Archive for category Upward Lightning

How Storm Chasers and Storm Spotters can contribute to #CitizenScience

Citizen Science – the collection and analysis of data relating to the natural world by members of the general public, typically as part of a collaborative project with professional scientists.

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This aspect of scientific research and understanding is rapidly growing primarily due to increased technology advancement, smartphone integration and interest by the general public.  Smart phones and associated apps can now collect valuable data quickly and easily.  I use my smartphone to collect data using the Globe Observer app and have made cloud observations from both polar regions and remote ocean locations.  I also make weather observations using the mPing app.

The contributions can be significant as was evident with the aurora-related phenomenon now known as STEVE.  Aurora chasers have recorded (and named STEVE) for quite awhile, but now their images and documentation combined with correlated scientific observations and analysis has lead to a better understanding of this phenomenon.

As a lightning research scientist, I am frequently approached with interesting lightning observations from the general public.  These usually come in the form of video and digital still images.  When I am able, I try to investigate these observations using what tools and analysis methods I have available, and often involve my willing colleagues that specialize in various aspects of lightning research.  I encourage these observations as they have shown us things we often cannot necessarily capture in a confined research project domain or timeframe.  Many of the images and video come from storm chasers and weather spotters.

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Our biggest challenge when analyzing these data is correlating them to a specific time and place so they can be compared with any other research data that might be available. There are now multiple lightning location networks operational as well as research lightning mapping arrays that continuously record lightning related data.

So what can you as a storm chaser or storm spotter do to contribute to citizen science?  I have a few suggestions that will greatly increase the value and usability of your video and image recordings for scientific analysis.

  1. Time is incredibly important for lightning analysis especially when we are discussing events that typically last less than a second.  Having the correct time set to within a couple of seconds on your cameras is very helpful if not essential for analysis.  I set my camera time every time I format my sd card after downloading any images.  I use the NavClock app but typically the mobile carrier time on your smartphone is accurate to within a few seconds so just using your phone time is good enough.  I also set all my cameras to GMT which is the standard for data collection and analysis.  It makes it easy when you don’t have to convert from the timezone where the image or video was captured.
  2. Location is the next important information needed for analysis.  Some cameras have built in GPS that will record position to metadata (exif) as well as set the camera time accurately.  I wish this was a standard feature on every camera, but unfortunately it is not.  I use the app Geotag Photos Pro to capture and add position information to my images and video.  The direction the camera was pointed is useful as well, but that parameter is more difficult to record as metadata.  I believe Canon has an external GPS encoder that can provide heading information as well.
  3. Thankfully, digital cameras record extensive metadata that describes the parameters set when images are captured.  These data are critical for photogrammetry analysis (e.g., sensor size, focal length, exposure time).  Always keep the exif data and export it with the image when providing it for analysis.  The metadata is embedded in jpg and dng file formats, but will be in a separate xmp sidecar file for native raw camera formats.
  4. The more data the better and the RAW camera format provides the maximum amount of data when capturing digital still images.  I recommend always shooting in the RAW format.

As far as getting your observations to the scientific community, the Science Operations Officer at National Weather Service forecast offices is a great place to start.  Twitter is also good for connecting with researchers.

Again, the importance of Citizen Science cannot be overstated.  It is integral part of scientific exploration and understanding, and I encourage all to participate when and how they can.  Besides its fun too.

 

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Thundersnow in Rapid City? Blame the Towers!

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Unlike most lightning that initiates in the thunderstorm cloud as a bidirectional and bipolar leader that travels both upward and downward towards oppositely charged regions, upward lightning is unique in that it initiates from a tall object and the unidirectional leader only travels upward towards opposite polarity storm charge or a preceding triggering lightning flash component.  Lightning-triggered upward lightning (LTUL) is caused by a nearby triggering lightning flash which has one of its components (either leader activity or a return stroke) pass close enough to the tall object to cause a large and rapid electric field change which in turn initiates a self-propagating upward leader from the object.  Self-initiated upward lightning (SIUL) does not require a preceding nearby triggering lightning flash.  Instead, the electric field due to storm charge generation within the cloud reaches a point at which a self-propagating leader initiates spontaneously.  However, in this case the storm charge region is usually much lower and closer to the tall object and sometimes even envelopes the object. In both cases, the shape and height of the tower enhances the electric field locally near the tip so that ionization of the air and resulting leader formation takes place much easier than that over flat ground.  In essence, if the tall objects (i.e., towers, wind turbines or buildings) where not there, the upward lightning would not occur.

We have researched upward lightning in Rapid City since 2004, and our findings show that the 10 tall towers along the ridge that runs through the city all have experience upward lightning. During the summer, we only observed lightning-triggered upward lightning and during intense winter storms with heavy snow and strong winds, we only observed self-initiated upward lightning.  During the summer months from 2004 through 2014 we recorded recorded 122 upward flashes from the towers all of which were LTUL.

However, during the winter months, we only documented upward flashes during two major snow events.  The first and most intense was the devastating blizzard of 4 Oct 2013.  During a 21 hour period, the towers in Rapid City initiated 25 SIUL flashes.  In addition, the South Dakota Public Broadcasting tower near Faith, South Dakota experienced 17 SIUL flashes. Although we focus our research during the summer months, we just happened to have an electric field meter and digital interferometer operating during the blizzard.  The challenge with observing SIUL during heavy snow is that you cannot see the towers because they are obscured by the snow and low clouds.  So you have to record the lightning by some other means.  The electric field meter recorded the ambient electric field 5 km west of the towers, and the digital interferometer, 23 km east of the towers, mapped lightning leader activity in two dimensions (azimuth and elevation).  The interferometer recorded five upward flashes before it lost power along with most of western South Dakota.  Below is a video animation of the data recorded by the digital interferometer for one of the upward flashes.  You can visualize that you are standing east of Rapid City looking west toward the towers.  Each of the individual data points represents the azimuth and elevation to electromagnetic radiation generated by the lightning leader (and received by the sensor) as the leader propagated.  The system records data in sequential 4 microsecond windows and determines the direction to the strongest signal in each time window.  Since lightning tends to branch as it grows, you see the source points plot the spreading branched leaders as they grow.  The leader clearly initiates from a single point and then spreads upward as it branches.  Occasionally, you can see a rapid succession of source points that travel back along a branch toward the tower.  These are recoil leaders which form on decayed branches in an attempt to reionize the branch.

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And here is some video taken from my house during one of the upward flashes.

The only other time that we documented self-initiated upward lightning from the towers in Rapid City was during a strong snow event on Christmas Day 2016.  There were three confirmed upward flashes.

So if it is snowing really hard in Rapid City and you hear thunder, chances are you can blame the towers.

If you would like to learn more about lightning, please visit my Education section

Here are two scientific journal paper citations on the subject:

Warner, T. A., T. J. Lang, and W. A. Lyons (2014), Synoptic scale outbreak of self-initiated upward lightning (SIUL) from tall structures during the central U.S. blizzard of 1–2 February 2011, J. Geophys. Res. Atmos., 119, doi:10.1002/2014JD021691.

Schultz, C. J., Lang, T. J., Bruning, E. C., Calhoun, K. M., Harkema, S., & Curtis, N. (2018). Characteristics of lightning within electrified snowfall events using lightning mapping arrays. Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1002/2017JD027821

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Upward Lightning Lights Up The Bay Area, 4/12/12

On the night of 12 Apr 2012, the Bay Area of California experienced a storm that literally lit up the skies with upward lightning.  Some iconic photographs and video were taken during this event which provided evidence that numerous tall objects developed upward leaders in response to nearby flashes.  The foremost images that illustrated what happened that night were taken by Phil McGrew.  He had his Canon 5D Mark III camera running continuously using 20 sec exposures.  During two of these exposures, his camera captured upward leaders that developed from the Bay Bridge and additional structures on the east side of the Bay.  For each of the two photographs that he posted, it is likely that all the upward leaders developed during the same flash that probably lasted less than one second.  He was located in a tall building on the east side of San Francisco downtown looking east along the Bay Bridge.

Below are embedding links as provided by Phil’s Flickr page where he has posted two images.  Click on the images to go to his Flickr page.  The exif data on his Flickr page indicates that the first of the two images was taken at 8:38:29 pm PDT using ISO 100, f/10, 20 sec exposure and a 28 mm lens.  In this image there appears to be 5 upward leaders from the Bay Bridge structure and 2 upward leaders from two separate structures on the east side of the bay (likely in the Oakland area).

The (Other) Bay Bridge Lightning Strike.

Again based on the exif data, the second image that Phil captured was at 8:42:41 pm PDT (4 min and 12 sec later) and used the same camera settings.  This image (which has rightfully received international acclaim) appears to show 6 upward leaders from the Bay Bridge structure and 4 additional leaders beyond the Bay Bridge likely from structures on the east side of the bay.

Bay Bridge Lightning Strike!

Phil’s photographs indicate they were separated by 4 min and 12 sec.  Not know the time accuracy of Phil’s camera, we compared the indicated times and time difference between the two images with National Lightning Detection Network (NLDN)  data.  Based on previous research findings, we suspected that these upward leaders were triggered by positive ground flashes (+CG) within 50 km of the Bay Bridge.  Two very large estimated peak current +CG strokes were recorded at 3:39:59.425  and 3:44:12.332 pm PDT.  They had estimated peak currents of +129.8 kA and +270.7 kA respectively and were separated by 4 min and 12.907 sec.  There was a +27.8 kA stroke at 03:39:22.773 (37 min earlier of the first big +CG) and 2 -CG strokes at 03:40:32.843 and 03:42:21.957 fell within the time spaning the two large +CGs.

Below are GIS plots of the NLDN indicated return strokes and cloud events.  The first figure shows the event location, event type by symbol (see legend) and estimated peak current based on relative symbol size.  Notice the size of the +CG return stroke symbols relative to the other events.

Plot of NLDN recorded events. Size is relative to estimated peak current.

Plot of NLDN recorded events. Size is relative to estimated peak current.

The next figure shows the NLDN event locations and their times.

NLDN event locations and times.

NLDN event locations and times.

The last figure shows the NLDN events and a label of the estimated peak current.

NLDN event locations and estimated peak current labeled.

NLDN event locations and estimated peak current labeled.

We suspect that the upward leaders that developed from the Bay Bridge were positive polarity and developed following the large estimated peak current positive cloud-to-ground return strokes that occurred inside the Bay.  These are examples of lightning triggered upward lightning in which the field change resulting from a preceding flash causes the development of upward leaders from nearby tall objects.

There were a number of other images from other people that showed upward leaders from tall objects during this same night and the other locations included the Golden Gate Bridge and tall buildings in Oakland.  We suspect that these upward leaders also developed during the same triggering flashes that caused the upward leaders to develop from the Bay Bridge.

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Recoil Leaders in Lichtenberg Figure Formation??

Below is a video on the creation of Lichtenberg figures.  Interesting is the subsequent bright short discharges that continue to take place after the initial discharge.  These seem similar in appearance to recoil leaders, which form on positive leaders branches that become cutoff from a main channel.  Compare the two videos below.

YouTube video of Lichtenberg creation.

Upward lightning (upward positive leaders) from a tower filmed at 9,000 images per second.

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CN Tower Experiences The Perfect Storm

On the night of 8/24/11, a leading-line/trailing stratiform mesoscale convective system developed and moved over Toronto, Canada.  The heart of the trailing stratiform region passed directly over the 553 m tall CN Tower and the people of Toronto were treated to an incredible light show as the tower unleashed at least 34 upward flashes over the span of an hour.  Wilke and Elizabeth See-Tho graciously provided me some video of the event and my analysis suggests that all of the upward flashes were triggered by preceding flash activity (lightning-triggered lightning) similar to what I observe in Rapid City, South Dakota.  For each case there was clearly in-cloud flash activity that preceded the upward leader initiation.  In addition, recoil leaders were visible in a large majority of the upward leaders suggesting they were positive polarity.

Below is a composite image where I stacked selected images from the See-Tho’s video.  As you can see, the CN Tower was literally ablaze with lightning leaders over the span of the storm.

Below is the edited video provided by the See-Tho’s.  This version plays in real time showing all 34 upward flashes and one spider lightning flash.

Below is the the same video sped up.

Below is video of each flash played at normal speed and in slow motion (total runtime 34 min).

Although I have not obtained nor analyzed lightning data for this storm, I suspect that a majority of the upward flashes were triggered by a preceding +CG flash within 50 km of the tower.  Horizontally extensive positive charge regions that form in the trailing stratiform regions of MCSs serve as potential wells for negative leaders that can travel upwards of 100 km.  This horizontally extensive negative leader development can take place during an intracloud flash and/or following a +CG return stroke.  The negative field change (atmospheric electricity sign convention) experienced at a tall tower by the approach of negative leaders or nearby +CG return stroke can initiate upward propagating positive leaders.  The conditions apparently were ideal for this triggering process and weather radar shows this was likely the case.

Below is a radar loop (base reflectivity, 0.5 degree tilt) of the storm development and passage over the CN Tower spanning from 00:02 – 03:41 UT, 8/25/11.  The See-Tho’s stated that the first upward flash was shortly after 02:00 UT.  This places the leading line convective region just east of the CN Tower with the tower in an area of decrease reflectivity between 30-40 dBz.  The tower would stay under this level of reflectivity (i.e., the trailing stratiform precipitation area) until 03:41 UT.  The last upward flash the See-Tho’s recorded was at approximately 03:06, but they thought there were a few more upward flashes that followed after they stopped filming.

This truly was a perfect storm to produce upward lightning flashes.  I suspect that many transient luminous events (TLEs) in the form of halos and/or sprites may have also been produced by the very same triggering flashes responsible for initiating the upward leaders.  The CN Tower is instrumented to measure current through the tower and there is an array of optical sensors including a high-speed camera within 3 km of the tower.  Hopefully, all the instrumentation was operational and an outstanding data set was captured.

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