Despite the present observational evidence and the noticeable progress made in numerical simulations on magnetic flux emergence, there are still many aspects of both approaches that require further study: mechanisms of formation, evolution and decay of ARs, and processes occurring during the interaction of the different magnetic flux system. Bringing together the observational and theoretical communities, we intend to combine our knowledge to improve our understanding of the physical processes operating in flux emergence. The combined knowledge will be used in two directions: one is to design and implement new observation campaigns to verify or reject various model predictions; another is to improve the general realism of the models and generate pseudo-observations, allowing for more direct comparison between theory and observations. Here we list a number of key points in the process to reach these general goals;

 

·         Use ground- (SST, DOT, VTT, NSO) and space-based (HINODE, SDO) high-resolution observations of emerging magnetic flux regions to investigate the sequence of phenomena that lead to the formation of fully evolved ARs or short-lived EFRs. Special emphasis will be on providing information of the dynamic and thermal state of the observed structures for easier comparison with numerical models.

·         Investigate, both observationally and via modelling, the interaction between emerging and pre-existing magnetic fields at different atmospheric layers. Study the impact that magnetic reconnection has on the dynamical evolution of the emergence process and investigate the evolution of associated dynamic events (e.g. small and large-scale brightenings, surges and jets).

·         Investigate whether CME-like eruptions, which come from an EFR, are the result of driven reconnection events within the active region (e.g. tether-cutting mechanism) or are due to MHD instabilities (e.g. either kink or torus instability).

·         Investigate how turbulent convection affects the emergence of magnetic fields at the photosphere and the outer atmosphere of the Sun.

·         Study the thermodynamical behaviour of the system by including an increasingly realistic energy equation in the numerical experiments. The aim is to investigate the effect that each individual process (e.g., heat conduction, radiation, cooling, etc) has on the emergence of the magnetic fields.

·         Compare the results obtained by observations and numerical experiments, in order to provide a better physical understanding of the emergence process. Use this knowledge both on further developing the numerical models in order to investigate not yet explained phenomena recorded in the observations and to guide new observations to look for predictions based on the numerical experiments.

 

These aims are ambitious and we do not expect to fulfill all of them with in the limited time of the project. The ISSI workshops will be used to initiate the process by providing an excellent environment for discussions and an excellent possibility for initiating new collaborations to attack outstanding issues.

 

 

Timelines of the Project

 

Before the launch of the Hinode and SDO missions it was impossible to obtain simultaneous, multi-wavelength high-resolution observations of the different atmospheric layers. Therefore even the observations carried out from the last generation high-resolution ground-based telescopes, could be used only to deduce the behavior of the emerging magnetic structures in the lower atmospheric layers. As a consequence, it was not possible to detect the signatures of the emergence of magnetic flux, simultaneously, in the entire solar atmosphere.

 

Nowadays, using the above mentioned instruments, it is possible to follow the evolution of the EFR from its very beginning and to detect whether the new flux is interacting with the ambient, coronal magnetic field. Some of the team members have presented a proposal for the observations of emerging active regions at the SST and DOT telescopes in the Canary Islands, and they obtained 10 days of observing run to be carried out during the summer 2010. The output of this Campaign, that will be coordinated with the Hinode satellite, will constitute an optimum data-set that will be used by the team members to reach their goals.

 

The numerical experiments conducted until now can be divided into three main classes. In the simple ones a relative simple stratified atmospheric model in which a highly twisted flux tube is initially positioned in the convection zone is used. An artificial mechanism triggers the rise of the tube, that is then followed as the tube emerges into the coronal domain, which may or may not contain a simple coronal magnetic field model. The second class of models is based on the long tradition of convection simulations into which different types of initial magnetic field structures are embedded and the evolution followed in time. These models have a realistic treatment of optical thick radiation and are therefore restricted to the convection zone and the layers just above the photosphere. Finally the third group, and more realistic experiments, spans the whole region with a fairly realistic treatment of the energy equation through out the domain and is as such the only models that can be used in direct comparisons with the full set of observational data.

 

Our aim is to utilize the three types of model to achieve different types of physical understanding of the emergence process and its implications on the development of the photospheric and coronal plasma. To achieve this a constructive discussions of important outstanding issues and their possible solutions must be undertaken before initiating a series of new numerical experiments.

 

 

Expected Output

 

By organising ISSI meetings, the proposers would like to foster international collaborations and discussions between experts working in the field of emergence, with strong emphasis on a close interaction between theory and observations. These goals perfectly fit in the aims of the Solaire Network (www.solairenetwork.eu), a research network approved and financed by the European Commission for the period June 2007 – May 2011. Several institutions participating in this proposal are also members of that network, providing a solid basis for further collaborations.

 

The first ISSI meeting will decide from the existing extensive databases which EFRs to investigate in detail both observationally and theoretically. New observing programmes, using Hinode, SDO and ground based facilities, will be proposed. Developments in simulation techniques and targets will be discussed and new collaborations  set up.

The second meeting will discuss progress and strengths and weaknesses of ongoing projects.

The final meeting will discuss the obtained results, further possible directions of progress and prepare review articles on both observational and numerical aspects of the emergence process for publications in international journals.

 

Moreover, team members will report on the results obtained at International Scientific Meetings, where the ISSI support will be acknowledged, as well as in each of the articles that will be published in peer review Journals.

 

 

Added Value from ISSI for the Implementation of the Project

 

We believe that the ISSI provides an excellent working environment for small groups of experts to concentrate on a well defined project and to discuss and confront their results, views and theories. Further to this, then having a small groups of people with comparable interests makes it much easier to start new collaborative projects.

 

 

Schedule

 

We plan three 4 day meetings at ISSI within 18 months from its start.

The 1st meeting is planned to take place on 7 – 11 February 2011.

The 2nd meeting should take place about 7-8 months after the first meeting.

The 3rd meeting would take place 8-9 months after the second meeting.

Completion of the project: June 2012

 

 

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