ERA5-based present-day ICON simulations with variable polar resolution

To evaluate the added value of regional refinement in the ICON model, this experiment focuses on present-day (PD) climate simulations using ERA5 boundary conditions. These simulations serve as a baseline for assessing how increased spatial resolution over polar regions affects the representation of key climate processes, large-scale circulation, and polar–midlatitude linkages. Comparing the uniform and refined configurations enables a systematic evaluation of the performance, internal consistency, and potential improvements introduced by two-way nested domains in a controlled present-day setup.

This experiment comprises three atmosphere-only simulations conducted with version 2.6.6 of the ICON model as part of WP2 of the EU Horizon 2020 project PolarRES. All simulations follow an AMIP-style setup and are forced with boundary conditions from ERA5, representing present-day climate conditions. The simulations differ only in their horizontal resolution over the polar regions.

PD_ERA_UNREF was performed using a globally uniform R3B5 grid, corresponding to a horizontal resolution of approximately 52.6 km. The two refined simulations, PD_ERA_REF_ARCTIC and PD_ERA_REF_ANTARC, are based on the same R3B5 base grid but include two nested domains over the Arctic and Antarctic, respectively. Each includes an intermediate-resolution nest (R3B6, ~26.3 km) north or south of 50° latitude, and a high-resolution nest (R3B7, ~13.2 km) beyond 57°N or 57°S. Two-way nesting was used to allow feedback from the refined domains to the global domain. All simulations used 90 vertical levels with a model top at approximately 75 km. The time step was halved with each nesting level to ensure numerical stability. All physical parameterisations were applied consistently across domains and chosen to perform robustly across the resolution range.

The simulations were initialised on 1 January 1984 using ERA5 data and integrated for 31 years. The first year is discarded as spin-up, yielding 30 years of output (1985–2014). Sea surface temperatures and sea ice concentrations were prescribed daily from ERA5 for the period 1984–2014. While sea ice concentration is prescribed, the model calculates sea ice thickness prognostically. Time-varying greenhouse gas concentrations (CO₂, CH₄, N₂O, and CFCs) follow CMIP6 historical forcings.

The ICON dynamical core is based on Zängl et al. (2015) and the model code is available via https://www.icon-model.org/ (release note for version 2.6.6: https://gitlab.dkrz.de/icon/icon-model/-/blob/release-2024.07-public/RELEASE_NOTES.md?ref_type=heads ). All three simulations used the ecRad radiation scheme (Hogan et al., 2018), a single-moment cloud microphysics scheme following Doms et al. (2011) and Seifert (2008), and a convection scheme based on Tiedtke (1989) and Bechtold et al. (2008). Turbulent processes are represented by a prognostic TKE-based turbulence scheme (Raschendorfer, 2001). Orographic drag is parameterised following Lott and Miller (1997), and non-orographic gravity wave drag is based on Orr et al. (2010). Parameter settings for subgrid-scale orographic and non-orographic gravity wave drag were guided by Köhler et al. (2021), with adaptations to our model resolution. The land surface is represented using the TERRA component for soil-vegetation-atmosphere transfer (Schrodin and Heise, 2001), with topography derived from the GLOBE dataset (Hastings et al., 1999) at ~1 km native resolution.

Post-processing included horizontal interpolation of selected variables to a regular 0.5° × 0.5° lat-lon grid for the global domain (UNREF), and to 0.125° × 0.125° for the high-resolution refined domains. Vertical interpolation to 19 pressure levels was applied to data on native model levels.

Date (Publication): 2025-07-21

Edition: 1

Citation identifier: PolarRES_ICON

Citation identifier: doi:10.26050/WDCC/PolarRES_ICON

Principal investigator

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dr. Raphael Koehler
www.awi.de

Author

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dr. Raphael Koehler
www.awi.de

Author

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dörthe Handorf
www.awi.de

Publisher

WDCC

Point of contact

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dr. Raphael Koehler
www.awi.de

Point of contact

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dörthe Handorf
www.awi.de

Name: NetCDF

Keywords

ICON atmosphere model

Keywords

amip-hist

Keywords

polar climate

Use limitation: CC-BY-4.0: Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/

Language: eng; USA

Begin date: 1985-01-01

End date: 2014-12-31

Supplemental Information: info:eu-repo/grantAgreement/EC/HE/101003590/BE//PolarRES: Polar Regions in the Earth System

Distribution format

NetCDF ()

Transfer size: 4899776

OnLine resource: https://www.wdc-climate.de/ui/entry?acronym=PolarRES_ICON

Hierarchy level: collection

Attribute description: surface_upwelling_longwave_flux_in_air_assuming_clear_sky

Descriptor: alias: surface_upwelling_longwave_flux_assuming_clear_sky

The surface called "surface" means the lower boundary of the atmosphere. Upwelling radiation is radiation from below. It does not mean "net upward". The sign convention is that "upwelling" is positive upwards and "downwelling" is positive downwards. The term "longwave" means longwave radiation. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds. [CF-Standard Name]; unit: W m-2

Attribute description: toa_outgoing_shortwave_flux

Descriptor: "shortwave" means shortwave radiation. "toa" means top of atmosphere. The TOA outgoing shortwave flux is the reflected and scattered solar radiative flux i.e. the "upwelling" TOA shortwave flux, sometimes called the "outgoing shortwave radiation" or "OSR". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: sea_ice_area_fraction

Descriptor: sea_ice_area_fraction [CF-Standard Name]; unit: 1

Attribute description: surface_upward_sensible_heat_flux

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). The surface sensible heat flux, also called "turbulent" heat flux, is the exchange of heat between the surface and the air by motion of air. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.[CF-Standard Name]; unit: W m-2

Attribute description: soil_moisture_content

Descriptor: "moisture" means water in all phases contained in soil. "Content" indicates a quantity per unit area. The "soil content" of a quantity refers to the vertical integral from the surface down to the bottom of the soil model. For the content between specified levels in the soil, standard names including content_of_soil_layer are used. [CF-Standard Name]; unit: kg m-2

Attribute description: toa_outgoing_shortwave_flux_assuming_clear_sky

Descriptor: toa_outgoing_shortwave_flux_assuming_clear_sky [CF-Standard Name]; unit: W m-2

Attribute description: toa_incoming_shortwave_flux

Descriptor: "shortwave" means shortwave radiation. "toa" means top of atmosphere. The TOA incoming shortwave flux is the radiative flux from the sun i.e. the "downwelling" TOA shortwave flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: air_pressure

Descriptor: air_pressure [CF-Standard Name]; unit: Pa

Attribute description: surface_roughness_length

Descriptor: The surface called "surface" means the lower boundary of the atmosphere.[CF-Standard Name]; unit: m

Attribute description: precipitation_amount

Descriptor: "Amount" means mass per unit area. "Precipitation" in the earths atmosphere means precipitation of water in all phases. [CF-Standard Name]; unit: kg m-2

Attribute description: surface_upwelling_longwave_flux_in_air

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "longwave" means longwave radiation. Upwelling radiation is radiation from below. It does not mean "net upward". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: surface_net_downward_longwave_flux

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "longwave" means longwave radiation. "Downward" indicates a vector component which is positive when directed downward (negative upward). Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.[CF-Standard Name]; unit: W m-2

Attribute description: surface_snow_area_fraction

Descriptor: surface_snow_area_fraction [CF-Standard Name]; unit: %

Attribute description: eastward_wind

Descriptor: "Eastward" indicates a vector component which is positive when directed eastward (negative westward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) [CF-Standard Name]; unit: m s-1

Attribute description: upward_air_velocity

Descriptor: vertical wind velocity A velocity is a vector quantity. "Upward" indicates a vector component which is positive when directed upward (negative downward). Upward air velocity is the vertical component of the 3D air velocity vector. [CF-Standard Name]; unit: m s-1

Attribute description: atmosphere_cloud_ice_content

Descriptor: atmosphere_mass_content_of_cloud_ice alias: atmosphere_cloud_ice_content

"Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. For the content between specified levels in the atmosphere, standard names including content_of_atmosphere_layer are used. [CF-Standard Name]; unit: kg m-2

Attribute description: surface_net_downward_longwave_flux_assuming_clear_sky

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "longwave" means longwave radiation. "Downward" indicates a vector component which is positive when directed downward (negative upward). Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: geopotential

Descriptor: Geopotential is the sum of the specific gravitational potential energy relative to the geoid and the specific centripetal potential energy.[CF-Standard Name]; unit: m2 s-2

Attribute description: wind_speed

Descriptor: Speed is the magnitude of velocity. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) The wind speed is the magnitude of the wind velocity.[CF-Standard Name]; unit: m s-1

Attribute description: ertel_potential_vorticity

Descriptor: ertel_potential_vorticity [CF-Standard Name]; unit: K m2 kg-1 s-1

Attribute description: height

Descriptor: Height is the vertical distance above the surface. [CF-Standard Name]; unit: m

Attribute description: atmosphere_water_vapor_content

Descriptor: "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. For the content between specified levels in the atmosphere, standard names including content_of_atmosphere_layer are used. Atmosphere water vapor content is sometimes referred to as "precipitable water", although this term does not imply the water could all be precipitated.[CF-Standard Name]; unit: kg m-2

Attribute description: surface_downward_eastward_stress

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). "Downward" indicates a vector component which is positive when directed downward (negative upward). "Downward eastward" indicates the ZX component of a tensor. A downward eastward stress is a downward flux of eastward momentum, which accelerates the lower medium eastward and the upper medium westward. The surface downward stress is the windstress on the surface. [CF-Standard Name]; unit: N m-2

Attribute description: omega

Descriptor: [CF-Standard Name]; unit: Pa/s

Attribute description: toa_outgoing_longwave_flux

Descriptor: "longwave" means longwave radiation. "toa" means top of atmosphere. The TOA outgoing longwave flux is the upwelling thermal radiative flux, often called the "outgoing longwave radiation" or "OLR". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: surface_downward_northward_stress

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "Northward" indicates a vector component which is positive when directed northward (negative southward). "Downward" indicates a vector component which is positive when directed downward (negative upward). "Downward northward" indicates the ZY component of a tensor. A downward northward stress is a downward flux of northward momentum, which accelerates the lower medium northward and the upper medium southward. The surface downward stress is the windstress on the surface. [CF-Standard Name]; unit: N m-2

Attribute description: relative_humidity

Descriptor: relative_humidity [CF-Standard Name]; unit: %

Attribute description: air_pressure_at_mean_sea_level

Descriptor: Air pressure at sea level is the quantity often abbreviated as MSLP or PMSL. Air pressure is the force per unit area which would be exerted when the moving gas molecules of which the air is composed strike a theoretical surface of any orientation. "Mean sea level" means the time mean of sea surface elevation at a given location over an arbitrary period sufficient to eliminate the tidal signals. [CF-Standard Name]; unit: Pa

Attribute description: surface_net_downward_shortwave_flux

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "shortwave" means shortwave radiation. "Downward" indicates a vector component which is positive when directed downward (negative upward). Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.[CF-Standard Name]; unit: W m-2

Attribute description: precipitation_flux

Descriptor: In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: kg m-2 s-1

Attribute description: surface_upward_latent_heat_flux

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). The surface latent heat flux is the exchange of heat between the surface and the air on account of evaporation (including sublimation). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.[CF-Standard Name]; unit: kg m-2 s-1

Attribute description: cloud_area_fraction

Descriptor: "X_area_fraction" means the fraction of horizontal area occupied by X. "X_area" means the horizontal area occupied by X within the grid cell. Cloud area fraction is also called "cloud amount" and "cloud cover". The cloud area fraction is for the whole atmosphere column, as seen from the surface or the top of the atmosphere. The cloud area fraction in a layer of the atmosphere has the standard name cloud_area_fraction_in_atmosphere_layer. [CF-Standard Name]; unit: %

Attribute description: toa_net_downward_shortwave_flux

Descriptor: "shortwave" means shortwave radiation. "toa" means top of atmosphere. "Downward" indicates a vector component which is positive when directed downward (negative upward). Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: convective_precipitation_flux

Descriptor: In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: kg m-2 s-1

Attribute description: surface_net_downward_shortwave_flux_assuming_clear_sky

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "shortwave" means shortwave radiation. "Downward" indicates a vector component which is positive when directed downward (negative upward). Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: air_temperature

Descriptor: Air temperature is the bulk temperature of the air, not the surface (skin) temperature. [CF-Standard Name]; unit: K

Attribute description: surface_snow_thickness

Descriptor: surface_snow_thickness [CF-Standard Name]; unit: m

Attribute description: surface_upward_latent_heat_flux

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). The surface latent heat flux is the exchange of heat between the surface and the air on account of evaporation (including sublimation). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.[CF-Standard Name]; unit: W m-2

Attribute description: snowfall_flux

Descriptor: In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: kg m-2 s-1

Attribute description: surface_air_pressure

Descriptor: The surface called "surface" means the lower boundary of the atmosphere.[CF-Standard Name]; unit: Pa

Attribute description: sea_surface_temperature

Descriptor: Sea surface temperature is usually abbreviated as "SST". It is the temperature of sea water near the surface (including the part under sea-ice, if any), and not the skin temperature, whose standard name is surface_temperature. For the temperature of sea water at a particular depth or layer, a data variable of sea_water_temperature with a vertical coordinate axis should be used. [CF-Standard Name]; unit: K

Attribute description: surface_temperature

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. The surface temperature is the (skin) temperature at the interface, not the bulk temperature of the medium above or below. [CF-Standard Name]; unit: K

Attribute description: specific_humidity

Descriptor: "specific" means per unit mass. Specific humidity is the mass fraction of water vapor in (moist) air.[CF-Standard Name]; unit: kg kg-1

Attribute description: surface_upwelling_shortwave_flux_in_air

Descriptor: The surface called "surface" means the lower boundary of the atmosphere. "shortwave" means shortwave radiation. Upwelling radiation is radiation from below. It does not mean "net upward". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: sea_ice_thickness

Descriptor: sea_ice_thickness [CF-Standard Name]; unit: m

Attribute description: northward_wind

Descriptor: "Northward" indicates a vector component which is positive when directed northward (negative southward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) [CF-Standard Name]; unit: m s-1

Attribute description: surface_upwelling_shortwave_flux_in_air_assuming_clear_sky

Descriptor: surface_upwelling_shortwave_flux_in_air_assuming_clear_sky [CF-Standard Name]; unit: W m-2

Attribute description: toa_outgoing_longwave_flux_assuming_clear_sky

Descriptor: A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "longwave" means longwave radiation. "toa" means top of atmosphere. The TOA outgoing longwave flux is the upwelling thermal radiative flux, often called the "outgoing longwave radiation" or "OLR". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. [CF-Standard Name]; unit: W m-2

Attribute description: lagrangian_tendency_of_air_pressure

Descriptor: "tendency_of_X" means derivative of X with respect to time. The Lagrangian tendency of a quantity is its rate of change following the motion of the fluid, also called the "material derivative" or "convective derivative". The Lagrangian tendency of air pressure, often called "omega", plays the role of the upward component of air velocity when air pressure is being used as the vertical coordinate. If the vertical air velocity is upwards, it is negative when expressed as a tendency of air pressure; downwards is positive.[CF-Standard Name]; unit: Pa/s

File identifier: wdc-climate.de:5285856 XML

Metadata language: eng; USA

Hierarchy level: collection

Hierarchy level name: PolarRES_ICON

Date stamp: 2026-02-04T10:21:32

Metadata standard name: ISO 19115

Metadata standard version: ISO 19115-2:2009

Point of contact

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dr. Raphael Koehler
www.awi.de

Point of contact

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research - Dörthe Handorf
www.awi.de

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