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Several recent research papers presented new discoveries about our Sun, the waxing and waning of sunspots, and the flipping of its magnetic field. Of special interest is how this impacts our weather 93 million miles away.
While I have no relevant expertise, this research is worth reporting. The principal authors are R. J. Leamon, S. W. McIntosh, and D. R. Marsh of the University of Maryland, NASA Goddard, and the National Center for Atmospheric Research.
It seems obvious that the Sun dominates Earth’s weather and climate — variations in solar exposure account for the differences between day and night, and between summer and winter. Yet, as the authors say, trying to link solar variations to our weather “has become ‘third-rail science’ — not to be touched at any cost”. I commend those who pursue knowledge without regard to political correctness.
Previous attempts to use sunspots to predict Earth’s weather had little success, perhaps due to the considerable variability of the 11-ish year sunspot cycle. Below is a close-up of several sunspots, with Earth superposed for scale.
Fairly recently, scientists realized sunspot cycles are correlated with the Sun’s magnetic field — its north and south magnetic poles flip every 11 years, on average. Sunspots increase when the magnetic field is strong in either polarity, and decrease as the field weakens.
The Sun’s cycles also affect its UV radiation, which varies by 7%, on average, between cycle maxima and minima, with the highest energy emissions varying by up to 85%. These changes can have major impacts in Earth’s stratospheric winds and ozone levels.
The new research has identified more reliable predictors of solar cycles. So called “terminators” occur when opposite polarity magnetic bands migrate to the solar equator and cancel one another. These abrupt events definitively mark the end of one solar cycle and the start of the next.
Major changes occur throughout the Sun within days of a terminator, including a rapid increase in magnetic field strength that partially shields our Solar System from external (“galactic”) cosmic rays.
A single cosmic ray can initiate a cascade of interactions (shown at left) that ionize myriad air molecules, creating a nucleation site for cloud formation.
The impact of cloud cover over our oceans can be very significant. In normal “neutral” conditions, modest cloud cover over the southwestern Pacific (e.g. Australia) reduces surface air pressure relative to the southeastern Pacific (e.g. Tahiti). This drives warm moist air westward, bringing rain (shown in red) to Australia and the western Pacific, as shown on the left below.
However, dense clouds over Tahiti (middle image) disrupt the normal airflow, causing El Niño: hot in the mid-pacific; drought in Australia; rain in California and Gulf Coast states; and less rain in the Midwest and East Coast. Conversely, very dense clouds over the southwestern Pacific (right image) have the opposite effect, causing La Niña. Hurricanes are more active in the Atlantic during La Niña, and in the Pacific during El Niño. Each weather pattern harms some regions and benefits others.
The authors say “dense clouds [in this region] shift some 30º East within one month…after the drop in cosmic rays”.
U.S. NOAO estimates the 1998 El Niño caused 24,000 deaths and cost $50 billion. Better prediction of these cycles could mitigate these enormous losses.
The authors examined records of solar activity over the last 140 years, and created the “band-o-gram” shown below, with dotted vertical lines marking cycle terminators. The durations of these 13 cycles range from 9.0 to 13.9 years, and average 10.75 years.
The upper plot shows the number of sunspots each day (black dots), and the 50-day running average (red band).
The middle “butterfly diagram” plots the latitude of each sunspot each day. Note that sunspots move toward the equator as each cycle matures.
The band-o-gram shows solar magnetic activity by latitude. Red and blue represent opposite polarities that flip from one cycle to the next. Terminators occur when the mid-latitude red and blue regions meet and cancel one another at the solar equator.
Comparing terminator events with our weather, the authors find “a coherent regular behavior…a striking change from a strong El Niño to La Niña at the terminator”.
While we still cannot explain the varying duration of solar cycles, we can now better determine when cycles end and begin. By knowing when the “clock starts”, we hope to better predict major weather changes.
The authors predict the next two terminators will occur in April 2020, and October 2031. They predict a strong El Niño in 2019, more El Niños in 2026 and 2031, and La Niñas in 2020-21, 2027-28, and 2032-33. They expect a particularly active Atlantic hurricane season in 2020-21.
Best Regards,
Robert
March 2019
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