Featured Research

from universities, journals, and other organizations

Bolts Of Blue Lightning Thrusting Upward And Other Weird Lightning Explained

Date:
March 30, 2008
Source:
Penn State
Summary:
The mechanism behind different types of lightning may now be understood, thanks to a combination of direct observation and computer modeling. Most people see lightning strikes that go from clouds to the ground, but some lightning goes upward, forming blue jets and gigantic jets. Perhaps the most dangerous lightning appears as "bolts from the blue" -- lightning that begins upward, but then moves sideways and then downward to hit the ground as much as three miles from a thunderstorm.

Most people see lightning strikes that go from clouds to the ground, but some lightning goes upward, forming blue jets and gigantic jets. Perhaps the most dangerous lightning appears as "bolts from the blue" -- lightning that begins upward, but then moves sideways and then downward to hit the ground as much as three miles from a thunderstorm.
Credit: iStockphoto/Martin Fischer

The mechanism behind different types of lightning may now be understood, thanks to a combination of direct observation and computer modeling reported by a team of researchers from New Mexico Tech and Penn State.

"Our explanation provides a unifying view of how lightning escapes from a thundercloud," the researchers report in the April edition of Nature Geoscience.

Most people see lightning strikes that go from clouds to the ground, but some lightning goes upward, forming blue jets and gigantic jets. Perhaps the most dangerous lightning appears as "bolts from the blue" -- lightning that begins upward, but then moves sideways and then downward to hit the ground as much as three miles from a thunderstorm.

About 90 percent of lightning occurs inside clouds and is not visible to the casual observer. The researchers wondered if lightning that appears within clouds and the lightning that escapes upward or downward shared the same development mechanisms.

"With the help of colleagues from New Mexico Tech, we were able to build a model of lightning and apply it to the various types of lightning," says Jeremy A. Riousset, graduate student in electrical engineering, Penn State. "Thanks to their observations and measurements, we know how lightning like 'bolts from the blue' happen. We know they develop like normal intracloud lightning before escaping the thundercloud at upper levels and branching toward the ground."

They also discovered that upward and sideward lightning events occurred shortly after normal downward lightning bolts occurred or intracloud lightning produced a local charge imbalance in the cloud.

Harald E. Edens, graduate student in physics, New Mexico Tech, working with Paul R. Krehbiel, professor of physics; Ronald J. Thomas, professor of electrical engineering, and William Rison, professor of electrical engineering, all at New Mexico Tech; and Mark A. Stanley, consultant, obtained detailed pictures of "bolts from the blue" using New Mexico Tech's Lightning Mapping Array, a three-dimensional lightning location system that uses multiple measurement stations to capture and time the VHF signal of the lightning. The Lightning Mapping Array can map lightning within clouds, something that normal optical photography or videography cannot do.

Riousset, working with Victor P. Pasko, associate professor, electrical engineering at Penn State, looked at the images from New Mexico and developed a model that explained the variety of lightning types. Lightning forms in clouds when different areas of the cloud become either positively or negatively charged. Once the electric field near a charged area exceeds a certain propagation level, lightning occurs. The type of lightning depends on where the charge builds and where the imbalance in charge exists in the clouds.

For intracloud lightning, the most common form of lightning, the transfer of charge occurs between the most negatively and most positively charged areas, the middle and upper parts of the cloud, respectively. Lightning that strikes the ground does so because precipitation or the storm's progression creates an excess of net negative charge in the mid-levels of the cloud. This results in either a direct ground strike or a bolt from the blue.

An alternative way to discharge a middle negative charge is through a gigantic jet, which propagates upward. The height of the clouds somewhat controls whether a gigantic jet or bolt from the blue propagates. The higher the top of the cloud, the more likely a gigantic jet will appear.

However, large positive charge in the upper levels of the storm causes blue jets.

"This is the first consistent definition of blue jets and gigantic jets," says Pasko.

In normal thunderstorms, blue jets are positive, originate in the uppermost part of the cloud and propagate continuously upward; while gigantic jets are negative, begin like a normal intracloud flash and propagate stepwise upward. Inverted polarity storms do exist and the charges of the various lightning types would then reverse.

The higher the cloud, the more likely either type of jet becomes. Thunderstorms in the tropics form with very high clouds increasing the chances of jets forming. Thunderstorms in the temperate United States do not have clouds quite so high, allowing a great number of bolts from the blue to occur. Bolts from the blue are very common in continental mid-latitude storms.

Every discharge of lightning from the cloud alters the charge status within the cloud, shifting the locations of the highest negatively or positively charged areas. These shifts along with mixing of the upper areas of the clouds can tip the storm toward bolts from the blue or jets depending on the circumstances.

"We are proposing a self-consistent, unified theory of lightning discharges inside and outside of clouds including blue jets, bolts from the blue and gigantic jets," says Pasko of Penn State. He adds that while their model can stipulate the requirements of each type of lightning, data collection during storms is too slow for the model to act in any predictive way.

The National Science Foundation supported this work.


Story Source:

The above story is based on materials provided by Penn State. Note: Materials may be edited for content and length.


Cite This Page:

Penn State. "Bolts Of Blue Lightning Thrusting Upward And Other Weird Lightning Explained." ScienceDaily. ScienceDaily, 30 March 2008. <www.sciencedaily.com/releases/2008/03/080328102738.htm>.
Penn State. (2008, March 30). Bolts Of Blue Lightning Thrusting Upward And Other Weird Lightning Explained. ScienceDaily. Retrieved October 20, 2014 from www.sciencedaily.com/releases/2008/03/080328102738.htm
Penn State. "Bolts Of Blue Lightning Thrusting Upward And Other Weird Lightning Explained." ScienceDaily. www.sciencedaily.com/releases/2008/03/080328102738.htm (accessed October 20, 2014).

Share This



More Earth & Climate News

Monday, October 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Powerful Hurricane Gonzalo Heads to Bermuda

Raw: Powerful Hurricane Gonzalo Heads to Bermuda

AP (Oct. 17, 2014) — Hurricane Gonzalo pounded Bermuda with wind and heavy surf on Friday, bearing down on the tiny British territory as a powerful Category 3 storm that could raise coastal seas as much as 10 feet. (Oct. 17) Video provided by AP
Powered by NewsLook.com
So, Kangaroos Didn't Always Hop

So, Kangaroos Didn't Always Hop

Newsy (Oct. 16, 2014) — Researchers believe an extinct kangaroo species weighed 500 pounds or more and couldn't hop. Video provided by Newsy
Powered by NewsLook.com
Hurricane Gonzalo Is A Category 4 And Heading To Bermuda

Hurricane Gonzalo Is A Category 4 And Heading To Bermuda

Newsy (Oct. 16, 2014) — Powerful hurricane could hit Bermuda this weekend, and even if it misses it will likely do some damage. Video provided by Newsy
Powered by NewsLook.com
The Largest Volcano In Centuries Is Spewing Toxic Gas

The Largest Volcano In Centuries Is Spewing Toxic Gas

Newsy (Oct. 16, 2014) — One of the largest volcanic eruptions in centuries is occurring on Iceland. The volcano Bardarbunga is producing high levels of sulfur dioxide. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins