Solar Magnetic Cycles
Unlike the Earth's magnetic field which changes slowly, the Sun's magnetic field can change quite rapidly. Small bits of field can change over a few minutes. During solar flares a whole section of the Sun's magnetic field can be disrupted in minutes or hours. For example, on April 14, 1994, a large-scale eruptive event occurred which resulted in a cloud of solar material weighing 1 billion tons moving towards the Earth at a speed of over 1 million miles per hour.
The most rapid changes to the Sun's magnetic field occur locally, in restricted regions of the magnetic field. However, the entire structure of the Sun's global magnetic field changes on an 11-year cycle. Every 11 years, the Sun moves through a period of fewer, smaller sunspots, prominences, and flares - called a "solar minimum" - and a period of more, larger sunspots, prominences and flares - called a "solar maximum." A maximum and a minimum, taken together, make up one solar cycle. During the 11 years, the strongest magnetic fields (in sunspots) slowly migrate towards the Sun's equator from locations about midway to the Sun's poles. After 11 years, when the next cycle starts, the magnetic field poles are reversed.
Diagrams illustrating past recorded solar activity are presented next:
Solar Maximum
Solar Minimum
Of course, 2001 saw the largest displays of solar activity ever recorded. All predictions have come true, the eleven-year cycle is more than just a theory.
There are instances that do not fit the pattern however. For example, in the late 1600's (A.D. 1645-1715) the cycle ceased briefly in what is known as the Maunder Minimum. It coincided with a period of colder-than-average temperatures in northern Europe called the Little Ice Age. Neither the Maunder Minimum nor the 11-year cycle is fully understood.
Now that you have a bit of Solar-Terrestrial physics under your belt, let’s move along to Space Weather.
Space Weather
Everything between the Sun and the Earth is part of the solar-terrestrial environment. The solar wind blows across the magnetosphere at about a million miles per hour, and in the event of a coronal mass ejection, larger solar flare, or high-speed energy stream, a geomagnetic storm can occur.
The Sun rotates at about one revolution per twenty-seven (27) Earth days. Any features coming up on the rising horizon of the visible solar surface will take anywhere from eleven to fourteen days to move across to the setting horizon. The surface of the Sun has storms, similar in magnitude as those found on the gas giant Jupiter, but they are not visible in the visible light spectrum. Images of solar activity are presented next:
For a vivid example of some recient activity, check out these links to cnn.com:
http://www.cnn.com/2001/TECH/space/02/16/sun.flips/index.html
http://www.cnn.com/2001/TECH/space/03/30/sun.activity/index.html
http://www.cnn.com/2001/TECH/space/04/04/solar.storm/index.html
To see the latest SOHO (Solar and heliospheric Observatory) satellite images, most of which are only delayed a few minutes or hours, go to:
http://www.sohowww.nascom.nasa.gov/SWN/
To find out what are current space weather conditions and to see geomagnetic activity forecasts, go to:
Copyright © 2001 Jared Freedman
