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Ice Lightning
By Randolph E. Schmid
Associated Press
posted: 12 August 2005
07:41 am ET
WASHINGTON (AP) ---- Poet Robert Frost once pondered whether the world would end in fire or in ice. Weather researchers say where you find ice you find fire -- at least in the form of lightning.
Whether the storm was over land, ocean or coastal areas, clouds with more ice produced more lightning, researchers studying satellite radar images report in the journal Geophysical Research Letters.
"The new thing is that when you look at different areas of the planet ... the hypothesis about the importance of ice holds up,'' Walter A. Petersen of the University of Alabama at Huntsville said Thursday.
He said weather scientists have known there was a relationship between ice and lightning, but were learning new details by studying the National Aeronautics and Space Administration satellite images which can look at both the number of lightning strikes and the volume of ice in a cloud at the same time.
Crucial is what is called precipitation-sized ice, particles of a millimeter or so which sometimes can be seen falling as small hail. "Where you have more of that, you tend to have more lightning,'' Petersen said.
These particles crash into smaller ice particles in the swirling winds inside storm clouds, resulting in a separation of electrical charge.
The charge separated between smaller and larger particles, with the smaller carrying a positive charge to the top of the thundercloud and the larger ones with the negative charge sinking to the bottom, he explained in a telephone interview.
"You effectively make a big battery with positive and negative ends,'' he said, with the charge building up until it is discharged as lightning.
The relationship between ice volume and lightning held true over such varied locations as the Himalaya Mountains, Central Africa, Madagascar, northern Australia and Florida, the researchers reported.
They found small areas of subtropical South America where lightning flash density seemed slightly less than would have been expected for the measured ice amount. Since they could find no physical reason for this the researchers said it may be a sampling error. They are doing more research on those areas.
The work was funded by the NASA's Earth Observing System and Earth Science Enterprise programs.
By Randolph E. Schmid
Associated Press
posted: 12 August 2005
07:41 am ET
WASHINGTON (AP) ---- Poet Robert Frost once pondered whether the world would end in fire or in ice. Weather researchers say where you find ice you find fire -- at least in the form of lightning.
Whether the storm was over land, ocean or coastal areas, clouds with more ice produced more lightning, researchers studying satellite radar images report in the journal Geophysical Research Letters.
"The new thing is that when you look at different areas of the planet ... the hypothesis about the importance of ice holds up,'' Walter A. Petersen of the University of Alabama at Huntsville said Thursday.
He said weather scientists have known there was a relationship between ice and lightning, but were learning new details by studying the National Aeronautics and Space Administration satellite images which can look at both the number of lightning strikes and the volume of ice in a cloud at the same time.
Crucial is what is called precipitation-sized ice, particles of a millimeter or so which sometimes can be seen falling as small hail. "Where you have more of that, you tend to have more lightning,'' Petersen said.
These particles crash into smaller ice particles in the swirling winds inside storm clouds, resulting in a separation of electrical charge.
The charge separated between smaller and larger particles, with the smaller carrying a positive charge to the top of the thundercloud and the larger ones with the negative charge sinking to the bottom, he explained in a telephone interview.
"You effectively make a big battery with positive and negative ends,'' he said, with the charge building up until it is discharged as lightning.
The relationship between ice volume and lightning held true over such varied locations as the Himalaya Mountains, Central Africa, Madagascar, northern Australia and Florida, the researchers reported.
They found small areas of subtropical South America where lightning flash density seemed slightly less than would have been expected for the measured ice amount. Since they could find no physical reason for this the researchers said it may be a sampling error. They are doing more research on those areas.
The work was funded by the NASA's Earth Observing System and Earth Science Enterprise programs.
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Re: Lightning research:
Thu, September 14, 2006 - 1:12 AMElectric Ice Gives Earth A Buzz
by Tony Phillips for NASA Science News
Huntsville AL (SPX) Sep 14, 2006
Here's something fun to try in your kitchen: Go to the freezer, open the door and pry loose an ice cube. Next, look around the freezing compartment for some frost-the crystalline fuzz that loves to coat your frozen English peas. Found it? Rub the ice cube gently across the frost.
Nothing happens. Well, what did you expect, a bolt of lightning?
Actually, that's just how lightning gets started. Miles above Earth in cumulonimbus clouds, tiny ice crystals are constantly bumping against larger ice pellets. The two kinds of ice rubbing together act like socks rubbing against carpet. Zap! Before you know it, the cloud is crackling with electric potential-and a bolt of lightning explodes to the ground.
It may seem hard to believe that a powerful bolt of lightning, which heats the air in its path three times hotter than the surface of the sun, could spring from little pieces of ice. But that's how it is, according to theory, and indeed laboratory experiments have confirmed that you can generate electricity from ice-ice collisions.
Still, it does sound fantastic. So, "we decided to check it out," says Walt Petersen, a lightning researcher at the National Space Science and Technology Center in Huntsville, Alabama.
Over a three year period, Petersen and his colleagues used the Tropical Rainfall Measurement Mission (TRMM) satellite to look inside more than one million clouds. "TRMM has a radar onboard to measure the amount of ice in a cloud. And it has an optical detector called LIS (lightning imaging sensor) to count lightning flashes." By comparing the ice content of a cloud to its flashes, they could tell if ice and lightning really go together.
They do. "We found a strong correlation between ice and lightning in all environments-over land, over sea and in coastal areas." On global scales, the correlation coefficient between lightning "flash density" (flashes per square-kilometer per month) and "ice water path" (kilograms of ice per square-meter of cloud) exceeded 90%. Even stronger correlations were found on the smaller scale of individual storm cells where, for example, about 10 million kilograms of ice would produce one lightning flash per minute.
10 million kilograms. No wonder you couldn't get a spark going in your freezer. A great deal more ice is required to make lightning.
In a real thundercloud, millions of pieces of ice are constantly bumping together, pushed by updrafts ranging in speed from 10 to 100 mph. Tiny ice crystals become positively charged and waft to the top of the cloud, while bulkier ice pellets (called "graupel") become negatively charged and plummet to the bottom. This separation creates mega-volts of electrical tension--and hence the lightning.
Now that the correlation between ice and lightning is so well established, it can be put to good use. Petersen explains:
"Computer programs we write to predict weather and climate need to know how much ice is in clouds. The problem is, ice is hard to track. We can't station a radar over every thundercloud to measure its ice content. To improve our computer forecasts, we need to know where the ice is."
Lightning can help. "Because there's such a strong correlation between lightning and ice, we can get a good idea of how much ice is 'up there' by counting lightning flashes." Sensors like LIS, which are inexpensive and can be stationed on the ground as well as in Earth orbit, make this easy to do.
Back to your freezer: You might want do something about those English peas.
A complete account of Petersen's research may be found in the proceedings of the LIS International Workshop, being held this week in Huntsville, Alabama.
Related Links
lis11.nsstc.uah.edu/
www.terradaily.com/reports/..._999.html
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Re: Lightning research:
Sun, August 23, 2009 - 2:48 PMLightning's mirror image... only much bigger
(PhysOrg.com) -- With a very lucky shot, scientists have captured a one-second image and the electrical fingerprint of huge lightning that flowed 40 miles upward from the top of a storm.
These rarely seen, highly charged meteorological events are known as gigantic jets, and they flash up to the lower levels of space, or ionosphere.
While they don't occur every time there is lightning, they are substantially larger than their downward striking cousins.
"Despite poor viewing conditions as a result of a full moon and a hazy atmosphere, we were able to clearly capture the gigantic jet," said study leader Steven Cummer, an electrical and computer engineer at Duke University in North Carolina.
A paper reporting Cummer's results appears online today in the journal Nature Geoscience.
Images of gigantic jets have only been recorded on five occasions since 2001. The Duke University team caught a one-second view and magnetic field measurements that are now giving scientists a much clearer understanding of these rare events.
"This confirmation of visible electric discharges extending from the top of a storm to the edge of the ionosphere provides an important new window on processes in Earth's global electrical circuit," said Brad Smull, program director in NSF's Division of Atmospheric Sciences, which funded the research.
"Our measurements show that gigantic jets are capable of transferring a substantial electrical charge to the lower ionosphere," Cummer said.
"They are essentially upward lightning from thunderclouds that deliver charge just like conventional cloud-to-ground lightning. What struck us was the size of this event."
It appears from the measurements that the amount of electricity discharged by conventional lightning and gigantic jets is comparable, Cummer said.
But the gigantic jets travel farther and faster than conventional lightning because thinner air between the clouds and ionosphere provides less resistance.
Whereas a conventional lightning bolt follows a six-inch channel and travels about 4.5 miles down to earth, the gigantic jet recorded by the scientists contained multiple channels and traveled about 40 miles upward.
"Given that reservoirs of electric charge in thunderstorms are the sources for both lightning and gigantic jets, and that both events involve contact between these reservoirs and a very large conducting surface, it is not surprising that their charge transfers are comparable," Cummer said.
Scientists don't know what conditions or what types of storms are conducive to gigantic jet formation.
It has been difficult in the past to obtain images of gigantic jets because they occur so quickly that cameras have to be trained on them at the precise moment they occur.
Cummer caught the gigantic jet almost by accident.
The equipment had been set to capture another phenomenon known as sprites, which were first photographed in 1989.
Sprites are electrical discharges that occur above storm clouds and are colored red or blue, with jellyfish-like tendrils hanging down.
Cummer maintains a low-light video camera trained to the sky and programmed to start recording when specific meteorological conditions occur.
At the same time, other equipment constantly measures radio emissions in the same sector to capture electrical events. A special GPS system ensures that the readings from all the equipment are synchronized.
Cummer is planning to install a low-light, high-speed camera to capture gigantic jet images in color, which could provide additional information about chemical processes and temperatures inside the phenomenon.
Source: National Science Foundation
www.physorg.com/news170254828.html
