AS2.13

AS2 EDI
Surface Exchange Processes in the Polar Regions: Physics, Chemistry, Isotopes, and Aerosols 

This session is intended to provide an interdisciplinary forum to bring together researchers working in the areas of high-latitude meteorology, atmospheric chemistry, stable isotope research, oceanography, and climate. The emphasis is on the role of boundary layer processes that mediate exchange of heat, momentum and mass between the Earth's surface (snow, sea-ice, ocean and land) and the atmosphere as well as the local to large-scale influences on these exchanges. An adequate understanding and quantification of these processes is necessary to improve modeling and prediction of future changes in the polar regions and their teleconnections with mid-latitude weather and climate, including meridional transport of heat, moisture, chemical trace species, aerosols and isotopic tracers (indicating airmass origins and atmospheric processes); and regional emission and vertical mixing of climate active trace gases and aerosol, such as cloud-forming particles (CCN/INP) and their precursors. It is expected that the recent implementation of new measurements such as those from pan-Arctic water vapor isotope networks, observations such as those obtained during the MOSAiC field program, and data from existing networks will help diagnose long-range moisture and aerosol sources and the coupling between local and large-scale dynamics. We encourage submissions such as (but not limited to):
(1) External controls on the boundary layer such as clouds, radiation and long-range transport processes
(2) Results from field programs, such as MOSAiC, and routine observatories, insights from laboratory studies, and advances in modeling and reanalysis,
(3) Use of data from pan-Arctic and Antarctic observing networks,
(4) Surface processes involving snow, sea-ice, ocean, land/atmosphere chemical and isotope exchanges, and natural aerosol sources
(5) The role of boundary layers in polar climate change and implications of climate change for surface exchange processes, especially in the context of reduced sea ice, wetter snow packs, increased glacial discharge and physical and chemical changes associated with an increasing fraction of first year ice and increasing open water.

Convener: William Neff | Co-conveners: Julia Schmale, Heather GuyECSECS, Daiki Nomura, Laura DietrichECSECS
Presentations
| Tue, 24 May, 17:00–18:24 (CEST)
 
Room F1

Presentations: Tue, 24 May | Room F1

Chairpersons: Julia Schmale, William Neff
17:00–17:06
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EGU22-9646
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ECS
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On-site presentation
Steven van der Linden and Cedrick Ansorge

The polar-night stable boundary layer, observed during MOSAiC, gives rise to extreme stabilities not found in typical mid-latitude SBLs. In a steady or near-steady synoptic environment, the boundary layer even attains a quasi-steady state for several hours, i.e., boundary-layer processes and profiles are equilibrated.

Such lab-like conditions of extreme stability remain a major challenge for turbulence modelling across scales. Previously, we have demonstrated that such situations can be qualitatively modelled by carefully-designed large-eddy simulations, using wintertime observations from Dome C, Antarctica (Van der Linden et al., 2020: J. Atmos. Sci., 77, 3343–3360). However, a quantitative comparison remained elusive due to a lack of turbulent flux observations at Dome C.

The high-frequency observations of wind, temperature, radiation and turbulent fluxes during the MOSAiC-campaign do allow us to quantitatively disentangle different mixing processes facilitating a one-to-one comparison between observation and simulation. Here, we will show the results of our simulations and discuss the specific challenges of performing large-eddy simulations of such harsh, but fascinating conditions.

Our results show that atmospheric radiation, which is usually neglected in large-eddy simulations of very stable cases, is a key thermal process in the evolution of the boundary layer due to the large thermal inversion near the surface. Radiative exchanges result in a deeper boundary-layer, which is in line with the observed boundary-layer height, as compared to the simulations without radiative exchanges. Although a larger boundary-layer depth is obtained, discrepancies between the observed more exponentially-shaped temperature profile and the simulated temperature profile still persist.

This is suspected to be caused by a wrong magnitude of the turbulent mixing near the surface, related to the interplay of roughness lengths, Monin–Obukhov similarity theory and the extreme surface-layer stratification. Initial tests, however, remain inconclusive on this complex interplay.

How to cite: van der Linden, S. and Ansorge, C.: The coldest days of MOSAiC – an LES study , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9646, https://doi.org/10.5194/egusphere-egu22-9646, 2022.

17:06–17:12
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EGU22-6165
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ECS
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Virtual presentation
Jannis-Michael Huss and Christoph Thomas

Our physical understanding of boundary-layer processes, particularly under the long-lived stable conditions of the polar night, is limited. In these weak-wind stable boundary layers, the exchange of energy, momentum, and matter, can be dominated by submeso-scale motions on scales larger than those of classical turbulence, which have been found to violate assumptions of local similarity concepts.

We investigated (1) whether the magnitude of non-local flux contributions, possibly arising from submeso-scale motions in concert with terrain, is systematically connected to certain boundary-layer states and flow directions, and (2) to what extent non-local forcings impact  turbulent heat fluxes as well as the local surface energy balance including advection.

Data were collected during the NYTEFOX (NY Alesund TurbulencE Fiber-Optic eXperiment) field campaign 2020 at the scientific AWIPEV Arctic station in Ny-Ålesund, Svalbard at the end of polar night. Non-local influences were detected and quantified by comparing the measured sensible heat flux from sonic anemometry to the flux modeled from local first-order closure using temperature profile observations from fiber-optic distributed sensing. The spatial structure of the time-variant flow and of the horizontal advection were computed from a unique set of observations from a large horizontal fiber-optic distributed sensing array spanning hundreds of meters.

First results indicate an influence of cloud cover with stronger non-local flux contributions during clear skies causing an increased radiative cooling of the surface. Additionally, such contributions were generated and/or guided by the heterogeneous terrain in the source area of the incoming flow. Steep mountain slopes caused very cold katabatic currents and, hence, promoted vertical decoupling. This resulted in stronger non-local impact on the local fluxes, causing large disagreement between modeled and measured sensible heat fluxes. The conditions featuring large non-local flux contributions were also associated with large magnitudes of horizontal advection of sensible heat.

Advection, as well as conditions that promote strong surface-based inversions, appear to cause an increased violation of the assumption of local similarity in the Arctic weak-wind stable boundary layer.

How to cite: Huss, J.-M. and Thomas, C.: Local surface heterogeneity and terrain drive disagreement between measured and modeled fluxes in the cloud-free Arctic stable boundary layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6165, https://doi.org/10.5194/egusphere-egu22-6165, 2022.

17:12–17:18
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EGU22-7185
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ECS
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On-site presentation
Jan Chylik, Benjamin Kirbus, Niklas Schnierstein, Manfred Wendisch, and Roel Neggers

The transformation of cloudy air masses plays a key role in the ongoing Arctic Amplification. The complex system of the interactions between aerosols, cloud layers and turbulence is not yet fully understood, mostly due to broad range of scales involved and the lack of reliable in-situ measurements. 
We try to fill this gap by using a high resolution numerical simulation constrained with observations as a virtual laboratory. The focus of this study is the transformation of boundary layer mixed-phase clouds in the presence of higher cloud decks advected above them. The recent MOSAiC field campaign provided us with unique observations of developing cloudy air mass on a closed trajectory. The same air mass was sampled twice in September 2020, first by the research vessel Polarstern during the MOSAiC drift, and later by airborne instruments during the MOSAiC-ACA, its sister-campaign northwest of Svalbard.  We configured a high-resolution Lagrangian large-eddy simulation based on ERA5 reanalysis data and constrained it by in-situ measurements of the surface boundary condition, vertical thermodynamic structure and aerosol concentrations. The results of the simulations are then validated against independent cloud measurements. Our virtual laboratory also provides us opportunities to investigate the sensitivity of the transformation of the boundary layer clouds to the composition of the advected mid-tropospheric cloud decks. The importance of the seeder-feeder mechanism and radiative fluxes will be discussed, as well as further implications for the Arctic Amplification and future studies.

How to cite: Chylik, J., Kirbus, B., Schnierstein, N., Wendisch, M., and Neggers, R.: Aerosol-Cloud-Turbulence Interaction in Multilayer Clouds Modeled on a Closed Trajectory between MOSAiC and MOSAiC-ACA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7185, https://doi.org/10.5194/egusphere-egu22-7185, 2022.

17:18–17:24
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EGU22-11574
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ECS
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On-site presentation
Camilla Francesca Brunello, Hanno Meyer, Moein Mellat, Mathieu Casado, Annette Rinke, Silvia Bucci, and Martin Werner

The Arctic atmosphere has undergone a process of moistening during the past decades. The loss of sea ice has led to enhanced transfer of heat and moisture from the ocean to the lower atmosphere, while strengthening of cyclonic events has enhanced the poleward transport of moisture from lower latitudes. Eventually, the increased humidity of the Arctic air masses serves today as a new, increasingly important source of moisture for the northern hemisphere. Still, to date, the relative contributions of local evaporation versus distant-moisture sources remains uncertain, as well as the processes responsible for exchanges within and between the hydrological compartments of the Arctic. Such uncertainties limit our ability to understand the importance of the Arctic water cycle to global climate change and to project its future.

In this study we use atmospheric water vapour isotopes to investigate the origin of the Arctic moisture and assess whether and which relevant changes occur within the coupled ocean-sea ice-atmosphere system (i.e., sea ice, sea water, snow, melt ponds). Stable isotopologues of water (HDO, H218O) have different saturation vapour pressures and molecular diffusivity coefficients in air. These differences lead to isotopic fractionation during each phase change of water, making water isotopes a powerful tracer of the Arctic hydrological cycle.

Water vapour humidity, delta-18O, and delta-D have been measured continuously by a Picarro L2140i Cavity Ringdown Spectrometer installed onboard research vessel Polarstern during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition, which took place in the Central Arctic Ocean from October 2019 to September 2020. Our measurements depict a clear seasonal cycle and a strong and significant covariance of delta-18O and delta-D with air temperature and specific humidity. At the synoptic time scale the dataset is characterized by the occurrence of events associated with humidity peaks and abrupt isotopic excursions. We use statistical analysis and backwards trajectories to i) identify the origin of the air masses and the relative contributions of distant vs. locally sourced moisture, and ii) illustrate the isotopic fingerprint of these two distinct moisture contributors and discuss on the source-to-sink processes leading to their differences.

Further, the MOSAiC observations are compared to an ECHAM6 simulation, nudged to ERA5 reanalysis data and enabled for water isotope diagnostics. The model-data comparison makes it possible to explore the spatial representativeness of our observations and assess whether the model can correctly simulate the observed isotopic changes. In the future, our observations may serve as a benchmark to test the parametrization of under(mis-)represented fractionation processes such as snow sublimation, evaporation from leads and melt ponds.

Our study provides the very first isotopic characterization of the Central Arctic moisture throughout an entire year and contributes to disentangling the influence of local evaporative processes versus large-scale vapour transport on the Arctic moistening.

How to cite: Brunello, C. F., Meyer, H., Mellat, M., Casado, M., Rinke, A., Bucci, S., and Werner, M.: The isotopic composition of water vapour in the Central Arctic during the MOSAiC campaign: local versus distant-moisture sources., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11574, https://doi.org/10.5194/egusphere-egu22-11574, 2022.

17:24–17:30
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EGU22-7062
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On-site presentation
Moein Mellat, Martin Werner, Camilla Francesca Brunello, Dorothea Bauch, Ellen Damm, Daiki Nomura, Alessandra D'Angelo, Jeffrey M. Welker, Martin Schneebeli, and Hanno Meyer

For the past two decades, the Arctic water cycle changed rapidly due to surface air temperatures (SATs) increasing at twice the global rate. Terrestrial ice (i.e. Greenland Ice Sheet) and marine sea-ice loss, alterations of ocean circulation patterns, and shifting atmospheric moisture sources and transport are some of the most pronounced changes caused by the Arctic amplification, fostering increased humidity levels. Stable water isotopes (δ18O, δ2H) and the secondary parameter d-excess are valuable tracers for hydrological changes, including how these shifts may affect the global climate system. However, it is only recently that we are using precipitation and water vapor networks to resolve water isotope patterns and processes in the Arctic. However, a fully coordinated study of the entire water cycle attributes year-long including sea ice, ocean water, vapor, and precipitation has until recently has been absent. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition provided a unique opportunity to collect, analyze, and synthesize discrete samples of the different hydrological compartments in the central Arctic, covering a complete one-year seasonal cycle using a combination of ship-based, the pan-Arctic Water Isotope Network (PAPIN). These observations can lead to new insights into coupled ocean-atmosphere climate processes operating in the Arctic, especially during extreme events, sea ice formation, sea ice retreat, and during a dichotomy of synoptic weather patterns over the MOSAiC-year.

We present the isotopic traits of more than 2,200 discrete samples (i.e., seawater, sea ice, snow, brines, frost flowers, lead ice, ridge ice, and precipitation) collected during MOSAiC. Snow has the most depleted δ18O values (-16.3 ± 9.1‰; the number of samples N=306), whereas seawater is the most enriched δ18O compartment (-1.5 ± 0.9‰; N=302) of the Arctic water cycle. Precipitation throughout the Arctic Basin varied from -10‰ to -35‰. Snow profiles are gradually enriched in δ18O from top to bottom by ~20‰ partially due to sublimation of deposited snow, as well as snow metamorphism and its effects on the water isotopes. Second-year ice (SYI) is isotopically relatively depleted in δ18O (-4.2 ± 2.6‰; N=200) compared to first-year ice (FYI) (-0.7 ± 2.1‰; N=635) and insulated FYI (i.e. FYI grown at the bottom of SYI) (-1.7 ± 2.4‰; N=214). The latter is likely caused by post-depositional exchange processes with snow. Open water leads (-1.6 ± 2.4‰; N=137) and melt ponds (-2.1 ± 2.7‰; N=109) on the surface of sea ice contribute to the moistening of the atmosphere in the Arctic on a regional scale.

Our dataset provides an unprecedented snapshot of the present-day isotopic composition of the Arctic water cycle during an entire year. The coupling of these discrete samples data with the continuous measurements of atmospheric water vapor may shed light on the relative contribution of snow, sea ice, seawater, open water leads, and melt ponds both spatially and temporally to regional and local moisture levels in the Arctic. Stable water isotopes will ultimately contribute to resolving the linkages between sea ice, ocean, and atmosphere during the critical transition from frozen ocean to open water conditions.

How to cite: Mellat, M., Werner, M., Brunello, C. F., Bauch, D., Damm, E., Nomura, D., D'Angelo, A., Welker, J. M., Schneebeli, M., and Meyer, H.: Isotope measurements of the Arctic water cycle and exchange processes between seawater, sea ice, and snow during MOSAiC, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7062, https://doi.org/10.5194/egusphere-egu22-7062, 2022.

17:30–17:36
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EGU22-13362
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On-site presentation
Mathieu Casado, Christophe Leroy-Dos Santos, Elise Fourré, Vincent Favier, Cécile Agosta, Laurent Arnaud, Frédéric Prié, Pete D. Akers, Leoni Janssen, Christoph Kittel, Joel Savarino, and Amaelle Landais

Stable water isotopes are a tracer of hydrological processes and a paleoclimate proxy from ice core records. The interpretation of the latter relies on fractionation processes throughout the hydrological cycle, from the evaporation over the ocean, during each precipitation event, and during post-deposition processes, in particular due to the exchanges between the snow and the moisture in the atmosphere. Thanks to new developments in infrared spectroscopy, it is now possible to monitor not only the snow isotopic composition but also the vapour continuously, and thus document exchanges between the snow and the vapour. On the East Antarctic Plateau, records of water vapour isotopic composition in Kohnen and Dome C during summer have revealed significant diurnal variability which can be used to address the exchange between surface snow and atmospheric water vapour as well as the stability of the atmospheric boundary layer. 

In this study, we present the first vapour monitoring on a transect across East Antarctica for a period of 3 months from November 2019 to February 2020 during the EAIIST traverse, covering more than 3600 km. In parallel, we also monitored the vapour isotopic composition at two stations: Dumont D’Urville (DDU), the starting point, and Dome C, half way through. Efforts on the calibration on each monitoring station, as well as cross-calibration of the different instruments offer a unique opportunity to compare both the spatial and temporal (diurnal variability or at the scale of several days) gradients of humidity, temperature and water vapour isotopic composition in East Antarctica during the summer season. 

With the use of the Modele Atmospherique Régional (MAR), we compare the variability measured in water vapour isotopic composition, temperature and humidity with the different systems (fixed or mobile location). Although further comparisons with the surface snow isotopic composition are required to quantify the impact of the snow-atmosphere exchanges on the local surface mass balance, these three simultaneous measurements of the vapour isotopic composition show the potential of using water stables isotopes to evaluate hydrological processes in East Antarctica.  

How to cite: Casado, M., Leroy-Dos Santos, C., Fourré, E., Favier, V., Agosta, C., Arnaud, L., Prié, F., Akers, P. D., Janssen, L., Kittel, C., Savarino, J., and Landais, A.: Water vapor isotopic signature along the EAIIST traverse, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13362, https://doi.org/10.5194/egusphere-egu22-13362, 2022.

17:36–17:42
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EGU22-9253
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Virtual presentation
Srinath Krishnan, Maria Sand, Camilla Stjern, Annica Ekman, and Sebastian Böö

Understanding how and when aerosols are transported to the Arctic is crucial to evaluating the contribution of remote aerosol emissions on Arctic Amplification. Climate models show large discrepancies in long-range aerosol transport, significantly impacting estimates of local aerosol-driven forcing at the Arctic. Long-range aerosol transport is intimately linked to moisture transport. Aerosol transport is generally high during periods of low precipitation (i.e. low wet scavenging) and strong temperature inversions (with low vertical mixing). But studies have shown the importance of intense moisture intrusion events for moisture transport, with almost 30% of total annual moisture being transported during these intervals. These events are associated with warm, cloudy moist air transport that leads to strong downwelling longwave radiation and warm surface temperatures at the Arctic. Notably, the blocking patterns established during these events also give rise to favourable conditions for long-range aerosol transport from the mid-latitudes. Here, we use two reanalysis datasets – Copernicus Atmospheric Monitoring Service (CAMS) and Modern-Era Retrospective analysis for Research and Application (MERRA-2) – to investigate moisture and aerosol transport into the Arctic for a 20-year period. We present a comparison of the relative importance of intrusion events to the total annual moisture transport into to the Arctic during intrusion events for the two different datasets and whether aerosols correlate with these moisture intrusions. This comparison can advance our understanding of aerosol transport to the Arctic and improve the representation of seasonal cycle of aerosols in climate models.  Finally, we investigate whether changes in aerosol transport during these events could have led to significant changes in local forcing at the Arctic.

How to cite: Krishnan, S., Sand, M., Stjern, C., Ekman, A., and Böö, S.: Aerosol transport to the Arctic during moisture intrusion events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9253, https://doi.org/10.5194/egusphere-egu22-9253, 2022.

17:42–17:48
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EGU22-13169
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ECS
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On-site presentation
Ruth Price, Andrea Baccarini, Julia Schmale, Paul Zieger, Ian Brooks, Paul Field, and Ken Carslaw

The aerosol budget of the Arctic plays a key role in determining the behaviour of clouds, which are important for the surface energy balance and thus for the region’s climate. A key question is the extent to which cloud condensation nuclei in the high Arctic summertime boundary layer are controlled by local emission and formation processes or by transport from outside. Each of these sources is likely to respond differently to future changes in ice cover. Here we use a global model and observations from ship and aircraft field campaigns to understand the source of high-Arctic aerosol in late summer. We find that particles formed remotely are the dominant source of boundary layer Aitken mode particles during the sea ice melt period up to the end of August. Such a remote particle source, mostly entrained from the free troposphere, explains the remarkably stable nucleation mode concentrations of around 100 cm-3. This source from outside the high Arctic declines as photochemical rates decrease towards the end of summer, and is largely replaced by local new particle formation driven by iodic acid associated with freeze up. Such a local source is consistent with strong fluctuations in nucleation mode concentrations that occur in September. Our results suggest a high Arctic aerosol regime shift in late summer, and only after this shift do cloud condensation nuclei become sensitive to local aerosol processes.

How to cite: Price, R., Baccarini, A., Schmale, J., Zieger, P., Brooks, I., Field, P., and Carslaw, K.: Remote new particle formation dominates the nucleation and Aitken aerosol modes in the central Arctic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13169, https://doi.org/10.5194/egusphere-egu22-13169, 2022.

17:48–17:54
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EGU22-8559
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ECS
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On-site presentation
Anisbel Leon, Bernd Heinold, and Manuela van Pinxteren

Marine organic aerosol is a major contributor to cloud condensation nuclei and ice nucleating particles over pristine open-ocean and coastal regions and thus has an important impact on radiation, precipitation, and atmospheric dynamics. In the Arctic, the summer-time loss of sea ice together with the rapid ice retreat are key factors for potentially increased marine aerosol emissions. In our planned studies with the aerosol-climate model ICON-HAM, we want to investigate the influence of primary marine organic aerosol on the Arctic climate and its rapid warming. Currently, the model development focuses on the implementation of a detailed, species-resolved ocean emission scheme. Here, we present the first results of an offline version following Burrows et al. (2014). The new emission scheme has been applied in ICON-HAM. This allows for including the marine organic aerosol’s life cycle and interactions with mixed–phase Arctic clouds, focusing on potential ice-active species.

How to cite: Leon, A., Heinold, B., and van Pinxteren, M.: Modelling marine organic aerosol and its impact on clouds in the Arctic , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8559, https://doi.org/10.5194/egusphere-egu22-8559, 2022.

17:54–18:00
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EGU22-1968
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On-site presentation
Antonio Donateo, Gianluca Pappaccogli, Mauro Mazzola, Stefano Decesari, and Daniela Famulari

Aerosols represent a fundamental component of the atmosphere, and their behaviour in the Arctic surface layer determines deposition on snow or ice surfaces. Deposition processes lead to a decrease in the snow albedo enhancing its melting, which has major impacts on climate change in polar regions, particularly in the Arctic. Many aerosols properties have been investigated in the Arctic region, with regards to chemical composition (Quinn et al, 2009; Köllner et al, 2021), total number and mass concentrations (Croft et al, 2016), optical properties (Ferrero et al, 2019), their ability to act as cloud condensation nuclei (Bulatovic et al., 2021), their number and size distribution (Lupi et al., 2016). Relatively few cases exist of aerosol deposition measurements on snow or iced surfaces, especially by eddy‐correlation (EC) method. The first example was reported by Duann et al. (1988), who analysed deposition of particles in two size ranges (0.15–0.30 and 0.5–1.0 mm) using the EC in a snow covered field in central Pennsylvania. Successively, the deposition velocity of particles larger than 10 nm in diameter over an iced surface in the Arctic (Nilsson and Rannik, 2001) and Antarctic (Contini et al, 2010) was measured using the EC method. The aim of the present work is to analyse the deposition velocity of atmospheric particles on snow surfaces at Ny-Ålesund (Svalbard Islands) in relation to local micrometeorological conditions. This work reports an analysis of the concentration, size distribution, and size segregated deposition velocity of atmospheric particles. Measurements were performed using the eddy‐correlation method at the research laboratory of Gruvebadet from March to August 2021. The measurement system was based on a condensation particle counter (CPC) able to measure particles down to 5 nm in diameter with a 50% efficiency and an Optical Particle Counter (OPC) for evaluating particle size fluxes in the accumulation mode (0.25 < dp < 0.58 μm) and coarse mode (0.65 < dp < 3 μm). The average number concentration was 595 cm−3, 25 cm−3 and 0.7 cm−3 for ultrafine, accumulation and coarse particles mode. Higher concentrations were observed at low wind velocities. Results gave an average deposition velocity of 3.66 mm/s for ultrafine particles. Deposition velocity was 18.89 mm/s and 52.83 mm/s for accumulation and coarse particles, respectively. Deposition increased with friction velocity. We present an overview of the results discussed in terms of average concentration, deposition velocity, and the relationship between deposition, friction velocity, and atmospheric stability.

Bulatovic et al., Atmospheric Chemistry and Physics, 21, 3871-3897, 2021
Contini et al., Journal of Geophysical Research, 115, 2010
Croft et al., Atmospheric Chemistry and Physics, 16, 3665-3682, 2016
Duann, B., Journal of Applied Meteorology, 27, 642-652, 1988
Ferrero et al., Science of the Total Environment 686, 452-467, 2019
Köllner et al., Atmospheric Chemistry and Physics, 21, 6509-6539, 2021
Lupi et al., Rendiconti Lincei – Scienze Fisiche e Naturali, ISSN 2037-4631, 27, 2016
Nilsson, E.D., and U. Rannik, Journal of Geophysical Research 106(D23), 32125-32137, 2001
Quinn et al., Atmos. Chem. Phys., 9, 8883-8888, 2009

How to cite: Donateo, A., Pappaccogli, G., Mazzola, M., Decesari, S., and Famulari, D.: Characterization of size-segregated turbulent fluxes and deposition velocity by eddy correlation method in an Arctic site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1968, https://doi.org/10.5194/egusphere-egu22-1968, 2022.

18:00–18:06
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EGU22-9595
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ECS
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On-site presentation
Julia Maillard, François Ravetta, Jean-Christophe Raut, Gilberto Fochesatto, and Kathy Law

The pre-ALPACA (Alaskan Layered Pollution And Chemical Analysis) 2019 winter campaign took place in Fairbanks, Alaska, in November—December 2019. One objective of the campaign was to study the life-cycle of surface-based temperature inversions and the associated surface energy budget changes. Several instruments, including a 4-component radiometer and sonic anemometer were deployed in the open, snow-covered UAF Campus Agricultural Field. The surface energy budget at the UAF field exhibited two preferential modes. In the first mode, turbulent sensible heat and net longwave fluxes were close to 0 W m−2 , linked to the presence of clouds and generally low winds. In the second, the net longwave flux was ≈ -50 W m−2 and the turbulent sensible heat flux was ≈ 15 W m−2 , linked to clear skies and the presence of a local flow. The development of surface temperature inversions at the UAF field was hindered compared to other locations in Fairbanks because the flow sustained vertical mixing. Indeed, the wind speed at 2 m was around 5 m s-1, above the estimated critical wind speed threshold for sustainable turbulence in the MWST (Minimum Wind speed for Sustainable Turbulence) framework. Despite the clear skies, the local flow maintained a weakly stable state of the boundary layer.

These results suggest there is significant variability of Arctic boundary-layer stability due to variations in the near surface wind speed, even in anticyclonic, clear-sky conditions. Accurate representation of the stable boundary-layer by meso-scale models therefore requires that they reproduce the wind-driven transition between weakly stable and strongly stable states correctly. The impact of parameters such as stability functions and roughness length on the modelled transition thus represents an important follow-up question to this study.

How to cite: Maillard, J., Ravetta, F., Raut, J.-C., Fochesatto, G., and Law, K.: Impact of wind speed variability on the surface energy balance and boundary-layer stability in central Alaska, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9595, https://doi.org/10.5194/egusphere-egu22-9595, 2022.

18:06–18:12
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EGU22-6621
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ECS
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On-site presentation
Freya Squires, Thomas Barningham, Anna Jones, Mike Rose, James France, Rolf Weller, and Linda Ort

The British Antarctic Survey (BAS) operates one of the most remote, advanced, and scientifically important research stations on the Antarctic continent – Halley. Located on the floating Brunt ice shelf, the station has provided meteorological and atmospheric observations since it was established in 1956. However, in the face of glaciological uncertainty, Halley Research Station had to close for the first time in its history during winter 2017. To overcome the subsequent data loss from the unmanned research station, engineering and science teams at BAS began automating the station.

In 2018-19, the Halley automation project began with scientific equipment adapted and the installation of an innovative micro-turbine electrical generator. Science experiments ran uninterrupted throughout the nine-month winter period, with the station preserving core science data streams such as Meteorology and Ozone Monitoring, Tropospheric Chemistry and Climate, and Space Weather and Upper Atmospheric Observations. The system proved its ability to withstand the Antarctic environment during the 2019 winter; unaffected by ambient temperatures as low as -55˚C and winds gusting up to 70 knots.

Work is ongoing to automate and reinstate the long-term atmospheric monitoring experiments at Halley. In December 2021, a new automated CO2 and CH4 analyser was installed in Halley’s Clean Air Sector (CAS) laboratory which will run continuously over the coming Antarctic winter. Halley’s coastal location provides an ideal platform to explore air-sea CO2 exchange in the Southern Ocean region. The Southern Ocean is a globally important carbon sink, estimated to account for ~75% of global ocean CO2 uptake but a sparsity of observations in the region has contributed to uncertainty around the inter-annual and seasonal nature of the Southern Ocean sink.

CO2 mixing ratios have been measured at Halley at high temporal resolution since 2013. Before the installation of the new autonomous system at Halley, measurements were relocated to the German coastal Antarctic research station, Neumayer, at the end of 2017. Both the Halley and Neumayer records show short-term variability in CO2 mixing ratios during the summer, with up to ~0.5 ppb decreases in CO2 over the course of a day, about 1/6 of the average annual growth rate. Trajectory analysis suggests that these decreases in mixing ratio correspond to periods where the air sampled has spent time over the Southern Ocean, suggesting CO2 uptake has occurred. This work will explore the possible drivers for the short-term variability in CO2 mixing ratios. An overview of the automation work carried out so far at Halley and plans for future seasons will also be presented.

How to cite: Squires, F., Barningham, T., Jones, A., Rose, M., France, J., Weller, R., and Ort, L.: Short-term variability in atmospheric carbon dioxide as observed from coastal Antarctica and an introduction to the Halley Autonomous Long-term Observational Science (HALOS) Platform , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6621, https://doi.org/10.5194/egusphere-egu22-6621, 2022.

18:12–18:18
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EGU22-6354
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On-site presentation
William Neff, Christopher Cox, and Mathew Shupe

Several observational programs have studied the atmospheric boundary layer (ABL) at South Pole Station, Antarctica, and Summit Station, Greenland, both sites at about 3km ASL on icecaps in both polar regions. In these field programs sodars played a key role in documenting the behavior of the boundary layer under distinctly different weather regimes: At the South Pole, high on the Antarctic ice sheet, the ABL is far from the Southern Ocean storm track and often exhibits prolonged quiescent cold spells punctuated by warm advection events above a shallow stable ABL[Keller et al., 2021; W D Neff, 1999]. Summit Station is adjacent the Atlantic storm track and influenced by extratropical storms with attendant Atmospheric Rivers [Mattingly et al., 2018; W Neff, 2018; W Neff et al., 2014], decaying hurricanes, and large-scale Atlantic blocking events that bring warm air and clouds over the relatively smaller icesheet. 

Sodar data from the South Pole were gathered in 1977, 1978, 1993, and 2003 (the final year in support of the Antarctic Tropospheric Chemistry Investigation, ANTCI [W Neff et al., 2018]).  Summit Station has seen sodar operations that started in 2008 in support of studies of the dynamics of ozone and nitrogen oxides at Summit Station [Van Dam et al., 2013] and beginning in 2010, extending through early 2021, in support of the ICECAPS (Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit) study of cloud and radiation influences on the energy balance over the ice sheet [Shupe et al., 2013].  Of particular interest at Summit Station is the internal boundary structure observed during fog episodes [Cox et al., 2019] and during changes in synoptic weather patterns e.g. Figure 3 in [Shupe et al., 2013] which also shows examples of supporting remote sensing observations. In this presentation we will compare and contrast sodar observations taken at these two icecap sites and describe several interesting events occurring in the last several summers over the Greenland icecap as seen in sodar and supporting observations at Summit Station.

 

Cox, C. J., D. C. Noone, M. Berkelhammer, M. D. Shupe, W. D. Neff, N. B. Miller, V. P. Walden, and K. Steffen (2019), Atmospheric Chemistry and Physics, 19(11), 7467-7485, doi:10.5194/acp-19-7467-2019.

Keller, L. M., K. J. Maloney, M. A. Lazzara, D. E. Mikolajczyk, and S. Di Battista (2021), Journal of Climate, 1-35, doi:10.1175/jcli-d-21-0404.1.

Mattingly, K. S., T. L. Mote, and X. Fettweis (2018), Journal of Geophysical Research: Atmospheres, doi:10.1029/2018JD028714.

Neff, W. (2018)Nature Climate Change, 8(10), 857-858, doi:10.1038/s41558-018-0297-4.

Neff, W., G. P. Compo, F. M. Ralph, and M. D. Shupe (2014),  Journal of Geophysical Research-Atmospheres, 119(11), 6520-6536, doi:10.1002/2014jd021470.

Neff, W., J. Crawford, M. Buhr, J. Nicovich, G. Chen, and D. Davis (2018), Atmos. Chem. Phys., 18(5), 3755-3778, doi:10.5194/acp-18-3755-2018.

Neff, W. D. (1999),, Journal of Geophysical Research: Atmospheres, 104(D22), 27217-27251, doi:https://doi.org/10.1029/1999JD900483.

Shupe, M. D., et al. (2013),  Bull. Amer. Meteorol. Soc., 94(2), 169-+, doi:10.1175/bams-d-11-00249.1.

Van Dam, B., D. Helmig, W. Neff, and L. Kramer (2013), Journal of Applied Meteorology and Climatology, 52(10), 2356-2362, doi:10.1175/jamc-d-13-055.1.

How to cite: Neff, W., Cox, C., and Shupe, M.: A bipolar perspective of the boundary layer and associated synoptic influences at South Pole Station, Antarctica and Summit Station, Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6354, https://doi.org/10.5194/egusphere-egu22-6354, 2022.

18:18–18:24
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EGU22-2959
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Virtual presentation
Sulphate source apportionment by a 10 yr-long record at Ny-Ålesund (Svalbard Islands)
(withdrawn)
Rita Traversi, Alessandra Amore, Silvia Becagli, Laura Caiazzo, Fabio Giardi, Mauro Mazzola, and Mirko Severi