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## Tracing sunspot groups to determine angular momentum transfer on the Sun

Sudar, Davor; Skokić, Ivica; Ruždjak, Domagoj; Brajša, Roman; Woehl, Hubertus
Tracing sunspot groups to determine angular momentum transfer on the Sun // Monthly notices of the Royal Astronomical Society, 439 (2014), 3; 2377-2385 doi:10.1093/mnras/stu099 (međunarodna recenzija, članak, znanstveni)

Naslov
Tracing sunspot groups to determine angular momentum transfer on the Sun

Autori
Sudar, Davor ; Skokić, Ivica ; Ruždjak, Domagoj ; Brajša, Roman ; Woehl, Hubertus

Izvornik
Monthly notices of the Royal Astronomical Society (0035-8711) 439 (2014), 3; 2377-2385

Ključne riječi
Sun: rotation - sunspots - Sun: photosphere - Sun: activity
(Sun: rotation - sunspots - Sun: photosphere - Sun: activity\)

Sažetak
The goal of this paper is to investigate Reynolds stresses and to check if it is plausible that they are responsible for angular momentum transfer toward the solar equator. We also analysed meridional velocity, rotation velocity residuals and correlation between the velocities. We used sunspot groups position measurements from GPR (Greenwich Photographic Result) and SOON/USAF/NOAA (Solar Observing Optical Network/United States Air Force/National Oceanic and Atmospheric Administration) databases covering the period from 1878 until 2011. In order to calculate velocities we used daily motion of sunspot groups. The sample was also limited to $\pm$58\degr in Central Meridian Distance (CMD) in order to avoid solar limb effects. We mainly investigated velocity patterns depending on solar cycle phase and latitude. We found that meridional motion of sunspot groups is toward the centre of activity from all available latitudes and in all phases of the solar cycle. The range of meridional velocities is $\pm10$ m s$^{; ; ; ; ; -1}; ; ; ; ;$. Horizontal Reynolds stress is negative at all available latitudes and indicates that there is a minimum value ($q\approx$ - 3000 m$^2$ s$^{; ; ; ; ; -2}; ; ; ; ;$) located at $b\approx\pm$30$\degr$. In our convention this means that angular momentum is transported toward the solar equator in agreement with the observed rotational profile of the Sun.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

Projekt / tema
007-0000000-1362 - Eruptivni procesi u Sunčevoj atmosferi (Bojan Vršnak, )
007-0000000-1364 - Fizikalni procesi u atmosferama Sunca i zvijezda (Vladimir Ruždjak, )

Ustanove
Geodetski fakultet, Zagreb

#### Časopis indeksira:

• Current Contents Connect (CCC)
• Web of Science Core Collection (WoSCC)
• Science Citation Index Expanded (SCI-EXP)
• SCI-EXP, SSCI i/ili A&HCI
• Scopus