User:E Muller

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General description

The ECMWF is one of the world's leading numerical modeling centres. It operates a set of global models and of data assimilation systems for the dynamics, thermodynamics and composition of the Earth's fluid envelope and interacting parts of the Earth-system. The data assimilation systems bring observations from ground stations, radiosondes, satellites and many other sources in balance with the meteorological equations to form a physically valid state of the atmosphere. These data is used as initial condition for the various forecast model sets.

In order to extend the period of analysis and to better perform the crop monitoring and yield forecasting, weather forecasts are integrated in the MCYFS. These data permit to have important information on the evolution of the main meteorological phenomena at mesoscale.

The ECMWF's model results are used to produce meteorological and derived agro-meteorological parameters that are visualized in dynamic maps and graphs by the MARS viewer and static maps quick-looks.

Data from the ECMWF's Ensemble Prediction System (EPS), Monthly forecast model (MON) and Seasonal forecast model (SEA) have multiple forecast results. As the atmosphere is a chaotic system where small differences in the initial conditions can lead to in huge differences in the resulting forecasts in 1992 ECMWF introduced an ensemble prediction system, providing information on the uncertainty of a weather forecast. Small perturbations of the initial state are used to produce (nowadays) 50 different initial conditions. Together with the unpertubated control run this results in an ensemble of 51 model results.

Before ECMWF forecasted weather data can be ingested in the MCYFS, the data have to be preprocessed in order to get the appropriate resolutions in time and space.

Pre-Processing of ECMWF model data in Marsop-3

Data acquisition from ECMWF

The data for surface and pressure levels is delivered by ECMWF in FM-92 GRIB format which is specified in WMO Publication 306 Manual on Codes.

6 products of the ECMWF model set are ingested into the MCYFS:

Model set with ECMWF's abbrevation Abbreviation within Marsop-3 Number of forecast days Members Gaussian/Spectral grid* Horizontal model resolution* Acquired resolution** Emission of data files and maps
ERA-Interim**** ERA 1 1 N128/T255 ~80km 0.75° x 0.75° Once
Analysis HRES OPE 1 1 N640/T1279 ~16km 0.25° x 0.25° Daily (10.30 hr)
Deterministic forecast HRES OPE 10 1 N640/T1279 ~16km 0.25° x 0.25° Daily (12.00 hr)
Ensemble Prediction System ENS ENS 15 50+1 N320 - N160 / T639 - T319 *** ~30km / ~60km*** 0.5° x 0.5° Daily (14.00 hr)
Monthly forecast model ENS extended MON 32 50+1 N320 - N160 / T639 - T319 *** ~30km / ~60km*** 0.5° x 0.5° Every Friday (03.00 hr)
Seasonal forecast model SEAS SEA 183 50+1 N128/T255 ~80km 0.75° x 0.75° Every 8th of the month (14.00 hr)

* resolution in which the model simulates the weather indicators (state: March 2014). Depending on the variable ECMWF uses either a Reduced Gaussian grid or a spectral model. The Gaussian grid names start with 'N' followed by number of lines by which latitude is divided. The spectral grids are named for the particular wave number where the spherical harmonic expansion is truncated, eg T1279 identifies truncation at wave number 1279. The results are made available by ECWMF on Gaussian or on corresponding regular lat-lon-grids.
** resolution in which the simulated indicators are acquired and loaded into the MCYFS. The simulated indicators are distributed over the earth using a WGS84 coordinate system.
*** The first 10 days are simulated on a N320 grid (~30km horizontal resolution). The remaining days on a N160 grid (~60km horizontal resolution).
**** In more detail: ECWMF runs ERA-Interim on IFS Version Cy31r1

ERA-Interim is only used as archive containing daily data covering the period January 1989 - March 2013. From the OPE model the forecast for the current day (analysis) is processed and added to the archive assuming this is the best estimator for weather indicators of that day. Sometimes the term HIS is used to refer to the archive composed by: 1) ERA-interim and 2) the first day of each daily issue of the OPE model.

The data of other models are replaced when a more recent data set comes available (OPE, EPS, MON and SEA). Therefore only the ERA-Interim, extended with HIS data is used to calculate climatology.

For the OPE and EPS models the ECMWF model is run twice per day based on 00 and 12 UTC observations. As the delivery needs to take place until 15.00 hours of each day in standard situation the 00 UTC model run can be used. Sometimes, the model emission is delayed so that as fallback the 12 UTC model data of the previous day is taken into account.

Spatial representation

The ECMWF models run on Gaussian grids, for certain parameters and model levels on spectral grids, with different resolutions. The central MCYFS database however requires the initial data in a specific grid resolution with regular latitudes and longitudes. Therefore conversions are needed.

OPE

The Deterministic forecast model and Analysis model (OPE) produce forecast weather for grid cells on a Gaussian N640 reduced grid (~16x~16km). The resolution is converted to a Gaussian N400 reduced grid (~25x~25km) and after this to a regular 0.25 x 0.25 degrees latitude longitude grid (OPE grid). For the OPE grid two height models are kept. First a height model calculated in the same way as the data sets: first aggregation on the Gaussian grid from a Gaussian N640 reduced grid (~16x~16km) to a Gaussian N400 reduced grid (~25x~25km) and next a conversion from the Gaussian grid to the OPE grid. In addition the height model of a previous version of OPE model (prior to January 2010) is available. The previous OPE version was run on a Gaussian N400 reduced grid (~25x~25km) and the related height model was directly converted into the OPE grid. The grid description is stored in table GRID_<MODEL>.

Black dots: Gaussian N640 reduced grid (~16x~16km) to regular 0.25 x 0.25 degrees latitude longitude. Gray lines: 25x25km climate grid.

EPS & MON

The first 10 forecast days (Leg A) of the Ensemble Prediction System and Monthly forecast are modelled for grid cells on a Gaussian N320 reduced grid (~30x~30km). Because the modelling of the remaining days (Leg B and C) is on the Gaussian N160 reduced grid (~60x~60km) it is not possible to switch for the whole forecast depth (EPS: 15 days and MON: 32 days) to a finer resolution. It means that the data of first 10 days must be aggregated. First the resolution is reduced to a Gaussian N200 reduced grid (~50x~50km) and finally converted to a regular 0.5 x 0.5 degrees latitude longitude grid. The height model of the latter grid is calculated in the same way as the data sets: first aggregation on the Gaussian grid from N320 (~30x~30km) to N200 (~50x~50km) and next a conversion from the Gaussian grid N200 to the regular 0.5 x 0.5 degrees latitude longitude grid.

Black dots: Gaussian N320 reduced grid (~30x~30km) to regular 0.5 x 0.5 degrees latitude longitude. Gray lines: 25x25km climate grid.

After the first 10 day, the resolution of the models for the remaining forecast days (Leg B and C) is at a Gaussian N160 reduced grid (~60x~60km). The results are directly converted into a regular 0.5 x 0.5 degrees latitude longitude grid.

Black dots: Gaussian N160 reduced grid (~60x~60km) to regular 0.5 x 0.5 degrees latitude longitude. Gray lines: 25x25km climate grid.

The grid description is stored in table GRID_<MODEL>.

SEA

All forecast days of the Seasonal forecast are calculated for a Gaussian N128 reduced grid (~80x~80km). The results are directly converted into a regular 0.75 x 0.75 degrees latitude longitude grid. The grid description is stored in table GRID_<MODEL>.
Black dots: Gaussian N128 reduced grid (~80x~80km) to regular 0.75 x 0.75 degrees latitude longitude. Gray lines: 25x25km climate grid.

ERA

The ERA data are calculated for a Gaussian N128 reduced grid (~80x~80km). The results are directly converted into a regular 0.75 x 0.75 degrees latitude longitude grid. The grid description is stored in table ECMWF_ERA_GRID_GLD (linked to view ECMWF_ERA_GRID).
Black dots: Gaussian N128 reduced grid (~80x~80km) to regular 0.75 x 0.75 degrees latitude longitude. Gray lines: 25x25km climate grid.

Decoding and extraction of GRIB data

Data is delivered in GRIB format and hence data is first decoded. In previous years the program ‘wgrib’ has been used which is capable of extracting GRIB content into ASCII files for further processing. Recently ECMWF has released version 1.2.0 of their GRIB API which is the successor of GRIBEX. While GRIBEX was used within FORTRAN programs the new GRIB API is designed for programs written in the C programming language.

During decoding additional indicators required by JRC and partners are calculated. This include aggregation to daily data, calculation of derived indicators and calculation of extreme weather events.

Aggregation to daily data

First of all an aggregation of 3-, 6- and 12-hourly data to daily data is calculated. Algorithms were developed in the ASEMARS project and differ per ECMWF model. The algorithms are presented in the box below.