European Solar Physics Online Seminar Archive

It is well understood that the dynamics of sunspots lead to energy being transferred to the solar atmosphere and stored in the coronal magnetic field. This provides a surplus of energy that may be released in solar eruptions. The driving mechanisms for this energy transfer may include sunspot rotations, both within individual sunspots and between sunspot pairs. Calculation of the rotations of individual sunspots have been carried out by several authors, but studies of the rotation of sunspot pairs has been less systematically investigated.Calculation of rotations in either case rely on careful tracking of the sunspots from observation to observation. Identification and tracking of sunspots is therefore essential to understanding the energies in play that lead up to solar eruptions. To date, this has predominantly been done manually which has restricted many studies to being a small number of case studies rather than large statistical samples. In order to construct large samples, the careful tracking of sunspots must be automated.We present a fully automatic method to identify and track sunspots in long sequences of data from the Solar Dynamics Observatory Helioseismic and Magnetic Imager (SDO/HMI) at a high temporal resolution. This includes registering the splitting and merging of sunspots, and allocating sunspots to active regions. This information can be fed into algorithms to measure the rotation of individual sunspots or used to calculate the relative motion of sunspots with respect to each other (including co-rotation).The method is applied to a four-month data set that has previously been analysed using a semi-automatic method where the basic sunspots were identified by eye, and the results are compared to determine any differences between the methods. From this data, sunspot dynamics such as sunspot rotation, shearing and merging are calculated, alongside sunspot pair interactions. Case studies of successfully tracked sunspots will be presented, showing examples of the individual sunspot rotations and some initial results involving sunspot pair interactions with correlations to solar activity. [more]

The prediction of geomagnetic storms is becoming more and more important, with the aim to take effective measures for avoiding the possible damage from the extreme events. One of the important parameters when modeling CMEs and CME-driven shocks, is their arrival time at Earth. We present a study of several halo CMEs with the propagation direction which significantly deviated from the Sun-Earth line and as a result, CMEs impacted Earth as flank-encounters. We modeled selected events with the default-setup of EUHFORIA and the Cone model for the CMEs. The aim of our study is to better understand the importance of the CME’s direction of propagation in the input parameters of the Cone model and improve the modeled arrival time at Earth. We selected events that were propagating strongly non-radialy in the low corona, in order to understand how important are the effects of the deflections in the low corona, in the direction of propagation. Our results show that, when the data from the DONKI database are used, the modeled arrival time has the largest discrepancy(≥10h) when compared with observations. When the input parameters are taken employing the GCS fitting technique though, up to the height of 12 Ro (solar radii), the accuracy of the modeled arrival time improves, shifting closer to the observed ones. This result reflects the characteristic that, up to the heights of about 10 Ro, CMEs experience all the low coronal deflections and have taken their final direction of propagation. [more]