Difference between revisions of "Meteorological data from ECMWF models"

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(Aggregation areas)
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|[[File:Map_world_zones.jpg|thumb|left|250px|Aggregation areas West, Central and East on world map.]]}
[[File:Map_world_zones.jpg|thumb|left|250px|Aggregation zones West, Central and East.]]

Revision as of 19:05, 19 October 2013

General description

The ECMWF is one of the world's leading numerical modeling centres. It operates various global circulation models in various forecast depths. To evaluate the initial state of the atmosphere the models integrate observations from ground stations, radiosondes, satellites and many other sources. Special techniques bring these observations in balance with the meteorological equations to form a physically valid state of the atmosphere.

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 assimilation data is used to produce meteorological and derived agro-meteorological parameters that are visualized in dynamic maps and graphs by the marsop3 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 result. Small perturbations of the initial state are used to produce respectively 51, 50 and 50 different model runs.

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.

preprocessing of ECMWF data

Data acquisition from ECMWF

The data is delivered by ECMWF in FM-92 GRIB format which is specified in WMO Publication 306 Manual on Codes. For the “Global Window” land and sea points are received. Filtering on land points takes place during decoding from GRIB format.

6 products of the ECMWF are ingested into the MCYFS:

Model Abbreviation Number of forecast days Members Gaussian grid* Horizontal model resolution* Acquired resolution** Delivery
ERA-Interim**** ERA 1 1 N128 ~80km 0.75° x 0.75° Once
Analysis model HIS 1 1 N640 ~16km 0.25° x 0.25° Daily (10.30 hr)
Deterministic forecast model OPE 10 1 N640 ~16km 0.25° x 0.25° Daily (12.00 hr)
Ensemble Prediction System EPS 15 51 N320 / N160*** ~30km / ~60km*** 0.5° x 0.5° Daily (14.00 hr)
Monthly forecast model MON 32 50 N320 / N160*** ~30km / ~60km*** 0.5° x 0.5° Every Friday (03.00 hr)
Seasonal forecast model SEA 183 50 N128 ~80km 1.5° x 1.5° / from 08/2013 onwards 0.75° x 0.75° Every 8th of the month (14.00 hr)

* resolution in which the model simulates the weather indicators. The points for which the indicators are simulated are distributed over the earth using a Reduced Gaussian grid. Grid names start with 'N' followed by number of lines by which latitude is divided.
** 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 1989-2010. From the HIS model only the forecast for the current day is processed (number of forecast days = 1) as best estimator for weather indicators of that day. The HIS data are stored as extension of the ERA_Interim archive. The data of other models are replaced when a more recent data set becomes available (OPE, EPS, MON and SEA). Therefore only the ERA-Interim, extended with HIS data is used to calculate climatolgy.

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 production is delayed so that a fallback to 12 UTC model data of the previous day will be taken into account.

Decoding and extraction of GRIB data

For the processing of the data it is needed to decode the data delivered in GRIB format. 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 calculated. Algorithms for this have been developed within ASEMARS project and are different for the different ECMWF models. The algorithms are presented in the box below.