E-Print Archive

There are 4559 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
Connecting Chromospheric Condensation Signatures to Reconnection-driven Heating Rates in an Observed Flare  

Jiong Qiu   Submitted: 2022-12-20 12:03

Observations of solar flare reconnection at very high spatial and temporal resolution can be made indirectly at the footpoints of reconnected loops into which flare energy is deposited. The response of the lower atmosphere to this energy input includes a downward-propagating shock called chromospheric condensation, which can be observed in the UV and visible. In order to characterize reconnection using high-resolution observations of this response, one must develop a quantitative relationship between the two. Such a relation was recently developed, and here we test it on observations of chromospheric condensation in a single footpoint from a flare ribbon of the X1.0 flare on 2014 October 25 (SOL2014-10-25T16:56:36). Measurements taken of Si IV 1402.77 Ň emission spectra using the Interface Region Imaging Spectrograph (IRIS) in a single pixel show the redshifted component undergoing characteristic condensation evolution. We apply the technique called the Ultraviolet Footpoint Calorimeter to infer energy deposition into one footpoint. This energy profile, persisting much longer than the observed condensation, is input into a one-dimensional, hydrodynamic simulation to compute the chromospheric response, which contains a very brief condensation episode. From this simulation, we synthesize Si IV spectra and compute the time-evolving Doppler velocity. The synthetic velocity evolution is found to compare reasonably well with the IRIS observation, thus corroborating our reconnection-condensation relationship. The exercise reveals that the chromospheric condensation characterizes a particular portion of the reconnection energy release rather than its entirety, and that the timescale of condensation does not necessarily reflect the timescale of energy input.

Authors: Ashfield, William H., IV; Longcope, Dana W. ; Zhu, Chunming; Qiu, Jiong
Projects: None

Publication Status: published in ApJ
Last Modified: 2022-12-20 14:42
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Correlated Spatio-temporal Evolution of Extreme-Ultraviolet Ribbons and Hard X-Rays in a Solar Flare  

Jiong Qiu   Submitted: 2022-12-20 12:01

We analyze the structure and evolution of ribbons from the M7.3 SOL2014-04-18T13 flare using ultraviolet images from the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), magnetic data from the SDO/Helioseismic and Magnetic Imager, hard X-ray (HXR) images from the Reuven Ramaty High Energy Solar Spectroscopic Imager, and light curves from the Fermi/Gamma-ray Burst Monitor, in order to infer properties of coronal magnetic reconnection. As the event progresses, two flare ribbons spread away from the magnetic polarity inversion line. The width of the newly brightened front along the extension of the ribbon is highly intermittent in both space and time, presumably reflecting nonuniformities in the structure and/or dynamics of the flare current sheet. Furthermore, the ribbon width grows most rapidly in regions exhibiting concentrated nonthermal HXR emission, with sharp increases slightly preceding the HXR bursts. The light curve of the ultraviolet emission matches the HXR light curve at photon energies above 25 keV. In other regions the ribbon-width evolution and light curves do not temporally correlate with the HXR emission. This indicates that the production of nonthermal electrons is highly nonuniform within the flare current sheet. Our results suggest a strong connection between the production of nonthermal electrons and the locally enhanced perpendicular extent of flare ribbon fronts, which in turn reflects the inhomogeneous structure and/or reconnection dynamics of the current sheet. Despite this variability, the ribbon fronts remain nearly continuous, quasi-one-dimensional features. Thus, although the reconnecting coronal current sheets are highly structured, they remain quasi-two-dimensional and the magnetic energy release occurs systematically, rather than stochastically, through the volume of the reconnecting magnetic flux.

Authors: Naus, S. J., Qiu, J., DeVore, C. R., Antiochos, S. K., Dahlin, J. T., Drake, J. F., Swisdak, M.
Projects: None

Publication Status: published in ApJ
Last Modified: 2022-12-20 14:42
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Variability of the Reconnection Guide Field in Solar Flares  

Jiong Qiu   Submitted: 2022-12-20 11:58

Solar flares may be the best-known examples of the explosive conversion of magnetic energy into bulk motion, plasma heating, and particle acceleration via magnetic reconnection. The energy source for all flares is the highly sheared magnetic field of a filament channel above a polarity inversion line (PIL). During the flare, this shear field becomes the so-called reconnection guide field (i.e., the nonreconnecting component), which has been shown to play a major role in determining key properties of the reconnection, including the efficiency of particle acceleration. We present new high-resolution, three-dimensional, magnetohydrodynamics simulations that reveal the detailed evolution of the magnetic shear/guide field throughout an eruptive flare. The magnetic shear evolves in three distinct phases: shear first builds up in a narrow region about the PIL, then expands outward to form a thin vertical current sheet, and finally is transferred by flare reconnection into an arcade of sheared flare loops and an erupting flux rope. We demonstrate how the guide field may be inferred from observations of the sheared flare loops. Our results indicate that initially the guide field is larger by about a factor of 5 than the reconnecting component, but it weakens by more than an order of magnitude over the course of the flare. Instantaneously, the guide field also varies spatially over a similar range along the three-dimensional current sheet. We discuss the implications of the remarkable variability of the guide field for the timing and localization of efficient particle acceleration in flares.

Authors: Dahlin et al.
Projects: None

Publication Status: published in ApJ
Last Modified: 2022-12-20 14:42
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Investigating pre-eruptive magnetic properties at the footprints of erupting magnetic flux ropes  

Jiong Qiu   Submitted: 2022-12-20 11:53

It is well established that solar eruptions are powered by free magnetic energy stored in current-carrying magnetic field in the corona. It has also been generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections (CMEs). What remains controversial is whether MFRs are present well before the eruption. Our aim is to identify progenitors of MFRs, and investigate pre-eruptive magnetic properties associated with these progenitors. Here we analyze 28 MFRs erupting within 45 deg from the disk center from 2010 to 2015. All MFRs'feet are well identified by conjugate coronal dimmings. We then calculate magnetic properties at the feet of the MFRs, prior to their eruptions, using Helioseismic and Magnetic Imager (HMI) vector magnetograms. Our results show that only 8 erupting MFRs are associated with significant non-neutralized electric currents, 4 of which also exhibit pre-eruptive dimmings at the foot-prints. Twist and current distributions are asymmetric at the two feet of these MFRs. The presence of pre-eruption dimmings associated with non-neutralized currents suggests the pre-existing MFRs. Furthermore, evolution of conjugate dimmings and electric currents within the foot-prints can provide clues about the internal structure of MFRs and their formation mechanism.

Authors: Wang et al.
Projects: None

Publication Status: ApJ in press
Last Modified: 2022-12-20 14:43
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Implications of High-density, High-temperature Ridges Observed in Some Two-ribbon Flares  

Jiong Qiu   Submitted: 2022-12-20 11:50

Several two-ribbon solar flares observed on the disk, notably including the Bastille flare of 2000 July 14, show an extended ridge of plasma running along the loop tops of the post-reconnection arcade. In that and two more recent examples, the ridge is visible in emission by Fe xxiv at roughly 17 MK, with a high, steadily increasing emission measure suggesting an expanding column of very dense plasma. We find that ridges are consistent with overhead views of long, vertical plasma sheets, such as seen above certain limb flares. Those vertical features show enhanced temperature and density over their entire lengths, making explanations in terms of termination shocks and evaporation collision seem less plausible. We use observations of several ridge events to argue in favor of compression and heating by slow magnetosonic shocks in the reconnection outflow. In this scenario, the ridge is built up as retracting flux piles hot, compressed plasma atop the post-flare arcade. Thanks to the overhead perspective offered by the ridge observations, we are able to measure the reconnection rate and show it to be consistent with the rate of increase in column emission measure across the ridge. This consistency supports the hypothesis that slow shocks and retraction compress the plasma seen in ridges, vertical plasma sheets, and possibly the high-temperature fans through which post-reconnection downflows are observed. Such a unified picture of these diverse features enhances our understanding of the role played by magnetic reconnection in solar flares.

Authors: Longcope et al.
Projects: None

Publication Status: published in ApJ
Last Modified: 2022-12-20 14:43
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Extracting the Heliographic Coordinates of Coronal Rays using Images from WISPR/Parker Solar Probe  

Jiong Qiu   Submitted: 2022-09-08 11:30

The Wide-field Imager for Solar Probe (WISPR) onboard Parker Solar Probe (PSP), observing in white light, has a fixed angular field of view, extending from 13.5 degree to 108 degree from the Sun and approximately 50 degree in the transverse direction. In January 2021, on its seventh orbit, PSP crossed the heliospheric current sheet (HCS) near perihelion at a distance of 20 solar radii. At this time, WISPR observed a broad band of highly variable solar wind and multiple coronal rays. For six days around perihelion, PSP was moving with an angular velocity exceeding that of the Sun. During this period, WISPR was able to image coronal rays as PSP approached and then passed under or over them. We have developed a technique for using the multiple viewpoints of the coronal rays to determine their location (longitude and latitude) in a heliocentric coordinate system and used the technique to determine the coordinates of three coronal rays. The technique was validated by comparing the results to observations of the coronal rays from Solar and Heliophysics Observatory (SOHO) / Large Angle and Spectrometric COronagraph (LASCO)/C3 and Solar Terrestrial Relations Observatory (STEREO)-A/COR2. Comparison of the rays' locations were also made with the HCS predicted by a 3D MHD model. In the future, results from this technique can be used to validate dynamic models of the corona.

Authors: P. C. Liewer, J. Qiu, F. Ark, P. Penteado, G. Stenborg, A. Vourlidas, J. R. Hall, P. Riley
Projects: PSP-WISPR

Publication Status: Solar Physics, in press
Last Modified: 2022-09-11 17:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Properties and Energetics of Magnetic Reconnection: I. Evolution of Flare Ribbons  

Jiong Qiu   Submitted: 2022-05-13 19:56

In this article, we measure the mean magnetic shear from the morphological evolution of flare ribbons, and examine the evolution of flare thermal and nonthermal X-ray emissions during the progress of flare reconnection. We analyze three eruptive flares and three confined flares ranging from GOES class C8.0 to M7.0. They exhibit well-defined two ribbons along the magnetic polarity inversion line (PIL), and have been observed by the Atmospheric Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager from the onset of the flare throughout the impulsive phase. The analysis confirms the strong-to-weak shear evolution in the core region of the flare, and the flare hard X-ray emission rises as the shear decreases. In eruptive flares in this sample, significant nonthermal hard X-ray emission lags the ultraviolet emission from flare ribbons, and rises rapidly when the shear is modest. In all flares, we observe that the plasma temperature rises in the early phase when the flare ribbons rapidly spread along the PIL and the shear is high. We compare these results with prior studies, and discuss their implications, as well as complications, related to physical mechanisms governing energy partition during flare reconnection.

Authors: J. Qiu & J. Cheng
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: Solar Physics, accepted
Last Modified: 2022-05-16 08:37
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

The Neupert Effect of Flare UltraViolet and Soft X-ray Emissions  

Jiong Qiu   Submitted: 2021-01-27 21:34

We model the Neupert effect that relates flare heating energy with the observed SXR emission. The traditional form of the Neupert effect refers to the correlation between the time-integrated HXR or microwave light curve and the SXR light curve. In this paper, instead, we use as the proxy for heating energy the ultraviolet (UV) emission at the foot-points of flare loops, and modify the model of the Neupert effect by taking into account the discrete nature of flare heating as well as cooling. In the modified empirical model, spatially resolved UV lightcurves from the transition region or upper chromosphere are each convolved with a kernel function characterizing the decay of the flare loop emission. Contributions by all loops are summed to compare with the observed total SXR emission. The model has successfully reproduced the observed SXR emission from its rise to decay. To estimate heating energies in flare loops, we also employ the UV Foot-point Calorimeter (UFC) method that infers heating rates in flare loops from these UV light curves and models evolution of flare loops with a zero-dimensional hydrodynamic code. The experiments show that a multitude of impulsive heating events do not well reproduce the observed flare SXR light curve, but a two-phase heating model leads to a better agreement with observations. Comparison of the two models of the Neupert effect further allows us to calibrate the UFC method, and improve the estimate of heating rates in flare loops continuously formed by magnetic reconnection throughout the flare evolution.

Authors: Jiong Qiu
Projects: SDO-AIA

Publication Status: accepted in ApJ
Last Modified: 2021-01-28 12:22
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Evolution of a Steamer-Blowout CME as Observed by Imagers on Parker Solar Probe and the Solar Terrestrial Relations Observatory  

Jiong Qiu   Submitted: 2020-12-11 09:41

On 26-27 January 2020, the wide-field imager WISPR on Parker Solar Probe (PSP) observed a coronal mass ejection (CME) from a distance of approximately 30 solar radii as it passed through the instrumentís 95 degree field-of-view, providing an unprecedented view of the flux rope morphology of the CMEís internal structure. The same CME was seen by STEREO, beginning on 25 January. Our goal was to understand the origin and determine the trajectory of this CME. We analyzed data from three well-placed spacecraft: Parker Solar Probe (PSP), Solar Terrestrial Relations Observatory-Ahead (STEREO-A), and Solar Dynamics Observatory (SDO). The CME trajectory was determined using the method described in Liewer et al. (2020) and verified using simultaneous images of the CME propagation from STEREO-A. The fortuitous alignment with STEREO-A also provided views of coronal activity leading up to the eruption. Observations from SDO, in conjunction with potential magnetic field models of the corona, were used to analyze the coronal magnetic evolution for the three days leading up to the flux rope ejection from the corona on 25 January. We found that the 25 January CME is likely the end result of a slow magnetic flux rope eruption that began on 23 January and was observed by STEREO-A/Extreme Ultraviolet Imager (EUVI). Analysis of these observations suggest that the flux rope was apparently constrained in the corona for more than a day before its final ejection on 25 January. STEREO-A/COR2 observations of swelling and brightening of the overlying streamer for several hours prior to eruption on January 25 led us to classify this as a streamer-blowout CME. The analysis of the SDO data suggests that restructuring of the coronal magnetic fields caused by an emerging active region led to the final ejection of the flux rope.

Authors: P. C. Liewer, J. Qiu, A. Vourlidas, J. R. Hall, P. Penteado
Projects: PSP-WISPR

Publication Status: accepted in Astronomy and Astrophysics
Last Modified: 2020-12-13 18:37
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Trajectory Determination for Coronal Ejecta Observed by WISPR/Parker Solar Probe  

Jiong Qiu   Submitted: 2020-09-22 20:58

The Wide-field Imager for Solar Probe (WISPR) onboard the Parker Solar Probe (PSP), observing in white light, has a fixed angular field of view, extending from 13.5 to 108 degrees from the Sun and approximately 50 degrees in the transverse directions. Because of the highly elliptical orbit of PSP, the physical extent of the imaged coronal region varies directly as the distance from the Sun, requiring new techniques for analysis of the motions of observed density features. Here, we present a technique for determining the 3D trajectory of CMEs and other coronal ejecta moving radially at a constant velocity by first tracking the motion in a sequence of images and then applying a curve-fitting procedure to determine the trajectory parameters (distance vs. time, velocity, longitude and latitude). To validate the technique, we have determined the trajectory of two CMEs observed by WISPR that were also observed by another white-light imager, either LASCO/C3 or STEREO-A/HI1. The second viewpoint was used to verify the trajectory results from this new technique and help determine its uncertainty.

Authors: P. C. Liewer, J. Qiu, P. Penteado, J. R. Hall, A. Vourlidas, R. A. Howard
Projects: PSP-WISPR

Publication Status: Solar Physics, accepted
Last Modified: 2020-09-23 13:10
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Comparison of Helioseismic Far-side Active Region Detections with STEREO Far-Side EUV Observations of Solar Activity  

Jiong Qiu   Submitted: 2017-09-25 11:30

Seismic maps of the Sun's far hemisphere, computed from Doppler data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) are now being used routinely to detect strong magnetic regions on the far side of the Sun (http://jsoc.stanford.edu/data/farside/). To test the reliability of this technique, the helioseismically inferred active region detections are compared with far-side observation of solar activity from the Solar TErrestrial RElations Observatory (STEREO), using brightness in extreme ultraviolet light (EUV) as a proxy for magnetic fields. Two approaches are used to analyze nine months of STEREO and HMI data. In the first approach, we determine whether or not new large east-limb active regions are detected seismically on the far side before they appear Earth side and study how the detectability of these regions relates to their EUV intensity. We find that, while there is a range of EUV intensities for which far-side regions may or may not be detected seismically, there appears to be an intensity level above which they are almost always detected and an intensity level below which they are never detected. In the second approach, we analyze concurrent extreme ultraviolet and helioseismic far-side observations. We find that 100% (22) of the far-side seismic regions correspond to an extreme ultraviolet plage; 95% of these either became a NOAA-designated magnetic region when reaching the east limb or were one before crossing to the far side. A low but significant correlation is found between the seismic signature strength and the EUV intensity of a farside region.

Authors: P. C. Liewer, J. Qiu, C. Lindsey
Projects: None

Publication Status: accepted in Solar Physics
Last Modified: 2017-09-26 13:44
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Coronal Holes and Open Magnetic Flux over Cycles 23 and 24  

Jiong Qiu   Submitted: 2017-07-08 13:03

As the observational signature of the footprints of solar magnetic field lines open into the heliosphere, coronal holes provide a critical measure of the structure and evolution of these lines. Using a combination of Solar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT), Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), and Solar Terrestrial Relations Observatory/Extreme Ultraviolet Imager (STEREO/EUVI A/B) extreme ultraviolet (EUV) observations spanning 1996 - 2015 (nearly two solar cycles), coronal holes are automatically detected and characterized. Coronal hole area distributions show distinct behavior in latitude, defining the domain of polar and low-latitude coronal holes. The northern and southern polar regions show a clear asymmetry, with a lag between hemispheres in the appearance and disappearance of polar coronal holes.

Authors: Lowder, Chris; Qiu, Jiong; Leamon, Robert
Projects: None

Publication Status: Solar Physics, Volume 292, Issue 1, article id.18, 23 pp.
Last Modified: 2017-07-11 11:23
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Gradual Solar Coronal Dimming and Evolution of Coronal Mass Ejection in the Early Phase  

Jiong Qiu   Submitted: 2017-07-08 13:01

We report observations of a two-stage coronal dimming in an eruptive event of a two-ribbon flare and a fast coronal mass ejection (CME). Weak gradual dimming persists for more than half an hour before the onset of the two-ribbon flare and the fast rise of the CME. It is followed by abrupt rapid dimming. The two-stage dimming occurs in a pair of conjugate dimming regions adjacent to the two flare ribbons, and the flare onset marks the transition between the two stages of dimming. At the onset of the two-ribbon flare, transient brightenings are also observed inside the dimming regions, before rapid dimming occurs at the same places. These observations suggest that the CME structure, most probably anchored at the twin dimming regions, undergoes a slow rise before the flare onset, and its kinematic evolution has significantly changed at the onset of flare reconnection. We explore diagnostics of the CME evolution in the early phase with analysis of the gradual dimming signatures prior to the CME eruption.

Authors: Qiu, J., Cheng, J.X.
Projects: None

Publication Status: The Astrophysical Journal Letters, Volume 838, Issue 1, article id. L6, 6 pp. (2017)
Last Modified: 2017-07-11 11:23
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Elongation of Flare Ribbons  

Jiong Qiu   Submitted: 2017-07-08 12:59

We present an analysis of the apparent elongation motion of flare ribbons along the polarity inversion line (PIL), as well as the shear of flare loops in several two-ribbon flares. Flare ribbons and loops spread along the PIL at a speed ranging from a few to a hundred km s-1. The shear measured from conjugate footpoints is consistent with the measurement from flare loops, and both show the decrease of shear toward a potential field as a flare evolves and ribbons and loops spread along the PIL. Flares exhibiting fast bidirectional elongation appear to have a strong shear, which may indicate a large magnetic guide field relative to the reconnection field in the coronal current sheet. We discuss how the analysis of ribbon motion could help infer properties in the corona where reconnection takes place.

Authors: Qiu, J., Longcope, D. W., Cassak, P. A., Priest, E. R.
Projects: None

Publication Status: The Astrophysical Journal, Volume 838, Issue 1, article id. 17, 17 pp. (2017)
Last Modified: 2017-07-11 11:23
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?  

Jiong Qiu   Submitted: 2016-04-18 13:50

Flare emissions in X-ray and EUV wavelengths have previously been modeled as the plasma response to impulsive heating from magnetic reconnection. Some flares exhibit gradually evolving X-ray and EUV light curves, which are believed to result from superposition of an extended sequence of impulsive heating events occurring in different adjacent loops or even unresolved threads within each loop. In this paper, we apply this approach to a long duration two-ribbon flare SOL2011-09-13T22 observed by the Atmosphere Imaging Assembly (AIA). We find that to reconcile with observed signatures of flare emission in multiple EUV wavelengths, each thread should be heated in two phases, an intense impulsive heating followed by a gradual, low-rate heating tail that is attenuated over 20-30 minutes. Each AIA resolved single loop may be composed of several such threads. The two-phase heating scenario is supported by modeling with both a zero-dimensional and a 1D hydrodynamic code. We discuss viable physical mechanisms for the two-phase heating in a post-reconnection thread.

Authors: Qiu, Jiong, Longcope, Dana, W.
Projects: SDO-AIA

Publication Status: ApJ, 820, 14
Last Modified: 2016-04-18 21:08
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

ULTRAVIOLET AND EXTREME-ULTRAVIOLET EMISSIONS AT THE FLARE FOOTPOINTS OBSERVED BY ATMOSPHERE IMAGING ASSEMBLY  

Jiong Qiu   Submitted: 2013-08-10 09:43

A solar flare is composed of impulsive energy release events by magnetic reconnection, which forms and heats flare loops. Recent studies have revealed a two-phase evolution pattern of UV 1600 Å emission at the feet of these loops: a rapid pulse lasting for a few seconds to a few minutes, followed by a gradual decay on timescales of a few tens of minutes. Multiple band EUV observations by the Atmosphere Imaging Assembly further reveal very similar signatures. These two phases represent different but related signatures of an impulsive energy release in the corona. The rapid pulse is an immediate response of the lower atmosphere to an intense thermal conduction flux resulting from the sudden heating of the corona to high temperatures (we rule out energetic particles due to a lack of significant hard X-ray emission). The gradual phase is associated with the cooling of hot plasma that has been evaporated into the corona. The observed footpoint emission is again powered by thermal conduction (and enthalpy), but now during a period when approximate steady-state conditions are established in the loop. UV and EUV light curves of individual pixels may therefore be separated into contributions from two distinct physical mechanisms to shed light on the nature of energy transport in a flare. We demonstrate this technique using coordinated, spatially resolved observations of UV and EUV emissions from the footpoints of a C3.2 thermal flare.

Authors: Jiong Qiu, Zoe Sturrock, Dana W. Longcope, James A. Klimchuk, and Wen-Juan Liu
Projects: None

Publication Status: ApJ, 774, 14
Last Modified: 2013-08-11 12:17
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Heating of Flare Loops With Observationally Constrained Heating Functions  

Jiong Qiu   Submitted: 2011-12-30 11:57

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Qiu J., Liu W-J, Longcope D. W.
Projects:

Publication Status: ApJ, in press
Last Modified: 2012-01-04 12:16
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

RECONNECTION AND ENERGETICS IN TWO-RIBBON FLARES: A REVISIT OF THE BASTILLE-DAY FLARE  

Jiong Qiu   Submitted: 2010-12-01 12:47

We conduct a semi-quantitative analysis of two-ribbon flares to investigate the observational relationship between magnetic reconnection and energetics by revisiting the Bastille-day flare, particularly the UV and hard X-ray (HXR) observations. The analysis establishes that prominent UV emission is primarily produced by precipitating electrons that also produce HXRs. In addition, reconnection and subsequent energy release along adjacent field lines along the polarity inversion line (PIL) combined with elongated decay of UV emission may account for the observed extended UV ribbons whereas HXR sources with rapid decay appear mostly as compact kernels. Observations also show that HXR sources and UV brightenings exhibit an organized parallel motion along the magnetic PIL during the rise of the flare, and then the perpendicular expansion of UV ribbons dominate during the peak. With a 2.5 dimensional approximation with the assumed translational dimension along the PIL, we derive geometric properties of UV ribbons and infer the pattern of reconnection as with a varying magnetic guide field during reconnection. It is shown that HXR and UV emissions evolve in a similar way to reconnection rates determined by the perpendicular ''motion.'' The analysis suggests that a relatively strong guide field may be present during the rise of the flare, whereas particle acceleration and non-thermal energy release are probably more efficient with an enhanced reconnection rate with a relatively weak guide field. We discuss the role of the guide field in reconnection and particle energization, as well as novel observational experiments that may be conducted to shed new light on these issues.

Authors: Jiong Qiu, WenJuan Liu, Nicholas Hill and Maria Kazachenko
Projects: None

Publication Status: ApJ, 725, 319
Last Modified: 2010-12-01 12:55
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Evaluating Mean Magnetic Field in Flaring Loops  

Jiong Qiu   Submitted: 2009-01-07 11:10

We analyze multiple-wavelength observations of a two-ribbon flare exhibiting apparent expansion motion of the flare ribbons in the lower atmosphere and rising motion of X-ray emission at the top of newly formed flare loops. We evaluate magnetic reconnection rate in terms of V m rB m r by measuring the ribbon expansion velocity (V m r) and the chromospheric magnetic field (B m r) swept by the ribbons. We also measure the velocity (V m t) of the apparent rising motion of the loop top X-ray source, and estimate the mean magnetic field (B m t) at the top of newly formed flare loops using the relation langle V m tB m t angle approx langle V m rB m r angle, namely, conservation of reconnection flux along flare loops. For this flare, B m t is found to be 120 and 60~G, respectively, during two emission peaks five minutes apart in the impulsive phase. An estimate of the magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding B = 250 and 120~G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately weighted value of magnetic field from the loop top to the loop leg. Therefore, the two methods to evaluate coronal magnetic field in flaring loops produce fully consistent results in this event.

Authors: Qiu, J., Gary, D. E., Fleishman, G. D.
Projects:

Publication Status: Solar Physics, 255, 107
Last Modified: 2009-02-24 19:12
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Observational Analysis of Magnetic Reconnection Sequence  

Jiong Qiu   Submitted: 2008-10-27 11:25

We conduct comprehensive analysis of an X2.0 flare to derive quantities indicative of magnetic reconnection in solar corona by following temporally and spatially resolved flare ribbon evolution in the lower atmosphere. The analysis reveals a macroscopically distinctive two-stage reconnection (Moore et al. 2001) marked by a clear division in morphological evolution, reconnection rate, and energy release rate. During the first stage, the flare brightening starts at and primarily spreads along the polarity inverion line (PIL) with the maximum apparent speed comparable to the local Alfvén speed. The second stage is dominated by ribbon expansion perpendicular to the PIL at a fraction of the local Alfvén speed. We further develop a data analysis approach, namely ''reconnection sequence analysis'', to determine the connectivity and reconnection flux during the flare between a dozen magnetic sources defined from partitioning the photospheric magnetogram. It is found that magnetic reconnection proceeds sequentially between magnetic cells, and the observationally measured reconnection flux in major cells compares favorably with computations by a topological model of magnetic reconnection. The 3D evolution of magnetic reconnection is discussed with respect to its implication on helicity transfer and energy release through reconnection.

Authors: Jiong Qiu
Projects: None

Publication Status: ApJ, 692, 1110
Last Modified: 2009-02-24 18:55
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


[Older Entries]
Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Connecting Chromospheric Condensation Signatures to Reconnection-driven Heating Rates in an Observed Flare
Correlated Spatio-temporal Evolution of Extreme-Ultraviolet Ribbons and Hard X-Rays in a Solar Flare
Variability of the Reconnection Guide Field in Solar Flares
Investigating pre-eruptive magnetic properties at the footprints of erupting magnetic flux ropes
Implications of High-density, High-temperature Ridges Observed in Some Two-ribbon Flares
Extracting the Heliographic Coordinates of Coronal Rays using Images from WISPR/Parker Solar Probe
Properties and Energetics of Magnetic Reconnection: I. Evolution of Flare Ribbons
The Neupert Effect of Flare UltraViolet and Soft X-ray Emissions
Evolution of a Steamer-Blowout CME as Observed by Imagers on Parker Solar Probe and the Solar Terrestrial Relations Observatory
Trajectory Determination for Coronal Ejecta Observed by WISPR/Parker Solar Probe
Comparison of Helioseismic Far-side Active Region Detections with STEREO Far-Side EUV Observations of Solar Activity
Coronal Holes and Open Magnetic Flux over Cycles 23 and 24
Gradual Solar Coronal Dimming and Evolution of Coronal Mass Ejection in the Early Phase
Elongation of Flare Ribbons
Long Duration Flare Emission: Impulsive Heating or Gradual Heating?
ULTRAVIOLET AND EXTREME-ULTRAVIOLET EMISSIONS AT THE FLARE FOOTPOINTS OBSERVED BY ATMOSPHERE IMAGING ASSEMBLY
Heating of Flare Loops With Observationally Constrained Heating Functions
RECONNECTION AND ENERGETICS IN TWO-RIBBON FLARES: A REVISIT OF THE BASTILLE-DAY FLARE
Evaluating Mean Magnetic Field in Flaring Loops
Observational Analysis of Magnetic Reconnection Sequence
On Magnetic Flux Budget in Low-corona Magnetic Reconnection and Interplanetary Coronal Mass Ejections
Hrd X-ray and Microwave Observations of Microflares
Impulsive and Gradual Nonthermal Emissions in an X-Class Flare
Flare-related Magnetic Anomaly with a Sign Reversal
Magnetic Reconnection and Mass Acceleration in Flare-Coronal Mass Ejection Events

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2000-2020 Solar Physics Group - Montana State University