10:30 AM | *New study suggests the Sun is even more important than we thought on Earth's climate due to its impact on cosmic rays*

This colorized picture of the sun is a mosaic of ultraviolet images from the orbiting TRACE satellite sensitive to light emitted by highly charged iron atoms. Growing in number, the intricate structures visible are the Sun's hot active regions with temperatures over a million degrees Fahrenheit and their associated magnetic loops (courtesy NASA) 

Overview
It has long been widely accepted that the sun is absolutely critical to all weather and climate here on Earth and yet there are still some aspects of this connection that are not too well understood and even controversial.  For example, there has been the belief by many atmospheric scientists that cosmic rays which penetrate the Earth’s atmosphere from outer space can play a significant role in the formation of clouds which, in turn, has a direct impact on climate.  Solar activity has a direct impact on the ability of cosmic rays to actually reach the Earth’s atmosphere.  A just published study has confirmed the notion that cosmic rays can indeed be an important player in Earth’s weather and climate and the role of the sun is critical.  
 

Cosmic rays and clouds
Cosmic rays are high-velocity particles of enormous energy that bombard the Earth from outside the solar system. They are accelerated toward Earth by distant supernova explosions and other violent events, are an important form of space weather. The exact origin of cosmic rays has long been somewhat of a mystery in the field of astronomy. Cosmic rays may produce showers of secondary particles that penetrate and impact the Earth's atmosphere and sometimes even reach the surface. The connection between cosmic rays and clouds has been under investigation in recent years and somewhat controversial. Some researchers have held the belief that cosmic rays hitting Earth's atmosphere create aerosols which, in turn, seed clouds and thereby help in the formation of clouds.  This would make cosmic rays an important player in weather and climate. Other researchers, however, have been dubious.  The skeptics have maintained that although some laboratory experiments have supported the idea that cosmic rays help to seed clouds, the effect is likely too small to substantially affect the cloudiness of our planet and have an important impact on climate.

Findings from a just published study
A new study just published in the Aug. 19th issue of Journal of Geophysical Research: Space Physics comes down in favor of cosmic rays. According to spaceweather.com, a team of scientists from the Technical University of Denmark (DTU) and the Hebrew University of Jerusalem has linked sudden decreases in cosmic rays to changes in Earth's cloud cover. These rapid decreases in the observed galactic cosmic ray intensity are known as “Forbush Decreases” and tend to take place following coronal mass ejections (CMEs) in periods of high solar activity. When the sun is active (i.e., solar storms, CMEs), the magnetic field of the plasma solar wind sweeps some of the galactic cosmic rays away from Earth.  In periods of low solar activity, more cosmic rays bombard the earth.  The term “Forbush Decrease” was named after the American physicist Scott E. Forbush, who studied cosmic rays in the 1930s and 1940s.

The research team led by Jacob Svensmark of DTU identified the strongest 26 “Forbush Decreases” between 1987 and 2007, and looked at ground-based and satellite records of cloud cover to see what happened.  In a recent press release, their conclusions were summarized as follows: "[Strong “Forbush Decreases”] cause a reduction in cloud fraction of about 2 percent corresponding to roughly a billion tonnes of liquid water disappearing from the atmosphere."

Current cosmic ray activity
We happen to be in a weak solar cycle (24) which is actually on pace to be the weakest cycle in more than one hundred years. Therefore, it would not be surprising to have relatively high cosmic ray penetration into the Earth’s atmosphere; especially, since we are now heading towards the next solar minimum phase when solar activity is generally even quieter. During solar maximum, CMEs are abundant and cosmic rays are held at bay.  

In fact, for the past year, neutron monitors around the Arctic Circle have sensed an increasing intensity of cosmic rays. Polar latitudes are a good place to make such measurements, because Earth’s magnetic field funnels and concentrates cosmic radiation there. As it turns out, Earth’s poles aren’t the only place cosmic rays are intensifying. “Spaceweather.com” has led an effort in the launching of helium balloons to the stratosphere to measure radiation, and they find the same trend increasing intensity of cosmic rays over California. Their latest data show an increase of almost 13% since 2015. [For more on this study click here]:

Cosmic rays have been steadily increasing in recent months during historically weak solar cycle 24; plot courtesy spaceweather.com and California data courtesy study sponsored by spaceweather.com 

In the plot, neutron monitor measurements from the University of Oulu Cosmic Ray Station are traced in red; gamma-ray/X-ray measurements over California are denoted in gray. The agreement between the two curves is remarkable. It means that the intensification of cosmic rays is making itself felt not only over the poles, but also over lower latitudes where Earth’s magnetic field provides a greater degree of protection against deep space radiation. There's a new section on spaceweather.com where you can monitor cosmic rays in the atmosphere.

Meteorologist Paul Dorian

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