A Framework to Study Mixing Processes in the Marine Boundary Layer Using Water Vapor Isotope Measurements

Benetti, Marion; Lacour, Jean‐Lionel; Sveinbjörnsdóttir, Árný E.; Aloisi, Giovanni; Reverdin, Gilles; Risi, Camille; Peters, Andrew J.; Steen‐Larsen, Hans Christian

doi:10.1002/2018gl077167

Cited by 24 publications

(31 citation statements)

References 41 publications

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“…Convective processes in lower parts of the troposphere can explain a substantial part of the variance in climate model estimates of equilibrium climate sensitivity (Bony et al., 2015; Sherwood et al., 2014). In this context, for example, water vapor isotopes were used to constrain mixing between the boundary layer and the lower troposphere (Bailey et al., 2013; Galewsky, 2015; Galewsky & Rabanus, 2016; Benetti et al., 2018; Feng et al., 2019; Risi et al., 2019), or to constrain the humidity of the subtropical troposphere (Galewsky et al., 2007; González et al., 2016; Guilpart et al., 2017; Hurley et al., 2012; Noone, 2012; Noone et al., 2011).…”

Section: Introductionmentioning

confidence: 99%

On the Isotopic Composition of Cold Pools in Radiative‐Convective Equilibrium

Torri

2021

JGR Atmospheres

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Cumulus clouds are a fundamental component of the Earth's climate. They strongly impact the radiation budget, hydrological processes, and transport of heat, momentum, and various chemical species. Uncertainties in our understanding of cumulus clouds and their interactions with the larger scales have important repercussions, for example, in future projections and estimates of climate sensitivity derived from model simulations (e.g., Zhao et al., 2016). Indeed, the representation of cumulus clouds in numerical models remains an outstanding challenge in climate science (Arakawa, 2004;Siebesma et al., 2020).Stable water isotopologues have proved to be important tools to better understand and constrain processes regarding cumulus clouds and, more generally, atmospheric convection (e.g.

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Section: Introductionmentioning

confidence: 99%

On the Isotopic Composition of Cold Pools in Radiative‐Convective Equilibrium

Torri

2021

JGR Atmospheres

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“…This result highlights the importance of convergence in affecting boundary layer vapor isotopic ratios, as it introduces dry, depleted air from aloft into the MBL. Such influence of upper atmosphere air on the boundary layer has been recognized by Benetti et al, (2015Benetti et al, ( , 2018, although for quiescent subsidence regions that our model does not treat. Furthermore, their conceptual treatment is still based on the closure assumption.…”

Section: The δD Vs δ 18 O Relationshipmentioning

confidence: 63%

Comment from the authors regarding Eqn. 16

Feng¹

2018

Preprint

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We develop a one-dimensional (1D) steady state isotope marine boundary layer (MBL) model that includes meteorologically important features missing in Craig and Gordon type models, namely height-dependent diffusion/mixing, lifting to deliver air to the free troposphere, and convergence of subsiding air. Kinetic isotopic fractionation results from this 10 height-dependent diffusion that starts as pure molecular diffusion at the air-water interface and increases with height due to turbulent eddies. Convergence causes mixing of dry, isotopically depleted air with ambient air. Model results fill a quadrilateral in δD-δ 18 O space, of which three boundaries are respectively defined by 1) vapor in equilibrium with various sea surface temperatures (SSTs); 2) mixing of vapor in equilibrium with seawater and vapor in subsiding air; and 3) vapor that has experienced maximum possible kinetic fractionation. Model processes also cause variations in d-excess of MBL 15 vapor. In particular, mixing of relatively high d-excess descending/converging air into the MBL increases d-excess, even without kinetic isotope fractionation. The model is tested by comparison with seven datasets of marine vapor isotopic ratios, with excellent correspondence. About 95% of observational data fall within the quadrilateral predicted by the model. The distribution of observations also highlights the significant influence of vapor from nearby converging descending air on isotopic variations within the MBL. At least three factors may explain the ~5% of observations that fall slightly outside of 20 the predicted regions in δD-δ 18 O and d-excess-δ 18 O space: 1) variations in seawater isotopic ratios, 2) variations in isotopic composition of subsiding air, and 3) influence of sea spray. Sound interpretation of isotopic data requires a thorough understanding of all processes in the hydrological cycle that affect isotopic variations. These include 1) surface evaporation and processes in the planetary boundary layer (PBL) through which vapor reaches the overlying free atmosphere; 2) rainout and other processes along the trajectory of air masses transported to a precipitation site; 3) nucleation, growth, coalescence, and reevaporation of hydrometeors between the moisture source area and the precipitation site; and 4) subsequent processes affecting precipitation as it falls through the air. This study focuses on 5 the first of these-surface evaporation and isotopologue concentrations within and fluxes through the PBL-in particular, the marine boundary layer (MBL), where ascending air delivers water vapor to the free atmosphere. The PBL and the MBL have a variety of qualitative and quantitative definitions, not all consistent. In this discussion, we use the phrase "Boundary Layer" to refer to the lower part of the planetary or marine atmosphere, in which the flux of water vapor is close to vertical and vapor transport is accomplished primarily by turbulent or convective mixing. Above the MBL, 10 the troposphere is often referred to as the "free atmosphere" or...

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“…Our interpretation of the d-excess VPs could be further evaluated by isotope-enabled circulation and weather models (Aemisegger et al, 2015;Pfahl et al, 2012;Schmidt et al, 2005). However, the simulation of convective BL processes with isotope-enabled models is complex (Benetti et al, 2018). The measurements reported here could help further develop current Atmos.…”

Section: Discussionmentioning

confidence: 92%

Vertical profile observations of water vapor deuterium excess in the lower troposphere

Salmon¹,

Welp²,

Baldwin³

et al. 2019

Preprint

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We use H 2 O v isotopic vertical profile measurements and complementary meteorological observations to examine how boundary layer, cloud, and mixing processes influence the vertical structure of deuterium-excess (d-excess = δD -8×δ 18 O) in the 15 boundary layer, inversion layer, and lower free troposphere. Airborne measurements of water vapor (H 2 O v ) stable isotopologues were conducted around two continental U.S. cities in February -March 2016. Nine research flights were designed to characterize the δD, δ 18 O, and d-excess vertical profiles extending from the surface to ≤2 km. We examine observations from three unique case study flights in detail. One case study shows H 2 O v isotopologue vertical profiles that are consistent with Rayleigh isotopic distillation theory coinciding with clear skies, dry adiabatic lapse rates within the boundary layer, and 20 relatively constant vertical profiles of wind speed and wind direction. The two remaining case studies show that H 2 O v isotopic signatures above the boundary layer are sensitive to cloud processes and complex air mass mixing patterns. These two case studies indicate anomalies in the d-excess signature relative to Rayleigh theory, such as low d-excess values at the interface of the inversion layer and the free troposphere, which is possibly indicative of cloud evaporation. We discuss possible explanations for the observed d-excess anomalies, such as cloud evaporation, wind shear, and vertical mixing. In situ H 2 O v stable isotope 25 measurements, and d-excess in particular, could be useful for improving our understanding of moisture processing and transport mixing occurring between the boundary layer, inversion layer, and free troposphere.

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A Framework to Study Mixing Processes in the Marine Boundary Layer Using Water Vapor Isotope Measurements

Cited by 24 publications

References 41 publications

On the Isotopic Composition of Cold Pools in Radiative‐Convective Equilibrium

On the Isotopic Composition of Cold Pools in Radiative‐Convective Equilibrium

Comment from the authors regarding Eqn. 16

Vertical profile observations of water vapor deuterium excess in the lower troposphere

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