Mystery of Bizarre Radar Echoes Solved, 50 Years Later
The mysterious phenomenon would show up only during daylight hours, vanishing at night.
More than 50 years after weird radio echoes were detected coming from Earth's upper atmosphere, two scientists say they've pinpointed the culprit. And it's complicated.
In 1962, after the Jicamarca Radio Observatory was built near Lima, Peru, some unexplainable phenomenon was reflecting the radio waves broadcast by the observatory back to the ground to be picked up by its detectors. The mysterious cause of these echoes was sitting at an altitude of between 80 and 100 miles (130 and 160 kilometers) above sea level.
"As soon as they turned this radar on, they saw this thing," study researcher Meers Oppenheim, of the Center for Space Physics at Boston University, said, referring to the anomalous echo. "They saw all sorts of interesting phenomena that had never been seen before. Almost all of it was explained within a few years." [In Photos: Mysterious Radar Blob Puzzles Meteorologists]
Peculiar radar echoes
Though the other phenomena detected by the observatory got explanations, these radar echoes continued to baffle scientists.
To see what was happening at that altitude, researchers at the time sent rockets, equipped with antennas and particle detectors, through the region. The instruments, which were designed to detect radar waves, "saw almost nothing," Oppenheim said.
Adding more peculiarity to the puzzle, the phenomenon showed up only during daylight hours, vanishing at night. The echo would appear at dawn every day at about 100 miles (160 km) above the ground, before descending to about 80 miles (130 km) and getting stronger. Then at Noon, the echo would start to rise back again toward its starting point at 100 miles above the ground. When plotted on a graph, the echoes appeared as a necklace shape.
And in 2011, during a partial solar eclipse seen over the National Atmospheric Research Laboratory in India, the echo went silent.
"And then there was a solar flare, and it sort of went a little nuts," Oppenheim said. "There was a solar flare, and the echo got really strong."
The sun takes charge
Now, with a lot of supercomputing effort, Oppenheim and Yakov Dimant, also at the Center for Space Physics, have simulated the bizarre radar echoes to find the culprit - the sun. [Infographic: Explore Earth's Atmosphere, Top to Bottom]
Ultraviolet radiation from the sun, it seems, slams into the ionosphere (the part of Earth's upper atmosphere located between 50 and 370 miles, or 80 and 600 km, above sea level), where the radio echoes were detected, they said. Then, the radiation, in the form of photons (particles of light), strips molecules in that part of the atmosphere of their electrons, resulting in charged particles called ions - primarily, positively charged of their electrons, resulting in charged particles called ions, primarily positively charged oxygen - and a free electron (a negatively charged particle that is not attached to an atom or molecule).
That ultra-energized electron, or photoelectron, zips through the atmosphere, which, at this altitude, is much cooler than the photoelectron, Oppenheim said.
Using a computer simulation, the scientists allowed these high-energy electrons to interact with other, less energized particles.
Because these high-energy electrons are racing through a cool, slow environment in the ionosphere, so-called kinetic plasma instabilities (turbulence, in a sense) occur. The result: The electrons start vibrating with different wavelengths.
"One population of very energetic particles moving through a population of much less energetic particles - it's like running a violin bow across the strings. The cold population will start developing resonant waves," Oppenheim explained.
"The next step is that those electron waves have to cause the ions to start forming waves too, and they do," Oppenheim said.
Though this last step isn't clearly understood, he explained that periodic waves of ions bunch up with no dominant wavelength winning out. "It's a whole set of wavelengths; it's a whole froth of wavelengths," he said.
That "froth" of wavelengths was strong enough to reflect radio waves back to the ground and to form the mysterious radar echoes.
"The reason it wasn't figured out for a long time is that it's a complicated mechanism," Oppenheim said.
As for why the rockets missed the bizarre echoes, Oppenheim pointed to the messy nature of the waves.
"Turns out, it looks like what the rockets saw is what we see with our simulation," he said. "You don't see strong coherent waves. What you see is sort of a froth of low-level waves, above the noise of thermal material," and those waves are sort of like "foam on the top of sea waves," he added.
Original article on Live Science.
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Radar echoes plotted over the course of two days show how the signal emerged at dawn, descended toward the ground, and then rose again over the course of the day.
March 13, 2013, marks 20 years since the W. M. Keck Observatory began taking observations of the cosmos. Located in arguably one of the most extreme and beautiful places on the planet -- atop Mauna Kea, Hawai'i, 13,803 ft (4,207 m) above sea level -- the twin Keck domes have observed everything from asteroids, planets, exoplanets to dying stars, distant galaxies and nebulae. Seen in this photograph, the Keck I and Keck II telescopes dazzle the skies with their adaptive optics lasers -- a system that helps cancel out the turbulence of the Earth's atmosphere, bringing science some of the clearest views attainable by a ground-based observatory.
To celebrate the last two decades of incredible science, Discovery News has assembled some of the most impressive imagery to come from Keck.
Starting very close to home, the Keck II captured this infrared image of asteroid 2005 YU55 as it flew past Earth on Nov. 8, 2011.
Deeper into the solar system, the Keck NIRC2 near-infrared camera captured this beautiful observation of the oddball Uranus on July 11-12, 2004. The planet's north pole is at 4 o'clock.
This is a mosaic false-color image of thermal heat emission from Saturn and its rings on Feb. 4, 2004, captured by the Keck I telescope at 17.65 micron wavelengths.
A nice image of Saturn with Keck I telescope with the near infrared camera (NIRC) on Nov. 6, 1998. This is a composite of images taken in Z and J bands (1.05 and 1.3 microns), with the color scaling adjusted so it looks like Saturn is supposed to look to the naked eye.
This is Saturn's giant moon Titan -- a composite of three infrared bands captured by the Near Infrared Camera-2 on the 10-meter Keck II telescope. It was taken by astronomer Antonin Bouchez on June 7, 2011.
Another multicolored look at Titan -- a near-infrared color composite image taken with the Keck II adaptive optics system. Titan's surface appears red, while haze layers at progressively higher altitudes in the atmosphere appear green and blue.
This image of Neptune and its largest Tritan was captured by Caltech astronomer Mike Brown in September 2011. It shows the wind-whipped clouds, thought to exceed 1,200 miles per hour along the equator.
A color composite image of Jupiter in the near infrared and its moon Io. The callout at right shows a closeup of the two red spots through a filter which looks deep in the cloud layer to see thermal radiation.
HR 8799: Three exoplanets orbiting a young star 140 light years away are captured using Keck Observatory's near-infrared adaptive optics. This was the first direct observation by a ground-based observatory of worlds orbiting another star (2008).
Now to the extremes -- an image of Stephan's Quintet, a small compact group of galaxies.
The Egg Nebula: This Protoplanetary nebula is reflecting light from a dying star that is shedding its outer layers in the final stages of its life.
This is WR 104, a dying star. Known as a Wolf Rayet star, this massive stellar object will end its life in the most dramatic way -- possibly as a gamma-ray burst. The spiral is caused by gases blasting from the star as it orbits with another massive star.
Narrow-field image of the center of the Milky Way. The arrow marks the location of radio source Sge A*, a supermassive black hole at the center of our galaxy.
A high resolution mid-infrared picture taken of the center of our Milky Way reveals details about dust swirling into the black hole that dominates the region.
A false-color image of a spiral galaxy in the constellation Camelopardalis.
A scintillating square-shaped nebula nestled in the vast sea of stars. Combining infrared data from the Hale Telescope at Palomar Observatory and the Keck II telescope, researchers characterized the remarkably symmetrical “Red Square” nebula.
Galaxy cluster Abell 2218 is acting as a powerful lens, magnifying all galaxies lying behind the cluster's core. The lensed galaxies are all stretched along the shear direction, and some of them are multiply imaged.
The central starburst region of the dwarf galaxy IC 10. In this composite color image, near infrared images obtained with the Keck II telescope have been combined with visible-light images taken with NASA’s Hubble Space Telescope.
Keck I (right) and Keck II (left) domes at Mauna Kea.
Keck I and Keck II aim their adaptive optics lasers at the galactic center.