DESCRIPTION OF INPUTS FOR GEO-iSHAI

A region configuration file and a GEO-iSHAI model configuration file (with the diverse parameters and options that are indicated by the user for calculation) are needed as mandatory parameters in order to execute the GEO-iSHAI command.
Both must be located in the $SAFNWC/config directory.

The other inputs are: satellite data ( HRIT SEVIRI files in the case of MSG satellites or netCDF file in the case of Himawari or GOES-R satellites), NWP data, a Cloud mask for the region to process and some ancillary data.

Below a more detailed description is made.

Region configuration file

The region configuration file sets the dimensions and positions where GEO-iSHAI product will be obtained (as an example “Spain.cfg” defines a region of 1500 x 1500 km centred at (40ºN, 4ºW)). Any valid region configuration file could be used for the GEO-iSHAI generation.

Since the region configuration file sets the name of the region, dimensions and position, these parameters are used later to build the ancillary files (geographical, topography, emissivity atlas, etc) and they are part of the name of the optional GEO-iSHAI binary output file.

In releases 2021 and  2018.1 the size of the region in the configuration file could be expressed in kilometres relatives to the size of the pixel at the centre position or in number of lines and elements.

note: since it is difficult to know the size (lines x columns) and centre position in the name of GEO-iSHAI optional binary files, the position of centre and the size in lines and columns are written (Clinc_colc_Ssizl_sizc)in the name of the optional GEO-iSHAI binary files. This has been done in order users to know the size and position of the region if they need to allocate 2D or 3D arrays before read the files and/or for the generation of netCDF or the optional binary files.

SATELLITE DATA INPUT:

• In the case of MSG satellite are needed the HRIT files in decompressed format (after the wavelet decompression from the HRIT disseminated ones).
• In the cases of Himawari satellites to use the NWC SAF native reader or the SAT2NC preprocessing (see correspondent documentation).
• In the cases of GOES-R satellites to use the NWC SAF native reader.

In the case of SEVIRI on board MSG, the following IR channels are needed at full IR spatial resolution:

BT6.2	BT7.3	BT9.7mm	BT10.8	BT12.0	BT13.4
Mandatory	Mandatory	Mandatory	Mandatory	Mandatory	Mandatory

In this version, the channels in the IR 9.7 microns region is only used to estimate the ozone profile using non-linear regressions if the user activates the TOZ calculation.

note: In the 2021 and 2018.1 versions of GEO-iSHAI, BTs in the IR 8.7 microns or in the IR 3.9 microns regions are not used.

Cloud Mask (GEO-CMA).

GEO-iSHAI is only generated in clear sky pixels. A cloud mask is a mandatory input to GEO-iSHAI. The Cloud Mask product for the region and slot must exist and for this reason GEO-CMA must be executed before GEO-iSHAI. NWC/GEO Task Manager synchronises the execution of the products and the first product that is generated upon the arrival of a new image is the cloud mask GEO-CMA.

The Cloud Mask netCDF file for the image and the region to process must be located in $SAFNWC/export/CMA directory.

Background NWP GRIB files.

Background numerical weather prediction GRIB files from t+00 to t+24 hour forecast are needed as another input. These NWP data need to be spatially, temporally and vertically interpolated to get NWP data collocated with SEVIRI data. Since it is not adequate to provide specific error matrices, EOFs, regression coefficients, etc for the great number of combination in user pressure levels, the interpolation of different NWP model to 54 RTTOV-11.2 pressure levels is performed.

The selection of P mode or HYB mode is a GEO-iSHAI configurable parameter. Users can choose between mode P or HYB editing in the GEO-iSHAI configuration file the keyword NWP_EXEC_MODE.

In the case of executing GEO-iSHAI in P mode:

This is the default mode to maintain continuity with others products of the NWC/GEO package. The same NWP GRIB files at fixed pressure levels used by other products can be used. This fixed pressure levels GRIB files are fully supported and managed by the NWCLIB software.

The spatial interpolation and the calculation of the specific humidity from relative humidity are made outside the GEO-iSHAI code with the tools existing in the NWCLIB of NWC/GEO package. This step is made executing the AllMappingNWP tool interactively or is made automatically on real time by the NWC SAF’s Task Manager. This is made using the usual NWC/GEO management of NWP:

• Users select their preferred NWP model to be used as input using the $SAFNWC/config/nwp_conf_file

• When executing AllMappingNWP tool or MappingNWP tool with cfs file, it is executed the spatial interpolation and generation of derived parameter for all keywords NWP_PARAM in all the product configuration files included in all the cfr files of the cfs file.

• In the case of the GEO-iSHAI configuration files the NWP_PARAM keywords are:

NWP_PARAM NWP_T 1 BLI

NWP_PARAM NWP_Q 1 BLI

NWP_PARAM NWP_OZ 1 BLI

NWP_PARAM NWP_SP 1 BLI

NWP_PARAM NWP_ST 1 BLI

NWP_PARAM NWP_SGEOP 1 BLI

NWP_PARAM NWP_2T 1 BLI

NWP_PARAM NWP_2Q 1 BLI

The parameter requested are: T, q and optionally Ozone profiles, surface pressure, skin temperature, surface geopotential, NWP topography and 2 metres T and q. T

he third and fourth arguments mean that all the fields are requested at satellite resolution using bilinear interpolation.

As the fixed pressure levels GRIB files contain relative humidity profile and not specific humidity the conversion from relative humidity to specific humidity is done within AllMappingNWP tool using code of the NWCLIB of NWC/GEO package.

In relation to TOZ it must be taken into account that: if users want TOZ they must activate fixing to 1 the keyword TOZ_CALCULATION and the GRIB files must include ozone profile.

Temporal interpolation is made at user supplied NWP pressure levels between previous and following available NWP files close to the time of the image. It is made using functions of the NWCLIB library.

The NWP GRIB files must be located in $SAFNWC/import/NWP_data with names:

S_NWC_NWP_YYYY-MM-DDThh:mm:00Z_FFF.grib

where: FFF is the number of hours ahead of the forecast (t+FFF )

This way GEO-iSHAI is able to use background NWP GRIB files with any number and distribution of fixed pressure levels if they can be managed by the NWC/GEO software packages. Then GEO-iSHAI should be able to work with any NWP model and it should accept the set of fixed pressure levels available on the NWP files provided by the users to the NWC/GEO package.

The same fixed pressure levels NWP GRIB files that are actually used with NWC/GEO releases 2021 and 2018.1 to generate other products can be used. Hence, any user that is running NWCSAF/GEO 2021 (or 2018.1) package should be able to run GEO-iSHAI.

As it can be concluded from the reading of the Validation Report, it is strongly recommended to users to provide as many fixed pressure levels with the most uniform and widest vertical distribution as he can provide from the selected NWP model to feed the NWCSAF/GEO package.

In the case of executing GEO-iSHAI in HYB mode:

In the case of GEO-iSHAI releases 2021 and 2018.1, ECMWF GRIB files on hybrid levels could be also used as inputs.

GEO-iSHAI allows the use of ECMWF GRIB files on hybrid levels as background NWP input. In this case the keyword NWP_EXEC_MODE is fixed to HYB in the configuration file (cfm extension)

The whole NWP management is made inside the GEO-iSHAI code. GEO-iSHAI opens directly the previous and next ECMWF GRIB files on hybrid levels to the time of the image, makes the vertical interpolation on ECMWF position to the 54 RTTOV-11.2 pressure levels, makes the temporal interpolation to the date of the image and finally makes the spatial interpolation just over clear air processed FOR.

The hybrid levels GRIB files must be located in $SAFNWC/import/NWP_data with names:

S_NWC_NWP-Hyb_YYYY-MM-DDThh:mm:00Z_FFF.grib

Since the specific humidity profile is read from the ECMWF GRIB files on hybrid levels the conversion from relative humidity to specific humidity is not needed.

If activated the TOZ calculation (keyword TOZ_CALCULATION), also the ozone profile is needed.

As it can be concluded from the Validation Report, it is strongly recommended to the users to provide as many fixed pressure levels as possible with the most uniform and widest vertical distribution from the selected NWP model to feed the NWC/GEO package. Thus, if possible it is recommended the use of GRIB files on hybrid levels for feed GEO-iSHAI.

GEO-iSHAI allows the use of ECMWF GRIB files in hybrid levels when executing in HYB mode. In the case of ECMWF the list of parameters needed to request to MARS for ECMWF GRIB files on hybrid levels is:

As an attempt to get experience and the user’s feedback, in releases 2016, 2018, 2018.1 and 2021 the identification codes for T, q, Ozone, SKT and P_sfc are now configurable parameters. That means that users could try to use their own NWP models with hybrid GRIB files as input to GEO-iSHAI in Hyb mode. Thus, it is also possible to use as input GRIB files on hybrid levels with NWP models on regular representation (equidistant lon-lat) configuring in GEO-iSHAI configuration files the codes of section 1 of GRIB header to identify T, q, O₃, SKT and P_sfc fields. It is also needed that users hybrid GRIB files have the half levels coefficients in every grid as in the ECMWF hybrid GRIB files. For this reason it has been added the below keywords NWP-HYB_?? in the GEO-iSHAI configuration file. As one example, the keywords for the hybrid levels ECMWF GRIB files are:

NWP-HYB_T t 130

NWP-HYB_Q q 133

NWP-HYB_OZ o3 203

NWP-HYB_ST skt 235

NWP-HYB_SP sp 152

NWP-HYB_GEOP z 129

The feedback of the users is expected in order to improve for future versions.

Note: GRIB files on fixed pressure levels are always needed in order to execute CMA before execution of GEO-iSHAI code.

Geographical files from NWCSAF functions.

Longitude, latitude and satellite zenith angles associated to selected region are computed on real time by functions available on the NWCSAF library.

As many NWC SAF PGEs need this geographical information, NWCLIB computes and archives it on $SAFNWC/tmp binary files avoiding to repeat the calculation. If these files are erased or a new region is needed, new binary files are created automatically by the first PGE that needs them.