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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Figure 1: 24-hour maximum wind gust (m/s) on 5 December based on ECMWF operational IFS forecasts at 00 UTC on 3 and 5 December (left and middle, respectively; with white contours for the mean sea level pressure in hPa on 12 UTC on 5 December) and from the observations (right). |
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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Figure 2: 24-hour precipitation amount (mm) between 6 UTC on 5 December and 6 UTC on 6 December, based on ECMWF operational IFS forecast at 00 UTC on 5 December (left; with cyan contours for the mean sea level pressure in hPa at 12 UTC on 5 December) and observations (right). |
Model experiments
Several experiments have been conducted with OpenIFS for both cases with the aim to test the effect of starting date and forecast length, initial condition as well as spatial resolution to the forecast quality. The details of experiments are summarized in Table 1.
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Experiment ID | Initial condition | Resolution | Starting date | Time step | Output frequency | ||||||||
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Xaver | 1. | ERA-Interim | T255L91 | 1 Dec 2013 | 2700 s | 3h | |||||||
2. | ERA_Interim | T639L137 | 900 s | 3h | |||||||||
3. | ERA5 | T255L91 | 2700 s | 3h | |||||||||
4. | ERA5 | T639L137 | 900 s | 3h | |||||||||
line | |||||||||||||
Desmond | 1. | gryg | ERA-Interim | T255L91 | 1 Dec 2015; 2 Dec 2015; | 2700 s | 3h | ||||||
2. | gs22 | ERA-Interim | T639L137 | 3 Dec 2015; 4 Dec 2015 | 900 s | 3h | |||||||
3. | gs23 | ERA-Interim | T1279L137 | 3 Dec 2015; 4 Dec 2015 | 600 s | 3h | |||||||
4. | gs0c | ERA5 | T255L91 | 3 Dec 2015; 4 Dec 2015 | 2700 s | 3h | |||||||
5. | gs04 | ERA5 | T639L137 | 3 Dec 2015; 4 Dec 2015 | 900 s | 3h |
!! 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:
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Size File name
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To run OpenIFS, the files highlighted above in green colour in the box above are needed, i.e., the initial conditions for the atmospheric model (files with ICM
) and the namelist (namelistfc
). The namelist contains controls the necessary settings , (e.g., the experiment ID, the time step, experiment ID) as well as the post-processing variables. Below the The most important namelist elements are listed below with their explanation:
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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 convective and 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
abovewith bold characters in the box above). Instead of the wind components at given pressure level, the direct model
outputsoutput 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 using the dv2uvl
commands 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):
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More information about the namelist settings can be found in the how-to articles: How to control OpenIFS output.
Post-processing
- how to prepare data for plotting
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]
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