Lothar storm
Introduction
The Lothar storm that swept across Europe during 24-27 December 1999 is provided as a sample case study to use with OpenIFS. This storm was one of several storms to hit Europe in December 1999 and Lothar severely affected northern France, Switzerland and Germany (for more details see: Ulbrich et al., 2001, Weather, 56, 70-80).
These storms were characterized by record-breaking windspeed observations and rapid development across Europe. There was also a band of extremely high baroclinity near the cyclone track over the N. Atlantic and partly into Europe associated with Lothar.
The ECMWF forecasting system of the time did not accurately capture the storm's intensity though the strong jet stream was predicted some 9 days earlier. The storm initiated from a small disturbance in the Atlantic. More recently, Wedi et al, 2012, ECMWF Newsletter, have shown that very high resolution (T7999; ~2.5km) is necessary to model accurately the high wind speeds observed, particularly over the mountainous regions of Europe.
A number of initial conditions are provided along with suggested exercises.
Initial conditions
Case study initial conditions for the Lothar storm are provided on the OpenIFS ftp site. The Lothar depression developed initially on 24th December off the North American east coast at 35N.
The initial conditions are available at a range of different resolutions and start dates for a 10 day forecast. The experiment ids are created at ECMWF and used for identifying the model forecasts on the ECMWF archive system (for those with access).
Note that ERA-Interim has a resolution of T255 and the operational resolution at that time was T319. Initial data has been spectrally interpolated to the model resolutions.
| Resolution | Expt id | Start date | Analysis | Filename | File size |
|---|---|---|---|---|---|
| T159L60 | fqar | 1999/12/24/12z | ERA-Interim | T159_1999122412_fqar.tgz | 22Mb |
| T255L60 | fqak | 1999/12/24/12z | ERA-Interim | T255_1999122412_fqak.tgz | 54Mb |
| T511L60 | fqaj | 1999/12/24/12z | ERA-Interim | T511_1999122412_fqaj.tgz | 205Mb |
| T1023L60 | fs2y | 1999/12/24/12z | ERA-Interim | T1023_1999122412_fs2y.tgz | 780Mb |
| T1279L60 | fqaf | 1999/12/24/12z | ERA-Interim | T1279_1999122412_fqaf.tgz | 1.2Gb |
To unpack files with .tgz, either use:
tar zxf T159_1999122412_fqar.tgz
or if your tar command does not support compression:
mv T159_1999122412_fqar.tgz T159_1999122412_fqar.tar.gz
gunzip T159_1999122412_fqar.tar.gz
tar xf T159_1999122412_fqar.tar
| Resolution | Exp id | Start dates | Analysis | Filename | File size |
|---|---|---|---|---|---|
| T255 | g8oz | 1999/12, 14th-25th, 12z | ERA-Interim | T255_199912_14-25_g8oz.tar.bz2 | 660Mb |
| T511 | g8su | 1999/12, 14th-25th, 12z | ERA-Interim | T511_199912_14-25_g8su.tar.bz2 | 2.3Gb |
| T1279 | g8t3 | 1999/12, 14th-25th, 12z | ERA-Interim | T1279_199912_14-19_g8t3.tar.bz2 T1279_199912_20-25_g8t3.tar.bz2 | 6Gb |
These files use the 'bzip2' command rather than 'gzip', to achieve a better compression.
Uncompressing may take a long time depending on your system.
To uncompress:
bzip2 -d T255_199912_14-25_g8oz.tar.bz2
tar xf T255_199912_14-25_g8oz.tar
Download instructions
% mkdir -p runs/lothar/t159 % cd runs % ftp ftp.ecmwf.int ftp> cd case_studies/lothar_storm ftp> binary ftp> get 1999122412_T159_fqar.tgz ftp> quit % tar zxf 1999122412_T159_fqar.tgz % ls 1999122412_T159.tgz ICMCLfqarINIT ICMGGfqarINIT ICMGGfqarINIUA ICMSHfqarINIT ecmwf % ls ecmwf NODE.001_01 namelistfc
The 'ecmwf' directory contains the files as used at ECMWF to run this experiment:
- namelistfc : copy this file to 'fort.4' to run the experiment (modify as required)
- NODE.001_01 : this is the model output file as run at ECMWF. If your run fails, it may be useful to compare with this file.
Suggested experiments
As ERA-Interim is an improved analysis, forecasts from these starting initial conditions will not reproduce the actual forecast of the storm. For that, the model should be run with operational data.
- What's the impact of the different 'lead times' on the forecast of the storm (i.e. starting from different dates)?
- What's the difference and why between forecasts started with the operational analysis of the time and the ERA-Interim analysis?
Sensitivity experiments
The IFS is highly tuned to give the best forecast over a range of initial conditions. However, it is instructive to try some sensitivity experiments to understand the role of various physical and dynamical processes.
- What's the impact of resolution on the forecast of the storm?
Reduce the timestep of the model - does this improve or worsen the forecast?
Reduce the gravity wave drag - how does this affect the forecast in the upper and lower levels?
Further reading
This article in a recent ECMWF Newsletter has a description of student projects at the University of Stockholm using the Lothar storm case study.
A. Hannachi, J. Kjellsson, M. Tjernström, G. Carver, 2012, Teaching with the OpenIFS at Stockholm University, ECMWF Newsletter No. 134, Winter 2012/13.
Wikipedia article:
Cyclone Lothar and Martin, Wikipedia article, retrieved 17/12/14.