Puzzling Property Of Night-shining Clouds At Edge Of Space Explained

[Nostalgia]

ScienceDaily (Sep. 26, 2008) — An explanation for a strange property of noctilucent clouds--thin, wispy clouds hovering at the edge of space at 85 km altitude--has been proposed by an experimental plasma physicist at the California Institute of Technology (Caltech), possibly laying to rest a decades-long mystery.


What is a Noctilucent Cloud? -- Polar mesospheric clouds,
as they are known to those who study them from satellite
observations, are also often called "noctilucent," or night
shining, clouds as seen by ground-based observers.
Because of their high altitude, near the edge of space,
noctilucent clouds shine at night when the Sun's rays hit
them from below while the lower atmosphere is bathed in
darkness.

Noctilucent clouds, also known as night-shining clouds, were first described in 1885, two years after the massive eruption of Krakatoa, a volcanic island in Indonesia, sent up a plume of ash and debris up to 80 km into Earth's atmosphere. The eruption affected global climate and weather for years and may have produced the first noctilucent clouds.

The effects of Krakatoa eventually faded, but the unusual electric blue clouds remain, nestled into a thin layer of Earth's mesosphere, the upper atmosphere region where pressure is 10,000 times less than at sea level. The clouds, which are visible during the deep twilight, are most often observed during the summer months at latitudes from 50 to 70 degrees north and south--although in recent years they have been seen as far south as Utah and Colorado. Noctilucent clouds are a summertime phenomenon because, curiously, the atmosphere at 85 km altitude is coldest in summer, promoting the formation of the ice grains that make up the clouds.

"The incidence of noctilucent clouds seems to be increasing, perhaps because of global warming," says Paul M. Bellan, a professor of applied physics at Caltech.

Twenty-five years ago, researchers at Poker Flat, Alaska, discovered that the clouds were highly reflective to radar. This unusual property has long puzzled scientists. Bellan, reporting in the August issue of the Journal of Geophysical Research-Atmospheres, now has an explanation: the ice grains in noctilucent clouds are coated with a thin film of metal, made of sodium and iron. The metal film causes radar waves to reflect off ripples in the cloud in a manner analogous to how X-rays reflect from a crystal lattice.

Sodium and iron atoms collect in the upper atmosphere after being blasted off incoming micrometeors. These metal atoms settle into a thin layer of vapor that sits just above the altitude at which noctilucent clouds occur. Astronomers recently have been using the sodium layer to create laser-illuminated artificial guide stars for adaptive optics telescopes that remove the distorting affects of atmospheric turbulence to produce clearer celestial images.

Measurements of the density of sodium and iron atomic vapor layers show that the metal vapor is depleted by over 80 percent when noctilucent clouds are present. "Noctilucent clouds have been shown to act very much like a flycatcher for sodium and iron atoms," Bellan says. Indeed, in laboratory experiments, other researchers have found that at the frigid temperatures (-123 degrees Celsius) within noctilucent clouds, atoms in sodium vapor quickly become deposited on the surface of ice to form a metallic film.

"If you have metal-coated ice grains in noctilucent clouds, the radar reflectivity can become enormous" he says. "This reflectivity is not the sum of reflections from individual ice grains, which would not produce a very large reflection. Instead, what happens is that ripples in the cloud of metal-coated ice grains reflect in unison and reinforce each other, somewhat like an army marching in step across a bridge causes the bridge to vibrate."

[Nostalgia]

Originally Posted by Nostalgia

Noctilucent clouds are a summertime phenomenon because, curiously, the atmosphere at 85 km altitude is coldest in summer, promoting the formation of the ice grains that make up the clouds.

Hmm, the last I heard noctilucent clouds were easier to see in mid summer due to the fact that the sun barely settles over the horizon and thus reflects off the clouds causing them to shine.

http://science.nasa.gov/headlines/y2003/19feb_nlc.htm

So given that

"The incidence of noctilucent clouds seems to be increasing,

which I have now witnessed myself for the past three years running, does it mean that these strange reflective clouds are actually above our heads all of the time now and are caused by something else?

Here is an image of a rocket plume not long after take off from Vandenburg airforce base California.

If you notice, this photograph looks as if it was taken at dusk just after the sun has gone down, which means that the sun has just gone over the horizon.
Can you see how "shiny" the contrail is?

[Nostalgia]

Twenty-five years ago, researchers at Poker Flat, Alaska, discovered that the clouds were highly reflective to radar.

Here is something about what goes on a Poker Flat, perhaps this might help explain why Noctilucent clouds are relective to radar.

Geophysical Institute, University of Alaska, Fairbanks

Abstract

Barium plasma clouds released at high latitudes characteristically become striated with many field-aligned rays. The rays which often resemble auroral features usually drift as a whole with the E × B/B² drift of the cloud and alter position only slowly (order of tens of seconds). On two evenings in 1968, in released from Andøya, Norway, anomalous field-aligned brightenings or emission enhancements of up to 3X were observed to move rapidly (10-20 km/s) through three different Ba+ clouds. Similar effects were observed in Ba+ clouds released from rockets launched from Poker Flat, Alaska: On March 21, 1973, in two Ba thermite releases and on March 22, 1980, in the Ba-shaped charge experiment “Miss Peggy.” On these occasions, auroras on or near the Ba+ L shell, also exhibited active rapid ray motions. This leads us to the assumption that the two phenomena are related and the expectation that an explanation of the rapid ray motions in the Ba+ clouds would lead to a better understanding of the physics of auroral ray motions and the auroral ionosphere. Seven possible mechanisms to produce the observed moving emission enhancements are discussed. Direct excitation by energetic electron bombardment is ruled out on the basis of energy fluxes required for realistic cross sections. Direct motion of an isolated Ba+ ray past the other rays by E × B/B² motion seems very unlikely due to the observed variations in the enhancements and the large E field required (>500 mV/m). Compressional waves do not seem to be of sufficient amplitude or velocity. Formation of folds or curls in a sheet beam instability require moving radial fields of 500 mV/m but would explain the auroral features as well as the Ba+ by the same mechanism. Qualitatively, the redistribution of Ba ions as a flux tube encounters a higher electron density in the ionosphere may result in enhancements. Absorption or radiation of Doppler shifted Ba+ emissions by ions gyrating or moving at a few kilometers per second seems to be the most promising mechanism for producing the enhancements. The observations provide compelling evidence for the existence of transient electric fields of order 100 mV/m at altitudes as low as 200 km during active aurora with rapid ray motions. The affected regions have dimensions of order a few kilometers across B and move eastward at 10-20 km/s.

Received 4 June 1992; accepted 16 October 1992.
http://www.agu.org/pubs/crossref/1993/92JA02559.shtml

PatentUS3751913: BARIUM RELEASE SYSTEM
chemical system for releasing a good yield of free barium (Ba°) atoms and barium ions (Ba+) to create ion clouds in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium.

Attorney, Agent or Firm: Manning, John R. ; Osborn, Howard J. ; Nelson, Wallace J. ;

Primary / Asst. Examiners: Padgett, Benjamin R.;


First Claim:
Show all 2 claims What is claimed as new and desired to be secured by Letters Patent of the United States is: 1. A method of releasing a good yield of free barium atoms and barium ions in a gaseous medium comprising the steps of:

* dissolving a barium salt selected from the group consisting of BaCl2, Ba(NO3)2 and a mixture of BaCl2 and Ba(NO3)2 in a liquid fuel selected from the group consisting of hydrazine and liquid ammonia,
* providing a liquid oxidizer selected from the group consisting of OF2, F2 and ClF2 for the fuel,
* releasing the liquid fuel containing the barium salt simultaneously with releasing the liquid oxidizer so that the two released liquids contact each other whereby a hypergolic reaction takes place to release a high yield of luminous barium atoms and barium ions in the resulting flame.

http://www.delphion.com/details?pn=US03751913__

[Nostalgia]

The Poker Flat Research Range is located about 50 km North of Fairbanks, Alaska, and it was established in 1968. It is operated by the Geophysical Institute with the University of Alaska Fairbanks, under NASA contract. About 250 major rocket launches have taken place from this site, and in 1994, a 16-meter long rocket was launched to help NASA "understand chemical reactions in the atmosphere associated with global climate change."

Similar experiments, but using Chemical Release Modules (CRM), have been launched from Churchill, Manitoba. In 1980, Brian Whelan's "Project Waterhole" disrupted an aurora borealis, bringing it to a temporary halt. In February 1983, the chemical released into the ionosphere caused an aurora borealis over Churchill. In March 1989, two Black Brant X's and two Nike Orion rockets were launched over Canada, releasing barium at high altitudes and creating artificial clouds. These Churchill artificial clouds were observed from as far away as Los Alamos, New Mexico.
http://onlinejournal.org/Commentary/...2205mazza.html