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

Further reading

Peter Bechtold, Noureddine Semane, Philippe Lopez, Jean-Pierre Chaboureau, Anton Beljaars, and Niels Bormann, 2014:
     
  1. P. Bechtold et al, 2014Representing Equilibrium and Nonequilibrium Convection in Large-Scale Models. J. Atmos. Sci., 71, 734–753.
      IFS manual - convection TODO
  1. http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-13-0163.1

  2. See section on convection in description of Atmospheric Physics: http://www.ecmwf.int/en/research/modelling-and-prediction/atmospheric-physics

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  2. More information about the N.American tornadoes can be found on the ECMWF Severe Event Catalogue - 201404 - Convection - Arkansas U.S

  3. IFS documentation, Part IV, Physical Processes - Chapter 6: convection (PDF).

  4. ECMWF Newsletter, summer 2014, number 140. Article on OpenIFS user workshop 2014 (Stockholm), page 2 (PDF)

 ECMWF Newsletter article TODO

Comments

The forecasting system at ECMWF makes use of "ensembles" of forecasts to account for errors in the initial state. In reality, the forecast depends on the initial state in a much more complex way than just the model resolution or starting date.  At ECMWF many initial states are created for the same starting time by use of "singular vectors" and "ensemble data assimilation" techniques which change the vertical structure of the initial perturbations.

As further reading and an extension of this case study, research how these methods work.

Acknowledgements

TODOWe are pleased to acknowledge the input from Peter Bechtold, Filip Vana, Sandor Kertesz in preparing the material for the OpenIFS user workshop in Stockholm 2014, from which the material on this page is derived.

 

 

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