIRs

• spectral forms similar to earlier surveys; much lower intensities at ~few MeV/n compared to active period

• CIRs observed sequentially from -B to -A, but not always seen; energetic particle intensity pattern did not corotate rigidly, probably due to magnetic connection effects to the CIR beyond 1 AU

• for 1994-2008 the most intense CIRs were during solar active periods, but cannot pinpoint simple cause for this

How do we define a CIR?

• 2007-2008 period had much better defined high speed solar wind streams than prior solar minimum in 1996-1997, and many more CIRs

• size distribution of CIRs shows a much sharper cutoff than 10 MeV SEP protons from GOES

• about 25% of CIRs show “dropouts” for a day or so apparently when connection to acceleration region beyond 1 AU changes

• some of the complex features of the CIRs appear to be due to relatively small coronal hole solar sources, wherein the different heliolatitude traces of STEREO-B, -A, and ACE played a significant role

published in STEREO Science Results at Solar Minimum

Mason et al. Solar Phys (2009) 256: 393-408 DOI 10.1007/s11207-009-9367-0

Comparison of CIR-associated electrons and ions on the first and third Ulysses southern

high-latitude excursions

D. Lario, E.C. Roelof

The Johns Hopkins University. Applied Physics Laboratory

(JGR, Vol. 112, A09107, doi:10.1029/2007JA012414, 2007)

Lario and Roelof [2007]

Lario and Roelof [2007]

No slow wind, but well correlated with CIRs observed in the ecliptic plane.

Sayle and Simnett [1998] Lario and Roelof [2007]

Maximum intensities at the CIR events

Third Southern Excursion•In contrast to the long-lived and well-defined ~26-day recurrent energetic particle intensity enhancements observed throughout the first southern pass, observations at the same heliocentric distance and heliographic latitude during the third Ulysses southern pass showed a more complicated structure.

•Transient events were more abundant and intense. Although CIRs are clearly present, their appearance was less regular.

•Intense energetic particle events associated with well-formed CIRs bounded by FS-RS pairs were not observed until Λ>30°S (at a higher latitude than in the first orbit). Particle events in these CIRs were remarkably similar to the recurrent and regular CIR events of the 1st southern pass.

•Ulysses remained immersed in the high-speed polar coronal hole solar wind flow once at Λ>39°S (36°S in the first orbit). Particle events observed during this period were also remarkably similar.

•The global CIR structure, once formed, is quite similar from one solar cycle to the other.

Imaging SIR/CIR Structures with the SECCHI Imagers

Angelos Vourlidas

NRL

Solar wind streams

Characteristic patterns in elongation/time maps

From Sheeley’s Hale Lecture

CIR Shapes in J-maps

So, how can we interpret the HI2 images?

– What are these wave-like structures? density enhancements due to stream interaction

– Why is the CIR brighter in HI2-B? B integrates along Parker spiral– Why are the shapes different? B detects streamer(?)– Where are they in the heliosphere? along Sun-Earth line

A B

A B

–Why are the shapes different? B detects streamer(?)

So, how can we interpret the HI2 images?

–What are these wave-like structures? density enhancements due to stream interaction (or maybe entrained CMEs)

–Why is the CIR brighter in HI2-B? HI-2B integrates along Parker spiral–Why are the shapes different? –Where are they in the heliosphere?

Conclusions

• Current status of CIR imaging w/ STEREO:– We can detect the density enhancements ahead of CIRs (or SIRs):

• Crossing over the s/c• Crossing over Earth (>0.3 AU away)• Crossing over other planets• With Δn ≥ 20 e/cm3!

– We can trace them in 3D space with good accuracy (~10º–20º)– We can measure their dynamics (speed, acceleration)– We can locate their formation time/distance

Using MHD Models to Understand CIR

Structure

Pete Riley, Jon Linker, Zoran Mikic, and Roberto Lionello

Predictive Science, San Diego, California.

SHINE WORKSHOPWolfville, Canada

Tuesday August 4th, 2009

Declining Phase

Solar Maximum

Riley et al. (2003)

CIR Formation in Three Dimensions

Global structure of heliosphere at

2.2 AU for WSM (Aug/Sept 1996)

Global structure of heliosphere at

2.2 AU for CR 2083 (May 2009)

• Basic features of CIR formation, structure, and evolution are understood:

– Global models can reproduce the large-scale in situ profiles– Dynamics of stream interactions is understood

• The current solar minimum is unique in many ways:

– The structure of the heliosphere is more complex, in spite of many parameters being ‘weaker’

– Ultimately, the solar magnetic field controls the structure we observe

Summary

Some Additional Questions/Comments

• Why do some CIRs produce energetic particle events at 1 AU when others do not? Can this question be addressed with models?

• At what radial distance do CIRs form? In situ experiments such as Helios suggest CIRs are well established by 0.3 AU, but SECCHI observations suggest they are just forming at that distance.

• We are still trying to disentangle spatial and temporal evolution of CIRs.