Showing papers by "Mark C. M. Cheung published in 2022"
TL;DR: The Multi-slit Solar Explorer (MUSE) as discussed by the authors provides high-cadence and sub-second-resolution spectroscopic rasters over an active region size of the solar transition region and corona.
Abstract: Abstract Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales of the coronal dynamics of solar flares and eruptive phenomena. The highest-resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by the Interface Region Imaging Spectrograph for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), subarcsecond-resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al., which focuses on investigating coronal heating with MUSE.
15 citations
TL;DR: Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetric in the near ultraviolet as discussed by the authors .
Abstract: Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in the near ultraviolet. This observatory offers unprecedented capabilities to obtain unique information on the magnetic and plasma properties of the magnetospheres of hot stars. We describe an observing program making use of the known population of magnetic hot stars to test the fundamental hypothesis that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the evolution of magnetic vs. non-magnetic stars.
8 citations
TL;DR: In this article , the magnetic and plasma properties of hot stars were studied and it was shown that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate.
Abstract: Several space missions and instruments for UV spectropolarimetry are in preparation, such as the proposed NASA MIDEX Polstar project, the proposed ESA M mission Arago, and the Pollux instrument on the future LUVOIR-like NASA flagship mission. In the frame of Polstar, we have studied the capabilities these observatories would offer to gain information on the magnetic and plasma properties of the magnetospheres of hot stars, helping us test the fundamental hypothesis that magnetospheres should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultaneously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the evolution of magnetic vs. non-magnetic stars.
6 citations
TL;DR: In this article , the authors investigated the potential and limitations of image-to-image translation by focusing on the permutation of four channels and an encoder-decoder based architecture, with particular attention to how morphological traits and brightness of the solar surface affect the neural network predictions.
Abstract: The Solar Dynamics Observatory (SDO), a NASA multispectral decade-long mission that has been daily producing terabytes of observational data from the Sun, has been recently used as a use case to demonstrate the potential of machine-learning methodologies and to pave the way for future deep space mission planning. In particular, the idea of using image-to-image translation to virtually produce extreme ultraviolet channels has been proposed in several recent studies, as a way to both enhance missions with fewer available channels and to alleviate the challenges due to the low downlink rate in deep space. This paper investigates the potential and the limitations of such a deep learning approach by focusing on the permutation of four channels and an encoder–decoder based architecture, with particular attention to how morphological traits and brightness of the solar surface affect the neural network predictions. In this work we want to answer the question: can synthetic images of the solar corona produced via image-to-image translation be used for scientific studies of the Sun? The analysis highlights that the neural network produces high-quality images over 3 orders of magnitude in count rate (pixel intensity) and can generally reproduce the covariance across channels within a 1% error. However, the model performance drastically diminishes in correspondence to extremely high energetic events like flares, and we argue that the reason is related to the rareness of such events posing a challenge to model training.
4 citations
12 May 2022
TL;DR: In this article , the authors developed a fast, global dB/dt forecasting model, which forecasts 30 min into the future using only solar wind measurements as input, based on a Gated Recurrent Unit (GRU).
Abstract: Geomagnetically Induced Currents (GICs) arise from spatio‐temporal changes to Earth's magnetic field, which arise from the interaction of the solar wind with Earth's magnetosphere, and drive catastrophic destruction to our technologically dependent society. Hence, computational models to forecast GICs globally with large forecast horizon, high spatial resolution and temporal cadence are of increasing importance to perform prompt necessary mitigation. Since GIC data is proprietary, the time variability of the horizontal component of the magnetic field perturbation (dB/dt) is used as a proxy for GICs. In this work, we develop a fast, global dB/dt forecasting model, which forecasts 30 min into the future using only solar wind measurements as input. The model summarizes 2 hr of solar wind measurement using a Gated Recurrent Unit and generates forecasts of coefficients that are folded with a spherical harmonic basis to enable global forecasts. When deployed, our model produces results in under a second, and generates global forecasts for horizontal magnetic perturbation components at 1 min cadence. We evaluate our model across models in literature for two specific storms of 5 August 2011 and 17 March 2015, while having a self‐consistent benchmark model set. Our model outperforms, or has consistent performance with state‐of‐the‐practice high time cadence local and low time cadence global models, while also outperforming/having comparable performance with the benchmark models. Such quick inferences at high temporal cadence and arbitrary spatial resolutions may ultimately enable accurate forewarning of dB/dt for any place on Earth, resulting in precautionary measures to be taken in an informed manner.
2 citations
TL;DR: In this paper , the untangling of small-scale coronal magnetic braids in different active regions is associated with impulsive heating of the gas in these braided loops, which is a source of energy to heat plasma in active region coronal loops.
Abstract: Relaxation of braided coronal magnetic fields through reconnection is thought to be a source of energy to heat plasma in active region coronal loops. However, observations of active region coronal heating associated with an untangling of magnetic braids remain sparse. One reason for this paucity could be the lack of coronal observations with a sufficiently high spatial and temporal resolution to capture this process in action. Using new observations with high spatial resolution (250-270 km on the Sun) and high cadence (3-10 s) from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, we observed the untangling of small-scale coronal braids in different active regions. The untangling is associated with impulsive heating of the gas in these braided loops. We assess that coronal magnetic braids overlying cooler chromospheric filamentary structures are perhaps more common. Furthermore, our observations show signatures of spatially coherent and intermittent coronal heating during the relaxation of the magnetic braids. Our study reveals the operation of gentle and impulsive modes of magnetic reconnection in the solar corona.
1 citations
TL;DR: In this article , the authors propose a solution to solve the problem of the problem: this article ] of "uniformity" and "uncertainty" of the solution.
Abstract: ,
1 citations
29 Dec 2022
TL;DR: In this paper , the authors combine remote sensing with in-situ observations to simulate a solar-like setup in terms of domain extent and time-scales, and the availability of data with a stable quality, time-duration, spatial coverage and cadence.
Abstract: Modeling of flare and CME events: Modeling of transient events in the solar atmosphere requires the confluence of 3 critical elements: (1) Models with a sufficient sophistication in terms of physics and their ability to simulate a solar-like setup in terms of domain extent and time-scales; (2) The availability of data (combination of remote sensing with in-situ observations) with a stable quality, time-duration, spatial coverage and cadence; (3) The ability to ingest these data into models and to continuously update and correct the model state to reflect the observed conditions on the Sun.
TL;DR: In this paper , the authors reported high-resolution, high-cadence observations of five small-scale coronal jets in an on-disk quiet Sun region observed with Solar Orbiter's EUI/HRIEUV in 174 Å.
Abstract: We report high-resolution, high-cadence observations of five small-scale coronal jets in an on-disk quiet Sun region observed with Solar Orbiter’s EUI/HRIEUV in 174 Å. We combine the HRIEUV images with the EUV images of SDO/AIA and investigate the magnetic setting of the jets using coaligned line-of-sight magnetograms from SDO/HMI. The HRIEUV jets are miniature versions of typical coronal jets as they show narrow collimated spires with a base brightening. Three out of five jets result from a detectable minifilament eruption following flux cancelation at the neutral line under the minifilament, analogous to coronal jets. To better understand the physics of jets, we also analyze five small-scale jets from a high-resolution Bifrost MHD simulation in synthetic Fe ix/Fe x emissions. The jets in the simulation reside above neutral lines and four out of five jets are triggered by magnetic flux cancelation. The temperature maps show evidence of cool gas in the same four jets. Our simulation also shows the signatures of opposite Doppler shifts (of the order of ±10 s of km s−1) in the jet spire, which is evidence of untwisting motion of the magnetic field in the jet spire. The average jet duration, spire length, base width, and speed in our observations (and in synthetic Fe ix/Fe x images) are 6.5 ± 4.0 min (9.0 ± 4.0 minutes), 6050 ± 2900 km (6500 ± 6500 km), 2200 ± 850 km, (3900 ± 2100 km), and 60 ± 8 km s−1 (42 ± 20 km s−1), respectively. Our observation and simulation results provide a unified picture of small-scale solar coronal jets driven by magnetic reconnection accompanying flux cancelation. This picture also aligns well with the most recent reports of the formation and eruption mechanisms of larger coronal jets.