| 1. |
- da Silva Santos, João Manuel, 1992-
(författare)
-
A multiwavelength approach to solar chromospheric heating : New insights from the millimeter continuum
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chromosphere is an intermediate layer of the Sun's atmosphere where radiative equilibrium breaks down. The standard chromospheric diagnostics such as the Mg II h and k and Ca II H and K spectral lines are formed under nonlocal thermodynamic equilibrium (NLTE) and they are only partially sensitive to the local conditions. Consequently, the interpretation of their profiles is not straightforward. In contrast, millimeter (mm) continuum radiation is produced by thermal free-free collisional interactions in the chromosphere under most solar conditions, and the observed brightness temperatures are better proxies for plasma temperatures. Observations at these long wavelengths have been recently enabled thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), but the Sun remains largely unexplored in this spectral range.In this thesis I explore the diagnostic potential of the mm continuum to study the solar chromosphere using inversions and radiation-magnetohydrodynamics (r-MHD) simulations. In particular, this work takes an unprecedented look at solar active-regions in the mm using some of the first solar ALMA observations.In Paper I, we investigated whether the mm continuum helps to constrain temperatures in NLTE inversions of the MgII and CaII resonance lines using synthetic data from a 3D r-MHD simulation. In Paper II, we applied the same inversion technique to observational data in order to constrain temperature and microturbulence in plage, and we detected signatures of wave heating in coordinated observations with the IRIS satellite. In Paper III, we reported the first results of a comprehensive effort to characterize the visibility of small-scale heating events in an active-region using multiwavelength observations from the mm to the extreme-ultraviolet. We detected multiple, dynamic, transient brightenings -- we called them "millimeter bursts", and we investigated magnetic reconnection using a simulation.This thesis shows that ALMA offers a complementary spectral diagnostic to the existing ones at visible and ultraviolet wavelengths and it underscores the importance of mm continuum observations for constraining models of the solar atmosphere.
|
|
| 2. |
|
|
| 3. |
- Telloni, Daniele, et al.
(författare)
-
Does Turbulence along the Coronal Current Sheet Drive Ion Cyclotron Waves?
- 2023
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 944:2
-
Tidskriftsartikel (refereegranskat)abstract
- Evidence for the presence of ion cyclotron waves (ICWs), driven by turbulence, at the boundaries of the current sheet is reported in this paper. By exploiting the full potential of the joint observations performed by Parker Solar Probe and the Metis coronagraph on board Solar Orbiter, local measurements of the solar wind can be linked with the large-scale structures of the solar corona. The results suggest that the dynamics of the current sheet layers generates turbulence, which in turn creates a sufficiently strong temperature anisotropy to make the solar-wind plasma unstable to anisotropy-driven instabilities such as the Alfven ion cyclotron, mirror-mode, and firehose instabilities. The study of the polarization state of high-frequency magnetic fluctuations reveals that ICWs are indeed present along the current sheet, thus linking the magnetic topology of the remotely imaged coronal source regions with the wave bursts observed in situ. The present results may allow improvement of state-of-the-art models based on the ion cyclotron mechanism, providing new insights into the processes involved in coronal heating.
|
|
| 4. |
- Telloni, Daniele, et al.
(författare)
-
Exploring the Solar Wind from Its Source on the Corona into the Inner Heliosphere during the First Solar Orbiter-Parker Solar Probe Quadrature
- 2021
-
Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 920:1
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter addresses the first Solar Orbiter (SO)-Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfven radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvenic solar corona to just above the Alfven surface.
|
|
| 5. |
- Telloni, Daniele, et al.
(författare)
-
Linking Small-scale Solar Wind Properties with Large-scale Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar Orbiter Observations
- 2022
-
Ingår i: Astrophysical Journal. - : IOP Publishing Ltd. - 0004-637X .- 1538-4357. ; 935:2
-
Tidskriftsartikel (refereegranskat)abstract
- The solar wind measured in situ by Parker Solar Probe in the very inner heliosphere is studied in combination with the remote-sensing observation of the coronal source region provided by the METIS coronagraph aboard Solar Orbiter. The coronal outflows observed near the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and 6.3 R (circle dot) above the eastern solar limb, can be associated with the streams sampled by PSP at 0.11 and 0.26 au from the Sun, in two time intervals almost 5 days apart. The two plasma flows come from two distinct source regions, characterized by different magnetic field polarity and intensity at the coronal base. It follows that both the global and local properties of the two streams are different. Specifically, the solar wind emanating from the stronger magnetic field region has a lower bulk flux density, as expected, and is in a state of well-developed Alfvenic turbulence, with low intermittency. This is interpreted in terms of slab turbulence in the context of nearly incompressible magnetohydrodynamics. Conversely, the highly intermittent and poorly developed turbulent behavior of the solar wind from the weaker magnetic field region is presumably due to large magnetic deflections most likely attributed to the presence of switchbacks of interchange reconnection origin.
|
|
| 6. |
- Telloni, Daniele, et al.
(författare)
-
Observation of a Magnetic Switchback in the Solar Corona
- 2022
-
Ingår i: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 936:2
-
Tidskriftsartikel (refereegranskat)abstract
- Switchbacks are sudden, large radial deflections of the solar wind magnetic field, widely revealed in interplanetary space by the Parker Solar Probe. The switchbacks' formation mechanism and sources are still unresolved, although candidate mechanisms include Alfvenic turbulence, shear-driven Kelvin-Helmholtz instabilities, interchange reconnection, and geometrical effects related to the Parker spiral. This Letter presents observations from the Metis coronagraph on board a Solar Orbiter of a single large propagating S-shaped vortex, interpreted as the first evidence of a switchback in the solar corona. It originated above an active region with the related loop system bounded by open-field regions to the east and west. Observations, modeling, and theory provide strong arguments in favor of the interchange reconnection origin of switchbacks. Metis measurements suggest that the initiation of the switchback may also be an indicator of the origin of slow solar wind.
|
|
| 7. |
- Young, Peter R., et al.
(författare)
-
Solar Ultraviolet Bursts
- 2018
-
Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 214:8
-
Forskningsöversikt (refereegranskat)abstract
- The term ultraviolet (UV) burst is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016-2017.
|
|
