The representation of soil moisture freezing and its impact on the stable boundary layer

作者：Pedro Viterbo, Anton Beljaars, Jean‐François Mahfouf, João Teixeira · 发表于：Quarterly Journal of the Royal Meteorological Society · 年份：1999 · DOI：10.1002/qj.49712555904 · 被引用次数：302 · 研究领域：Climate variability and models、Climate change and permafrost、Meteorological Phenomena and Simulations

Abstract The 1993 to 1996 version of the European Centre for Medium‐Range Weather Forecasts model had a pronounced near‐surface cold bias in winter over continental areas. the problem is illustrated in detail with help of tower observations. It is shown that a positive feedback exists in the land surface boundary‐layer coupling that has the potential to amplify model biases. If the surface is cooled too much the boundary layer becomes too stable, reducing the downward heat flux and making the surface even colder. This positive feedback is believed to be stronger in the model than in the real atmosphere, resulting in diurnal temperature cycles that are too large and in excessive soil cooling on a seasonal time‐scale in winter. An important contributor to the excessive winter cooling turns out to be the lack of soil moisture freezing in the model. the importance of this process is obvious from soil temperature observations. the seasonal soil temperature evolution shows a clear ‘barrier’ at 0°C due to the thermal inertia of freezing and thawing. A more quantitative illustration is the result of a simple calculation. This shows that the amount of energy necessary to freeze/thaw 1 m3 of wet soil, would cool/warm this soil by about 50 K if the phase transition was not taken into account. To reduce the winter cold bias in the model, three model changes have been tested and are described: (i) the introduction of the process of soil moisture freezing; (ii) revised stability functions ...