GEOS-5 issues

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On this page we list some of the problems (and fixes!) that we have encountered during the implementaton of the GMAO GEOS-5 met fields into GEOS-Chem.

Wrong unit tag for RH in GEOS-5 raw data files

The GEOS-5 raw met data files (both in versions 5.0.1 and 5.1.0) at 0.5 x 0.667 resolution have the wrong unit tag for the 3-D relative humidity field. The field is given as a fraction but the unit tag in the HDF file says percent.

The quick fix is to just multiply RH * 100 as soon as it is read from disk in a6_read_mod.f.

Bob Yantosca (yantosca@seas.harvard.edu) wrote:

Hi Rob,
I think I may have found a slight bug in one of the GEOS-5 fields. The Relative Humidity variable in the tavg3d_dyn_v files seems to have the wrong unit tag. The RH data is unitless but the data tag says percent.
I looked at the file:
   DAS.ops.asm.tavg3d_dyn_v.GEOS510.20080320_0000.V01.hdf
and I was able to read it into IDL with HDF_BROWSER, which gives info about each data block:
   ** Structure <108eeeb8>, 15 tags, length=152, data length=136, refs=2:
      ...
      LABEL           STRING    'Relative humidity'
      NAME            STRING    'RH'
      ... 
      TYPE            STRING    'FLOAT'
      UNIT            STRING    'percent'

But then if you print out the min and max of the data I got:
    Time      Time from           Date          Time
    Index     1993 (s)       (YYYYMMDD)      (HHMMSS)
   ===============================================================================
       1   480124806.0        20080320        000000

    ### RH min, max:   0.0000000E+00   1.113281   
If it were % it would be 111.3281%. So there is a factor of 100 difference. Can you confirm this?
I believe that RH is unitless for both the 5.0.1 and the 5.1.0 data. I checked a couple of data files that I had created from both data sets:
     date    time  field    min        max  
   20050101 180000 RH     0.000001   1.052381  --> 2x25 file regridded from GEOS-5.0.1 data
   20080101 180000 RH     0.000000   1.055233  --> 2x25 file regridded from GEOS-5.1.0 data
Also, the last version of the GEOS-5 file spec) that I have says RH is %.
For the time being I'll put a line of code into GEOS-Chem to multiply RH by 100 (our algorithm expects RH in %). That is the easiest fix.
Thanks much,
Bob Y.

Rob Lucchesi (rlucchesi@gmao.gsfc.nasa.gov) replied:

Bob,
You are right. RH as written by the model is a fraction, not a percentage. We will have to modify the documentation and metadata in future products to reflect this. Note that the RH derived from the analysis (in the inst3d_met_p product) is a percentage. RH in the MERRA products is also fractional, but the documentation reflects that.
Thanks for the info.
Rob Lucchesi
GMAO

--Bmy 10:11, 1 April 2008 (EDT)

Wet scavenging in GEOS-5

09-Jan-2008

There can be significant differences in the amount of tracer lost to wet scavenging in GEOS-5 as compared to the equivalent run in GEOS-4. Click HERE to view a powerpoint that describes some of the differences.