Rads on a Plane: New Results

Oct. 3, 2018: Many people think that only astronauts need to worry about cosmic radiation. Not so. Ordinary air travelers are exposed to cosmic rays, too. A recent study from researchers at Harvard found that flight attendants have a higher risk of cancer than members of the general population, and the International Commission on Radiological Protection has classified pilots as occupational radiation workers.

How much radiation do you absorb? SSpaceweather.com and the students of Earth to Sky Calculus have been working to answer this question by taking cosmic ray detectors onboard commercial airplanes. Flying since 2015, we have collected more than 22,000 GPS-tagged radiation measurements over 27 countries, 5 continents, and 2 oceans.


(A) A global overview of our flights. This map shows where we have been. (B) To show the density of our data, we zoom in to the Four Corners region of the USA. There are three major hubs in the map: Phoenix, Las Vegas, and Denver. You can’t see them, however, because they are overwritten by pushpins.

Here is what we have learned so far:

  1. Radiation always increases with altitude, with dose rates doubling every 5000 to 6000 feet. This make sense: The closer you get to space, the more cosmic rays you will absorb.
  2. At typical cruising altitudes, cosmic radiation is 40 to 60 times greater than natural sources at sea level.
  3. Passengers on cross-country flights across the USA typically absorb a whole body dose equal to 1 or 2 dental X-rays.
  4. On international flights, the total dose can increase ~five-fold with passengers racking up 5 to 6 dental X-rays.

Using our database, we can investigate patterns of radiation around the world. For instance, this plot compares aviation radiation over the tropics vs. the Arctic:


We see that the Arctic is a high radiation zone. This comes as no surprise. Researchers have long known that particles from space easily penetrate Earth’s magnetic field near the poles, while the equator offers greater resistance. That’s why auroras are in Sweden instead of Mexico. Generally speaking, passengers flying international routes over the poles absorb 2 to 3 times more radiation than passengers at lower latitudes.

We can also look at individual countries–e.g., Sweden vs. the USA vs. Chile:


As an Arctic country, Sweden has the most radiation–no surprise. The continental USA straddles the middle–again, no surprise. A mid-latitude country can be expected to have middling radiation. Chile, however, is more of a puzzle.

Although Chile does not cross the equator, it has some of the lowest readings in our database. This phenomenon is almost certainly linked to Chile’s location on the verge of the South Atlantic Anomaly–a distortion in Earth’s magnetic field that affects radiation levels. We are actively investigating the situation in Chile with additional flights, and will report results in a future blog.

Because our home base is in the USA, we spend a lot of time flying there. The US dataset is so dense, we can investigate regional differences across the country–for example, New England vs. the Southwest:


The two curves are indistinguishable below ~30,000 feet, but at higher altitudes they diverge. By the time a plane reaches 40,000 feet, it would experience 30% more radiation over New England than the same plane flying above the desert Southwest. According to our measurements so far, New England is the “hottest” region of the continental USA, radiation-wise, with the Pacific Northwest a close second.

Perhaps the most important outcome of our work so far is E-RAD–a new predictive model of aviation radiation. We can now predict dose rates on flights in areas where we have flown before. Because it is constantly updated with new data, E-RAD naturally keeps up with variables that affect cosmic rays such as the solar cycle and changes in Earth’s magnetic field.

Here is an example of a recent flight we took from Baltimore to Las Vegas, comparing E-RAD’s predictions with actual measurements:


The two agree within 10% for most of the flight. These errors are constantly shrinking as we add new readings to our database.

The results in this report are offered as a preview of what we are learning. Our database is growing almost-daily with new flights to new places, and we will have more results to share in the weeks ahead. We’ve created a website to showcase what we are learning and ultimately to let you, the reader, interact with our databases as well: RadsonaPlane.com.

Visit RadsonaPlane.com


Student-Built Space Weather Satellite Targets Killer Electrons

Sept. 20, 2018: Last Saturday, a Delta II rocket blasted off at dawn from the Vandenberg AFB in California. Soon thereafter NASA reported the successful deployment of the ICESat-2 satellite, designed to make 3D laser images of Earth’s surface.

Here’s what most news stations did not report: A pair of tiny satellites were tucked inside the rocket, and they were successfully deployed as well. Built by students at UCLA, ELFIN-A and ELFIN-B are now orbiting Earth, monitoring the ebb and flow of “killer electrons” around our planet.

“We’ve just received our first downlink of data from ELFIN-A,” reports Ryan Caron, Development Engineer at UCLA’s Department of Earth, Planetary, and Space Sciences. Click to listen:


That may sound like ordinary static, but the signal is full of meaning. As mission controllers turn on ELFIN’s science instruments, the static-y waveforms will carry unique information about particles raining down on Earth from the inner Van Allen Radiation Belt.

“Sensors onboard our two cubesats detect electrons in the energy range 50 keV to 4.5 MeV,” says Caron. “These are the so-called ‘killer electrons,’ which can damage spacecraft and cause electrical disruptions on the ground. They also give rise to the majestic aurora borealis.”

“ELFIN is doing something new,” says Vassilis Angelopoulos, a UCLA space physicist who got his doctorate at UCLA and serves as ELFIN’s principal investigator. “No previous mission was able to measure the angle and energy of killer electrons as they rain down on Earth’s atmosphere. ELFIN will help us investigate how disturbances called ‘Electromagnetic Ion Cyclotron waves’ knock these electrons out of the Van Allen Belts and scatter them down toward Earth.”

ELFIN-A and ELFIN-B are cubesats, each weighing about eight pounds and roughly the size of a loaf of bread. They are remarkable not only for their cutting edge sensors, but also for their origin. The two satellites were almost completely designed and built by undergraduate students at UCLA. Working for more than 5 years, a succession of 250 students created the two Electron Losses and Fields Investigation CubeSats –“ELFIN” for short.

“Just seeing all the hundreds of hours of work, the many sleepless nights, the stressing out that you’re not going to make a deadline — just seeing it go up there … I’m probably going to cry,” says Jessica Artinger, an astrophysics major and geophysics and planetary science minor who helped build the satellites and witnessed their launch.

The ELFIN website has interactive tools so the public can track and listen to the spacecraft as it passes overhead twice a day. The CubeSats are expected to remain in space for two years, after which they will gradually fall out of orbit and burn up in the atmosphere like shooting stars.

ELFIN has been supported with funding from the National Science Foundation and NASA, with technical assistance from the Aerospace Corporation among other industry partners and universities.


Earth to Sky Cosmic Ray Sensors

When cosmic rays hit the top of Earth’s atmosphere, they create a spray of secondary radiation that penetrates airplanes and even reaches the ground below. For years, the students of Earth to Sky Calculus have been measuring secondary cosmic rays on airplanes and high-altitude balloons using two types of sensors.

First are the neutron bubble chambers:


Each bubble pictured above is formed by an energetic neutron (200 keV – 15 MeV) passing through the chamber. Counting bubbles yields the total dose.

Second, we monitor X-rays and gamma rays using sensors based on Geiger tubes:


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.

A New Type of Aurora is Not an Aurora at All

Aug. 20, 2018: A new type of aurora nicknamed “STEVE” may not be an aurora at all, according to a new paper published August 20th in the Geophysical Research Letters. A group of researchers combined satellite data with ground-based imagery of STEVE during a geomagnetic storm to investigate how STEVE is formed. “Our main conclusion is that STEVE is not an aurora,” said Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study.


STEVE, photographed by Greg Ash of Ely, Minnesota, on May 5, 2018

STEVE is a purple ribbon of light that amateur astronomers in Canada have been photographing for decades, belatedly catching the attention of the scientific community in 2016. It doesn’t look exactly like an aurora, but it often appears alongside auroras during geomagnetic storms. Is it an aurora — or not? That’s what Gallardo-Lacourt’s team wanted to find out.

Auroras appear when energetic particles from space rain down on Earth’s atmosphere during geomagnetic storms. If STEVE is an aurora, they reasoned, it should form in much the same way. On March 28, 2008, STEVE appeared over eastern Canada just as NOAA’s Polar Orbiting Environmental Satellite 17 (POES-17) passed overhead. The satellite, which can measure the rain of charged particles that causes auroras, went directly above the purple ribbon. Gallardo-Lacourt’s team looked carefully at the old data and found … no rain at all.

“Our results verify that this STEVE event is clearly distinct from the aurora borealis since it is characterized by the absence of particle precipitation,” say the researchers. “Interestingly, its skyglow could be generated by a new and fundamentally different mechanism in Earth’s ionosphere.”

Another study has shown that STEVE appears most often in spring and fall. With the next equinox only a month away, new opportunities to study STEVE are just around the corner. Stay tuned and, meanwhile, read the original research here.

Realtime STEVE Photo Gallery

A Mystery in the Mesosphere

August 15, 2018: This summer, something strange has been happening in the mesosphere. The mesosphere is a layer of Earth’s atmosphere so high that it almost touches space. In the rarefied air 83 km above Earth’s surface, summertime wisps of water vapor wrap themselves around speck of meteor smoke. The resulting swarms of ice crystals form noctilucent clouds (NLCs), which can be seen glowing in the night sky at high latitudes.

And, no, that’s not the strange thing.

Northern sky watchers have grown accustomed to seeing these clouds every summer in recent years. They form in May, intensify in June, and ultimately fade in July and August. This year, however, something different happened. Instead of fading in late July, the clouds exploded with unusual luminosity. Kairo Kiitsak observed this outburst on July 26th from Simuna, Estonia:


“It was a mind-blowing display,” says Kiitsak. “The clouds were visible for much of the night, with intense ripples for 3 hours.”

Other observers saw similar displays in July and then, in August, the clouds persisted. During the first half of August 2018, reports of NLCs to Spaceweather.com have tripled compared to the same period in 2017. The clouds refuse to go away.

Researchers at the University of Colorado may have figured out why. “There has been an unexpected surge of water vapor in the mesosphere,” says Lynn Harvey of  Colorado’s Laboratory for Atmospheric and Space Physics (LASP).  This plot, which Harvey prepared using data from NASA’s satellite-based Microwave Limb Sounder (MLS) instrument, shows that the days of late July and August 2018 have been the wettest in the mesosphere for the past 11 years:


The red curve traces water vapor levels in the mesosphere for 2018.

“July went out like a lion!” says Harvey.

In addition to being extra wet, the mesosphere has also been a bit colder than usual, according to MLS data. The combination of wet and cold has created favorable conditions for icy noctilucent clouds.

Harvey and her colleagues are still working to understand how the extra water got up there. One possibility involves planetary wave activity in the southern hemisphere which can, ironically, boost the upwelling of water vapor tens of thousands of miles away in the north. The phenomenon could also be linked to solar minimum, now underway. It is notable that the coldest and wettest years in the mesosphere prior to 2018 were 2008-2009–the previous minimum of the 11-year solar cycle.

Stay tuned for updates and, meanwhile, be alert for NLCs.

Realtime Noctilucent Cloud Photo Gallery


Fun Ways to Observe a Partial Solar Eclipse

August 9, 2018: A partial solar eclipse happens when the Moon passes in front of the sun, off center, turning the solar disk into a fiery crescent. There are usually one or two partial solar eclipses somewhere on Earth every year. They look like this:


Dennis Put photographed this partial solar eclipse over Maasvlakte, The Netherlands, on Jan. 4, 2011.

The first thing to remember about a partial eclipse is don’t stare at it. Even the tiniest sliver of sun left uncovered by the Moon can hurt your eyes. Instead, look at the ground. Beneath a leafy tree, you might be surprised to find hundreds of crescent-shaped sunbeams dappling the grass. Overlapping leaves create a natural array of pinhole cameras, each one casting an image of the crescent-sun onto the ground beneath the canopy.

No trees? Try this trick: Criss-cross your fingers waffle-style and let the sun shine through the matrix of holes. You can cast crescent suns on sidewalks, driveways, friends, cats and dogs—you name it. Hand shadows are fun, too, like the crescent-eyed turkey shown above.

Because partial eclipses typically last for more than an hour, there is plenty of time for shadow play and photography using safely-filtered telescopes and cameras.

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:


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.

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!

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.


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.”


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:


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.


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:


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.”


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.

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.