Here is an inspection of the GLM Background and DQP to get a feel for the reliability of the GLM flash extent density (FED) data.  Below you will notice a four panel display with GLM quality on the upper left, the GLM background image on the upper right, the GLM flash extent density on the bottom left, and the 0.64 visible satellite imagery on the bottom right.

You should be able to make out a sub-array boundary going horizontally (upper left panel) AND also in the GLM background image (upper right panel). In the top right and both bottom panels you can make out strong convection taking place with two cells (one in the southern portion of the CWA, and one just to the south and along the CWA border). I did my best to put my AWIPS cursor along the sub array boundary.  You will notice in the bottom right corner that the cursor is actually between the two convective cells.  However, you can make out some weaker GLM FED signals along the sub array boundary where you are in-between the two cells.  This demonstrates uncertainty around the validity of the GLM data just to the south of the northern convective cell.  They are weaker GLM FED returns with only a minute or so of lag among the various elements being shown. And with these returns being upshear of the northern cell it is likely that this is not related to anvil lightning activity.  In this example with the relatively close proximity of the two cells one cannot be sure that the GLM data is incorrect, but with the GLM returns showing up on the sub array boundary this does increase uncertainty around this portion of the GLM flash extent density data.

Below is the same four panel, but with the ground based earth lightning detection network showing as verification for lightning.

Notice how there is a weaker return with the GLM flash extent density on the southern portion of the northern cell, but the detection (lower right panel displays best) shows the lightning verification within the convective cloud shield and not past the southern portion of the northern cell like in the GLM FED (bottom left panel).  This demonstrates that one should question a portion of the GLM flash extent density output. By using the GLM data quality and background products one can get a better feel for where the GLM FED data may not be reliable.  If something doesn’t make sense with regard to GLM output then this product can verify that suspicion.

– 5454wx

As we are watching a cluster of thunderstorms develop across Nebraska, we’re in a region where GLM may not be able to most efficiently detect flashes in the region. However, underneath the shadow of the cirrus blow off, the flash detection efficiency increases, and the stoplight colormap begins to suggest that the data quality is better. Perhaps this offers a bit of hope when forecasting charge moving along with the anvil.

Honestly, for warning operations, I am used to using/focusing on the GLM Flash Extent Density and on the warmer color pixels and trends when lighting increases. I also wouldn’t consider myself an expert on lightning – I came into this HWT not having a lot of knowledge on the details of these products, the instrument, and the specifics of lightning. So, I am really grateful that I continue to learn more about this and GLM in general (thanks HWT and SMEs!).

GLM-DQP: It’s really useful to know where the subarray areas are, in case the GLM data looks “funky” (near/at saturation). I feel that this would not only be useful for my “home CWA” but also for when we back up other offices. It was also interesting that we (WFO DMX) found a case today where a storm passed through the subarray line and the GLM FED data pixels looked like it “dipped”, but the flashes stayed relatively the same (or even increased after passing through) when comparing with the ground network.

Forecaster Cumulus

A glint was observed on various data sources tracking westward across northern South America and Panama between about 1630Z and 2000Z on May 24.

The glint is plainly evident on visible imagery (bottom right) and GLM Background (top right). On the GLM Data Quality, you can witness pixels that reach saturation over South America (directly related to the glint) — but there is also an area of convection that gets to near saturation over Panama. It appears that the most direct sun angle roughly coincides with the mature phase of these thunderstorms over Panama, leading to a period of near-saturation that eventually fades as the convection weakens. Convection can be confirmed by the presence of GLM flashes, but there does appear to be a relative min in GLM flash detections coincident with the near-saturation area.

–Insolation

When we started the testbed the GLM products were being displayed on a a four panel display (GIF. 1). This display works fine to find areas of poor data quality, like where the white and yellow pixels pop up in the top left of image 1. However, in it’s four panel setup, I felt that the display took up too much space. As a group, we worked to merge them into a single panel.

Image 1: GLM data quality suite, with Data Quality in the upper left, Background image i nthe upper right, Day cloud phase in the bottom left overlaid with GLM flash density, and the Ch.2 Red visible in the bottom left. Please note that the background image has an erroneous color curve on this display; it is usally closer to the red visible in brightness.

Below are examples of single panel displays created. In general, folks preferred the display in GIF two, but I thought there were ways for ways to merge the two designs. My desire would be to have the GLM background image provide texture to the data quality product like in GIF three, but to have the data quality product maintain the sharp good/bad color curve shown in GIF two. Even more preferred is a color bar like in GIF four, where the “could be poor” but not nearly or fully saturated values are highlighted in another color (red in this example).

 

GIF 3:  A single panel version of the GLM suite of products. The GLM data quality product is plotted unchanged. Overlayed and the reason for the blue-ish hue is the GLM Background Image which has been made transparent in the black.

GIF 4: The same as Gif 2, except that the poor-ish data quality from 10 to 40 percent is highlighted in red.

What did you think was the best single panel layout?

 

 

I also want to share something about the data quality scale (Img. 1). In its current format, the scale is not intuitive. Good data quality ranges from roughly 50% to 90% on this scale (blues and greens). Poor data quality is from 50% to 10. Then, the poorest data quality is white and yellow, and represents nearly and full saturation. I was ready this wrongly, such that 50% to 90% was poor because it was closest to the nearly and fully saturated parts of the scale. Instead, it is reversed. Before this product goes to operations, I would want to see the color bar made more intuitive.

 

 Image 1: GLM Data Quality, focusing on the scale in the upper left. Poor data goes from 10%, at worst, up to 90%, then nearly and fully saturated after 90% in the center-right of the scale.