[Met_help] [rt.rap.ucar.edu #41741] History for MODE SLP Question

[RAL HelpDesk {for John Halley Gotway}]

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  Initial Request
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I am using mode to track some SLP centers in WRF output.  I am using the WRF
analysis as ground truth (I know that is the preferred method).  When I run
the code, MODE either defines no objects or defines 1 object which appears
to be the entire theater.  The config file and PS output files are attached.

 

I am using a threshold of less than 99000 PA.  There appears to be several
pressure centers lower than this value so several objects should be defined.
What am I doing wrong?

 

Thanks Again

 

Bob Craig

 



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  Complete Ticket History
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Subject: Re: [rt.rap.ucar.edu #41741] MODE SLP Question
From: John Halley Gotway
Time: Tue Oct 26 12:54:01 2010

Bob,

I think I see what's going on here.

The short answer is, please make the following changes in your config
file:
fcst_raw_thresh   = "ge0.0";
obs_raw_thresh    = "ge0.0";
fcst_conv_thresh  = "lt99000";
obs_conv_thresh   = "lt99000";

And then try rerunning.

The long answer is this...

The "conv_thresh" settings are what MODE uses to actually DEFINE
objects.  So that's where you should put your object-definition
thresholds.

Most users will not generally need to use the "raw_thresh" settings
and should leave them set to their default value of "ge0.0".    These
thresholds really perform more of a filtering operation.  They
are useful when running MODE on two fields where there is some
difference in how the raw data is defined.  In particular, this came
up for the convective weather group here at NCAR-RAL.  They were
trying to compare discontinuous forecasts of convection (with values
of 30dBZ and higher) to continuous observations of convection
(including values below 30dBZ).  We found that when we used the same
convolution radius and threshold, the observations objects ended up
being bigger than the forecast objects.  The convolution/threshold
process produced bigger objects when values of 30 were surrounded
by values of 29 (as in the obs) as opposed to values of 30 surrounded
by values of 0 (as in the fcst).  The solution was to apply a
"raw_thresh" of "ge30.0" so that we zeroed out any values less than
30.  This made it so that both fields had values of 30 surrounded by
values of 0, and the object definition process treated both fields in
the same way.

Unless you find yourself in a situation similar to the one described
above, stick with the default threshold value.

Please let us know if that doesn't solve the problem.

Thanks,
John


On 10/26/2010 12:09 PM, RAL HelpDesk {for Craig, Robert J Civ USAF
AFWA 16 WS/WXN} wrote:
>
> Tue Oct 26 12:09:42 2010: Request 41741 was acted upon.
> Transaction: Ticket created by craigr at offutt.af.mil
>        Queue: met_help
>      Subject: MODE SLP Question
>        Owner: Nobody
>   Requestors: craigr at offutt.af.mil
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=41741 >
>
>
> I am using mode to track some SLP centers in WRF output.  I am using
the WRF
> analysis as ground truth (I know that is the preferred method).
When I run
> the code, MODE either defines no objects or defines 1 object which
appears
> to be the entire theater.  The config file and PS output files are
attached.
>
>
>
> I am using a threshold of less than 99000 PA.  There appears to be
several
> pressure centers lower than this value so several objects should be
defined.
> What am I doing wrong?
>
>
>
> Thanks Again
>
>
>
> Bob Craig
>
>
>
>

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