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.

STEVE Visits the USA

May 6, 2018: On Saturday, May 5th, a stream of solar wind engulfed Earth, sparking G1 and G2-class geomagnetic storms through the weekend. High atop Earth’s atmosphere, hot ribbons of plasma began to flow through our planet’s magnetic field. Suddenly, STEVE appeared. Alan Dyer photographed the mauve ribbon of light over Gleichen, Alberta:

“STEVE, the strange auroral arc, put in quite the appearance on Sunday night, with a fine show over southern Alberta lasting about an hour,” says Dyer. “It started as a faint arc in the east, then intensified, cutting across the entire sky.”

STEVE (Strong Thermal Emission Velocity Enhancement) was discovered by sky watchers in Alberta only a few years ago, although the phenomenon was surely active long before. The narrow ribbon is related to auroras, but has a distinct shape, color, and habitat. Researchers are now beginning to understand STEVE as a manifestation of hot plasma currents in the upper atmosphere.

Elizabeth MacDonald of NASA’s Goddard Space Flight Center recently published a paper on STEVE. In it, they link STEVE to a phenomenon called “subauroral ion drifts” (SAIDs). Satellites have tracked thousands of SAIDs: They tend to appear most often during spring and fall and seem to prefer latitudes near +60 degrees.

This weekend, STEVE traveled farther south than usual. Greg Ash saw the ribbon over Ely, Minnesota, at latitude +47.9 N:

“As you can imagine, I was totally stoked,” says Ash. “This was my first STEVE sighting and it was unforgettable. It was visible with the naked eye and I could see the pulsations of green with the purple.”

Elsewhere, STEVE was sighted in Tofte, Minnesota (+47.6N), Buxton, North Dakota (+47.6 N), Arcadia, Michigan, (+44.5N) and Fort Frances, Ontario (+48.6N). These relatively low latitude apparitions are an encouraging sign for sky watchers who wish to see the strange ribbon for themselves. You don’t have to travel to the Arctic Circle to meet STEVE. He might be coming to you. Free: Aurora Alerts.

Realtime STEVE Photo Gallery

Blue Moon Lunar Eclipse

Jan. 25, 2018: On Wednesday, Jan. 31st, there’s going to be a “Blue Moon”–the second full Moon in a calendar month. People who go outside to look may see a different hue: bright orange. This Blue Moon is going to be eclipsed, swallowed by copper-colored shadow of Earth for more than an hour. The eclipse will be visible from Asia, Australia, and most of North America: visibility map.

Other time zones: UT, EST, CST, MST, PST, HST. Credit: Larry Koehn.

The bright orange color of the eclipse may be chalked up to volcanic activity–or rather, lack thereof. Atmospheric scientist Richard Keen from the University of Colorado explains:

“During a lunar eclipse, most of the light illuminating the Moon passes through Earth’s stratosphere where it is reddened by scattering,” he says. “If the stratosphere is loaded with dust from volcanic eruptions, the eclipse will be dark. The cataclysmic explosion of Tambora in 1815, for instance, turned the Moon into a dark, starless hole in sky during two subsequent eclipses.”

But Earth is experiencing a bit of a volcanic lull. We haven’t had a major volcanic blast since 1991 when Mt Pinatubo awoke from a 500 year slumber and sprayed ten billion cubic meters of ash, rock and debris into Earth’s atmosphere. Recent eruptions have been puny by comparison and have failed to make a dent on the stratosphere. To Keen, the interregnum means one thing: “This eclipse is going to be bright and beautiful.”

From “Two Centuries of Volcanic Aerosols Derived from Lunar Eclipse Records” by R.  Keen

Keen studies lunar eclipses because of what they can tell us about Earth’s energy balance. A transparent stratosphere “lets the sunshine in” and actually helps warm the Earth below. “The lunar eclipse record indicates a clear stratosphere has contributed about 0.2 degrees to warming since the 1980s.”

“Mt. Pinatubo finished a 110-year episode of frequent major eruptions that began with Krakatau in 1883,” he says. “Since then, lunar eclipses have been relatively bright, and the Jan. 31st eclipse should be no exception.”

In the USA, the best time to look is during the hours before sunrise. Western states are favored: The Moon makes first contact with the core of Earth’s shadow at 3:48 am Pacific Time, kicking off the partial eclipse. Totality begins at 4:52 am PST as Earth’s shadow engulfs the lunar disk for more than an hour. “Maximum orange” is expected around 5:30 am PST. Easternmost parts of the USA will miss totality altogether.

“I welcome any and all reports on the brightness of this eclipse for use in my volcano-climate studies,” says Keen.  While actual brightness measurements (in magnitudes) made near mid-totality are most useful, I can also make use of Danjon-scale ratings. Please be sure to note the time, method, and instruments used in your reports.” Observations may be submitted here.


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.


Nov. 23, 2017: On Nov. 22nd, the face of the sun was unblemished by sunspots, and NOAA classified solar activity as “very low.”  Nevertheless, the skies above Tromsø, Norway, exploded with a remarkable outburst of pink auroras. “Suddenly, the whole valley turned white (with a hint of pink),” says Frank Meissner, who witnessed and photographed the display. “It was over after about 20 seconds.”

How bright was it? “The brightness of the auroras may be compared to the car lights in the background of my photo,” points out Meissner.

In nearby Kvaløya, aurora tour guide Marianne Bergli witnessed a surge of pink that was, if anything, even more dramatic:

“Ironically, our guests stopped taking pictures,” says Bergli. “They were awestruck and frozen to the spot by the incredible pink and green lights overhead.”

This outburst was powered by a stream of solar wind flowing from a hole in the sun’s atmosphere. Such holes are common during Solar Minimum, and they require no sunspots to form. That’s why auroras continue throughout the 11-year solar cycle.

The pink color of the outburst tells us something interesting about the solar wind on Nov. 22nd: it seems to have been unusually penetrating. Most auroras are green–a verdant glow caused by energetic particles from space hitting oxygen atoms 100 km to 300 km above Earth’s surface. Pink appears when the energetic particles descend lower than usual, striking nitrogen molecules at the 100 km level and below.

In recent winters, big displays of pink and white auroras have coincided with spotless suns often enough to make observers wonder if there is a connection.  If so, more outbursts are in the offing as the sun continues its plunge toward a deep Solar Minimum. Stay tuned for pink!

Realtime Aurora Photo Gallery