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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 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 Does reducing the model 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
    titleHow 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
    titleHow 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
    titleHow 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) - how does this affect surface & near-surface fields?

    Expand
    titleHow to change the model code (click here to expand)

    For this change, two files need to be edited:

    Code Block
    titleifs/phys_ec/suvdf.F90
     line 53: RLAM   = 75.0_jprb  !! 150._JPRB: reduce to 75m

    and:

    Code Block
    titleifs/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?

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