A Parameterization of Subgrid-Scale Land-Atmosphere Interactions for Atmospheric Models

在大气的计算机模型中，计算是以水平间隔进行的。因此，计算代表了自然变化的细微细节被抹去的区域。至少在某种统计意义上，模型中包含的试图解释这种细节的重要热力和动力效应的公式被称为“参数”。特别是陆地表面，在典型尺度(从中尺度模式的10平方公里到全球范围的模式的100万平方公里)的模式网格正方形内，通常包含地形、植被覆盖、水分和热特征的显著水平变化。目前最先进的两种参数化方法要么没有考虑复杂生物物理机制的亚格子尺度的异质性，要么忽略了已知的亚格子尺度的陆地-大气相互作用的影响，如坡谷风、湖风和由变化的植被覆盖引起的其他热循环。在实施当前模型计算机算法的改进之前，重要的是评估这种变化对模型在不同空间尺度上的行为的影响。Avissar计划通过使用非常灵活的(在可选分辨率方面)和经过良好测试的计算机模型(科罗拉多州立大学-区域大气模拟系统)和过去两个观测计划中通过在丘陵、裸露、农业和森林地区上空的飞行横断面进行的详细低层测量相结合的方式来进行此类评估。国际大气研究所以前在边界层和农业气象学方面的研究以及在发展区域大气模式方面的工作将有助于在这一问题领域取得进展，这将应用于改进短期、中期和长期预报，以及在区域和全球范围内研究气候变化。

In computer models of the atmosphere, calculations are carried out at horizontal intervals. Thus a calculation is representative of an area in which the fine-grain detail of natural variations is smeared out. Formulas included in the model that attempt to account for important thermal and dynamic effects of such detail, at least in some statistical sense, are referred to as "parameterizations". The land surface, in particular, norm- ally contains significant horizontal variations in topography, vegetative cover, moisture, and thermal characteristics within a model grid square of typical dimensions (ranging from 10 sq km in mesoscale models to 1 million sq km in models of global extent). The two approaches used in current state-of-the art parameter- izations either do not account for subgrid-scale heterogenity of complex biophysical mechanisms, or neglect the effects of known subgrid scale land-atmosphere interactions such as slope-valley winds, lake breezes, and other thermal circulations caused by varying vegetative cover. Before improvements in current model computer algorithms are implemented it is important to assess the impact of such variations on the models' behaviour at differing spatial scales. Avissar proposes to carry out such assesments, by using a combination of a very flexible (in terms of optional resolution) and well-tested computer model (the Colorado State University- Regional Atmospheric Modelling System), and detailed low-level measurements made by flight transects over hilly, bare, agricultural, and forested areas in two past observational programs. The PI's prior research in boundary-layer and agricultural meteorology as well as in developing regional models of the atmosphere will contribute to advances in this problem area, which has application to improvement of short, medium and long- term forecasting, as well as research in climate change on regional and global scales.