Where is the level of neutral buoyancy for deep convection?
Where is the level of neutral buoyancy for deep convection?
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DOI：
10.1029/2012gl052638
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发表时间：
2012-08
影响因子：
5.2
通讯作者：
Hanii Takahashi;Z. Luo
中科院分区：
文献类型：
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作者：
Hanii Takahashi;Z. Luo
这项研究重新审视了气象学中的一个旧概念-中性浮力水平（LNB）。LNB的经典定义来自于包裹理论，可以通过环境探测（LNB_sounding）来估计，而无需观察任何实际的对流云发展。然而，在现实中，对流以复杂的方式与环境相互作用;它最终将设法找到自己有效的LNB，并通过解除训练群众和发展铁砧（LNB_observation）来体现它。本文利用CloudSat卫星资料对热带深对流的LNB_观测进行了近全球调查，并与相应的LNB_探测进行了比较。主要发现如下：第一，尽管LNB_sounding提供了对流发展的合理上限，但LNB_sounding和LNB_观测之间的相关性很低，表明环境探测包含的用于准确预测实际LNB的信息有限。第二，最大质量外流位于LNB_测深线以下3 km以上。因此，从对流输送的角度来看，LNB_sounding是一个显着高估的“目的地”的高度水平的疏散质量。第三，LNB_观测在陆地上始终高于海洋，尽管LNB_探测在陆地和海洋之间是相似的。这种差异可能与陆地和海洋之间对流强度和环境的差异有关。最后，我们估计了与观测到的深对流相关的体积卷吸率，这可以作为调整GCM积云参数化的观测基础。
This study revisits an old concept in meteorology ‐ level of neutral buoyancy (LNB). The classic definition of LNB is derived from the parcel theory and can be estimated from the ambient sounding (LNB_sounding) without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually manage to find its own effective LNB and manifests it through detraining masses and developing anvils (LNB_observation). This study conducts a near‐global survey of LNB_observation for tropical deep convection using CloudSat data and makes comparison with the corresponding LNB_sounding. The principal findings are as follows: First, although LNB_sounding provides a reasonable upper bound for convective development, correlation between LNB_sounding and LNB_observation is low suggesting that ambient sounding contains limited information for accurately predicting the actual LNB. Second, maximum mass outflow is located more than 3 km lower than LNB_sounding. Hence, from convective transport perspective, LNB_sounding is a significant overestimate of the “destination” height level of the detrained mass. Third, LNB_observation is consistently higher over land than over ocean, although LNB_sounding is similar between land and ocean. This difference is likely related to the contrasts in convective strength and environment between land and ocean. Finally, we estimate the bulk entrainment rates associated with the observed deep convection, which can serve as an observational basis for adjusting GCM cumulus parameterization.