Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06
Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06
复制标题
对 VOCALS-REx RF06 中观察到的开孔周围的中尺度动力学和夹带的大涡模拟
DOI：
10.5194/acp-11-10525-2011
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发表时间：
2011
影响因子：
6.3
通讯作者：
R. Wood
中科院分区：
文献类型：
--
作者：
A. Berner;C. Bretherton;R. Wood
抽象的。基于VOCALS区域实验（雷克斯）NSF C-130研究飞行06的大涡模拟的一个口袋的开孔（POC）进行了分析和比较飞机的观察。在覆盖反演附近采用192 km × 24 km的双周期区域，水平网格间距为125 m，垂直网格间距为5 m。POC实现在模型中作为一个固定的96公里宽的区域减少云滴数浓度（N C）的基础上观测值;初始化和强迫是统一的，否则整个域。该模型再现飞机观测到的差异边界层结构和降水组织之间的混合良好的阴天区域和一个解耦的POC与开孔沉淀积云，虽然模拟的云量是太大的POC。一项灵敏度研究，其中N c被允许平流湍流后，给出了几乎相同的结果超过16小时的模拟长度（从晚上开始，到第二天下午）。模拟的卷吸率几乎是一个因素的两个小的湍流POC比在更多的湍流阴天区。然而，反转上升在整个域几乎均匀的速率，因为强大的浮力恢复力抵消水平反转高度梯度。二次环流发展的模式，转移下沉的自由对流层空气远离POC到周围的阴天区域，抵消较弱的夹带在POC与当地较弱的沉降。
Abstract. Large-eddy simulations of a pocket of open cells (POC) based on VOCALS Regional Experiment (REx) NSF C-130 Research Flight 06 are analyzed and compared with aircraft observations. A doubly-periodic domain 192 km × 24 km with 125 m horizontal and 5 m vertical grid spacing near the capping inversion is used. The POC is realized in the model as a fixed 96 km wide region of reduced cloud droplet number concentration ( N c ) based on observed values; initialization and forcing are otherwise uniform across the domain. The model reproduces aircraft-observed differences in boundary-layer structure and precipitation organization between a well-mixed overcast region and a decoupled POC with open-cell precipitating cumuli, although the simulated cloud cover is too large in the POC. A sensitivity study in which N c is allowed to advect following the turbulent flow gives nearly identical results over the 16 h length of the simulation (which starts at night and goes into the next afternoon). The simulated entrainment rate is nearly a factor of two smaller in the less turbulent POC than in the more turbulent overcast region. However, the inversion rises at a nearly uniform rate across the domain because powerful buoyancy restoring forces counteract horizontal inversion height gradients. A secondary circulation develops in the model that diverts subsiding free-tropospheric air away from the POC into the surrounding overcast region, counterbalancing the weaker entrainment in the POC with locally weaker subsidence.