scholarly journals Stable water isotopes as a tool to investigate tropospheric moisture transport pathways over the eastern subtropical North Atlantic

2020 ◽  
Author(s):  
Fabienne Dahinden ◽  
Franziska Aemisegger ◽  
Sabine Barthlott ◽  
Emanuel Christner ◽  
Christoph Dyroff ◽  
...  
Keyword(s):  
North Atlantic ◽  
Moisture Transport ◽  
Water Cycle ◽  
Phase Changes ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Physical Processes ◽  
Air Masses ◽  
Saharan Air Layer ◽  
Sahel Region

<div> <div> <div> <p>The subtropical atmospheric water cycle is a key component in the climate system. Free-tropospheric humidity and low-level cloud cover over the subtropical oceans strongly affect the global radiative balance via the greenhouse and albedo effects. However, the complex interaction of dynamical processes controlling the subtropical tropospheric moisture budget is still not fully understood. Stable water isotopes have proven to be highly useful to investigate the physical mechanisms involved in the atmospheric water cycle. These natural tracers of water phase changes capture the moist diabatic history experienced by air parcels. Additionally, due to the distinct fingerprints of air masses with different origin, the isotopic composition of water vapor can further provide information about atmospheric processes that do not involve phase changes, for instance, turbulent mixing or large-scale water vapor transport. To enhance the understanding of the mechanisms controlling the subtropical tropospheric humidity, we performed dedicated high-resolution simulations with the isotope-enabled regional weather and climate prediction model COSMOiso. Comparison with ground-based remote sensing (Fourier transform infrared spectroscopy) and aircraft-based in situ isotope observations from the project MUSICA enables us to evaluate and constrain the representation of relevant physical processes in the model.</p> <p>Our simulations confirm the current state of knowledge about the contrasting moisture transport conditions over the eastern subtropical North Atlantic, resulting from an interplay between humid, isotopically enriched air primarily coming from Africa on the one hand and dry, depleted air mainly originating from the upper-level extratropical North Atlantic on the other hand. Additionally, we show that North African air masses that are affected by the Saharan heat low (SHL) and air masses which come from the Sahel region further south are associated with a distinct isotope signature. This difference is mainly due to the fact that air masses from the Sahel region have experienced moist convection and cloud processing, whereas the Saharan air layer is a well-mixed air mass with a more homogenous isotope composition. We systematically assess the dynamical drivers behind these contrasting conditions. In particular, we investigate the importance of the SHL dynamics on moistening the free troposphere over the eastern subtropical North Atlantic. In summer, the SHL induces low-level convergence of air masses from different sources, which are then convectively lifted to higher altitudes and are eventually transported within the Saharan air layer across the North Atlantic, where they mix with dry, descending free tropospheric air. Detailed analysis of isotopic signals along kinematic back- trajectories of different air masses arriving over the Canary Islands allows to disentangle governing physical processes and relevant moisture sources that affect the free tropospheric humidity. The adopted Lagrangian isotope perspective notably enhances our understanding of air mass mixing and offers a sound interpretation of the free tropospheric humidity and isotopic variability on time scales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic.</p> </div> </div> </div>

Linking Lagrangian model simulations with stable water isotope measurements in Arctic weather systems.

2021 ◽  
Author(s):  
Aina Johannessen ◽  
Alena Dekhtyareva ◽  
Andrew Seidl ◽  
Harald Sodemann
Keyword(s):  
Water Cycle ◽  
Lagrangian Model ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Atmospheric Water ◽  
Model Simulations ◽  
Evaporation Source ◽  
Isotope Measurements ◽  
Water Isotope ◽  
Eulerian Models

<p>Transport of water from an evaporation source towards a precipitation sink is the essence of the atmospheric water cycle. However, there are significant challenges with the representation of the atmospheric water cycle in models. For example, incomplete representation of sub-grid scale processes like evaporation, mixing or precipitation can lead to substantial model errors. Here we investigate the combined use of Lagrangian and Eulerian models and in-situ observations of stable water isotopes to reduce such sources of model error. The atmospheric water cycle in the Nordic Seas during cold air outbreaks (CAOs) is confined to a limited area, and thus may be used as a natural laboratory for hydrometeorological studies. We apply Lagrangian and Eulerian models together with observations taken during the ISLAS2020 field campaign in the Arctic in spring 2020 for characterising source-sink relationships in the water cycle. During the field campaign, we observed an alternating sequence of cold air outbreaks (CAO) and warm air intrusions (WAI) over the key measurement sites of Svalbard and northern Norway. Thereby, meteorological and stable water isotope measurements have been performed at multiple sites both upstream and downstream of the CAOs and WAIs. The Lagrangian model FLEXPART has been run with the input data from the regional convection-permitting numerical weather prediction model AROME Arctic at 2.5 km resolution to investigate transport patterns. The combination of observations and model simulations allows us to quantify the connection between source and sink for different weather systems, as well as the link between large-scale transport and stable water isotopes. Findings will lead to a better understanding of processes in the water cycle and the degree of conservation of isotopic signals during transport. This study may also serve as a guideline on how to evaluate the performance of Lagrangian transport models using stable water isotope measurements, and on how to detect constraints for quantifying the transport route and evaporation source from stable water isotope measurements for future work, including an aircraft campaign planned in 2021.</p>

scholarly journals Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

2016 ◽  
Vol 20 (9) ◽  
pp. 3873-3894 ◽  
Author(s):  
Natalie Orlowski ◽  
Philipp Kraft ◽  
Jakob Pferdmenges ◽  
Lutz Breuer
Keyword(s):  
Land Use ◽  
Soil Water ◽  
Hydrological Model ◽  
Water Cycle ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Age Dynamics ◽  
Isotopic Signatures ◽  
Spatially Distributed ◽  
Water Isotope

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

scholarly journals Exploring water cycle dynamics through sampling multitude stable water isotope pools in a small developed landscape of Germany

2015 ◽  
Vol 12 (2) ◽  
pp. 1809-1853 ◽  
Author(s):  
N. Orlowski ◽  
P. Kraft ◽  
L. Breuer
Keyword(s):  
Land Use ◽  
Soil Water ◽  
Agricultural Land ◽  
Water Cycle ◽  
Mean Transit Time ◽  
Arable Land ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Isotopic Signatures ◽  
Water Isotope

Abstract. Conducting a dual stable water isotope (δ2H and δ18O) study in the developed landscape of the Schwingbach catchment (Germany) helped to unravel connectivity and disconnectivity between the different water cycle components. The two-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are decoupled from the annual precipitation cycle but showed bidirectional interactions between each other. Seasonal variations based on temperature effects were observed in the precipitation signal but neither reflected in stream nor in groundwater isotopic signatures. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ-values. A spatially distributed snapshot sampling of soil water isotopes in two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that top soil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils explaining the isotopic similarities between top and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence smoothed out with depth and soil water approached groundwater δ-values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depth > 0.9 m and constant values were observed through space and time. Little variation in individual isotope time series of stream and groundwater restricted the use of classical isotope hydrology techniques e.g. mean transit time estimation or hydrograph separation. Still, tracing stable water isotopes through the water cycle was valuable for determining interactions between different water cycle components and gaining catchment specific process understanding in a developed, human-impacted landscape.

scholarly journals Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

2021 ◽  
Vol 21 (21) ◽  
pp. 16319-16347
Author(s):  
Fabienne Dahinden ◽  
Franziska Aemisegger ◽  
Heini Wernli ◽  
Matthias Schneider ◽  
Christopher J. Diekmann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Isotopic Composition ◽  
Canary Islands ◽  
North Atlantic ◽  
Moisture Transport ◽  
Specific Humidity ◽  
Free Troposphere ◽  
Physical Processes ◽  
Transport Pathways

Abstract. Due to its dryness, the subtropical free troposphere plays a critical role in the radiative balance of the Earth's climate system. But the complex interactions of the dynamical and physical processes controlling the variability in the moisture budget of this sensitive region of the subtropical atmosphere are still not fully understood. Stable water isotopes can provide important information about several of the latter processes, namely subsidence drying, turbulent mixing, and dry and moist convective moistening. In this study, we use high-resolution simulations of the isotope-enabled version of the regional weather and climate prediction model of the Consortium for Small-Scale Modelling (COSMOiso) to investigate predominant moisture transport pathways in the Canary Islands region in the eastern subtropical North Atlantic. Comparison of the simulated isotope signals with multi-platform isotope observations (aircraft, ground- and space-based remote sensing) from a field campaign in summer 2013 shows that COSMOiso can reproduce the observed variability of stable water vapour isotopes on timescales of hours to days, thus allowing us to study the mechanisms that control the subtropical free-tropospheric humidity. Changes in isotopic signals along backward trajectories from the Canary Islands region reveal the physical processes behind the synoptic-scale isotope variability. We identify four predominant moisture transport pathways of mid-tropospheric air, each with distinct isotopic signatures: air parcels originating from the convective boundary layer of the Saharan heat low (SHL) – these are characterised by a homogeneous isotopic composition with a particularly high δD (median mid-tropospheric δD=-122‰), which results from dry convective mixing of low-level moisture of diverse origin advected into the SHL; air parcels originating from the free troposphere above the SHL – although experiencing the largest changes in humidity and δD during their subsidence over West Africa, these air parcels typically have lower δD values (median δD=-148‰) than air parcels originating from the boundary layer of the SHL; air parcels originating from outside the SHL region, typically descending from tropical upper levels south of the SHL, which are often affected by moist convective injections from mesoscale convective systems in the Sahel – their isotopic composition is much less enriched in heavy isotopes (median δD=-175‰) than those from the SHL region; air parcels subsiding from the upper-level extratropical North Atlantic – this pathway leads to the driest and most depleted conditions (median δD=-255‰) in the middle troposphere near the Canary Islands. The alternation of these transport pathways explains the observed high variability in humidity and δD on synoptic timescales to a large degree. We further show that the four different transport pathways are related to specific large-scale flow conditions. In particular, distinct differences in the location of the North African mid-level anticyclone and of extratropical Rossby wave patterns occur between the four transport pathways. Overall, this study demonstrates that the adopted Lagrangian isotope perspective enhances our understanding of air mass transport and mixing and offers a sound interpretation of the free-tropospheric variability of specific humidity and isotope composition on timescales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic.

scholarly journals Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

2021 ◽  
Author(s):  
Fabienne Dahinden ◽  
Franziska Aemisegger ◽  
Heini Wernli ◽  
Matthias Schneider ◽  
Christopher J. Diekmann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Isotopic Composition ◽  
Time Scales ◽  
Canary Islands ◽  
North Atlantic ◽  
Moisture Transport ◽  
Free Troposphere ◽  
Physical Processes ◽  
Transport Pathways

Abstract. Due to its dryness, the subtropical free troposphere plays a critical role in the radiative balance of the Earth’s climate system. But the complex interactions of the dynamical and physical processes controlling the variability in the moisture budget of this sensitive region of the subtropical atmosphere are still not fully understood. Stable water isotopes can provide important information about several of the latter processes, namely subsidence drying, turbulent mixing, dry and moist convective moistening. In this study, we use high-resolution simulations of the isotope-enabled version of the regional weather and climate prediction model of the Consortium for Small-Scale Modelling (COSMOiso) to investigate predominant moisture transport pathways in the Canary Islands region in the eastern subtropical North Atlantic. Comparison of the simulated isotope signals with multi-platform isotope observations (aircraft-based in situ measurements, ground-based and space-based remote sensing observations) from a field campaign in summer 2013 shows that COSMOiso can reproduce the observed variability of stable water vapour isotopes on time scales of hours to days, and thus allows studying the mechanisms that control the subtropical free-tropospheric humidity. Changes of isotopic signals along backward trajectories from the Canary Islands region reveal the physical processes behind the short-term isotope variability. We identify four predominant moisture transport pathways of mid-tropospheric air, each with distinct isotopic signatures: (1) Air parcels originating from the convective boundary layer of the Saharan heat low (SHL). These are characterised by a homogenous isotopic composition with a particularly high δD (median mid-tropospheric δD = −122 ‰), which results from dry convective mixing of low-level moisture of diverse origin advected into the SHL. (2) Air parcels originating from the free troposphere above the SHL. Although experiencing the largest changes in humidity and δD during their subsidence over West Africa, these air parcels typically have lower δD values (median δD = −148 ‰) than air parcels originating from the boundary layer of the SHL. (3) Air parcels originating from outside the SHL region, typically descending from tropical upper levels south of the SHL, which are often affected by moist convective injections from mesoscale convective systems in the Sahel. Their isotopic composition is much less enriched in heavy isotopes (median δD = −175 ‰) than those from the SHL region. (4) Air parcels subsiding from the upper-level extratropical North Atlantic. This pathway leads to the driest and most depleted conditions (median δD = −255 ‰) in the middle troposphere near the Canary Islands. The alternation of these transport pathways explains to a large degree the observed high variability in humidity and δD on synoptic time scales. We further show that the four different transport pathways are related to specific large scale-flow conditions. In particular, distinct differences in the location of the North African mid-level anticyclone and of extratropical Rossby wave patterns occur between the four transport pathways. Overall, this study demonstrates that the adopted Lagrangian isotope perspective enhances our understanding of air mass transport and mixing and offers a sound interpretation of the free-tropospheric variability of specific humidity and isotope composition on time scales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic.

Air Moisture Climatology and Related Physical Processes in the Antarctic on the Basis of ERA5 Reanalysis

2021 ◽  
Vol 34 (11) ◽  
pp. 4463-4480
Author(s):  
Tuomas Naakka ◽  
Tiina Nygård ◽  
Timo Vihma
Keyword(s):  
Relative Humidity ◽  
Moisture Transport ◽  
Inversion Layer ◽  
Specific Humidity ◽  
Physical Processes ◽  
Air Masses ◽  
Dry Air ◽  
Open Sea ◽  
Moisture Conditions ◽  
The Antarctic

AbstractAtmospheric moisture is a key component in the water cycle and radiative transfer. In this study, a comprehensive picture of air moisture climatology and related physical processes is presented for the first time for the circumpolar area south of 50°S. The results are based on the most modern global reanalysis, ERA5, which manages reasonably well to close the Antarctic water budget. We show that over the ocean transient cyclones have the dominant role in determining moisture conditions, whereas over the continent the moisture conditions are largely affected by the mean circulation. Over the open sea, moisture transport from lower latitudes is an equally important source of moisture compared to the local evaporation, but practically all precipitating moisture over the plateau is provided by the horizontal transport. Over the ocean and continental slopes, southward moisture transport brings warm and moist air masses from lower latitudes, notably increasing atmospheric water vapor and cloud water, and simultaneously decreasing local evaporation over the open sea. On the Antarctic plateau, radiative cooling leads to high relative humidity and causes condensation of moisture especially near the surface, causing a nearly permanent specific humidity inversion layer. As a consequence, dry air masses with extremely low specific humidity are formed. These dry air masses are transported downward from the plateau by katabatic winds, experiencing adiabatic warming. This leads to a decrease in relative humidity and to a downward-directed sensible heat flux, which enable efficient surface evaporation on the coastal slopes and farther over coastal polynyas and leads.

scholarly journals Moisture Sources for Tropical Cyclones Genesis in the Coast of West Africa through a Lagrangian Approach

2020 ◽  
Vol 4 (1) ◽  
pp. 3
Author(s):  
Albenis Pérez-Alarcón ◽  
Rogert Sorí ◽  
José Carlos Fernández-Alvarez ◽  
Raquel Nieto ◽  
Luis Gimeno
Keyword(s):  
West Africa ◽  
Atlantic Ocean ◽  
Tropical Cyclones ◽  
Moisture Transport ◽  
Moisture Uptake ◽  
Air Masses ◽  
Moisture Sources ◽  
The North ◽  
Sahel Region ◽  
North And South

Atmospheric moisture transport plays an important role in the genesis of tropical cyclones (TCs). In this study, the moisture sources associated with the genesis of TCs in the tropical Atlantic Ocean near West Africa, from June to November in the period 1980–2018, were identified. To detect the location of the TCs geneses, the HURDAT2 database from the National Hurricane Center was used. Additionally, global outputs of the Lagrangian FLEXPART model were used to determine the moisture sources that provided water vapor for the genesis of TCs. This model permitted us to track backward in time the air masses from the genesis region of the TCs and identify regions where air masses uptake moisture before reach the target regions. The results reveal that 18.1% (108 TC) of the total number of TCs that formed in the North Atlantic basin were originated in the region of study. The largest frequency for the TCs geneses was observed in August and September, with each one representing approximately 45% of the total. The transport of moisture associated with the genesis of TCs mainly comes from the east of the North and South Atlantic Ocean, as well as from West Africa and the Sahel region. The patterns of moisture uptake confirmed an interhemispheric moisture transport. Finally, during the El Niño, the moisture uptake is more intense over the Atlantic Ocean close to West Africa around 15 °N of latitude, while during La Niña, the pattern is slightly weaker but covers a wider area over the Atlantic Ocean and the north of Africa.

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