[gradsusr] Warning from LOG10: Data has 182085 values <= zero

Jeff Duda jeffduda319 at gmail.com
Tue Oct 27 13:04:57 EDT 2020

Math rule: log10(0) = -inf

If I were you I would not attempt to fill in undefined data points with
zeros. Those areas (with zero rain) will end up with a reflectivity value
of negative infinity, which is pretty useless when plotting. In practice,
those areas will be represented as "no data", which is equivalent to
"undefined" in GrADS. Just leave it as undefined so GrADS won't even plot
values. It will simplify things.

Jeff Duda

On Tue, Oct 27, 2020 at 11:00 AM Perry, Aaron <
axp09171 at alumni.northernvermont.edu> wrote:

> Good Afternoon All,
> I am trying to use a formula to convert some data in GrADS v2.2.1.
> *Excel Formula:*
> =10*LOG10(200*RainfallRate^1.6)
> *GrADS Formula (Broken down step-by-step for troubleshooting):*
> 'define pratemmhr = (PRATEsfc.1*3600.0)' *converting mm/sec to mm/hour
> 'define step1 = pow(pratemmhr,1.6)'
> 'define step2 = (200.0*step1)'
> 'define step3 = log10(const(step2,0,-u))'
> 'define step4 = (10.0*step3)'
> 'define prate2dbz = step4'
> I am receiving the following error in my Linux terminal:
> *Warning from LOG10:  Data has 182085 values <= zero*
> *These were set to the undefined value*
> What's going wrong here?
> *Note, in Step 3, I have attempted to convert all undefined values to
> zeroes while log10() is called upon.
> Best,
> *Aaron Perry*
> Meteorologist
> Class of '16
> Northern Vermont University-Lyndon
> (formerly Lyndon State College)
> Boston, Mass.
> Twitter: @AaronPerryWx <https://twitter.com/AaronPerryWx>
> <https://twitter.com/arnpry> <https://twitter.com/AaronPerryWx>
> Email: Aaron.Perry at lyndonstate.edu
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Jeff Duda, Research Scientist
University of Colorado Boulder
Cooperative Institute for Research in Environmental Sciences
NOAA/OAR/ESRL/Global Systems Laboratory
Boulder, CO
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