Solar Plumes Research Articles

Plumelets: Dynamic Filamentary Structures in Solar Coronal Plumes

Abstract Solar coronal plumes long seemed to possess a simple geometry supporting spatially coherent, stable outflow without significant fine structure. Recent high-resolution observations have challenged this picture by revealing numerous transient, small-scale, collimated outflows (“jetlets”) at the base of plumes. The dynamic filamentary structure of solar plumes above these outflows, and its relationship with the overall plume structure, have remained largely unexplored. We analyzed the statistics of continuously observed fine structure inside a single representative bright plume within a mid-latitude coronal hole during 2016 July 2–3. By applying advanced edge-enhancement and spatiotemporal analysis techniques to extended series of high-resolution images from the Solar Dynamics Observatory's Atmospheric Imaging Assembly, we determined that the plume was composed of numerous time-evolving filamentary substructures, referred to as “plumelets” in this paper, that accounted for most of the plume emission. The number of simultaneously identifiable plumelets was positively correlated with plume brightness, peaked in the fully formed plume, and remained saturated thereafter. The plumelets had transverse widths of 10 Mm and intermittently supported upwardly propagating periodic disturbances with phase speeds of 190–260 km s−1 and longitudinal wavelengths of 55–65 Mm. The characteristic frequency (≈ 3.3 mHz) is commensurate with that of solar p-modes. Oscillations in neighboring plumelets are uncorrelated, indicating that the waves could be driven by p-mode flows at spatial scales smaller than the plumelet separation. Multiple independent sources of outflow within a single coronal plume should impart significant fine structure to the solar wind that may be detectable by Parker Solar Probe and Solar Orbiter.

Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion

Identifying the origin of noble gases in Earth's mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth's history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth's volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

A 17 June 2011 polar jet and its presence in the background solar wind

AbstractHigh‐speed jet responses in the polar solar wind are enigmatic. Here we measure a jet response that emanates from the southern polar coronal hole on 17 June 2011 at the extreme speed of over 1200 km/s. This response was recorded from the Sun‐Earth line in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and Large Angle and Spectrometric Coronagraph/C2 and both Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager and COR2 coronagraphs when the three spacecraft were situated ~90° from one another. These certify the coronal 3‐D location of the response that is associated with an existing solar plume structure and show its high speed to distances of over 14 RS. This jetting is associated with magnetic flux changes in the polar region as measured by the SDO/Helioseismic and Magnetic Imager instrumentation over a period of several hours. The fastest coronal response observed can be tracked to a time near the period of greatest flux changes and to the onset of the brightest flaring in AIA. This high‐speed response can be tracked directly as a small patch of outward moving brightness in coronal images as in Yu et al. (2014) where three slower events were followed from the perspective of Earth. This accumulated jet response has the largest mass and energy we have yet seen in 3‐D reconstructions from Solar Mass Ejection Imager observations, and its outward motion is certified for the first time using interplanetary scintillation observations. This jet response is surrounded by similar high‐speed patches, but these are smoothed out in Ulysses polar measurements, we speculate about how these dynamic activities relate to solar wind acceleration.

A Time-Evolving 3D Method Dedicated to the Reconstruction of Solar Plumes and Results Using Extreme Ultraviolet Data

An important issue in the tomographic reconstruction of the solar poles is the relatively rapid evolution of the polar plumes. We demonstrate that it is possible to take into account this temporal evolution in the reconstruction. The difficulty of this problem comes from the fact that we want a four-dimensional reconstruction (three spatial dimensions plus time) whereas we only have three-dimensional data (two-dimensional images plus time). To overcome this difficulty, we introduce a model that describes polar plumes as stationary objects whose intensity varies homogeneously with time. This assumption can be physically justified if one accepts the stability of the magnetic structure. This model leads to a bilinear inverse problem. We describe how to extend linear inversion methods to these kinds of problems. Studies of simulations show the reliability of our method. Results for SOHO/EIT data show that we can estimate the temporal evolution of polar plumes to improve the reconstruction of the solar poles from only one point of view. We expect further improvements from STEREO/EUVI data when the two probes will be separated by about 60°.

Present and Future Observing Trends in Atmospheric Magnetoseismology

With modern imaging and spectral instruments observing in the visible, EUV, X-ray, and radio wavelengths, the detection of oscillations in the solar outer atmosphere has become a routine event. These oscillations are considered to be the signatures of a wave phenomenon and are generally interpreted in terms of magnetohydrodynamic (MHD) waves. With multiwavelength observations from ground- and space-based instruments, it has been possible to detect waves in a number of different wavelengths simultaneously and, consequently, to study their propagation properties. Observed MHD waves propagating from the lower solar atmosphere into the higher regions of the magnetized corona have the potential to provide excellent insight into the physical processes at work at the coupling point between these different regions of the Sun. High-resolution wave observations combined with forward MHD modeling can give an unprecedented insight into the connectivity of the magnetized solar atmosphere, which further provides us with a realistic chance to reconstruct the structure of the magnetic field in the solar atmosphere. This type of solar exploration has been termed atmospheric magnetoseismology. In this review we will summarize some new trends in the observational study of waves and oscillations, discussing their origin and their propagation through the atmosphere. In particular, we will focus on waves and oscillations in open magnetic structures (e.g., solar plumes) and closed magnetic structures (e.g., loops and prominences), where there have been a number of observational highlights in the past few years. Furthermore, we will address observations of waves in filament fibrils allied with a better characterization of their propagating and damping properties, the detection of prominence oscillations in UV lines, and the renewed interest in large-amplitude, quickly attenuated, prominence oscillations, caused by flare or explosive phenomena.

Solar Wind Outflow in Polar Plumes from 1.05 to 2.4 R ⊙

An earlier publication (Paper I), which measured the outflow velocity in solar plumes out to 1.35 R☉ using the Doppler dimming technique, has here been extended out to 2.4 R☉ by including observations from SOHO UVCS. It is shown that plume outflow velocities, greater than interplumes at lower heights, have lower acceleration and fall below interplume velocities at heights greater than 1.6 R☉. This analysis resolves what has been an apparent disagreement between previously published work. The mass flow rate in plumes is shown to decrease with height, presumably through mass transfer to the interplume regions.

Properties of longitudinal flux tube waves

We discuss the analytic properties of longitudinal tube waves taking into account ambient wind flows. This is an extension of the studies of Papers I and II, which assumed a mean flow speed of zero and also dealt with a simplified horizontal pressure balance. Applications include the study of longitudinal flux tube waves in stars with significant mass loss and the heat- ing and dynamics of plumes in the solar wind. Slow magnetosonic waves, also called longitudinal waves, have been observed in solar plumes and are likely an important source of heating. We show that the inclusion of ambient wind flows considerably alters the limiting shock strength as well as the energy damping length of the waves.

The Contribution of Polar Plumes to the Fast Solar Wind

The Doppler dimming technique is used for the first time to study ultraviolet polar plumes in the height range of 1.05-1.35 R☉, using observations from the spectrometer SUMER on the Solar and Heliospheric Observatory. It is found that, contrary to a number of published suggestions, outflow velocities in the plumes exceed those in the interplume regions. Plume velocities are in excess of 60 km s-1 and are approximately constant throughout this height region. They tend to converge with the velocity of the accelerating interplume material at some height above our region of study. The analysis suggests that plume material makes a substantial contribution to the total line of sight, favoring either a curtain model for plumes or a chance alignment of a number of elementary cylindrical plumes. The intrinsic local density of plume material is some 20%-50% in excess of the interplume regions. Estimation of the total mass outflow indicates that approximately half of the fast solar wind at 1.1 R☉ arises from plumes, with the remainder from interplume material. This result validates the published electron temperature profile of David et al. for the fast wind onset, which had been questioned over the suggestion that the flow velocity might be negligible in solar plumes.

The onset region of the fast solar wind

Over a range of spatial scales, the onset regions of the fast solar wind are influenced or controlled by the structure of the local magnetic fields. This is demonstrated for the large scale structures that determine coronal holes, as well as for the supergranulation network. It is likely that reconnexion effects in small-scale emerging fields play a role in the initial accelerating mechanism. The role of magnetic fields in outflowing solar plumes is at present less clear.

Dynamics of nonlinear resonant slow MHD waves in twisted flux tubes

Abstract. Nonlinear resonant magnetohydrodynamic (MHD) waves are studied in weakly dissipative isotropic plasmas in cylindrical geometry. This geometry is suitable and is needed when one intends to study resonant MHD waves in magnetic flux tubes (e.g. for sunspots, coronal loops, solar plumes, solar wind, the magnetosphere, etc.) The resonant behaviour of slow MHD waves is confined in a narrow dissipative layer. Using the method of simplified matched asymptotic expansions inside and outside of the narrow dissipative layer, we generalise the so-called connection formulae obtained in linear MHD for the Eulerian perturbation of the total pressure and for the normal component of the velocity. These connection formulae for resonant MHD waves across the dissipative layer play a similar role as the well-known Rankine-Hugoniot relations connecting solutions at both sides of MHD shock waves. The key results are the nonlinear connection formulae found in dissipative cylindrical MHD which are an important extension of their counterparts obtained in linear ideal MHD (Sakurai et al., 1991), linear dissipative MHD (Goossens et al., 1995; Erdélyi, 1997) and in nonlinear dissipative MHD derived in slab geometry (Ruderman et al., 1997). These generalised connection formulae enable us to connect solutions obtained at both sides of the dissipative layer without solving the MHD equations in the dissipative layer possibly saving a considerable amount of CPU-time when solving the full nonlinear resonant MHD problem.

Millimeter-radio, SOHO/EIT 171 Å features and the polar faculae in the polar zones of the Sun

In this work we study different manifestations of activity in the polar zones of the Sun in order to gain understanding on the phenomenon of enhanced radio temperature regions (ETR) at high solar latitudes. We have obtained simultaneous radio and optical data during 9 days in 1997. The radio data from the Metsahovi radio telescope, Finland, consisted of 37 GHz and 87 GHz solar maps. White light observations at the Kislovodsk solar mountain station in Russia were used to measure the coordinates of polar faculae groups and diffuse bright structures. We also compared our data with the 171 AEUV SOHO/EIT images for the same time periods. We find the ETRs in general coincide with the relatively dark areas seen in the SOHO/EIT images. Bright structures in the SOHO/EIT maps are, in general, encircled by the polar faculae groups and diffuse bright structures visible in white light. Some of the EUV bright structures appear to be bases of solar plumes. Connections between ETRs and polar faculae are complicated; sometimes polar faculae groups and diffuse bright structures are situated around the ETR maxima or at their borders, sometimes we see the polar faculae groups distributed over the whole ETR area. Some faint ETRs appear to have no associated polar faculae. However, in general there is a correlation between the ETRs, the polar faculae groups, and the bright structures (bases of the plumes and some other features), indicating that they are different manifestations of the same underlying activity. It is possible that magnetic loops in the active areas, traced by the polar faculae, are responsible for the observed radio enhancements.