Abstract
Newly improved formulations of the bare soil evaporation and the surface temperature are presented, using the multilayer land surface scheme TERRA of the Consortium for Small-scale Modeling (COSMO) atmospheric model. The simulations were carried out in offline mode with atmospheric forcing data from the Meteorological Observatory Lindenberg–Richard-Aßmann-Observatory of the German Meteorological Service. The results show that the bare soil evaporation simulated by the reference version of TERRA is substantially overestimated under wet conditions, and underestimated under dry conditions. Furthermore, the amplitude of the diurnal cycle of the surface temperature is systematically underestimated. In contrast, the diurnal cycles of the temperatures in the soil are overestimated instead. The new description of the bare soil evaporation in TERRA is based on a resistance formulation analogue to Ohm’s law, while the surface temperature is now based on the skin temperature formulation by Viterbo and Beljaars. The new formulation improves the simulated bare soil evaporation substantially. In particular, the overestimation under wet conditions is reduced, also acting against an extensive drying of the soil during the annual cycle. Additionally, the underestimation under dry conditions is reduced as well. Furthermore, the simulated amplitude of the diurnal cycle of the surface temperature is substantially increased. In particular, a nocturnal warm bias is systematically reduced. In addition to this, the new formulations were also applied in coupled mode in the COSMO model, resulting in improved diurnal cycles of near-surface temperature and dew point.
Highlights
The processes at the land surface significantly affect the conditions in the low-level atmosphere.They control the surface radiation budget and turbulent heat fluxes and determine how much energy and water is available to heat and moisten the air over land
The new formulations were applied in coupled mode in the Consortium for Small-scale Modeling (COSMO) model, resulting in improved diurnal cycles of near-surface temperature and dew point
Of the Consortium for Small-scale Modeling (COSMO) mesoscale atmospheric model [3] was found to be systematically overestimated under wet conditions and underestimated under dry conditions
Summary
The processes at the land surface significantly affect the conditions in the low-level atmosphere They control the surface radiation budget and turbulent heat fluxes and determine how much energy and water is available to heat and moisten the air over land. Beside these deficiencies in the bare soil evaporation, it turned out that the diurnal temperature range, i.e., the difference between the daily maximum and minimum temperature, at the surface is systematically underestimated. Further applications are in hydrology, agriculture, forestry, and renewable energies, road conditions and urban modelling [15] All these fields rely on a high accuracy of the forecasts of near-surface temperature and humidity. In the attempt to choose a canopy description of intermediate level of complexity, which is consistent with the one of TERRA and does not introduce several new parameters which need to be determined, like e.g., the Community Land Model [17] would do, the so-called skin temperature formulation [18] was selected and implemented in TERRA [19]
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