{ "id": 4560, "url": "https://svs.gsfc.nasa.gov/4560/", "page_type": "Visualization", "title": "Alfvén Waves - Basic", "description": "Alfven waves represented by undulation in the magnetic field vector. || AlfvenWaveBasic_staticXwide_inertial.HD1080i.0300_print.jpg (1024x576) [158.5 KB] || AlfvenWaveBasic_staticXwide_inertial.HD1080i.0300_thm.png (80x40) [4.6 KB] || AlfvenWaveBasic_staticXwide_inertial.HD1080i.0300_web.png (320x180) [71.9 KB] || WavesOnly (1920x1080) [128.0 KB] || AlfvenWaveBasic_staticXwide.HD1080i_p30.mp4 (1920x1080) [34.0 MB] || AlfvenWaveBasic_staticXwide.HD1080i_p30.webm (1920x1080) [4.9 MB] || ", "release_date": "2017-03-31T09:00:00-04:00", "update_date": "2023-05-03T13:47:47.746075-04:00", "main_image": { "id": 415648, "url": "https://svs.gsfc.nasa.gov/vis/a000000/a004500/a004560/AlfvenWaveParticles.Basic.MediumGyro.vzAlfvenDG4_staticXclose_inertial.HD1080i.0200_print.jpg", "filename": "AlfvenWaveParticles.Basic.MediumGyro.vzAlfvenDG4_staticXclose_inertial.HD1080i.0200_print.jpg", "media_type": "Image", "alt_text": "A closeup view of the particles from the movie above.", "width": 1024, "height": 576, "pixels": 589824 }, "main_video": { "id": 415638, "url": "https://svs.gsfc.nasa.gov/vis/a000000/a004500/a004560/AlfvenWaveBasic_staticXwide.HD1080i_p30.mp4", "filename": "AlfvenWaveBasic_staticXwide.HD1080i_p30.mp4", "media_type": "Movie", "alt_text": "Alfven waves represented by undulation in the magnetic field vector.", "width": 1920, "height": 1080, "pixels": 2073600 }, "main_credits": { "Visualizations by": [ { "name": "Tom Bridgman", "employer": "Global Science and Technology, Inc." } ], "Scientific consulting by": [ { "name": "Daniel J. 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Less known is the fourth state of matter, plasma, when the atoms themselves break down into electrons and ions. Plasmas are actually more common in the universe than the better known solid, liquids and gas, because they tend to exist at temperatures and densities beyond our human experience.

Plasmas exhibit behaviors similar to fluids and gases, but with added complexity of containing magnetic (and occasionally electric) fields. In 1942, Hannes Alfvén combined the mathematics of fluid mechanics and electromagnetism to predict that plasmas could support wave-like variation in the magnetic field, a wave phenomenon that now bears his name, Alfvén waves. This would become the foundational paper for the study of magneto-hydrodynamics, or MHD, for which Alfvén would receive the Nobel prize in 1970.

Since they were hypothesized, Alfven waves have been seen in plasmas on Earth and in space.

Like conventional fluids, plasmas can support waves, but with more variety than in conventional fluids. The waves initially proposed by Alfvén are considered \"basic\". They have a characteristic that they are compressional, which means that magnetic field variation of the Alfvén waves is in the direction of the wave motion. Charged particles moving through a plasma with these waves have very little alteration of their trajectory. These types of waves are represented in the visualizations below.

But Alfvén waves can exhibit more variety. A variant is the \"kinetic\" Alfvén wave which is transverse, with strong magnetic field variation perpendicular to the wave motion, so can trade energy between the different frequencies which might propagate through a plasma. This also means it can exchange energy with the particles in the plasma, in some cases, trapping particles in the troughs of the waves and carrying them along. Visualizations of kinetic Alfvén waves are presented at Alfvén Waves - Kinetic.

References/Links
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In defiance of all logic, its atmosphere gets much, much hotter the farther it stretches from the Sun’s blazing surface.Temperatures in the corona — the tenuous, outermost layer of the solar atmosphere — spike upwards of 2 million degrees Fahrenheit, while just 1,000 miles below, the underlying surface simmers at a balmy 10,000 F. How the Sun manages this feat remains one of the greatest unanswered questions in astrophysics; scientists call it the coronal heating problem. A new, landmark mission, NASA’s Parker Solar Probe — scheduled to launch no earlier than Aug. 11, 2018 — will fly through the corona itself, seeking clues to its behavior and offering the chance for scientists to solve this mystery.From Earth, as we see it in visible light, the Sun’s appearance — quiet, unchanging — belies the life and drama of our nearest star. Its turbulent surface is rocked by eruptions and intense bursts of radiation, which hurl solar material at incredible speeds to every corner of the solar system. This solar activity can trigger space weather events that have the potential to disrupt radio communications, harm satellites and astronauts, and at their most severe, interfere with power grids.Above the surface, the corona extends for millions of miles and roils with plasma, gases superheated so much that they separate into an electric flow of ions and free electrons. Eventually, it continues outward as the solar wind, a supersonic stream of plasma permeating the entire solar system. And so, it is that humans live well within the extended atmosphere of our Sun. To fully understand the corona and all its secrets is to understand not only the star that powers life on Earth, but also, the very space around us.Read more on NASA.gov. || ", "release_date": "2018-07-25T14:00:00-04:00", "update_date": "2023-05-03T13:46:35.139868-04:00", "main_image": { "id": 405605, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a012900/a012903/CHP_Discovery_1080_4.00001_print.jpg", "filename": "CHP_Discovery_1080_4.00001_print.jpg", "media_type": "Image", "alt_text": "Discovering the Sun’s Mysteriously Hot Atmosphere Something mysterious is going on at the Sun. In defiance of all logic, its atmosphere gets much, much hotter the farther it stretches from the Sun’s blazing surface.Temperatures in the corona — the Sun’s outer atmosphere — spike to 3 million degrees Fahrenheit, while just 1,000 miles below, the underlying surface simmers at a balmy 10,000 F. How the Sun manages this feat is a mystery that dates back nearly 150 years, and remains one of the greatest unanswered questions in astrophysics. 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