The sun has gone quiet…solar cycle 24 continues to rank as one of the weakest cycles more than a century
Overview Ten days ago, the sun was quite active and peppered with several large spots. Now the sun has gone quiet and it is nearly completely blank. It appears that the solar maximum phase for solar cycle 24 may have been reached and it is not very impressive. It looks as if this solar cycle is “double-peaked” (see below) which is not all that uncommon; however, it is somewhat rare that the second peak in sunspot number during the solar max phase is larger than the first. In fact, this solar cycle continues to rank among the weakest on record which continues the recent trend for increasingly weaker cycles. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906. Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its maximum phase. For this reason, many solar researchers are calling this current solar maximum a “mini-max”. Solar cycle 24 began after an unusually deep solar minimum that lasted from 2007 to 2009. In fact, in 2008 and 2009, there were almost no sunspots, a very unusual situation during a solar minimum phase that had not happened for almost a century.
Consequences of a weak solar cycle First, the weak solar cycle has resulted in rather benign “space weather” in recent times with generally weaker-than-normal geomagnetic storms. By all Earth-based measures of geomagnetic and geoeffective solar activity, this cycle has been extremely quiet. However, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle. In other words, there is still a chance for significant solar activity in the months and years ahead.
Second, it is pretty well understood that solar activity has a direct impact on temperatures at very high altitudes in a part of the Earth’s atmosphere called the thermosphere. This is the biggest layer of the Earth’s atmosphere which lies directly above the mesosphere and below the exosphere. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation and are highly dependent on solar …