Global Cosmic Radiation Measurements

June 10, 2018: For the past two years, Spaceweather.com and the students of Earth to Sky Calculus have been traveling around the world, launching cosmic ray balloons to map our planet’s radiation environment. Our sensors travel from ground level to the stratosphere and bring their data back to Earth by parachute. Here is a plot showing radiation vs. altitude in Norway, Chile, Mexico, and selected locations in the USA:


Note: Data from Sweden and several other US states are omitted for the clarity of the plot.

We’re about to add a new country to the list: New Zealand. On June 18th, a team of students from Earth to Sky is traveling to New Zealand’s north island to launch 3 cosmic ray balloons in only 10 days. Soon, we will know more about cosmic rays above Earth’s 8th continent.

Cosmic rays are, essentially, the subatomic debris of dying stars, accelerated to nearly light speed by supernova explosions. They travel across space 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.

The purpose of our mapping project is to study how well Earth’s atmosphere and magnetic field protects us from cosmic rays. As the plot shows, the shielding is uneven. More radiation gets through to the poles (e.g., Norway) and less radiation penetrates near the equator (e.g., Mexico).

But there’s more to the story. Our launch sites in Chile and California are equidistant from the equator, yet their radiation profiles are sharply different. Chile is on the verge of the South Atlantic Anomaly, which almost surely distorts the radiation field there. Our flights over New Zealand may shed some light on this, because our launch sites in New Zealand will be the same distance from the equator as the sites in Chile. Stay tuned!

Technical note: The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.

What is the Regener-Pfotzer Maximum?

June 7, 2018: About once a week, Spaceweather.com and the students of Earth to Sky Calculus launch a helium balloon with radiation  sensors to the stratosphere over California. This is a unique monitoring program aimed at tracking the cosmic ray situation in Earth’s atmosphere. During each flight, our balloon passes through something called the Regener-Pfotzer Maximum, a layer of peak radiation about 20 km above Earth’s surface. This plot of radiation vs. time taken during a July 2015 balloon flight illustrates the peak:

figure1_aguImage source: Phillips, T., et al. (2016), Space Weather Ballooning, Space Weather, 14, 697–703, doi: 10.1002/2016SW001410.

What is this peak? To understand it, let us begin in deep space. Cosmic rays are, essentially, the subatomic debris of dying stars, accelerated to nearly light speed by supernova explosions. They travel across space 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. Physicists Eric Regener and Georg Pfotzer discovered the maximum using balloons in the 1930s and it is what we are measuring today.

In some ways, secondary cosmic rays are like froth on the ocean. By watching the froth, you can learn a lot about the underlying water. Likewise, by watching secondary cosmic rays, we learn a lot about primary cosmic rays hitting the top of the atmosphere. Indeed, our balloon measurements have recently confirmed what NASA spacecraft are finding: The cosmic ray situation is worsening.

cr_strip

For many years, the Regener-Pfotzer Maximum was called, simply, the “Pfotzer Maximum.” Regener’s name is less recognized by present-day physicists largely because in 1937 he was forced to take early retirement by the National Socialists as his wife had Jewish ancestors. This interesting story weaving science, politics, and human nature has recently been told by historians of science P. Carlson and A. A. Watson. Ref: Hist. Geo Space. Sci., 5, 175-182, 2014.

Technical note: The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.

Jellyfish Sprites over Oklahoma

May 25, 2018: Last night, a swarm of luminous jellyfish appeared over Oklahoma. “A swarm of jellyfish sprites, that is,” says Paul Smith, who photographed them rising above an intense thunderstorm near Oklahoma City:

“The sprites were about 80 miles away from me,” says Smith. “At that distance I could see over the tops of the storm cells where the jellyfish appear. I’ve photographed many sprites from 200 to 300 miles away. These, however, were unusually nearby, and they are my best pictures yet.”

Sprites are an exotic form of upward directed lightning. Although the forms have been seen for at least a century, many scientists did not believe they existed until after 1989 when sprites were photographed by cameras onboard the space shuttle. Now “sprite chasers” like Smith routinely photograph them from their own homes.

“I have been recording sprites since last summer when I accidentally caught a few during the Perseid meteor shower,” says Smith. “I have a couple of hundred events on camera now and I am out almost every night there are storms in my vicinity. This month I have driven for five hours some nights trying to find a clear view over active cells.”


The blue pushpin is Smith’s location; the arrow points to the sprites he saw on May 24, 2018.

Oklahoma is the epicenter of a region that we call “Sprite Alley”–a corridor stretching across the US Great Plains where intense thunderstorms produce lots of upward directed lightning. Already this year we have received reports of sprites and their stronger cousins, Gigantic Jets, from Texas to Nebraska. And summer thunderstorm season isn’t even fully underway yet.

Some researchers think that sprites may be linked to cosmic rays: Subatomic particles from deep space strike the top of Earth’s atmosphere, producing secondary electrons that trigger the upward bolts. If this is true, then sprites could multiply in the months and years ahead as cosmic rays intensify due to the decline of the solar cycle. More sprite images may be found on Paul Smith’s Facebook page.

Realtime Sprite Photo Gallery

Atmospheric Radiation Update

May 21, 2018: Cosmic rays over California continue to intensify, according to high-altitude balloons launched by Spaceweather.com and the students of Earth to Sky Calculus. We’ve been monitoring secondary cosmic rays in the stratosphere with regular launches from Bishop CA since 2015. In the data plot below, 3 of the 4 highest radiation measurements have occurred just in the past few months:

The worsening cosmic ray situation is linked to the solar cycle. Right now, the sun is heading toward a deep Solar Minimum. As the outward pressure of solar wind decreases, cosmic rays from deep space are able to penetrate the inner solar system with increasing ease. This same phenomenon is happening not only above California, but all over the world.

Take another look at the data plot. The general trend in radiation is increasing, but it is not perfectly linear. From launch to launch we see significant up and down fluctuations. These fluctuations are not measurement errors. Instead, they are caused by natural variations in the pressure and magnetization of the solar wind.

How does the overall increase affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews enough that pilots are classified as occupational radiation workers by the International Commission on Radiological Protection (ICRP). Some research suggests that cosmic rays can seed clouds and trigger lightning, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

The sensors we send to the stratosphere measure X-rays and gamma-rays, which are produced by the crash of primary cosmic rays into Earth’s atmosphere. The energy range of the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines and airport security scanners. Stay tuned for updates as the monitoring program continues.

North Korea and Aviation Radiation

April 26, 2018:  For the past 4 years, Spaceweather.com and Earth to Sky Calculus have been flying radiation sensors onboard airplanes to map the distribution of cosmic rays around our planet. Our database currently contains more than 17,000 GPS-tagged radiation measurements spanning 5 continents and 43,000 feet of altitude. Yesterday, we realized we could use this database to investigate a current event–namely, the possibility of a radiation leak from North Korea.


Above: Earth to Sky Calculus X-ray/gamma radiation sensors onboard a plane

North Korea recently surprised observers by announcing a suspension of its underground nuclear testing program. Geologists in China quickly offered an explanation: Mount Mantap, which sits atop of the test site, had collapsed. The mountain crumbled in Sept. 2017 minutes after the North Korean regime exploded a 100 kiloton prototype weapon. According to the South China Morning Post, the China Earthquake Administration believes the collapse may have created a “chimney” that allows the escape of radioactive materials.

Is there any sign of radioactivity in the air space around North Korea? Our database contains four flights near the Korean Peninsula–two in March 2016 (before the collapse), and two more in Feb. 2018  (after the collapse). These are shown in the map, below, where orange circles of 350 miles and 700 miles radius are centered on nuclear test site. During each flight we sampled X-rays and gamma-rays in the energy range 10 keV to 20 MeV at one minute intervals, accumulating more than 600 data points. Low energy X-rays have been used in the past to trace radioactive fallout from atomic tests, so our measurements may have some bearing on the question.


Above: Red dots show where we have collected radiation data in airspace near N. Korea.

And the answer is …. no. Comparing radiation levels pre-collapse vs. post-collapse, we found no significant difference. For instance, radiation dose rates in March 2016 at 31,500 feet were 0.9 uGy/hr (18 times the natural rate at sea level). Radiation dose rates in February 2018 at the same altitude were 1.0 uGy/hr (20 times sea level), a slight increase within the uncertainty of the measurements. If radiation is leaking from the collapsed mountain site, it is not having a detectable effect on aviation over neighboring countries.

The Worsening Cosmic Ray Situation

March 5, 2018: Cosmic rays are bad–and they’re getting worse.

That’s the conclusion of a new paper just published in the research journal Space Weather. The authors, led by Prof. Nathan Schwadron of the University of New Hampshire, show that radiation from deep space is dangerous and intensifying faster than previously expected.

cr_strip

The story begins four years ago when Schwadron and colleagues first sounded the alarm about cosmic rays. Analyzing data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard NASA’s Lunar Reconnaissance Orbiter (LRO), they found that cosmic rays in the Earth-Moon system were peaking at levels never before seen in the Space Age. The worsening radiation environment, they pointed out, was a potential peril to astronauts, curtailing how long they could safely travel through space.

This figure from their original 2014 paper shows the number of days a 30-year old male astronaut flying in a spaceship with 10 g/cm2 of aluminum shielding could go before hitting NASA-mandated radiation limits:

missionduration_strip

In the 1990s, the astronaut could spend 1000 days in interplanetary space. In 2014 … only 700 days. “That’s a huge change,” says Schwadron.

Galactic cosmic rays come from outside the solar system. They are a mixture of high-energy photons and sub-atomic particles accelerated toward Earth by supernova explosions and other violent events in the cosmos. Our first line of defense is the sun:  The sun’s magnetic field and solar wind combine to create a porous ‘shield’ that fends off cosmic rays attempting to enter the solar system. The shielding action of the sun is strongest during Solar Maximum and weakest during Solar Minimum–hence the 11-year rhythm of the mission duration plot above.

The problem is, as the authors note in their new paper, the shield is weakening: “Over the last decade, the solar wind has exhibited low densities and magnetic field strengths, representing anomalous states that have never been observed during the Space Age. As a result of this remarkably weak solar activity, we have also observed the highest fluxes of cosmic rays.”

Back in 2014, Schwadron et al used a leading model of solar activity to predict how bad cosmic rays would become during the next Solar Minimum, now expected in 2019-2020.  “Our previous work suggested a ∼ 20% increase of dose rates from one solar minimum to the next,” says Schwadron. “In fact, we now see that actual dose rates observed by CRaTER in the last 4 years exceed the predictions by ∼ 10%, showing that the radiation environment is worsening even more rapidly than we expected.” In this plot bright green data points show the recent excess:

excess_crater_strip

The data Schwadron et al have been analyzing come from CRaTER on the LRO spacecraft in orbit around the Moon, which is point-blank exposed to any cosmic radiation the sun allows to pass. Here on Earth, we have two additional lines of defense: the magnetic field and atmosphere of our planet. Both mitigate cosmic rays.

But even on Earth the increase is being felt. The students of Earth to Sky Calculus have been launching space weather balloons to the stratosphere almost weekly since 2015. Sensors onboard those balloons show a 13% increase in radiation (X-rays and gamma-rays) penetrating Earth’s atmosphere:

balloon_data_strip

X-rays and gamma-rays detected by these balloons are “secondary cosmic rays,” produced by the crash of primary cosmic rays into Earth’s upper atmosphere. They trace radiation percolating down toward our planet’s surface. The energy range of the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines and airport security scanners.

How does this affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified by the International Commission on Radiological Protection as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

Cosmic rays will intensify even more in the years ahead as the sun plunges toward what may be the deepest Solar Minimum in more than a century. Stay tuned for updates.

References:

Schwadron, N. A., et al (2014), Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep space exploration?, Space Weather, 12, 622–632, doi:10.1002/2014SW001084.

Schwadron, N. A., et al (2018), Update on the worsening particle radiation environment observed by CRaTER and implications for future human deep-space exploration, Space Weather, doi: 10.1002/2017SW001803.

 

Atmospheric Radiation is Increasing

Dec. 9, 2017: Since the spring of 2015, Spaceweather.com and the students of Earth to Sky Calculus have been flying balloons to the stratosphere over California to measure cosmic rays. Soon after our monitoring program began, we quickly realized that radiation levels are increasing. Why? The main reason is the solar cycle. In recent years, sunspot counts have plummeted as the sun’s magnetic field weakens. This has allowed more cosmic rays from deep space to penetrate the solar system. As 2017 winds down, our latest measurements show the radiation increase continuing apace–with an interesting exception, circled in yellow:

In Sept. 2017, the quiet sun surprised space weather forecasters with a sudden outburst of explosive activity. On Sept. 3rd, a huge sunspot appeared. In the week that followed, it unleashed the strongest solar flare in more than a decade (X9-class), hurled a powerful CME toward Earth, and sparked a severe geomagnetic storm (G4-class) with Northern Lights appearing as far south as Arkansas. During the storm we quickened the pace of balloon launches and found radiation dropping to levels we hadn’t seen since 2015. The flurry of solar flares and CMEs actually pushed some cosmic rays away from Earth.

Interestingly, after the sun’s outburst, radiation levels in the stratosphere took more than 2 months to fully rebound. Now they are back on track, increasing steadily as the quiet sun resumes its progress toward Solar Minimum. The solar cycle is not expected to hit rock bottom until 2019 or 2020, so cosmic rays should continue to increase, significantly, in the months and years ahead. Stay tuned for updates as our balloons continue to fly.

Technical note: The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies, which span the range of medical X-ray machines and airport security scanners, trace secondary cosmic rays, the spray of debris created when primary cosmic rays from deep space hit the top of Earth’s atmosphere.

CME Sweeps Aside Cosmic Rays

July 18,2017: On July 16th, a CME hit Earth’s magnetic field, sparking two days of geomagnetic storms and beautiful southern auroras. The solar storm cloud also swept aside some of the cosmic rays currently surrounding Earth. Spaceweather.com and the students of Earth to Sky Calculus launched a space weather balloon to the stratosphere hours after the CME arrived. We detected a 7% decrease in X-rays and gamma-rays (two tracers of secondary cosmic rays). Neutron monitors in the Arctic and Antarctic recorded similar decrements. For instance, these data from the Bartol Research Institute show a nearly 8% drop in cosmic ray neutrons reaching the South Pole:

This is called a “Forbush Decrease,” named after physicist Scott E. Forbush who first described it in the 20th century. Wherever CMEs go, cosmic rays are deflected by magnetic fields inside the solar storm clouds. As a result, when solar activity is high, cosmic radiation around Earth is relatively low–a yin-yang relationship that holds throughout all phases of the solar cycle.

Lately, cosmic rays around Earth have been intensifying as the solar cycle plunges toward minimum. The CME of July 16th reversed that trend–but only for a few days. Solar activity has returned to low levels and cosmic rays are on the rise again.

Why do we care about cosmic rays? For one thing, they penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger lightning, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

Cosmic Rays Intensify: May 2017

May 7, 2017: 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 radiation levels in the stratosphere with frequent high-altitude balloon flights over California. Here are the latest results, current as of May 6, 2017:

The data show cosmic ray levels intensifying with an approximately 13% increase since March 2015.

Cosmic rays are high-energy photons and subatomic particles accelerated in our direction by distant supernovas and other violent events in the Milky Way. Usually, cosmic rays are held at bay by the sun’s magnetic field, which envelops and protects all the planets in the Solar System. But the sun’s magnetic shield is weakening in 2017 as the solar cycle shifts from Solar Maximum to Solar Minimum. More and more cosmic rays are therefore reaching our planet.

How does this affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews enough that pilots are classified as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger lightning, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

The sensors we send to the stratosphere measure X-rays and gamma-rays, which are produced by the crash of primary cosmic rays into Earth’s atmosphere. The energy range of the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines and airport security scanners.

Neutrons on a Plane

March 18, 2017: Among researchers, it is well known that air travelers are exposed to cosmic rays. High-energy particles and photons from deep space penetrate Earth’s atmosphere and go right through the hulls of commercial aircraft. This has prompted the International Commission on Radiological Protection (ICRP) to classify pilots and flight attendants as occupational radiation workers.

Many studies of this problem focus on ionizing radiation such as x-rays and gamma-rays. On March 16th we turned the tables and measured neutrons instead. During a 12-hour flight from Stockholm to Los Angeles, Spaceweather.com and the students of Earth to Sky Calculus used bubble chambers to monitor neutron activity inside a Scandinavian Airlines jetliner.

In the photo above, taken 35,000 feet above Greenland, each bubble shows where a neutron passed through the chamber and vaporized a superheated droplet. By the time the long flight was over, we measured almost 20 uSv (microsieverts) of radiation from neutrons–similar to the dose from a panoramic X-ray at your dentist’s office. This confirms that neutrons are an important form of aviation radiation relevant to both air travelers and future space tourists.

Where do these neutrons come from? Mainly, they are secondary cosmic rays. When primary cosmic rays from deep space hit Earth’s atmosphere, they produce a spray of secondary particles including neutrons, protons, alpha particles, and other species. Cosmic ray neutrons can reach the ground; indeed, researchers routinely use neutron counters on Earth’s surface to monitor cosmic ray activity above the atmosphere. Now we’re doing the same thing onboard airplanes.

Earlier in the week, we flew these bubble chambers to the Arctic stratosphere using a space weather balloon. Interestingly, the 12-hour plane flight yielded ~6 times more neutrons than the shorter (2 hour) but far higher (97,000 ft) balloon flight to the stratosphere. What does it mean? We’re still analyzing the data and will have more insights to share in the days ahead. Stay tuned!