I.V. Oreshina

Magnetic-topology evolution in NOAA AR 10501 on 2003 November 18

Context. NOAA AR 10501 produced three flares on 2003 November 18. Two of them were associated with coronal mass ejections (CMEs). Aims. We model the magnetic-field structure of the active region, study the magnetic-topology evolution, and propose a scenario of the observed events. Methods. The coronal magnetic field is reconstructed using a topological model (also called magnetic-charge model). We present an automatic method of choosing the magnetic charges for the case where the charges are located beneath the photosphere. The new method improves quantitative analysis of magnetograms and makes processing faster. Results. We demonstrate that coronal conditions became more favourable for magnetic reconnection before the flaring events. It is also shown that the magnetic-field configuration at the time of both CMEs was critical, close to what is called “topological trigger”. We assume that the topological trigger played a key role in the initiation of these CMEs.

Evolution of the photospheric magnetic field and coronal null points before solar flares

Based on a topological model for the magnetic field of a solar active region (AR), we suggest a criterion for the existence of magnetic null points on the separators in the corona. With the problem of predicting solar flares in mind, we have revealed a model parameter whose decrease means that the AR evolves toward a major eruptive flare. We analyze the magnetic field evolution for AR 9077 within two days before the Bastille Day flare on July 14, 2000. The coronal conditions are shown to have become more favorable for magnetic reconnection, which led to a 3B/X5.7 eruptive flare.

On the causes of the observed magnetic field imbalance in solar active regions

Based on a topological magnetic field model for active region (AR) 8086 observed on September 15–21, 1997, we calculate the evolution of the magnetic flux imbalance during its disk passage. We have established possible causes of the observed imbalance. Using model ARs produced by perfectly balanced magnetic field sources as examples, we show that even in this case, the observed imbalance can reach a significant value, depending on the AR size and location. The peculiar properties of the magnetic field imbalance in ARs predicted by the topological model must be taken into account when present-day magnetographic observations of the Sun are interpreted.

Topological model for the large solar flare of July 14, 2000

Using observational data obtained with the Yohkoh, SOHO, and TRACE satellites, it is shown that the three-dimensional structure of the large solar flare of July 14, 2000 was determined by the topology of the large-scale magnetic field of the active region giving rise to the flare. The locations and shapes of chromospheric ribbons and brightness centers on these ribbons are explained. The observed behavior of the flare is attributed to rapid magnetic reconnection in the corona. The electric field accelerating particles in the reconnecting current sheets is estimated.

Methods of complex analysis in model calculations of the magnetospheres of relativistic stars

In this paper the two-dimensional problem is solved for the magnetosphere of a relativistic compact star. The direct and reverse currents in the magnetotail are calculated, as well as the force exerted by the magnetic field on the edge of the current layer. The dependence of the solution on the parameters of the model is investigated.

A Simple Topological Model of the Bastille Day Flare (2000, July 14)

We present results of three‐dimensional numerical modelling of the coronal magnetic field in the active region NOAA 9077, where a large two‐ribbon flare (3B/X57) occurred on 2000, July 14. The coronal field was reconstructed using a potential approach on the base of photospheric magnetograms obtained by the SOHO/MDI. An analysis of the computed structure is performed. Two‐ribbon nature of the flare observed in different wavelengths by spacecrafts Yohkoh and TRACE, is shown to be a consequence of the field topology. A place and a form of bright chromospheric ribbons and the apparition of bright kernels along the edges of ribbons are explained. Note that the advantage of our model consists in the simplicity and the clearness.