Water vapour and precipitation isotope measurements from different platforms during the IGP campaign, Iceland, in 2018 connect evaporation sources to precipitation sinks

2020 ◽  
Author(s):  
Harald Sodemann ◽  
Alexandra Touzeau ◽  
Chris Barrell ◽  
John F. Burkhart ◽  
Andrew Elvidge ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Data Quality ◽  
Water Vapour ◽  
Isotope Composition ◽  
Cloud Microphysics ◽  
Heat Fluxes ◽  
The Arctic ◽  
Stable Water Isotopes ◽  
Coupled Models ◽  
Isotope Measurements

<p>The water cycle in atmospheric and coupled models is a major contributor to model uncertainty, in particular at high-latitudes, where contrasts between ice-covered regions and the open ocean fuel intense heat fluxes. However, observed atmospheric vapour concentrations do not allow us to disentangle the contributions of different processes, such as evaporation, mixing, and cloud microphysics, to the overall moisture budget. As a natural tracer, stable water isotopes provide access to the moisture sources and phase change history of atmospheric water vapour and precipitation.</p><p>Here we present a unique dataset of stable isotope measurements in water vapour and precipitation from the IGP (Iceland Greenland Seas Project) field campaign that took place during February and March 2018. The dataset includes simultaneous measurements from three platforms (a land-station at Husavik, Iceland, the R/V Alliance, and a Twin Otter aircraft) during winter conditions in the Arctic region. Precipitation was collected on an event basis on the research ship, and along two north-south transects in Northern Iceland, and analysed at two stable isotope laboratories. Airborne vapour isotope data was obtained from 10 flights covering a large geographic range (64 °N to 72 °N). Careful data treatment was applied to all stable isotope measurements to ensure sufficient data quality in a challenging measurement environment with predominantly cold and dry conditions, and characterised by strong isotope and humidity gradients. Data quality was confirmed by inter-comparison of the vapour isotope measurements both between ship and aircraft, and between the aircraft and Husavik station.</p><p>We exemplify the value of the observations from the analysis of several flights dedicated to the study of the atmosphere-ocean interactions, from low-levels legs and vertical sections across the boundary layer during Cold Air Outbreak (CAO) conditions. The precipitation in Northern Iceland collected at the precipitation sampling network shows clear co-variation with the upstream water vapour measurements at Husavik station, indicative of the wider spatial representativeness of the isotope signals. The land-based snow and vapour measurements are furthermore consistent with the isotope composition in upstream ocean regions sampled by the research vessel, and as linked from aircraft measurements.</p>

scholarly journals The stable isotope composition of water vapour above Corsica during the HyMeX SOP1: insight into vertical mixing processes from lower-tropospheric survey flights

2016 ◽  
Author(s):  
Harald Sodemann ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Mark Bitter ◽  
Ulrich Corsmeier ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Isotope ◽  
Water Vapour ◽  
Isotope Composition ◽  
Water Isotopes ◽  
High Temporal Resolution ◽  
Stable Isotope Composition ◽  
Stable Water Isotopes ◽  
Mixing Processes ◽  
Strong Inversion

Abstract. Stable water isotopes are powerful indicators of meteorological processes on a broad range of scales, reflecting evaporation, condensation, and airmass mixing processes. With the recent advent of fast laser-based spectroscopic methods it has become possible to measure the stable isotopic composition of atmospheric water vapour in situ at high temporal resolution, enabling to tremendously extend the measurement data base in space and time. Here we present the first set of airborne spectroscopic stable water isotopes measurements over the western Mediterranean. Measurements have been acquired by a customised Picarro L2130-i cavity-ring down spectrometer deployed onboard of the Dornier 128 D-IBUF aircraft together with a meteorological flux measurement package during the HyMeX SOP1 field campaign in Corsica, France during September and October 2012. Taking into account memory effects of the air inlet pipe, the typical time resolution of the measurements was about 15–30 s, resulting in an average horizontal resolution of about 1–2 km. Cross-calibration of the water vapour measurements from all humidity sensors showed good agreement in most flight conditions but the most turbulent ones. In total 21 successful stable isotope flights with 59 flight hours have been performed. Our data provide quasi-climatological autumn average conditions of the stable isotope parameters δD, δ18O and d-excess during the study period. A time-averaged perspective of the vertical stable isotope composition reveals for the first time the mean vertical structure of stable water isotopes over the Mediterranean at high resolution. A d-excess minimum in the overall average profile is reached in the region of the boundary layer top due to precipitation evaporation, bracketed by higher d-excess values near the surface due to non-equilibrium fractionation and above the boundary layer due to the non-linearity of the d-excess definition. Repeated flights along the same pattern reveals pronounced day-to-day variability due to changes in the large-scale circulation. During a period marked by a strong inversion at the top of the marine boundary layer, vertical gradients in stable isotopes reached up to 25.4 ‰ 100 m−1 for δD.

Airborne water vapor isotope measurements over the Iceland Sea in winter conditions

2021 ◽  
Author(s):  
Alexandra Touzeau ◽  
Hans-Christian Steen-Larsen ◽  
Ian Renfrew ◽  
Þorsteinn Jónsson ◽  
Andrew Elvidge ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Isotope ◽  
Sea Ice ◽  
Water Vapour ◽  
Cloud Cover ◽  
Isotope Composition ◽  
Specific Humidity ◽  
Free Troposphere ◽  
Cold Air ◽  
Isotope Measurements

<p>Improved understanding of evaporation and condensation processes is critical to improve the representation of the water cycle in atmospheric models. Thereby, in-situ measurements along the entire moisture transport pathway, covering evaporation, mixing between different air masses in the atmospheric boundary layer and the free troposphere, and resulting precipitation are highly valuable to obtain new insight. In particular, coherent measurements of the stable isotope composition in atmospheric vapour can provide additional constraints on phase change processes of water vapour from source to sink, enabling direct comparison within isotope-enabled models.</p><p>Here we present stable isotope measurements from the Iceland Greenland Seas Project field campaign that took place in February-March 2018. This unique dataset includes simultaneous measurements from a land-station in Husavik, Iceland, a ship and an air plane in the subpolar region. Alternation between cold-air outbreaks and mid-latitude airmasses characterized the measurement period. Here we focus on the stable water isotope composition in water vapour obtained from 10 research flights, covering a large geographic range (64 °N to 72 °N). Careful data treatment was applied to ensure the quality of isotope measurements in the predominant cold, dry conditions with large gradients in isotope composition and humidity.</p><p>From an intercomparison flight over the Husavik station, we find good agreement between ground and airborne measurements. Out of 7 flights dedicated to the study of atmosphere-ocean-ice interactions, with both low-levels legs and vertical sections in predominant Cold Air Outbreak (CAO) conditions, we focus on the marginal ice zone and regions covered by shallow cumulus clouds. For open water flights, we find the horizontal and vertical distribution of δ<sup>18</sup>O in the marine boundary layer to covary with cloud cover. Thereby, downdrafts bring dry and <sup>18</sup>O-depleted air from the free troposphere towards the surface, corresponding to openings in cloud cover. For flights passing over sea ice edge, both δ<sup>18</sup>O and specific humidity show a clear east-west gradient, with increasing values towards the open sea reflecting ocean moisture availability. Additionally, open leads in the sea ice also have a visible impact on isotope values. Lastly, relatively low d-excess values are observed over the sea-ice, which could either be caused by local processes or advection.</p>

scholarly journals Observed microphysical changes in Arctic mixed-phase clouds when transitioning from sea ice to open ocean

2016 ◽  
Author(s):  
G. Young ◽  
H. M. Jones ◽  
T. W. Choularton ◽  
J. Crosier ◽  
K. N. Bower ◽  
...  
Keyword(s):  
Sea Ice ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Heat Fluxes ◽  
The Arctic ◽  
Cloud Base ◽  
Surface Boundary ◽  
Sea Ice Extent ◽  
Near Surface

Abstract. In situ airborne observations of cloud microphysics, aerosol properties and thermodynamic structure over the transition from sea ice to ocean are presented from the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign. A case study from 23 March 2013 provides a unique view of the cloud microphysical changes over this transition under cold air outbreak conditions. Cloud base and depth both increased over this transition, and mean droplet number concentrations also increased from approximately 80 cm−3 over the sea ice to 90 cm−3 over the ocean. The ice properties of the cloud remained approximately constant. Observed ice crystal concentrations averaged approximately 0.5–1.5 L−1, suggesting only primary ice nucleation was active; however, there was evidence of crystal fragmentation at cloud base over the ocean. The liquid-water content increased almost four-fold over the transition and this, in conjunction with the deeper cloud layer, allowed rimed snowflakes to develop which precipitated out of cloud base. Little variation in aerosol particle number concentrations was observed between the different surface conditions; however, some variability with altitude was observed, with notably greater concentrations measured at higher altitudes (> 800 m) over the sea ice. Near-surface boundary layer temperatures increased by 13 °C from sea ice to ocean, with corresponding increases in surface heat fluxes and turbulent kinetic energy. These significant thermodynamic changes were concluded to be the primary driver of the microphysical evolution of the cloud. This study represents the first investigation, using in situ airborne observations, of cloud microphysical changes with changing sea ice cover and addresses the question of how the microphysics of Arctic stratiform clouds may change as the region warms and sea ice extent reduces.

scholarly journals Mercury isotopes reveal atmospheric gaseous mercury deposition directly to the Arctic coastal snowpack

2021 ◽  
Author(s):  
Thomas Douglas ◽  
Joel Blum
Keyword(s):  
Stable Isotope ◽  
Dry Deposition ◽  
Isotope Composition ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Mercury Deposition ◽  
Coastal Watershed ◽  
Reactive Surface ◽  
Gaseous Mercury

Springtime atmospheric mercury depletion events (AMDEs) lead to snow with elevated mercury concentrations (>200 ng Hg/L) in the Arctic and Antarctic. During AMDEs gaseous elemental mercury (GEM) is photochemically oxidized by halogens to reactive gaseous mercury which is deposited to the snowpack. This reactive mercury is either photochemically reduced back to GEM and reemitted to the atmosphere or remains in the snowpack until spring snowmelt. GEM is also deposited to the snowpack and tundra vegetation by reactive surface uptake (dry deposition) from the atmosphere. There is little consensus on the proportion of AMDE-sourced Hg versus Hg from dry deposition that is released in spring runoff. We used mercury stable isotope measurements of GEM, snowfall, snowpack, snowmelt, surface water, vegetation, and peat from a northern Alaska coastal watershed to quantify Hg sources. Although high Hg concentrations are deposited to the snowpack during AMDEs, we estimate that ∼76 to 91% is released back to the atmosphere prior to snowmelt. Mercury deposited to the snowpack as GEM comprises the majority of snowmelt Hg and has a Hg stable isotope composition similar to Hg deposited by reactive surface uptake of GEM into the leaves of trees in temperate forests. This GEM-sourced Hg is the dominant Hg we measured in the spring snowpack and in tundra peat permafrost deposits.

scholarly journals Arctic cloud cover bias in ECHAM6 and its sensitivity to cloud microphysics and surface fluxes

2018 ◽  
Author(s):  
Jan Kretzschmar ◽  
Marc Salzmann ◽  
Johannes Mülmenstädt ◽  
Johannes Quaas
Keyword(s):  
Cloud Cover ◽  
Climate Models ◽  
Cloud Amount ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The Arctic ◽  
Phase Partitioning ◽  
Low Level

Abstract. Among the many different feedback mechanisms contributing to the Arctic Amplification, clouds play a very important role in the Arctic climate system through their cloud radiative effect. It is therefore important that climate models simulate basic cloud properties like cloud cover and cloud phase correctly. We compare results from the global atmospheric model ECHAM6 to observations from the CALIPSO satellite active lidar instrument using the COSP satellite simulator. Our results show that the model is able to reproduce the spatial distribution and cloud amount in the Arctic to some extent, but that cloud cover has a positive bias (caused by an overestimation of low-level, liquid containing cloud) in regions where the surface is covered by snow or ice. We explored the sensitivity of cloud cover to the strength of surface heat fluxes, but only by increasing surface mixing the observed cloud cover bias cloud be reduced. As ECHAM6 already mixes too strongly in the Arctic, the cloud cover bias can mainly be attributed to cloud microphysical processes. Improvements in the phase partitioning of Arctic low-level clouds could be achieved by a more effective Wegener–Bergeron–Findeisen process but total cloud cover remained still overestimated. By allowing for a slight supersaturation with respect to ice within the cloud cover scheme, we were able to also reduce this positive cloud cover bias.

scholarly journals Arctic clouds in ECHAM6 and their sensitivity to cloud microphysics and surface fluxes

2019 ◽  
Vol 19 (16) ◽  
pp. 10571-10589 ◽  
Author(s):  
Jan Kretzschmar ◽  
Marc Salzmann ◽  
Johannes Mülmenstädt ◽  
Johannes Quaas
Keyword(s):  
Cloud Cover ◽  
Cloud Amount ◽  
Cloud Microphysics ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The Arctic ◽  
High Latitudes ◽  
Positive Bias ◽  
Ice Clouds ◽  
Low Level

Abstract. Compared to other climate models, the MPI-ESM/ECHAM6 is one of the few models that is able to realistically simulate the typical two-state radiative structure of the Arctic boundary layer and also is able to sustain liquid water at low temperatures as is often observed in high latitudes. To identify processes in the model that are responsible for the abovementioned features, we compare cloud properties from ECHAM6 to observations from CALIPSO-GOCCP using the COSP satellite simulator and perform sensitivity runs. The comparison shows that the model is able to reproduce the spatial distribution and cloud amount in the Arctic to some extent but a positive bias in cloud fraction is found in high latitudes, which is related to an overestimation of low- and high-level clouds. We mainly focus on low-level clouds and show that the overestimated cloud amount is connected to surfaces that are covered with snow or ice and is mainly caused by an overestimation of liquid-containing clouds. The overestimated amount of Arctic low-level liquid clouds can be related to insufficient efficiency of the Wegener–Bergeron–Findeisen (WBF) process but revising this process alone is not sufficient to improve cloud phase on a global scale as it also introduces a negative bias over oceanic regions in high latitudes. Additionally, this measure transformed the positive bias in low-level liquid clouds into a positive bias of low-level ice clouds, keeping the amount of low-level clouds almost unchanged. To avoid this spurious increase in ice clouds, we allowed for supersaturation with respect to ice using a temperature-weighted scheme for saturation vapor pressure but this measure, together with a more effective WBF process, might already be too efficient at removing clouds as it introduces a negative cloud cover bias. We additionally explored the sensitivity of low-level cloud cover to the strength of surface heat fluxes; by increasing surface mixing, the observed cloud cover and cloud phase bias could also be reduced. As ECHAM6 already mixes too strongly in the Arctic regions, it is questionable if one can physically justify it to increase mixing even further.

scholarly journals High-resolution stable isotope signature of a land-falling atmospheric river in southern Norway

2021 ◽  
Vol 2 (3) ◽  
pp. 713-737
Author(s):  
Yongbiao Weng ◽  
Aina Johannessen ◽  
Harald Sodemann
Keyword(s):  
Surface Water ◽  
High Resolution ◽  
Water Vapour ◽  
Isotope Composition ◽  
Initial Period ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Near Surface ◽  
Surface Precipitation ◽  
Moisture Source

Abstract. Heavy precipitation at the west coast of Norway is often connected to elongated meridional structures of high integrated water vapour transport known as atmospheric rivers (ARs). Here we present high-resolution measurements of stable isotopes in near-surface water vapour and precipitation during a land-falling AR in southwestern Norway on 7 December 2016. In our analysis, we aim to identify the influences of moisture source conditions, weather system characteristics, and post-condensation processes on the isotope signal in near-surface water vapour and precipitation. A total of 71 precipitation samples were collected during the 24 h sampling period, mostly taken at sampling intervals of 10–20 min. The isotope composition of near-surface vapour was continuously monitored in situ with a cavity ring-down spectrometer. Local meteorological conditions were in addition observed from a vertical pointing rain radar, a laser disdrometer, and automatic weather stations. We observe a stretched, “W”-shaped evolution of isotope composition during the event. Combining paired precipitation and vapour isotopes with meteorological observations, we define four different stages of the event. The two most depleted periods in the isotope δ values are associated with frontal transitions, namely a combination of two warm fronts that follow each other within a few hours and an upper-level cold front. The d-excess shows a single maximum and a step-wise decline in precipitation and a gradual decrease in near-surface vapour. Thereby, the isotopic evolution of the near-surface vapour closely follows that of the precipitation with a time delay of about 30 min, except for the first stage of the event. Analysis using an isotopic below-cloud exchange framework shows that the initial period of low and even negative d-excess in precipitation was caused by evaporation below cloud base. The isotope signal from the cloud level became apparent at ground level after a transition period that lasted up to several hours. Moisture source diagnostics for the periods when the cloud signal dominates show that the moisture source conditions are then partly reflected in surface precipitation and water vapour isotopes. In our study, the isotope signal in surface precipitation during the AR event reflects the combined influence of atmospheric dynamics, moisture sources, and atmospheric distillation, as well as cloud microphysics and below-cloud processes. Based on this finding, we recommend careful interpretation of results obtained from Rayleigh distillation models in such events, in particular for the interpretation of surface vapour and precipitation from stratiform clouds.

High-resolution stable isotope signature of a land-falling Atmospheric River in southern Norway

2021 ◽  
Author(s):  
Weng Yongbiao ◽  
Aina Johannessen ◽  
Harald Sodemann
Keyword(s):  
Surface Water ◽  
High Resolution ◽  
Stable Isotope ◽  
Water Vapour ◽  
Isotope Composition ◽  
Convective Precipitation ◽  
Near Surface ◽  
Surface Precipitation ◽  
Moisture Sources ◽  
Isotopic Signal

<p>Heavy precipitation at the west coast of Norway is often connected to high integrated water vapour transport within Atmospheric Rivers (AR). Here we present high-resolution measurements of stable isotopes in near-surface water vapour and precipitation during a land-falling AR event in southwestern Norway on 07 December 2016. We analyze the influences of moisture sources, weather system characteristics, and post-condensation processes on the isotopic signal in near-surface water vapour and precipitation.</p><p>During the 24-h sampling period, a total of 71 precipitation samples were collected, sampled at intervals of 10-20 min. The isotope composition of near-surface vapour was continuously monitored with a cavity ring-down spectrometer. In addition, local meteorological conditions were monitored from a vertical pointing rain radar, a laser disdrometer, and automatic weather stations.</p><p>During the event, we observe a "W"-shaped evolution of the stable isotope composition. Combining isotopic and meteorological observations, we define four different stages of the event. The two most depletion periods in the isotope δ values are associated with frontal transitions, namely a combination of two warm fronts that follow each other within a few hours, and an upper-level cold front. The d-excess shows a single maximum, and a step-wise decline in precipitation and a gradual decrease in near-surface vapour. Thereby, isotopic evolution of the near-surface vapour closely follows the precipitation with a time delay of about 30 min, except for the first stage of the event. Analysis using an isotopic below-cloud exchange model shows that the initial period of low and even negative d-excess in precipitation was most likely caused by evaporation below cloud base. At the ground, a near-constant signal representative of the airmass above is only reached after transition periods of several hours. For these steady periods, the moisture source conditions are partly reflected in the surface precipitation.</p><p>Based on our observations, we revisit the interpretation of precipitation isotope measurements during AR events in previous studies. Given that the isotopic signal in surface precipitation reflects a combination of atmospheric dynamics through moisture sources and atmospheric distillation, as well as cloud microphysics and below-cloud processes, we recommend caution regarding how Rayleigh distillation models are used during data interpretation. While the isotope compositions during convective precipitation events may be more adequately represented by idealized Rayleigh models, additional factors should be taken into account when interpreting a surface precipitation isotope signal from stratiform clouds.</p>

scholarly journals Observed microphysical changes in Arctic mixed-phase clouds when transitioning from sea ice to open ocean

2016 ◽  
Vol 16 (21) ◽  
pp. 13945-13967 ◽  
Author(s):  
Gillian Young ◽  
Hazel M. Jones ◽  
Thomas W. Choularton ◽  
Jonathan Crosier ◽  
Keith N. Bower ◽  
...  
Keyword(s):  
Sea Ice ◽  
Cloud Microphysics ◽  
Heat Fluxes ◽  
Cloud Layer ◽  
The Arctic ◽  
Cloud Base ◽  
Surface Boundary ◽  
Sea Ice Extent ◽  
Near Surface

Abstract. In situ airborne observations of cloud microphysics, aerosol properties, and thermodynamic structure over the transition from sea ice to ocean are presented from the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) campaign. A case study from 23 March 2013 provides a unique view of the cloud microphysical changes over this transition under cold-air outbreak conditions. Cloud base lifted and cloud depth increased over the transition from sea ice to ocean. Mean droplet number concentrations, Ndrop, also increased from 110 ± 36 cm−3 over the sea ice to 145 ± 54 cm−3 over the marginal ice zone (MIZ). Downstream over the ocean, Ndrop decreased to 63 ± 30 cm−3. This reduction was attributed to enhanced collision-coalescence of droplets within the deep ocean cloud layer. The liquid water content increased almost four fold over the transition and this, in conjunction with the deeper cloud layer, allowed rimed snowflakes to develop and precipitate out of cloud base downstream over the ocean. The ice properties of the cloud remained approximately constant over the transition. Observed ice crystal number concentrations averaged approximately 0.5–1.5 L−1, suggesting only primary ice nucleation was active; however, there was evidence of crystal fragmentation at cloud base over the ocean. Little variation in aerosol particle number concentrations was observed between the different surface conditions; however, some variability with altitude was observed, with notably greater concentrations measured at higher altitudes ( >  800 m) over the sea ice. Near-surface boundary layer temperatures increased by 13 °C from sea ice to ocean, with corresponding increases in surface heat fluxes and turbulent kinetic energy. These significant thermodynamic changes were concluded to be the primary driver of the microphysical evolution of the cloud. This study represents the first investigation, using in situ airborne observations, of cloud microphysical changes with changing sea ice cover and addresses the question of how the microphysics of Arctic stratiform clouds may change as the region warms and sea ice extent reduces.

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