What is E-RAD?

July 4,  2018: E-RAD is a new model of aviation radiation from Spaceweather.com and Earth to Sky Calculus. It can predict how much cosmic radiation a passenger will absorb flying on any commercial jet across the USA.

Researchers have long known that cosmic rays penetrate the hulls of commercial aircraft. At typical cruising altitudes, pilots, flight attendants and passengers typically receive a dose rate 40 to 70 times higher than natural radiation on the ground below. The higher a plane flies, the more radiation it receives. This has prompted the International Commission on Radiological Protection (ICRP) to classify pilots as occupational radiation workers–just like nuclear power plant engineers.

Image result for cosmic rays aviation radiation

Most people stepping onboard an airplane have no idea they are about to encounter cosmic rays–much less do they know what the dose rate might be. And that is where E-RAD comes in. Enter a flight number and voila!–E-RAD predicts your exposure to cosmic rays.

This new model has been years in the making. Since Jan. 2015, Spaceweather.com and the students of Earth to Sky Calculus have been monitoring cosmic rays in airplanes. Our method is simple: We board planes carrying the same cosmic ray payload we routinely fly to the stratosphere on space weather balloons. Inside the airplane we measure X-rays, gamma-rays and neutron dose rates, along with GPS altitude, latitude and longitude.

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Above: Flight paths forming the basis of our aviation radiation study. 2015-2017

Our data set is impressive. So far we have gathered 18,518 GPS-tagged radiation measurements during 72 flights over 2 oceans and 5 continents. We have spent 276.6 hours onboard planes taking data. These numbers are increasing rapidly with new flights every month.

The E in E-RAD stand for “Empirical.” In other words, the model is based on real-life measurements, not theoretical calculations that might be wrong. Moreover, our data-set is fresh. Because it is constantly being updated, E-RAD naturally keeps up with variables that affect cosmic rays–for instance, the waxing and waning of the solar cycle and changes in Earth’s magnetic field.

At the moment, the bulk of our data (70%) are concentrated over the continental USA, and that is where our predictions are best. For instance, here is a flight from Eugene, OR, to San Francisco, CA, in January 2018:

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The orange curve traces radiation dose rates actually observed inside the airplane, while the blue curve is E-RAD’s prediction. The two agree within 20% for most of the flight. These errors are constantly shrinking as we add new readings to our database.

We are also improving our model outside the continental USA. Recent trips to Nepal and Hong Kong have added thousands of data points in southeast Asia. And later this month we will gather more than 100 hours of measurements over the South Pacific, Australia and New Zealand.

Stay tuned for updates from 35,000 feet.

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.

Sunspots Vanishing Faster than Expected

May 1, 2018: Sunspots are becoming scarce. Very scarce. So far in 2018 the sun has been blank almost 60% of the time, with whole weeks going by without sunspots. Today’s sun, shown here in an image from NASA’s Solar Dynamics Observatory, is typical of the featureless solar disk:

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The fact that sunspots are vanishing comes as no surprise. Forecasters have been saying for years that this would happen as the current solar cycle (“solar cycle 24”) comes to an end. The surprise is how fast.

“Solar cycle 24 is declining more quickly than forecast,” announced NOAA’s Space Weather Prediction Center on April 26th. This plot shows observed sunspot numbers in blue vs. the official forecast in red:

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“The smoothed, predicted sunspot number for April-May 2018 is about 15,” says NOAA. “However, the actual monthly values have been [significantly] lower.”

“Official” forecasts of the solar cycle come from NOAA’s Solar Cycle Prediction Panel–a group of experts from NOAA, NASA, the US Air Force, universities and other research organizations. They have been convening at intervals since 1989 to predict the timing and intensity of Solar Max. The problem is, no one really knows how to predict the solar cycle. The most recent iteration of the panel in 2006-2008 compared 54 different methods ranging from empirical extrapolations of historical data to cutting-edge supercomputer models of the sun’s magnetic dynamo. None fully described what is happening now.

It’s important to note that solar minimum is a normal part of the sunspot cycle. Sunspots have been disappearing (or nearly so) every ~11 years since 1843 when German astronomer Samuel Heinrich Schwabe discovered the periodic nature of solar activity. Sometimes they go away for decades, as happened during the Maunder Minimum of the 17th century.  We’ve seen it all before. Or have we….?

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Researchers are keeping a wary eye on the sun now because of what happened the last time sunspots disappeared. The solar minimum of 2008-2009 was unusually deep. The sun set Space Age records for low sunspot number, weak solar wind, and depressed solar irradiance. When the sun finally woke up a few years later, it seemed to have “solar minimum hangover.” The bounce-back Solar Max of 2012-2015 was the weakest solar maximum of the Space Age, prompting some to wonder if solar activity is entering a  phase of sustained quiet. The faster-than-expected decline of the sunspot cycle now may support that idea.

Newcomers to the field are often surprised to learn that a lot happens during solar minimum: The sun dims, albeit slightly. NASA recently launched a new sensor (TSIS-1) to the International Space Station to monitor this effect. With less extreme UV radiation coming from the sun, Earth’s upper atmosphere cools and shrinks. This allows space junk to accumulate in low Earth orbit.

neutrons_stripAbove: A neutron bubble chamber in an airplane 35,000 feet above Greenland. Spaceweather.com and the students of Earth to Sky Calculus are flying these sensors to measure aviation radiation during solar minimum. [more]

The most important change, however, may be the increase in cosmic rays. Flagging solar wind pressure during solar minimum allows cosmic rays from deep space to penetrate the inner solar system. Right now, space weather balloons and NASA spacecraft are measuring an uptick in radiation due to this effect. Cosmic rays may alter the chemistry of Earth’s upper atmosphere, trigger lightning, and seed clouds.

Air travelers are affected, too. It is well known that cosmic rays penetrate airplanes. Passengers on long commercial flights receive doses similar to dental X-rays during a single trip, while pilots have been classified as occupational radiation workers by the International Commission on Radiological Protection (ICRP). Ongoing measurements by Spaceweather.com and Earth to Sky Calculus show that dose rates at cruising altitudes of 35,000 feet are currently ~40 times greater than on the ground below, values which could increase as the solar cycle wanes.

Solar minimum is just getting started. Stay tuned for updates.

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.

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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:

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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:

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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:

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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.

 

Rads on a Plane: The Data

Feb. 21, 2018: Many people think that only astronauts have to worry about cosmic radiation. Not so. Ordinary air travelers are exposed to cosmic rays, too. On a typical flight over the continental USA, radiation dose rates in economy class are more than 40 times higher than on the ground below. Cosmic rays penetrate the walls of aircraft with ease. This has  prompted the International Commission on Radiological Protection (ICRP) to classify pilots as occupational radiation workers–just like nuclear power plant engineers.

Since Jan. 2015, Spaceweather.com and the students of Earth to Sky Calculus have been monitoring cosmic rays in airplanes. Our method is simple: We board planes carrying the same cosmic ray payload we routinely fly to the stratosphere on space weather balloons. Inside the airplane we measure X-ray, gamma-ray and neutron dose rates along with GPS altitude, latitude and longitude

flightpaths
Above: Flight paths forming the basis of our aviation radiation study. 2015-2017

Three years after our first flight, our data set is impressive. We have 14,183 GPS-tagged radiation measurements collected during 67 flights over 2 oceans and 5 continents. We have spent 236.4 hours onboard planes taking data. If you accumulated that into a single flight, it would amount to 9.8 uninterrupted days on a plane.

This substantial data set is allowing us to explore how radiation varies with altitude around the globe. It’s not the same everywhere. The Arctic, for example, differs sharply from the equator, and there are interesting departures from “normal” near the South Atlantic Anomaly. We’re also discovering how Earth’s natural magnetism shields travelers from radiation: there’s a strong correlation in our data between dose rate and the geomagnetic field around the airplane.

Best of all, we can now predict dose rates for flights that haven’t even taken off yet. Using the data from 2015-2017, we’re building an empirical predictive model and actively testing it against new flights in 2018. Early results show that it works well over the continental USA, and we are beginning to check international flights, too.

Stay tuned for updates!

The Pacific Radiation Bowl

Jan. 22, 2018: For years, Spaceweather.com and the students of Earth to Sky Calculus have been flying balloons to the stratosphere to monitor cosmic rays penetrating Earth’s atmosphere. Lately, we’ve been flying the same payloads onboard airplanes. We want to map Earth’s radiation environment at aviation altitudes where millions of people are routinely exposed to elevated levels of cosmic rays.

Recently we encountered an interesting feature in data taken over the Pacific Ocean: a “radiation bowl.” On Nov. 30th, 2017, Hervey Allen, a computer scientist at the University of Oregon, carried our radiation sensors onboard a commercial flight from San Francisco, California, to Auckland, New Zealand: map. As his plane cruised at a nearly constant altitude (35,000 ft) across the equator, radiation levels gracefully dipped, then recovered, in a bowl-shaped pattern:

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In one way, this beautiful curve is no surprise. We expect dose rates to reach a low point near the equator, because that is where Earth’s magnetic field provides the greatest shielding against cosmic rays. Interestingly, however, the low point is not directly above the equator. A parabolic curve fit to the data shows that the actual minimum occurred at 5.5 degrees N latitude.

Is Earth’s “radiation equator” offset from the geographic equator? Very likely it is. Earth’s magnetic field is tilted with respect to Earth’s spin axis and, moreover, there are many inhomogeneities in our planetary magnetic field that may create radiation zones of interest in unexpected places.

We are now planning additional trips across the equator to map the band of least radiation girdling our planet. In fact, we are working on a dataset now that includes an equator-crossing between the USA and Chile. Stay tuned for updates.

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!

Radiation Clouds at Aviation Altitudes

Jan. 20, 2017: A new study published in the peer-reviewed journal Space Weather reports the discovery of radiation “clouds” at aviation altitudes. When airplanes fly through these clouds, dose rates of cosmic radiation normally absorbed by air travelers can double or more.

“We have flown radiation sensors onboard 264 research flights at altitudes as high as 17.3 km (56,700 ft) from 2013 to 2017,” says Kent Tobiska, lead author of the paper and PI of the NASA-supported program Automated Radiation Measurements for Aerospace Safety (ARMAS). “On at least six occasions, our sensors have recorded surges in ionizing radiation that we interpret as analogous to localized clouds.”

The fact that air travelers absorb radiation is not news.  Researchers have long known that cosmic rays crashing into Earth’s atmosphere create a spray of secondary particles such as neutrons, protons, electrons, X-rays and gamma-rays that penetrate aircraft.  100,000 mile frequent flyers absorb as much radiation as 20 chest X-rays—and even a single flight across the USA can expose a traveler to more radiation than a dental X-ray.

Conventional wisdom says that dose rates should vary smoothly with latitude and longitude and the height of the aircraft.  Any changes as a plane navigates airspace should be gradual.  Tobiska and colleagues have found something quite different, however: Sometimes dose rates skyrocket for no apparent reason.

“We were quite surprised to see this,” says Tobiska.

All of the surges they observed occurred at relatively high latitudes, well above 50 degrees in both hemispheres. One example offered in their paper is typical: On Oct 3, 2015, an NSF/NCAR research aircraft took off from southern Chile and flew south to measure the thickness of the Antarctic ice shelf.  Onboard, the ARMAS flight module recorded a 2x increase in ionizing radiation for about 30 minutes while the plane flew 11 km (36,000 feet) over the Antarctic Peninsula.  No solar storm was in progress.  The plane did not abruptly change direction or altitude.  Nevertheless, the ambient radiation environment changed sharply. Similar episodes have occurred off the coast of Washington state.

Above: Radiation measurements made by ARMAS while flying over Antarctica. The colored points are from ARMAS. The black points are from a NASA computer model (NAIRAS) predicting radiation dose rates. Throughout the flight, ARMAS observed higher dose rates than predicted by the model, including a surge highlighted in pink.

What’s going on?

“We’re not sure,” says Tobiska, “but we have an idea.”

Earth’s magnetic field, he explains, traps many cosmic rays and solar energetic particles in structures called “magnetic bottles.”  These bottles can be leaky.  Even minor gusts of solar wind can cause the trapped particles to squirt out the ends of the bottle, sending beams of particles down toward the Earth below.

“Basically, we think we might be flying through some of these leaky particle beams,” says Tobiska.

Tobiska notes that a team of South Korean researchers has observed similar variations in radiation while flying sensors onboard a military aircraft near the border between the two Koreas (Lee et al 2015).  If the phenomena are the same, the Korean measurements would suggest that “radiation clouds” may exist at middle latitudes, too.

The ARMAS program has a busy flight schedule in 2017. “We’ll be looking carefully for more ‘clouds’ as we continue to characterize the radiation environment at aviation altitudes,” says Tobiska.

Stay tuned for updates and, meanwhile, read Tobiska et al’s original research at this URL:  http://onlinelibrary.wiley.com/doi/10.1002/2016SW001419/abstract

Intercontinental Space Weather Balloon Network

For the past 2 years, Spaceweather.com and the students of Earth to Sky Calculus have been launching “space weather balloons” to measure cosmic rays in the atmosphere.  Regular flights over California show that atmospheric radiation is intensifying in response to changes in the solar cycle.  Now, our monitoring program is going global.  In recent months we have been developing launch sites in multiple US states as well as South America and Europe. This is what the International Space Weather Ballooning Network looks like in October 2016:

Recent additions expand our coverage north of the Arctic Circle (Sweden) and closer to the core of the South Atlantic Anomaly (Argentina).  We also hope to add a site in Antarctica in 2018.

The purpose of launching balloons from so many places is to map out the distribution of cosmic rays around our planet. A single launch site is simply not enough to reveal the nonuniform shielding of our planet’s magnetic field and the complicated response of our atmosphere to changes in solar activity.

Our first test of the network validated these ideas. During a 48 hour period from August 20th-22nd we launched 4 balloons in quick succession from southern Chile, California, Oregon, and Washington. The ascending payloads sampled atmospheric radiation (X-rays and gamma-rays) from ground level to the stratosphere over a geographical range of more than 10,000 km. Here are the results:

The curves show radiation levels vs. altitude for each of the four sites. Numbers in parentheses are magnetic latitude–a measure of distance from Earth’s magnetic equator.

At a glance we can see that atmospheric radiation is a strong function of magnetic latitude. Washington State at +53o has more than twice the amount of radiation as southern Chile at -29o–despite the fact that the Chilean balloon flew into the outskirts of the South Atlantic Anomaly. Clearly, Earth’s magnetic field provides very uneven protection against cosmic rays.

To explore these findings further, we are planning additional network launches every month from now on, adding new sites as often as possible. A launch from inside the Arctic Circle in January 2017 is highly anticipated. Stay tuned for updates from the Intercontinental SWx Balloon Network.