Representing Soil Moisture Heterogeneity in the "Super-Parameterized" Community Earth System Model

Abstract:

An approach to representing soil moisture heterogeneity in land-surface models using bins of soil moisture, advancing on the method developed by Sellers et al., 2003 is presented.

Structuring land-surface models in this fashion presents a desirable structure for coupling to atmospheric models utilizing the "multi-scale modeling framework", called "super-parameterization" in the Community Earth System Model, CESM. The multi-scale modeling framework substitutes conventional cloud parameterizations with a 2-D cloud-resolving model.

By considering soil moisture heterogeneity, the land-surface model is able to utilize the distribution of precipitation simulated by the cloud-resolving model in the super-parameterization, rather than it's summed total.

Additionally, treatments of gravitational drainage and runoff in the binned model are proposed and assessed. This is, in general, a conceptual addition to the binned approach of Sellers et al.; but it is also particularly motivated by the fine grid resolution of the cloud-resolving model used in super-parameterization, typically 2km.

Preliminary results suggest that the binned-approach improves model representation of dry-down following rain events and may help mitigate some of the excessive latent heat fluxes simulated by the standard land model in the CESM.