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首页> 外文学位 >Advancing assessments on aerosol radiative effect by measurement-based direct effect estimation and through developing an explicit climatological convective boundary layer model.
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Advancing assessments on aerosol radiative effect by measurement-based direct effect estimation and through developing an explicit climatological convective boundary layer model.

机译：通过基于测量的直接效应估计并通过建立明确的气候对流边界层模型来推进对气溶胶辐射效应的评估。

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The first part of the thesis assesses the aerosol direct radiative effect (ADRE) with a focus on ground-based AERONET and satellite MODIS measurements. The AERONET aerosol climatology is used, in conjunction with surface albedo and cloud products from MODIS, to calculate the ADRE and its normalized form (NADRE) for distinct aerosol regimes. The NADRE is defined as the ADRE normalized by optical depth at 550 nm and is mainly determined by internal aerosol optical properties and geographical parameters. These terms are evaluated for cloud-free and cloudy conditions and for all-mode and fine-mode aerosols. Because of stronger absorption (smaller single-scattering albedo) by the smoke over South Africa, the average NADRE over South America is ∼35% larger at the TOA but ∼38% smaller at the surface than that over South Africa. As the surface albedo varies from ∼0.1 to ∼0.35, it is observed that the dust NADRE ranges from -44 to -17 Wm-2tau-1 at the TOA and from -80 to -48 Wm-2tau -1 at the surface over the Saharan deserts, Arabian Peninsula, and their surrounding oceans. We find that the NADRE of fine-mode aerosol is larger at the TOA but smaller at the surface in comparison to that of all-mode aerosol because of its larger single-scattering albedo and smaller asymmetry factor. Cloudy-sky ADRE is usually not negligible for the observed cloud optical thickness but the TOA ADRE with clouds is sensitive to the relative location of aerosols and cloud layer. The high-resolution MODIS land surface albedo is applied, together with aerosol optical properties from an integrated MODIS retrieval and a chemical transport model simulation, to study the clear-sky ADRE over North Africa and the Arabian Peninsula for summer 2001, where surface is highly reflective with considerable spatial variability but poorly described by modeling. TOA ADRE shows the high spatial variability with close similarity to that of surface albedo. The albedos derived from the Common Land Model changes the regionally averaged positive TOA ADRE (3 ∼ 4 Wm-2) based on MODIS albedo to negative (∼ -2 Wm-2).; The second part of the thesis is to develop a 2-D conceptual model for a climatological convective boundary layer over land as a persistent and distinct component in climate models, where the convective-scale motion is explicitly described by fluid dynamics and thermodynamics while the smaller scale effect is parameterized for a neutral stratification. Our conceptual model reasonably reproduces essential statistics of a convective boundary layer in comparison to large eddy simulations. The major difference is that our model produces a better organized and more constrained spatial distribution with coherent convective cells. The simulations for a climatological convective boundary layer are conducted for a prescribed constant and homogenous surface heat flux and a specified cooling term representing the background large scale thermal balance. The results show: the 2-D coherent structures of convective cells with horizontal and vertical characteristic scales comparable with PBL height; downward maximum velocities being 70-80% of the accompanying upward maxima; vertical profiles of a constant potential temperature and linear decreasing heat fluxes; a nearly proportional increase in the mixed-layer temperature and square-root increase in the velocity magnitude with increasing surface heat flux.
机译：本文的第一部分评估了气溶胶直接辐射效应（ADRE），重点是基于地面的AERONET和卫星MODIS测量。 AERONET气溶胶气候学与MODIS的表面反照率和云产品一起用于计算不同气溶胶方案的ADRE及其归一化形式（NADRE）。 NADRE定义为通过550 nm的光学深度归一化的ADRE，主要由内部气溶胶光学特性和地理参数确定。这些术语针对无云和多云条件以及全模式和精细模式的气溶胶进行评估。由于南非对烟雾的吸收更强（单散射反照率较小），因此，南美洲的平均NADRE在TOA处比南非的平均NADRE大约35％，而在地表的平均NADRE小38％。当表面反照率在〜0.1至〜0.35之间变化时，可以观察到在TOA处，粉尘NADRE的范围为-44至-17 Wm-2tau-1，而在整个表面，尘埃NADRE的范围为-80至-48 Wm-2tau -1撒哈拉沙漠，阿拉伯半岛及其周围的海洋。我们发现，与全模式气溶胶相比，精细模式气溶胶的NADRE在TOA处较大，但在表面较小，这是因为其单散射反照率较大且不对称系数较小。对于观察到的云层光学厚度，通常不能忽略多云天空ADRE，但是带有云层的TOA ADRE对气溶胶和云层的相对位置敏感。应用高分辨率的MODIS陆地表面反照率，以及来自集成的MODIS检索和化学传输模型模拟的气溶胶光学特性，以研究2001年夏季北非和阿拉伯半岛上空晴空的ADRE反射，具有很大的空间变异性，但建模效果不佳。 TOA ADRE显示了高空间变异性，与表面反照率相似。从共同土地模型得出的反照率将基于MODIS反照率的区域平均正TOA ADRE（3〜4 Wm-2）变为负（〜-2 Wm-2）。论文的第二部分是为土地上的气候对流边界层建立一个二维概念模型，作为气候模型中的一个持久而独特的组成部分，其中对流尺度运动由流体动力学和热力学来明确描述，而较小的则由流体动力学和热力学来描述。参数化比例效果以实现中性分层。与大型涡流模拟相比，我们的概念模型合理地再现了对流边界层的基本统计数据。主要区别在于我们的模型使用相干对流细胞产生了更好的组织性和更受约束的空间分布。对气候对流边界层的模拟是针对规定的恒定且均匀的表面热通量和代表背景大规模热平衡的指定冷却项进行的。结果表明：对流单元的二维相干结构具有与PBL高度相当的水平和垂直特征尺度。下降的最大速度是伴随的上升最大值的70-80％；恒定电位温度和线性递减的热通量的垂直剖面；随着表面热通量的增加，混合层温度几乎成比例增加，速度幅度的平方根增加。

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