21 February 2023 | 14:00 - 15:30 (GMT+1)
21 February 2023 | 16:00 - 18:00 (GMT+1)
Open Session - HYBRID
Room: Hörsaal 2
Session Conveners: Priscilla A. Mooney (NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Norway); Risto Makkonen (Finnish Meteorological Institute / University of Helsinki, Finland); Jennie Thomas (Université Grenoble Alpes, CNRS, IRD / Sorbonne Université, UVSQ, CNRS, France)
The interactions between the atmosphere, ocean and sea ice play an important role in shaping the polar climates. However, existing knowledge of the physical, chemical, and biogeochemical processes that underly the exchanges of mass, energy and momentum between these components remain poorly understood.
Closing knowledge gaps on the interactions between the atmosphere, ocean and sea-ice can considerably advance our ability to understood recent changes, and anticipate future changes in the Arctic and Antarctic climate systems. In particular, closing these knowledge gaps will improve our ability to represent them in our modelling systems and increase confidence in projections of future climate change in the polar regions.
This session will highlight 1) recent advances in our knowledge of atmosphere-ocean-sea ice interactions and 2) new and emerging tools and datasets that can close these knowledge gaps.
We welcome observational and numerical modelling studies of physical and chemical atmospheric and ocean processes that underly interactions in the coupled climate system in both the Arctic and Antarctic. This includes but is not limited to:
- Cloud microphysics and aerosol-cloud interactions, and their role in the coupled system;
- Atmospheric Boundary Layer (ABL) dynamics and its interactions with the sea-ice surface;
- Sea ice dynamics and thermodynamics, e.g. wind driven sea-ice drift, snow on ice;
- Upper ocean mixing processes;
- Sea ice biogeochemistry and interactions at interfaces with sea ice;
- Snow on sea ice and it’s role in the coupled ocean-ice-atmosphere system;
- Surface energy budget of the coupled system, including contributions of ABL-dependent turbulent fluxes, clouds and radiative fluxes, precipitation and factors controlling snow/sea ice albedo.
Presentations showcasing recent or emerging tools, observational campaigns, or remote sensing datasets are encouraged.
unfold_moreSea ice: An extraordinary and unique, yet fragile, biome
Letizia Tedesco1; Eric Post
1Marine and Freshwater Solutions Unit
Sea ice – a unique and extraordinary biome in its nature and dynamics – is under threat. I will review here how ocean warming, sea-ice decline, and altered seasonality endanger the simple, vulnerable, and low resilient sea-ice and ice-associated food webs in both polar oceans.
unfold_moreSea ice production in the 2016 and 2017 Maud Rise polynyas
Lu Zhou1; Céline Heuzé1
1University of Gothenburg
Sea ice production within polynyas, an outcome of the atmosphere - ice - ocean interaction, is a major source of dense water and hence key to the global overturning circulation, but is poorly quantified over open-ocean polynyas. Using the two recent extensive open-ocean polynyas within the wider Maud Rise region of the Weddell Sea in 2016 and 2017, we here explore the surface ice energy budget and estimate their ice production based on satellite retrievals, in-situ hydrographic observations, and the Japanese 55-year Reanalysis (JRA55). We find that the oceanic heat flux amounts to 36.1 and 30.7 W m-2 within the 2016 and 2017 polynyas, respectively. We find that the 2017 open-ocean polynya produced nearly 200 km3 of new sea ice, which is comparable to the production in the largest Antarctic coastal polynyas. Finally, we find that ice production is highly correlated with the 2 m air temperature and wind speed, which affect the turbulent fluxes. It is also highly sensitive to uncertainties in the atmospheric air temperature and mixed layer depth, which urgently need to be better monitored at high latitudes.
unfold_moreImpact of Atmospheric Rivers on Poleward Moisture Transport and Sea Ice on Interannual Timescales
University of Groningen
The projected increase in poleward moisture transport (PMT) towards warmer climate has mainly been linked to the larger moisture holding capacity of warmer air masses. However, the future of interannual fluctuations of PMT is fairly uncertain, as are the drivers of these year-to-year fluctuations. The presented study demonstrates the extent to which atmospheric rivers (ARs) explain the interannual variability of PMT, as well as related variables such as temperature and precipitation. Such linkages help to clarify if extreme precipitation or melt events over Arctic regions are dominantly caused by the occurrence of ARs. A main focus is set on the impact of ARs on Arctic sea ice on interannual timescales, which so far has been poorly studied, and varies from colder to warmer climates. To robustly study these interannual linkages of ARs and Arctic Climate, this study examines Arctic ARs in long climate runs of one present and two future climates (+2°C and +3°C), simulated by the global climate model EC-Earth 2.3. To enhance the significance of the results, three different moisture thresholds were used to detect ARs. Further, the use of additional thresholds relative to the 2°C and 3° warmer climates allowed a distinction between thermodynamic and dynamic processes that lead to changes of ARs from colder to warmer climates. It is found that most PMT variability is driven by ARs, and that the share of ARs which explain moisture transport increases towards warmer climates. Moreover, the study presents a strong correlation between ARs and precipitation and temperature in all climates, while the impact of AR variability on sea ice extent is more complex and strongly depends on the season.
unfold_moreNew Insights into Cyclone Impacts on Sea Ice in the Atlantic Sector of the Arctic Ocean in Winter
Lars Aue1; Timo Vihma2; Petteri Uotila3; Leonie Röntgen1; Wolfgang Dorn1; Gunnar Spreen4; Annette Rinke1
1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research; 2Finnish Meteorological Institute; 3University of Helsinki; 4University of Bremen
Transient cyclones are a dominant feature of short-term atmospheric variability in the Arctic winter impacting local wind speed and direction and transporting heat and moisture from lower latitudes to the Arctic. Consequences for the Arctic sea ice cover are increased wind-induced ice drift and deformation as well as ice melt or reduced ice growth due to increased downward fluxes of longwave radiation and sensible heat at the snow/ice surface. Based on the ERA5 reanalysis and a storm tracking algorithm, we report on statistically significant impacts of transient cyclones on sea ice concentration (SIC) in the Atlantic sector of the Arctic Ocean in winter under 'New Arctic' conditions (2000 - 2020). A reduction in SIC is found prior to and during cyclones for the whole study domain, while an increase in SIC following cyclones is limited to the Barents Sea. This results in a regional difference between increased SIC in the Barents Sea and reduced SIC in the Greenland Sea as the net effect from 3 days prior to 5 days after the cyclone passage. Hereby, largest SIC changes occur during intense cyclones, in particular when preconditioned by locally low to medium SIC. We further provide evidence that cyclone impacts on SIC have amplified compared to the 'Old Arctic' (1979 - 1999), particularly in the Barents Sea. To decompose cyclone impacts on sea ice into dynamics and thermodynamics, we analyze three intense winter cyclones that occurred in February 2020 in the Barents Sea utilizing nudged coupled model simulations. The first results indicate that the response of the sea ice cover to cyclones is dominated by dynamic processes in winter, while the advection of warm and moist air masses only plays a secondary role on timescales of a few weeks.
unfold_moreTowards more precise comparisons of complete coupled Arctic budgets from observations, reanalyses and CMIP6
Susanna Winkelbauer1; Leopold Haimberger1; Michael Mayer1
1University of Vienna
We assess various Arctic energy and water budget components in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Oceanic exchanges across the Arctic main gateways play a crucial role in shaping the Arctic climate. However, the calculation of oceanic transports is not always straight forward, as oceanic models often use rotated/distorted model grids to avoid singularities over the ocean. We developed a tool that enables transport calculations at any given oceanic section on various model grids used in ocean reanalyses and throughout CMIP6 (e.g., various versions of NEMO, MOM, LICOM). Transports are calculated by either using line integrals (summing up transports on the native grid along a continuous line) or by using vector projection algorithms. The second method is useful for instance to visualize currents and temperature profiles in the vertical plane of any oceanic section.
We use those tools to compare transport estimates in the main Arctic gateways from reanalyses and CMIP6 models, to those gained from observations. Beyond this, we diagnose other major energy and water budget terms of atmosphere, ocean, and sea ice (lateral transports, exchanges at the surface, storage rates) from the CMIP models and validate them against consistent observationally constrainted estimates.
unfold_moreReducing parametrization errors for polar surface turbulent fluxes using machine learning
Donald Cummins1; Virginie Guemas1; Sebastien Blein1; Ian Brooks2; Ian Renfrew3; Andrew Elvidge3
1Centre National de Recherches Météorologiques; 2University of Leeds; 3University of East Anglia
In this study,new data-driven parametrizations have been developed for surface turbulent fluxes of momentum, sensible heat and latent heat in the Arctic. rely on sparse observations.(i.e. representing the form drag, or the presence of ridges) developed specifically for polar conditions Parametrizations the conditions found in the Arctic.require specific tuning towhich anddeveloped using data from the tropics or mid-latitudes initially which wereFluxes are typically calculated using bulk formulas, based on the Monin-Obukhov similarity theory, GCMs. in sea ice over esturbulent heat fluxface rsuof parametrizationstheremain in large model errors And yet, . teleconnections between the Arctic and non-polar regionsand potentially the development of atmospheric circulation anomalies, melting rate, sea ice influence the Arctic are known toatmosphere the between sea ice and sHeat exchange Recent observational campaigns promise to provide new observations of turbulent fluxes in the Arctic. As well as enabling validation of existing bulk formulations developed for polar conditions, the new observationsraise the possibility of entirely data-driven flux parametrizations. Machine learning has already been used outside the polar regions to provide accurate and computationally inexpensive flux estimates. To investigate the feasibility of this approach in the Arctic, we have used observations from a reference dataset (SHEBA) to develop data-driven parametrizations of surface turbulent fluxes. Accuracy of the new parametrizations has been tested using data from other observational campaigns andis found to be comparable toand in some cases substantially better than that of state-of-the-art bulk formulations.
unfold_moreUsing a 1km model to explore the role of aerosol-cloud interactions in Arctic atmosphere-ice-ocean relationships
Ruth Price1; Andrew Orr1; Paul Field2
1British Antarctic Survey; 2UK Met Office
Low-level clouds are strongly coupled to the behaviour of Arctic sea ice. The presence or absence of clouds can exert a major control on the net surface radiation, in turn influencing the onset of the melting and freezing seasons. However, such interactions between clouds and the surface are themselves controlled by the surface albedo, creating a system of complex interactions that are difficult to untangle.Low-level Arctic clouds are particularly sensitive to aerosol-cloud interactions, since cloud condensation nuclei (CCN) concentrations and cloud droplet number concentrations (CDNC) can be low, particularly in summer. However, previous modelling studies have struggled to capture this important link, in part due to the use of fixed aerosol concentrations, CCN concentrations, or CDNC which cannot properly simulate the way conditions change.Here, we use a the UK Met Office Unified Model (UM) in a 1 km resolution regional configuration to model case studies of different sea ice conditions in the Arctic. The model uses two-moment cloud and aerosol microphysics scheme, which enables prognostic calculation of CDNC from online aerosol concentrations. This represents the state-of-the-art in aerosol-cloud interaction modelling.We will present the first results from the case studies using the UM, including simulations of the Arctic Ocean 2018 icebreaker campaign. This work is being carried out as part of the PolarRES project.
unfold_moreEvaluation of Arctic aerosol and low-level cloud properties within NorESM2 and WRF-Chem using observations from the Arctic Ocean 2018 expedition at the North pole
Julia Asplund1; Rémy Lapere2; Jennie L. Thomas2; Louis Marelle3; Paul Zieger1; Sara Blichner1; Annica Ekman2; Julia Schmale4
1Stockholm University; 2Université Grenoble Alpes; 3Sorbonne Université; 4Extreme Environments Research Laboratory
The abundance of aerosol particles is typically very low in the Arctic. This means that small changes to source or growth processes can result in relatively large changes to the aerosol population. Aerosol particles are necessary to form cloud droplets in atmospheric conditions, and therefore these changes also affect the physical properties of Arctic clouds. They are a major component in the radiation budget over the region, and may thereby also have a key role in the enhanced warming of the Arctic, i.e. the Arctic Amplification. Current and future warming of the Arctic region will further change the role of aerosols in the climate system, and models are essential tools for investigating how. However, neither Arctic aerosol source and growth processes, nor aerosol-cloud interactions, are adequately represented in current climate models, making them an important contributor to the overall uncertainties in projecting future climate in the region. We present an evaluation of the performance of NorESM2, a global model (participant of the sixth Coupled Model Intercomparison Project), and WRF-Chem, a regional model, regarding Arctic aerosol and low-level clouds specifically. Observations from the Arctic Ocean 2018 campaign on board the Swedish icebreaker Oden of aerosol size distributions, chemical composition, and cloud properties at ship level, are compared with corresponding parameters in the model outputs. Using model simulations with nudged meteorology and high frequency output allows us to make a detailed comparison between the output and observations, highlighting key weaknesses and pathways for improvements in the models.
unfold_moreInvestigating the horizontal and vertical variability of aerosol particles affected by a shallow atmospheric boundary layer observed with two airborne systems during MOSAiC
Barbara Harm-Altstädter1; Christian Pilz2; Falk Pätzold1; Lutz Bretschneider1; Sven Bollmann1; Andreas Schlerf1; Magnus Asmussen1; Konrad Bärfuss1; Ralf Käthner2; Birgit Wehner2; Astrid Lampert1
1Technische Universtität Braunschweig; 2Leibniz Institute for Tropospheric Research
A more profound understanding of formation, mixing and transport of aerosol particles is of crucial importance in the Arctic atmospheric boundary layer (ABL). In particular, as aerosol particles are considered to be one of the most important factors in causing uncertainties of future scenarios regarding the Arctic Amplification. In order to assess a detailed 4-dimensional picture of aerosol particles and their interaction with atmosphere and sea ice, two different airborne systems were deployed for field activity during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition. The helicopter-borne system HELiPOD was mainly applied for investigating the horizontal variability close to sea ice during transects of 45-60 km lengths and the tethered balloon-borne system BELUGA-CAMP performed vertical profiles up to a height of 1 km. Both systems are equipped with meteorological instrumentation and aerosol sensors for measuring the aerosol particle number concentration of different sizes (e.g. nucleation and accumulation mode), as well as for identifying black carbon mass concentration (BC) via particle light absorption coefficient. This study focuses on observations that were carried out during mainly clear sky on 22 July 2020. The investigation area was influenced by a shallow ABL, wind speed of 9 m/s in the lowermost 150 m and clean air masses which originated from Greenland. The stably stratified ABL suppressed mixing processes, so that a sharp gradient of Aitken mode particles occurred in the vertical scale. However, the horizontal observations show a generally homogeneous distribution of aerosol particles, leading to the assumption of a regional particle source at the measurement site.
unfold_morePolar sea-salt aerosols in CMIP6 models
Rémy Lapere1; Jennie L. Thomas1; Louis Marelle2
1Université Grenoble Alpes; 2Sorbonne Université
We present an inter-comparison of simulated sea-salt aerosols (SSA) in CMIP6 models, including an evaluation against station observations in the Artic and Antarctic regions and satellite data. Drivers of model diversity are investigated. Historical and future trends are also explored and connected to their driving mechanisms. Additionally, the sensitivity of the polar radiative budget to SSA in CMIP6 models is quantified and put in relation to present-day uncertainties and future trends.
Comparisons suggest (i) a large inter-model spread in SSA surface concentrations mostly driven by the diversity in source functions, (ii) an important overestimation of SSA surface concentrations compared to measurement stations but reasonable agreement with optical depth from satellite data, (iii) difficulties in properly capturing the annual cycle of SSA at both poles, particularly at higher latitude. A generally increasing trend in SSA concentrations is found in CMIP6 over the last decades and in future scenarios. CMIP6 models show that SSA contribute to cooling the poles significantly, implying possible uncertainties of several W/m2 in the present-day polar radiative budget.
unfold_moreYear-round satellite measurements of methane concentrations over the Arctic seas
University of Maryland Baltimore County
The diverse range of mechanisms driving the Arctic amplification and global climate are not completely understood and, in particular, the role of the greenhouse gas methane (CH4) in the Arctic warming remains unclear. Strong sources of methane at the ocean seabed in the Barents Sea and other polar regions are well documented. Nevertheless, some of those publications suggest that negligible amounts of methane fluxed from the seabed enter the atmosphere, with roughly 90% of the methane consumed by bacteria. Most in situ observations are taken during summer, which is favorable for collecting data but also characterized by a stratified water column. We present perennial observations of three Thermal IR space-borne spectrometers in the Arctic between 2002 and 2020. According to estimates derived from the data synthesis ECCO (Estimating the Circulation and Climate of the Ocean), in the ice-free Barents Sea the stratification in winter weakens after the summer strong stability. The convection, storms, and turbulent diffusion mix the full-depth water column. CH4 excess over a control area in North Atlantic, measured by three sounders, and the oceanic Mixed Layer Depth both maximize in winter. A significant seasonal increase of sea-air exchange in ice-free seas is assumed. The amplitude of the seasonal methane cycle for the Kara Sea significantly increased since the beginning of the century. This may be explained by a decline of ice concentration there. The annual CH4 emission from the Arctic seas is estimated as 2/3 of land emission. The Barents/Kara seas contribute between 1/3 and 1/2 into the Arctic seas annual emission.
unfold_moreThe relative importance of open-ocean sourced sea spray and sea-ice sourced SSA in boundary layer bromine in Ny-Ålesund, Svalbard
British Antarctic Survey
Sea salt aerosol (SSA) is a large source of reactive bromine in marine boundary layer. In polar regions, SSA can be generated from open ocean (via wave breaking and bubble bursting) and sea ice (via blowing snow). However, these two types of salts are different in both physical and chemical characters. For example, freshly emitted sea spray is alkaline, while sea-ice sourced SSA is largely acidic. Moreover, they are different in size spectrum and the emission flux under the same wind speeds is also different. Therefore, they may work differently as a direct source of reactive bromine in polar tropospheric chemistry. In this study, we present ground-based BrO vertical column densities derived by Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) deployed at Ny-Ålesund (78.92°N, 11.93°E), Svalbard in March 2017 and then focus on one big bromine explosion event (BEE) observed during 16-18 March. Back trajectory and meteorology data clearly indicated this BEE is associated with a transported cyclone: before UTC 6 March 16 Svalbard was mainly under open ocean influence, followed by sea ice influence after that time. MAX-DOAS data show BrO surges from a background level on March 16 to a peak of 1.23×1015 molec/cm2 on March 17. We used global chemistry transport model (p-TOMCAT) to reproduce this event, and the model result confirms that it is sea-iced sourced SSA rather than sea spray causing the BEE and and near surface ozone depletion