GEOS-FP implementation details

On this page we list the necessary modifications to GEOS-Chem for compatibility with the GEOS-FP meteorological data. GEOS-FP is the current NASA/GMAO operational met data product. It is produced with a native resolution of 0.25° (lon) x 0.3125° (lat) x 72 hybrid vertical layers. GEOS-FP replaced the older GEOS-5 operational data product in June 2013.

Overview

The GEOS-FP data product (aka GEOS5-FP) is the newest version of the operational meteorological data produced by NASA/GMAO. Overall, the structure of GEOS-FP is very similar to MERRA and MERRA-2 met data products.. Therefore, within GEOS-Chem we can (for the most part) treat GEOS-FP in the same way as we do for the MERRA and MERRA-2.

The table below compares many features of GEOS-FP with other met field products.

Feature	MERRA-2	GEOS-FP	MERRA	GEOS-5
Native vertical grid	0.5° lat x 0.625° lon	0.25° lat x 0.3125° lon	0.5° lat x 0.667° lon (surface fields) 1° lat x 1.25° lon (most 3D fields) 1.25° x 1.25° lon (moist quantities)	0.5° lat x 0.667° lon
Native horizontal grid	Same as GEOS-FP	72 hybrid levels	Same as GEOS-FP	Same as GEOS-FP
Time-invariant fields	Same as GEOS-FP	FRLAKE FRLAND FRLANDIC(E) FROCEAN PHIS	Same as GEOS-FP	Same as GEOS-FP
Time archiving: surface fields	Same as GEOS-FP	A1 (1-hr time averaged)	Same as GEOS-FP	A3 (6-hr time average)
Time archiving: 3D fields	Same as GEOS-FP Same as GEOS-FP	A3 (3-hr time averaged) I3 (3-hr instantaneous)	A3 (3-hr time average) I6 (6-hour instantaneous)	A6 (6-hr time average) and I6 (6-hr instantaneous)
Timestamps	See this wiki page	See this wiki page	See this wiki page	See this wiki page
Precipitation fields	Same as GEOS-FP	DQRCU, DQRLSAN, PFICU, PFILSAN, PFLCU, PFLLSAN, REEVAPCN, REEVAPLSAN	Same as GEOS-FP	DQIDTMST DQLDTMST DQVDTMST MOISTQ = DQIDTMST + DQLDTMST + DQVDTMST
Temperature	Same as GEOS-FP Same as GEOS-FP	T [K] I3 (3-hr instantaneous)	Same as GEOS-FP A3 (6-hr time average)	Same as GEOS-FP A6 (6-hr time average)
Relative humidity	Same as GEOS-FP Same as GEOS-FP	RH [1] A3 (3-hr time average)	Same as MERRA-2 I3 (6-hr instantaneous)	Same as MERRA-2 A6 (6-hr time-averaged)
Specific humidity	Same as GEOS-FP Same as GEOS-FP	QV [kg kg-1] I3 (3-hr instantaneous)	Same as GEOS-FP A3 (3-hr time average)	Same as GEOS-FP A6 (6-hr time-averaged)
Vertical pressure velocity	Same as GEOS-FP Same as GEOS_FP	OMEGA [Pa s-1] A3 (3-hr time average)	Same as GEOS-FP I6 (6-hr instantaneous)	Same as GEOS-FP A6 (6-hr time-averaged)
Ertel potential vorticity	Same as GEOS-FP Same as GEOS-FP	PV [K m2 kg-1 s-1] A1 (1-hr time average)	Same as GEOS-FP I6 (6-hr instantaneous)	TROPP (hPa) A6 (3-hr time-average)
Snow mass	Same as GEOS-FP Same as GEOS-FP Same as GEOS-FP	SNOMAS [kg/m2] A1 (3-hr time average) Missing coverage at poles is now corrected, as per MERRA	Same as MERRA-2 Same as MERRA-2 Same as MERRA-2	SNOMAS [m] A3 (3-hr time average)
Sea level pressure	SLP [Pa] Same as GEOS-FP) Converted to hPa when read from disk	SLP [hPa] A1 (1-hr time average)	Same as GEOS-FP Same as GEOS-FP	Same as GEOS-FP I6 (3-hr instantaneous)
Surface pressure	PS [Pa] Same as GEOS-FP	PS [hPa] I3 (3-hr instantaneous)	Same as GEOS-FP I6 (6-hr instantaneous)	Same as GEOS-FP I6 (3-hr instantaneous)
Tropopause pressure	TROPPT [Pa] Same as GEOS-FP	TROPPT [hPa] A1 (1-hr time average)	Same as GEOS-FP Same as GEOS-FP	TROPP [hPa] A3 (3-hr time average)
GEOS-Chem convection routine	Same as GEOS-FP	DO_MERRA_CONVECTION (in convection_mod.F)	Same as GEOS-FP	NFCLDMX (in convection_mod.F)
GEOS-Chem wet deposition routine	Same as GEOS-FP	WETDEP_MERRA (wetscav_mod.F)	Same as GEOS-FP	WETDEP (wetscav_mod.F)
GEOS-Chem transport routine	Same as GEOS-FP	TPCORE_FVDAS (tpcore_fvdas_mod.F90)	Same as GEOS-FP	Same as GEOS-FP
File format read by GEOS-Chem	netCDF-4	netCDF-3	binary	binary

Resolved issues

Fractional sea ice

In order to preserve some information about sea ice leads during the regridding process, we have binned the fractional sea ice coverage into deciles (0-10%, 10-20% ... 90-100% coverage) and saved those as separate fields in the GEOS-FP data archive for GEOS-Chem. We have used the same algorithm we developed for MERRA met fields to do the binning.

--Bob Y. 16:12, 24 January 2012 (EST)

SNOMAS

The SNOMAS (snow depth) fields in both GEOS-FP and MERRA differ from that in GEOS-5. It appears that in GEOS-5 a default snow mass value was applied to grid boxes that had > 90% land ice coverage. This was not done in MERRA or GEOS-FP. Bob Yantosca had implemented an algorithm to adjust the MERRA SNOMAS field to be backwards-compatible with GEOS-5. We have used this algorithm to adjust the GEOS-FP SNOMAS field accordingly.

Dust emissions

The dust emissions in GEOS-Chem rely on "tunable parameters" to scale the dust emissions to a specified total. This is because the dust emissions are very highly dependent on the surface winds, and a small difference in winds (e.g. from GEOS-5 to GEOS-FP) can cause a huge difference in dust emission flux.

Wet deposition and scavenging

Helen Amos, Bess Corbitt, and Qiaoqiao Wang had implemented an updated algorithm for wet scavenging that takes advantage of the new precipitation fields from the MERRA data archive. This was included in GEOS-Chem v9-01-01 and higher versions.

Because GEOS-FP contains the same precipitation data fields as MERRA (i.e. DQRCU, DQRLSAN, PFICU, PFILSAN, PFLCU, PFLLSAN, REEVAPCN, REEVAPLSAN), we can use the new wet deposition algorithm with the GEOS-FP met data.

Implementation history

Initial source code modifications for GEOS-FP

This update was tested in the 1-month benchmark simulation v9-01-03g and approved on 27 Feb 2012.

1. Modify the Headers, GeosUtil, and GeosCore directories for GEOS-FP
2. Update the GeosApm and GeosTomas directories, primarily to synchronize files with GeosCore
3. Add NcdfUtil directory
4. Resolve several issues, including: Fractional sea ice, SNOMAS, Wet deposition and scavenging

--Melissa Payer 17:29, 24 February 2012 (EST)

Make sure State_Met%T is initialized properly for GEOS-FP simulations

For simulations with the GEOS-FP met fields, temperature is an I3 (i.e. 3-hr instantaneous) met field. We need to read temperature at times t and t+3hrs, and then interpolate linearly to the proper time.

At time t=0 of a GEOS-FP simulation, the initial temperature is read from netCDF files into State_Met%TMPU1. However, we must also save this into State_Met%T. Otherwise, temperature will be not initialized properly until the first call to INTERP. This can cause a floating-point error further upstream.

We have added the following code to routine Geos57_Read_I3_1 in GeosCore/geosfp_read_mod.F90:

     ! For now, copy State_Met%TMPU1 to State_Met%T.  At the next met field 
     ! read, we will State_Met%T from the values of State_Met%TMPU1 and
     ! State_Met%TMPU2. (bmy, 9/6/13)
     State_Met%T = State_Met%TMPU1

This error condition was caught by the GEOS-Chem unit tester when compiling with option FPE=yes.

--Bob Y. 13:13, 12 September 2013 (EDT)