Solar Variability and Terrestrial Climate

• Report rights infringement
• published: 09 Dec 2017
• views: 3

Jan.8, 2013:  In the galactic scheme of things, the Sun is a remarkably constant star.While some stars exhibit dramatic pulsations, wildly yo-yoing in size and brightness, and sometimes even exploding, the luminosity of our own sun varies a measly 0.1% over the course of the 11-year solar cycle.There is, however, a dawning realization among researchers that even these apparently tiny variations can have a significant effect on terrestrial climate.A new report issued by the National Research Council (NRC), "The Effects of Solar Variability on Earth's Climate," lays out some of the surprisingly complex ways that solar activity can make itself felt on our planet.Understanding the sun-climate connection requires a breadth of expertise in fields such as plasma physics, solar activity, atmospheric chemistry and fluid dynamics, energetic particle physics, and even terrestrial history.No single researcher has the full range of knowledge required to solve the problem.To make progress, the NRC had to assemble dozens of experts from many fields at a single workshop.The report summarizes their combined efforts to frame the problem in a truly multi-disciplinary context.One of the participants, Greg Kopp of the Laboratory for Atmospheric and Space Physics at the University of Colorado, pointed out that while the variations in luminosity over the 11-year solar cycle amount to only a tenth of a percent of the sun's total output, such a small fraction is still important."Even typical short term variations of 0.1% in incident irradiance exceed all other energy sources (such as natural radioactivity in Earth's core) combined," he says.Of particular importance is the sun's extreme ultraviolet (EUV) radiation, which peaks during the years around solar maximum.Within the relatively narrow band of EUV wavelengths, the sun’s output varies not by a minuscule 0.1%, but by whopping factors of 10 or more.This can strongly affect the chemistry and thermal structure of the upper atmosphere.Several researchers discussed how changes in the upper atmosphere can trickle down to Earth's surface.There are many "top-down" pathways for the sun's influence.For instance, Charles Jackman of the Goddard Space Flight Center described how nitrogen oxides (NOx) created by solar energetic particles and cosmic rays in the stratosphere could reduce ozone levels by a few percent.Because ozone absorbs UV radiation, less ozone means that more UV rays from the sun would reach Earth's surface.Isaac Held of NOAA took this one step further.He described how loss of ozone in the stratosphere could alter the dynamics of the atmosphere below it."The cooling of the polar stratosphere associated with loss of ozone increases the horizontal temperature gradient near the tropopause,” he explains.“This alters the flux of angular momentum by mid-latitude eddies.[Angular momentum is important because] the angular momentum budget of the troposphere controls the surface westerlies." In other words, solar activity