Alina-Catalina Donea

Standard local helioseismic diagnostics of large sunspots show the signature of anomalously strong compact scatterers of p-modes within about 1 Mm beneath their photospheres. We applied standard “subjacent-vantage phase-correlation helioseismic holography” to the major sunspot umbra and inner penumbra in NOAA AR12192 as it crossed central solar meridian on 2014 October 23. This diagnostic delivers diffraction-limited maps of the phase delay in the echos of p-mode noise in the 2.5–4.5 mHz acoustic spectrum impinging upward from the underlying solar interior into the sunspot photosphere. What we recognize as the nominal sunspot umbra sends its echos back into the solar interior up to about 1.2 minutes ahead of those reflected from the quiet Sun. In addition to this, we find multiple compact regions approximately 5 Mm in horizontal diameter whose echos are expedited by a further 30 s ahead of the nominal umbral echos. These “strong acoustic scatterers” appear in both umbrae and inner penumbrae, but in a sunspot whose umbra is large enough to accommodate several of them, they show a decided affinity for the boundary separating the two. Standard focus–defocus depth diagnostics pin the anomalies to within about 1 Mm of the base of the photosphere. We propose that the strong acoustic scatterers are the helioseismic signature of fragmentation of magnetic flux beneath sunspot photospheres predicted by E. N. Parker 4.5 decades ago as a crucial accommodation for the stability of sunspot magnetic flux subject to warpage by a precipitous ambient vertical pressure gradient.

High-resolution helioseismology observations with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) provide a unique three-dimensional view of the solar interior structure and dynamics, revealing a tremendous complexity of the physical processes inside the Sun. We present an overview of the results of the HMI helioseismology program and discuss their implications for modern theoretical models and simulations of the solar interior.

One key aspect of understanding the solar dynamo mechanism and the evolution of solar magnetism is to properly describe the emergence of solar active regions. In this Letter, we describe the Lagrangian photospheric flows dynamics during a simulated flux emergence that produces an active region formed by pores. We analyze the lower photospheric flow organization prior, during and following the rise of an active region, uncovering the repelling and attracting photospheric structures that act as sources and sinks for magnetic element transport. Our results show that around 10 hr before the simulated emergence, considerable global changes are taking place on mesogranular scales indicated by an increase of the number of regions acting as a source to the multiple and scattered emergences of small-scale magnetic flux. At the location of active region’s appearance, the converging flows become weaker and there is an arising of a diverging region 8 hr before the emergence time. Our study also indicates that the strong concentration of magnetic field affects the flow dynamics beyond the area of the actual simulated pores, leading to complex and strongly diverging flows in the neighboring regions. Our findings suggest that the Lagrangian analysis is a powerful tool to describe the changes in the photospheric flows due to magnetic flux emergence.

We present observations of recurrent active region coronal jets, and derive their thermal and non-thermal properties, by studying the physical properties of the plasma simultaneously at the base footpoint and along the outflow of jets. The sample of analyzed solar jets were observed by SDO-AIA in extreme ultraviolet and by RHESSI in the X-ray domain. The main thermal plasma physical parameters, such as temperature, density, energy flux contributions, etc., are calculated using multiple inversion techniques to obtain the differential emission measure from extreme-ultraviolet filtergrams. The underlying models are assessed, and their limitations and applicability are scrutinized. Complementarily, we perform source reconstruction and spectral analysis of higher energy X-ray observations to further assess the thermal structure and identify non-thermal plasma emission properties. We discuss a peculiar penumbral magnetic reconnection site, which we previously identified as a “Coronal Geyser.” Evidence supporting cool and hot thermal emission, as well as non-thermal emission, is presented for a subset of geyser jets. These active region jets are found to be energetically stronger than their polar counterparts, but we find their potential influence on heliospheric energetics and dynamics to be limited. We scrutinize whether the geyser does fit the non-thermal erupting microflare picture, finding that our observations at peak flaring times can only be explained by a combination of thermal and non-thermal emission models. This analysis of geysers provides new information and observational constraints applicable to theoretical modeling of solar jets.

We present observations of recurrent active region coronal jets and derive their thermal and non-thermal properties, by studying the physical properties of the plasma simultaneously at the base footpoint, and along the outflow of jets. The sample of analyzed solar jets were observed by SDO-AIA in Extreme Ultraviolet and by RHESSI in the X-Ray domain. The main thermal plasma physical parameters: temperature, density, energy flux contributions, etc. are calculated using multiple inversion techniques to obtain the differential emission measure from extreme-ultraviolet filtergrams. The underlying models are assessed, and their limitations and applicability are scrutinized. Complementarily, we perform source reconstruction and spectral analysis of higher energy X-Ray observations to further assess the thermal structure and identify non-thermal plasma emission properties. We discuss a peculiar penumbral magnetic reconnection site, which we previously identified as a ``Coronal Geyser''. Evidence supporting cool and hot thermal emission, and non-thermal emission, is presented for a subset of geyser jets. These active region jets are found to be energetically stronger than their polar counterparts, but we find their potential influence on heliospheric energetics and dynamics to be limited. We scrutinize whether the geyser does fit the non-thermal erupting microflare picture, finding that our observations at peak flaring times can only be explained by a combination of thermal and non-thermal emission models. This analysis of geysers provides new information and observational constraints applicable to theoretical modeling of solar jets.

We report the discovery of ultra-impulsive acoustic emission from a solar flare, emission with a seismic signature that indicates submersion of its source approximately a Mm beneath the photosphere of the active region that hosted the flare. Just over two decades ago V. V. Zharkova and A. G. Kosovichev discovered the first acoustic transient released into the Sun’s interior by a solar flare. These acoustic waves, refracted back upward to the solar surface after their release, make conspicuous Doppler ripples spreading outward from the flaring region that tell us a lot about their sources. The mechanism by which these transients are driven has stubbornly eluded our understanding. Some of the source regions, for example, are devoid of secondary Doppler, magnetic, or thermal disturbances in the outer atmosphere of the source regions that would signify the driving agent of an intense seismic transient in the outer atmosphere. In this study, we have applied helioseismic holography, a diagnostic based upon standard wave optics, to reconstruct a 3D image of the sources of acoustic waves emanating from the M9.3-class flare of 2011 July 30. These images contain a source component that is submerged a full Mm beneath the active-region photosphere. The signature of acoustic sources this deep in the solar interior opens new considerations into the physics that must be involved in transient acoustic emission from flares—and possibly of flare physics at large. We develop analogies to seismicity remotely triggered by tremors from distant earthquakes, and consider prospects of new insight into the architecture of magnetic flux beneath flaring active regions.

Solar active region jets are small-scale collimated plasma eruptions that are triggered from magnetic sites embedded in sunspot penumbral regions. Multiple trigger mechanisms for recurrent jets are under debate. Vector magnetic field data from Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) observations are used to analyze a prolific photospheric configuration, identified in extreme ultraviolet observations as a “coronal geyser,” that triggered a set of at least 10 recurrent solar active region jets. We focus on interpreting the magnetic fields of small-scale flaring sites aiming to understand the processes that govern recurrent jet eruptions. We perform a custom reprocessing of the SDO-HMI products, including disambiguation and uncertainty estimation. We scrutinized the configuration and dynamics of the photospheric magnetic structures. The magnetic configuration is described, via the analysis of the photospheric magnetic vertical fields, to identify the process that is responsible for driving the jet eruptions. We report that the two widely debated magnetic trigger processes, namely magnetic flux cancellation and magnetic flux emergence, appear to be responsible on a case by case basis for generating each eruption in our set. We find that 4 out of 10 jets were due to flux cancellation, while the rest were clearly not and were more likely due to flux emergence.

Solar active region jets are small-scale collimated plasma eruptions that are triggered from magnetic sites embedded in sunspot penumbral regions. Multiple trigger mechanisms for recurrent jets are under debate. Vector magnetic field data from SDO-HMI observations are used to analyze a prolific photospheric configuration, identified in extreme ultraviolet observations as a `Coronal Geyser', that triggered a set of at least 10 recurrent solar active region jets. We focus on interpreting the magnetic fields of small-scale flaring sites aiming to understand the processes that govern recurrent jet eruptions. We perform a custom reprocessing of the SDO-HMI products, including disambiguation and uncertainty estimation. We scrutinized the configuration and dynamics of the photospheric magnetic structures. The magnetic configuration is described via the analysis of the photospheric magnetic vertical fields, to identify the process is responsible for driving the jet eruptions. We report that the two widely debated magnetic trigger processes, namely magnetic flux cancellation and magnetic flux emergence, appear to be responsible on a case by case basis for generating each eruption in our set. We find that 4 of 10 jets were due to flux cancellation while the rest were clearly not, and were more likely due to flux emergence.

Coronal jets are transitory small-scale eruptions that are omnipresent in solar observations. Active regions jets produce significant perturbations on the ambient solar atmosphere and are believed to be generated by microflare reconnection. Multiple sets of recurrent jets are identified in extreme-ultraviolet filter imaging. In this work we analyze the long timescale recurrence of coronal jets originating from a unique footpoint structure observed in the lower corona. We report the detection of penumbral magnetic structures in the lower corona. These structures, which we call “coronal geysers,” persist through multiple reconnection events that trigger recurrent jets in a quasi-periodical trend. Recurrent jet eruptions have been associated with Type-III radio bursts that are manifestations of traveling non-thermal electron beams. We examine the assumed link, as the coronal sources of interplanetary Type-III bursts are still open for debate. We scrutinized the hypothesized association by temporally correlating a statistically significant sample of six Geyser structures that released at least 50 recurrent jets, with correspondent Type-III radio bursts detected in the interplanetary medium. Data analysis of these phenomena provides new information on small-scale reconnection, non-thermal electron beam acceleration, and energy release. We find that the penumbral Geyser-like flaring structures produce recurring jets. They can be long-lived, quasi-stable, and act as coronal sources for Type-III bursts, and, implicitly, upward accelerated electron beams.

Type III solar radio bursts are the Sun’s most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection events are identified definitively in Solar Dynamics Observatory UV-EUV data, with strong upward and downward pairs of jets, current sheets, and cusp-like geometries on top of time-varying magnetic loops, and strong outflows along pairs of open magnetic field lines. Type III bursts imaged by the Murchison Widefield Array and detected by the Learmonth radiospectrograph and STEREO B spacecraft are demonstrated to be in very good temporal and spatial coincidence with specific reconnection events and with bursts of X-rays detected by the RHESSI spacecraft. The reconnection sites are low, near heights of 5–10 Mm. These images and event timings provide the long-desired direct evidence that semi-relativistic electrons energized in magnetic reconnection regions produce type III radio bursts. Not all the observed reconnection events produce X-ray events or coronal or interplanetary type III bursts; thus different special conditions exist for electrons leaving reconnection regions to produce observable radio, EUV, UV, and X-ray bursts.