Thursday, May 24, 2018

GLM parallax issues?

We've been watching t-storms across central/southern SD and northeast ND today. A few storms were severe with reports of hail 1" or greater. I was kind of
expecting to see some GLM FED lightning jumps with these storms as they became severe, but that just wasn't the case.

Could this be a parallax issue?

This far N (roughly a similar latitude to Toronto, only farther W, so that there are even MORE potential parallax problems), the GLM is likely not sampling storms very well (at more of a side angle), so perhaps it can't actually "see" all of the lightning occurring within a storm.

If that is the case, watching for lightning jumps within a storm might not be a good "warning determination method" for a forecaster across the Northern High Plains and Northern Mississippi Valley...

Or...

Maybe we can still see lightning jumps in more northern/western storms, but due to parallax, we should expect more storms to have lower lightning values, hence lower lightning jump thresholds?

Other parallax-related questions I have include:

How does parallax affect other GLM products like the Total Energy and Avg Flash/Group Areas?

If the GLM is sampling more of the side of a storm across the northern US, can we expect storms to look brighter or darker?

Should we expect the areal extent of lightning flashes within a storm appear to increase or decrease as parallax increases?

How parallax affects GLM data is a mystery to me at this point and certainly another area of research that GLM developers should explore.

- Thomas Bell

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