WRF model experiments on the atmospheric boundary layer over the Ronne polynya

The Weather Research and Forecasting (WRF) Model ARW V3.3 was applied to simulate the atmospheric boundary layer (ABL) modification over the Ronne Polynya in March 2010. The model results were validated against airborne observations from two research aircrafts. These observations were made during the campaign Joint Airborne Study of the Peninsula Region (JASPER) by the British Antarctic Survey and the Alfred Wegener Institute. Throughout the 36-h-long simulation period on 1-2 March, there was a south to south-westerly mean flow, coming from the ice shelf towards the polynya, which was approximately 10 km wide. Three model experiments were made, all of them receiving boundary conditions from the ECMWF operational analyses. The only difference between the model runs was in the sea ice concentration. The first model run was conducted with the sea ice concentration of the ECMWF operational analysis, which was available in a resolution of 16 km. For the second model run, a sea ice dataset with a much finer resolution was used, the AMSR-E dataset refined by the ARTIST Sea Ice algorithm, in a resolution of 6.25 km. In the third model run the polynya was manually replaced by a compact sea ice cover. Thereby the sensitivity of the ABL modification over the polynya to the sea ice data was analyzed. It is shown that the finer spatial resolution of the AMSR-E sea ice data allows a better simulation of the local polynya effects on the ABL, especially an increase in air temperature, humidity, and near-surface wind speeds. The validation against the observations revealed a cold temperature bias in the model within the ABL under stable to near-neutral conditions, and above the ABL regardless of stratification. The surface fluxes of heat and moisture and the ABL height were investigated along three cross-sections across the polynya. Additionally, an ice breeze from the sea ice surrounding the polynya towards the center of the polynya, and back to the sea ice at higher altitudes, was found in the WRF simulation with the AMSR-E sea ice dataset

On the effective aerodynamic and scalar roughness length of Weddell Sea ice

We study the effective aerodynamic roughness length z0_eff and scalar roughness length for temperature zT_eff over different compact sea ice types in the Antarctic Weddell Sea by aircraft measurements during two austral summer seasons. z0_eff and zT_eff are highly variable in the Weddell Sea ice area. The averaged value of in all main sea ice areas was smaller than the averaged value of . The ratio between the two roughness lengths was relatively small for new/young sea ice with / ≈ 2, but the ratio became significantly large for the multiyear pack ice with / ≈ 227. For the pack ice area, with sea ice concentration ranging between 95% to 100%, we determined a median = 4.1 × 10−03 m and a median = 1.8 × 10−05 m. In the new, young sea ice area, with sea ice concentration ranging between 98% and 100%, we observed a median = × 10−04 m and a median = 2.2 × 10−04 m. These values of and differ from published observations conducted in a pack ice and new, young sea ice area in the northern hemisphere, such as the Arctic. Most model parameterizations require the roughness lengths as constant values as boundary input parameters. Our study shows that by using the $\overline{z_{0}\_ {\rm eff}}$ and values of this study, instead of commonly used sea ice roughness length values, the accuracy of parameterized heat and momentum fluxes in the Weddell Sea ice area can significantly be improved

The THINICE field campaign: Interactions between Arctic cyclones, tropopause polar vortices, clouds and sea ice in summer

The THINICE field campaign, based from Svalbard in August 2022, provided unique observations of summertime Arctic cyclones, their coupling with cloud cover, and interactions with tropopause polar vortices and sea ice conditions. THINICE was motivated by the need to advance our understanding of these processes and to improve coupled models used to forecast weather and sea ice, as well as long-term projections of climate change in the Arctic. Two research aircraft were deployed with complementary instrumentation. The Safire ATR42 aircraft, equipped with the RALI (RAdar-LIdar) remote sensing instrumentation and in-situ cloud microphysics probes, flew in the mid-troposphere to observe the wind and multi-phase cloud structure of Arctic cyclones. The British Antarctic Survey MASIN aircraft flew at low levels measuring sea-ice properties, including surface brightness temperature, albedo and roughness, and the turbulent fluxes that mediate exchange of heat and momentum between the atmosphere and the surface. Long duration instrumented balloons, operated by WindBorne Systems, sampled meteorological conditions within both cyclones and tropospheric polar vortices across the Arctic. Several novel findings are highlighted. Intense, shallow low-level jets along warm fronts were observed within three Arctic cyclones using the Doppler radar and turbulence probes. A detailed depiction of the interweaving layers of ice crystals and supercooled liquid water in mixed-phase clouds is revealed through the synergistic combination of the Doppler radar, the lidar and in-situ microphysical probes. Measurements of near-surface turbulent fluxes combined with remote sensing measurements of sea ice properties are being used to characterize atmosphere-sea ice interactions in the marginal ice zone

The THINICE field campaign: Interactions between Arctic cyclones, tropopause polar vortices, clouds and sea ice in summer

International audienceThe THINICE field campaign, based from Svalbard in August 2022, provided unique observations of summertime Arctic cyclones, their coupling with cloud cover, and interactions with tropopause polar vortices and sea ice conditions. THINICE was motivated by the need to advance our understanding of these processes and to improve coupled models used to forecast weather and sea ice, as well as long-term projections of climate change in the Arctic. Two research aircraft were deployed with complementary instrumentation. The Safire ATR42 aircraft, equipped with the RALI (RAdar-LIdar) remote sensing instrumentation and in-situ cloud microphysics probes, flew in the mid-troposphere to observe the wind and multi-phase cloud structure of Arctic cyclones. The British Antarctic Survey MASIN aircraft flew at low levels measuring sea-ice properties, including surface brightness temperature, albedo and roughness, and the turbulent fluxes that mediate exchange of heat and momentum between the atmosphere and the surface. Long duration instrumented balloons, operated by WindBorne Systems, sampled meteorological conditions within both cyclones and tropospheric polar vortices across the Arctic. Several novel findings are highlighted. Intense, shallow low-level jets along warm fronts were observed within three Arctic cyclones using the Doppler radar and turbulence probes. A detailed depiction of the interweaving layers of ice crystals and supercooled liquid water in mixed-phase clouds is revealed through the synergistic combination of the Doppler radar, the lidar and in-situ microphysical probes. Measurements of near-surface turbulent fluxes combined with remote sensing measurements of sea ice properties are being used to characterize atmosphere-sea ice interactions in the marginal ice zone

The THINICE field campaign: Interactions between Arctic cyclones, tropopause polar vortices, clouds and sea ice in summer

The THINICE field campaign, based from Svalbard in August 2022, provided unique observations of summertime Arctic cyclones, their coupling with cloud cover, and interactions with tropopause polar vortices and sea ice conditions. THINICE was motivated by the need to advance our understanding of these processes and to improve coupled models used to forecast weather and sea ice, as well as long-term projections of climate change in the Arctic. Two research aircraft were deployed with complementary instrumentation. The Safire ATR42 aircraft, equipped with the RALI (RAdar-LIdar) remote sensing instrumentation and in-situ cloud microphysics probes, flew in the mid-troposphere to observe the wind and multi-phase cloud structure of Arctic cyclones. The British Antarctic Survey MASIN aircraft flew at low levels measuring sea-ice properties, including surface brightness temperature, albedo and roughness, and the turbulent fluxes that mediate exchange of heat and momentum between the atmosphere and the surface. Long duration instrumented balloons, operated by WindBorne Systems, sampled meteorological conditions within both cyclones and tropospheric polar vortices across the Arctic. Several novel findings are highlighted. Intense, shallow low-level jets along warm fronts were observed within three Arctic cyclones using the Doppler radar and turbulence probes. A detailed depiction of the interweaving layers of ice crystals and supercooled liquid water in mixed-phase clouds is revealed through the synergistic combination of the Doppler radar, the lidar and in-situ microphysical probes. Measurements of near-surface turbulent fluxes combined with remote sensing measurements of sea ice properties are being used to characterize atmosphere-sea ice interactions in the marginal ice zone