Month: August 2016

Cosmic Rays vs. Clouds

/ Dr.Tony Phillips

The connection between cosmic rays and clouds has long been controversial.  Some researchers hold that cosmic rays hitting Earth’s atmosphere create aerosols which, in turn, seed clouds.  This could make cosmic rays an important player in weather and climate.  Other researchers are less convinced.  Although some laboratory experiments support the idea that cosmic rays help seed clouds, skeptics say the effect is too small to substantially affect the cloudiness of our planet or to avert the course of climate change.

A new study just published in the Aug. 19th issue of Journal of Geophysical Research: Space Physics comes down in favor of cosmic rays. A team of scientists from the Technical University of Denmark (DTU) and the Hebrew University of Jerusalem has linked sudden decreases in cosmic rays (called “Forbush Decreases”) to changes in Earth’s cloud cover.

Forbush Decreases occur when solar storms called “coronal mass ejections (CMEs)” sweep past Earth.  Magnetic fields in CMEs deflect cosmic rays and, essentially, sweep some of the cosmic rays away from our planet.  The research team led by Jacob Svensmark of DTU identified the strongest 26 Forbush Decreases between 1987 and 2007, and looked at ground-based+satellite records of cloud cover to see what happened.  In a press release, their conclusions were summarized as follows: “[Strong Forbush Decreases] cause a reduction in cloud fraction of about 2 percent corresponding to roughly a billion tonnes of liquid water disappearing from the atmosphere.”

If true, that’s amazing.  It would also underscore the importance of measuring cosmic rays in the atmosphere.  Recent balloon flights by Spaceweather.com and Earth to Sky Calculus show that cosmic rays are intensifying. Cloudy days, anyone?

Space Lightning Over China

/ Dr.Tony Phillips

On Aug. 13th in China, photographer Phebe Pan was photographing the night sky, hoping to catch a Perseid meteor. Instead, he witnessed a spectacular bolt of “space lightning.” Working atop Shi Keng Kong, the highest mountain peak in the Guangdong province, “I was using a fisheye lens to capture as much of the sky as possible,” says Pan. “Suddenly we saw a flash of blue and purple ejected from the top of a nearby thundercloud.”

“It just looked like a tree with branches, and grew up very fast,” says Pan. “It lasted just less than one second. So awesome!”

Oscar van der Velde, a member of the Lightning Research Group at the Universitat Politècnica de Catalunya, explains what Pan saw: “This is a very lucky capture of a gigantic jet. It’s the first time I’ve seen one captured using a fisheye lens!”

Think of them as sprites on steroids: Gigantic jets are lightning-like discharges that spring from the tops of thunderstorms, reaching all the way to the ionosphere more than 50 miles overhead. They’re enormous and powerful.

“Gigantic jets are much more rare than sprites,” says van der Velde. “While sprites were discovered in 1989 and have since been photographed by the thousands, it was not until 2001-2002 that gigantic jets were first recorded from Puerto Rico and Taiwan.” Only a few dozen gigantic jets have ever been seen.

Like their cousins the sprites, gigantic jets reach all the way up to the edge of space alongside meteors, noctilucent clouds, and some auroras. This means they are a true space weather phenomenon. Indeed, some researchers believe cosmic rays help trigger these exotic forms of lightning, but the link is controversial.

Realtime Sprite Photo Gallery

Perseid Meteor Outburst

/ Dr.Tony Phillips

Every year in August, Earth passes through a stream of debris from Comet Swift-Tuttle, source of the annual Perseid meteor shower. The shower is beloved by sky watchers. It is rich in fireballs and plays out over a two-week period of warm, starry summer nights.

This year’s display is going to be even better than usual. “Our models predict an outburst on Aug. 11-12 with peak rates greater than 200 meteors/hour under ideally dark skies,” explains Bill Cooke of NASA’s Meteoroid Environment Office. “That’s about twice as many Perseids as usual.”


Perseids in Aug. 2015, a composite image by Petr Horalek of Kolonica, Slovakia [more]

In ordinary years, Earth grazes the edge of Swift-Tuttle’s debris zone. Occasionally, though, Jupiter’s gravity tugs the huge network of dust trails closer, and Earth plows through closer to the middle. This appears to be one of those years. Experts at NASA and elsewhere agree that three or more streams are on a collision course with Earth–hence the outburst.

Observing tips: Go outside between midnight and dawn on the morning of Aug. 12th. Allow about 45 minutes for your eyes to adjust to the dark. Lie on your back and look straight up. Perseids can appear anywhere in the sky, but their tails will point back to a single point in the constellation Perseus: sky map. Increased activity may also be seen on the morning of Aug. 13th.

Got clouds? NASA is planning a live broadcast of the Perseid meteor shower overnight on Aug. 11-12 and Aug. 12-13, beginning at 10 p.m. EDT. You can also listen to radar echoes from the Perseids on Space Weather Radio. More webcasts: from Israel, from Alabama.

Realtime Perseid Photo Gallery

A Mysterious Form of Aurora

/ Dr.Tony Phillips

Humans have been watching the aurora borealis for thousands of years, with scientific studies of the phenomenon underway for centuries.  Despite all that watching and studying, however, there are still some auroral forms that remain a mystery–namely, the “proton arc.” This one appeared over the Grande Cache area of Alberta, Canada, on July 29th:

“As I was driving to the Kakwa river, I saw a purple ‘proton arc’ crossing the sky from east to west, pulsing and dancing with the Northern lights,” says photographer Catalin Tapardel. “Quite a show….”

Aurora photographers see these structures from time to time–tight ribbons of light, sometimes red, sometimes green, writhing across the night sky.  They are commonly called “proton arcs.”

Yet aurora scientists say they probably have nothing to do with protons.

“My opinion, and I believe the consensus of most aurora scientists, is that these arcs are not proton related, ” says Jason Ahrns, a researcher at the University of Alaska Fairbanks, “but I don’t know what does cause them.”

“Ordinary auroras we see from the ground and space are caused by electrons precipitating down into the atmosphere,” says Dennis Gallagher of the NASA Marshall Space Flight Center. “Protons can cause auroras, too, but they are different. For one thing, proton auroras are brightest in the UV part of the spectrum, invisible to the human eye.”

There is some visible light from proton auroras, but the structures they make are not tight and filamentary, but rather broad and diffuse–“in part because the gyroradius of protons is large,” says Ahrns. In other words, massive protons circle around magnetic fields in broad lazy arcs unlike lightweight electrons, which can tightly circle magnetic fields to form narrow structures.

Ahrns photographed an authentic proton aurora in February 2014: photo. “It appearance matched the description of proton arcs in the scientific literature – ‘a dim and diffuse glow’ with ‘very little structure in the observed brightness’ with a total brightness of only a few kiloRayleighs, which is just on the verge of visual threshold (Lummerzheim 2001).”

So what are the “proton arcs” often photographed by amateur aurora chasers? “I don’t know,” says Ahrns, “but it is something many of us would like to get to the bottom of!”  For more examples of this mystery in the sky, browse the Proton Arc Photo Gallery.

Realtime Proton Arc Photo Gallery

Realtime Aurora Photo Gallery