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Solar Physics header image

The Solar Wind

THE SUN 

Why We Study the Sun <whysolar.htm> 
The Big Questions <quests.htm> 
Magnetism - The Key <the_key.htm> 

SOLAR STRUCTURE 

The Interior <interior.htm> 
The Photosphere <surface.htm> 
The Chromosphere <chromos.htm> 
The Transition Region <t_region.htm> 
The Corona <corona.htm> 
The Solar Wind <sun_wind.htm> 
The Heliosphere <heliosph.htm> 

SOLAR FEATURES 

Photospheric Features <feature1.htm> 
Chromospheric Features <feature2.htm> 
Coronal Features <feature3.htm> 
Solar Wind Features <feature4.htm> 

THE SUN IN ACTION 

The Sunspot Cycle <sunspots.htm> 
Solar Flares <flares.htm> 
Post Flare Loops <loops.htm> 
Coronal Mass Ejections <cmes.htm> 
Surface and Interior Flows <flows.htm> 
Helioseismology <p_modes.htm> 

The MSFC Solar Group 

_The People <people.htm>_
Their Papers <papers.htm> 

RESEARCH AREAS 

Flare Mechanisms <flaremag.htm> 
3D Magnetic Fields <3dfields.htm> 
The Solar Dynamo <dynamo.htm> 
Sunspot Cycle Predictions <predict.htm> 
Coronal Heating <coronal_heating.htm> 
Solar Wind Dynamics <wind_dynamics.htm> 

PREVIOUS PROJECTS 

Orbiting Solar Observatories <OSO.htm> 
Skylab <skylab.htm> 
Solar Maximum Mission <smm.htm> 
SpaceLab 2 <sl2.htm>
MSSTA <mssta.htm> 
The GOES SXI Instruments <sxi.htm> 
Yohkoh <yohkoh.htm>

CURRENT PROJECTS 

MSFC Tower Magnetograph  <maggraph.htm>
MSFC Dome Magnetograph  <exvm.htm>
The RHESSI Mission <http://hessi.ssl.berkeley.edu/> 
The Ulysses Mission <ulysses.htm> 
The GONG Project <http://helios.tuc.noao.edu/homepage.html> 
The SOHO Mission <http://sohowww.nascom.nasa.gov/> 
The TRACE Mission <http://vestige.lmsal.com/TRACE/> 
The Sun in Time (EPO) <suntime/suntime.htm> 

FUTURE PROJECTS 

The Solar B Mission <solar-b.stm> 
The STEREO Mission <http://sd-www.jhuapl.edu/STEREO/> 
The SDO Mission <http://sdo.gsfc.nasa.gov/> 
Solar Probe
<http://science.msfc.nasa.gov/ssl/pad/solar/suess/SolarProbe/SolarProbe.htm> 
Interstellar Probe <suess/Interstellar_Probe/ISP-Intro.html> 

The solar wind streams off of the Sun in all directions at speeds of
about 400 km/s (about 1 million miles per hour). The source of the solar
wind is the Sun's hot corona <corona.htm>. The temperature of the corona
is so high that the Sun's gravity cannot hold on to it. Although we
understand why this happens we do not understand the details about how
and where the coronal gases are accelerated to these high velocities.
This question is related to the question of coronal heating
<quests.htm#Coronal Heating>.

DialPlot.jpg (12900 bytes) <images/DialPlot.jpg>

/Click on image for larger version./

Solar Wind Variations

The solar wind is not uniform. Although it is always directed away from
the Sun, it changes speed and carries with it magnetic clouds
<feature4.htm#Magnetic Clouds>, interacting regions
<feature4.htm#Corotating Interactive Regions> where high speed wind
catches up with slow speed wind, and composition variations
<feature4.htm#Composition Variations>. The solar wind speed is high (800
km/s) over coronal holes <feature3.htm#Coronal Holes> and low (300 km/s)
over streamers <feature3.htm#Helmet Streamers>. These high and low speed
streams interact with each other and alternately pass by the Earth as
the Sun rotates. These wind speed variations buffet the Earth's magnetic
field and can produce storms in the Earth's magnetosphere.

The /Ulysses/ <ulysses.htm> spacecraft has now completed one orbit
through the solar system during which it passed over the Sun's south and
north poles. Its measurements of the solar wind speed, magnetic field
strength and direction, and composition have provided us with a new view
of the solar wind.

The Advanced Composition Explorer
<http://helios.gsfc.nasa.gov/ace/ace.html> (ACE) satellite was launched
in August of 1997 and placed into an orbit about the L1 point between
the Earth and the Sun. The L1 point is one of several points in space
where the gravitational attraction of the Sun and Earth are equal and
opposite. This particular point is located about 1.5 million km (1
million miles) from the Earth in the direction of the Sun. ACE has a
number of instruments that monitor the solar wind and the spacecraft
team provides real-time information on solar wind conditions at the
spacecraft.

Solar wind conditions for the last seven days
<http://sec.noaa.gov/ace/MAG_SWEPAM_7d.html>

Solar wind conditions for the last 24 hours
<http://sec.noaa.gov/ace/MAG_SWEPAM_24h.html>

*Web Links*

*Advanced Composition Explorer Mission
<http://helios.gsfc.nasa.gov/ace/ace.html> *

*The Ulysses Mission <http://helio.estec.esa.nl/ulysses/> *

*Return to Solar Physics Home <default.htm> *

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* Author: Dr. David H. Hathaway, david.h.hathaway at nasa.gov
<mailto:david.h.hathaway at nasa.gov>, (256) 961-7610
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812   *

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* Responsible Official: Dr. John M. Davis, john.m.davis at nasa.gov, (256)
961-7600
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812 *

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* Curator </ssl/curator.htm> *

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* Last revised 2003 January 06 - D. H. Hathaway*