The Sensitivity of Convective Initiation to the Lapse Rate of the Active Cloud-Bearing Layer
The Sensitivity of Convective Initiation to the Lapse Rate of the Active Cloud-Bearing Layer
复制标题
对流起始对活动含云层消逝率的敏感性
DOI：
10.1175/mwr3449.1
复制
发表时间：
2006
影响因子：
3.2
通讯作者：
D. Niyogi
中科院分区：
文献类型：
--
作者：
A. Houston;D. Niyogi
使用理想化的云解析模型进行数值实验，以探索深对流起始（DCI）对活动云层递减率的敏感性[ACBL；自由对流水平以上的大气层（LFC）]。云是使用一种新技术启动的，该技术涉及初始化预先存在的气团边界，使得模型状态变量对施加的边界的（不切实际的）调整与对流模拟分离。实验套件中使用的参考状态环境具有相同的对流抑制、CAPE 和 LFC 混合层值以及相同的相对湿度和风分布。在为实验集进行的六次模拟中，只有具有最大 ACBL 失效率的三个环境支持 DCI。尽管存在基于表面的边界，模拟的深层对流还是从高处源头（对流云中的部分起源于 1300 m 附近）发起的。研究发现，在 ACBL 递减率较大的实验中，热不稳定释放的可能性更大，因为先前存在的边界处的强制上升更强（尽管边界深度几乎相同），而且无论地块稀释程度如何，地块的 LFC 都较低。在一项没有深度对流的实验中，即使释放了热不稳定性，也会发生 DCI 故障。该实验的结果以及启发式拉格朗日模型的结果揭示了依赖于环境递减率的两种对流状态的存在：能够支持 DCI 的超临界状态和不太可能支持 DCI 的亚临界状态。在超临界条件下，由于包裹上升而导致的浮力增加率超过了由于稀释而导致的浮力减少率。在亚临界条件下，由于包裹上升而导致的浮力增加率超过了由于稀释而导致的浮力减少率。总体而言，结果表明 ACBL 的失效率对于诊断和/或预测 DCI 很有用。
Numerical experiments are conducted using an idealized cloud-resolving model to explore the sensitivity of deep convective initiation (DCI) to the lapse rate of the active cloud-bearing layer [ACBL; the atmospheric layer above the level of free convection (LFC)]. Clouds are initiated using a new technique that involves a preexisting airmass boundary initialized such that the (unrealistic) adjustment of the model state variables to the imposed boundary is disassociated from the simulation of convection. Reference state environments used in the experiment suite have identical mixed layer values of convective inhibition, CAPE, and LFC as well as identical profiles of relative humidity and wind. Of the six simulations conducted for the experiment set, only the three environments with the largest ACBL lapse rates support DCI. The simulated deep convection is initiated from elevated sources (parcels in the convective clouds originate near 1300 m) despite the presence of a surface-based boundary. Thermal instability release is found to be more likely in the experiments with larger ACBL lapse rates because the forced ascent at the preexisting boundary is stronger (despite nearly identical boundary depths) and because the parcels’ LFCs are lower, irrespective of parcel dilution. In one experiment without deep convection, DCI failure occurs even though thermal instability is released. Results from this experiment along with the results from a heuristic Lagrangian model reveal the existence of two convective regimes dependent on the environmental lapse rate: a supercritical state capable of supporting DCI and a subcritical state that is unlikely to support DCI. Under supercritical conditions the rate of increase in buoyancy due to parcel ascent exceeds the reduction in buoyancy due to dilution. Under subcritical conditions, the rate of increase in buoyancy due to parcel ascent is outpaced by the rate of reduction in buoyancy from dilution. Overall, results demonstrate that the lapse rate of the ACBL is useful in diagnosing and/or predicting DCI.