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Not all of the suggested experiments are applicable to both cases, indicated in brackets.


  • What's the impact of the different 'lead times' on the forecast of the convection (i.e. starting from different dates)? (N.America only)

  • What's the impact of resolution on the forecast of the convection? (both)

  • Does reducing the model timestep improve or worsen the forecast? (both)
     

  • Turn off deep convection (both)

    Expand

    Do this by editing fort.4, find the namelist block NAMCUMF and add a line:

    LMFPEN=false,            ! disable deep convection

  • Impact of the improved diurnal cycle of convection. (Africa only)
    In this sensitivity experiment, look at the timing of convective and precipitation events by changing how the model parametrizes the diurnal cycle.

    Expand
    titleHow to change the representation of diurnal convection (click here to expand...)
    Info

    OpenIFS has 3 options for the controlling the diurnal cycle. To change between them:

    - Edit the fort.4 file

    - Find the namelist NAMCUMF and change the parameter RCAPDCYCL accordingly:

       RCAPDCYCL = 2 (default) activates the diurnal cycle using sub-cloud CAPE,

       RCAPDCYCL = 1 diurnal cycle using surface sensible heat flux,

       RCAPDCYCL = 0 reverts the code to a setting before the diurnal cycle for convection was implemented.

  • Increase the precipitation auto conversion rate - what impact does this have? (both)

    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)

  • Impact of the convective time scale adjustment (both)
    An optimization factor in the parametrization is used for tuning the diurnal cycle. This can be altered by changing a value in the model namelist.

    Expand
    titleHow to change the time scale (click here to expand...)

    To change the timescale:

    - Edit the fort.4 file

    - Find the namelist  NAMCUMF, parameter RTAUA.

    - The default value is RTAUA=1. Sensible choices lie between values of et it to

    - Run two sensitivity experiments with values of RTAUA = 0.33 and 3.)

    The ratio between the actual cloud base mass flux and the unit (initial) cloud base mass flux:

    Mathdisplay
    \frac{M_{base}}{M^*_{base}} = \frac{PCAPE - PCAPE_{bl}}{\tau}

    Look at the amplitude of precipitation.

     

     

  • Sensitivity to entrainment rate

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  • (both)

    Expand

    To change the entrainment rate:

    - Edit the fort.4 file

    - Find the namelist block NAMCUMF, parameter ENTRORG

    - The default value is ENTRORG= 1.75E-3

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  • ENTRORG= 5.8E-4 reduced by factor 3 (mostly shallow convection regime)

    ENTRORG= 5.25E-3 multiplied by factor 3 (mostly deep convection regime)

    Look at the cloud top height, precipitation and eventually changes in temperature and moisture

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  • fields with respect to the reference. Note also this is having less impact with the diurnal cycle

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  • activated.

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Additional questions

  • How important is the correct diurnal cycle of precipitation and radiation for 2m temperature and dewpoint forecast?

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