Forecast Settings

This page gives some details and advice on appropriate settings for the HARMONIE-AROME forecast

Microphysics

OCND2

This option was implemented in ICE3/ICE4 microphysics in 2014 in order to improve the performance of the HARMONIE-AROME model configuration in Winter over the Arctic/Subarctic region. See OCND2 for more info.

ICE-T

Switch ICE-T on by setting LICET=.TRUE. in harmonie_namelist.pm under &NAMPARAR in %arome. When using ICE-T (LICET), LOCND2 should be set to True, and LMODICEDEP preferably to False. LICET will override LKOGAN, so by default LKOGAN=F. Documentation: (Engdahl et al., 2020)

Description: ICE-T is a modified cloud microphysics scheme that builds upon ICE3 and OCN2D, with elements from the Thompson scheme from WRF. ICE-T was developed in cy40h1.1 for the purpose of better representation of supercooled liquid water, and downstream forecasts of atmospheric icing. The changes include stricter conditions for ice nucleation, less efficient collection of liquid water by snow and graupel, and variable rain size distribution depending on the source of the rain. (Rain originating from melting snow or graupel have larger drops, than rain originating from warm processes.)

Shallow Convection

LSHALLOWMF activates (.TRUE.) or de-activates (.FALSE.) the DUAL (dry and moist) mass flux shallow convection parameterisation. Note that with LSHALLOWMF=.FALSE. the mass flux activity as a source term for TKE in the turbulence scheme (energy cascade) will be also eliminated. Also the moist updraft transport contribution to the cloud scheme is eliminated with LSHALLOWMF=.FALSE.. See for details of the convection scheme and links to the cloud and turbulence scheme: https://doi.org/10.5194/gmd-15-1513-2022.

The scale-aware convection scheme is activated by setting LSCAWAREMF=.TRUE.. Setting this reduces the dry and moist (if present) mass flux using a tangent function scaled with the dry boundary layer height $h$ for the dry updraft and sub-cloud height plus cloud layer depth $h+h_c$ for the moist updraft:

\[f = \tanh\left(1.86 \frac{\Delta x}{h+h_c}\right)\]

NOTE: this option can only be used when LSHALLOWMF=.TRUE..

To support the model when it is trying to build up convection itself, the setting LWTHRESH=.TRUE. can be used. Depending on the gridsize, a vertical velocity threshold is defined. If the absolute value of the vertical velocity in a grid column exceeds this threshold the shallow convection is shut down.

LWTHRESH option is updated as the vertical velocity is now only diagnosed in the lowest 6km , this to prevent that high vertical velocities not related to convection are used.

LWTHRESHMOIST option works similarly to option LWTHRESH but now only the paramterized moist convection is shut down as the threshold is met, the dry convection is not affected by this option (but could be affected by LSCAWAREMF).

Turbulence scheme

HARATU

HARATU (HArmonie with RAcmo TUrbulence scheme) is the default (HARATU=yes in config_exp.h) turbulence scheme in HARMONIE-AROME originally developed for RACMO (Regional Atmospheric Climate MOdel). The length scale of this turbulence scheme is described by @(Lenderink and Holtslag, 2004). Note that HARATU is only tested in combination with LSHALLOWMF=.TRUE. and CMF_UPDRAFT='DUAL'. The later convection scheme provides input to the HARATU turbulence scheme to present the important energy cascade (from large to small scales), see https://doi.org/10.5194/gmd-15-1513-2022