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SlowSolarWind
Slow Solar Wind (dotted redlines)
• 200-600 km/s• Very Low Density: about 5-
10 particles (electrons andprotons) per cm3 at 1AU
• Highly variable, canchange by factor of 2 in 24hrs
• Lower latitudes, thusaffects the planets morethan fast wind
• Associated with closedfield lines Extreme UV from SOHO Spacecraft
SlowSolarWind
• Slow solar windoriginates fromclosed magneticfield lines at base ofhelmet streamersthat are confined tolow latitudes
FastSolarWind
Fast Solar Wind (solid redlines)
• ~ 750 km/s• Very Low Density: about
half as dense as the slowsolar wind
• Associated with open fieldlines (coronal holes)
Extreme UV from SOHO Spacecraft
Coronal Holes
• A coronal hole is a region of very low plasma density in thecorona that shows up as a dark region in X-ray images.
• The correspond to regions ofthe solar magnetic field thatextend radially away from thephotosphere (no looping).
• The low plasma density isdue to the radial nature of thefield, plasma escapes bymoving along the magneticfield.• The result is a directed beamof very high velocity plasma.
ParkerSpiral• Sun rotates (~25 day
period at equator)• Solar wind flows out
radially with magneticfield “frozen” in it
• Field lines tied to thesun, so rotation resultsin a spiral magneticfield
• Resultant field is like alawn sprinkler
• Eugene Parkertheorized this in the1950’s
ParkerSpiralandthePlanets
• At increasing distancesfrom the sun, themagnetic field gets moreand more twisted
• 450 at Earth• 900 at Jupiter’s orbit
(~10 AU)
Wheredoesthesolarwindstop?
• Other stars have winds too, called stellarwinds
• Hence, universe is not really a vacuum.• Tenuous magnetized plasma (and a little dust)
known as the local interstellar medium (LISM)fills interstellar space.
• But “near” to our sun, the solar winddominates over the LISM.
• This bubble where the solar wind dominates isknown as the heliosphere
Theboundarybetweenthesolarwindandinterstellarmedium
1. Bow shock: regionwhere the LISM beginsto slow
2. Termination shock:region where the solarwind begins to slow
3. Heliopause: regionwhere the solar windand LISM are inbalance
The two magnetized plasmas “bounce” off of each other in the outersolar system. At the boundary:
Doweknowexactlywheretheheliopauseislocated?
• Voyager I and II spacecrafts• Launched in 1977• First close-up images of
Jupiter, Saturn, Uranus,Neptune
• Presently about 104 and 84AU from earth (or 13/11 lighthours)