Heliophysics Education Resources

Visualizations useful for illustrating key concepts.

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Heliospheric Physics

Space Weather

  • Halloween Solar Storms - 2003
    2012.09.20
    This is a 1024x1024 pixel version of solar storms providing a more complete view of the SOHO/LASCO/C3 field-of-view.

    Here is a view of the solar disk in 195 Å ultraviolet light (colored green in this movie) and the Sun's extended atmosphere, or corona, (blue and white in this movie). The corona is visible to the SOHO/LASCO coronagraph instruments, which block the bright disk of the Sun so the significantly fainter corona can be seen. In this movie, the inner coronagraph (designated C2) is combined with the outer coronagraph (C3). This movie covers a two week period in October and November 2003 which exhibited some of the largest solar activity events since the advent of space-based solar observing.

    As the movie plays, we can observe a number of features of the active Sun. Long streamers radiate outward from the Sun and wave gently due to their interaction with the solar wind. The bright white regions are visible due to their high density of free electrons which scatter the light from the photosphere towards the observer. Protons and other ionized atoms are there as well, but are not as visible since they do not interact with photons as strongly as electrons. Coronal Mass Ejections (CMEs) are occasionally observed launching from the Sun. Some of these launch particle events which can saturate the cameras with snow-like artifacts.

    Also visible in the coronagraphs are stars and planets. Stars are seen to drift slowly to the right, carried by the relative motion of the Sun and the Earth. The planet Mercury is visible as the bright point moving left of the Sun. The horizontal 'extension' in the image is called 'blooming' and is due to a charge leakage along the readout wires in the CCD imager in the camera.

  • Multi-Sun Composition
    2008.12.18
    This movie is a composition of multiple solar datasets synchronized in time. The time frame is late October and early November of 2003, the time of some record-breaking solar activity.

    The background of the movie shows the view of the wide-angle coronagraphs (blue/white), or LASCO instruments, aboard SOHO. They show streams of electrons outbound from the Sun, part of the solar atmosphere. The central green image is the Sun in ultraviolet light from the EIT instrument. Note that flashes of solar flares in the ultraviolet quickly propagate out from the Sun and are visible in LASCO. These events are coronal mass ejections, or CMEs.

    Overlaid on the upper left is a better view of the EIT ultraviolet image at a wavelength of 195 angstroms (19.5 nanometers).

    On the lower left, the orange movie is the EIT ultraviolet movie at 304 angstroms (30.4 nanometers).

    On the upper right is a solar magnetogram, taken by the MDI instrument. The white regions correspond to positive (north) magnetic flux and the dark regions to negative (south) magnetic flux.

    The colors for the sequences above are not real. They are chosen by convention since the properties recorded by the cameras are not visible to the human eye.

    The final image on the lower right is also from MDI. It is a combination of several optical wavelengths and is the best representation from SOHO of the Sun in visible light, as we would see it through ground-based telescopes.

    The movies that are part of this composition are also available individually on the SVS site:

  • Dynamic Earth-A New Beginning
    2016.06.16
    The visualization 'Excerpt from "Dynamic Earth"' has been one of the most popular visualizations that the Scientific Visualization Studio has ever created. It's often used in presentations and Hyperwall shows to illustrate the connections between the Earth and the Sun, as well as the power of computer simulation in understanding those connections.
    There is one part of this visualization, however, that has always seemed a little clumsy to us. The opening shot is a pullback from the limb of the sun, where the sun is represented by a movie of 304 Angstrom images from the Solar Dynamics Observatory (SDO). It is difficult to pull back from the limb of a flat sun image and make the sun look spherical, and the problem was made more difficult because the original sun images were in a spherical dome show format. As a result, the pullback from the sun showed some odd reprojection artifacts.
    The best solution to this issue was to replace the existing pullout with a new one, one which pulled directly out from the center of the solar disk. For the new beginning, we chose a series of SDO images in the 171 Angstrom channel that show a visible coronal mass ejection (CME) in the lower right corner of the solar disk. Although this is not the specific CME that is seen affecting Venus and Earth later in this visualization, its presence links the SDO animation thematically to the later solar storm. The SDO images were also brightened considerably and tinted yellow to match the common perception of the Sun as a bright yellow object (even though it is actually white).
    Please go to the original version of this visualization to see the complete credits and additional details.

Solar Physics

Additional Useful Resources: Classifying Solar Eruptions
  • Solar Dynamo
    List
    A computer simulation of how the solar magnetic field changes over the course of the 22- year solar cycle.
  • Solar Pole Flip
    2013.12.05
    Model of the solar magnetic field during the course of a solar magnetic pole flip.
  • Multi-wavelength view of a Solar Flare
    2014.05.07
    Covering optical light to gamma-rays.
  • Multi-wavelength Sun
    List
    How multiple wavelengths of light provide insight on solar physics
  • Solar Eruptions on Multiple Scales
    List
    Solar active events take place on many different spatial and temporal scales.
  • The Dynamic Solar Magnetic Field
    2016.01.29
    While the sun is well known as the overwhelming source of visible light in our solar system, a substantial part of its influence is driven by some aspects less visible to human perception - the magnetic field. Most of the solar photosphere has a magnetic field intensity of a few gauss while the active regions which form around sunspots can have magnetic fields of a few thousand gauss. Modern space-based instruments such as HMI (Helioseismic and Magnetic Imager) on the Solar Dynamics Observatory (SDO) enable us to measure the intensity of the magnetic field at the visible surface of the sun. In this visualization, the sphere represents the solar photosphere, with neutral grey indicating a magnetic field of near zero intensity, black representing a magnetic field pointing INTO the sun (south or negative polarity) and white representing a magnetic field pointing OUT of the sun (north or positive polarity). We see that these magnetic regions often appear in nearby pairs of opposite polarities - which in visible light would often correspond to a pair of sunspots. Using this measured magnetic field on the photosphere, combined with mathematical models based on Maxwell's equations and plasma physics, we can construct how the magnetic field would look above the photosphere. Here, the white magnetic field lines are considered 'closed'. The move up, and then return to the solar surface. We often see these closed lines associated with pairs of active regions on the sun. The green and violet lines represent field lines that are considered 'open'. Green represents positive magnetic polarity, and violet represents negative polarity. These field lines do not connect back to the sun but with more distant magnetic fields in space. Here we build one of the simpler magnetic field models, called Potential Field Source Surface or PFSS, to construct how the magnetic 'lines of force' might look above the sun. The PFSS model represents the simplest and most steady magnetic field possible, though here we sample the field each day to illustrate the slow changes of the magnetic structure over time, in this case between January 1, 2011 through December 30, 2014. This camera view is fixed in Carrington Heliographic coordinates, so it moves with an 'average' solar rotation value with a period of 25.38 days. The solar equator moves faster than this, and high latitudes move slower. This makes active regions near the equator appear to move to the right (on average) while higher latitude regions move leftward. Some might note that this model looks rather different than an earlier version The Sun's Magnetic Field. In the earlier version, we were interested in the magnetic field structure significantly above the solar surface and so the model is examined favoring the field lines that reach high above the photosphere. In the model presented here, we are more interested in the magnetic field around the solar active regions, so we examine the model much closer to the photosphere, which favors magnetic field lines clustered around the active regions. An artifact in this visualization is a 'jump' of change that sweeps through the magnetic loops about once per month based on the timestamp in the lower left corner. This is an artifact of the fact that these types of magnetic field measurements can only be done on one side of the sun at a time. As the sun rotates, the features disappear over the limb and new ones appear on the opposite limb. While on the far-side of the sun from Earth, we have no direct measurements. However, we do have models that can simulate the slow changes in the field while not visible from Earth (described in the science paper Photospheric and heliospheric magnetic fields by Carolus J. Schrijver and Marc L. De Rosa). The 'jump' is created at the seam where the less accurate model gets overwritten by newer data.

Magnetospheric Physics (Earth)

  • Magnetospheres vs. CMEs
    List
    Space weather modeling helps predict Earth's geomagnetic response to coronal mass ejections.
  • Earth's Magnetosphere
    2017.07.12
    Earth's magnetic field creates a 'bubble' around Earth that helps protect our planet from some of the more harmful effects of energetic particles streaming out from the sun in the solar wind. Some of the earliest hints of this interaction go back to the 1850s with the work of Richard Carrington, and in the early 1900s with the work of Kristian Birkeland and Carl Stormer. That this field might form a type of 'bubble' around Earth was hypothesized by Sidney Chapman and Vincent Ferraro in the 1930s. The term 'magnetosphere' was applied to magnetic bubble by Thomas Gold in 1959. But it wasn't until the Space Age, when we sent the first probes to other planets, that we found clear evidence of their magnetic fields (though there were hints of a magnetic field for Jupiter in the 1950s, due to observations from radio telescopes).
  • Aurora Mosaic
    2009.07.07
    A view of an auroral substorm from multiple ground-based cameras.
  • Reconnection in Earth's Magnetosphere
    2007.01.17
    Animation of the reconnection process in Earth's magnetotail.
  • Geospace Coordinate Systems
    2014.10.08
    Coordinate systems used in studying the near-Earth plasma environment.
  • Radiation Belts & Plasmapause
    2014.11.26
    The near-Earth space enviroment is a complex interaction between Earth's magnetic field, cool plasma moving up from Earth's ionosphere, and hotter plasma coming in from the solar wind. This interactions combine to maintain the radiation belts around Earth. Plasma interactions can generate sharply delineated regions in these belts. In addition to the inner and outer radiation belts, the cooler plasma of the plasmasphere interacts so that it keeps out the higher-energy electrons from outside its boundary (called the plasmapause). In this visualization, the radiation belts (rainbow-color) and plasmapause (blue-green surface) surround Earth, its structure largely determined by Earth's dipole magnetic field (represented by cyan curved lines). The radiation belt is sliced open, simultaneously revealing representative confined charged particles spiraling around the magnetic field structure. Yellow particles represent negative-charged electrons, blue particles represent positive-charged ions. However, if realistically scaled for particle mass and energies, the spiral motion would not be visible at this distance so particle masses and size scales are adjusted to make them visible. The inner blue-green plasmapause boundary is then sliced open to reveal more of the inner structure of the radiation belts, including the innermost belt.

Planetary Magnetospheres

  • Jupiter's Magnetosphere
    2017.07.12
    Earth's magnetic field creates a 'bubble' around Earth that helps protect our planet from some of the more harmful effects of energetic particles streaming out from the sun in the solar wind. Some of the earliest hints of this interaction go back to the 1850s with the work of Richard Carrington, and in the early 1900s with the work of Kristian Birkeland and Carl Stormer. That this field might form a type of 'bubble' around Earth was hypothesized by Sidney Chapman and Vincent Ferraro in the 1930s. The term 'magnetosphere' was applied to magnetic bubble by Thomas Gold in 1959. But it wasn't until the Space Age, when we sent the first probes to other planets, that we found clear evidence of their magnetic fields (though there were hints of a magnetic field for Jupiter in the 1950s, due to observations from radio telescopes).
  • Saturn's Magnetosphere
    2017.07.12
    Earth's magnetic field creates a 'bubble' around Earth that helps protect our planet from some of the more harmful effects of energetic particles streaming out from the sun in the solar wind. Some of the earliest hints of this interaction go back to the 1850s with the work of Richard Carrington, and in the early 1900s with the work of Kristian Birkeland and Carl Stormer. That this field might form a type of 'bubble' around Earth was hypothesized by Sidney Chapman and Vincent Ferraro in the 1930s. The term 'magnetosphere' was applied to magnetic bubble by Thomas Gold in 1959. But it wasn't until the Space Age, when we sent the first probes to other planets, that we found clear evidence of their magnetic fields (though there were hints of a magnetic field for Jupiter in the 1950s, due to observations from radio telescopes).
  • Uranus' Magnetosphere
    2017.07.12
    Earth's magnetic field creates a 'bubble' around Earth that helps protect our planet from some of the more harmful effects of energetic particles streaming out from the sun in the solar wind. Some of the earliest hints of this interaction go back to the 1850s with the work of Richard Carrington, and in the early 1900s with the work of Kristian Birkeland and Carl Stormer. That this field might form a type of 'bubble' around Earth was hypothesized by Sidney Chapman and Vincent Ferraro in the 1930s. The term 'magnetosphere' was applied to magnetic bubble by Thomas Gold in 1959. But it wasn't until the Space Age, when we sent the first probes to other planets, that we found clear evidence of their magnetic fields (though there were hints of a magnetic field for Jupiter in the 1950s, due to observations from radio telescopes).
  • Neptune's Magnetosphere
    2017.07.12
    Earth's magnetic field creates a 'bubble' around Earth that helps protect our planet from some of the more harmful effects of energetic particles streaming out from the sun in the solar wind. Some of the earliest hints of this interaction go back to the 1850s with the work of Richard Carrington, and in the early 1900s with the work of Kristian Birkeland and Carl Stormer. That this field might form a type of 'bubble' around Earth was hypothesized by Sidney Chapman and Vincent Ferraro in the 1930s. The term 'magnetosphere' was applied to magnetic bubble by Thomas Gold in 1959. But it wasn't until the Space Age, when we sent the first probes to other planets, that we found clear evidence of their magnetic fields (though there were hints of a magnetic field for Jupiter in the 1950s, due to observations from radio telescopes).

Upper Atmosphere Physics

  • Exploring Earth's Ionosphere: Limb view
    2017.01.13
    This visualization presents several 'Reference models' for studying Earth's ionosphere. It presents a close-up view of Earth's limb and ionospheric data-driven models, over a fixed geographic location - off the Atlantic coast of South America. Reference models are used to define well-established knowledge and facilitate mapping out areas for future exploration. The models might be described as semi-empirical, in that they are generated using many measurements at a varietly of locations, and those measurements are used to constrain a theoretical model which is used to estimate measurements at locations where an actual measurement is not available. Three models important in ionospheric physics are presented in this visualization.

    International Reference Ionosphere (IRI)

    This model provides parameters such as electron temperature and density, ion temperature and the densities of various ions (O+, H+, He+, NO+, O2+). In this visualization, we display the atomic oxygen positive ion (a single atom ion) density at an altitude of 350 kilometers. On the limb of Earth, we present a vertical cross-section of the model, illustrating how the density varies with altitude and providing an altitude scale for comparison. This dataset exhibits two notable characteristics.
    1. Daily variation: The oxygen ion density increases during the day and then decreases after nightfall. This is due to photoionization by solar ultraviolet light, which increases with sunrise to a maximum at local noon, and then decreases towards evening.
    2. Appleton Anomaly: One of the more striking features of the ion density is the daytime enhancement is split into two regions, distributed symmetrically above and below the magnetic equator. This feature was discovered by Edward Appleton in 1946. It is now understood to be an effect of the interaction of Earth's geomagnetic field with upper atmosphere electric fields, and often referred to as the 'fountain effect,' explained in 1965. The electric fields lift ions and electrons upward by E-cross-B drift (Plasma Zoo). At higher altitudes, the upward drift decreases and the geomagnetic field and gravity dominate the motion, guiding the charged particles earthward.

    Horizontal Wind Model (HWM)

    This model provides speed and direction of horizontal (parallel to Earth's surface) winds constructed from over 70 million ground-based and satellite measurements. Two altitude levels are displayed in this visualization: 350 kilometers (same altitude as the IRI oxygen ion data) in violet glyphs, and 100 kilometers (white glyphs). This model only extends to 60 degrees latitude, so there are gaps around the poles in this visualization. One of the most notable characteristics in this dataset, particularly the 350 kilometer data, is how the winds are driven by the daily solar heating cycle. As the sun rises, the upper atmosphere is heated by solar ultraviolet light. This creates a high-pressure region which drives the atmosphere away from direct sunlight; westward in the morning and eastward in the afternoon. As the sun sets and the atmosphere cools, we see the wind reverse, filling in the now cooler and lower-pressure region.

    International Geomagnetic Reference Field-12 (IGRF-12)

    This model provides the structure of Earth's magnetic field which is a dominant influence on the motion of electrons and ions in the ionosphere. The geomagnetic field changes very slowly over decades. For this visualization, we display only a few field lines (golden wire-like structures) near the geomagnetic equator. As we observe the daily variation of the data, particularly the oxygen ions, we see the Appleton anomaly is hedged in by the low-latitude geomagnetic field.

    References

  • Interface to Space: The Equatorial Fountain
    2018.01.31
    This is a visualization of the Equatorial Fountain process in the ionosphere, whereby ions are driven away from the equator forming ion density enhancements to the north and south of the equator. This visualization is depicted near 50 degrees west longitude, where the magnetic equator crosses the geographic equator. Magnetic field lines near Earth are represented by the gold lines. Particles appear in a blue-white flash, representing the point where atoms are ionized, becoming positively charged and releasing an electron. Now these charged particles can 'feel' the near-Earth electric and magnetic fields. Their motion becomes a combination of circular gyromotion (see Plasma Zoo: Gyromotion in Three Dimensions) due to the magnetic field and E-cross-B drift (see Plasma Zoo: E-cross-B Drift). At higher altitudes, the electric field is weaker, reducing the vertical motion, and the ion motion becomes dominated by the magnetic field and gravity, allowing the ion to 'slide' down the magnetic field line back to Earth. At lower altitudes, the ions combine with free electrons in a process called recombination, represented by a red flash and fading of the particle trail. A slice of data from the IRI (International Reference Ionosphere) model represents the density of singly-ionized oxygen atoms is faded-in to compare to the particle motion. Red represents high ion density, green represents low ion density. The camera finally pulls out from Earth, providing an overview of the enhanced ion density (red) above and below the magnetic equator on the dayside of Earth. This enhancement was discovered by Edward Appleton in 1946. The Fountain effect is just one of the many of complex processes which occur in the layer of thinning atmosphere that forms Earth's interface to the space environment. A conceptual inventory of some of these processes are presented in the graphic at Terrestrial Atmosphere ITM Processes. What creates the dayside near-Earth electric field? As the sun warms Earth's atmosphere during the day, the temperature and pressure differences create wind flows. In the upper atmosphere, where the solar ultraviolet photons also break atoms into negative-charged electrons and positive-charged ions, these winds carry the charges creating currents and electric fields. The major current from this process is called the equatorial electrojet and travels along the magnetic equator (not quite aligned with the geographic equator). This motion of charges also creates a west-to-east directed electric field. Are the particles in this visualization at a realistic scale? The particles in this visualization are generated to be representative of the motion in the fountain effect to the appropriate altitudes and latitudes, but items such as the size of the gyromotion, and the particle size, are not to be regarded as physically accurate.

    References

  • Ionosphere & CINDI
    2008.12.15
    The Coupled Ion Dynamics Investigation (CINDI) is a joint NASA/Air Force funded Ionospheric plasma sensor. This animation shows how the ionosphere changes between Daytime and nighttime.
  • 4-D Ionosphere
    2008.04.30
    NASA-funded researchers have unveiled a new '4D' live model of Earth's ionosphere at the Space Weather Workshop, Boulder, CO. Without leaving home, anyone can fly through the dynamic layer of ionized gases that encircles Earth at edge of space itself. All that's required is a connection to the Internet. Airline flight controllers can use this tool to plan long-distance flights over the poles, saving money and time for flyers.
  • Notcilucent Clouds from Space
    2007.12.10
    Noctilucent clouds are a seasonal feature in Earth's polar regions.

Narrated Movies

Wave & Plasma Zoo

A collection of visualizations illustrating the different microscopic and macroscopic phenomena observed in electromagnetic waves and plasmas.
  • Gyromotion in 2-Dimensions
    2015.02.02
    Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations. Consider a magnetic field which fills a region of space with uniform intensity and direction. Here we represent that magnetic field (designated with the letter 'B') as a cyan (light green) arrow, its direction representing the direction of the field vector. One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). In the simplest case, this curves the particle path into a circle. The direction of the force also depends on the charge of the particle, with negative particles (labelled '-') being directed in circles in a sense opposite to positive particles (labelled '+'). If we view along the direction the magnetic field is pointing, we will see that the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. In this visualization, we have two charged particles, with the same mass and speed, one positive and one negative, moving in a plane. The magnetic field is uniform and directed perpendicular to the plane. Under these conditions, we see that the two charged particles, starting out in the same direction, have their trajectories bent into circles and traverse the circular path in opposite directions. Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed.
  • Gyromotion in 3-Dimensions
    2015.02.02
    Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations. Consider a magnetic field which fills a region of space with uniform intensity and direction. Here we represent that magnetic field (designated with the letter 'B') as a cyan (light green) arrow, its direction representing the direction of the field vector. One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). In the simplest case, this curves the particle path into a circle. The direction of the force also depends on the charge of the particle, with negative particles (labelled '-') being directed in circles in a sense opposite to positive particles (labelled '+'). If we view along the direction the magnetic field is pointing, we will see that the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. In this visualization, we have two charged particles, with the same mass and speed, one positive and one negative, moving in a 3-dimensional space. Similar to the resuts we see in Plasma Zoo: Gyromotion in Two Dimensions, we see that the two charged particles, starting out in the same direction, have their trajectories bent into circles and traverse the circular path in opposite directions. The magnetic field is uniform and directed perpendicular to the plane. In this case, the circular path of the particle becomes a helical path. Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed.
  • Particle Drift in Magnetic Gradient
    2015.02.02
    Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations. One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). The resulting force directs the motion in a curve such that if we view along the direction the magnetic field is pointing, we will see the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. Consider a magnetic field which fills a region of space with uniform intensity and direction. Here we represent that magnetic field (designated with the letter 'B') as a cyan (light green) arrow, its direction representing the direction of the field vector. In examples Plasma Zoo: Gyromotion in Two Dimensions and Plasma Zoo: Gyromotion in Three Dimensions, we looked at cases where the magnetic field has a constant magnitude and direction through the region of space. But what happens if the magnetic field intensity varies in the region where the particles are moving? Such changes in intensity with position are called gradients. When a road is sloping, such as on a hillside, we describe the angle of the slope as the grade of the road, which is a term derived from the similar concept. In this example, the magnetic field is constant in one direction, but is stronger further away from the observer (represented by the longer cyan arrow) and weaker closer to the observer (represented by the shorter cyan arrow). So what happens with the particle motion? In regions where the magnetic field is stronger the gyro-radius is smaller - the particle wants to move in a tighter circle. In regions where the field is weaker, the gyro-radius is larger - the particle wants to move in a tighter circle. The net effect of the gyro-radius changing as the particle moves is these differing gyro-radii add up to make the particle slowly drift in one direction. Note that the particles drift in opposite directions depending on their electric charge is positive ('+') or negative ('-'). While the positive charge is moving away from the observer, and a negative charge is moving towards the observer, these two motions contribute to a net positive charge away from the observer. This motion in a magnetic gradient drives the ring current (Wikipedia) in Earth's magnetosphere. Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed.
  • Field-Aligned Current
    2015.02.02
    Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations. One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). The resulting force directs the motion in a curve such that if we view along the direction the magnetic field is pointing, we will see the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. In the previous examples (Plasma Zoo: Gyromotion in Two Dimensions, Plasma Zoo: Gyromotion in Three Dimensions and Plasma Zoo: Particle Drift in a Magnetic Gradient) we examined the motion of charged particles exclusively in magnetic fields, represented by cyan arrows and the letter 'B'. In this example, we include a constant electric field, designated by a magenta arrow and the letter 'E', which will point in the same direction as the magnetic field. We again include two charged particles of the same mass and speed and with positive ('+') and negative ('-') charge. As in the examples before, the charged particles are directed into circular motions (gyro-motion) by the magnetic field, moving around the circular path in opposite directions. In this case, the electric field adds an additional motion. The positive charge ('+') accelerates in the direction of the electric field, so its path forms a helix with pitch that changes as the particle moves faster in the direction of the electric field (rather like stretching of a spring). The negative charge ('-') accelerates similarly, but in the opposite direction. These motions combine to form a net (positive) current in the upward direction. This configuration is sometimes referred to as a field-aligned current in the literature. It may also be called a Birkeland current, after Kristian Birkeland (Wikipedia) who suggested their role in the formation of the aurora in the early 1900s. Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed. A new version with a revised camera motion to better illustrate the charge particle motion along the electric field was added February 9, 2015.
  • E-cross-B Drift
    2015.02.02
    Motions of charged particles in electromagnetic fields are important in understanding the behaviors of plasmas in space. In Plasma Zoo, we present visualizations of particle motions in simple electromagnetic field configurations. One of the more fundamental motions of charged particles in a magnetic field is gyro-motion, or cyclotron motion. If a charged particle is moving in a magnetic field, the particle experiences a force perpendicular to the direction of the charge motion and the field. This direction is determined by the Right-Hand Rule (Wikipedia). The resulting forcedirects the motion in a curve such that if we view along the direction the magnetic field is pointing, we will see the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. In the previous examples (Plasma Zoo: Gyromotion in Two Dimensions, Plasma Zoo: Gyromotion in Three Dimensions and Plasma Zoo: Particle Drift in a Magnetic Gradient) we examined the motion of charged particles exclusively in magnetic fields, represented by cyan arrows and the letter 'B'. In this example, like Plasma Zoo: Field-Aligned Current (Birkeland Current), we include a constant electric field, designated by a magenta arrow and the letter 'E', but this time it will point in a direction at right angles (perpendicular) to the magnetic field. We again include two charged particles of the same mass and speed and with positive ('+') and negative ('-') charge. As in the examples before, the charged particles are directed into circular motions (gyro-motion) by the magnetic field, moving around the circular path in opposite directions. If we view along the direction the magnetic field is pointing, we will see that the positive particles gyrate anti-clockwise while the negative particles gyrate clockwise. But this time, the perpedicular electric field creates an effect that is counter-intuitive. While you might expect the positive particles to drift in the direction of the electric field, and the negative particles to drift opposite the electric field direction, in fact, the positive and negative particles drift in a direction perpendicular to the electric and magnetic field directions! This is called E-cross-B drift, sometimes written ExB drift from the mathematical notation. To understand why this is, consider just the motion of the positive particle. As the particle accelerates in the electric field, the magnetic field starts directing the particle in a curved path. The faster the particle, the larger the radius of the curved path. Eventually, the curving of the path redirects the positive particle so it is moving in a direction opposite the electric field. Through this region, the electric field acts to slow down the particle, and the curvature of the path gets smaller. The net effect of these competing motions is a net motion perpendicular to the fields. The negative particle is accelerated in the opposite sense by the electric field, which gives a net motion in the same direction. This configuration also has the interesting effect that a neutral plasma moving perpendicular to a magnetic field, will induce an electric field perpendicular to both the magnetic field and the plasma motion. This electric field is important in the motion of the solar wind. Important Note: The example here shows particles with the same speed and mass. If the masses are different (for example, a positive proton has about 1836 times more mass than an electron), the radius of the gyromotion will be proportionally larger for the same speed.
  • Shock Drift Acceleration (SDA)
    2016.11.14
    Particle acceleration mechanisms are one of the more challenging questions in space physics. Hot plasmas are generally very simple to understand, but occasionally we detect charged particles accelerated to unusually high energies that cannot be explained by a basic hot plasma. We usually find these high-energy charged particles associated with interfaces between domains of plasma - regions where a plasma dominated by one configuration of charges and magnetic fields, collides with a different configuration of charges and magnetic fields. This collision can generate changes in the field configuration which can accelerate charged particles. One proposed mechanism for this acceleration is called shock drift acceleration (SDA), illustrated in this visualization. A blob of plasma on the left is colliding with plasma on the right. The region where they collide forms a layer (the vertical red band) representing the shock wave that forms. We have chosen a camera which travels along with the shock wave, so the wave is stationary to our camera. The region has a magnetic field (represented by cyan, or light green, arrows) directed out of the plane of the screen, towards the viewer. The magnetic field has a different intensity in the two regions. An electric field is also present (magenta arrows), directed 'up' in the view and the interaction of the two regions in the shock wave generates an increase in the electric field. We launch a batch of electrons and protons in the left blob towards the region of the shock. In the magnetic field, the positive proton trajectories curve downward, while the negative electron trajectories curve upward. A group of electrons (yellow, with '-' sign on them) with a range of speeds and directions, along with a group of 'protons' (blue, with a '+' sign on them) are launched towards the shock. Actually, the yellow particles are not quite electrons as their mass is large, set to only one-fifth of the proton mass, so their motion will stay in the scale of this screen view. As the particles pass through the shock, they get a little 'push' from the slightly stronger electric field which exists there. Depending on the direction of entry and the charge of the particle, the field can either accelerate or decelerate the particle. Once they pass through the shock, they enter the region with a slightly stronger magnetic field which tightens the radius of their orbits. The new orbit may still be large enough to allow the particles to pass back into the increased electric field of the shock, adding a little more energy to the particle. The E-cross-B drift moves electron and positive ions in the same general direction. But their gyro motions are still driven in opposite directions. Therefore, once the center of the gyro motion circle passes to the right side of the shock, each pass of the particles back into the shock allows them to gain a little more energy. Positive particles get a boost in the same direction as the electric field, while negative particles get a boost in the opposite direction to the electric field. They keep receiving this addition speed boost until they move clear of the shock.
  • Electromagnetic Waves and Polarization
    2017.07.07
    A huge amount of our remote sensing capability depends on the light, AKA electromagnetic radiation, which we receive from distant objects. In addition to the light's wavelength and frequency (which tell us the speed of the radiation - which can be slower than 'c' in some environments), the polarization of the waves can reveal more insights on the source of the light, and the region through which it has passed.
  • Plasma Zoo: Gyroresonant Scattering
    2018.05.29
    In regions like planetary magnetospheres, a number of more complex interactions can occur between charged particles, fields, and electromagnetic waves. One of these processes is called gyroresonant scattering or alternatively pitch-angle scattering.