HART: An Efficient Modeling Framework for Simulated Solar Imaging

Leonid Benkevitch (MIT Haystack Observatory),
Mark. D. Benjamin (REU student, Princeton University), Divya. Oberoi (MIT Haystack Observatory, Igor. V. Sokolov (AOSS, University of Michigan)


Abstract


We present a modeling framework HART (Haystack and AOSS Ray Tracer) developed in
view of solar studies using the latest generation of low-frequency (<300 MHz)
interferometer arrays, such as Murchison Widefield Array (MWA) and Low Frequency
Acquisition and Ranging array (LOFAR). Solar science based on modern low
frequency radio telescopes requires reliable numerical tools for image
interpretation. Low frequency radio rays suffer significant refraction and
scattering in the corona, hence the need for simulated images of the sun
exhibiting various features (coronal streamers etc.) obtained through ray
tracing. A correct analysis of low frequency images is impossible without
quality ray tracing software.

HART is based on a native high-efficiency ray tracing algorithm, allowing fast
computation of multi-pixel solar brightness temperature (Tb) images. The
algorithm uses no assumptions on symmetries of the electron density distribution
and can be used for tracing the rays in arbitrary geometries. It also implements
ray scattering based on density fluctuation power spectra. Since any point in
the solar system can be taken for the observer position, HART can be used for
simulating images from heliospheric satellites. The software implementation
works in parallel using modern multi-core processors. We are planning to employ
it on GPUs in the near future. The Tb computation method allows rendering both
unpolarized and circularly polarized images, which is instrumental in studying
solar magnetic fields and Alfven waves. To prevent numerical instabilities, we
developed a method of smooth polynomial ′stitching′ distributions of different
dimensionalities (e.g., Saito's coronal model is 2D while that of the
chromosphere is 1D). Electron density and magnetic field in the numerical domain
can be provided both as analytical models and in the form of ′data cubes′ with
results of an MHD simulation, e.g. from the SWMF framework. The HART framework
includes mechanisms for modeling coronal streamers in both density and magnetic
field. The resultant images can be immediately plotted or the sequences of
images can be saved in multi-dimensional FITS files.

To ensure both high efficiency and user convenience, the HART framework
has a three-layer structure. The fast algorithms at the lower level are coded
in the C language. The middle layer is a Python module. It allows convenient
access to all the simulation parameters and arrays in the Python
environment at the command prompt. The upper layer is the GUI, also written in
Python. It lets a user specify important parameters and includes an interactive
interface for specification of locations on the solar disk where to place
streamer models or at which ray traces are to be plotted in 3D. Visualization
in HART is based on the Matplotlib package.

HART integrates many techniques into a simulation system with a high-level
interface, while providing easy access to every simulation parameter. HART's
design philosophy facilitates its further development and extension.

Paper ID: P010

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