Droplet activation parameterization: the population-splitting concept revisited
Droplet activation parameterization: the population-splitting concept revisited
复制标题
液滴激活参数化：重新审视群体分裂概念
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
A. Nenes
中科院分区：
文献类型：
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作者：
R. M. Betancourt;A. Nenes
抽象的。在这项工作中，我们假设，实施和评估修改的“人口分裂”的概念，介绍了Nenes和Seinfeld（2003），在液滴激活参数化的水凝结率的计算。群体分裂近似法将增长的液滴群体分为两类：在暴露于大于其临界过饱和度的过饱和度后经历显著增长的液滴群体，以及不会增长得比其临界直径大得多的液滴群体。这里介绍的修改导致的参数化派生的最大过饱和度，smax，和液滴数浓度，Nd，确定通过比较对那些详细的数值模拟的活化过程的准确性和精度的提高。对参数化Nd对输入变量χi的一阶导数Δ Nd/Δ χj进行了数值计算，并与相应的粒子模型导出的灵敏度进行了比较，从而全面评估了参数化能力对气溶胶特性响应的影响。对Nd和smax的参数化计算与活化过程的详细数值模拟进行的评估显示，smax的相对误差为−6.0% ± 6.2%，Nd的相对误差为−2.7% ± 4.8%，这表明与早期版本的参数化相比，预测偏差大大降低。拟议的修改只需要根据人口分类概念对现有守则中的数字执行进行微小的修改。
Abstract. In this work, we postulate, implement and evaluate modifications to the "population-splitting" concept, introduced by Nenes and Seinfeld (2003), for calculation of water-condensation rates in droplet-activation parameterizations. The population-splitting approximation consists of dividing the population of growing droplets into two categories: those that experience significant growth after exposed to a supersaturation larger than their critical supersaturation, and those that do not grow much larger than their critical diameter. The modifications introduced here lead to an improved accuracy and precision of the parameterization-derived maximum supersaturation, smax, and droplet-number concentration, Nd, as determined by comparing against those of detailed numerical simulations of the activation process. A numerical computation of the first-order derivatives ∂ Nd/∂ χj of the parameterized Nd to input variables χi was performed and compared against the corresponding parcel-model-derived sensitivities, providing a thorough evaluation of the impacts of the introduced modifications in the parameterization ability to respond to aerosol characteristics. An evaluation of the parameterization computation of Nd and smax against detailed numerical simulations of the activation process showed a relative error of −6.0% ± 6.2% for smax, and −2.7% ± 4.8% for Nd, which represents a considerable reduction in prediction bias when compared to earlier versions of the parameterization. The proposed modifications require only minor changes for their numerical implementation in existing codes based on the population-splitting concept.