Archive for category Negative Leaders
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.
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.
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.
- 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.
- 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.
- 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.
- 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.
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.
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.