Solar Physics最新文献

The Fluxgate Magnetometer (MAG) is one of the seven instruments on board Aditya-L1 spacecraft to sample the local magnetic field environment around the first Lagrangian point (L1) while continuously observing the Sun. These in situ magnetic field measurements are crucial in detecting coronal mass ejections (CMEs), as well for space weather studies in the vicinity of the Earth, and the apparent detection of solar plasma wave signatures at L1. The MAG payload has a set of fluxgate magnetic sensors mounted on the Sun-viewing panel deck and is configured to deploy along the negative roll direction of the spacecraft. Two sets of triaxial fluxgate sensors are mounted on a 6-m long boom with one set at the tip of the boom and the other at the centre of the boom around 3 m away from the spacecraft towards the boom tip. The boom is mounted to be deployed along the –roll axis of the spacecraft. The power supply and the processing electronics for the MAG payload are enclosed in a box, which is placed inside the +yaw panel of the spacecraft. Each of the two triaxial fluxgate sensors measures the interplanetary magnetic field vectors at L1 in the default range of ± 256 nT per axis once every 125 ms. The observed magnetic field data is time stamped at the spacecraft with the on board clock and transmitted to ground once every day when the visibility is for 12 hours, along with the house-keeping parameters, ephemeris, and the science data from the other six payloads.

In this technical paper, the Aditya-L1 MAG instrument details are presented, along with the initial observations in the halo-orbit around L1.

We have conceived, designed, and evaluated components for an All Sky Heliospheric Imager (ASHI), suitable for flight on future space missions both in Earth orbit and in deep space. ASHI was tested in the summer of 2022 on a NASA-sponsored topside balloon flight; in this paper, we highlight the images taken and the current state of the data reduction from this instrument’s successful overnight flight. The data reduction involves the removal of starlight, zodiacal light, and atmospheric glow to enable the measurements of the outward flow of heliospheric structures. A key photometric specification for ASHI is better than 0.05% differential photometry in one-degree sky bins at 90° elongation. The ASHI balloon flight exceeded expectations and reached to a background white light level of small-scale solar wind structure variations beyond ∼ 60° from the Sun considerably lower than this. Used as a simple, light weight (∼ 8 kg) and relatively inexpensive spaceflight instrument, ASHI has the principal objective of providing a minute-by-minute and day-by-day near real time acquisition of precision Thomson-scattering photometric maps of the inner heliosphere over nearly a hemisphere of sky starting a few degrees from the Sun. This has large potential benefits for improving space-weather nowcast and forecast capabilities of small heliospheric structures.

The magnetic field of the low corona above quiet Sun regions is extremely challenging to observe directly, and the topology is difficult to discern from extreme ultraviolet (EUV) image data due to the lack of distinct loops that are present in, for example, active regions. We aim to show that the velocity field of faint propagating disturbances (PD) observed on-disk in the quiet corona can be interpreted in terms of the underlying magnetic topology. The PD are observed in Atmospheric Imaging Assembly/Solar Dynamics Observatory (AIA/SDO) time series in three channels: 304, 171, and 193 Å corresponding to the high chromosphere, transition region/low corona, and the corona, respectively. An established Time-Normalised Optical Flow method enhances the PD and applies a Lucas–Kanade algorithm to gain their velocity field. From the velocity field, we identify the source and sink locations of the PDs, and compare these locations between channels and with the underlying photospheric network. Source regions tend to be located above the photospheric network, and sink regions with the internetwork. Sink regions in the internetwork suggest either that closed field can be concentrated rather than evenly distributed in the internetwork, or that fieldlines opening into the corona can sometimes be concentrated above internetwork regions. We find regions of almost exact alignment between channels, and other regions where similar-shaped structures are offset by a few pixels between channels. These are readily interpreted as vertical or non-vertical alignment of the magnetic field relative to the observer viewing from above. Regions of isolated source regions in the cold (304 Å) or hotter (171 and 193 Å) channels can be interpreted in terms of the magnetic topology, but support for this is weaker. These results offer support for the future use of PD velocity fields as a coronal constraint on magnetic extrapolation models.

The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument on the Aditya-L1 mission of the Indian Space Research Organization (ISRO) launched on 2 September 2023. SUIT continuously provides near-simultaneous full-disk and region-of-interest images of the Sun, slicing through the photosphere and chromosphere and covering a field of view up to 1.5 solar radii. For this purpose, SUIT uses 11 filters tuned at different wavelengths in the 200 – 400 nm range, including the Mg ii h and k and Ca ii H spectral lines. The observations made by SUIT help us understand the magnetic coupling of the lower and middle solar atmosphere. In addition, for the first time, this allows for the measurements of spatially resolved solar broad-band radiation in the near- and mid-ultraviolet, which will help constrain the variability of the solar ultraviolet irradiance in a wavelength range that is central for the chemistry of ozone and oxygen the Earth’s stratosphere. This paper discusses the details of the instrument and data products.

As known, large near-Earth proton enhancements usually occur after major eruptive solar flares accompanied by strong microwave bursts. Typically, the spectral-maximum frequency of such a burst exceeds 10 GHz, and the flux exceeds (10^{4}) sfu. Ground-level cosmic-ray enhancements (GLEs) are the most energetic subset of large proton events, and it seems that microwave bursts in GLE-associated flares should follow this pattern. This is true in most cases, but in individual events that have produced GLEs, only moderate microwave bursts have been observed. In particular, in the SOL2012-05-17 event responsible for GLE71, the spectral-maximum frequency of the microwave burst did not exceed 10 GHz, and the flux did not reach (10^{3}) sfu. We found that the temporal profile of the microwave burst followed the smoothed magnetic-reconnection rate, lagging behind it by about 50 s and that the burst properties were determined by the following circumstances: i) the magnetic configuration was asymmetric, and ii) the sources of the gyrosynchrotron emission were the entire flare arcade and a compact region above the sunspot umbra. Observations directly demonstrated these features, which were previously inferred for the SOL2001-12-26 event responsible for GLE63. A long-known discrepancy was observed between the estimates of the electron spectrum obtained from hard X-rays and microwaves. However, the hardening of the spectrum of trapped electrons that has been invoked to explain this discrepancy was not found in this event. Indications of a relationship between flare processes and proton acceleration are discussed.

Due to the rapid increase in spectral data generation as well as storage and transmission constraints, data compression has become particularly important for the New Vacuum Solar Telescope (NVST) at Yunnan Observatory. In this paper, we present a method for compressing NVST Ca II (8542 Å) spectral data based on a Convolutional Variational Autoencoder (VAE). Our results show that the compression ratios of the VAE-based approach may achieve as high as 107, while keeping the error between the decompressed data and the original data within the inherent error range of the raw data. This is much better than the appropriate compression ratio of 30 that is attained using the current PCA-based approach. Furthermore, the stability of the VAE approach is demonstrated by the almost constant differences between the VAE-compressed data and the raw data when the compression ratio ranges from 8 to 107. We also investigated Doppler velocity images deduced from the VAE-compressed data and found that the error in Doppler velocity is significantly less than 5 km s⁻¹ when the compression ratio does not exceed 107.

A self-similar solution of the linearised magnetohydrodynamic equations describing the propagation of the Alfvén pulse in an axially symmetric magnetic tube of variable diameter is obtained. The electric field component induced by the non-linear Alfvén wave and directed along the tube surface, i.e., accelerating particles along the magnetic field, is determined on the basis of the perturbation theory and specified to the case of a magnetic flux tube homogeneous over its cross-section. For the chromospheric tubes, whose configuration is given by the barometric law of plasma pressure decrease, the conditions for achieving the super-Dreicer electric field limit necessary to drive the accelerated high-energy electrons into the coronal part of the loop are established.

Magnetic helicity is a key geometrical parameter to describe the structure and evolution of solar coronal magnetic fields. The accumulation of magnetic helicity is correlated with the nonpotential magnetic field energy, which is released in the solar eruptions. Moreover, the relative magnetic helicity fluxes can be estimated only relying on the line-of-sight magnetic field (e.g. Démoulin and Berger 2003). The payload Full-disk MagnetoGraph (FMG) on the Advanced Space-based Solar Observatory (ASO-S) currently has been supplying the continuous evolution of line-of-sight magnetograms for the solar active regions, which can be used to estimate the magnetic helicity flux. In this study, we use eight-hour line-of-sight magnetograms of NOAA 13273, at which the Sun–Earth direction speed of the satellite is zero to avoid the oscillation of the magnetic field caused by the Doppler effect on polarization measurements. We obtain the helicity flux by applying fast Fourier transform (FFT) and local correlation tracking (LCT) methods to obtain the horizontal vector potential field and the motions of the line-of-sight polarities. We also compare the helicity flux derived using data from the Heliosesmic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) and the same method. It is found that the flux has the same sign and the correlation between measurements is 0.98. The difference of the absolute magnetic helicity normalized to the magnetic flux is less than 4%. This comparison demonstrates the reliability of ASO-S/FMG data and that it can be reliably used in future studies.

Two similar-looking, two-part interplanetary type II burst events from 2003 and 2012 are reported and analysed. The 2012 event was observed from three different viewing angles, enabling comparisons between the spacecraft data. In these two events, a diffuse wide-band type II radio burst was followed by a type II burst, which showed emission at the fundamental and harmonic (F-H) plasma frequencies, and these emission bands were also slightly curved in their frequency-time evolution. Both events were associated with high-speed, halo-type coronal mass ejections (CMEs). In both events, the diffuse type II burst was most probably created by a bow shock at the leading front of the CME. However, for the later appearing F-H type II burst, there are at least two possible explanations. In the 2003 event, there is evidence of CME interaction with a streamer, with a possible shift from a bow shock to a CME flank shock. In the 2012 event, a separate white-light shock front was observed at lower heights, and it could have acted as the driver of the F-H type II burst. There is also some speculation on the existence of two separate CMEs, launched from the same active region, close in time. The reason for the diffuse type II burst being visible only from one viewing direction (STEREO-A) and the ending of the diffuse emission before the F-H type II burst appears still need explanations.

We suggest the Kuramoto chain model with four coupled oscillators as a way to describe the phase evolution and departures from synchronization of solar indices at low and high latitudes in the northern and southern hemispheres. Our model simulates the basic properties of the phase differences between the near-equatorial sunspot areas and the polar facula series provided by the Pulkovo and Mount Wilson (MWO) observatories. Temporal variations of the meridional circulation are represented through slow, regular oscillations of natural frequencies. We consider the Gleissberg range (GR) oscillations to have the North-South asymmetry and the 22-year oscillation to be symmetric. The overall synchronization of polar and equatorial solar indices is confirmed. We use it to reconstruct model parameters from the phase difference of solar indices. The synchronization allows for reducing the space of model parameters to a 2D plane, where the eventual departures from the synchronization cut out a narrow zone of accurate estimates. We discuss revealed relations between the low-frequency variations of the solar meridional circulation, the North-South asymmetry, and the desynchronization events.