Solar Cycle 24 Main Discussion XI Jul 7, 2011 9:26:43 GMT
Post by breakingitdown on Jul 7, 2011 9:26:43 GMT
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 : )