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Introduction

Meteorological evaluation of the OpenIFS outputs is demonstrated here on case studies. Two weather events have been chosen in order to show the model's capabilities on the one hand, and on the other hand, to provide reference cases for the users (to compare the results of their installed model version with the ones run at the ECMWF or to inter-compare the results of different model versions). Important aspects at selection of the cases were their geographical scope and their physical background, i.e., those storm events were preferred which had severe impact over Europe and were governed by large-scale dynamical forcings. Cases both with weak and good operational forecast skill were considered.

Case studies

Storm Xaver

On the 5 December 2013 a large and violent cyclonic storm hit the North Sea region and several adjacent countries. Problems were caused both by the high wind speeds and the related storm surge. The surge reached 6 metres in Hamburg for example and was the highest along the England east-coast for 60 years. In the aftermaths of the cyclone a blizzard hit Sweden. The storm system was named Xaver by Berlin's Free University; other names assigned elsewhere include Bodil, Sven and St. Nicholas (Hewson et al., 2014). T he cyclone developed around 00 UTC on 4 December northeast of Newfoundland and it was situated between converging northerly and southerly airstreams. Due to the westerly wind jet accelerated by the convergence, the cyclone moved to northeast and east, deepening explosively. It had an intense meso-vortex hanging back to west, which enhanced the strong wind (see Figure 1). The cyclone was presented in the operational forecasts 8-9 days before the event and the forecasts indicated the very strong wind gust 3-4 days in advance. (Although some strength overestimation over Germany as well as timing error in surface pressure were concluded.)

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Storm Desmond

Storm Desmond caused severe flooding, travel disruption and a power outage across northern England, parts of Scotland and Ireland on 5 December 2015. Cumbria in northwestern part of England is one of the worst affected regions with more than 200 mm of rain in 24 hours recorded in that area. Storm Desmond broke the United Kingdom's 24-hour rainfall record, with 341.4 mm of rain falling in Honister Pass, Cumbria. On Saturday, 5 December, UK Met office issued a red warning of heavy rain for Cumbria. The cyclone also led to flooding in southern Norway.

Orographical enhancement of precipitation played a major role in the event and the operational model of the ECMWF picked well the highest rainfall amounts over the orographical barriers. However, the forecast underestimated the peak values of about 100 mm in 24 hours in Cumbria and overestimated the precipitation amount in lee of the hills (Figure 2).

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Model experiments

!! The input data and the namelists needed to run the experiments can be downloaded from the ECMWF FTP server: download.ecmwf.int/openifs/evalution. !!

The files are packed in .tgz files and structured into directories named after the case studies (i.e., Xaver_201312, Desmond_201512) and subdirectories indicating the main experiment characteristics (e.g., T255L91_ERA5). The archive files were prepared by starting dates (e.g., gs0c_2015120300.tgz). Typical content of a .tgz file is as follows:

To run OpenIFS, the files highlighted in green in the box above are needed, i.e., the initial conditions for the atmospheric model (files with ICM) and the namelist (namelistfc). The namelist controls the necessary settings (e.g., time step, experiment ID) as well as the post-processing. The most important namelist elements are listed below with their explanation:

In the evaluation, we would like to investigate the following variables:

• 2-meter temperature: its GRIB code number is 167;
• precipitation: it is composed from large-scale and convective precipitation with code numbers 142 and 143, respectively;
• mean sea level pressure: its code number is 151;
• 10-meter wind gust: its code number is 49;
• temperature at 850 hPa level: its code number is 130;
• relative humidity at 700 hPa level: its code number is 157;
• geopotential at 500 hPa level: its code number is 129;

• u and v wind components at 250 and 100 hPa.

The listed variables have to be included in the namelist among the post-processing variables (see the code numbers and levels highlighted with bold characters in the box above). Instead of the wind components at given pressure level, the direct model output contains vorticity and divergence (with code number 138 and 155; see the highlight in red above). To obtain the horizontal wind components, an external post-processing is needed, which calculates u and v from the vorticity and divergence (see later). More information about the namelist settings and GRIB field codes can be found in the how-to articles: How to control OpenIFS output.

!! To run the model, the paths of the input data and the namelist have to be set in the job.  ..... Acceptance testing OpenIFS after installation

Preparation of data for visualization

After the job run is completed, the outputs are split into 2 files (located in the working directory): ICMGG for the gridpoint fields and ICMSH for the spectral ones. The two files should include all the necessary variables set in the namelist. However, before visualisation of the results, some steps are still needed.

Post-processing of model outputs

The Metview macros prepared for visualisation desires the meteorological variables in GRIB files separated by variables and day with the following names:

• t2_${day}.grib for 2-meter temperature,
• p_${day}.grib for precipitation,
• mslp_${day}.grib for mean sea level pressure,
• gust_${day}.grib for 10-meter wind gust,
• t850_${day}.grib for temperature at 850 hPa,
• q700_${day}.grib for relative humidity at 700 hPa,
• z500_${day}.grib for geopotential at 500 hPa,
• u250_${day}.grib for horizontal wind components at 250 hPa,
• u100_${day}.grib for horizontal wind components at 100 hPa,

where day is the given date in format of yyyymmdd (e.g., 20151203). All the files should contain data for 8 timesteps per day (i.e., in every 3 hours).

The 2-meter temperature, the precipitation, the mean sea level pressure and the windgust are expected in gridpoint representation, so will be taken from the ICMGG files. To prepare the needed input files for the Metview macros, the next operations are needed on the raw ICMGG outputs:

where expID is the 4-digit experiment ID and step is the post-processing step (every 3 hours). For precipitation, both the convective and large-scale precipitation components have to be in the same file:

The pressure level data are required in spectral representation, so they will be taken from ICMSH files. To prepare the needed input files for the Metview macros, the next operations are needed on the raw ICMSH outputs:

For wind, the files should include the u and v wind components. To obtain wind components from the vorticity and divergence, we will use the dv2uvl command of CDO (Climate Data Operators) software (more information about the possibilities in CDO can be found in the how-to articles: How to convert GRIB to netCDF):

The size of the resulted files varies by the spatial resolution and the representation. For instance, the file size is 10 MB and 8 MB per variables for gridpoint and spectral fields, respectively, at T255L91 resolution, whereas these values increases to 35 MB and 26 MB at T639L137, to 233 MB and 179 MB at T1279L137.

Preparation of reference data

As reference data we will apply re-analysis, both ERA-Interim (REFERENCE) and ERA5 (REFERENCE) datasets can be utilized.

What are the changes from ERA-Interim to ERA5?

Metview macros

- where they are, how to set them up .. etc

Catalogue

References

Hewson, T. , Magnusson, L. , Breivik, O. , Prates, F ., Tsonevsky, I. , de Vries, H.J.W. , 2014: Windstorms in northwest Europe in late 2013. ECMWF Newsletter 139, 22–28. [PDF]