Scientists Discover New Physics Missing From Existing Models of Magnetic Reconnection

Magnetotail Current Sheets

The Earth’s magnetosphere can undergo global compression due to solar wind. This compression creates thin and non-ideal current sheets in the magnetotail. NASA’s MMS spacecraft fly through this compressed, thin current sheet, and reveal that a small-scale electric field forms (blue line on plot) which generates a highly sheared electron flow that drives lower hybrid waves (bright spots in plot) while the plasma density is relatively flat (orange dashed line on plot). Understanding the formation of these current sheets and the small-scale structures and dynamics within is important because they are thought to be important in the processes that initiate magnetic reconnection, which can drive intense space weather in the Earth’s magnetosphere. Credit: Dr. Bill Amatucci, NRL

Micro-Scale Current Sheets Unleash Macro-Scale Space Weather

NRL scientists discover new physics missing from existing models of magnetic reconnection.

While movies show Earth as existing in a calm, pristine corner of the universe, in reality the near-Earth space environment is dangerous and dynamic. On any given day, hot charged particles and blobs of plasma, called the solar wind, travel from the sun and are deflected by the Earth’s magnetic field, causing beautiful aurora around north and south poles. During solar storms, however, the solar wind can compress the Earth’s magnetic field, causing the magnetic field lines to rearrange and reconnect (also known as magnetic reconnection), shooting hot, dense plasma back toward the Earth. Processes like these are commonly referred to as space weather. Because of the effect that these space-based disruptions can have on key elements of our modern society, such as telecommunication systems and power grids, obtaining a good understanding of these processes is just as essential as understanding ground-based weather.

A major challenge in understanding magnetic reconnection in the Earth’s magnetosphere has been the difficulty in resolving the smaller kinetic-scale processes in satellite observations. NASA’s Magnetospheric Multi-Scale (MMS) spacecraft, however, recently made it possible to make detailed studies of this previously unseen micro-scale physics.

Scientists at the U.S. Naval Research Laboratory (NRL) in Washington, D.C. have been using MMS data to study the micro-scale physics that occurs in the Earth’s magnetotail, a thin portion of the magnetosphere that is illustrated in Figure 1. The magnetotail is formed when the Earth’s magnetosphere is compressed by the solar wind into a thin current sheet, creating an ideal location to study magnetic reconnection.

NRL scientists recently made the first observation of plasma waves driven by highly sheared electron flows (velocity shear) in one of these compressed current sheets. The velocity shear is created in the current sheet when a localized electric field oriented perpendicular to the background magnetic field arises as the current sheet is compressed. These waves are a rich source of local enhanced diffusivities, which can trigger the magnetic reconnection process.

NRL scientists also used these observations to discover a key component missing from existing theoretical models of thin current sheets and magnetic reconnection—an ambipolar electric field that forms perpendicular to the current sheet and intensifies as the current sheet undergoes strong compression. A new theoretical model has since been developed and indicates that the ambipolar electric field can self-consistently develop in response to global compression of the plasma. This in turn produces the velocity shear that can drive the waves observed in the spacecraft data. The current driven by the electron flow also changes the magnetic field profiles and allows for the formation of current sheets that are both thin and non-ideal, features which cannot simultaneously be explained by the standard models. The theoretical model results shine a new light on the key connection between the micro-scale and macro-scale physics.

These findings challenge the existing understanding of the physics of thin current sheets, and the identification of the shear-driven plasma waves also establishes the significance of the localized ambipolar electric field and the highly inhomogeneous conditions that drive the physics. This deeper understanding of the physics at small scales, when combined with the larger scale models, will lead to a more complete knowledge of the global dynamics and especially the energy flux in the heliosphere from the sun into the Earth’s immediate neighborhood that affects near-Earth space weather.

Meeting: 63rd Annual Meeting of the APS Division of Plasma Physics

GI01.00002: Structure and Dynamics of a Compressed Current Sheet in the Earth’s Magnetotail

This work is supported by the NRL base funds.

2 Comments on "Scientists Discover New Physics Missing From Existing Models of Magnetic Reconnection"

  1. warning warning mind the gap
    its an aerial attack aerial bombardment due in 30 minutes
    all hands on deck deploy defense shield operation immediately
    red alert red alert
    deploy your first line of defense move with speed like a military machine speed trumps perfection
    the offensive attack is occurring 150,000,000 kilometres out
    the defensive line where is it
    do you know your location location location
    do you have a coordinate position
    do you know your left flank from your right
    do you know your aerial flight path
    do you know the terrestrial force operations theatre
    do you know the submarine or sub terrain force position
    right deploy your defense shield and lets have a total shut down against a force as powerful as your dream sandcastle being attacked by a hurricane
    your first line of defense
    your location location location are you summer solstice bound are you equatorial aligned or are you winter solstice bound 365 days of the year divide by two = 182.5 defensive positions are they all mapped out and that damn leap year day
    now from what i read you seem to be facing the sun but you call it a tail what sort of nomenclature are you using
    its noon on any of the 182.5 defensive lines days but what line of latitude is the direct line from the centre of the earth to the centre of the sun or the storm force that on its way
    now that the defense line has been organised like a military operation lets look to our first defensive shield
    no its not at your fingertips its way way way way out there at the orbit of mercury .?au 198,000,000 kilometres out is it transit aligned or is it a spy in the enemy camp is it going to assist the storm by directing it earthward or is it an ally and deflecting it off course
    well you know the rest there is no need to go is there
    second defensive line venus .?au 61,000,000 kilometres out female spy or ally
    third defensive line the moon 384,400 kilometres out female spy or ally
    and now our fourth line of defense
    this is broken into two leading and lagging
    whats it called again the leading van allen belt 40,000 kilometres out macroscale
    the lagging van allen belt 8,000 kilometres microscale my foot
    so the defense has been deployed where the heck is the attacker
    red alert read alert aerial bombardment has arrived dont you see it
    what size is it what does it look like do you hear anything the silence is deafening
    the attacking wavefront is 24,000 kilometres wide and high and its about to make its full frontal assault
    its 40,000 kilometres out and wham bang wallop and slam
    its stopped halted its unsteady on its feet its hovering there 40,000 to 47,000 kilometres out and its steadying itself to stand up tall again
    so from your picture you are showing a thin current sheet in profile extending from the earth equator out to where and as you say its a tail i hope its in the direction of the solar sun face
    and if it is then that thin current sheet in yellow is where the some of the attacking force has broken through the fourth shield
    both the leading 40,000 kilometre one
    and the lagging 8,000 kilometre one where your space station and communication satelites are hovering for a direct hit heck its time to get out of here
    dont care if the internet and the telephones facebook and snapchat go down
    no its the full frontal force that still heading inwards 8000 more kilometres to go and hit the surface of the terrestrial globe or marine globe and ionised water particles coriolis like take to the air and dump their load on u or me preferably u in a typhoon force
    thats the scouting mission accomplished by the attacking force
    now for the real attack coming to a comments page some day near u

  2. where are they where are they
    they were out there 40,000 kilometres i saw them didnt you
    hawk eye pipes up
    out there at 12 noon i saw them it was the biggest force i ever saw 24,000 kilometres wide double the size of ours and they split into five
    we just recieved sneak reconn force came straight through at the equator line we took a hit
    but the other lot look
    one has weaved its way dawn side of the globe and its advancing at twice the rate as we saw it before what is everyone going to wake up to over there
    the other force it snook the other way dusk side and is slowing down into a nice cool breeze
    the other third split it went northwards to reconnect to north dynamo polarity
    the last fourth split it went southwards to reconnect to south dynamo polarity
    the gas thing is most of the force has gone submarine under the south pole and aerial over the north pole that is 6000 kilometres of the solar stream in both poles above over them
    and the first and second which went dawn and dusk well 6000 kilometres of the wave front by passed by did you feel the breeze
    so what the heck was that all about
    the war with the sun has begun has anyone been killed yet any casualities any wounded bring on the first aid the medics let them in to bring the bleeding and wounded to heal the war aint over its just begun as the solar maximum starts to ramp up its cycle
    why why sun are you attacking me and we and blue ball earth
    why my friend dont you know its your iron core im after to tear and rip your heart out anyone dead yet

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