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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.
The ERA-Interim analysis is an improvement over the original analysis which did not have as many observations. The scientific content of the IFS operational model at that time was significantly different to the more modern OpenIFS. A rough proxy for the how the forecast at the time performed would be to run OpenIFS at T255, the resolution of the initial data.
As OpenIFS is a spectral model, the 'T' number refers to the triangular truncation is spectral space. Equivalent grid-pt resolutions are: |
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% 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:
As ERA-Interim is an improved analysis, forecasts from these starting initial conditions will not reproduce the operational forecast of the storm. Because of changes to the forecasting system, this is impossible to do with OpenIFS. A proxy is to run the model at the same resolution as the ERA-Interim data (T255) as this is close to the resolution of the operational model of the time.
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.
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?
Edit the source code to half the gravity wave drag coefficient File: ifs/phys_ec/sugwd.F90, change:
to:
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Increase the precipitation auto conversion rate - what impact does this have?
Edit the source code to increase the auto conversion rate by 20% File: ifs/phys_ec/sucldp.F90, change:
to:
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Change the surface transfer coefficient in the turbulence scheme
Reduce the coefficient by 20%. Alter surf/module/surfexcdriver_ctl_mod.F90 from :
to:
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Reduce (halve) the asymptotic mixing length scale (K)
For this change, two files need to be edited:
and:
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Ulbrich et al., 2001, Weather, 56, 70-80
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.
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