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Post by breakingitdown on Jul 7, 2011 9:26:43 GMT
Dr. Svalgaard, What is the real definition of "time of reversal of the magnetic polar fields"? Is it the first time that the reversal takes place, e.g. March 2011 (concerning the reversal of the northern polar field)? Or is it the time when the reversal becomes more definite, e.g. end of this year or first months of 2012 (if it then will happen)? Perhaps is that the reason why www.solen.info/solar/polarfields/polarfieldsfiltered.gif did not yet mention the reversal of March 2011? During the course of a year, the solar rotation axis tips away (N pole March 7) and towards (N pole September 9) the observer by 7.25 degrees. Due to a combination of a strong concentration of the flux very near the pole and projection effects stemming from the line-of-sight field measurements, the observed polar fields vary by a factor of up to two through the year [Svalgaard et al., 1978; Babcock and Babcock, 1955] during most of the solar cycle. The onset of this variation is the important new ingredient in determining the phase within the cycle at which to compare the polar field strength with the subsequent cycle amplitude. The polar field reversal is caused by unipolar magnetic flux from lower latitudes moving to the poles, canceling out opposite polarity flux already there, and eventually establishing new polar fields of reversed polarity [Harvey, 1996]. Because of the large aperture of the WSO instrument, the net flux over the aperture will be observed to be zero (the ‘‘apparent’’ reversal) about a year and a half before the last of the old flux has disappeared as opposite polarity flux moving up from lower latitudes begins to fill the equatorward portions of the aperture. The new flux is still not at the highest latitudes where projection effects are the strongest. The result is that the yearly modulation of the polar fields is very weak or absent for about three years following the (apparent) polar field reversal. Only after a significant amount of new flux has reached the near pole regions does the yearly modulation become visible again. So, one could say that the definitive reversal is when the yearly modulation disappears. That has not happened yet. ______________________________________________ sorry to be such a Noob : P i have been avidly reading this forum since december 2007 ive come to learn quite a bit but i really would like to understand your last statement i feel the process behind it has a huge importance when it comes to understanding how this solar cycle is going to unfold. My question now is this. When the yearly modulation disappears will there be a significant change in the solar activity/surface? What implications are there when the modulation disappears? thanks : ) |
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loly
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Post by loly on Jul 7, 2011 9:55:11 GMT
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loly
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Posts: 154
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Post by loly on Jul 7, 2011 14:16:36 GMT
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Post by justsomeguy on Jul 7, 2011 14:58:30 GMT
Shhh, everyone be quiet, the sun is taking a nap...
Is this the quietest near solar max in modern history?
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Post by lsvalgaard on Jul 7, 2011 17:41:15 GMT
During the course of a year, the solar rotation axis tips away (N pole March 7) and towards (N pole September 9) the observer by 7.25 degrees. Due to a combination of a strong concentration of the flux very near the pole and projection effects stemming from the line-of-sight field measurements, the observed polar fields vary by a factor of up to two through the year [Svalgaard et al., 1978; Babcock and Babcock, 1955] during most of the solar cycle. The onset of this variation is the important new ingredient in determining the phase within the cycle at which to compare the polar field strength with the subsequent cycle amplitude. The polar field reversal is caused by unipolar magnetic flux from lower latitudes moving to the poles, canceling out opposite polarity flux already there, and eventually establishing new polar fields of reversed polarity [Harvey, 1996]. Because of the large aperture of the WSO instrument, the net flux over the aperture will be observed to be zero (the ‘‘apparent’’ reversal) about a year and a half before the last of the old flux has disappeared as opposite polarity flux moving up from lower latitudes begins to fill the equatorward portions of the aperture. The new flux is still not at the highest latitudes where projection effects are the strongest. The result is that the yearly modulation of the polar fields is very weak or absent for about three years following the (apparent) polar field reversal. Only after a significant amount of new flux has reached the near pole regions does the yearly modulation become visible again. So, one could say that the definitive reversal is when the yearly modulation disappears. That has not happened yet. ______________________________________________ sorry to be such a Noob : P i have been avidly reading this forum since december 2007 ive come to learn quite a bit but i really would like to understand your last statement i feel the process behind it has a huge importance when it comes to understanding how this solar cycle is going to unfold. My question now is this. When the yearly modulation disappears will there be a significant change in the solar activity/surface? What implications are there when the modulation disappears? thanks : ) It is sort of the other way around: at the beginning of the cycle the polar fields are strong. Then as more and more new cycle spots develop [and die] their flux slowly erodes the polar fields. At the height of the cycle the polar fields will have eroded away [and therefore do not show any annual modulation]. Following that as the cycle progresses further, the new polar fields [with opposite polarities] slowly build up until they stop growing at the next minimum [because there are no more spots to feed them]. Then the cycle repeats. |
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Post by justsomeguy on Jul 7, 2011 19:36:53 GMT
Just a thought, but could a grand minima be caused because the magnetism of the spots drops and the polar field thus get "stuck" as the magnetism of the spots is not enough to erode them, and thus the polar fields do not recycle and they break down much more slowly?
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bop
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Post by bop on Jul 7, 2011 19:39:11 GMT
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Post by lsvalgaard on Jul 7, 2011 21:14:13 GMT
Just a thought, but could a grand minima be caused because the magnetism of the spots drops and the polar field thus get "stuck" as the magnetism of the spots is not enough to erode them, and thus the polar fields do not recycle and they break down much more slowly? That might be one mechanism, but it is 'too strong' as the polar fields must be regenerated. They are 'advected' into the Sun forming the seed of the next cycle, so will soon disappear and the solar dynamo would grind to a halt. It would be difficult to start it up again. We also know from cosmic ray proxies that the solar modulation was maintained during Grand Minima. It is more likely that the magnetic cycle continued but the field was not strong enough to form visible spots. |
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loly
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Post by loly on Jul 8, 2011 16:22:43 GMT
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loly
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Post by loly on Jul 8, 2011 16:31:00 GMT
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loly
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Post by loly on Jul 9, 2011 2:53:24 GMT
Giant Explosion
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loly
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Post by loly on Jul 9, 2011 13:06:09 GMT
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loly
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Post by loly on Jul 9, 2011 19:10:50 GMT
CME:
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loly
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Post by loly on Jul 9, 2011 22:07:59 GMT
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loly
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Post by loly on Jul 10, 2011 14:55:32 GMT
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