Code update for HR4_roughness

[grantfirl]

Description

From @Qingfu-Liu:
The overall features for the updates are:

The current wave model derived momentum roughness increases with increasing 10m wind speed, which can lead to too much drag in high winds and consequent reduction of TC intensity. In order to reduce the negative hurricane intensity biases when coupled with the wave model, in the modified code the momentum roughness is limited to a constant value in high winds wind speeds larger than about 30 m/s). Also, in the modification molecular viscosity effect is included to avoid too much reduction of exchange coefficients for heat and moisture in weak winds. More detailed discussion for this issue can be found here.

The HR2 coupled runs with the above modified surface layer scheme have been completed for the 2020 hurricane season (July 21 - Nov. 20, 2020) by Wei Li, and the hurricane stats have been evaluated by Jiayi Peng. The impacts of this change are neutral. However, the observations indicate drag reduction in high wind speed (> about 30m/s at 10m), this change is more consistent with the observation.

Background diffusivity (K0) in the inversion layers near the PBL top is increased from 0.15 m^2/s to 0.4 m^2/s to reduce too much stratocumulus formation in the coastal areas of the east Pacific and east Atlantic oceans [https://www.emc.ncep.noaa.gov/gmb/jhan/vsdbw/hr2d04/: hr2d01 (K0=0.15 m^2/s); hr2d02 (K0=0.3 m^2/s); hr2d03 (K0=0.4 m^2/s; hr2d04 (K0=0.5 m^2/s)].

Maximum allowable TKE-dependent entrainment enhancement is reduced from 15 times to 10 times in the shallow convection scheme to avoid a potential numerical instability due to too much entrainment increase. cmxfac=10 also improve hurricane forecasts in the HAFS.

Issue(s) addressed

N/A

Testing

RTs on Hera. See log in ufs-community/ufs-weather-model#2022.

Dependencies

• waiting on Code update for HR4_roughness, background diffusivity and shallow convection ufs-community/ccpp-physics#119

[grantfirl]

@zach1221 ufs-community/ccpp-physics#119 was merged and this branch has been updated and ready to approve/merge.

[zach1221]

@jkbk2004 we have approval here. Can you please merge this PR?