30 research outputs found
Observatories of the Solar Corona and Active Regions (OSCAR)
Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are
major sources of magnetic storms on Earth and are therefore considered to be
the most dangerous space weather events. The Observatories of Solar Corona and
Active Regions (OSCAR) mission is designed to identify the 3D structure of
coronal loops and to study the trigger mechanisms of CMEs in solar Active
Regions (ARs) as well as their evolution and propagation processes in the
inner heliosphere. It also aims to provide monitoring and forecasting of geo-
effective CMEs and CIRs. OSCAR would contribute to significant advancements in
the field of solar physics, improvements of the current CME prediction models,
and provide data for reliable space weather forecasting. These objectives are
achieved by utilising two spacecraft with identical instrumentation, located
at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will
be separated by an angle of 68° to provide optimum stereoscopic view of the
solar corona. We study the feasibility of such a mission and propose a
preliminary design for OSCAR
Slow solar wind sources
Context. The origin of the slow solar wind is still an open issue. One possibility that has been suggested is that upflows at the edge of an active region can contribute to the slow solar wind.
Aims. We aim to explain how the plasma upflows are generated, which mechanisms are responsible for them, and what the upflow region topology looks like.
Methods. We investigated an upflow region using imaging data with the unprecedented temporal (3 s) and spatial (2 pixels = 236 km) resolution that were obtained on 30 March 2022 with the 174 Å channel of the Extreme-Ultraviolet Imager (EUI)/High Resolution Imager (HRI) on board Solar Orbiter. During this time, the EUI and Earth-orbiting satellites (Solar Dynamics Observatory, Hinode, and the Interface Region Imaging Spectrograph, IRIS) were located in quadrature (∼92°), which provides a stereoscopic view with high resolution. We used the Hinode/EIS (Fe XII) spectroscopic data to find coronal upflow regions in the active region. The IRIS slit-jaw imager provides a high-resolution view of the transition region and chromosphere.
Results. For the first time, we have data that provide a quadrature view of a coronal upflow region with high spatial resolution. We found extended loops rooted in a coronal upflow region. Plasma upflows at the footpoints of extended loops determined spectroscopically through the Doppler shift are similar to the apparent upward motions seen through imaging in quadrature. The dynamics of small-scale structures in the upflow region can be used to identify two mechanisms of the plasma upflow: Mechanism I is reconnection of the hot coronal loops with open magnetic field lines in the solar corona, and mechanism II is reconnection of the small chromospheric loops with open magnetic field lines in the chromosphere or transition region. We identified the locations in which mechanisms I and II work
A Space Weather mission concept: Observatories of the Solar Corona and Active Regions (OSCAR)
Evolution of dynamic fibrils from the cooler chromosphere to the hotter corona
Dynamic fibrils (DFs) are commonly observed chromospheric features in solar active regions. Recent observations from the Extreme Ultraviolet Imager (EUI) aboard the Solar Orbiter have revealed unambiguous signatures of DFs at the coronal base in extreme ultraviolet (EUV) emission. However, it remains unclear if the DFs detected in the EUV are linked to their chromospheric counterparts. Simultaneous detection of DFs from chromospheric to coronal temperatures could provide important information on their thermal structuring and evolution through the solar atmosphere. In this paper, we address this question by using coordinated EUV observations from the Atmospheric Imaging Assembly (AIA), Interface Region Imaging Spectrograph (IRIS), and EUI to establish a one-to-one correspondence between chromospheric and transition region DFs (observed by IRIS) with their coronal counterparts (observed by EUI and AIA). Our analysis confirms a close correspondence between DFs observed at different atmospheric layers and reveals that DFs can reach temperatures of about 1.5 million Kelvin, typical of the coronal base in active regions. Furthermore, the intensity evolution of these DFs, as measured by tracking them over time, reveals a shock-driven scenario in which plasma piles up near the tips of these DFs and, subsequently, these tips appear as bright blobs in coronal images. These findings provide information on the thermal structuring of DFs and their evolution and impact through the solar atmosphere
Evolution of dynamic fibrils from the cooler chromosphere to the hotter corona
Dynamic fibrils (DFs) are commonly observed chromospheric features in solar
active regions. Recent observations from the Extreme Ultraviolet Imager (EUI)
aboard the Solar Orbiter have revealed unambiguous signatures of DFs at the
coronal base, in extreme ultraviolet (EUV) emission. However, it remains
unclear if the DFs detected in the EUV are linked to their chromospheric
counterparts. Simultaneous detection of DFs from chromospheric to coronal
temperatures could provide important information on their thermal structuring
and evolution through the solar atmosphere. In this paper, we address this
question by using coordinated EUV observations from the Atmospheric Imaging
Assembly (AIA), Interface Region Imaging Spectrograph (IRIS), and EUI to
establish a one-to-one correspondence between chromospheric and transition
region DFs (observed by IRIS) with their coronal counterparts (observed by EUI
and AIA). Our analysis confirms a close correspondence between DFs observed at
different atmospheric layers, and reveals that DFs can reach temperatures of
about 1.5 million Kelvin, typical of the coronal base in active regions.
Furthermore, intensity evolution of these DFs, as measured by tracking them
over time, reveals a shock-driven scenario in which plasma piles up near the
tips of these DFs and, subsequently, these tips appear as bright blobs in
coronal images. These findings provide information on the thermal structuring
of DFs and their evolution and impact through the solar atmosphere.Comment: Accepted for publication in A&A Letters. Animation files are
available
https://drive.google.com/drive/folders/17-fqQz_P2T18llJ1jB6MJISMRvT5063F?usp=sharin
Signatures of dynamic fibrils at the coronal base: Observations from Solar Orbiter/EUI
The solar chromosphere hosts a wide variety of transients, including dynamic
fibrils (DFs) that are characterised as elongated, jet-like features seen in
active regions, often through H diagnostics. So far, these features
have been difficult to identify in coronal images primarily due to their small
size and the lower spatial resolution of the current EUV imagers. Here we
present the first unambiguous signatures of DFs in coronal EUV data using
high-resolution images from the Extreme Ultraviolet Imager (EUI) on board Solar
Orbiter. Using the data acquired with the 174~{\AA} High Resolution Imager
(HRI) of EUI, we find many bright dot-like features (of size 0.3-0.5
Mm) that move up and down (often repeatedly) in the core of an active region.
In a space-time map, these features produce parabolic tracks akin to the
chromospheric observations of DFs. Properties such as their speeds (14
km~s), lifetime (332~s), deceleration (82 m~s) and lengths
(1293~km) are also reminiscent of the chromospheric DFs. The EUI data strongly
suggest that these EUV bright dots are basically the hot tips (of the cooler
chromospheric DFs) that could not be identified unambiguously before because of
a lack of spatial resolution.Comment: Accepted for publication in A&A Letters. Event movie can be
downloaded from
https://drive.google.com/file/d/1o_4jHA5JbyQtrpUBtB3ItE_s3HjF6ncc/view?usp=sharin
Erratum: A space weather mission concept: Observatories of the solar corona and active regions (oscar) (Journal of Space Weather and Space Climate (2015) 5 (A4) DOI: 10.1051/swsc/2015003)
In this erratum we acknowledge EASCO as one of the inspirational mission concepts that helped the development of our original mission concept OSCAR
Three Eruptions Observed by Remote Sensing Instruments Onboard Solar Orbiter
On February 21 and March 21 – 22, 2021, the Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter observed three prominence eruptions. The eruptions were associated with coronal mass ejections (CMEs) observed by Metis, Solar Orbiter’s coronagraph. All three eruptions were also observed by instruments onboard the Solar–TErrestrial RElations Observatory (Ahead; STEREO-A), the Solar Dynamics Observatory (SDO), and the Solar and Heliospheric Observatory (SOHO). Here we present an analysis of these eruptions. We investigate their morphology, direction of propagation, and 3D properties. We demonstrate the success of applying two 3D reconstruction methods to three CMEs and their corresponding prominences observed from three perspectives and different distances from the Sun. This allows us to analyze the evolution of the events, from the erupting prominences low in the corona to the corresponding CMEs high in the corona. We also study the changes in the global magnetic field before and after the eruptions and the magnetic field configuration at the site of the eruptions using magnetic field extrapolation methods. This work highlights the importance of multi-perspective observations in studying the morphology of the erupting prominences, their source regions, and associated CMEs. The upcoming Solar Orbiter observations from higher latitudes will help to constrain this kind of study better
First Perihelion of EUI on the Solar Orbiter mission
Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists
of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in
Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI
started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from
the largest scales in the extended corona off limb, down to the smallest
features at the base of the corona and chromosphere. EUI is therefore a key
instrument for the connection science that is at the heart of the Solar Orbiter
mission science goals. Methods. The highest resolution on the Sun is achieved
when Solar Orbiter passes through the perihelion part of its orbit. On 2022
March 26, Solar Orbiter reached for the first time a distance to the Sun close
to 0.3 au. No other coronal EUV imager has been this close to the Sun. Results.
We review the EUI data sets obtained during the period 2022 March-April, when
Solar Orbiter quickly moved from alignment with the Earth (2022 March 6), to
perihelion (2022 March 26), to quadrature with the Earth (2022 March 29). We
highlight the first observational results in these unique data sets and we
report on the in-flight instrument performance. Conclusions. EUI has obtained
the highest resolution images ever of the solar corona in the quiet Sun and
polar coronal holes. Several active regions were imaged at unprecedented
cadences and sequence durations. We identify in this paper a broad range of
features that require deeper studies. Both FSI and HRIEUV operate at design
specifications but HRILya suffered from performance issues near perihelion. We
conclude emphasising the EUI open data policy and encouraging further detailed
analysis of the events highlighted in this paper
What drives decayless kink oscillations in active-region coronal loops on the Sun?
Here, we present a study of the phenomena of decayless kink oscillations in a system of active-region (AR) coronal loops. Using high-resolution observations from two different instruments, namely the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we follow these AR loops for an hour each on three consecutive days. Our results show significantly more resolved decayless waves in the higher resolution EUI data compared with the AIA data. Furthermore, the same system of loops exhibits many of these decayless oscillations on Day 2, while we detect very few oscillations on Day 3, and find none at all on Day 1. Analysis of photospheric magnetic field data reveals that, most of the time, these loops were rooted in sunspots, where supergranular flows are generally absent. This suggests that supergranular flows, which are often invoked as drivers of decayless waves, are not necessarily driving such oscillations in our observations. Similarly, our findings also cast doubt on other possible drivers of these waves, such as a transient driver or mode conversion of longitudinal waves near the loop footpoints. In conclusion, our analysis suggests that none of the commonly suspected sources proposed to drive decayless oscillations in active-region loops seem to be operating in this event, and therefore the search for that elusive wave driver needs to continue