[gradsusr] GFS total cloud cover

[Sam Wilson]

Hi Jeff,

I plotted a quick and dirty cloud animation using the data - each step is 1 hour from f001 through f015 in the attached.

It appears that they are averages over time - you can see the bigger jumps at steps 8 and 14 (the transition from 0-6hr avg to 6-7hr and from 6-12hr avg to 12-13hr).

Marian - thank you for the feedback.  Sounds like using the hourly data for cloud cover may not be a good idea, unless someone else has a solution.

Thanks,
Sam

From: <gradsusr-bounces at gradsusr.org<mailto:gradsusr-bounces at gradsusr.org>> on behalf of Jeff Duda <jeffduda319 at gmail.com<mailto:jeffduda319 at gmail.com>>
Reply-To: GrADS Users Forum <gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>>
Date: Wednesday, November 2, 2016 at 3:21 PM
To: GrADS Users Forum <gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>>
Subject: Re: [gradsusr] GFS total cloud cover

Sam,
That might just be a wgrib table thing. Have you actually plotted the field over those times? If it's truly an averaged field, you should be able to see some indication of that in the texture and smoothness of the fields as you progress through increasing averaged times.

My guess is that this is just some arbitrary setting in wgrib and does not reflect the true nature of the field. But I could be wrong. If there are any NCEP folks who work on the GFS on this forum, perhaps one of them could set the record straight.

Jeff

On Wed, Nov 2, 2016 at 4:54 PM, Sam Wilson <sam at surfline.com<mailto:sam at surfline.com>> wrote:
Thanks for the response Jeff - it’s strange to me as well!

Running wgrib2 on the data files for forecast hours 001 through 007 gives the following for TCDCclm:

f001:
17:7991683:d=2016110212:TCDC:entire atmosphere:0-1 hour ave fcst:
f002:
17:8082626:d=2016110212:TCDC:entire atmosphere:0-2 hour ave fcst:
f003:
17:8059826:d=2016110212:TCDC:entire atmosphere:0-3 hour ave fcst:
f004:
17:8057865:d=2016110212:TCDC:entire atmosphere:0-4 hour ave fcst:
f005:
17:8119289:d=2016110212:TCDC:entire atmosphere:0-5 hour ave fcst:
f006:
17:8172510:d=2016110212:TCDC:entire atmosphere:0-6 hour ave fcst:
f007:
17:8013825:d=2016110212:TCDC:entire atmosphere:6-7 hour ave fcst:

And it continues on..once the files go to 3 hourly (after hour 120), we have:

f123:
17:7687687:d=2016110212:TCDC:entire atmosphere:120-123 hour ave fcst:
f126:
17:7778871:d=2016110212:TCDC:entire atmosphere:120-126 hour ave fcst:
f129:
17:7728042:d=2016110212:TCDC:entire atmosphere:126-129 hour ave fcst:

And finally the 12 hourly files (past hour 240) are all just 12 hour average forecasts:

f252:
17:6845416:d=2016110212:TCDC:entire atmosphere:240-252 hour ave fcst:

I did think about the method you suggested (tcdcclm - tcdcclm(t-1)) but stopped there for the reason you mentioned..

Strange indeed - unless I’m missing something..

Thanks,
Sam

From: <gradsusr-bounces at gradsusr.org<mailto:gradsusr-bounces at gradsusr.org>> on behalf of Jeff Duda <jeffduda319 at gmail.com<mailto:jeffduda319 at gmail.com>>
Reply-To: GrADS Users Forum <gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>>
Date: Wednesday, November 2, 2016 at 2:08 PM
To: GrADS Users Forum <gradsusr at gradsusr.org<mailto:gradsusr at gradsusr.org>>
Subject: Re: [gradsusr] GFS total cloud cover

It seems a little strange to me that the total cloud cover product would be averaged over time. Is that really the case?

Anyway, if you really do have an average over overlapping and increasing windows, with nothing else to go on and without applying the equations of motion in reverse, you'd have to assume a linear averaging, so subtraction of subsequent slices of the field (i.e., tcdcclm - tcdcclm(t-1)) would give you piecewise temporal averages. However, that method would give you negative cloud cover values which is clearly nonsensical, which again is why I question whether or not that array contains a temporal average. That just doesn't make a lot of sense.

Jeff Duda

On Wed, Nov 2, 2016 at 3:27 PM, Sam Wilson <sam at surfline.com<mailto:sam at surfline.com>> wrote:
Hi,

I’m working with hourly GFS total cloud cover (TCDCclm) and I’m a bit stumped on the following..

Given TCDCclm for hours 0-1, 0-2, 0-3, 0-4, 0-5, and 0-6, what is the proper way to determine TCDCclm for hours 1-2, 2-3, 3-4, 4-5, and 5-6?

I may be making the problem more difficult than it is..but wanted to ping this group to be sure.

Is there an existing grads script that handles this already and if not, does anyone here have any insight?

Thanks so much for your time.

Best,
Sam

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--
Jeff Duda
Post-doctoral research associate
University of Oklahoma School of Meteorology

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--
Jeff Duda
Post-doctoral research associate
University of Oklahoma School of Meteorology
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