Stuart Mumford

SunPy - Python for Solar Physics

SunPy is a data analysis toolkit which provides the necessary software for analyzing solar and heliospheric datasets in Python. SunPy aims to provide a free and open-source alternative to the current standard, an IDL- based solar data analysis environment known as SolarSoft (SSW). We present the latest release of SunPy, version 0.3. Though still in active development, SunPy already provides important functionality for solar data analysis. SunPy provides data structures for representing the most common solar data types: images, lightcurves, and spectra. To enable the acquisition of scientific data, SunPy provides integration with the Virtual Solar Observatory (VSO), a single source for accessing most solar data sets, and integration with the Heliophysics Event Knowledgebase (HEK), a database of transient solar events such as solar flares or coronal mass ejections. SunPy utilizes many packages from the greater scientific Python community, including NumPy and SciPy for core data types and analysis routines, PyFITS for opening image files, in FITS format, from major solar missions (e.g., SDO/AIA, SOHO/EIT, SOHO/LASCO, and STEREO) into WCS-aware map objects, and pandas for advanced time-series analysis tools for data from missions such as GOES, SDO/EVE, and Proba2/LYRA, as well as support for radio spectra (e.g., e-Callisto). Future releases will build upon and integrate with current work in the Astropy project and the rest of the scientific python community, to bring greater functionality to SunPy users.

Magnetohydrostatic equilibrium – I. Three-dimensional open magnetic flux tube in the stratified solar atmosphere

A system of multiple open magnetic flux tubes spanning the solar photosphere and lower corona is modeled analytically, within a realistic stratified atmosphere subject to solar gravity. This extends results for a single magnetic flux tube in magnetohydrostatic equilibrium, described in Gent et al. Self-similar magnetic flux tubes are combined to form magnetic structures, which are consistent with high-resolution observations. The observational evidence supports the existence of strands of open flux tubes and loops persisting in a relatively steady state. Self-similar magnetic flux tubes, for which an analytic solution to the plasma density and pressure distribution is possible, are combined. We calculate the appropriate balancing forces, applying to the equations of momentum and energy conservation to preserve equilibrium. Multiplex flux tube configurations are observed to remain relatively stable for up to a day or more, and it is our aim to apply our model as the background condition for numerical studies of energy transport mechanisms from the solar surface to the corona. We apply magnetic field strength, plasma density, pressure, and temperature distributions consistent with observational and theoretical estimates for the lower solar atmosphere. Although each flux tube is identical in construction apart from the location of the radial axis, combinations can be applied to generate a non-axisymmetric magnetic field with multiple non-uniform flux tubes. This is a considerable step forward in modeling the realistic magnetized three-dimensional equilibria of the solar atmosphere.

Photospheric logarithmic velocity spirals as MHD wave generation mechanisms

High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the solar plasma. These spirals vary in properties, but are observed to be abundant at the solar surface. In this work, these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfven waves and other MHD waves. This work employs numerical simulations of a self-similar magnetic flux tube embedded in a realistic, gravitationally stratified, solar atmosphere to study the effects of a single magnetic flux tube perturbed by a logarithmic velocity spiral driver. The expansion factor of the logarithmic spiral driver is varied and multiple simulations are run for a range of values of the expansion factor centred around observational constraints. The simulations are analysed using ‘flux surfaces’ constructed from the magnetic field lines so that the vectors perpendicular, parallel and azimuthal to the local magnetic field vector can be calculated. The results of this analysis show that the Alfven wave is the dominant wave for lower values of the expansion factor, whereas for the higher values the parallel component is dominant. This transition occurs within the range of the observational constraints, meaning that spiral drivers, as observed in the solar photosphere, have the potential to generate a variety of MHD wave modes.

Varying driver velocity fields in photospheric MHD wave simulations

Torsional motions are ubiquitous in the solar atmosphere. In this work, we perform 3D numerical simulations which mimic a vortex-type photospheric driver with a Gaussian spatial profile. This driver is implemented to excite MHD waves in an axially symmetric, 3D magnetic flux tube embedded in a realistic solar atmosphere. The Gaussian width of the driver is varied and the resulting perturbations are compared. Velocity vectors were decomposed into parallel, perpendicular and azimuthal components with respect to pre-defined magnetic flux surfaces. These components correspond broadly to the fast, slow and Alfven modes, respectively. From these velocities the corresponding wave energy fluxes are calculated, allowing us to estimate the contribution of each mode to the energy flux. For the narrowest driver (0.15 Mm) the parallel component accounts for ∼55 − 65% of the flux. This contribution increases smoothly with driver width up to nearly 90% for the widest driver (0.35 Mm). The relative importance of the perpendicular and azimuthal components decrease at similar rates. The azimuthal energy flux varied between ∼35% for the narrowest driver and <10% for the widest one. Similarly, the perpendicular flux was ∼25 − 10%. We also demonstrate that the fast mode corresponds to the sausage wave in our simulations. Our results therefore show that the fast sausage wave is easily excited by this driver and that it carries the majority of the energy transported. For this vortex-type driver the Alfven wave does not contribute a significant amount of energy.