The solar corona is the primary driver of the space environment in both the heliosphere and near Earth, but the connection between the inner corona and the large scale structures in the heliosphere is still not well understood. One set of coronal features that clearly probes this connection are large scale coronal fans, structures that are composed of hot plasma on both open and closed magnetic field lines that extend from the low corona to the heliosphere. In recent years, fans have become better explored, but they are still not fully understood. The lack of observations of fans' connection between the low corona, seen by EUV imagers, and extended corona, seen by white light coronagraphs, is largely due to a lack of instrumentation capable of observing this region of the middle corona.
In the past five years, new EUV imagers (for example, STEREO/EUVI and PROBA2/SWAP) with larger fields of view and better temporal resolution have led to increasing interest in this region of the corona and its connection to space weather. In particular, the development of novel image processing techniques have improved our ability to isolate, track, and study these features. In the coming years, several additional instruments, such as GOES-R/SUVI, Solar Orbiter/EUI, PROBA3/ASPIICS, will further enhance our ability to observe this relatively poorly explored region of the corona, in which coronal fans are one of the most important features.
At this point in time, in preparation for the next generation of instruments, we need to make a concerted effort to understand coronal fans and the environment of the middle corona. Likewise, it is important to develop better link between observations from imagers and the in-situ data we expect to get from upcoming missions (for example, DISCOVR, Solar Orbiter, GOES-R, and Solar Probe Plus). This ISSI team will bring together scientists working on these present and near-future observations, image analysis techniques, theoretical and numerical models of the large-scale corona, and those currently developing the next generation of instrumentation.
By combining images, in-situ data, and models of the corona, we plan to explore several fundamental questions in solar and heliospheric physics through the lens of coronal fans. These include the processes that heat extended structures in the corona, what dictates the boundary between open and closed magnetic fields in the corona, and how the plasma environments of these two magnetic domains are different. Since solar wind outflow occurs in these open field regions, understanding their properties is key to understanding the solar wind itself and its connection to space weather in the near-Earth environment.
Figure 1. An example of a coronal fan as seen by the PROBA2 SWAP EUV imager
We have formed a small team of scientists who are experts in observations of the large-scale extended solar corona, magnetic field modelling, and image- and in-situ-based observations of the heliosphere. Together we will develop coordinated model-supported observation campaigns of coronal fans and their connection to the heliosphere using the broad variety of existing instruments. Using the output from these campaigns, we will develop new analysis techniques and observing strategies that can be implemented using future instrumentation.
To explore coronal Fans we will hold 2 to 3 small workshops based at the European Space Astronomy Centre (ESAC), European Space Agency, Spain and at the Royal Observatory of Belgium, Belgium. the first workshop will be held at ESAC between 29 Nov and 1 Dec 2016.
Here we have a rough schedule, the whole point of the meeting is to invoke discussions on the subject, the schedule should be treated as a guideline rather than a rigid plan. It would be nice to have some introductory talks on the first day, discussing what we know, followed by looking at a case study on day 2. Day 3 should be used to work out what we can learn from, discussing what observations we need, how can we further our understanding of fans?
29-Nov-2016 - Where Are We?
Introductions - Meeting the team
Introduction to Fans and long term analysis on their evolution + link to white light images
Introduction to SWAP observations
Introduction to Modelling?
Future instruments - Dan / Sabrina?
30-Nov-2016 - Case Study
For the second day I propose we perform a case study. In particular, the large fan structure seen throughout Carrington Rotation 2153. A movie of the rotation can be seen below.
The FITs files (100 minute stacks) for this movie can be obtained here
01-Dec-2016 - How do we move forward?
Day 3 should start with a summary of the facts and unknowns? We can build that up together as a team, to have a starting point for planning further research.