(Chart Image Copyrighted (c) 2002 by Solar Terrestrial Dispatch. May be used if copyright notice is retained.)
As we proceed through the decline of the current solar cycle, a popular opinion seems to have arisen with the media and others that geomagnetic activity and auroral activity ("northern / southern lights") will begin to subside ever increasingly (if not halt altogether). We present the plot above in order to bring some truth to this myth.
The plot above shows the last six solar cycles and our progress through the current solar cycle (cycle number 23). The smoothed monthly sunspot numbers for each month since 1932 are shown as a series of interconnected (small) black dots. This plot line is extended at the end using the color green to depict the predicted behavior of sunspot numbers through to the next solar minimum (which is currently expected to occur in late 2006). Our current stage in the solar cycle (as of March/April 2002) is the location in the graph where the black and green plot lines intersect.
Superimposed on this plot are red dots that represent the months during each solar cycle where at least one or more severe geomagnetic storm intervals occurred (where the planetary Kp index reached at least 8 - Kp indices are rated from 0 [dead quiet] to 9 [extremely disturbed storm conditions]). Such high Kp indices are typically only observed during major to severe geomagnetic storms and they are often associated with significant sightings of auroral activity across the world.
The blue dots are identical to the red dots except that they are plotted horizontally. This is done to retain perspective. Since the horizontal axis of the chart has much higher resolution than the vertical axis, dots that appear near the solar maximums may appear (falsely) to be more numerous than during the decline of the solar cycles because the red dots are spaced closer together. This illusion largely disappears when you examine the blue dots.
The chart portrays the fact that severe geomagnetic and auroral storm intervals can occur at almost any time during the solar cycle, but there is a slightly heavier preference for the years around the solar maximum and during the declining years of the solar cycle. Intervals of severe activity are less frequent during the years immediately around the solar minimum and during the ascending years of the sunspot cycle.
By comparing our current position in the solar cycle with similar positions in the last 6 solar cycles, it becomes clear that we are perhaps only about half way through the interval where severe space weather storms occur most frequently during the solar cycle. In fact, we are just barely beginning to see the real decline in this cycles sunspot numbers (most solar maximums have a fairly lengthy plateau of several years and we are just barely at the end of this plateau).
Historically, some of the most intense geomagnetic and auroral storms have occurred during the declining years of the solar cycle. For example, the most severe geomagnetic storm on record occurred on 17 September 1941. That was 53 months after the solar maximum! To place this into better perspective, the Sun is currently in about its 23rd post-solar maximum month (solar maximum occurred about 23 months ago). In fact, this 1941 storm occurred during a time when the sun was closer to the solar minimum than the solar maximum. Severe geomagnetic storms have also occurred within just a few months of the Sun's actual solar minimum as well, which confirms the fact that significant space weather activity can occur at any time during the solar cycle.
We hope that this information will help dispell the popular myth that geomagnetic and auroral storm activity on the Earth will stop now that we have passed the solar maximum. This couldn't be further from the truth. Statistically, the declining years of the solar cycle are the most stormy in terms of geomagnetic and auroral activity.
It is safe to say that we can expect at least several more years of potentially violent space weather activity.
Monitor that activity with your own space weather monitoring system here.