An evaluation of size-resolved cloud microphysics scheme numerics for use with radar observations Part II: Condensation and evaporation
An evaluation of size-resolved cloud microphysics scheme numerics for use with radar observations Part II: Condensation and evaporation
复制标题
用于雷达观测的尺寸分辨云微物理方案数值评估第二部分：凝结和蒸发
DOI：
10.1175/jas-d-20-0213.1
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发表时间：
2021
影响因子：
3.1
通讯作者：
A. Ackerman
中科院分区：
文献类型：
--
作者：
Hyunho Lee;A. Fridlind;A. Ackerman
云和降水的精确数值模拟对天气预报和气候变化研究至关重要。虽然尺寸分辨（bin）云微物理模型预测颗粒尺寸分布而不影响形状，但由于与各种过程相关的数值扩散，结果受到人为尺寸分布扩大的影响。虽然第1部分讨论了碰撞-聚结，但这里我们研究了在解决冷凝和蒸发时发生的数值扩散。在包层模式框架下，随着质量网格的细化，所研究的所有数值方案都收敛于一个凝结和蒸发的解，并且基于平流的方案比重新分配方案更值得推荐。在列中加入欧拉垂直平流在一定程度上限制了收敛性，但这种限制发生在足够细的质量网格上，求解垂直平流的迭代次数应尽量减少，以减少数值扩散。如果碰撞-聚并也很活跃，那么在求解凝结过程中的非实质性数值扩散就会被放大，而如果考虑到湍流对碰撞的影响，这种扩散又会被大大减弱。毛毛雨层积云场的大涡模拟表明，采用不同质量网格得到的多普勒谱矩变化与简化框架得到的谱矩变化一致，采用有效减小数值扩散的质量网格得到的谱矩通常更接近观测值。模拟和观测之间的显著差异仍然存在，我们的结果表明，需要考虑所采用的基本过程方案中数值扩散以外的因素是否会导致这种差异。
Accurate numerical modeling of clouds and precipitation is essential for weather forecasting and climate change research. While size-resolved (bin) cloud microphysics models predict particle size distributions without imposing shapes, results are subject to artificial size distribution broadening owing to numerical diffusion associated with various processes. Whereas Part 1 addressed collision-coalescence, here we investigate numerical diffusion that occurs in solving condensation and evaporation. In a parcel model framework, all of the numerical schemes examined converge to one solution of condensation and evaporation as the mass grid is refined, and the advection-based schemes are recommended over the reassigning schemes. Including Eulerian vertical advection in a column limits the convergence to some extent, but that limitation occurs at a sufficiently fine mass grid, and the number of iterations in solving vertical advection should be minimized to reduce numerical diffusion. Insubstantial numerical diffusion in solving condensation can be amplified if collision-coalescence is also active, which in turn can be substantially diminished if turbulence effects on collision are incorporated. Large-eddy simulations of a drizzling stratocumulus field reveal that changes in moments of Doppler spectra obtained using different mass grids are consistent with those obtained from the simplified framework, and that spectral moments obtained using a mass grid designed to effectively reduce numerical diffusion are generally closer to observations. Notable differences between the simulations and observations still exist, and our results suggest a need to consider whether factors other than numerical diffusion in the fundamental process schemes employed can cause such differences.