Intriguing Global Atmospheric Phenomenon Found by NCKU Researchers
The first detailed global guide to the location of elves, sprites, produced by a three-year space survey, was disclosed by the New Scientist, which has attained recognition as the world’s No.1 science & technology news agent. This survey was carried out by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL), a dedicated instrument on board the FORMOSAT-2 satellite and conducted by a National Cheng Kung University (NCKU) research team.
According to Dr. Alfred Chen, a member of the ISUAL team, the ISUAL has spotted 5,434 elves, but only 633 sprites over 3 years, which revealed surprising and significant details about the spooky lights’ preferred habitats. Dr. Chen added that this discovery showed higher elves occurrence rate than sprites, which reverse the past discovery. Professor Rue-Ron Hsu, the co-investigator of this ISUAL team explained that elves, unlike the sprites which mainly congregate over continents, are found mostly over oceans.
Dr. Alfred Chen says that elves possibly may have an important global effect on the lower ionosphere and the total electron content. Dr. Chen also stressed that elf hotspots may increase the electron density of the ionosphere by up to 5%, which could interfere with ground and space communication as well as navigation.
On the basis of a 3-year survey data from the ISUAL/FORMOSAT-2 experiment, 80% of recorded transient luminous events (TLEs) are elves, while 20% of them are sprites, halos and blue jets. The NCKU research team found that the relative observation frequency of elves, and also the relative observation frequency of greater than 80 kA peak current lightning, is 10 times higher over oceans than over lands. The strong dependence of elves occurrence over the sea, when surface temperature is greater than 26 degrees C, indicates that the warm tropical oceans provide the heat source to drive vertical convection and produce intense oceanic lightning, which in turn induces a large fraction of the ISUAL recorded elves. This is a manifestation of ocean-atmosphere-ionosphere coupling. The increase of free electrons in the lower ionosphere from elves at global and local levels was also evaluated. The NCKU research team indicated that the global free electron contribution from elves is 1% approximately; however, the free electron content above elves hot zones could be elevated by more than 5%.
About elves
Elves are rapidly expanding (up to 300 miles across) disk-shaped regions of luminosity, lasting less than a thousandth of a second, which occur high above energetic cloud-to-ground lightning of positive or negative polarity. Elves are most likely resulted when an energetic electromagnetic pulse (EMP) propagates into the ionosphere. Though they can be accompanied by sprites, the causative mechanism is of an entirely different nature. Predicted to exist in 1991and discovered with a low-light video camera aboard the Space Shuttle in 1992, elves got their name as an acronym for Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources.
About sprites
Red sprites are large but weak luminous flashes that appear directly above an active thunderstorm system and are coincident with powerful positive cloud-to-ground lightning strokes. Their spatial structures range from small single or multiple vertically elongated spots, to bright groupings which extend from above the cloud tops to altitudes up to almost 60 miles (about 95 km). Sprites are predominantly red and they usually last no more than a few milliseconds. The brightest region lies in the altitude range 40 to 45 miles (about 65-75 km) from the sea level, above which there is often a faint red glow or wispy structure that extends to about 55 miles (90 km). Below the bright red region, blue tendril-like filamentary structures often extend downward to as low as 20 miles (30 km). Some events are loosely packed and may extend across horizontal distances of 30 miles (50 km) or more. Their shapes can be variously described as resembling jellyfish, carrots, or columns. Because of their low surface brightness, they have only been imaged at night (primarily with highly sensitive cameras). However, if ones eyes are sufficiently dark-adapted, one can actually detect them without any visual aid. The first images of a sprite were accidently obtained in 1989, although anecdotal reports of "rocket-like" and other optical emissions above thunderstorms go back more than a century. Early research reports for these events referred to them by a variety of names, including "upward lightning”, "upward discharges", "cloud-to-stratosphere discharges," and "cloud-to- ionosphere discharges." Now they are simply referred to as sprites, a whimsical term that evokes a sense of their fleeting nature, while at the same time remaining nonjudgmental about physical processes that have yet to be determined.
About New Scientist
New Scientist is a weekly international science magazine and website covering latest developments in science and technology for a general English-speaking audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of Reed Elsevier. New Scientist has maintained a website since 1996, publishing daily news. As well as covering current events and news from the scientific community, the magazine often features speculative articles, ranging from the technical to the philosophical.
About ISUAL:
ISUAL is the acronym for Imager of Sprites and Upper Atmospheric Lightnings. It is a set of scientific payload instruments on the FORMOSAT-2 satellite, which is the second satellite from Taiwan, ROC. ISUAL project is an international collaboration supported by the National Space Program Office in Taiwan, with additional contributions from the National Cheng Kung University, Taiwan, the Space Science Laboratory of the University of California at Berkeley, USA, and Tohoku University, Japan.
The scientific goals of this mission are to investigate lightning induced, luminous atmospheric phenomena, polar aurora and upper atmospheric airglow. This scientific cooperation includes the design and construction of a scientific instrument package, its integration on the FORMOSAT-2 satellite, its placement into orbit and its on orbit operation for five years. This mission is scheduled to launch on 16 January, 2004.
According to Dr. Alfred Chen, a member of the ISUAL team, the ISUAL has spotted 5,434 elves, but only 633 sprites over 3 years, which revealed surprising and significant details about the spooky lights’ preferred habitats. Dr. Chen added that this discovery showed higher elves occurrence rate than sprites, which reverse the past discovery. Professor Rue-Ron Hsu, the co-investigator of this ISUAL team explained that elves, unlike the sprites which mainly congregate over continents, are found mostly over oceans.
Dr. Alfred Chen says that elves possibly may have an important global effect on the lower ionosphere and the total electron content. Dr. Chen also stressed that elf hotspots may increase the electron density of the ionosphere by up to 5%, which could interfere with ground and space communication as well as navigation.
On the basis of a 3-year survey data from the ISUAL/FORMOSAT-2 experiment, 80% of recorded transient luminous events (TLEs) are elves, while 20% of them are sprites, halos and blue jets. The NCKU research team found that the relative observation frequency of elves, and also the relative observation frequency of greater than 80 kA peak current lightning, is 10 times higher over oceans than over lands. The strong dependence of elves occurrence over the sea, when surface temperature is greater than 26 degrees C, indicates that the warm tropical oceans provide the heat source to drive vertical convection and produce intense oceanic lightning, which in turn induces a large fraction of the ISUAL recorded elves. This is a manifestation of ocean-atmosphere-ionosphere coupling. The increase of free electrons in the lower ionosphere from elves at global and local levels was also evaluated. The NCKU research team indicated that the global free electron contribution from elves is 1% approximately; however, the free electron content above elves hot zones could be elevated by more than 5%.
About elves
Elves are rapidly expanding (up to 300 miles across) disk-shaped regions of luminosity, lasting less than a thousandth of a second, which occur high above energetic cloud-to-ground lightning of positive or negative polarity. Elves are most likely resulted when an energetic electromagnetic pulse (EMP) propagates into the ionosphere. Though they can be accompanied by sprites, the causative mechanism is of an entirely different nature. Predicted to exist in 1991and discovered with a low-light video camera aboard the Space Shuttle in 1992, elves got their name as an acronym for Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources.
About sprites
Red sprites are large but weak luminous flashes that appear directly above an active thunderstorm system and are coincident with powerful positive cloud-to-ground lightning strokes. Their spatial structures range from small single or multiple vertically elongated spots, to bright groupings which extend from above the cloud tops to altitudes up to almost 60 miles (about 95 km). Sprites are predominantly red and they usually last no more than a few milliseconds. The brightest region lies in the altitude range 40 to 45 miles (about 65-75 km) from the sea level, above which there is often a faint red glow or wispy structure that extends to about 55 miles (90 km). Below the bright red region, blue tendril-like filamentary structures often extend downward to as low as 20 miles (30 km). Some events are loosely packed and may extend across horizontal distances of 30 miles (50 km) or more. Their shapes can be variously described as resembling jellyfish, carrots, or columns. Because of their low surface brightness, they have only been imaged at night (primarily with highly sensitive cameras). However, if ones eyes are sufficiently dark-adapted, one can actually detect them without any visual aid. The first images of a sprite were accidently obtained in 1989, although anecdotal reports of "rocket-like" and other optical emissions above thunderstorms go back more than a century. Early research reports for these events referred to them by a variety of names, including "upward lightning”, "upward discharges", "cloud-to-stratosphere discharges," and "cloud-to- ionosphere discharges." Now they are simply referred to as sprites, a whimsical term that evokes a sense of their fleeting nature, while at the same time remaining nonjudgmental about physical processes that have yet to be determined.
About New Scientist
New Scientist is a weekly international science magazine and website covering latest developments in science and technology for a general English-speaking audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of Reed Elsevier. New Scientist has maintained a website since 1996, publishing daily news. As well as covering current events and news from the scientific community, the magazine often features speculative articles, ranging from the technical to the philosophical.
About ISUAL:
ISUAL is the acronym for Imager of Sprites and Upper Atmospheric Lightnings. It is a set of scientific payload instruments on the FORMOSAT-2 satellite, which is the second satellite from Taiwan, ROC. ISUAL project is an international collaboration supported by the National Space Program Office in Taiwan, with additional contributions from the National Cheng Kung University, Taiwan, the Space Science Laboratory of the University of California at Berkeley, USA, and Tohoku University, Japan.
The scientific goals of this mission are to investigate lightning induced, luminous atmospheric phenomena, polar aurora and upper atmospheric airglow. This scientific cooperation includes the design and construction of a scientific instrument package, its integration on the FORMOSAT-2 satellite, its placement into orbit and its on orbit operation for five years. This mission is scheduled to launch on 16 January, 2004.
Provider:
新聞中心
Date:
2008-08-29
