Meteorological data from ECMWF models

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General description

The ECMWF is one of the world's leading numerical modelling 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. This 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. The data permits to have important information on the evolution of the main meteorological phenomena at mesoscale.

The ECMWF model results are used to produce meteorological and derived agro-meteorological parameters that are visualized in dynamic maps and graphs in analyst viewers and static map quick-looks.

Data from ECMWF's Ensemble Prediction System (ENS and ENSextended) and Seasonal forecast model (SEAS) have multiple forecast results. As the atmosphere is a chaotic system where small differences in the initial conditions can lead to 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 has to be preprocessed in order to get the appropriate resolutions in time and space.

Pre-Processing of ECMWF model data

Data acquisition from ECMWF

Model results for surface and pressure levels is provided by ECMWF in FM-92 GRIB format which is specified in WMO Publication 306 Manual on Codes.

Data from six products of the ECMWF model suite is ingested into the MCYFS:

Model set with ECMWF's abbrevation Abbreviation within MCYFS Number of forecast days used for MCYFS Number of ensemble members Original ECMWF grid* Corresponding original horizontal model resolution* Acquired resolution in MCYFS** Delivery of data files and maps*****
ERA-Interim**** ERA 1 1 N128 reduced Gaussian grid ~80 km 0.75° x 0.75° 2nd quarter of new year for the previous year
Deterministic model as analysis HRES OPE 1 1 O1280 octahedral grid*** ~9 km *** 0.25° x 0.25° Daily (10.30 hr)
Deterministic forecast HRES OPE 10 1 O1280 octahedral grid*** ~9 km *** 0.25° x 0.25° Daily (12.00 hr)
Ensemble Prediction System ENS ENS 15 50+1 O640 octahedral grid *** ~18 km *** 0.5° x 0.5° Daily (14.00 hr)
Monthly forecast ENS extended ENSEXT 32 50+1 O640/O320 octahedral grid ***/****** ~18 km / ~36 km ***/****** 0.5° x 0.5° Every Friday (03.00 hr)
Seasonal forecast system SEAS SEAS 183 50+1 0320 octahedral grid ******* ~36 km 0.4° x 0.4° Every 8th of the month (14.00 hr)

* Grid in which the model simulates the weather indicators (state: July 2016). Depending on the model subset, ECMWF uses for surface and pressure levels either a Octahedral grid or a Reduced Gaussian grid. The octahedral grid names start with ‘O’ followed by the number of latitude lines between the pole and equator. Gaussian grid names start with 'N' followed by number of lines by which latitude is divided.
** Spatial 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.
*** Before March 08th 2016, for surface parameters a Reduced Gaussian grid was used. The HRES was computed on a N640 grid what corresponds to a horizontal grid size of approximately 16km. ENS and ENSextended was computed during the first 10 days on a N320 grid (~30km horizontal resolution), the remaining days on a N160 grid (~60km horizontal resolution).
**** In more detail: ECMWF runs ERA-Interim on the 2006 release of the integrated forecasting system (IFS) version, Cy31r2.
***** HRES and ENS are run by ECMWF twice daily, based on 00 and 12 UTC observations. The ENSextended is computed by ECMWF twice weekly, basing on Mon 00 and Thu 00 UTC observations. Finally, the SEAS is started by ECMWF each 01st of the month as 00 UTC-run. Depending on the forecast horizon it takes between 5.5 hours (+0 hours HRES) and nearly 9 days (last day SEAS) until the centre disseminates the results.
****** During the first 15 days of the forecast horizon ENS and ENSEXT are the same model. After day 15, the ENS is stopped and the ENSEXT is run on a coarser grid. For surface parameters, this is octahedral O320 grid, what translates into a spatial resolution of approximately 36 kilometres.
******* Before November 2017, a N128 Reduced Gaussian grid was used, and provided to MCYFS on a 0.75° x 0.75° grid.

The short range results of the subsequent, overlapping HRES model are processed as analysis of the previous day and added to the archive (as HIS), assuming this is the best estimator for weather indicators of that day. Details are described below.

The other data of the forecasting suite is replaced when a more recent forecast becomes available (OPE forecast, ENS, ENSEXT and SEAS). As the delivery into the MCYFS databases needs to take place until 15.00 hours of each day in standard situation the 00 UTC model runs are used. In the rare case that the model dissemination is delayed as fallback the 12 UTC model result of the previous day is taken into account.

ECMWF’s reanalysis data set ERA-Interim is used to build a consistent archive of gridded model results from January 1979 onwards. Below, details are described.

Spatial representation

The ECMWF model computes surface parameters of HRES, ENS and ENSextended on octahedral grids, with different resolutions (since 08 March 2016). Previous model cycles, as well as the current version of the SEAS and the ERA-Interim use a reduced Gaussian grid. The central MCYFS database however requires the initial data in a specific grid resolution with regular latitudes and longitudes, see section Data acquisition from ECMWF. Therefore, conversion is needed.

OPE

The deterministic forecast model, within MCYFS addressed as OPE, including the short range forecast which is used as analysis, produces forecast weather for grid cells currently on a Octahedral O1280 grid (~9x~9km). This resolution is converted by ECMWF to a reduced Gaussian N640 grid (~16x~16km). Next a conversion of the N640 to a regular 0.25 x 0.25 degrees latitude longitude grid (OPE grid) is done.

Several height models at the regular 0.25 x 0.25 degrees latitude longitude exists:

  • the height model for the OPE is calculated in the same way as the data itself: first the Octahedral grid is converted to a Gaussian N640 reduced grid and next to the regular 0.25° OPE grid (~25x~25km).
  • in addition, the height model of a previous version of OPE model (prior to March 2016) is available. The previous OPE version was run on a Gaussian N640 reduced grid and the related height model was directly converted into the OPE grid.
  • in addition, the height model of a previous version of OPE model (2008-2010) is available. This OPE version was run on a Gaussian N400 reduced grid and the related height model was directly converted into the OPE grid

For the grid conversion, original software from ECMWF (EMOS-lib) is applied. The grid description is stored in table GRID_HIS including the elevation models originating from two previous OPE versions: ~16km (N640) and ~25km (N400).

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

ENS

All surface parameters of the ENS forecast are calculated on a Octahedral O640 grid (~18x~18km). This resolution is converted by ECMWF to a reduced Gaussian N200 grid. Next a conversion of the N200 to a regular 0.5 x 0.5 degrees latitude longitude grid (ENS grid) is done. The height model for the ENS is calculated in the same way as the data sets: first the Octahedral grid is converted to a Gaussian N200 reduced grid and next to the regular 0.5° ENS grid. In addition, the height model of a previous version of ENS model (prior to March 2016), ran on a N320 reduced Gaussian grid, is available. For the grid conversion original software from ECMWF (EMOS-lib) is applied. The grid description is stored in table GRID_ENS, the elevation of the previous ENS model (prior to March 2016) is stored in column ALTITUDE.

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

ENSEXT

The first 15 forecast days of the extended ensemble forecast ENSEXT are based on the ENS forecast of the same run. After day 15, the remaining days of the ENSEXT are computed on a coarser grid, what is an octahedral O320 grid for surface parameters. This translates into a spatial resolution of approximately 36 kilometres. To deliver the required regular 0.5° grid, ENSEXT is ingested from ECMWF on a reduced Gaussian N128 grid and then converted into the requested regular 0.5° grid. The height model is calculated in the same way as the data sets: first the Octahedral O320 grid is converted to a Gaussian N128 reduced grid and next to the regular 0.5° ENSEXT grid. In addition, the height model of a previous version of ENSEXT model (prior to March 2016), ran on a N160 reduced Gaussian grid, is available. For the grid conversion original software from ECMWF (EMOS-lib) is applied. The grid description is stored in table GRID_ENSEXT, the elevation of the previous ENSEXT model (prior to March 2016) is stored in column ALTITUDE.

SEAS

All forecast days of the seasonal forecast are calculated at O320 octahedral grid (~36x~36km). The results are directly converted into a regular 0.4 x 0.4 degrees latitude longitude grid. The height model for the SEAS is calculated in the same way as the data sets: from the octahedral O320 reduced grid to the regular 0.4° SEAS grid. For the grid conversion original software from ECMWF (EMOS-lib) is applied. The grid description is stored in table GRID_SEAS, the elevation is stored in column ALTITUDE.

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 height model for ERA is calculated in the same way as the data sets: from the Gaussian N128 reduced grid to the regular 0.5° ERA grid. For the grid conversion original software from ECMWF (EMOS-lib) is applied. The grid description is stored in table GRID_ERA, the elevation is stored in column ALTITUDE.

Applied parameters from ECMWF grib deliveries

In total, analysis and forecast for 35 parameters of the ECMWF re-analysis and forecasting suite is used for the various applications in MCYFS and the production of the static maps.

ECMWF disseminates the model results for the surface layer in WMO FM 92 GRIB format, according WMO specifications, Manual on Codes in WMO Publication Nr 306. To extract the required parameters from the ECMWF data package(s) and to decode the binary GRIB formats the ECMWF GRIB API application program interface for C is used.

As a next step after acquisition and scaling to the regular lat-lon-grids, derived elements and daily indicators are calculated

Aggregation to daily data

First, aggregates of the 3- or 6-hourly data to daily means, extremes or sums are calculated. Total precipitation and global radiation are provided by ECMWF as accumulated values since the begin of the model runtime and therefore differences for the 24-hourly daily sums need to be computed. The box below summarizes the algorithms.

Calculation of additional indicators

The following indicators are retrieved from other elements. These include:

  • Snow depth (thickness snow cover)
  • Climate water balance (for mapping purposes)

Snow depth

The snow depth (thickness of the snow layer, Dsn) is derived from snow depth water equivalent and snow density.

Climatic water balance

Climatic water balance is calculated based on evapotranspiration calculated through the equation of Penman-Monteith (ET0) and the total precipitation of a day. This calculated ET0 is only used for mapping purposes. Note that in the downstream processing, and after spatial scaling operations, ET0 is calculated again (see calculation of additional parameters after downscaling).


Calculation of extreme weather events

For the static map production (quicklooks) it is necessary to derive additional parameters out of the raw ECMWF data set. This especially concerns probabilities and aggregated counts of number of days where a special condition is met. To compute the probability for the exceedance of thresholds (e.g. probability of freezing days) first the daily value for each separate ensemble member is computed and then the amount of members which fit the corresponding constraint (p.e. exceed 20 mm of daily precipitation sum) is counted. To compute the number of days where a parameter exceed a threshold first the numbers for each separate ensemble member is calculated (from the daily values of each ensemble member). Afterwards the median is derived for presentation on map. The deterministic run and the ensemble control run are treated like any other ensemble member. Probabilities for anomalies require comparison with ECMWF model climate and are therefore only visualized where available in the ECMWF catalogue.

Aggregation to 10-daily, weekly and monthly data

For the production of the maps, as well an aggregation to 10-daily, weekly and monthly aggregates of the daily data takes place. Therefore the average of mean temperature, maximum temperature, minimum temperature, snow depth and the sum of precipitation, ET0, climatic water balance and global radiation is computed.

Extraction of data into files

After processing data are exported as data files and static maps that can be distributed to users and other MCYFS processes.

A simple file naming scheme for the data files was adopted with the general format: <ROI>_<model_code>_<yyyy><mm><dd>_<member>.dat

In which:

  • ROI = region (GLD, EUR, ASI)
  • model_code = ECMWF model (ERA, OPE, ENS, ENSEXT or SEAS)
  • yyyy = the year (four digits),
  • mm = the month number (two digits),
  • dd = the day in the month (two digits)
  • member = the member number (two digits)

The date in the filename links to the forecast day = 0 (FORECAST_OFFSET = 0). In case of OPE and ERA only member 00 is allowed; in case of the ENS, the ENSEXT and the SEAS the member number runs from 0 to 50.

An example of a file name for each of the 4 models is:

  • GLO_OPE_20160715_00.dat OPE data issued July 15, 2016 (only member 00 allowed)
  • GLO_ENS_20160704_35.dat ENS data issued July 4, 2016, member 35
  • EUR_ENSEXT_20160721_32.dat ENSEXT data basing on ECMWF run July 21, 2016, member 32*
  • EUR_SEAS_20160601_34.dat SEAS data basing on ECMWF run June 1*, 2016, member 34

* ENSEXT is initialized by ECMWF with the observations of Thu 00 and delivered into MCYFS approximately 27 hours later.

An input file basically contains the following structure:

  • A header providing geo referencing information
  • Blocks of data for the first forecast date (for each variable)
  • Blocks of data for the second forecast date (for each variable)
  • etc.

For simplification purposes, below a simple example is given with a detailed explanation.

The data files are loaded in the MCYFS database, tables WEATHER_<MODEL>_GRID_RAW where <MODEL> is to be replaced by the abbreviation of one of the five ECMWF products (OPE, ENS, ENSEXT or SEAS). During loading two actions are executed:

  • additional unit conversion
  • plausible range checks

Extraction of data into maps

The static maps are exported as flat images and animated images with full layout and directly made available to analysts that use them during analysis of weather indicators. The geographic extent of the static maps for Europe is defined by the upper-left corner at 75° North/25° West and the lower-right corner 20° North/70° East, the global maps cover a domain 75° North/180° West to 50° South/180° East. This production line includes GrADS mapping software which is able to create maps directly from GRIB files.

Static map of maximum temperature on 7-feb-2011 with a spring breeze in Central and Western Europe.
Animated Rainfall, emitted 20-dec-2010 with the forecasted precipitation of low "Petra". Petra's snow masses retarded travel in many regions of Europe before Christmas 2010. Large animation
Static map with the forecasted number of days with significant rain (>5mm) within the next 10 days. Forecast issued 20 July 2016.
Static map with the forecasted probability for a cold anomaly > 2K in June 2016, forecasted by the SEAS run initialized 01 June 2016.


Messages to the Project Management Board

Information on successfull completion of the various processing steps is sent to the Project Management Board (PMB).