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An Observational Comparison of Level of Neutral Buoyancy and Level of Maximum Detrainment in Tropical Deep Convective Clouds
Journal of Geophysical Research: Atmospheres ( IF 3.8 ) Pub Date : 2020-07-30 , DOI: 10.1029/2020jd032637
Dié Wang 1 , Michael P. Jensen 1 , Jennifer A. D'Iorio 2 , Gina Jozef 3 , Scott E. Giangrande 1 , Karen L. Johnson 1 , Zhengzhao Johnny Luo 4 , Mariusz Starzec 5 , Gretchen L. Mullendore 5
Affiliation  

Tropical deep convective clouds are important drivers of large‐scale atmospheric circulation representing the main vertical transport pathway through the depth of the troposphere for heat, momentum, water, and chemical species. The strength and depth of this transport are impacted by the convective updraft size and intensity that are driven by buoyancy, dynamical forcing, and mixing of environmental air, that is, entrainment. In this study, we identify tropical deep convective systems with well‐defined forward anvils using Atmospheric Radiation Measurement (ARM) ground‐based profiling radars, at three ARM fixed sites in the Tropical Western Pacific (TWP; i.e., Manus, Nauru, and Darwin) and three ARM Mobile Facility deployments in Niamey, Niger; Gan Island, Maldives; and Manacapuru, Brazil. We use the difference between the level of neutral buoyancy (LNB) and the level of maximum detrainment (LMD) as a proxy for the effective bulk convective entrainment (ε p r o x y ). The LNB, the theoretical height that a parcel raised above the level of free convection would reach with no mixing, is calculated based on preconvection radiosonde measurements using parcel theory. The LMD is the height of the maximum reflectivity observed in forward anvil clouds by profiling radars. Deep convective systems over the TWP show higher LNBs that extend to 16.3 km on average and larger ε p r o x y (median value of LNB minus LMD up to 6.5 km) compared to their continental counterparts in the Amazon and West Africa. Oceanic conditions show larger convective available potential energy (CAPE) coupled with higher moisture at low levels, which favors larger ε p r o x y . In contrast, continental cases initiate and develop, under high convective inhibition, steeper environmental lapse rate, and high wind shear conditions, which show smaller offset between LNB and LMD. Deep convective cases that promote significant cold pools at the surface experience less ε p r o x y . Using a Random Forest regression algorithm, CAPE is associated with the highest feature importance score for predicting convective ε p r o x y , followed by low‐level relative humidity. For continental cases, the low‐level wind shear also indicates higher importance.

中文翻译:

热带深层对流云中性浮力水平和最大减量水平的观测比较

热带深层对流云是大规模大气环流的重要驱动力,代表了通过对流层深度传热,动量,水和化学物质进入对流层深度的主要垂直传输路径。这种运输的强度和深度受对流上升气流的大小和强度的影响,对流上升气流的大小和强度受浮力,动力强迫和环境空气混合(即夹带)的驱动。在这项研究中,我们使用大气辐射测量(ARM)地基剖面雷达在热带西太平洋(TWP)的三个ARM固定站点(即Manus,Nauru和Darwin)中,使用定义明确的前砧确定热带深对流系统)以及在尼日尔尼亚美的三个ARM Mobile Facility部署;马尔代夫甘岛;和巴西马那卡普鲁。ε p - [R ö X ÿ)。LNB是基于包裹理论的对流探空仪测量值,计算出在不混合的情况下上升到高于自由对流水平的包裹将达到的理论高度。LMD是通过轮廓雷达在前砧云中观察到的最大反射率的高度。在TWP深对流系统显示出更高的LNB延伸到上平均,以及较大的16.3公里ε p - [R ø X ÿ(LNB减去LMD的中值,最长可达6.5公里),与亚马逊和西非的大陆同类相比。海洋条件示出加上在较低水平较高的水分,这有利于较大的较大的对流有效位能(CAPE)ε p - [R ø X ý。相反,在强对流抑制,较陡的环境消失率和高风切变条件下,大陆性案例开始发生并发展,这表明LNB和LMD之间的偏移较小。强对流情况下,在表面少一分促进显著冷池ε p [R Ø X ÿ。使用随机森林回归算法,CAPE与最高特征重要性分数预测对流相关ε p - [R ø X ÿ,接着低级别的相对湿度。对于大陆性案例,低水平的风切变也显示出更高的重要性。
更新日期:2020-08-11
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