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Changing default value for three namelists #1325

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weiwangncar
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This PR changes the default value for the following namelists: config_sfc_albedo (new value = false), config_microp_re (new value = true) and config_ysu_pblmix (new value = true).

With config_sfc_albedo set to false, the model will use table values to define albedo based on landuse values. This should be a better representation for models that have resolution better than the climatological albedo which is at about 5.5 km resolution.

With config_microp_re set to true, this will allow model to compute effective radii from microphysics variables and use them in radiation. This should better represent interactions between microphysics and radiation.

With config_ysu_pblmix set to true, it will account for top-down radiation-driven mixing at the PBL top.

@weiwangncar weiwangncar changed the base branch from master to develop May 28, 2025 00:45
@mgduda mgduda requested a review from ldfowler58 May 28, 2025 00:50
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MPAS and WRF are models that have followed separate developmental paths since 2010, including different default values for namelist parameters prescribed in their respective Registry. As MPAS continues to evolve independently from WRF, and WRF is becoming less supported by MMM, I do not see the need for MPAS to replicate verbatim what is done in WRF.

Since the default values for config_sfc_albedo, config_microp_re, and config_ysu_pblmix have been defined in Registry.xml since their implementation in MPAS (i.e. many years ago), it would be confusing and a disservice to MPAS users to suddenly change their default values (Note that most MPAS users have never used WRF either). How would WRF users react if the default values of those parameters were switched? I also particularly disagree with using "table" values for config_sf_albedo in a global model.

Therefore, as the main developer of the MPAS physics in MPAS, I do not want to change the default values set in Registry.xml.

@weiwangncar
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I agree that MPAS does not need to follow everything that WRF does. But if an option represents good science for a particular physics, it should be employed whether it is in WRF or MPAS. Even though the options are documented, most users would not go through them and they would use what are in default. This comes from our experience working with WRF users. Yes, WRF has changed default values for a number of options, the ones regarding effective radii and top-down mixing in YSU PBL are two of them. When we change them, we do so and announce them in major releases.

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mgduda commented Jun 2, 2025

We could at least include config_sfc_albedo, config_microp_re, and config_ysu_pblmix in the default namelist.atmosphere file so that users will be aware that these options exist.

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