Steps toward a high precision solar rotation profile: Results from SDO/AIA coronal bright point data

Coronal bright points (CBP) are ubiquitous small brightenings in the solar corona associated with small magnetic bipoles. We derive the solar differential rotation profile by tracing the motions of CBPs detected by the Atmospheric Imaging Assembly (AIA) instrument aboard the Solar Dynamics Observatory (SDO). We also investigate problems related to detection of coronal bright points resulting from instrument and detection algorithm limitations. To determine the positions and identification of coronal bright points we used a segmentation algorithm. A linear fit of their central meridian distance and latitude versus time was utilised to derive velocities. We obtained 906 velocity measurements in a time interval of only 2 days. The differential rotation profile can be expressed as $\omega_{rot} = (14.47\pm 0.10 + (0.6\pm 1.0)\sin^{2}(b) + (-4.7\pm 1.7)\sin^{4}(b))$\degr day$^{-1}$. Our result is in agreement with other work and it comes with reasonable errors in spite of the very short time interval used. This was made possible by the higher sensitivity and resolution of the AIA instrument compared to similar equipment as well as high cadence. The segmentation algorithm also played a crucial role by detecting so many CBPs, which reduced the errors to a reasonable level. Data and methods presented in this paper show a great potential to obtain very accurate velocity profiles, both for rotation and meridional motion and, consequently, Reynolds stresses. The amount of coronal bright point data that could be obtained from this instrument should also provide a great opportunity to study changes of velocity patterns with a temporal resolution of only a few months. Other possibilities are studies of evolution of CBPs and proper motions of magnetic elements on the Sun

ODREĐIVANJE ELEMENATA SUNČEVE ROTACIJE i, Ω I PERIODA OPAŽANJIMA SUNČEVIH PJEGA RUĐERA BOŠKOVIĆA 1777. GODINE

In September 1777, Ruđer Bošković observed sunspots for six days. Based on these measurements, he used his own methods to calculate the elements of the Sun’s rotation, the longitude of the node, the inclination of the solar equator and the period. He published a description of the methods, the method of observation and detailed instructions for calculations in the second chapter of the fifth part of the Opera in 1785. In this paper, Bošković’s original calculations and repeated calculations by his procedure are published. By analysing the input quantities, procedures, and results, the input quantities of the error, and the calculation results are discussed. The reproduction of Bošković’s calculations is successfully reproduced and we obtained very similar results. The conclusion proposes a relationship of Bošković’s research with mod ern astronomy.U rujnu 1777. godine Ruđer Bošković šest je dana opažao Sunčeve pjege. Na osnovi tih mjerenja vlastitim je metodama izračunao elemente Sunčeve rotacije, longitudu čvora, inklinaciju Sunčeva ekvatora i period. Opis metoda, način opažanja i detaljne upute za računanje objavio je u drugome poglavlju petoga dijela Opera 1785. godine. U ovome radu objavljeni su originalni Boškovićevi izračuni i ponovljena su računanja njegovim postupcima. Analizom ulaznih veličina, postupaka i rezultata diskutirane su ulazne veličine, pronađene pogreške i rezultati računanja. Reprodukcija Boškovićevih izračuna uspješno je ponovila postupke i dobila vrlo slične rezultate. Zaključkom su predložena povezivanja Boškovićevih istraživanja s modernom astronomijom

Are There Radio-quiet Solar Flares?

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 - 4000MHz range (type I - V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100MHz were accompanied by metric typeIII emission below 100MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the sourc

Preliminary results on the solar rotation determined tracing SDO/AIA coronal bright points

In this paper we present preliminary results on the solar differential rotation measured tracing coronal bright points in SDO/AIA images. An automatic recognition method was applied to the series of images taken in the test period, 1-2 January 2011. Coronal bright points are suitable tracers for the determination of the solar differential rotation, because they are localized objects which are very well distributed over solar disc. Results presented in this paper show that the SDO/AIA data are very useful for that aim, due to the high spatial and temporal resolution of the images

An analysis of the solar differential rotation from the Kanzelhoehe sunspot drawings

We present here the results of the behaviour of the solar differential rotation during solar cycles no. 20 and no. 22, derived from Kanzelhoehe sunspot drawings (Kanzelhoehe Observatory for Solar and Environmental Research, University of Graz, Austria). The positions of sunspot groups were determined using a special software Sungrabber. Sunspot groups were identified with the help of the Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering solar cycles no. 20 and no. 22, respectively. In order to calculate the sidereal angular rotation rate ω and subsequently solar rotation parameters A and B we used two procedures: a) daily motion of sunspot groups and b) linear least-square fit from the function CMD(t) for each tracer, where CMD denotes the Central Meridian Distance. The sample was limited to ±58º in CMD in order to avoid solar limb effects. We mainly investigated velocity patterns depending on the solar cycle phase and latitude

An analysis of the solar differential rotation from the Kanzelhoehe sunspot drawings

We present here the results of the behaviour of the solar differential rotation during solar cycles no. 20 and no. 22, derived from Kanzelhoehe sunspot drawings (Kanzelhoehe Observatory for Solar and Environmental Research, University of Graz, Austria). The positions of sunspot groups were determined using a special software Sungrabber. Sunspot groups were identified with the help of the Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering solar cycles no. 20 and no. 22, respectively. In order to calculate the sidereal angular rotation rate ω and subsequently solar rotation parameters A and B we used two procedures: a) daily motion of sunspot groups and b) linear least-square fit from the function CMD(t) for each tracer, where CMD denotes the Central Meridian Distance. The sample was limited to ±58º in CMD in order to avoid solar limb effects. We mainly investigated velocity patterns depending on the solar cycle phase and latitude