Observations of the Solar Corona from Space
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Observations of the Solar Corona from Space Ester Antonucci1 · Louise Harra2 · Roberto Susino1 · Daniele Telloni1
Received: 23 July 2020 / Accepted: 27 September 2020 © The Author(s) 2020
Abstract Space observations of the atmosphere of the Sun, obtained in half a century of dedicated space missions, provide a well established picture of the medium and large-scale solar corona, which is highly variable with the level of solar activity through a solar cycle and evolves with the long-term evolution of the magnetic cycles. In this review, we summarize the physical properties and dynamics of the medium and large-scale corona, consisting primarily of active regions, streamers and coronal holes; describe the dependence of coronal patterns on the magnetic field patterns changing through the solar cycle and the properties of the regions of open magnetic flux channeling the solar wind; the ubiquitous presence of fluctuations in the outer corona; the rotational properties of the large-scale corona; and the persistent hemispheric asymmetries in the emergence of magnetic fields and the distribution of the coronal emission. Keywords Solar physics · Space observations · Solar corona · Solar wind
1 Introduction The picture of the solar corona derived from ground-based and space observations is that of a hot inhomogeneous magnetized atmosphere, which is constantly evolving and consisting of features developing on different scales in the various phases of the solar activity cycle. Active regions are dominant in the ascending phase of the solar cycle and at solar maximum when the relatively simple poloidal configuration of the solar magnetic field typically observed at solar minimum is disrupted by the emergence of the toroidal field of the new cycle. Coronal holes and quiescent streamers, reflecting long-lived large-scale patterns, are
B E. Antonucci
[email protected]
1
Istituto Nazionale di Astrofisica (INAF), Osservatorio Astrofisico di Torino, Via Osservatorio, 20, 10125, Pino Torinese (TO), Italy
2
Physikalisch-Meteorologische Observatorium Davos/World Radiation Center and Eidgenössische Technische Hochschule-ETH Zürich, Zürich, Switzerland
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prevalent in the declining to minimum phase of solar activity when the magnetic field becomes organized according to lower order multipoles. When the level of activity increases, magnetic energy is sporadically released in sudden and powerful reconnection events occurring at coronal heights. These events are characterized by the emission of highly energetic electromagnetic radiation and particle acceleration, frequently associated with huge plasma ejections, inducing transient changes and a reorganization of the structure of the corona. The X-ray image of the Sun, obtained by the Naval Research Laboratory scientists during a sub-orbital rocket flight on April 19, 1960, in the form of a crude low-resolution photograph, revealed for the first time the hottest layers of the solar atmosphere against the bright disk. The solar corona appear
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