A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain

Graf, Pascal; Wernli, Heini; Sodemann, Harald

doi:10.5194/acp-2018-482

Cited by 25 publications

(51 citation statements)

References 20 publications

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“…For example, precipitation from high d vapor, from continental recycling or rapid evaporation from the ocean that experiences subcloud evaporation may not exhibit very low d , whereas low d vapor, such as vapor from a humid, cool oceanic boundary layer may exhibit less subcloud evaporation but produce the same d . However, the range of seasonal average d observed in our data set matches the range of d from three studies (Chen et al, ; Graf et al, ; Wang et al, ) that measured precipitation isotope ratios and modeled a strong contribution of subcloud evaporation to the observed d .…”

Section: Resultssupporting

confidence: 87%

A Global Perspective on Local Meteoric Water Lines: Meta‐analytic Insight Into Fundamental Controls and Practical Constraints

Putman

Fiorella

Bowen

et al. 2019

Water Resources Research

141

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Local meteoric water lines (LMWLs) represent the site‐specific long‐term covariation of hydrogen and oxygen stable isotope ratios. LMWLs have practical utility as a hydrologic framework and as benchmarks for evaluating hydroclimatic processes in isotope‐enabled climate models. In this manuscript, we characterize the global distribution of LMWLs and compare them to LMWLs from model data. To evaluate the sensitivity of the covariance of stable isotope ratios to data set length, we paired time series rarifaction with Bayesian ellipse estimation. We then applied a threshold of 48 months and estimated LMWLs at 398 sites in 25 Köppen climate classes using orthogonal distance regression. Slopes ranged from 4.8 to 10.9, with an average of 7.64 ± 0.64. Intercepts ranged from −24‰ to 27‰, with an average of 6.85 ± 6.2‰. We identified three processes: (1) subcloud evaporation of rain, (2) atmospheric remoistening by rainfall evaporation, and (3) conditions of snow formation as important controls on slopes and intercepts in arid, humid, and seasonally snowy regions, respectively. We compared observational LMWLs with those from a suite of isotope‐enabled climate models. At arid and snowy sites, model data produced higher slopes and intercepts than observational data. At humid sites, model data exhibited dampened variability in slopes and intercepts relative to observational data. These results indicate potential for improvement in the precipitation and/or isotope parameterizations of raindrop evaporation, advection of reevaporated water, evapotranspiration fractionation, and supersaturation in mixed‐phase clouds. This meta‐analysis demonstrates LMWLs utility for identifying specific hydroclimatic and isotopic processes in observations and models.

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Section: Resultssupporting

confidence: 87%

A Global Perspective on Local Meteoric Water Lines: Meta‐analytic Insight Into Fundamental Controls and Practical Constraints

Putman

Fiorella

Bowen

et al. 2019

Water Resources Research

141

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“…Data availability. All observation data presented in this study are openly available from the ETH Research Collection at https://doi.org/10.3929/ethz-b-000271617 (Graf et al, 2018). P. Graf et al: Below-cloud effects on stable water isotopes been implemented: Growth by vapour deposition in mixedphase or ice clouds, and riming of liquid cloud droplets on frozen particles.…”

Section: Discussionmentioning

confidence: 99%

A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain

et al. 2019

Self Cite

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Abstract. 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 ΔdΔδ=-0.30 in the phase space, indicating a potentially characteristic signature of below-cloud processes for this type of rain event.

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“…These variations integrate all processes along air mass trajectories (Figure 4, blue dashed square). The third term (Figure 4, magenta dashed square) represents a combination of precipitation‐vapor disequilibrium effects (due to variations in condensation altitude or postcondensation processes such as rain evaporation), variations in the vertical gradients between the surface (where the precipitation achieves its last equilibration, e.g., Graf et al, 2019) and 5 km (where the water vapor δ 2 H is observed by IASI) and small‐scale variations in water vapor δ 2 H (leading to difference between the water vapor δ 2 H observed by IASI and that with which the precipitation locally equilibrates).…”

Section: Methodsmentioning

confidence: 99%

Variability of Isotope Composition of Precipitation in the Southeastern Tibetan Plateau from the Synoptic to Seasonal Time Scale

Shi

Risi

et al. 2020

JGR Atmospheres

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Daily precipitation samples were collected at four sites in Mount Yulong and Mount Meili regions of southeastern Tibetan Plateau and analyzed for isotopic composition. Combined with water vapor isotopic composition derived from satellites data (Infrared Atmospheric Sounding Interferometer, Tropospheric Emission Spectrometer, and Greenhouse gases Observing Satellite), the factors controlling the variability in the isotopic composition of precipitation are investigated at the synoptic, intraseasonal, and seasonal time scales. At the seasonal scale, the isotope composition in precipitation is controlled by processes along air mass trajectories affecting the water vapor at the large scale (>200 km), especially upstream deep convection and air mass origin, and by local processes transforming the large‐scale water vapor isotopic composition into the precipitation composition, especially rain evaporation and local circulation. At the intraseasonal and synoptic scales, the isotope composition in precipitation is mainly controlled by these local processes. The shorter the time scale of isotopic variations, the smaller the spatial imprint of these variations. The fact that different factors control the isotopic variability at different time scales calls for caution when applying relationships observed at these time scales to interpret isotopic variations at paleoclimatic time scales. While general circulation models successfully capture the isotopic variability and its controlling factors at the seasonal scale, it fails to simulate them at shorter time scales, because it fails to simulate the local processes.

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A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain

Cited by 25 publications

References 20 publications

A Global Perspective on Local Meteoric Water Lines: Meta‐analytic Insight Into Fundamental Controls and Practical Constraints

A Global Perspective on Local Meteoric Water Lines: Meta‐analytic Insight Into Fundamental Controls and Practical Constraints

A new interpretative framework for below-cloud effects on stable water isotopes in vapour and rain

Variability of Isotope Composition of Precipitation in the Southeastern Tibetan Plateau from the Synoptic to Seasonal Time Scale

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