GLM flash rate, size, and RGB with IR

GLM IR, FED, and MFA loop
Loop on 22 May 2019, 21:36-22:06 UTC, showing a combined view of ABI Ch 1610.3 micron IR and GLM minimum flash area and flash extent density (top left). Other panels show the individual channels that contribute: FED (red), AFA (green) and IR (blue)

This pair of supercells near Tulsa, OK illustrates how flash rate and flash area information can complement one another. High flash rates and small flashes usually go together in a small updraft. However, at 2145 UTC the flash rate is much higher in the southern storm at the same time its minimum flash size is larger, with the opposite pattern in the northern storm. The northern storm was tornadic at this time. Shortly thereafter, the large flash rates decreased in the southern cell, and the average flash size became smaller, while cloud top brightness temperatures rapidly cooled and the extent of the anvil spread. The southern cell would soon go on to produce its own tornado.

The RGB panel in the top left combines the flash information together with the ABI 10.3 thermal infrared data: the coldest cloud tops and small flashes lead to a bright cyan color, and high flash rates push the colors further toward white. Early on the northern cell exhibits cyan colors while the southern cell is green and burgundy. Later, the southern cell becomes more cyan, while the northern cell takes on a more green hue.

Apparently, the jump in flash rate in the southern cell was an indicator of a strengthening updraft and the development of a mesocyclone. The drop in flash rate and minimum flash size might have been due to (1) a shift to small flashes that didn’t make as much light, (2) extinction of light by an increasingly ice-rich, optically thick cloud, or (3) other instrument artifacts. While the explanation is less than clear-cut, synthesis of multiple sources of information improves the ability to understand the observations.