气候变化领域集成服务门户(CCPortal): A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain

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DOI	10.5194/acp-19-747-2019
	A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain
	Graf P.; Wernli H.; Pfahl S.; Sodemann H.
发表日期	2019
ISSN	16807316
起始页码	747
结束页码	765
卷号	19 期号:2
英文摘要	Raindrops interact with water vapour in ambient air while sedimenting from the cloud base to the ground. They constantly exchange water molecules with the environment and, in sub-saturated air, they evaporate partially or entirely. The latter of these below-cloud processes is important for predicting the resulting surface rainfall amount. It also influences the boundary layer profiles of temperature and moisture through evaporative latent cooling and humidity changes. However, despite its importance, it is very difficult to quantify this process from observations. Stable water isotopes provide such information, as they are influenced by both rain evaporation and equilibration (i.e. the exchange of isotopes between raindrops and ambient air). This study elucidates this option by introducing a novel interpretative framework for stable water isotope measurements performed simultaneously at high temporal resolution in both near-surface vapour and rain. We refer to this viewing device as the ΔδΔd-diagram, which shows the isotopic composition (δ2H, d-excess) of equilibrium vapour from precipitation samples relative to the ambient vapour. It is shown that this diagram facilitates the diagnosis of below-cloud processes and their effects on the isotopic composition of vapour and rain since equilibration and evaporation lead to different pathways in the two-dimensional phase space of the ΔδΔd-diagram, as investigated with a series of sensitivity experiments with an idealized below-cloud interaction model. The analysis of isotope measurements for a specific cold front in central Europe shows that below-cloud processes lead to distinct and temporally variable imprints on the isotope signal in surface rain. The influence of evaporation on this signal is particularly strong during periods with a weak precipitation rate. After the frontal passage, the near-surface atmospheric layer is characterized by higher relative humidity, which leads to weaker below-cloud evaporation. Additionally, a lower melting layer after the frontal passage reduces time for exchange between vapour and rain and leads to weaker equilibration. Measurements from four cold frontal events reveal a surprisingly similar slope of Δd/Δδ= -0:30 in the phase space, indicating a potentially characteristic signature of below-cloud processes for this type of rain event. © Author(s) 2019.
语种	英语
scopus关键词	cloud cover; cold front; evaporation; isotopic composition; raindrop; stable isotope; water vapor; Central Europe
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144709
作者单位	Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland; Institute of Meteorology, Freie Universität Berlin, Berlin, Germany; Geophysical Institute, University of Bergen, Bergen, Norway; Bjerknes Centre for Climate Research, Bergen, Norway
推荐引用方式 GB/T 7714	Graf P.,Wernli H.,Pfahl S.,et al. A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain[J],2019,19(2).
APA	Graf P.,Wernli H.,Pfahl S.,&Sodemann H..(2019).A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain.Atmospheric Chemistry and Physics,19(2).
MLA	Graf P.,et al."A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain".Atmospheric Chemistry and Physics 19.2(2019).