SUMMARY OF CHANGES WITH RESPECT TO PREVIOUS VERSIONS (FORMER PGE13 SPhR VERSION 2013)

The base algorithm was provided by Dr. Jun Li of CIMSS-Wisconsin in 2007 in two Visiting Scientist Activities (VSAs). The base algorithm was adapted to use NWP SAF RTTOV as radiative transfer model and SEVIRI and the product PGE13 MSG Physical Retrieval (SPhR) was introduced in version 2010 (Martinez, 2010).

GEO-iSHAI release 2016 has some major updates due to the introduction of the new NWC/GEO NWCLIB and the use of RTTOV-11.2 in version 2016.

The input and output of the GEO-iSHAI processor has been rewritten.

It has also been introduced the integration in the same processor of the management of NWP in GRIB files with fixed pressure levels and with hybrid pressure levels.

The use of RTTOV-11.2 (whilst in version 2013 was used RTTOV-9.3) implied that the number of RTTOV pressure levels have increased from 43 to 54. For this reason all the coefficients are now calculated using the GEO-iSHAI validation dataset with vertical dimensions adjusted to the 54 RTTOV-11.2 pressure levels.

NWC/GEO package version 2016 remains with the mandatory input of background NWP for all products of GRIB files with fixed pressure levels. This is due to the fact that NWC/GEO NWCLIB in version 2016 maintains the management only in fixed pressure levels and one pre-processing of NWP GRIB files using AllMappingNWP tool is needed.

But together with regular GEO-iSHAI mode using as background fixed pressure GRIB files, GEO-iSHAI (like PGE13 SPhR in version 2013) also allows using as inputs GRIB files on hybrid pressure levels directly from the hybrid GRIB files. As in PGE13 SPhR version, GEO-iSHAI allows the use of ECMWF GRIB files in hybrid levels when executing in HYB mode. As an attempt to get experience and user’s feedback, in release 2016 the identification codes for T, q, Ozone, SKT and Psfc 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; it is needed that their hybrid GRIB files must have regular longitude-latitude representation and a structure similar to the ECMWF hybrid GRIB files. The feedback of the users is expected in order to improve future versions.

The software for HYB and P mode has been combined in the same executable program, sharing as much as possible the code. Since lowest RTTOV-11.2 pressure levels have a large value (1050 hPa), the extrapolation below surface pressure level to these bottom RTTOV-11.2 pressure levels has been improved. This has allowed that the coefficients for hybrid and regular (fixed pressure based) modes could be the same. This fact also means that as the number of vertical levels available in fixed pressure level increases, the performance of the fixed pressure mode will converge to the hybrid mode performance. This change has allowed the unification of the processing of vertical interpolation and extrapolation of the profiles from hybrid or P levels to the 54 RTTOV-11.2 pressure levels. Thus the vertical interpolation/extrapolation is the same for both modes and this makes the FG regression and physical retrieval steps being now the same for the two modes, sharing coefficients and validation.

Besides, all the GEO-iSHAI coefficients have been updated and they have been calculated with 2013 period GEO-iSHAI validation dataset. A similar approach to v2013 has been followed for the release 2016 of GEO-iSHAI: all coefficients have been calculated using only MSG images and ECMWF profiles of the GEO-iSHAI training and validation dataset (former PGE13 validation dataset).

In release 2016, two new parameters, skin temperature (SKT) and total ozone (TOZ), have been introduced.

SKT and diffSKT=(SKTretrieved – SKTnwp) were calculated internally in previous versions of PGE13 SPhR but they were not available to users as outputs and no validation was made. In any case, GEO-iSHAI SKT does not pretend to be an alternative to SST or LST products because more temporal and spatial controls should be needed. They have been introduced in order users and forecasters could use them as nowcasting parameters. The temporal evolution and spatial gradients of SKT and the diffSKT could be used in several nowcasting applications as monitoring of pixel not well screen out by cloud mask, detection of fogs, advice for very fast increase of SKT as triggering convection mechanism, advice users of bad SKT, etc

TOZ and diff(TOZretrieved – TOZnwp) has been also introduced as optional parameters. That means that user must activate them and provide NWP GRIB file with ozone profiles. For this reason the IR9.7 channel is also now a mandatory channel. The retrieval of TOZ is based on statistical retrieval using non-linear regression from ozone profile, SEVIRI IR channels (including IR9.7 channel) and the GEO-iSHAI T profile and GEO-iSHAI SKT.

In GEO-iSHAI the channel IR8.7 is not used.

Also the emissivity atlases have been changed because emissivities atlases are now common ancillary files.

The same approach have been made with the bias BT correction coefficients that are now common NWC/GEO files with associated functions in the NWCLIB.