Source code changes to the Integrated Forecasting System (IFS) for nextGEMS simulations

On top of IFS Cycle 48r1, we used in nextGEMS Cycle 3 a combination of model changes targeting a reduced TOA radiation imbalance, mostly affecting cloud amount, which is documented in this repository. Moreover, in km-scale simulations in which the deep convection parameterisation is switched off, convective cells tend to be too localised, too intense, and they lack organisation into larger convective systems. To address these issues, instead of switching the deep convection scheme off completely, we have reduced its activity by reducing the cloud-base mass flux as listed below.

More details can be found in Rackow, Pedruzo-Bagazgoitia, Becker, Milinski, Sandu et al. : Multi-year simulations at kilometre scale with the Integrated Forecasting System coupled to FESOM2.5/NEMOV3.4

This work was supported by the European Union's Horizon 2020 collaborative project NextGEMS (grant number 101003470). For more infos about the nextGEMS project, see https://nextgems-h2020.eu (last access: 29.11.2023) 

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cloudsc.F90:

changes for cloud edge erosion:

-calculate saturation deficit wrt env. RH rather than domain mean RH

-assume fixed effective cloud spacing rather than fixed effective cloud scale

changes for rain and snow evaporation:

-remove RH-dependent threshold for rain and snow evaporation by setting ZZRH=1

-introduce sub-grid RH enhancement scheme, using Tiedtke (1993) top-hat assumption

-precipitation fraction is reduced proportionally when rain evaporates

-add factors RXRAINEVAP and RXSNOWSUBL that control rate of rain/snow evaporation

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cumastrn.F90:

-introduced RDXFAC (possibility to scale cloud base mass flux)