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titleKey questions and tasks using the control forecast

 

  1. Understand the weather situation over Africa.
  2. What is the role of large scale in this case (compare with N.America case).
  3. Look at the diurnal variation of key parameters (2m temperature, surface heat fluxes, precipitation, outgoing-longwave-radiation) for location 0N,25E.
  4. Compare differences in convection profiles between Central Africa and (i) open ocean, and (ii) Amazonia.

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.

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  • 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.

    - 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 (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

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

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