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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 for how the forecast at the time performed would be to run OpenIFS at T255, the resolution of the initial data.
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As OpenIFS is a spectral model, the 'T' number refers to the triangular truncation is in spectral space. Equivalent grid -pt resolutions are: |
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The 'ecmwf' directory contains the files as used produced at ECMWF to run when this experiment was run:
- 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.
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As ERA-Interim is an improved analysis, forecasts from these starting initial conditions will not reproduce the operational forecast of the storm as it was in 1999. Because of changes to the forecasting system, this is impossible to do reproduce 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.
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- What's the impact of the different 'lead times' on the forecast of the storm (i.e. starting from different dates)?
- What's the impact of resolution on the forecast of the storm: both for it's development and impact over areas worse hit in Europe?
- 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?
Expand title How to change the code (click here to expand) Edit the source code to half the gravity wave drag coefficient
File: ifs/phys_ec/sugwd.F90, change:
Code Block Line 108: ! Revised gwd parameter values Line 109: GKDRAG =0.15_JPRB
to:
Code Block Line 108: ! Revised gwd parameter values Line 109: GKDRAG = 0.075_JPRB ! half GWD coefficient: 0.15_JPRB
Increase the precipitation auto conversion rate - what impact does this have?
Expand title How to change the code (click here to expand…) Edit the source code to increase the auto conversion rate by 20%
File: ifs/phys_ec/sucldp.F90, change:
Code Block line 123: RKCONV=1._JPRB/6000._JPRB ! 1/autoconversion time scale (s)
to:
Code Block line 123: ! RKCONV=1._JPRB/6000._JPRB ! 1/autoconversion time scale (s) line 124: RKCONV=1.2_JPRB/6000._JPRB ! default scaled by 20%: 1/autoconversion time scale (s)
Change the surface transfer coefficient in the turbulence scheme
Expand title How to change the model code (click here to expand) Reduce the coefficient by 20%.
Alter surf/module/surfexcdriver_ctl_mod.F90 from :
Code Block line 671: DO JL=KIDIA,KFDIA line 672: IF (JTILE == IFRMAX(JL)) THEN line 673: PKHLEV(JL)=ZKHLEV(JL) line 674: ENDIF line 675: ENDDO
to:
Code Block line 671: DO JL=KIDIA,KFDIA line 672: IF (JTILE == IFRMAX(JL)) THEN line 673: PKHLEV(JL)=ZKHLEV(JL) line 674: ENDIF line 675: ! reduce surface transfer coeff by 20% in turbulence scheme line 676: ZCFMTI(JL,JTILE)=0.8_JPRB*ZCFMTI(JL,JTILE) line 677: ENDDO
Reduce (halve) the asymptotic mixing length scale (K)
Expand title How to change the model code (click here to expand) For this change, two files need to be edited:
Code Block title ifs/phys_ec/suvdf.F90 line 53: RLAM = 75.0_jprb !! 150._JPRB: reduce to 75m
and:
Code Block title ifs/phys_ec/vdfexcu.F90 ZKLEN = 75.0_jprb !! 150.0_JPRB ! asymptotic K length scale troposphere - Reduce to 75m
- For these last 4 cases where the model's parametrizations have been altered, which make the biggest difference and why? Does any of the changes improve the forecast in any way?
- If you were providing forecasts for wind and precipitation to the general public based on these experiments, what could you say with certainty and what is less certain? How would this change over different countries?
Further reading
Ulbrich et al., 2001, Weather, 56, 70-80
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