Archive for category 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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Blinded by the Light

On May 13th, my daughter and I went out to chase storms that were forming over the Black Hills. A nice cluster of storms moved over Sturgis, South Dakota (home of the Sturgis Motorcycle Rally), and we filmed some close flashes as the storms passed over us. We then followed the cluster toward Bear Butte which is an isolated uplifted hill on the east side of the Black Hills, northeast of Sturgis.

Our primary target decayed and so we focused on new storms that had formed over the Black Hills and were moving directly toward us.  They put down some nice CGs, and as they reached us, I repositioned to have Bear Butte in my field of view.  A few minutes later we were treated to two spectacular CG lightning flashes directly in front of us and close.  They were very bright and very loud.  I suspected they were +CGs given their long duration continuing current and exceptional brightness.  The Black Hills area and Northern High Plains for that matter exhibits an atypically high percentage of +CG flashes, and trying to understand and explain this anomoly was part of a study I was involved in during the UPLIGHTS research campaign.

For the first flash, I had my infrared triggered cameras set to f/8 and ISO100 in aperture priority mode.  Although this setting is ideal for the average CG flash between 5-15 km, the LCD image review showed significant saturation.  I reset the aperture to f/11 and the second flash was still somewhat saturated.

Below is the image for the first flash. You will notice there is two CG channels, one in front of Bear Butte and one beyond.

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National Lightning Detection Data provided by Vaisala, Inc. indicated the closer CG was in fact positive (electrons traveled upward along the channel) with an impressive 159.6 kA estimated peak current.  It struck 2.5 km away.  NLDN data indicated the second channel was also a positive CG 12.6 km away and had an estimated peak current of 58.4 kA.

The second flash which is shown below only had one CG termination point.

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NLDN data indicated it was a +CG, 2.2 km away with a peak current of 143.1 kA.

Positive CG flashes tend to exhibit higher peak current compared to negative CGs on average and usually do not have multiple return strokes.  If my memory serves, I believe the latest published scientific literature has the average peak current for -CGs around 30 kA and 50 kA for +CGs.  So these flashes were exceptionally strong.  Unlike what we were taught in school, they DO NOT always originate from the top of a thunderstorm or anvil area and DO NOT always strike away from the main storm and rain area.  It all depends on where the charge regions form, and in the Northern High Plains, we see a lot of storms with inverted charge regions, which leads to more +CGs.  In the near future, I will be adding an education section on my blog which explains this in more detail.

Below is video of the two flashes captured on a Panasonic HPX-170 at 1280x720p60 which uses a global shutter (no annoying rolling shutter artifacts).  In the slow playback you will see an artifact on the frame preceding the return stroke.  This is saturating brightness bleed over from the subsequent return stroke that occurs in the following frame. After the CCD records a frame, the voltage values from each photosite (which corresponds to each pixel in the image) are shifted to an adjacent storage photosite that is covered. The voltage is then read out from the covered storage photosites while the next exposure is taking place in the non-covered photosites.  If the non-covered photosites experience a saturating brightness, some of the voltage can bleed over into the adjacent storage photosites during their readout adding a voltage increase to their recorded values.  Since the covered photosites are readout row by row with the data shifting up the CCD array to higher covered photosites after each row is read, the artifact will usually show up lower in the image as the “image data” from the previous frame has moved up when the saturating brightness occurs.  These artifacts are often misidentified as attempted leaders that occur close to the camera, when in fact they are only “ghost images” of the bright return stroke channel that occurs in the subsequent frame but shows up on the previous frame (forward in time…que Twilight Zone music.)

You will also notice the integrated recoil leader activity associated with descending positive leaders in the distant second CG during the first flash. This integrated recoil leader activity is a clear identifying characteristic of positive leaders, and I explain this in the previous post.

Below are some additional images from flashes we captured before the storm moved over Bear Butte.

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Unique Image Showing Lightning Leader Development in a Possible Potential Well

On the evening of 16 July 2012, a weak cluster of storms moved north over Rapid City, South Dakota.  A single visible rainshaft formed on the leading edge of the approaching development.  At the time of the rainshaft formation, there was no lightning activity along the leading edge.  However, lightning flashes were visible to the distant south in the more active trailing portion of the storms. At 04:20:35, (17 July 2012) UT two digital still cameras captured a ground flash near the rainshaft.  This was the first visible flash along the leading edge.  One camera, a Canon 5D2 Mark III, captured the image using a 16 mm lens set at f/2.8 using ISO 800 and an exposure time of 11 sec.  This camera was capturing continuous 11 sec exposures for a timelapse sequence.  A second camera, a Canon 7D, captured the image using a 20 mm lens set at f/8 using ISO 100 and an exposure time of 30 sec.

The captured images, which show the entire flash due to the long exposure times, showed a unique feature that I have not seen previously with any flash images that I have captured.  The visible channels below cloud base show that there was a main vertical channel that connected with ground and a branch that propagated somewhat horizontally to the left and did not connect with ground.  This second branch appeared to propagate toward the rainshaft and upon entering the rain, spread out vertically in both directions while branching extensively. The change in propagation direction and increase in branching appears isolated to inside the rainshaft, and is not apparent on any other channel segments.

Negative cloud-to-ground flash in which a negative leader branch propagated into a rainshaft and spread out vertically

An analysis of National Lightning Detection Network (NLDN) data revealed the NLDN recorded a corresponding 6.8 kA estimated peak current, negative cloud to ground stroke (-CG) 8 km southwest of the cameras.  This location correlated in both time and direction, and all other preceding NLDN-indicated flash activity was south of the area by 20 km.

I believe that this image provides evidence that a negative leader branch propagated into a positively charged rainshaft that served as a positive potential well favorable for negative leader propagation (Coleman et al., 2003 and Coleman et al., 2008).

Coleman, L. M., T. C. Marshall, M. Stolzenburg, T. Hamlin, P. R. Krehbiel, W. Rison, and R. J. Thomas (2003), Effects of charge and electrostatic potential on lightning propagation, J. Geophys. Res., 108(D9), 4298, doi:10.1029/2002JD002718.

Coleman, L. M., M. Stolzenburg, T. C. Marshall, and M. Stanley (2008), Horizontal lightning propagation, preliminary breakdown, and electric potential in New Mexico thunderstorms, J. Geophys. Res., 113, D09208, doi:10.1029/2007JD009459.

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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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A funny thing happened while filming lightning…

Over the past six years my research colleagues and I have filmed lightning using high-speed digital cameras.  In total we have captured 776 naturally occurring lightning flashes with recording speeds as high as 100,000 images per second.  158 of these flashes were cloud flashes in which some of the lightning leaders propagated outside of the clouds.  372 of theses flashes were negative cloud-to-ground flashes (-CG) and 206 were positive cloud-to-ground flashes (+CG).  41 of the flashes were upward flashes originating from tall towers in Rapid City.

During this last summer, we pursued a storm into the Badlands of South Dakota.  The Badlands are a beautiful area of erosion in the plains creating incredibly photogenic landscapes, and it is personally one of my favorite places to photograph lightning.  On this particular day, I was filming from the Pinnacles Overlook looking east across a road.  I filmed a number of flashes, but during one instance I not only captured a +CG flash, I also captured a rare wild tourist roaming the South Dakota plains.  Because I film from a highly modified truck with cameras and gadgets sticking out of it, he was a bit curious by the appearance of my vehicle.  However, he was clearly more interested in getting to the next viewpoint and quickly scurried off never to be seen again.  Here is the video…

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