An aerodynamic roughness length map derived from extended Martian rock abundance data
An aerodynamic roughness length map derived from extended Martian rock abundance data
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从扩展的火星岩石丰度数据导出的空气动力学粗糙度长度图
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
F. Forget
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作者：
É. Hébrard;C. Listowski;P. Coll;B. Marticorena;G. Bergametti;A. Määttänen;F. Montmessin;F. Forget
火星大气环流模型 (MGCM) 中模拟的许多边界层过程（包括控制从火星表面上升的尘埃的过程的描述）对空气动力粗糙度长度 z0 高度敏感。根据从不同火星着陆点和地球模拟站点推断出的岩石尺寸频率分布，我们首先确定对数正态模型的岩石尺寸频率分布能够正确再现观测到的火星岩石群。我们验证了这样的假设：给定区域的岩石丰度 ζ 可以根据其热物理特性（即热惯性 I 和反照率 α）进行一阶估计。我们已经证明了使用岩石丰度 ζ 来估计火星上的粗糙度密度 λ 并随后通过使用基于陆地风洞和现场测量的半经验关系来检索空气动力粗糙度长度的可能性。通过将我们的方法与火星全球勘测者号上的热发射光谱仪的遥感测量相结合，我们得出了整个火星表面的风沙空气动力学粗糙度长度的全球地图，分辨率为 1/8° × 1/8°。与通常的假设相反，火星风积空气动力粗糙度长度在空间上是高度异质的。在最高分辨率下，火星空气动力粗糙度长度从 10−3 厘米到 2.33 厘米不等。大约 84% 的火星表面似乎具有低于 1 厘米的风成空气动力粗糙度长度值，这是最近大多数 MGCM 模拟所假设的空间均匀值。由于气动粗糙度长度 z0 是推导侵蚀阈值风速的关键参数，因此我们预计我们的研究结果将对未来 MGCM 扬尘效率产生重大影响。
Many boundary layer processes simulated within a Mars General Circulation Model (MGCM), including the description of the processes controlling dust rising from the Martian surface, are highly sensitive to the aerodynamic roughness length z0. On the basis of rock-size frequency distributions inferred from different Martian landing sites and Earth analog sites, we have first established that lognormal-modeled rock-size frequency distributions are able to reproduce correctly the observed Martian rock populations. We have validated the hypothesis that the rock abundance ζ of a given area could be estimated at a first order from its thermophysical properties, namely its thermal inertia I and its albedo α. We have demonstrated the possibility of using rock abundance ζ to estimate the roughness density λ on Mars and to retrieve subsequently the aerodynamic roughness length by using semi-empirical relationships based on terrestrial wind-tunnel and field measurements. By combining our methodology with remote sensing measurements of the Thermal Emission Spectrometer aboard Mars Global Surveyor, we have derived a global map of the aeolian aerodynamic roughness length with a 1/8° × 1/8° resolution over the entire Martian surface. Contrary to what is often assumed, the Martian aeolian aerodynamic roughness length is spatially highly heterogeneous. At the fullest resolution, the Martian aerodynamic roughness length varies from 10−3 cm to 2.33 cm. About 84% of the Martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm, the spatially uniform value that most of the MGCMs simulations have assumed recently. Since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities, we anticipate a significant impact of our findings on the efficiencies for lifting dust in future MGCMs.