Soil temperature spin-up in land surface schemes
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Land surface schemes used in atmospheric and hydrologic models require the specification of initial soil-temperature profiles. However, detailed soil temperature information is generally unavailable, hence modellers sometimes recur to specifying simplified initial conditions such as vertically constant profiles, assuming that the harmonic heating at the soil surface induces a rapid equilibrium to a steady periodic state. In this paper, using both numerical and analytical approaches, it is shown that such a transition to a steady periodic state is not always very rapid. In particular, it is demonstrated that the characteristic time required to reach equilibrium is highly dependent on the precise timing of initialisation with respect to the cycle of surface heating, and that initialising at the instant coincident with the occurrence of the maximum soil heat flux is the preferred mode.
The research described here was carried out in the project “Measuring urban surfaces’ thermal inertia” (MUSTI), which is supported by the PRODEX programme of the European Space Agency (ESA) and the Belgian Science Policy Office. We would also like to acknowledge support from EU COST Action 728 “Enhancing mesoscale meteorological modelling capabilities for air pollution and dispersion applications”.
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