api2arl_v4: unable to convert precipitation rate

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Fabio.Dioguardi
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Joined: August 17th, 2018, 12:36 pm
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api2arl_v4: unable to convert precipitation rate

Post by Fabio.Dioguardi » February 25th, 2020, 5:31 am

Hi,

I am converting GFS 0.25deg grib files into arl format. It works almost perfectly, with the exception of the 1-hour precipitation. This causes hysplit to fail when wet removal is activated.
I attach the api2arl.cfg file I am using and the original grib file. Is there anything wrong in the api2arl.cfg file? Or is this related to the fact that the GFS files has two fields named "PRATE" (1 hour fcst and 0-1 hour ave fcst)?

Thanks a lot!
Fabio
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alicec
Posts: 234
Joined: February 8th, 2016, 12:56 pm
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Re: api2arl_v4: unable to convert precipitation rate

Post by alicec » February 25th, 2020, 9:19 am

In your api2arl.cfg file you are telling the conversion program that the TPP1 variable (HYSPLIT terminology)
has the short name 'tp' in the grib file. The TPP1 should be the accumulated precip over 1 hour.
If your grib file doesn't have that in it, then the ARL file you produce will not have precip.

alicec
Posts: 234
Joined: February 8th, 2016, 12:56 pm
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Re: api2arl_v4: unable to convert precipitation rate

Post by alicec » February 25th, 2020, 9:36 am

Is it a 1 hour precipitation rate in your grib file?
HYSPLIT can currently utilize a 3 or 6 hour precipitation rate (PRT3, PRT6).
Adding a 1 hour precip rate would not be hard, but it currently isn't there.

So if you had a 3 hour precip rate, then in your api2arl.cfg file you would need
to specify the short name of the variable and tell HYSPLIT it was a 3 hour precip rate by
using PRT3

sfcgrb = 'orog','sp','prate','hpbl','uflx','vflx','dswr','shtf','lhtf','2t','r','10u','10v',
sfccat = 3, 3, 1, 19, 2, 17, 4, 0, 0, 0, 1, 2, 2,
sfcnum = 5, 0, 8, 3, 17, 18, 0, 11, 10, 0, 1, 2, 3,
sfccnv = 1.0,0.01,.001, 1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,
sfcarl = 'SHGT','PRSS','PRT3','PBLH','UMOF','VMOF','DSWF','SHTF','LHTF','T02M','RH2M','U10M','V10M',

If you have a 1 hour precip rate, then you will need a modified HYSPLIT library to accept a PRT1.

Fabio.Dioguardi
Posts: 31
Joined: August 17th, 2018, 12:36 pm
Registered HYSPLIT User: Yes

Re: api2arl_v4: unable to convert precipitation rate

Post by Fabio.Dioguardi » February 25th, 2020, 10:14 am

Hi,

OK thank you for the clarification.
Yes it's over 1 hour. Actually if you look at the grib file, there are two "PRATE" fields: one is the "instantaneous" precipitation rate (valid at the time step) and the other is the average. This is a bit more complicated. For the attached case, the averaged value is the average from 0 to 1 hour step; if I opened the 3rd step, this second PRATE would be the average from 0 to 3 hour step and so on. At the time step +7, the averaging process restart from the step +6.
Therefore I am wondering whether actually I already have these 3 or 6 hours precipitation rates...

Thanks
Fabio

Fabio.Dioguardi
Posts: 31
Joined: August 17th, 2018, 12:36 pm
Registered HYSPLIT User: Yes

Re: api2arl_v4: unable to convert precipitation rate

Post by Fabio.Dioguardi » February 25th, 2020, 10:25 am

OK I can confirm that, by setting PRT3 as you suggested, I am able to read the PRATE data from the grb file.
I take the opportunity to ask another question: where do I find the complete list of parameters and instructions on how to set the values of sfccat, sfcnum and sfccnv correctly?

Thanks
Fabio

alicec
Posts: 234
Joined: February 8th, 2016, 12:56 pm
Registered HYSPLIT User: Yes

Re: api2arl_v4: unable to convert precipitation rate

Post by alicec » February 26th, 2020, 1:35 pm

There is a lot of information in the
Readme_api2arl.txt file

The documentation on the HYSPLIT met data variables lists the most common
HYSPLIT met parameters but is not currently comprehensive.
https://ready.arl.noaa.gov/hysplitusersguide/S141.htm

sfcgrb and atmgrb give the short name for the variable of interest in the surface and pressure level files respectively.
atncnv and stccnv give the conversion factor to convert from the units found in the grib file to the units that HYSPLIT expects.
atmcat and sfcat give the parameterCategory in the grib file for the variable
atmnum and sfcnum give the parameterNumber in the grib file for the variable
atmarl and sfarl give the HYSPLIT identification code for the variable.

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