Examples of Computational Magnetospheric Research
Director: Jeffrey Hughes, Boston University
Anyone who has witnessed a thunderstorm, tornado, or hurricane can appreciate the serious effects of terrestrial weather. Just as the dynamics of the atmosphere have important consequences, the mostly unseen dynamics of the Earth’s space environment are also important to us on the ground. Satellites can be destroyed by enhanced radiation or set tumbling by changes in the local magnetic field, and communications and power distribution grids can be disrupted. As more of our technological base becomes dependent on space-based assets, the development of accurate forecast models for “Space Weather” becomes more and more important.
The National Science Foundation has recently funded a Science and Technology Center at Boston University, The Center for Integrated Space Weather Modeling (CISM), to address this need. The Center’s charter is to develop a coupled chain of physics-based simulations for space weather effects that runs from the surface of the Sun to the Earth’s atmosphere. In this effort, CISM will be partnering with the Scientific Computing and Visualization group and the Center for Computational Science at Boston University.
Examples of Computational Magnetospheric Research
A visualization of a magnetospheric simulation is pictured at the left. The yellow sphere off the simulation grid to the left represents the Sun (not to scale), and the Earth (to scale) is embedded within the inner boundary of the grid. Also shown are two sets of magnetic field lines originating at different latitudes on the Earth. Globally, the magnetized super-sonic solar wind interacts with the Earth’s magnetic field to cause Space Weather.
The red and white surfaces illustrated here bound regions that are magnetically dominated by the Earth’s magnetic field. The solar wind is blowing in from left to right. During certain times, solar wind energy can open these boundaries and flow through the magentospheric system. Extreme cases of driving can result in a geomagnetic storm.
This figure shows one example of how energy is transferred into the near-Earth region. Two intersecting planes are color-coded with plasma velocity; blue corresponds to fast flow away from the Sun, and red corresponds to fast sunward flow. Where the flow exceeds a threshold, white vectors indicate the direction of plasma penetration into near-Earth space.
The polar aurora is one effect of a geomagnetic storm in the Earth’s ionosphere. This viewpoint is from above the Earth’s north pole, with the Sun shining from the top. The ionospheric simulation domain is colored with the flux of precipitating particles into the northern ionosphere. These particles produce the aurora, but present radiation hazards for Space Station astronauts and polar airline flights that pass through these high latitudes.
The field of Space Weather prediction is at much the same point that terrestrial weather forecasting was in the 1960′s, when the first computer models were being implemented. With the activity of CISM and its partners, SCV and CCS, Boston University is positioned to take a leading role in the development of realistic and worthwhile forecasting of the Earth’s space environment.
We have rendered twelve movies from the CISM data provided by various CISM researchers and they are provided here, along with descriptions of the movies. These movies were originally shown in stereo on our traveling high-resolution stereo display at the Supercomputing 2005 and 2006 conferences at a resolution of 2048 x 1536. For the web versions here, they have been downsampled to 720 x 540 mono and are available in Microsoft AVI and Apple Quicktime formats. The Quicktime versions are of somewhat higher quality but are also 3-5 times as large files.
The original stereo high resolution movies were all produced by Ray Gasser and the downsampling and web conversion was done by Aaron D. Fuegi, both members of the Scientific Computing and Visualization group at Boston University.
This movie shows a model visualization of the Sun’s magnetic field in the solar corona. The sphere in the center represents the sun’s visible surface, and the color scale represents values of the observed surface magnetic field (red is pointing inward and blue out). The solar magnetic field is generated by current flows deep in the sun, but it is modified by the solar wind flowing out from the sun. Initially, only the field-lines at the poles are represented in white. These lines are “open” meaning that they do not connect directly back to the sun but continue on to interstellar space. As the movie continues, closed field lines are added near the sun. The movie ends with the last closed field lines (in purple) and the first open field lines (in red) that are draped around the closed field lines. (Courtesy S. McGregor) (31MB AVI, 190MB QuickTime)
The movie shows a model visualization of the Sun’s outer atmosphere, the corona. The sphere in the center represents the sun’s visible surface, and the gray-scale values are derived from observations of the surface magnetic field. The model magnetic field lines that are computed from that inner boundary are colored in red, and the surface at which the magnetic field polarity reverses is the current sheet, visualized as the surface near the heliospheric equator. This current sheet is colored with the value of solar wind radial velocity. (Courtesy S. McGregor) (14MB AVI, 60MB QuickTime)
This illustrates the way the magnetospheric model is initialized. Initially, there is a dipole field set up in the center of the simulation axes. Drawn are two sets of magnetic field lines, starting at two different latitudes on the earth. First, unmagnetized solar wind is blown into the simulation domain which will form a realistic magnetospheric cavity. At some later time, the solar wind direction changes (according to the real orientation of the Earth’s dipole field relative to the solar wind) and the solar wind magnetic field is convected in, stripping some of the earth’s field away and varying according to upstream spacecraft measurements. (Courtesy John Lyon & T. Guild) (16MB AVI, 47MB QuickTime)
This movie is a substorm simulation with the plane colored in the logarithm of the density, a translucent isosurface of the plasma sheet volume, and red vectors that show the flows within the plasma sheet. Now there are also two sets of field lines (gray & gold) that are started at different latitudes. Note near the middle of the movie, there is a region in the plasma sheet where the flow vectors start diverging, and some of the plasma goes very quickly toward the earth, whereas some goes quickly away from the earth. Also see the surface break and some of it go away from the earth. This is the time sequence of a substorm, and the plasma going away from the earth is called a plasmoid. (Courtesy T. Guild) (78MB AVI, 385MB QuickTime)
This movie is a substorm simulation as viewed from above (and behind) the north pole. This visualization shows the velocity colored on the equatorial plane, with blue indicating fast flow away from the sun (solar wind) and red indicating fast flow toward the sun (inside the magnetosphere, and it’s called flow bursts). When the velocity is faster than 350 km/s red vectors are drawn. This illustrates the meso-scale structure inherent in the substorm energy transfer event. It’s not just a divergence of flows, as you would expect from the previous substorm simulation movies but has a very complicated structure in the equatorial plane. (Courtesy T. Guild) (77MB AVI, 291MB QuickTime)
This is a view of the magnetosphere from the side, with the plane colored in the logarithm of the density. There are white terrestrial magnetic field lines, which are usually only connected to the Earth. Whenever the plasma flow is going sunward fast (> 350 km/s) we draw red arrows indicating the direction and magnitude. This is a simulation of a substorm, where a small amount of solar wind energy couples into the Earth’s magnetosphere. The solar wind magnetic field turns opposite to the earth’s field at the front of the magnetosphere, reconnection allows the magnetosphere to load with the solar wind energy, and once the stress is too great in the tail (behind the earth), reconnection happens again, ejecting plasma earthward and tailward. (Courtesy T. Guild) (70MB AVI, 269MB QuickTime)
Viewed from above. The plane is colored in the logarithm of the density, there are yellow magnetic field lines, two vectors upstream of the grid are the incoming velocity vector, and interplanetary magnetic field (IMF) vector. The translucent surface anti-sunward of the earth is the plasma sheet, a region of hot plasma through which energy gets transferred into the near-Earth region. Inside that, are red vectors which show the velocity of flows. This is a short demo, comprising only a few time steps of the simulation. (Courtesy T. Guild) (3MB AVI, 13MB QuickTime)
This visualization illustrates everything from the substorm simulation in the previous visualizations. Movies 2, 3, and 4 on this page show the substorm from a fixed vantage point, whereas this one flies the camera through the volume. Shown are planes colored in density, two sets of field lines, red vectors during fast flows, and a translucent surface bounding the plasma sheet. (Courtesy T. Guild) (62MB AVI, 244MB QuickTime)
This visualization was made by a CISM undergraduate. It shows an isosurface of density in the magnetosphere, and the surface is painted with the value of the magnetic field. The value of the density defining the isosurface changes as a function of time, from high to low density. The camera flies through the volume where that isosurface changes as a function of time. (Courtesy A. Pembroke) (17MB AVI, 64MB QuickTime)
This is a visualization of the TING (Thermosphere-Ionosphere Nested Grid) model. The thermosphere is the tenuous region of the upper atmosphere, dominated by an increasing temperature profile with altitude. The ionosphere is the conducting layer within the thermosphere, which directly participates in space weather dynamics, as driven by the magnetosphere. Shown in this visualization is the temperature profile of the upper atmosphere ions as computed by the TING model (colored slice) and an isosurface of electron density. The peak of electron density is usually at noon, due to the solar ultraviolet light ionizing atmospheric species. (Courtesy M. Wiltberger) (10MB AVI, 34MB QuickTime)