Abstract
An idealized study with two land surface models (LSMs): TERRA-Multi Layer (TERRA-ML) and Community Land Model (CLM) alternatively coupled to the same atmospheric model COSMO (Consortium for Small-Scale Modeling), reveals differences in the response of the LSMs to initial soil moisture. The bulk parameterization of evapotranspiration pathways, which depends on the integrated soil moisture of active layers rather than on each discrete layer, results in a weaker response of the surface energy flux partitioning to changes in soil moisture for TERRA-ML, as compared to CLM. The difference in the resulting surface energy flux partitioning also significantly affects the model response in terms of the state of the atmospheric boundary layer. For vegetated land surfaces, both models behave quite differently for drier regimes. However, deeper reaching root fractions in CLM align both model responses with each other. In general, differences in the parameterization of the available root zone soil moisture, evapotranspiration pathways, and the soil-vegetation structure in the two LSMs are mainly responsible for the diverging tendencies of the simulated land atmosphere coupling responses.
Highlights
Many numerical weather prediction (NWP) models still rely on the relatively simple representation of the terrestrial ecosystem with second generation land surface models (LSMs), which do not simulate carbon fluxes
We explore the nature and strength of land atmosphere coupling in such transitions based on idealized settings for both, TERRA-ML and Community Land Model (CLM) coupled to the same atmospheric model
In the VSMR experiment, the overall soil moisture decrease enhances for TSMP with the ∆η peak shifting downwards. These results indicate that the soil moisture decrease due to bare soil evaporation and canopy transpiration differ between the two LSMs, especially for the drier regimes (Sw < 0.5), which will affect the flux and atmospheric boundary layer (ABL) evolutions which is discussed
Summary
Many numerical weather prediction (NWP) models still rely on the relatively simple representation of the terrestrial ecosystem with second generation land surface models (LSMs), which do not simulate carbon fluxes. The inclusion of a land surface model with a more process-based representation of vegetation including the lateral flow of soil moisture led to improvements in the predicted local weather over Western Germany [1]. Their model simulation showed better agreements to measured surface energy fluxes, atmospheric boundary layer (ABL) structure, and precipitation. The use of a third generation LSM (Community Land Model; CLM) led to improvements in the simulated summertime surface air temperature over the western U.S.A., as compared to observations [2].
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