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Posted at 02:20 PM ET, 07/19/2012

Dissecting a derecho bolt: more to lightning than meets the eye (and camera lens)


The lightning photograph above, shot on June 29 at 11:24 PM, shows only a small fraction of the entire lightning flash that occurred in the sky. Much of the lightning was blocked from view by clouds. The lightning plot, also from June 29 at 11:24 PM, was created by NOAA’s Scott Rudlosky using data from the Washington D.C. Lightning Mapping Array (DCLMA). Note, the inserted lightning photo is not to the exact scale and perspective of the plot, but it serves to illustrate that the visible lightning was a small portion of a much larger lightning flash that occurred in the sky over Washington and surrounding suburbs.

Over a year ago, NOAA’s Scott Rudlosky and I began discussing an effort to match a lightning photograph with its corresponding lightning data recorded by the Washington D.C. Lightning Mapping Array (DCLMA). We felt that we could learn more about the lightning that we see flashing across the sky by investigating the data behind the flash, such as where it originated, where it traveled, its elevation, and where it struck ground. But we needed a good lightning photo to compare with the data, and the lightning photograph needed to be taken within the DCLMA boundaries which spans much of the greater Washington area.

Finally, on the evening of June 29 - the night of the destructive derecho storm, we had our opportunity. During an intense storm chase with Ian Livingston, I photographed a unique lightning discharge over Washington. I emailed the photo to Scott with the time/date stamp and he began his investigative work.

Read below for the rest of the story to see the lightning plot, the lightning photo, and a 3D video of the lightning data.


Lightning over Washington on June 29, 2012 at 11:24 PM. NOAA’s Scott Rudlosky analyzed this photo with the DCLMA data and summarized the following: The flash appears to have initiated ~22,000 feet above Landover, Md., before striking ground in the District near Brookland (right bolt) and again near Rock Creek Park (left bolt). The flash was well over 50 miles long, covering over 200 square miles. The upper branches propagated horizontally at ~40,000 feet all the way to Rockville, Md., while the branches that struck ground remained near the cloud base, propagating horizontally at ~13,500 feet. Here is a larger view of the image. (photo by Kevin Ambrose)

It was amazing what Scott learned about the lightning that I had photographed. The visible lightning in the photo, which seemed limited to downtown D.C., was really a small portion of a much larger lightning flash that spanned a distance from Rockville, Md. to well east of Landover, Md., an area covering over 200 square miles. Much of the upper portion of the lightning was obscured by clouds and the camera only photographed a small section of the lower lightning flash. Scott had all the data points to prove it.

The flash initiated ~22,000 feet above Landover, Md., before striking ground in the District near Brookland and again near Rock Creek Park. The flash was well over 50 miles long. The upper branches propagated horizontally at ~40,000 feet all the way west to Rockville, Md.

From the lightning data points, Scott created 2D and 3D vector representations of the lightning. Those representations can be viewed below as a 2D image and a 3D video. Note, because hills, trees, and buildings partially block the lightning sensors, the very lowest portion of the lightning, near the ground, is often not detected and thus not represented on the plots.

I will continue to photograph lightning and perhaps Scott and I can find lightning to research and post about in the future. After this initial project, however, I will never “view” lightning the same way again.


This plot provides a 2-D depiction of a lightning flash recorded by the Washington D.C. Lightning Mapping Array (DCLMA) on June 29 at 11:24 PM. The 11:24 PM time stamp on the photo was used to find the matching DCLMA lightning data. Note, because hills, trees, and buildings partially block the lightning sensors, the very lowest portion of the lightning, near the ground, is often not detected and represented on the plot. (plot by Scott Rudlosky)

From Scott Rudlosky, about the DCLMA project:

The DCLMA is a joint demonstration project involving NASA, NOAA, New Mexico Tech, and a number of local sponsors. The network consists of 10 sensors that monitor very high frequency (VHF) radio waves (radiation sources) emitted by lightning flashes. A computer algorithm then combines the individual radiation sources into lightning flashes based on spatial and temporal criteria. The network is most sensitive to the radio frequencies emitted by portions of lightning flashes that remain in the clouds, but it also detects portions of cloud-to-ground lightning channels, especially when the network is at peak performance (i.e., 10 of 10 sensors operational).

The video above provides a 3-D depiction of a lightning flash recorded by the Washington D.C. Lightning Mapping Array (DCLMA) and CWG Photographer Kevin Ambrose on June 29 at 11:24 PM. Note, because hills, trees, and buildings partially block the lightning sensors, the very lowest portion of the lightning, near the ground, is often not detected and represented on the plot. (video by Scott Rudlosky)

The DCLMA is a research system providing real-time data to NWS forecasters to improve user readiness for the next generation geostationary satellite series (GOES-R). GOES-R will house a Geostationary Lightning Mapper (GLM) that will provide a public source of real-time lightning information throughout the United States and adjacent oceans for the first time. Thus, insights gained using the DCLMA information will be applied following launch of GOES-R. Meanwhile, the DCLMA continues to provide detailed 3-D lightning observations that help inform decision makers regarding severe weather and lightning threats.

Related post: Lightning gone wild during Washington D.C.’s derecho

By and Scott D. Rudlosky Ph.D.  |  02:20 PM ET, 07/19/2012

Categories:  Latest, Science, Thunderstorms, Photography

 
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