11:50 AM | *Solar cycle 24 declining even more quickly than forecast*

While the sun has been spotless more than half the time this year, there are currently three sunspot regions visible to Earth.  This particular channel is especially good at showing areas where cooler dense plumes of plasma (filaments and prominences) are located above the visible surface of the sun. Many of these features either can't be seen or appear as dark lines in the other channels. The bright areas show places where the plasma has a high density. Image courtesy NASA/SDO

Overview
Solar cycle 24 is rapidly approaching the next solar minimum and while the sun currently has three sunspots region visible to Earth, much of the year has seen a spotless sun.  In fact, the sun has been blank on 73 days in 2018 which amounts to 57% of the year.  The last time the sun was this blank in a given year on a percentage basis was 2009 during the last solar minimum when 71% of the time was spotless. That last solar minimum actually reached a nadir in 2008 when an astounding 73% of the year featured a spotless sun - the most spotless days in a given year since 1913. The current solar cycle is the 24th solar cycle since 1755 when extensive record-keeping of sunspot activity began and it on pace to be the weakest sunspot cycle since cycle 14 peaked in February 1906. As a result of the last unusually long and deep solar minimum and very weak bounce back during solar cycle 24’s maximum phase, much attention will be focused on the rapidly approaching solar minimum and subsequent solar cycle #25 to see if the sun may be entering an extended period of quiet.
 

The circled region shows the recent actual monthly sunspot numbers (in blue) and the predicted values (in red) from the official forecast by NOAA/NASA’s Solar Cycle Prediction Panel.  According to NOAA/NASA, the smoothed, predicted sunspot number for April-May 2018 is about 15; however, the actual monthly values have been significantly lower. Source

Discussion
Solar cycle 24 is declining more quickly than forecast and all indications are the upcoming solar minimum may be even quieter than the last one which was the deepest in nearly a century.  Solar cycle 24 began in December 2008 and had minimal activity until early 2010 and then reached a maximum in April 2014.  Solar cycle 24 continues a recent trend of weakening solar cycles which began when solar cycle 21 peaked around 1980 and some are already forecasting the next solar cycle (#25) to be even weaker than this current weak one.

Total solar irradiance (TSI) is a measure of the absolute intensity of solar radiation, integrated over the entire solar irradiance spectrum.  The top plot shows the TSI since 1978 as observed from nine different satellites and it is currently in decline as the next solar minimum rapidly approaches.  The bottom plot shows the sunspots number in recent solar cycles which have been in an overall weakening trend since the solar cycle 21 peaked around 1980. Source

It’s important to note that solar minimum is a normal part of the sunspot cycle. Sunspots have been disappearing every 11 years or so since 1843 when German astronomer Samuel Heinrich Schwabe discovered the periodic nature of solar activity. Sometimes they go away for decades, as happened during the Maunder Minimum of the second half of the 17th century and early part of the 18th century in a cold period now referred to as the “Little Ice Age”. 

The “Maunder Minimum” was an extended period of low solar activity during the latter half of the 17th century and the beginning of the 18th century in a cold period now referred to as the “Little Ice Age”.

 
One of the natural consequences of lower solar activity during the solar minimum phase is the weakening of the solar wind and its magnetic field which, in turn, allows for the intensification of cosmic rays and easier access to Earth. In addition, the total solar irradiance (TSI) drops as solar minimum approaches and there has already been a measured drop of nearly 0.1% compared to the output during the solar cycle 24 maximum phase which took place from 2012-2014. A change of 0.1% may not sound like much, but the sun deposits a lot of energy on the Earth, approximately 1,361 watts per square meter. Summed over the globe, a 0.1% variation in this quantity exceeds all of Earth’s other energy sources (such as natural radioactivity in Earth’s core) combined. NASA recently launched a new sensor (TSIS-1) to the International Space Station to closely monitor these TSI changes.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com