ALBERT

Description: Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.

Description: With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore cross-cutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge. The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic.

Description: Cloud-droplet, -ice as well as CCN and INP concentrations, stand as key parameters to improve our knowledge of cloud microphysics and dynamics and to approach a better understanding of aerosol impacts on Earth's radiative and precipitation budgets. This contribution will focus on the relationship between aerosol- and liquid-cloud properties by means of long-term observations with dual-field-of-view polarization lidars, which allow the spatiotemporal sampling of aerosol-microphysical properties, relevant for CCN and INP estimates from the ground-up to the Stratosphere, and of the droplet-number concentration and effective radius at liquid-cloud layers, only possible with the new dual-field-of-view feature. We performed measurements since 2019 at three strategic locations: in the pristine Punta Arenas (south tip of Chile), in the dry and often-polluted city of Dushanbe (in Central Asia), and in the Arctic on board of Polarstern. This lidar-based dataset of collocated aerosol and cloud properties was used to investigate the cloud response to local conditions, in which we found similar cloud-droplet numbers for Punta Arenas and the Arctic (in the order of 100 cm-3), but much larger concentrations for Central Asia reaching values in the order of 500 cm-3 in Dushanbe. Preliminary results on the co-variability of cloud-droplet and CCN number (aerosol-cloud-interaction index) show the highest correlations at Punta Arenas, close to 0.85 on the monthly scale. The potential of these aerosol-cloud scenes to learn about the aerosol-cloud radiative effect, as well as to look into cloud processes will be discussed, giving focus to the observational scale.

Description: The interaction of aerosol particles with radiation, clouds, and precipitation is a critical issue in understanding the atmosphere in the mid- and high latitudes of the southern hemisphere. The high abundance of supercooled liquid water in clouds above the Southern Ocean and coastal Antarctica is still puzzling. Atmospheric scientists cannot explain yet to which extent vertical dynamics or pristine aerosol conditions control the persistence of liquid layers. Furthermore, virtually nothing is known about how the abundant supercooled-liquid water influences precipitation formation and the radiative budget. This is especially true in the remote region of Antarctica, where detailed vertically resolved observations of aerosol, cloud, and precipitation are scarce and prevent one to capture the complex cloud processes. We will present a unique observation campaign that will help to address the open questions by contributing a one-year remote-sensing dataset for a coastal ice shelf in Dronning Maud Land in the Atlantic sector of Antarctica. The mobile ground-based remote-sensing supersite OCEANET-Atmosphere is deployed at Neumayer Station III (70.67°S, 8.27°W) in 2023. The synergistic combination of a multi-wavelength polarization Raman lidar, a 35-Ghz polarimetric cloud radar, a microwave radiometer, and a Doppler lidar provides valuable profile information of cloud and aerosol properties as well as their interaction. The remote-sensing data is augmented by the stations long-term records of meteorological parameters and aerosol physics and chemistry. Through case studies, we will demonstrate the supersites’ capabilities to relate cloud-relevant aerosol properties with cloud-microphysics and discuss the potential to address the science questions based on the dataset.

Description: To understand the feedbacks driving the amplified changes in the Arctic a quantification of the contribution of the involved processes is necessary. Here a detailed study of low-level Arctic clouds on the surface radiation budget is presented. These clouds frequently occur below the lowest detection range of most state-of-the-art remote-sensing instruments and were observed in summertime during 25% of the time over the marginal sea ice zone. The low altitude of these clouds poses challenges on their observation and characterization by remote-sensing techniques. Ground-based remote sensing and surface radiation flux measurements performed during the Arctic cruise PS106 in 2017 were combined with radiative transfer simulations to study low-level clouds. A multiwavelength lidar PollyXT with near-range observations capabilities down to 50m and a cloud radar with a lowest detection limit at 165m altitude were operated continuously. The liquid-water microphysical properties of clouds missed by the cloud radar were estimated using measurements of a microwave radiometer HATPRO and the lidar-detected cloud base. Thereby the surface radiative effect of these clouds was quantified. A closure between the observed and modelled radiative surface fluxes was achieved with a realistic representation of low-level liquid-containing clouds in the radiative transfer model. When omitting these low-level clouds, the cloud radiative effect at the surface was misestimated by 43Wm−2. The presented study highlights the importance of improving cloud retrievals for low-level liquid-containing clouds as they are frequently encountered in the high Arctic, together with observational capabilities, both in terms of cloud remote sensing and radiative flux observations.

Description: Significant uncertainties in the prediction of future warming in the Arctic arise from our lack of understanding of governing processes, including cloud radiative feedbacks. The present study compares preliminary simulations of 1D radiative fluxes based on the Cloudnet and ShupeTurner cloud retrievals for the yearlong Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The analysis is conducted in the context of a radiative closure study at the surface and the top-of-the atmosphere for the upward and downward broadband solar and terrestrial radiative fluxes. The consistency of our simulations and satellite-based estimates from the Clouds and the Earth’s Radiant Energy System (CERES) are analysed by considering several atmospheric and surface-type conditions. Particular focus is given to the effect of clouds on the radiation budget. Based on our simulations and CERES estimates, we find that clouds increase the net radiative fluxes at the surface by about 35.5 W/m² for the entire MOSAiC expedition period. Nevertheless, based on in-situ observations, it is argued that significant uncertainties in the solar and terrestrial affect this estimate of cloud radiative effects. Our research will also address the spatiotemporal variability of clouds and how this might impact the comparison between the point-like ground measurements with the CERES satellite footprint.