Mentors:A.R. Yeates & P.C.H. Martens

Point of Contact: A.R. Yeates Email: ayeates_at_cfa.harvard.edu

1 Aim

Loss of equilibrium of magnetic flux ropes is a leading candidate for the origin of solar coronal mass ejections (CMEs). Recently, Yeates & Mackay (2009) have explored the number of flux rope ejections in global simulations of the magnetic field evolution in the solar corona. These simulations use a simplified MHD model, which is novel in that it follows a sequence of (nonlinear force-free) equilibria allowing for the development of twisted and sheared magnetic fields and of free magnetic energy. The number of flux ropes forming in the simulation and the number of these that lose equilibrium depend on simulation parameters, including the newly-emerging active regions (which we insert into the simulation to match their observed counter- parts) and the turbulent diffusivity in the corona. Yeates & Mackay (2009) find that the model produces about 50% of the observed CME rate. How- ever, the analysis in that paper considered only a single 6-month period, in the rising phase of the 11-year solar activity cycle. The aim of this REU project is to repeat the simulation using input data from several stages of the solar cycle, and to determine how the formation and ejection flux ropes changes in di?erent phases of the cycle. This is motivated by coronagraph observations of CMEs, which show variations both in occurrence rate and in latitudinal distribution (Yashiro et al., 2004; Robbrecht et al., 2009; see also Gopalswamy et al., 2003). The student will gain experience in the mechanics of simulating the magnetic field, analysing simulation data, and comparing with observations. They will also learn about an interesting area of current research in theoretical solar physics, and (hopefully) have fun.

2 Nature of project

• Numerical simulation/parallel computing: using existing FORTRAN code, no programming needed.
• Data analysis using IDL: using existing code to analyse simulation results and calculate flux rope statistics, writing new IDL routines to plot and compare the statistics with observed CME rates.
• Background reading: recommended but the breadth and/or depth will depend on student's interests.
• Note: The project involves specific software so don't hesitate to ask for a lot of help from the advisors!

3 Work Plan

1. Discussion of project and scientific aims with advisors; familiarize with Yeates & Mackay (2009) paper.
2. Learn to use "getemerge" IDL code to detect bipoles; produce bipole data files for chosen simulation periods; plot bipole statistics (i.e. learn basic IDL).
3. Learn how to use CMS to visualize global simulations (with example output); create initial potential fields.
4. Learn how to setup/compile/run "fff3" FORTRAN code; run repeat of our previous simulation; vizualize.
5. Learn how to use "ropes" IDL program to find and vizualize flux ropes; reproduce Fig. 6 of Yeates & Mackay (2009); make 3D plots of variety of flux ropes, including a loss of equilibrium.
6. Familarize with "daystats" and "eruptstats" IDL codes for plotting flux rope statistics, and reproduce Figs. 7 and 9.
7. Run simulations for new periods.
8. Reproduce ßux rope statistics for each period individually. 9. Write new IDL code to illustrate:
(a) Variation in rate of eruptions over cycle.
(b) Histograms of latitudes over cycle.
(c) Add observed LASCO rates (from CDAW or CacTUS) to these plots.
10. Write a final report/presentation.
Note: This plan is a guide only and may need to be adjusted depending on progress and issues that arise.

References