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Explosive Activity of the Sun -- Don Michels

08/10/1999


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Table of Contents

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Earthís dipole magnetic field is aligned approximately parallel to the rotation axis

As with Earth, the Sun also has a dipole field (sometimes!)

The solar wind

Charged particles, electrons and protons, when moving in a magnetic field, do not move across the direction of the field, they move only parallel to it. In fact, they spiral around and move along the field lines, getting trapped on them, like beads on a necklace string.

The Sunís dipole magnetic field is stretched and distorted by the outflowing solar wind

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Origins of solar activity: 1. The Sun, like Earth, has an internal dynamo, that generates a magnetic field. 2. Unlike Earth, the Sunís outer layer rotates differentially. The differential is large: visible features at the equator rotate fully in about 25 days, whereas at the poles, they take nearly 35 days. This complicates the Sunís magnetism, making it highly variable.

Owing to the differential rotation of outer solar layers, magnetic field lines within the convection zone in the Sun experience shear, stress, and a resulting magnetic bouyancy. When they break through the visible photospheric surface they float high into the corona, often forming arcades of beautiful arches.

At times of minimum solar activity there are just a few such isolated loop systems, but as the sunspot cycle approaches its maximum (as at present!) the corona becomes filled with numerous overlying and interacting arcades. This is a signal that the Sunís field can no longer be represented as a simple dipole.

Galileo was the first to notice sunspots. He immediately began counting them and recording the numbers. In the ensuing centuries, we have learned that the sunspot number varies with an 11-year periodicity.

In the outer regions, Earthís dipole field is also distorted by the flow of the solar wind.

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Some interesting facts about the Sun*

Energetic plasma releases in the solar corona

Author: Don Michels

Email: michels@lasco11.nascom.nasa.gov

Workshop Home Page: http://www-istp.gsfc.nasa.gov/istp/outreach/workshop/

Above is background material for archival reference only.

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