The Principal Investigator will simulate solar eruptions based on his recently developed 3D MHD solar active region (AR) evolution model, which is driven by actual observations. The new model has already shown promise in reproducing the non-potential magnetic field evolution of an active region AR8100. He will investigate potential triggers for solar eruptive events using available photospheric measurements, in order to determine the factors contributing to the initiation of a solar eruption. Specifically, the PI plans to study issues related to the magnetic configuration and free magnetic energy of active regions; the effects of magnetic flux emergence and submergence/cancellation on solar eruptions; contributions of energy and helicity flux through the photosphere to the growth of ARs; and the energy threshold for solar eruption. He also will perform a correlative study of the evolution of energy/helicity flux and non-potential magnetic field parameters.
The most important innovation in the Principal Investigator's new model is the incorporation of actual photospheric measurements. In addition, self-consistent and time-dependent characteristic boundary conditions are fully implemented in the model to correctly input these changing photospheric observations. The PI states that effects caused by sub-photospheric and convective zone dynamics will be directly reflected through the surface boundary conditions, and thus his model will be able to couple the sub-photosphere and the solar corona.
A graduate student will be supported in this project. The PI will continue his multiple European collaborations, including a 'US-Slovak Space Weather' initiative, which attracts many foreign scientists and graduate students, some of whom eventually come to work in the US. The 'US-Slovak Space Weather' project has held several annual workshops in Europe and has received the support of the NSF Office of International Science & Engineering (OISE).
Highlights of the FINAL REPORT of NSF Grant ATM-0754378 entitled: "Analysis of Observed Magnetic Field Characteristics for the Understanding of Solar Eruptons Physics Using a Data Driven 3D MHD Model" Period of Performance: 6/1/08 - 5/31/12 During the period of performance, June 2008 – May 2012, a total of twenty articles were published in JGR, ApJ and Solar Physics and three were published on conference proceedings. A total to 18 presentations were given in various countries. The PI also organized sessions at fall AGU meetings. Among these published works, we will summarize the important highlights as follows: Modeling Solar Emission Using a Three-Dimensional Data-Driven MHD model Using our data-driven 3D MHD model, we simulated the sun’s emission and magnetic field topology. The inputs to the model is the LOS magnetic field from SOLIS (high resolution) and GONG’s transverse velocity for CR2900. model is tested by using GONG’s measurements of LOS (line-of-sight) magnetic field and transverse velocity fields as the inputs to obtain the radiative emission and magnetic field topology of the solar atmosphere. We found that inputs of both magnetic field and velocity measurements are very critical for prediction of radiative emissions because, we have employed five observed quantities on the lower boundary to match five characteristics according to the theory of method of characteristics. Fig. 1 shows the model output of the radiative emission on the photosphere and the 3D magnetic field topology is depicted in Fig. 2. From these new robust simulations, we note that the closed field loop-structure produces high emission and the open field region exhibits low emission with high speed solar wind. Also, we have tested without inputs of the velocity measurements in which the emission does not show cohesive pattern. Our conclusion is that we need more complete measurements (density, 3D magnetic fields and 3D velocity fields) on the solar surface to have more realistic forecasting results. Discovery of an additional Condition for Solar Eruption: Framentation of the Magnetic Shear of the Major Neutral Line By analyzing AR10720 using our 3D Data-Driven MHD model (Wu et al. 2006), we have discovered a new feature for triggering solar flares (Wu et al. 2009). This new feature is the appearance of fragmentation of the length of the magnetic shear of the main neutral line. This feature also appeared at AR11117 as shown in Figure 3. It is noted that the length of the magnetic shear grows longer (Fig. 3a) at 19:00 UT, October 25, 2010 and then fragmented (Fig 3b) at 22:00UT, then a C-2 flare was observed at 22:10 UT. To understand this fragmentation (or non-uniform) shear, we used the masured magnetic field of R11117 to construct the variation of the shear angle along the major neutral line as shown in Fig. 4 which shoes significant variation of the shear angle. It impllies that the highly complexity of the field configuration will enhance the MHD instability which leads to solar eruption.
