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Key questions to address with the control forecast

TODO: Add maps.

Case study: N.America deep convection

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Note
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titleKey questions and tasks using the control forecast

  1. Understand the weather situation resulting in tornadoes
  2. Evaluate the control forecast and compare it to the analysis ECMWF reanalysis and observations
  3. What is the area of threat according to the control forecast? TODO: explain
  4. How does the convective adjustment process takes place and and what is the role of large scale forcing (why and where it happens)?

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Case study: African deep convection

TODO: note area of interest (show WV image?)

Note
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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.

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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.

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)? Note that this only makes sense for the North American convection(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)

     

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

    How to change the representation of diurnal convection (click here to expand...
    Expand
    title
    )
    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.
  • Impact of the convective time scale adjustment
    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 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.
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