China’s Space Astronomy and Solar Physics in 2011—2012

In the first part of this paper,we describe briefly the mid and long-term plan of Chinese space astronomy,its preliminary study program,the current status of satellite missions undertaken, and the current status of astronomy experiments in China's manned space flight program.In the second part,the recent research progress made in the fields of solar physics is summarized briefly, including solar vector magnetic field,solar flares,CME and filaments,solar radio and nonthermal processes,EUV waves,MHD waves and coronal waves,solar model and helioseismology,solar wind and behavior of solar cycle.

Recent progress of solar physics research in China

Owing to the largely improved facilities and working conditions, solar physics research in China has recently shown marked development. This paper reports on the recent progress of solar physics research in China's Mainland, mainly focusing on several hot issues, including instrumentations, magnetic field observations and research, solar flares, filaments and their eruptions, coronal mass ejections and related processes, as well as active regions and the corona, small-scale phenomena, solar activity and its predictions. A vision of the future is also described.

Space Solar Physics in China

The activities of Chinese space solar physics in 2018–2020 are going on smoothly.Besides the missions of ASO-S and CHASE which are in the engineering phases,there are quite a number of projects which are in the pre-study stage(conception study)or have finished the pre-study stage,constituting a rich pond for the selection of next solar mission(s).This paper describes in brief the status of all these related projects.

Space Solar Physics in China:2020-2022

To follow up the last report two years ago,what happened from 2020 to 2022 deserves specially mentioning:CHASE was successfully launched on 14 October 2021;ASO-S will finish soon its Phase-D study and is scheduled for launch in October 2022;four solar mission candidates are being undertaken the engineering project evaluations;three solar mission proposals are being undertaken the background project evaluations;there are also quite a number of pre-study space solar physics projects getting either newly supported or finished.This paper describes in brief the status of all these related projects.

Status of the Advanced Space-based Solar Observatory

The Advanced Space-based Solar Observatory(ASO-S)was formally approved at the end of 2017.In the past two years,ASO-S underwent its official Phase-B and Phase-C studies.The Phase-B study was successfully accomplished by the end of April 2019,and the Phase-C study is being now undertaken until August 2020.Then the flight model is planned to finish within 16 months.Around the end of 2021,ASO-S will be ready in the launch state.We briefly summarize the history of ASO-S,the phase-B studies,and the phase-C studies.

Introduction to the Chinese Hα Solar Explorer(CHASE)Mission

The Chinese HαSolar Explorer(CHASE)mission,dubbed as“Xihe”——Goddess of the Sun,was launched on 14 October 2021 as the first solar space mission of China National Space Administration(CNSA).The CHASE mission aims to test an ultra-high precision and stability platform,and to acquire solar HαSpectroscopic observations with high temporal and spectral resolutions.Since its launch,the in-orbit performance of the scientific payload——HαImaging Spectrograph(HIS)has been excellent.The first set of data has been calibrated and analyzed recently.The CHASE science data are expected to advance our understanding of the plasma dynamics in the solar lower atmosphere,and to investigate the Sun as a star for stellar physics.

Progress Report on ASO-S

The Advanced Space-based Solar Observatory(ASO-S)started officially its engineering phases at the beginning of 2018.In the past two years from 2020 to 2022 ASO-S completed smoothly the Phase-C study and is now undertaking the Phase-D study.The launch date is finally set in October of 2022.We here briefly summarize the progress of ASO-S from the late Phase-C to the current Phase-D studies,and plan the scientific affairs around the launch.

The Chinese Hα Solar Explorer(CHASE) mission: An overview

The Chinese Hα Solar Explorer(CHASE), dubbed “Xihe”—Goddess of the Sun, was launched on October 14, 2021 as the first solar space mission of China National Space Administration(CNSA). The CHASE mission is designed to test a newly developed satellite platform and to acquire the spectroscopic observations in the Hα waveband. The Hα Imaging Spectrograph(HIS)is the scientific payload of the CHASE satellite. It consists of two observational modes: raster scanning mode and continuum imaging mode. The raster scanning mode obtains full-Sun or region-of-interest spectral images from 6559.7 to 6565.9 ? and from 6567.8 to 6570.6 ? with 0.024 ? pixel spectral resolution and 1 min temporal resolution. The continuum imaging mode obtains photospheric images in continuum around 6689 ? with the full width at half maximum of 13.4 ?. The CHASE mission will advance our understanding of the dynamics of solar activity in the photosphere and chromosphere. In this paper, we present an overview of the CHASE mission including the scientific objectives, HIS instrument overview, data calibration flow, and first results of on-orbit observations.

The meridional circulation of the Sun: Observations, theory and connections with the solar dynamo

The meridional circulation of the Sun, which is observed to be poleward at the surface, should have a return flow at some depth. Since large-scale flows like the differential rotation and the meridional circulation are driven by turbulent stresses in the convection zone, these flows are expected to remain confined within this zone. Current observational(based on helioseismology)and theoretical(based on dynamo theory) evidences point towards an equatorward return flow of the meridional circulation at the bottom of the convection zone. Assuming the mean values of various quantities averaged over turbulence to be axisymmetric,we study the large-scale flows in solar-like stars on the basis of a 2D mean field theory. Turbulent stresses in a rotating star can transport angular momentum, setting up a differential rotation. The meridional circulation arises from a slight imbalance between two terms which try to drive it in opposite directions: a thermal wind term(arising out of the higher efficiency of convective heat transport in the polar regions) and a centrifugal term(arising out of the differential rotation). To make these terms comparable,the poles of the Sun should be slightly hotter than the equator. We discuss the important role played by the meridional circulation in the flux transport dynamo model. The poloidal field generated by the Babcock-Leighton process at the surface is advected poleward, whereas the toroidal field produced at the bottom of the convection zone is advected equatorward. The fluctuations in the meridional circulation(with coherence time of about 30-40 yr) help in explaining many aspects of the irregularities in the solar cycle. Finally, we discuss how the Lorentz force of the dynamo-generated magnetic field can cause periodic variations in the large-scale flows with the solar cycle.

Calibration procedures for the CHASE/HIS science data

The Hα line is an important optical line in solar observations containing the information from the photosphere to the chromosphere. To study the mechanisms of solar eruptions and the plasma dynamics in the lower atmosphere, the Chinese Hα Solar Explorer(CHASE) was launched into a Sun-synchronous orbit on October 14, 2021. The scientific payload of the CHASE satellite is the Hα Imaging Spectrograph(HIS). The CHASE/HIS acquires, for the first time, seeing-free Hα spectroscopic observations with high spectral and temporal resolutions. It consists of two observational modes. The raster scanning mode provides full-Sun or region-of-interest spectra at Hα(6559.7-6565.9 ?) and Fe I(6567.8-6570.6 ?) wavebands. The continuum imaging mode obtains full-Sun photospheric images at around 6689 ?. In this paper, we present detailed calibration procedures for the CHASE/HIS science data, including the dark-field and flat-field correction, slit image curvature correction, wavelength and intensity calibration, and coordinate transformation. The higher-level data products can be directly used for scientific research.