Difference between revisions of "User:E Muller"
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|Snow depth HIS, OPE, ENS, MON, SEA, ERA||SD<sub>12</sub>||SD<sub>06</sub>||SD<sub>00</sub>
|Snow depth HIS, OPE, ENS, MON, SEA, ERA||SD<sub>12</sub>||SD<sub>06</sub>||SD<sub>00</sub>
==Calculation of advanced parameters==
==Calculation of advanced parameters==
Revision as of 22:24, 9 March 2014
The 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.
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.
Data acquisition from ECMWF
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 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 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.
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.
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>.
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.
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.
The grid description is stored in table GRID_<MODEL>.
SEAAll 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>.
ERAThe 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).
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 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.
|Abbreviations used in relation with ECMWF indicators|
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.
|Algorithms for aggregation to daily data|
|Abbreviations are specified in section Decoding and extraction of GRIB data. Subscript numbers behind the indicator abbreviations indicate the time of the day.
To consider the earth's different times zones aggregation rules for 3 different areas (East, Central, West) have been defined. The aggregation rules for the model data refer to the report schedule of synoptical weather stations (e.g. maximum air temperature in Europe and Africa refers to the period between 06 and 18 UTC of the corresponding day).
The following table summarized the deviation rules for the different aggregation zones and data sets.
Calculation of advanced parameters
Not all indicators can be retrieved directly from the models. These include:
In general, the evapotranspiration from a reference surface, the so-called reference crop evapotranspiration or reference evapotranspiration can be described by the FAO‑Penman-Monteith (Allen et all., 1998).
Evapotranspiration from a wet bare soil surface (ES0) and from a crop canopy (ET0) is calculated with the well-known Penman formula (Penman, 1948). In general, the evapotranspiration from a water surface can be described by the Penman formula. Only the albedo and surface roughness differs for these two types of evapotranspiration as explained below.
The net absorbed radiation depends on incoming global radiation, net outgoing long-wave radiation, the latent heat and the reflection coefficient of the considered surface (albedo). For ET0, ES0, and ET0 albedo values of 0.05, 0.15 and 0.20 are used respectively. The evaporative demand is determined by humidity, wind speed and surface roughness. For a free water surface and for the wet bare soil (E0, ES0) a surface roughness value of 0.5 is used. For a more detailed description of the underlying formulae we refer to Supit et al. (1994) and van der Goot (1997).
Climatic water balance
Climatic water balance is calculated based on evapotranspiration calculated through the equation of Penman-Monteith and the total precipitation of a day.
The snow height (thickness of the snow layer) is derived from snow depth (water equivalent) and snow density.
Calculation of extreme weather events
For the static map production over Europe it is necessary to derive additional parameters out of the raw data set. This especially concerns probabilities and aggregated counts of number of days where a special condition is met. Some of the probabilities to be mapped are available directly from ECMWF. Other probabilities need to be derived from individual ensemble runs. In this case it is checked for how many of the ensemble members a certain condition applies (e.g. TempMin < 0°C). The probability of the event is the fraction of ensemble members forecasting it against the total number of ensemble members. The operational run and the ensemble control run are treated like any other ensemble member.
Aggregation to 10-daily and monthly data
After each 10-day period and at the end of each month aggregation for this 10-day/month period takes place. Additionally a forecast of the next dekad, basing on aggregated forecasts for the next 10 days (resp. 8/9/11 days for the last dekad) is delivered. The daily data are aggregated from days to dekads by taking the average of mean temperature, maximum temperature, minimum temperature, snow depth and the sum of precipitation, ET0 and global radiation.
Additionally for the map production the number of occurrences of certain events (such as frost, hot or rainy days) is counted.
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 was adopted with the general format:
Note the OPE and EPS start with member number 0 while the MON and SEA start with member number 1. The date in the filename links to the forecast day = 0 (FORECAST_OFFSET = 0).
* Model runs the 8th but has a hindcast of 8 days
An input file basically contains the following structure:
For simplification purposes, below a simple example is given with a detailed explanation.
Extraction of data into maps
The static maps are exported as flat images or 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 is defined by the upper-left corner at 75° North/25° West and the lower-right corner 20° North/70° East. This production line includes GrADS mapping software which is able to create maps directly from GRIB files. For the weekly and monthly maps the absolute difference to long-term average values are calculated.