Session CR7.7

CR7.7 | Atmosphere-ocean-ice interactions in the polar climate system

Atmosphere-ocean-ice interactions in the polar climate system

Co-organized by AS4/CL2

Convener: Priscilla Mooney | Co-conveners: Konstanze HaubnerECSECS, Risto Makkonen, Chen ZhaoECSECS, Jennie L. Thomas, Jan Landwehrs, Christoph KittelECSECS

Orals

| Thu, 18 Apr, 16:15–18:00 (CEST)

Room 1.34

Posters on site

| Attendance Thu, 18 Apr, 10:45–12:30 (CEST) | Display Thu, 18 Apr, 08:30–12:30

Hall X5

The interactions between the atmosphere, ocean and 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 ice can considerably advance our ability to understand 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-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 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 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/ice albedo.
Presentations showcasing recent or emerging tools, observational campaigns, or remote sensing datasets are encouraged.

Orals: Thu, 18 Apr | Room 1.34

Chairpersons: Priscilla Mooney, Jennie L. Thomas

16:15–16:20

5-minute convener introduction

16:20–16:30

EGU24-5813

ECS

On-site presentation

Antarctic sea ice sensitivity to the orographic gravity wave drag in a fully coupled climate model

Maria Vittoria Guarino, Jeff Ridley, Riccardo Farneti, Fred Kucharski, and Adrian Tompkins

Low-level winds over Antarctica are overwhelmingly controlled by the local orography. They, in turn, exert a large control on sea ice formation and transport.

In Global Circulation Models, the influence of orography on the climate system is modelled via orographic gravity wave drag (OGWD) parameterizations. Models usually partition the drag exerted on the atmosphere by the sub-grid scale orography into two components due to flow blocking and gravity waves.

In this work, we investigate the relationship between Antarctic sea ice and the parameterized OGWD in the UK Earth System Model (UKESM). We present results from sensitivity tests performed using the UKESM-CMIP6 historical runs.
In these simulations, the partition between the “flow-blocking” component and the “gravity wave” component of the OGWD parameterization was altered to simulate “flow-over” and “flow-blocking” regimes. These experiments show that sea ice strongly responds to changes in the orographic gravity wave drag. The strong sea ice decline simulated by the control run from 1980 to 2015, not matched by the observational record, is halted and is delayed by 15-20 years (across the ensemble members) in our flow-blocking regime simulation. Conversely, in the flow-over regime simulation, sea ice begins declining about 10 years earlier than in the control run. The systematic response of the coupled system suggests the existence of a dynamical relationship between sea ice and OGWD.

The pan-Antarctic signal for sea ice decline derives from the Weddell Sea sector. The pathway through which OGWD influences sea ice is via modifications of the flow regime across the Antarctic Peninsula, and thus the surface wind stress across the Weddell Sea sector, which in turn alters the occurrence of oceanic deep convection. This happens because the flow regime across the Antarctic Peninsula is critical in determining the strength and pattern of the surface winds on both the windward side (Bellingshausen and Amundsen Seas sector) and the lee side (Weddell Sea sector) of the mountain ridge.

How to cite: Guarino, M. V., Ridley, J., Farneti, R., Kucharski, F., and Tompkins, A.: Antarctic sea ice sensitivity to the orographic gravity wave drag in a fully coupled climate model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5813, https://doi.org/10.5194/egusphere-egu24-5813, 2024.

16:30–16:40

EGU24-11497

On-site presentation

How well do the regional atmospheric, oceanic and coupled models describe the Antarctic sea ice albedo?

Kristiina Verro, Cecilia Äijälä, Roberta Pirazzini, Damien Maure, Willem Jan van de Berg, Petteri Uotila, and Xavier Fettweis

A realistic representation of the Antarctic sea ice surface albedo, especially during the melting period, is essential to obtain reliable atmospheric and oceanic model predictions. Antarctic sea ice cover influences the atmosphere by reflecting solar radiation and acting as a barrier between the atmosphere and the ocean, for example. The Antarctic sea ice consists of ice floes of varying thickness, usually covered by snow, and broken up by cracks, leads and polynyas. Therefore, the optical properties of sea ice can vary greatly.

We use regional atmospheric (HCLIM-AROME), oceanic (MetROMS-UHel) and coupled (MAR-NEMO) models to compare the representation of the basic sea ice characteristics: sea ice albedo, snow and ice thickness, and meteorological data during the melt periods of two Antarctic domains with very different sea ice conditions, using data of the ISPOL and Marsden field campaigns. During the ISPOL campaign (Dec 2004; Hellmer et al. 2008) RV Polarstern was moored to an ice floe in the Weddell Sea, where snow-covered multi-year ice persists. The Marsden field campaign (Nov. 2022; Dadic et al. 2023) was established over 2.4m thick land-fast ice of McMurdo Sound, where snow thickness ranged from 0 to 40 cm in patches over the roughest ice. We aim to bridge the models to observations, by comparing model output to various levels of observations, from in-situ measurements of the ISPOL and Marsden campaigns to smaller/larger scale satellite observations over Weddell and Ross Seas.

The first comparisons revealed that HCLIM, with a simplistic 1D thermodynamic sea ice scheme (SICE, Bartrak et al. 2018), was underestimating snow albedo up to 30%, and needed retuning for Antarctic conditions. Overall, preliminary results indicate that the models do well reproducing the snow-covered sea ice during the ISPOL campaign, when the weather was warm, with the air temperature mostly above −5◦C. MetROMS-UHel, which uses the Delta-Eddington multiple scattering radiative transfer model to calculate the sea ice albedo, even reproduced similar diurnal variability than observed. The Marsden field campaign took place in an area of complex topography, cold weather conditions, and greatly varying sea ice. The models tend to overestimate the albedo of the land-fast ice of the Marsden field campaign, as a uniform, instead of patchy, snow layer is modelled. Models also cannot reproduce the variety of sea ice, such as freshly formed ice, in the McMurdo Sound area apparent on the satellite images.

How to cite: Verro, K., Äijälä, C., Pirazzini, R., Maure, D., van de Berg, W. J., Uotila, P., and Fettweis, X.: How well do the regional atmospheric, oceanic and coupled models describe the Antarctic sea ice albedo?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11497, https://doi.org/10.5194/egusphere-egu24-11497, 2024.

16:40–16:50

EGU24-12637

ECS

On-site presentation

Does Strength Matter? An Exploration into Cyclone Strength and the Impact on Arctic Sea Ice

Elina Valkonen, Chelsea Parker, and Linette Boisvert

Arctic cyclones are an integral part of the polar climate system. They import moisture and energy from the midlatitude and impact the underlying surface through dynamic adn thermodynamic interactions. The rapid warming and sea ice decline in the Arctic makes it more important than ever to understand the tightly coupled interactions between the Arctic sea ice and episodic weather events, such as cyclones.

In this presentation, we use a Lagrangian ice parcel database to study the impact different strength cyclones have on the Arctic Sea ice. The database includes daily 25km Arctic ice parcel tracks and associated atmospheric and sea ice conditions, including passing cyclone track data from 2002-2021. We divide these cyclone tracks into three distinctive groups based on their central pressure and average wind speed. After this, we split the ice parcel tracks and associated atmospheric data based on these cyclone groups: ice affected by weak cyclones, ice affected by normal cyclones, and ice affected by extreme cyclones.

We will then utilize these parcel groups to study the atmospheric conditions (precipitation, temperature, radiative balance) and sea ice changes for three days before, during, and three days after the cyclone passes. We will average the ice parcel and associated atmospheric variable data over the ice parcel life cycle and across the before, during, and after cyclone pass timescales. We will then apply statistical pattern recognition on these averaged sea ice and atmospheric variable fields. This analysis will allow us to better understand the role cyclone strength has in cyclone-sea ice interactions. We will present these results separately for individual seasons, locations, and surrounding SIC.

How to cite: Valkonen, E., Parker, C., and Boisvert, L.: Does Strength Matter? An Exploration into Cyclone Strength and the Impact on Arctic Sea Ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12637, https://doi.org/10.5194/egusphere-egu24-12637, 2024.

16:50–17:00

EGU24-12913

On-site presentation

Do clouds care about aerosol from sea ice sources (blowing snow, open leads) during Arctic winter/ spring? – a case study from MOSAiC 2019-20

Markus Frey, Floor van den Heuvel, Amélie Kirchgäßner, Simran Chopra, Thomas Lachlan-Cope, Ronny Engelmann, Albert Ansmann, Heike Wex, Ananth Ranjihkumar, Xin Yang, Jessica Mirrielees, Kerri Pratt, Ivo Beck, Julia Schmale, and Xianda Gong

Aerosols play a key role in Arctic warming via radiative direct and indirect effects. It is well-known that increased aerosol concentration due to Arctic haze raises cloud longwave emissivity, resulting in surface warming. Recently, a MOSAiC study demonstrated that blowing snow above sea ice generates fine sea salt aerosol, which results in up to tenfold enhancement of cloud condensation nuclei leading to potentially significant surface warming rivalling that due to Arctic haze. Yet, radiative properties of aerosol emitted by sea ice sources, vertical coupling and interaction with clouds remain major uncertainties in quantifying the aerosol impact on Arctic climate change.

We use MOSAiC observations to analyse the coupled ocean-ice/snow-atmosphere system and assess contributions of sea ice sources (blowing snow, open leads) to atmospheric cloud-forming particles in particular ice-nucleating particles (INP). Choosing the 2020 winter/spring transition with profound seasonal changes in sea ice and air mass origin, we discuss the importance of sea ice aerosol to low-level clouds in comparison to advected aerosol. We consider measurements of snow particles, physico-chemical properties and INP content of aerosol and snow on sea ice, vertical profiles linking ground observations to the level of cloud formation, and assess climate sensitivity using the UKESM model.

How to cite: Frey, M., van den Heuvel, F., Kirchgäßner, A., Chopra, S., Lachlan-Cope, T., Engelmann, R., Ansmann, A., Wex, H., Ranjihkumar, A., Yang, X., Mirrielees, J., Pratt, K., Beck, I., Schmale, J., and Gong, X.: Do clouds care about aerosol from sea ice sources (blowing snow, open leads) during Arctic winter/ spring? – a case study from MOSAiC 2019-20, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12913, https://doi.org/10.5194/egusphere-egu24-12913, 2024.

17:00–17:10

EGU24-14392

ECS

On-site presentation

Impact of Weakened Antarctic Circumpolar Current on the Northern Hemisphere Climate

Peixi Wang, Yuhui Han, Song Yang, Jun Ying, Zhenning Li, Xichen Li, and Xiaoming Hu

Recent findings show a remarkable linkage between the Northern Hemisphere and Southern Hemisphere climates. Previous studies have focused on the impact of the climate change in the northern high-latitudes on that in the Southern Hemisphere, but few studies concerned the impact of Southern Ocean circulation on the Northern Hemisphere, especially the Arctic climate. In this study, we close the Drake Passage (DP) to slow down the Antarctic Circumpolar Circulation (ACC) in the fully coupled Community Earth System Model, to investigate the impact of weakened ACC on the Northern Hemisphere.

Two model experiments, DP opened and DP closed experiments, are performed. Relative to the DP opened case, a warmer Antarctic with less sea ice cover but a colder Arctic with more sea ice cover appear in the DP closed case resulting from weaker ACC and Atlantic Meridional Overturning Circulation (AMOC). Especially, the changes in surface air temperature in the two poles are largest in winter.

Compared to the DP opened case, the anomalous southward heat transport by weakened ACC is largest in winter, contributing to the winter amplification in the Antarctic. However, the seasonal difference in AMOC change is insignificant. To understand the winter amplification in the Arctic, we further analyze local surface heat flux changes in the Arctic. The anomalous downward longwave radiation and sensible and latent heat fluxes are stored in the ocean in summer and released to the atmosphere in the following winter. Although the ocean heat content warms the surface, the upward sensible and latent heat fluxes cool the surface more significantly in winter. This local atmosphere-ocean-ice interaction contributes to the winter amplification in the Arctic.

When DP is closed, the westerlies become stronger and move poleward in the Northern Hemisphere because of the increased meridional temperature gradients, especially in winter. The change in surface temperature also contribute to the weakening of Aleutian Low in winter. The warming in the Antarctic and the cooling in the Arctic leads to the notable weakening of Hadley circulation in the Southern Hemisphere. Additionally, compared to the DP opened case, the Intertropical Convergence Zone shifts southward and the Walker circulation and trade winds over the Pacific strengthen. These results shed light on understanding the interhemispheric interaction and the pole-to-pole connection.

How to cite: Wang, P., Han, Y., Yang, S., Ying, J., Li, Z., Li, X., and Hu, X.: Impact of Weakened Antarctic Circumpolar Current on the Northern Hemisphere Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14392, https://doi.org/10.5194/egusphere-egu24-14392, 2024.

17:10–17:20

EGU24-15744

ECS

On-site presentation

Topographically constrained tipping point for complete Greenland Ice Sheet melt

Michele Petrini, Meike D. W. Scherrenberg, Laura Muntjewerf, Miren Vizcaino, Raymond Sellevold, Gunter Leguy, William H. Lipscomb, and Heiko Goelzer

A major impact of anthropogenic climate change is the potential triggering of tipping points, such as the complete loss of the Greenland Ice Sheet (GrIS). Currently, the GrIS is losing mass at an accelerated pace, mainly due to a steep decrease in its Surface Mass Balance (SMB, snow accumulation minus surface ablation from melt and associated runoff). Here, we investigate a potential SMB threshold for complete GrIS melt, the processes that control this threshold, and whether it exhibits characteristics commonly associated with tipping points, such as a non-linear response to external forcings. To do this, we adopt a semi-coupled approach, forcing the Community Ice Sheet Model v.2 (CISM2) with different SMB levels previously calculated at multiple elevation classes with the Community Earth System Model v.2 (CESM2). The SMB calculation in CESM2 and the elevation class method allow us to account for the SMB-elevation feedback based on snow/firn processes and energy fluxes at the ice sheet surface. We find a positive SMB threshold for complete GrIS melt of 230±84 Gt/yr, corresponding to a 60% decrease from the GrIS simulated pre-industrial SMB. The ice sheet shows a highly non-linear response to sustained melt, and its final state is determined by the effect of the SMB-height feedback in response to surface melt and Glacial Isostatic Adjustment (GIA). The GrIS is tipping from nearly 50% equilibrium volume towards complete melt when the ice margin in the central west unpins from a coastal region with high bedrock elevation and SMB. We find that this relatively small coastal region is important to determine the ice sheet stability in response to sustained warming. Based on the ice sheet geometry in previous modelling studies of the GrIS during the last interglacial, we suggest that a stabilizing effect of the bedrock topography in the central West might have occurred in the past.

How to cite: Petrini, M., Scherrenberg, M. D. W., Muntjewerf, L., Vizcaino, M., Sellevold, R., Leguy, G., Lipscomb, W. H., and Goelzer, H.: Topographically constrained tipping point for complete Greenland Ice Sheet melt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15744, https://doi.org/10.5194/egusphere-egu24-15744, 2024.

17:20–17:30

EGU24-16827

On-site presentation

Ocean-driven basal channel growth at Fimbulisen

Qin Zhou, Tore Hattermann, Chen Zhao, Rupert Gladstone, Ashely Morris, and Petteri Uotila

Small-scale basal features, such as channels and crevasses, are abundant on many ice shelves. These features may, either directly or via modulating basal melting, impact ice shelf stability and, therefore, also global sea level. However, simulating the effect of these features on ice shelves at a hundred-meter scale or smaller is still challenging even for dedicated regional simulations, which typically ignore the small-scale features and smooth the ice draft. Fine-resolution (8 m) basal topography retrieved from the Reference Elevation Model of Antarctica (REMA) data reveals that channelized basal features of several tens of kilometers traverse the ice base both along and across the Jutulstraum ice stream on the Fimbulisen Ice Shelf (FIS). The FIS cavity is currently filled with fresh and cold Eastern Shelf Water (ESW), and recent observations have shown a sustained inflow of Warm Deep Water (WDW) since 2016. In this study, we first assess the effect of the basal channels on the cavity circulation and basal melting of the FIS with a fine-scale unstructured grid Finite-Volume Community Ocean Model (FVCOM) model of the FIS ice cavity. The grid resolution varies from 50 m in the focused region along the ice stream to 1500 m in the open ocean. Sensitivity studies are carried out using the high-resolution ice draft from REMA and a smoothed version of it, combined with varying proportions of WDW in the cavity. Our results show that the basal channels lead to (i) a redistribution of basal melting, (ii) a net melt increase at the deep ice area, and (iii) the entrapment of melt-modified WDW in the channels where WDW reaches the deep ice area. Using an idealized ice sheet model, we demonstrate that this entrapment of warm water in the channel results in a net melt increase with a preferential melt that promotes channel growth and migration, forming a positive feedback loop. We further investigate the positive feedback mechanism using an Elmer/Ice–FVCOM model setup with the same fine-scale mesh as the ocean model. This ocean-driven coupled evolution of the channelized system may occur on other shelves in East Antarctica where ESW and WDW coexist. Considering this coupled process in generating sea level projections could constrain East Antarctica's contribution to future sea level rise.

How to cite: Zhou, Q., Hattermann, T., Zhao, C., Gladstone, R., Morris, A., and Uotila, P.: Ocean-driven basal channel growth at Fimbulisen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16827, https://doi.org/10.5194/egusphere-egu24-16827, 2024.

17:30–17:40

EGU24-17841

ECS

On-site presentation

Response of EC-Earth3 to Antarctic meltwater

André Jüling, Erwin Lambert, Philippe Le Sager, and Sybren Drijfhout

Ice-sheet meltwater affects ocean stratification and circulation, sea ice, and ultimately the global climate through various feedback mechanisms. Most current generation global climate models do not include interactive ice sheets and as such do not capture the projected increases in additional meltwater under future emission scenarios. We use the EC-Earth3 coupled climate model to investigate the climate response to various scenarios of Antarctic meltwater input. With the idealized experiments of the Southern Ocean Freshwater Input from Antarctica Model Intercomparison Project (SOFIAMIP), as well as a plausible future meltwater release experiment, we investigate the sensitivity to both amount and location of the freshwater forcing in both the eddy-permitting (0.25°) and the standard, non-eddying (1°) resolution model versions. We find that the amount of freshwater strongly controls the sea ice with associated atmospheric adjustments and feedbacks. We also see that while inserting additional meltwater at the surface enhances stratification increasing sea ice cover, inserting it at depth decreases stratification and enables more ocean heat to be released at the surface. Our results represent improved model physics and support calls for using prescribed Antarctic meltwater input as forcing in the Coupled Model Intercomparison Project to, for example, improve modelled sea ice evolution and sea level trends.

How to cite: Jüling, A., Lambert, E., Le Sager, P., and Drijfhout, S.: Response of EC-Earth3 to Antarctic meltwater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17841, https://doi.org/10.5194/egusphere-egu24-17841, 2024.

17:40–17:50

EGU24-18887

ECS

On-site presentation

Do ice-ocean feedbacks influence a regime shift of the Filchner-Ronne ice shelf cavity?

Ronja Reese and Jan De Rydt

17:50–18:00

EGU24-15858

ECS

On-site presentation

Contrasting trends of marine bromoform emissions in a future climate

Dennis Booge, Jerry Tjiputra, Dirk Olivié, Birgit Quack, and Kirstin Krüger

Bromoform (CHBr₃) from the ocean is the most important organic compound for atmospheric bromine with an atmospheric lifetime of ~2-4 weeks. Natural production, being the main source of oceanic CHBr₃, is high at the coasts and in open ocean upwelling regions due to production by macroalgae and phytoplankton. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and its emissions are still poorly constrained in observations and are mostly neglected in Earth System Model (ESM) climate projections. Anthropogenically forced climate change may lead to considerable changes in ocean temperature and ocean acidification, and will also influence primary productivity. Especially biogeochemical processes in the Arctic will be strongly influenced by climate change in the near future. However, the future trend of the marine emissions of bromoform and other very short-lived substances (VSLS) remains unclear. Two studies projected an increase of the relative importance of brominated VSLS for stratospheric ozone loss in contrast to other ozone depleting substances, due to increasing oceanic emissions of the brominated VSLS. Both studies applied constant (observation based) oceanic concentrations for the emission calculations in a future warming ocean, which assumes a production increase. Thus, a consistent way of addressing the bromoform production and concentration in the global ocean, its air-sea gas exchange and concentration in the atmosphere with high spatial and temporal resolution is ultimately needed to further progress with our understanding of potential future climate trends.

Here, we show first model results of fully coupled ocean-atmosphere bromoform interactions in the Norwegian ESM (NorESM) with the ocean model BLOM and the ocean biogeochemistry component iHAMOCC for the period from 2015 to 2100 (SSP585 scenario). Model data for the historical period until 2014 is validated with oceanic and atmospheric observations listed in the HalOcAt (Halocarbons in the Ocean and Atmosphere) data base.

On global average, our model results indicate decreasing oceanic CHBr₃ concentrations and emissions until the end of this century. In contrast, atmospheric CHBr₃mixing ratios are projected to increase during the same period. The results indicate that the lifetime of atmospheric CHBr₃ increases until 2100 compared to current days as atmospheric loss due to photolysis and reaction with hydroxyl radicals is projected to decrease.

In contrast, bromoform in the Arctic shows an increasing trend of marine CHBr₃ concentrations, their emissions and atmospheric mixing ratios. Moreover, annual mean Arctic marine bromoform concentrations in 2100 (5.2 pmol L^-1) are projected to exceed global values (4.5 pmol L^-1). Increasing sea surface temperature and sea ice retreat in the Arctic drives the higher CHBr₃productivity. The resulting emissions in the Arctic are projected to increase by 67% until 2100 indicating this region to be a significant source of brominated VSLS in a future climate. The relevance and uncertainties of the model results are discussed.

How to cite: Booge, D., Tjiputra, J., Olivié, D., Quack, B., and Krüger, K.: Contrasting trends of marine bromoform emissions in a future climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15858, https://doi.org/10.5194/egusphere-egu24-15858, 2024.

Posters on site: Thu, 18 Apr, 10:45–12:30 | Hall X5

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 12:30

Chairpersons: Jan Landwehrs, Konstanze Haubner

X5.239

EGU24-2610

Similarities and differences in circulation beneath the Filchner-Ronne and Ross Ice Shelves: Lagrangian point of view

Vladimir Maderich, Roman Bezhenar, Igor Brovchenko, Dias Fabio Boeira, Cecilia Äijälä, and Petteri Uotila

The two world’s largest ice shelves, the Filchner-Ronne Ice Shelf (FRIS) and the Ross Ice Shelf (RIS) account for half the area of Antarctic ice shelves. They play a key role in transforming water masses on the shelf and forming Antarctic Bottom Water.

The objective of the work was to study the similarities and differences of circulation under the FRIS and RIS using the data of numerical simulation of currents, temperature, and salinity in the Weddell and Ross Seas from the Whole Antarctica Ocean Model (WAOM). The modelling results were used to run the particle-tracking model Parcels for computing Lagrangian particle trajectories. Three Lagrangian characteristics were calculated for FRIS and RIS: (i) Visitation frequency is defined as the percentage of the particles P visited each 2x2 km grid column at least once in a period of modelling (20 y); (2) Representative particle trajectory is the particle trajectory which deviates least from rest of trajectories; (iii) The mean age is the age of particles visited each 2x2 km grid column at least once.

The representative particle trajectories show that anticyclonic circulation beneath the FRIS and RIS is caused by the inflow of High Salinity Shelf Water (HSSW) through troughs off the western coast of the Weddell and Ross Seas. Transformed into ISW water, it flows out through the troughs in these seas. Part of the transformed water under the FRIS flows out through the Filchner Trough between Berkner Island, while water under RIS flows into the Ross Sea in the strait between Roosevelt Island and the shore. The eastern part of RIS is not ventilated by water inflowing from Ross Island. It is slowly ventilated by water entering a trough between Roosevelt Island and the eastern coast of the Ross Sea. Visitation frequency and representative trajectories suggest similar paths for water mass entering RIS in all seasons. Except December-February particles in anticyclonic gyre can return under RIS. Meanwhile, for particles released in January-August, outflows from FRIS took place through both the Ronne and Filchner ice fronts. In the October-December release the outflow through the Ronne ice front essentially exceeds flow through the Filchner depression.

How to cite: Maderich, V., Bezhenar, R., Brovchenko, I., Fabio Boeira, D., Äijälä, C., and Uotila, P.: Similarities and differences in circulation beneath the Filchner-Ronne and Ross Ice Shelves: Lagrangian point of view, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2610, https://doi.org/10.5194/egusphere-egu24-2610, 2024.

X5.240

EGU24-450

ECS

Impact of stratospheric polar vortex variability on Antarctic surface climate and sea ice

Bianca Mezzina, Froila M. Palmeiro, and Hugues Goosse

The interannual variability of Antarctic sea ice is considered to be mainly driven by tropospheric and oceanic processes. However, the stratosphere also constitutes a possible source of sea ice variability. The stratospheric variability in the southern high latitudes is dominated by the stratospheric polar vortex (SPV), an extremely cold air mass confined to the pole by strong westerly winds. The SPV is characterized by a large seasonal cycle, peaking in austral winter and breaking down in late spring (with the so-called stratospheric final warming, SFW), but also by interannual variations. While there is robust evidence of a downward impact of the polar stratospheric variability on the Northern Hemisphere surface climate, including sea ice, whether a similar link is present in the Southern Hemisphere is still unsettled.

Here, we perform a multi-model assessment of the impact of the dynamical state of the SPV on Antarctic surface climate and sea ice by applying the same experimental protocol to three state-of-the-art general circulation models (GCMs): EC-EARTH, CMCC-ESM and CanESM. The three GCMs have similar ocean and sea ice components but different atmosphere.

First, we examine 200-year control experiments and compare them to observations. To assess the impact of the SPV state on the surface and sea ice, we build composites of “strong” and “weak” SPV years based on the late-winter stratospheric conditions. We then compare the anomalous patterns of sea ice concentration during the following spring, as well as anomalies of atmospheric fields such as sea-level pressure and surface temperature. To detect the possible downward stratosphere-troposphere coupling, we also compute the temporal evolution of vertical profiles of zonal-mean zonal wind and temperature. A similar analysis is also carried out using composites based on the timing of the SFW (“early” versus “late”).

To further isolate the potential role of the polar stratosphere in driving Antarctic surface climate, we run an additional set of sensitivity experiments with suppressed stratospheric variability. For each model, we build 200-member ensembles of 1-year long runs initialized from the control experiment, with the polar stratosphere nudged to the models' climatology, while the troposphere and the extra-polar stratosphere evolve freely. We then compare the variability of Antarctic sea ice and surface climate in these sensitivity experiments to that of the control run and investigate changes in the suggested mechanisms for the stratospheric downward influence.

How to cite: Mezzina, B., Palmeiro, F. M., and Goosse, H.: Impact of stratospheric polar vortex variability on Antarctic surface climate and sea ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-450, https://doi.org/10.5194/egusphere-egu24-450, 2024.

X5.241

EGU24-2781

Two distinct declining trend of autumn Arctic sea ice concentration before and after 2002

Zhina Jiang

This study investigates the Arctic sea ice concentration trend during 1979-2021 and explores why the autumn Arctic sea ice loss is accelerated after 2002 and its trend declining center shifts from the Chukchi Sea to the Barents-Kara-Laptev Seas. Attribution analysis reveals that the enhanced summer sea ice concentration negative trend in large part explains the autumn sea ice concentration accelerating reduction, whereas it is the trend center shift of increased downward longwave radiation that accounts for mostly of the autumn sea ice concentration decline center shift. Further analysis suggests the downward longwave radiation trend is closely related to large-scale atmospheric circulation changes. A tendency towards a dipole structure with an anticyclonic circulation over Greenland and the Arctic Ocean and a cyclonic circulation over Barents-Kara Seas enhances (suppresses) the downward longwave radiation over Western (Eastern) Arctic by warming and moistening (cooling and drying) the lower troposphere during 1979-2001. In comparison, a tendency towards a stronger Ural anticyclone combined with positive phase of the North Atlantic Oscillation pattern significantly promotes the increase of downward longwave radiation over Barents-Kara-Laptev Seas during 2002-2021. Our results set new insights into the Arctic sea ice variability and deepen our understanding of the climate change.

How to cite: Jiang, Z.: Two distinct declining trend of autumn Arctic sea ice concentration before and after 2002, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2781, https://doi.org/10.5194/egusphere-egu24-2781, 2024.

X5.242

EGU24-7523

ECS

Amplified Interannual Variation of the Summer Sea Ice in the Weddell Sea, Antarctic After the Late 1990s

Yuanyuan Guo, Xiaodan Chen, Sihua Huang, and Zhiping Wen

X5.243

EGU24-8422

ECS

The impact of atmospheric forcing on wintertime sea-ice lead patterns in the Southern Ocean

Umesh Dubey, Sascha Willmes, Alexander Frost, and Gunther Heinemann

Sea-ice leads are narrow, linear fractures in sea ice, and are an important basis for understanding the mechanism of the atmosphere-sea ice-ocean system in the Southern Ocean. We use monthly sea-ice lead frequencies based on satellite thermal imagery with 1 km² grid resolution to investigate potential causes for the observed spatial and temporal variabilities of sea-ice leads during wintertime (April-September), 2003-2023, using ERA5 winds and sea level pressure, as well as climate indices El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). The presented investigation provides evidence for correlations between mean monthly lead frequency and monthly wind divergence, as well as monthly sea level pressure across the majority of the circum-Antarctic regions (significantly in the Weddell Sea, Ross Sea and Amundsen & Bellingshausen Sea). Furthermore, our investigation evaluates the influence of wintertime ENSO and SAM on sea-ice lead patterns in the Southern Ocean. Results reveal a positive correlation between sea-ice leads and SAM, in the Weddell Sea and specific regions of the Ross Sea. Moreover, a positive correlation is found between sea-ice leads and ENSO, particularly in the Ross Sea, Western Pacific Ocean, and certain portions of the Indian Ocean. While the driving mechanisms for these observations are not yet understood in detail, the presented results can contribute to opening new hypotheses on atmospheric forcing and sea-ice interactions. The contribution of atmospheric forcing to regional lead dynamics is complex, and a more profound understanding requires detailed investigations in combination with considerations of ocean processes. This study provides a starting point for further research into the detailed relationships between sea-ice leads and atmosphere, ocean, combined effect of ENSO-SAM, respectively in the Southern Ocean.

How to cite: Dubey, U., Willmes, S., Frost, A., and Heinemann, G.: The impact of atmospheric forcing on wintertime sea-ice lead patterns in the Southern Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8422, https://doi.org/10.5194/egusphere-egu24-8422, 2024.

X5.244

EGU24-8652

SSP3-7.0 projections of Antarctic sub-ice-shelf melting with the Energy Exascale Earth System Model

Xylar Asay-Davis, Darin Comeau, Alice Barthel, Carolyn Begeman, Wuyin Lin, Mark Petersen, Stephen Price, Andrew Roberts, Irena Vankova, Milena Veneziani, Jonathan Wolfe, and Shixuan Zhang

To date, few Earth System Models (ESMs) have the ability to simulate the flow in the ocean cavities below Antarctic ice shelves and its influence on basal melting. Yet capturing both this flow and the resulting melt patterns is critical for representing local, regional, and global feedbacks between the climate and sub-ice-shelf melting. Here, we present a small ensemble of historical simulations and SSP3-7.0 projections in an ESM that includes Antarctic ice-shelf cavities, the Energy Exascale Earth System Model (E3SM) v2.1. The simulations have active ocean, sea-ice, atmosphere, land and river components. The model domain has 12 km horizontal resolution around Antarctica, which is adequate for capturing dynamics in the larger ice-shelf cavities, melt fluxes aggregated across Antarctic regions, and water masses across most of the Antarctic continental shelf. The projections show significant warming and freshening of water masses on the Antarctic continental shelf, a deepening and poleward shift of the Amundsen Sea Low (ASL), and a significant increase in Antarctic melting through the 20th and 21st centuries. We also see a significantly more modest drift in water-mass properties and melt rates in our control simulation with constant 1950 conditions from which the historical runs were branched. In addition to providing an estimate of future melting and other changes in regional and global climate under SSP3-7.0, these simulations are also a steppingstone to coupled ice sheet-ocean simulations planned for the near future. We briefly discuss these plans and the coupling strategy that we are developing.

How to cite: Asay-Davis, X., Comeau, D., Barthel, A., Begeman, C., Lin, W., Petersen, M., Price, S., Roberts, A., Vankova, I., Veneziani, M., Wolfe, J., and Zhang, S.: SSP3-7.0 projections of Antarctic sub-ice-shelf melting with the Energy Exascale Earth System Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8652, https://doi.org/10.5194/egusphere-egu24-8652, 2024.

X5.245

EGU24-10555

ECS

Towards an improved Antarctic sea-ice representation in HadGEM3-GC5

Tarkan Bilge, Kaitlin Naughten, Paul Holland, Edward Blockley, David Storkey, and Jeff Ridley

The historical runs of CMIP6-era coupled climate models generally exhibit negative biases in Antarctic sea ice, as identified across a range of models during the CMIP6 simulations (Roach et al. 2020). The UK's national coupled climate model, HadGEM3, has been no exception to this. The CMIP6 version, HadGEM3-GC3, underestimated Antarctic sea ice in historical simulations owing to a Southern Ocean warm bias (Andrews et al. 2020). As part of the DEFIANT (Drivers and Effects of Fluctuations in sea Ice in the ANTarctic) project, in this research we perform an analysis of the representation of sea ice in HadGEM3-GC5, a more recent version of the coupled model. Analysis of existing HadGEM3-GC5 simulations has identified unrealistic convection events associated with open water polynyas. We have started to perform a suite of sensitivity experiments to investigate the importance of the freshwater budget and ocean mixing parameterisation scheme on these convection events, and subsequently on pan-Antarctic sea ice. These initial experiments take the form of short simulations with constant year-2000 forcings, incorporating various parameter perturbations and modifications to freshwater input. We present evidence of the improved characterisation of pan-Antarctic sea ice in HadGEM3-GC5 compared to HadGEM3-GC3, and the preliminary analysis of perturbation simulations aimed at understanding and addressing the remaining challenges in the model coupled climate system.

How to cite: Bilge, T., Naughten, K., Holland, P., Blockley, E., Storkey, D., and Ridley, J.: Towards an improved Antarctic sea-ice representation in HadGEM3-GC5, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10555, https://doi.org/10.5194/egusphere-egu24-10555, 2024.

X5.246

EGU24-14537

Should we worry about the massive increase of satellite reentry debris in the polar regions?

Linda Megner

X5.247

EGU24-15589

ECS

Advancing the understanding of cyclone impacts on Arctic sea-ice concentration and sea-ice lead formation

Lars Aue and Annette Rinke

Cyclones are an important driver of heat and moisture transport into the Arctic and additionally cause high wind speeds and abrupt wind direction changes during their passage. The subsequent impacts on the Arctic sea ice cover consist of i) a thermodynamic stalling/enhancement of the seasonal sea-ice growth/melt, and ii) enhanced drift and deformation of sea ice. The statistical quantification of these cyclone impacts on the Arctic sea-ice cover is a very recent research topic.

By conducting a climatological monthly analysis based on the ERA5 reanalysis and a cyclone tracking algorithm, we reveal a distinct seasonal cycle of cyclone impacts on sea-ice concentration in the Atlantic Arctic Ocean (strong impacts from autumn to spring, but weak impacts in summer). We further demonstrate that the cyclone impacts have changed significantly throughout the last four decades in a warming Arctic, magnitude-wise strongest in the Barents Sea in autumn.

Still, open questions remain with respect to the impacts of cyclones on the Arctic sea ice in the present climate and regarding their possible changes in a warming Arctic. Specifically, the influence of cyclone passages on the formation of leads in the sea-ice cover has not been statistically analyzed so far. Thus, we extend our analysis to cyclone related changes in sea-ice lead fraction derived from horizontally high-resolved (down to 1km²) MODIS sea-ice observations.

Our results indicate that cyclone passages significantly increase sea-ice lead fraction in large parts of the central Arctic Ocean. Mixed results are found for the Arctic marginal seas. The analysis of particular cyclone cases further suggests that groups of consecutive cyclones traversing the sea ice within short time are particularly effective in driving changes in sea-ice concentration and lead fraction. The statistical quantification of the importance of such a temporal clustering of cyclones for their sea-ice impacts is topic of ongoing research.

How to cite: Aue, L. and Rinke, A.: Advancing the understanding of cyclone impacts on Arctic sea-ice concentration and sea-ice lead formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15589, https://doi.org/10.5194/egusphere-egu24-15589, 2024.

X5.248

EGU24-16385

ECS

Simulating Arctic aerosol-cloud interactions in a warm air intrusion event during the MOSAiC campaign

Ruth Price, Paul R. Field, Bjørg Jenny Kokkvoll Engdahl, Oskar Landgren, Annette Rinke, and Andrew Orr

Aerosols play a crucial role in determining the characteristics and radiative impacts of Arctic clouds. Parameterisations of aerosols and clouds in climate models remain uncertain, confounding efforts to improve our understanding of their behaviour both now and in the future. Moreover, model biases in cloud microphysics are compounded by interlinked biases in Arctic boundary layer structure, surface properties and large-scale meteorology. This interdependence among variables poses significant hurdles for modelers attempting to accurately simulate Arctic atmospheric processes.

In this study, we have used a regional atmospheric model, the UK Met Office Unified Model, coupled to a cloud microphysical model (Cloud Aerosol Interacting Microphysics, CASIM) and an aerosol-chemistry-climate model (UK Chemistry and Aerosols, UKCA). This integrated approach has been employed to investigate warm air intrusion events during April 2020 of the MOSAiC campaign. Our results provide vital information on the behaviour of model processes that have been tuned for mid-latitude regimes, such as cloud droplet activation, in the Arctic environment during warm air intrusion events that had clear impacts on the surface energy budget.

How to cite: Price, R., Field, P. R., Engdahl, B. J. K., Landgren, O., Rinke, A., and Orr, A.: Simulating Arctic aerosol-cloud interactions in a warm air intrusion event during the MOSAiC campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16385, https://doi.org/10.5194/egusphere-egu24-16385, 2024.

X5.249

EGU24-16632

Bounding the contribution of open leads to sea spray aerosol emissions in the high Arctic

Rémy Lapere, Jennie L. Thomas, Louis Marelle, and Pierre Rampal

In the Arctic ocean, open leads have the ability to release sea spray into the atmosphere. However, the magnitude and seasonality of this flux are relatively unknown, which is a limitation to our understanding of the polar climate. Most atmospheric models do not include sea spray from leads, because of the lack of existing parameterization. In this work we propose a parameterization for sea spray fluxes from open leads in the Arctic, which leverages aerosol flux measurements from a past campaign combined with the latest generation of sea ice modeling.

Based on our parameterization, the annual total emitted mass of sea salt from open leads, [0.1–1.5] Tg/yr, is comparable to emissions from blowing snow and to the transported mass of sea salt from open ocean coming from the lower latitudes. Furthermore, the seasonality of open lead and blowing snow sea salt emissions have opposite phases, and their spatial distribution across the Arctic is also different. Therefore, we find that including both open lead and blowing snow sea salt fluxes can improve the reproduction of the annual cycle of sea salt aerosol atmospheric concentration at high latitude stations.

Using sea ice concentration fields from the neXtSimv2 sea ice model and implementing our parameterization in the WRF-Chem chemistry-transport model, we evaluate the impacts of open lead emissions on sea salt concentrations and clouds in the high Arctic.

How to cite: Lapere, R., Thomas, J. L., Marelle, L., and Rampal, P.: Bounding the contribution of open leads to sea spray aerosol emissions in the high Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16632, https://doi.org/10.5194/egusphere-egu24-16632, 2024.

X5.250

EGU24-17682

ECS

Changes of clouds and sea ice in EC-Earth- and ERA5-driven retrospective ensemble hindcasts with the fully coupled ice-sheet–ocean–sea ice–atmosphere–land circum-Antarctic model PARASO

Florian Sauerland, Pierre-Vincent Huot, Sylvain Marchi, Hugues Goosse, and Nicole van Lipzig

We created 4 retrospective hindcasts using PARASO, a five-component (ice sheet, ocean, sea ice, atmosphere, and land) fully coupled regional climate model over an Antarctic circumpolar domain: a control run forced with reanalysis data from ERA5 and ORAS5, and an ensemble of 3 members forced by 3 different EC-Earth global hindcasts. We compare the ocean and sea ice properties of the ERA5-driven simulation to the ensemble mean of the EC-Earth-driven ones, to separate the impact of the different source of boundary conditions from internal variability generated by the different ensemble members. Moreover, we analyse if and how the different ocean temperatures and sea ice extents influence the formation of clouds. We compare the moisture and heat fluxes at the ocean surface between the EC-Earth-driven ensemble and the ERA5-driven hindcast, as well as the moisture and cloud water contents in the atmosphere. This not only provides information on the contribution of external and internal variability inside the PARASO domain for those variables, but by comparing the variability in fluxes to the variability of clouds, we can also estimate the importance of ocean-cloud-interactions. Our results also show that the increasing trend observed in Antarctic sea ice extent observed prior to 2015 is well represented in the ERA5-driven run, but not in the EC-Earth-driven ensemble, indicating a stronger influence of mid-latitude forcings compared to local processes.

How to cite: Sauerland, F., Huot, P.-V., Marchi, S., Goosse, H., and van Lipzig, N.: Changes of clouds and sea ice in EC-Earth- and ERA5-driven retrospective ensemble hindcasts with the fully coupled ice-sheet–ocean–sea ice–atmosphere–land circum-Antarctic model PARASO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17682, https://doi.org/10.5194/egusphere-egu24-17682, 2024.

X5.251

EGU24-381

ECS

Effects of Arctic sea-ice concentration on turbulent surface fluxes in four atmospheric reanalyses

Tereza Uhlíková, Timo Vihma, Alexey Karpechko, and Petteri Uotila

A prerequisite for understanding the local, regional, and hemispherical impacts of Arctic sea-ice decline on the atmosphere is to quantify the effects of sea-ice concentration (SIC) on the turbulent surface fluxes of sensible and latent heat in the Arctic.

The best available information in data-sparse regions such as the Arctic is provided by global atmospheric reanalyses. Because each reanalysis uses its own forecast model, data-assimilation system, and often also different atmospheric and surface observations to create the data sets, their atmospheric and surface variables, and boundary conditions often differ. While the differences between reanalyses in variables SIC, latent and sensible heat flux have been demonstrated via comparisons against observations and inter-comparisons between reanalyses, how much these data sets scatter in the effects of SIC on surface turbulent fluxes is not known.

To fill these knowledge gaps, we analyse these effects utilising four global atmospheric reanalyses: ERA5, JRA-55, MERRA-2, and NCEP/CFSR (CFSR and CFSv2), and evaluate their uncertainties arising from inter-reanalysis differences in SIC and in the sensitivity of the turbulent surface fluxes to SIC.

Using daily field means in nine Arctic basins, the magnitude of the differences in SIC is up to 0.15, but typically around 0.05 during all four seasons. Bilateral orthogonal-distance regression analyses indicate that the greatest sensitivity of both the latent and the sensible heat flux to SIC occurs in the cold season, November to April. For these months, using daily means of data, the average sensitivity is 400 W m^-2 for the latent heat flux and over 800 W m^‑2 for the sensible heat flux per unit of SIC (change of SIC from 0 to 1, positive sign referring to the downward flux). The differences between reanalyses are as large as 300 W m^-2 for the latent heat flux and 600 W m^-2 for the sensible heat flux per unit of SIC. The sensitivity is highest for the NCEP/CFSR reanalysis. Comparing two study periods 1980–2000 and 2001–2021, we find that the effect of SIC on turbulent surface fluxes has weakened, due to the increasing surface temperature of sea ice and the sea-ice decline.

Multilateral ordinary-least-square regression analyses show that the effect of SIC on turbulent surface fluxes arises mostly via its effect on atmosphere-surface differences in temperature and specific humidity, whereas the effect of SIC on wind speed (via surface roughness and atmospheric-boundary-layer stratification) partly cancels out in the turbulent surface fluxes, as the wind speed increases the magnitude of both upward and downward fluxes.

How to cite: Uhlíková, T., Vihma, T., Karpechko, A., and Uotila, P.: Effects of Arctic sea-ice concentration on turbulent surface fluxes in four atmospheric reanalyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-381, https://doi.org/10.5194/egusphere-egu24-381, 2024.

X5.252

EGU24-9796

ECS

Development of Polar Lows in Future Climate Scenarios over the Barents Sea

Ting Lin, Anna Rutgersson, and Lichuan Wu

Polar lows (PLs) are intense mesoscale cyclones that form over polar oceans during colder months. Characterized by high wind speeds and heavy precipitation, they profoundly impact coastal communities, shipping, and offshore activities. Amid the substantial environmental changes in polar regions due to global warming, PLs are expected to undergo noteworthy transformations. In this study, we investigate the response of PL development in the Barents Sea to climate warming based on two representative PLs. Sensitivity experiments were conducted including the PLs in the present climate and the PLs in a pseudo-global warming scenario projected by the late 21st century for SSP 2-4.5 and SSP 3-7.0 scenarios from CMIP6. In both warming climate scenarios, there is an anticipated decrease in PL intensity, in terms of the maximum surface wind speed and minimum sea level pressure. Despite the foreseen increase in latent heat release in the future climate, contributing to the enhancement of PL intensity, other primary factors such as decreased baroclinic instability, heightened atmospheric static stability, and reduced overall surface heat fluxes play pivotal roles in the overall decrease in PL intensity in the Barents Sea under warming conditions. The augmentation of surface latent heat flux, however, results in increased precipitation associated with PLs by enhancing the latent heat release. Furthermore, the regional steering flow shifts in the warming climate can influence the trajectory of PLs during their development.

How to cite: Lin, T., Rutgersson, A., and Wu, L.: Development of Polar Lows in Future Climate Scenarios over the Barents Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9796, https://doi.org/10.5194/egusphere-egu24-9796, 2024.

X5.253

EGU24-5533

ECS

Updated sea ice code and atmospheric forcing improve the Antarctic summer sea ice of an ocean model

Cecilia Äijälä, Yafei Nie, Lucia Gutierrez-Loza, Chiara De Falco, Siv Kari Lauvset, Bin Cheng, and Petteri Uotila

The ocean and sea ice play an important role in the Antarctic climate system, and the atmosphere plays an important role in forcing the sea ice and the ocean. A better understanding of these interactions is needed to understand recent changes and anticipate future changes in the Antarctic.

We present a regional ocean model MetROMS-UHel for a quarter-degree resolution domain of the Antarctic Ocean. MetROMS-UHel is based on the MetROMS-Iceshelf model that uses ROMS (Regional Ocean Modeling System), with ocean-ice shelf thermodynamics. For the sea ice, MetROMS-Iceshelf uses CICE (Community Ice CodE) 5.1.2., while MetROMS-UHel has been updated to CICE 6.3.1. We run both models with two different atmospheric forcings, ERA-Interim (ECMWF Re-Analysis ERA-Interim from 1992 to 2018) and ERA5 (ECMWF Reanalysis v5 from 1992 to 2023). The atmospheric reanalysis plays an important role in the results, and this way we see which changes are due to the updated sea-ice model and which are from the updated atmospheric forcing.

The models simulate the interannual variability of the Antarctic sea ice extent reasonably well. The sea ice extent is similar for all model runs and close to observed in all seasons except JFM. In JFM the extent varies between the models especially in the Ross and Weddell Seas, with the largest, and closest to observed extent produced by the MetROMS-UHel CICE 6, ERA5 run. Important watermasses are well represented by the models, with cold waters being slightly fresher in the MetROMS-UHel runs.

How to cite: Äijälä, C., Nie, Y., Gutierrez-Loza, L., De Falco, C., Lauvset, S. K., Cheng, B., and Uotila, P.: Updated sea ice code and atmospheric forcing improve the Antarctic summer sea ice of an ocean model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5533, https://doi.org/10.5194/egusphere-egu24-5533, 2024.

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