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Still Images and Movies, of surges of solar wind on Earth's Magnetosphere - triggering auroras are located on Auroral Activity Page 3 page
QUESTION:
There are areas on the Web Site where questions are asked and those question have simple answers. Like this one. We will review a little background through some background information so the reader will not have to bounce around to other pages.
The answer starts below with the solar wind
The solar wind is an outflow of solar particles and portions of the Sun's magnetic field that have been ripped away from the Sun. The Sun's magnetic field is often called the Interplanetary Magnetic Field ( IMF ). Hopefully the answer to exactly what makes up solar particles will come quickly as the samples from the Genesis project are analyzed.
The IMF is projected as a spiral shape, its massive size encompasses all of the generally accepted nine planets. The spiral effect is due in part to the Sun's rotation. The rotational effect of the expanding solar wind effects the vector of forces manipulating the size and shape of Earth's magnetic field. We observe modulation of some of the solar wind's attributes in its turbulence, cavitations, and cannibal effects.
Using the GMS ( Geocentric Solar Magnetic Coordinate System ) Coordinate System, the north - south
component of the magnetic field vector, Bz, indicates, in the short run, the turbulence, eddies, and whirlpools generated by the not so steady or smooth outer laminates of the solar wind stream. In our opinion, Bz is a transient measurement. This was discussed when we answered the question of "how does Bz enter into HF propagation forecasts"
Note: material at the end of this link is strictly a personal observation. It is not the policy of this Web Site to publish conjecture. This was a direct question. It was handled on the Web Site rather than return e-mail because the question may have had a wider interest than one reader. Statements made concerning Bz and the vector's role in propagation forecasting are NOT based on fact.
Forces that accelerate main portions of the solar wind stream ( to > 500 km/sec ) and increase the transient north - south, often rapid changing, Bz, include: Coronal Holes, Coronal Mass Ejection, collapsing filaments, and solar flares.
The above processes go on throughout Earth's year. These gusts sweep past Earth year-round, which returns us to the original question: "why do auroras appear more often during spring and autumn?"
ANSWER: The Sun and Earth shift their positions in a number of planes as they go about their dependant orbits. Earth's magnetic field is mostly enclosed by the magnetosphere. The area where Earth's magnetosphere ( approximately 50,000 km in diameter NASA ) contacts the Sun's Interplanetary Magnetic Field ( encloses all of the planets and more ) is called the magnetopause.
During Earth's spring and fall the relative positions of the Sun's IMF and Earth's magnetosphere are positioned such that magnetic lines of force of the two bodies line up with one another.
Earth's magnetosphere points primarily in a northward direction. The direction and shape of the magnetosphere can be distorted by the solar wind. The distortion starts with the solar wind pushing on the boarder of Earth's magnetosphere at the magnetopause.
The velocity of the solar wind can distort the magnetosphere to the point that magnetic lines of force from Earth can line up with the magnetic lines of force from the Sun's IMF and flow directly into one another ( closing the magnetic loop ). This can occur when the IMF points strongly southward. Solar wind particles can penetrate the magnetosphere, and if persistent and with sufficient energy, cause ionization of the ionosphere.
To cause ionization of the ionosphere sufficient to cause auroras and effect high frequency radio wave propagation, the Sun's IMF must stay continually pointing south for a long enough period of time that solar wind particles can penetrate the magnetosphere and cause ionization.
Auroras are formed by ionization of the ionosphere caused by the influx of the solar wind.
LEFT: "Coronal holes appear as dark areas in ultraviolet and x-ray images of the Sun. A solar wind stream flowing from this hole buffeted Earth's magnetosphere on Sept. 10th 2002 and triggered Northern Lights. Credit Steele Hill and SOHO." NASA
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Juha Kinnunen,
Jyväskylä, Finland
10 Sep 2002
What's your geomagnetic latitude? Check out these NOAA maps: North America, Eurasia, South Africa & Australia, South America
Auroral Activity Report from the NOAA Polar-orbiting Operational Environmental Satellite (POES). This report will be available during times of High Power Flux over the poles - when viewing auroral activity is most likely. Data for the North and South Poles are included.
POES satellites continually monitor the Power Flux carried by
the electrons and protons that
produce the aurora. Data is collected over a
single pass of the POES satellite over the polar regions. This pass takes about
25 minutes. Data from each pass is analyzed using the NOAA
POES historical database which represents over 100,000 satellite passes.
"The database is used to construct a statistical pattern of auroral power flux for each of ten levels of auroral activity as defined by the Total Power Dissipation illustrated on the following table." NOAA
|
Total Power Dissipation in Gigawatts |
Activity Index |
Kp Index |
|
4-6 |
3 |
1+ |
|
10-16 |
5 |
2+ |
|
24-39 |
7 |
3+ |
|
61-96 |
9 |
5- |
"Energetic auroral particles (primarily electrons) not only produce the visible aurora but also greatly influence the properties of the ionosphere and are connected with strong electrical currents (as much as several million amperes) that flow in the ionosphere and connect along the geomagnetic field to dynamo processes at high altitude in the magnetosphere." NOAA
Thus, this same display provides a similar "best-guess" estimate of the geographic locations that may be subject to geomagnetic fluctuations that result from electrical currents flowing in the ionosphere. These currents produce auroral activity and the same radio propagation paths that may be degraded because of increased absorption of the radio signal by the disturbed ionosphere. edited KC4COP
Go to Explanation of Auroral Activity displayed on World Map. (automatically updated every 10 minutes) slow loading
Go to Northern Hemisphere Plot (automated updates every 10 minutes) slow loading
Go to Southern Hemisphere Plot ( automated updates every 10 minutes) slow loading
What's your geomagnetic latitude? Check out these NOAA maps: North America, Eurasia, South Africa & Australia, South America
Putting It All Together -- Can I, or can't I, see the Aurora? A very good "How-To" article by NOAA
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Page was last updated on 19 December, 2007 11:47 AM CDT