Atmospheric Radiation Update: July 2018

July 30, 2018: As the sunspot cycle declines, we expect cosmic rays to increase. Is this actually happening? The answer is “yes.” Spaceweather.com and the students of Earth to Sky Calculus have been monitoring cosmic radiation in the atmosphere with frequent high-altitude balloon flights over California. Here are the latest results, current as of July 2018:

X-ray/gamma-ray dose rates in the stratosphere over California. Energy range: 10 keV – 20 MeV

The data show radiation levels intensifying with an approximately 18% increase in monthly averages since March 2015. This comes as sunspot counts have dipped to a ~10-year low in June and July 2018.

Cosmic rays are the subatomic debris of dying stars, accelerated to nearly light speed by supernova explosions. They travel across the galaxy and approach Earth from all directions, peppering our planet 24/7. When cosmic rays crash into Earth’s atmosphere, they produce a spray of secondary particles and photons that is most intense at the entrance to the stratosphere. This secondary spray is what we measure.


Above: An artist’s rendering of secondary cosmic rays. [more]

Sunspots and cosmic rays have a yin-yang relationship. At the peak of the sunspot cycle, strong solar magnetic fields and solar wind hold many cosmic rays at bay. During solar minimum, however, the sun’s magnetic field weakens and the outward pressure of the solar wind decreases. This allows more cosmic rays from deep space to penetrate the inner solar system and our planet’s atmosphere.

The increase is widespread. Every place in the USA where we have launched multiple balloons exhibits the same pattern. There are upward trends from coast to coast:

The plot, above, shows more than 150 stratospheric radiation measurements we have made using balloons flown over the continental USA. Because California is our home base, it is more densely sampled than other states. Adding additional points outside California remains a key goal of the monitoring program.

How do cosmic rays affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified as occupational radiation workers by the International Commission on Radiological Protection (ICRP). According to a recent study from researchers at the Harvard School of Public Health, flight attendants face an elevated risk of cancer compared to members of the general population. The investigators listed cosmic rays among several risk factors. Weather and climate may also be affected, with some research linking cosmic rays to to the formation of clouds and lightning.

In August-December 2018 we will conduct a new campaign of coordinated balloon launches from the USA (including sites in California, Washington, Kansas, Oregon, and Maine), Chile, and New Zealand to further probe the evolving cosmic ray situation. As solar activity declines we expect to find increasing radiation around the globe. Stay tuned for updates.

Lunar Eclipse and Martian Conjunction

July 25, 2018: Friday, July 27th, is a big night for astronomy. Three reasons: First, Mars will be at opposition–directly opposite the sun and making a 15-year close approach to Earth. Second, Mars and the full Moon will be in conjunction–less than 10 degrees apart. Third, the Moon will pass through the shadow of Earth, producing the longest lunar eclipse in a century.

Graphic artist Larry Koehn of ShadowandSubstance.com created this montage of the eclipse:

eclipsemontage07272018

An animation of the eclipse may be found here.

Almost everyone on Earth (except North Americans) can see the eclipse as the sunset-colored shadow of our planet swallows the Moon for almost 2 hours. During totality, the Moon will turn almost the same red color as Mars right beside it–an incredible sight.

Visibility_Lunar_Eclipse_2018-07-27
Because Mars is opposite the sun, it will rise at sunset and stay up all night long.  The best time to look is around midnight when the Moon-Mars pair will be at their highest in the sky. The Red Planet will have no trouble being seen through the glare of the full Moon because Mars itself is so luminous–almost three times brighter than Sirius, the brightest star in the sky.

People in North America will not be able to see the eclipse. The shadow play happens mostly on the opposite side of the world. They can, however, witness the conjunction. Swinging a backyard telescope between the Moon and Mars in quick succession will reveal the dusty-red martian disk alongside lunar mountains and craters. It’s a special night. Enjoy the show!

Spiders and Space Weather

July 20, 2018: Did you know that spiders can fly? Biologists call it “ballooning.” Spiders spin a strand of silk, it juts into the air, and off they go. Airborne arachnids have been found as high as 4 km off the ground. Originally, researchers thought spiders were riding currents of air, but there’s a problem with that idea. Spiders often take flight when the air is calm, and large spiders fly even when air currents are insufficient to support their weight. It’s a mystery.

Scientists from the University of Bristol may have found the solution. In a paper published in the July 5th edition of Current Biology, they proved that spiders can propel themselves using electric fields.

ballooningspider_strip

Just before ballooning, spiders adopt a posture shown here called “tiptoeing.”

“We exposed adult Linyphiid spiders (Erigone) to electric fields similar to those which naturally occur in Earth’s atmosphere,” explains the paper’s lead author, Erica Morley. “Spiders showed a significant increase in ballooning in the presence of electric fields.” A remarkable video of their experiment shows one spider flying when the fields were switched on, then landing when the fields were off again. It appears conclusive.

The electric fields spiders use for propulsion are part of Earth’s global atmospheric electric circuit (GEC)–a planet-sized circuit of electricity that researchers have known about since the 1920s. In a nutshell, thunderstorms help build up a charge difference between the ground and the ionosphere 50 km overhead. The voltage drop is a staggering 250,000 volts. This sets up electric fields linking Earth to the edge of space. Cosmic rays ionize Earth’s atmosphere, turning it into a weak conductor that allows currents to flow through the GEC. [Ref]

gec_crop

This diagram, borrowed from K. A. Nicoll’s 2014 review paper “Space Weather influences on Atmospheric Electricity,” illustrates the role of thunderstorms and cosmic rays in creating electric fields.

Spiders evolved inside the global electric circuit, so it’s no surprise that they have learned to tap into it. But how? Peter W. Gorham of the Dept. of Physics and Astronomy at the University of Hawaii notes that “the complex protein structure of spider silk includes charge-bearing amino acids glutamic acid and arginine, which might be generated in a charged state as part of the spinning process. [Alternately, those acids might be able to attract charge] from the local launching surface as strands are spun from the sharp nozzles of the spinneret.” [Ref]

Researchers have long wondered about the role of electricity in spider flight. Charles Darwin may have been the first. He wrote about it during his voyages on the HMS Beagle (1831-1836). One day, the ship was 60 miles off the coast of Argentina when the deck was inundated by ballooning spiders. “The day was hot and apparently quite calm,” he wrote, yet “I repeatedly observed the same kind of small spider, either when placed or having crawled on some little eminence, elevate its abdomen, send forth a thread, and then sail away horizontally, but with a rapidity which was quite unaccountable.” He was particularly struck by spiders using multiple strands of silk that splayed out in fan-like shapes. Instead of tangling as they moved through the air, the strands remained separate. Were they repelled by an electrostatic force? Darwin wondered in his writings. The work of Erica Morley and her collaborator Daniel Robert closes the loop on a train of thought almost 200 years old.

spiderhairs_crop

Hairs on the legs of spiders called “trichobothria” twitch when electric fields are present–a signal to the spider that ballooning may commence.

All of this raises the possibility that spiders may be affected by space weather as electric fields are perturbed by cosmic rays and solar activity. Research groups have demonstrated connections between space weather and atmospheric electricity on a variety of time scales.  Days: Coronal mass ejections (CMEs) from the sun can sweep aside cosmic rays as they pass by Earth, causing temporary reductions in atmospheric ionization as large as 30%. Our own Spaceweather.com/Earth to Sky cosmic ray balloons have measured these events. [RefMonths: Measurements at the Reading University Atmospheric Observatory in the UK have shown that voltages can fluctuate +-15% as Earth dips in and out of the heliospheric current sheet (a huge corrugated magnetic structure centered on the sun) every ~27 days. [RefYears: During the 20th century, fair weather atmospheric voltages at sites in Scotland and the UK decreased by factors of ~25% due to a long-term decrease in cosmic rays. [Ref] That slow trend is now reversing itself as cosmic rays intensify again.

Could the migration patterns of ballooning spiders be affected by space weather? “It’s entirely possible, but we simply don’t yet know,” says Morley. “The experiments we have carried out are mostly lab-based, which helps eliminate confounding variables. A next step in the project is to take this all into the field and look for patterns. Factoring in solar activity could be very interesting.”

Stay tuned.

Three Weeks Without Sunspots

July 17, 2018: As July 17th comes to a close, the sun has been without spots for 21 straight days. To find an equal stretch of spotless suns in the historical record, you have to go back to July-August 2009 when the sun was emerging from a century-class solar minimum. This is a sign that the sun is entering another solar minimum, possibly as deep as the last one.

bigblanksun

Solar minimum is a normal part of the solar cycle. Every 11 years or so, sunspot production sputters. Dark cores that produce solar flares and CMEs vanish from the solar disk, leaving the sun blank for long stretches of time. These quiet spells have been coming with regularity since the sunspot cycle was discovered in 1859.

However, not all solar minima are alike. The last one in 2008-2009 surprised observers with its depth and side-effects. Sunspot counts dropped to a 100-year low; the sun dimmed by 0.1%; Earth’s upper atmosphere collapsed, allowing space junk to accumulate; and the pressure of the solar wind flagged while cosmic rays (normally repelled by solar wind) surged to Space Age highs. These events upended the orthodox picture of solar minimum as “uneventful.”

solarcycle_july2018_strip

Space weather forecasters have been wondering, will the upcoming solar minimum (2018-2020) be as deep as the previous one (2008-2009)? A 21-day stretch of blank suns is not enough to answer that question. During the solar minimum of 2008-2009, the longest unbroken interval of spotlessness was ~52 days, adding to a total of 813 intermittent spotless days observed throughout the multi-year minimum. The corresponding totals now are 21 days and 244 days, respectively. If this solar minimum is like the last one, we still have a long way to go.

How does this affect us on Earth? Contrary to popular belief, auroras do not vanish during solar minimum. Instead, they retreat to polar regions and may change color. Arctic sky watchers can still count on good displays this autumn and winter as streams of solar wind buffet Earth’s magnetic field. The biggest change brought by solar minimum may be cosmic rays. High energy particles from deep space penetrate the inner solar system with greater ease during periods of low solar activity. NASA spacecraft and space weather balloons are already detecting an increase in radiation. Cosmic rays alter the flow of electricity through Earth’s atmosphere, trigger lightning, potentially alter cloud cover, and dose commercial air travelers with extra “rads on a plane.”

At the moment there are no nascent sunspots on the solar disk, so the spotless days counter is likely to keep ticking. Stay tuned for more blank suns and … welcome to solar minimum.

Cosmic Radiation Detected on Commercial Flights over the South Pacific

July 9, 2018: Last month, flight attendants got some bad news. According to a new study from researchers at Harvard University, the crews of commercial airlines face an elevated risk of cancer compared to members of the general population. The likely reason: cosmic rays. High energy particles from space hitting the top of Earth’s atmosphere create a spray of secondary radiation that penetrates the walls of airplanes above ~20,000 feet.

We have some new data pertinent to this topic. On June 19th, Spaceweather.com and students of Earth to Sky Calculus flew from California to New Zealand to launch a series of space weather balloons. Naturally, we took our radiation sensors onboard the aircraft. Here is what we measured:

data2

Within minutes after takeoff from Los Angeles, radiation in the passenger compartment multiplied 25-fold and remained high until we landed again in Brisbane 13 hours later. Peak dose rates were almost 40 times greater than on the ground below. In total, we absorbed a whole body dose approximately equal to a panoramic dental X-ray.

Our sensors measure three types of radiation: neutrons, X-rays and gamma-rays. Using bubble chambers, we found that about 1/3rd of our exposure came from neutrons.

neutronchambers_600

Each bubble pictured above is formed by an energetic neutron (200 keV – 15 MeV) passing through the chamber. Counting bubbles yields the total dose–about 8 uGy (micro-greys) of neutrons during the entire flight.

The remaining 2/3rd of our measured exposure came from X-rays and gamma-rays (10 keV to 20 MeV). We detected those forms of radiation using sensors based on Geiger tubes:

xraygammaray

Adding it all together, we detected about 24.3 uGy of neutrons + X-rays + gamma rays during the Los Angeles to Brisbane leg of our flight. For comparison, a panoramic dental X-ray yields between 14 uGy and 24 uGy.

Now for more bad news. Cosmic rays at aviation altitudes are a cocktail of different things: e.g., neutrons, protons, pions, electrons, X-rays, and gamma rays spanning a wide range of energies. Our sensors sample only three ingredients of that cocktail (neutrons, X-rays, gamma-rays) at relatively low energies typical of medical X-rays and airport security devices. This means our data are only the tip of the iceberg. Flight crews and passengers absorb even more radiation than we can detect.

We have taken these sensors on airplanes before, many times. Last year, we took another long international flight, but instead of crossing the equator, we crossed the Arctic Circle. During a polar flight from Los Angeles to Stockholm in March 2017, our sensors detected 43.6 uGy of radiation, almost twice the 24.3 uGy we measured en route to Brisbane in June 2018. This difference is well understood: Earth’s polar magnetic field provides less shielding against cosmic rays, so we expect polar flights to be more “radioactive.”

changingcocktail

What we didn’t expect was the difference in neutrons:  During our Arctic flight, neutron radiation made up fully half of our dose. During our equatorial flight, neutrons amounted to only 1/3rd. In other words, the cocktail changed. These are potentially important differences because neutrons are a biologically effective form of radiation of keen interest to cancer researchers.

Stay tuned for updates as we continue to process our haul of data from 5 plane flights and 3 balloon flights in New Zealand.