Naslov
Comparison of the sidereal angular velocity of subphotospheric layers and small bright coronal structures during the declining phase of solar cycle 23
(Comparison of the sidereal angular velocity of sub-photospheric layers and small bright coronal structures during the declining phase of solar cycle 23)

Autori
Zaatri, Amel ; Woehl, Hubertus ; Roth, Markus ; Corbard, Thierry ; Brajša, Roman

Izvornik
Astronomy & Astrophysics (0004-6361) 504 (2009), 2; 589-594

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
sun: rotation; sun: helioseismology; sun: corona; methods: data analysis

Sažetak
We compare solar differential rotation of sub-photospheric layers derived from local helioseismology analysis of GONG++ dopplergrams and the one derived from tracing small bright coronal structures (SBCS) using EIT/SOHO images for the period August 2001 - December 2006 which corresponds to the declining phase of solar cycle 23. The study aims to find and inter-relationship between the rotation of small bright coronal structures and the sub-photospheric sidereal angular velocity. The north-south asymmetries of both rotation velocity measurements are also investigated. Sub-photospheric differential rotation has been derived using ring diagram analysis of GONG++ full disk dopplergrams of 1 min cadence. The coronal rotation is derived by using an automatic method to identify and track the small bright coronal structures in EIT full disk images of 6 hours cadence. We find that SBCS rotate faster than the considered upper sub-photospheric layer (3Mm) by about 0.5 deg/day at the equator. This result joins the results of several other magnetic features (sunspots, plages, faculae, etc.) with a higher rotation than that of the solar plasma. The latitudinal gradient of the SBCS rotation rate is very similar to that of the sub-photospheric layers. The SBCS motion shows an acceleration of about 0.005 deg/day/month during the declining phase of solar cycle 23 whereas the angular velocity of subsurface layers does not display any evident variation with time. Finally, both subphotospheric and coronal rotation of the southern hemisphere are predominantly larger than those of the northern hemisphere. The latitudinal behaviour of the north-south asymmetry of the SBCS rotation velocity with activity is opposite to that of the sub-photospheric asymmetry

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA