Volume 647, March 2021
|Number of page(s)||13|
|Section||The Sun and the Heliosphere|
|Published online||31 March 2021|
Photospheric downflows observed with SDO/HMI, HINODE, and an MHD simulation
Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, UPS, CNES, 14 Avenue Edouard Belin, 31400 Toulouse, France
2 Charles University, Astronomical Institute, V Holešovičkách 2, 18000 Prague 8, Czech Republic
3 Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165 Ondejov, Czech Republic
4 Observatoire de Paris, LESIA, 5 Place Janssen, 92195 Meudon, France
5 PSL Research University, CNRS, Sorbonne Universités, Sorbonne Paris Cité, Paris, France
6 Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, 3251 Hanover Street CA 94303, USA
Accepted: 5 February 2021
Downflows on the solar surface are suspected to play a major role in the dynamics of the convection zone, at least in its outer part. We investigate the existence of the long-lasting downflows whose effects influence the interior of the Sun but also the outer layers. We study the sets of Dopplergrams and magnetograms observed with Solar Dynamics Observatory and Hinode spacecrafts and an magnetohydrodynamic (MHD) simulation. All of the aligned sequences, which were corrected from the satellite motions and tracked with the differential rotation, were used to detect the long-lasting downflows in the quiet-Sun at the disc centre. To learn about the structure of the flows below the solar surface, the time-distance local helioseismology was used. The inspection of the 3D data cube (x, y, t) of the 24 h Doppler sequence allowed us to detect 13 persistent downflows. Their lifetimes lie in the range between 3.5 and 20 h with a sizes between 2″ and 3″ and speeds between −0.25 and −0.72 km s−1. These persistent downflows are always filled with the magnetic field with an amplitude of up to 600 Gauss. The helioseismic inversion allows us to describe the persistent downflows and compare them to the other (non-persistent) downflows in the field of view. The persistent downflows seem to penetrate much deeper and, in the case of a well-formed vortex, the vorticity keeps its integrity to the depth of about 5 Mm. In the MHD simulation, only sub-arcsecond downflows are detected with no evidence of a vortex comparable in size to observations at the surface of the Sun. The long temporal sequences from the space-borne allows us to show the existence of long-persistent downflows together with the magnetic field. They penetrate inside the Sun but are also connected with the anchoring of coronal loops in the photosphere, indicating a link between downflows and the coronal activity. A links suggests that EUV cyclones over the quiet Sun could be an effective way to heat the corona.
Key words: Sun: granulation / Sun: photosphere / Sun: atmosphere
© T. Roudier et al. 2021
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