Pulsed Flows Along a Cusp Structure Observed with SDO/AIA

 B. J. Thompson1, P. Démoulin2, C. H. Mandrini3, M. L. Mays1, L. Ofman4, S. L. Savage1, L. Van Driel-Gesztelyi5, N. M. Viall1

1NASA GSFC, 2Observatoire de Paris, Meudon, France, 3Facultad de Ciencias Exactas y Naturales, FCEN-UBA, Argentina, 4NASA GSFC/Catholic University, 5Konkoly Observatory of the Hungarian Academy of Sciences, Hungary

We present observations of a cusp-shaped structure that formed after a flare and coronal mass ejection on 14 February 2011. Throughout the evolution of the cusp structure, blob features up to several Mm in size were observed flowing along the legs and stalk/spine of the cusp.

The flows were observable in multiple AIA EUV wavelengths, but they were most distinct in the 171 and 304 Å bandpasses. The tracked flows had projected speeds ranging from 50 to 200 km/sec, but the cusp structure was oriented out of the plane of the image, so the actual speeds were closer to 75 to 250 km/sec. 

We were able to track the flows of dozens of blobs from their origin along one of the legs of the cusp.  Flows at that location were divergent from an apparent reconnection "X-point." 

 

 

The feature of interest formed at the site of a major (M2.2) flare and a fast (1250 km/sec) CME. The cusp-shape was visible in all of the AIA EUV wavelengths, but overall the loop structure was most easily seen in the hotter lines, and the blobs/flows were easiest to see in the cooler lines.

On February 14, 2011 an M2.2 flare occurred, beginning at 17:20 UT and peaking at 17:26 Signs of the accompanying CME, including "raining" cool material, were observable over much of the visible disk of the Sun. A "two-tiered" cusp formed, with the stalk of the primary cusp extending from the point marked "A." The secondary cusp is marked at point "B."

A

B

14 February 2011 AIA 335 Å

AB

A C

B

D

Flow plots

To track the many flows along the complex structure, five points were identified to "characterize" the evolution:

A) The junction point of the primary cusp

B) The junction point of the secondary cusp

C) An elbow bend along the right branch of the cusp leg

D) A point far along the cusp stalk/spine (difficult to see sometimes)

The coordinates for points A – D were tracked and interpolated in time, so that the flows along the lines AB, AC and AD could be compared.

335 Å 07:41 UT

AC

B

D

171 Å 18:00 UT

Flows along the cusp spine (defined by the line connecting points A and D) were observed in multiple wavelengths, but 171 and 304 Å were clearest. The y-axis of the plot below shows the the maximum emission along the line AD obtained by sampling five pixels perpendicular to the line.  The x-axis is time.

In general, the slope decreased over time, indicating that either the flow speeds were decreasing, or that the orientation of the cusp spine was becoming increasingly radial.

Flow plots

D

A

D

A

B

C

A

B

Flow plotsFrom 17:45 UT to around 18:20 UT, blobs moving along the line defined by points A and B were observed flowing in both directions. A clear "herringbone" structure, with dozens of ribs,  is visible for much of the time.

The approximate point of divergent flow is marked by "X" in the figure at left, but its location was not constant and trended towards the point A (the primary cusp vertex).  After 18:35 UT there is some evidence of the herringbone shape along the line AC as well.

The figure at left reconstructs the prevailing sense of flow from 17:40 – 18:30 UT. There was an apparent temporal connection between the pulses flowing towards point A and the two directions of flow away from A, indicating that they originated at point "X".

 

"X"

A

B

C

Arrows denote 100 km/sec

Over time, the topology evolved from a "two-tiered" cusp to a simpler structure. 

The cusp feature was located slightly southwest of solar disk center, but the feature pointed to the northeast.  Therefore, the feature was inclined far from the radial direction.

 Similar-looking cusp features were observed after other flares. An attempt was made to determine the angle of the cusp feature using tomography, assuming that the cusp features had similar orientations. However, this was not successful.

 

A similar-looking cusp formed after the C7.1 flare at 3:24 UT on 2011 February 14.  

A radial feature was observed in STEREO EUVI-A images around the time of the cusp flows discussed in this paper, and it is possible it was the same feature as seen in the AIA images.  If that is so, than the radial feature was inclined approximately 40 degrees from the plane of the sky.

What is the angle of the cusp stalkrelative to the plane of the sky??

STEREO EUVI-A  195 Å17:55 UT

Magnetic field structure of flaring/erupting region

MDI_mag_2011.02.14_09-39.

MDI_mag_2011.02.14_17-35

Emergence

The active region (AR) was the site of significant flut emergence, resulting in two dozen flares and multiple CMEs over the course of a couple of days.  The two-lobe cusp and spine configuration with the appearance of a pseudo-streamer (drawn in yellow) formed on the NE side of the AR centered over the positive polarity of an emerging bipole (indicated in red).    

14 February 2011 09:39 UT

14 February 2011 17:35 UT

Location of primary cusp and

spine

The field lines from the +ve polarity connect the to the opposite (-ve) polarity of the emerging bipole. However, connections to other pre-existing –ve polarities within the AR, as well as towards the quiet-sun, also develop.  This forms a partial “anemone”. 

Above the center of the anemone, a spine field line extends upward. This magnetic configuration is present for long time, but it only becomes visible after the coronal mass ejections, which appear to come primarily from the East side of the active region near the emeging flux and anemone structure. 

The expanding CME compresses the magnetic configuration, resulting in heating and an increase of densities in the loops it contains, consequently the structure brightens. After the CME is gone, the brightness is decreasing as the cusp-spine structure relaxes.  The brightening of the cusp-spine structure (which is a 3D enveloping structure of the anemone) is dominantly due to compression-heating by the CME, which erupted 10 minutes earlier.  

 Flows seen along the cusp structure can be due to compression (squeezing material out) as well as cooling downflows and magnetic reconnection. The flows are probably driven by a combination of mechanisms. 

Magnetic field structure of cusp structure

The CME is gone away

Well before (~ 17:30), a small ejection, say CME, was ejected from this region (emerging region), and it moves in region 1

It compress the surrounding fields,in particular region 2. The boundarybetween the two regions (pseudo streamer) was compressed and shows of. Probably reconnection was also involved.

At the time of the image the CME is far away. The magnetic pressure in region 1 has decreased (magnetic shear/ twist was transported away),So now it is region 2 which is in overpressure compared to region 1.

pseudo-streamer

Region 1

Region 2

Vector extrapolations (Xudong Sun)

Region 2 is in overpressure

compression

Current sheet formation

Motion due to compressionwith a plausible contribution of reconnection (still your movie is showing a current sheet growing so it is more building up than reconnecting).

These flows are likely more due to reconnection than compression

Current sheet

Simplified magnetic configuration

-

-

+

The speeds of the blobs flowing from the "X" point ranged from 75 – 120 km/sec, while the flows along the stalk were  typically closer to 150 km/sec.  If the direction of motion was 40 degrees out of the plane of the sky, which gives 80 – 230 km/sec.

Speeds of blobs ranged from 50 – 150 km/sec, typically closer to 150 km/sec.  If the direction of motion was 40 degrees out of the plane of the sky, that gives 80 – 230 km/sec.

Seriously, I need help with the orientation of the structure!!

Typical size of blobs in the plane of the sky is 5-10 Mm, 7-15 Mm when assuming the feature is moving 40 degrees out of the plane.  Clusters of blobs were spaced 30 – 60 seconds apart.  

2011/02/13  17:28:00 17:38:00 17:30:00  M6.6       CME   PA = 86   MaxV  = 595 2011/02/13  20:42:00 20:47:00 20:45:00  B4.8  2011/02/13  21:17:00 21:22:00 21:20:00  C1.1 2011/02/13  21:26:00 21:31:00 21:29:00  B5.1 2011/02/14  01:31:00 01:48:00 01:37:00  B9.3 2011/02/14  02:35:00 02:46:00 02:42:00  C1.6 2011/02/14  03:24:00 05:08:00 04:48:00  C7.1 2011/02/14  04:29:00 05:09:00 04:49:00  C8.3 2011/02/14  06:51:00 07:03:00 06:58:00  C6.6 2011/02/14  08:39:00 09:04:00 08:49:00  C1.8 2011/02/14  11:51:00 12:26:00 12:00:00  C1.7 2011/02/14  12:41:00 12:58:00 12:45:00  C9.4 2011/02/14  13:47:00 14:42:00 14:27:00  C7.0 2011/02/14  16:48:00 16:57:00 16:53:00  B7.9 2011/02/14  17:20:00 17:32:00 17:26:00  M2.2 2011/02/14  19:23:00 19:36:00 19:30:00  C6.6 2011/02/14  23:14:00 23:26:00 23:19:00  C1.2 2011/02/14  23:40:00 23:57:00 23:46:00  C2.7 2011/02/15  00:31:00 00:48:00 00:38:00  C2.7 2011/02/15  01:44:00 01:56:00 01:45:00  X2.2 2011/02/15  04:27:00 04:37:00 04:31:00  C4.8 2011/02/15  10:02:00 10:16:00 10:07:00  C1.0 2011/02/15  14:32:00 14:51:00 14:44:00  C4.8 2011/02/15  19:30:00 20:53:00 20:33:00  C6.7