Attention-Based Deep Learning Model for Image Desaturation of SDO/AIA

The Atmospheric Imaging Assembly(AIA)onboard the Solar Dynamics Observatory(SDO)captures full-disk solar images in seven extreme ultraviolet wave bands.As a violent solar flare occurs,incoming photoflux may exceed the threshold of an optical imaging system,resulting in regional saturation/overexposure of images.Fortunately,the lost signal can be partially retrieved from non-local unsaturated regions of an image according to scattering and diffraction principle,which is well consistent with the attention mechanism in deep learning.Thus,an attention augmented convolutional neural network(AANet)is proposed to perform image desaturation of SDO/AIA in this paper.It is built on a U-Net backbone network with partial convolution and adversarial learning.In addition,a lightweight attention model,namely criss-cross attention,is embedded between each two convolution layers to enhance the backbone network.Experimental results validate the superiority of the proposed AANet beyond state-of-the-arts from both quantitative and qualitative comparisons.

The Decay Process of an α-configuration Sunspot

The decay of sunspot plays a key role in magnetic flux transportation in solar active regions(ARs).To better understand the physical mechanism of the entire decay process of a sunspot,an α-configuration sunspot in AR NOAA 12411 was studied.Based on the continuum intensity images and vector magnetic field data with stray light correction from Solar Dynamics Observatory/Helioseismic and Magnetic Imager,the area,vector magnetic field and magnetic flux in the umbra and penumbra are calculated with time,respectively.Our main results are as follows:(1) The decay curves of the sunspot area in its umbra,penumbra,and whole sunspot take the appearance of Gaussian profiles.The area decay rates of the umbra,penumbra and whole sunspot are-1.56 MSH day^(-1),-12.61 MSH day^(-1) and-14.04 MSH day^(-1),respectively;(2) With the decay of the sunspot,the total magnetic field strength and the vertical component of the penumbra increase,and the magnetic field of the penumbra becomes more vertical.Meanwhile,the total magnetic field strength and vertical magnetic field strength for the umbra decrease,and the inclination angle changes slightly with an average value of about 20°;(3) The magnetic flux decay curves of the sunspot in its umbra,penumbra,and whole sunspot exhibit quadratic patterns,their magnetic flux decay rates of the umbra,penumbra and whole sunspot are-9.84 × 10^(19)Mx day^(-1),-1.59 × 10^(20)Mx day^(-1) and -2.60 × 10^(20)Mx day^(-1),respectively.The observation suggests that the penumbra may be transformed into the umbra,resulting in the increase of the average vertical magnetic field strength and the reduction of the inclination angle in the penumbra during the decay of the sunspot.

Chinese Hα Solar Explorer(CHASE)——a complementary space mission to the ASO-S

The Chinese HαSolar Explorer(CHASE)is designed to test a newly developed satellite platform and conduct solar observations.The scientific payload of the satellite is an Hαimaging spectrograph(HIS),which can,for the first time,acquire full-disk spectroscopic solar observations in the Hαwaveband.This paper briefly introduces CHASE/HIS including its scientific objectives,technical parameters,scientific application system,etc.The CHASE mission is scheduled to launch in 2021.It will complement the observations by on-orbit solar spacecraft(such as SDO,IRIS,STEREO and PSP),as well as future solar missions of the Solar Orbiter and Advanced Space-based Solar Observatory(ASO-S).

Lyα science from the LST aboard the ASO-S mission

We review the status of solar Lyαscience in anticipation of the upcoming Advanced Spacebased Solar Observatory(ASO-S)mission,planned for a late 2021(or 2022)launch.The mission carries a pair of the LyαSolar Telescopes(LST)capable of high resolution disk and off-limb imaging,which will provide the first synoptic Lyαimaging observations of the solar atmosphere.We discuss the history of Lyαimaging and latest results,and outline the open questions that ASO-S could address.ASO-S will launch at an optimal time for Lyαscience.Several other Lyαtelescopes will be in operation.We identify the synergies between ASO-S and other missions as well as serendipitous non-solar science opportunities.We conclude that ASO-S has the potential for breakthrough observations and discoveries in the chromosphere-corona interface where the Lyαemission is the major player.

Image Desaturation for SDO/AIA Using Mixed Convolution Network

The Atmospheric Imaging Assembly(AIA)onboard the Solar Dynamics Observatory(SDO)provides full-disk solar images with high temporal cadence and spatial resolution over seven extreme ultraviolet(EUV)wave bands.However,as violent solar flares happen,images captured in EUV wave bands may have saturation in active regions,resulting in signal loss.In this paper,we propose a deep learning model to restore the lost signal in saturated regions by referring to both unsaturated/normal regions within a solar image and statistical probability model of massive normal solar images.The proposed model,namely mixed convolution network(MCNet),is established over conditional generative adversarial network(GAN)and the combination of partial convolution(PC)and validness migratable convolution(VMC).These two convolutions were originally proposed for image inpainting.In addition,they are implemented only on unsaturated/valid pixels,followed by certain compensation to compensate the deviation of PC/VMC relative to normal convolution.Experimental results demonstrate that the proposed MCNet achieves favorable desaturated results for solar images and outperforms the state-of-the-art methods both quantitatively and qualitatively.

Ellerman Bombs, Type Ⅱ White-light Flares and Magnetic Reconnection in the Solar Lower Atmosphere

Ellerman bombs and Type Ⅱ white-light flares share many common features despite the large energy gap between them. Both are considered to result from local heating in the solar lower atmosphere. This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere, with the aim to account for the common features of the two phenomena. Our numerical results manifest the following two typical characteristics of the assumed reconnection process: (1) magnetic reconnection saturates in -600-900 s, which is just the lifetime of the two phenomena; (2) ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection, making the heating effect most significant in the lower chromosphere. The application of the reconnection model to the two phenomena is discussed in detail.