lecture4

# lecture4 - ECE2984 Lecture4: SPACEENVIRONMENT:THESOLARWIND

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ECE 2984 Lecture 4: SPACE ENVIRONMENT: THE SOLAR WIND Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space

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Plasma A plasma is an ionized gas consisting of approximately equal umbers f ositively d egatively arged articles numbers of positively and negatively charged particles. Plasmas are characterized by “ Collective Behavior ”i nt h e presence of externally applied electromagnetic fields (i.e. the electromagnetic fields act over long distances and the plasma particles move together as a fluid). Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space
Plasma Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space

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Space Plasmas Charged particles in plasmas like to spiral (gyrate) along magnetic field lines. For the most part, the charged particles prefer not to move across magnetic p, g p p g field lines unless there is an electric field, or the magnetic field is tangled. The mathematical description of a plasma is called “ Magnetohydrodynamics (or “MHD”) and is derived by combining: 1) MAXWELL’S EQUATIONS which describe the electromagnetic behavior 2) NAVIER STOKES EQUATIONS which describe the fluid behavior e HD uations n e sed escribe hole ost f aves lasmas The MHD Equations can be used to describe a whole host of waves in plasmas: Ion acoustic waves (c.f. regular sound waves) Alfven waves (c.f. twanging the magnetic field lines like guitar strings) Slow and Fast waves that travel across magnetic field lines In most space plasmas the density is so low that the particles can be assumed to never collide with each other (i.e. the plasma is “collisionless”). Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space For example, the mean distance between collisions for a solar wind particle is larger than the Sun Earth distance.
The Corona s we learned last lecture, the Corona is the outermost Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space As we learned last lecture, the Corona is the outermost layer of the Sun’s atmosphere.

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Coronal Magnetic Field ORONAL HOLE: CORONAL HOLE: Open Magnetic Field Lines Low Plasma Density Dark ORONAL STREAMER: CORONAL STREAMER: Closed Magnetic Field Lines High Plasma Density Bright Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space
The Coronal Magnetic Field The Sun’s main field changes polarity every solar cycle ( 11 years) to Joseph Baker (ECE Dept) Lecture 4: The Solar Wind ECE 2984:Exploration of Space give a solar magnetic cycle with period of about 22 years.

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Coronal Mass Ejections Coronal Mass Ejections (CMEs) are oradic jections f rge ounts sporadic ejections of large amounts of mass (10 15 10 16 g) at speeds as high as 1000 km/s.
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## This note was uploaded on 09/19/2011 for the course ENGE 1114 taught by Professor Twknott during the Fall '06 term at Virginia Tech.

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lecture4 - ECE2984 Lecture4: SPACEENVIRONMENT:THESOLARWIND

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