期刊
JOURNAL OF THE ATMOSPHERIC SCIENCES
卷 77, 期 5, 页码 1559-1574出版社
AMER METEOROLOGICAL SOC
DOI: 10.1175/JAS-D-19-0135.1
关键词
Cumulus clouds; Marine boundary layer; Mixed layer; Mass fluxes; transport; Dropsondes; Large eddy simulations
资金
- CNRS
- Sorbonne Universite
- Labex L-IPSL
- CNES
- Ecole Polytechnique
- European Research Council (ERC) project EUREC4A under the European Union's Horizon 2020 research and innovation programme [694768]
This paper develops a method to estimate the shallow-convective mass flux M at the top of the subcloud layer as a residual of the subcloud-layer mass budget. The ability of the mass-budget estimate to reproduce the mass flux diagnosed directly from the cloud-core area fraction and vertical velocity is tested using real-case large-eddy simulations over the tropical Atlantic. We find that M reproduces well the magnitude, diurnal cycle, and day-to-day variability of the core-sampled mass flux, with an average root-mean-square error of less than 30% of the mean. The average M across the four winter days analyzed is 12 mm s(-1), where the entrainment rate E contributes on average 14 mm s(-1) and the large-scale vertical velocity W contributes -2 mm s(-1). We find that day-to-day variations in M are mostly explained by variations in W, whereas E is very similar among the different days analyzed. Instead E exhibits a pronounced diurnal cycle, with a minimum of about 10 mm s(-1) around sunset and a maximum of about 18 mm s(-1) around sunrise. Application of the method to dropsonde data from an airborne field campaign in August 2016 yields the first measurements of the mass flux derived from the mass budget, and supports the result that the variability in M is mostly due to the variability in W. Our analyses thus suggest a strong coupling between the day-to-day variability in shallow convective mixing (as measured by M) and the large-scale circulation (as measured by W). Application of the method to the EUREC(4)A field campaign will help evaluate this coupling, and assess its implications for cloud-base cloudiness.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据