Innovative Strategies for Observation in the Arctic Atmospheric Boundary Layer

The main goal of the ISOBAR (Innovative Strategies for Observation in the Arctic Atmospheric Boundary Layer) project is to increase our understanding of turbulence and turbulent exchange processes under stable atmospheric conditions, in particular in the Arctic atmosphere. Knowledge gaps in this field are one of the main reasons that our weather forecasts and climate models have considerable problems and uncertainties in Polar Regions. The project combines atmospheric measurements performed by different types of small, unmanned aircraft, so-called RPAS (Remotely Piloted Aircraft Systems) and different atmospheric model approaches to understand and describe the relevant physical processes better. At the end of the project this results will be implemented into the existing numerical models to reduce the identified shortcomings. The Geophysical Institute of the University of Bergen is the host institution and coordinates this project that includes several national and international research partners. Those are Uni Research, the University Centre on Svalbard (UNIS), the Finnish Meteorological Institute, and the Universities of Tübingen, Hannover und Ostwestfalen-Lippe in Germany. The project has a overall budget of 12.3 MNOK out of which 9 MNOK are funded by the Research Council of Norway. A total of three measurement campaigns have been performed within the project. A two week campaign was conducted at the Andøya Space Center in November/December 2016 and had the main goal to test the RPA systems of the different partners and to compare and validate the corresponding sensor systems. This was an important preparation for the first main field campaigns of the project that was performed during 3 weeks in February/March 2017 at Hailuoto, Finland over sea ice in the Baltic Sea. A combination of advanced ground-based in-situ and remote-sensing technology has been deployed in addition to intensive vertical profiling of the stable atmospheric boundary layer by various fixed- and rotary wing RPAS. With more than 150 measurement flights, the campaign was highly successful and provides a unique data set for the improved characterization and understanding of the stable atmospheric boundary layer. A detailed description of the campaign and first results are published in a peer review publication (Kral et al., 2018; https://www.mdpi.com/2073-4433/9/7/268). The second major field campaign has been performed during 4 weeks in February 2018, again at Hailuoto, Finland (https://isobar2018campaign.w.uib.no/). Based on the results and experiences from the year before we adapted and tuned the deployed instrumentation and measurement strategy for an even better probing of the stable atmospheric boundary layer. Continuous remote sensing of the wind field and turbulence structure and more than 350 measurement flights with different unmanned aircraft systems provide a so far unprecedented data set for future stable boundary layer research. Through its two main campaigns, the ISOBAR project has collected a unique and highly valuable data set for stable and very stable atmospheric boundary layers in moderately inhomogeneous terrain. The raw data of all measurement systems in use have been intensively quality controlled and are now available both in NetCDF and Matlab-format in different temporal resolutions between 20 Hz for the turbulence data and in various averaging intervals of 1, 10, and 30 minutes. In parallel have a series of model simulations been performed and stored. Those included WRF simulations over the entire experimental periods, using various boundary layer parameterization schemes, and intensive case studies on selected situations by WRF single column mode (SCM) simulations, as well as, high resolution LES runs with PALM. The combination of high-quality observational data sets and fine-scale modelling activities has considerably increased our understanding of turbulent exchange processes in the stable and very stable boundary layer, in particular with respect to the intermittent nature of turbulence under these conditions. By that, we managed to fulfill most of the ISOBAR project goals, however, the development and implementation of an improved parameterization scheme for numerical weather forecast and climate models is still unsettled.

The ISOBAR data sets will have a large impact in the field of general boundary layer meteorology, as they provide an up to now unmatched level of detail in the structure of stable and very stable boundary layers. As other comparable campaigns in the past (e.g. CASES-99 or SHEBA) ISOBAR will provide scientists with material for detailed analysis in the years to come. At present, ISOBAR data are the basis for two ongoing PhD projects (Stephan Kral (GFI/UiB) and Brian Greene (University of Oklahoma)) and are thus directly related to the competence development of Early Stage Researchers. The material has also potential for additional PhD and master projects and will play a key role in research based education at the participating institutions. Links have been established with the modelling community of the YOPP (Year of Polar Prediction) to use ISOBAR observations as validation and benchmark data set on the way to further improvement of our modeling capacities for stable boundary layers.

The purpose of the basic research project ISOBAR (is to increase our understanding of the Atmospheric Boundary Layer (ABL) in the Arctic. In particular, we aim to study the physical processes governing the turbulent exchange under stable conditions, which are not well represented in current Numerical Weather Prediction (NWP) and climate models, due to insufficient parameterization schemes for the Stable Boundary Layer (SBL). Applying new innovative observation strategies, which include meteorological Remotely Piloted Aircraft Systems (RPAS) in addition to well-established ground based and profiling systems, we will provide data sets on the turbulent structure of the SBL, with unique spatial and temporal resolution. The project includes the test and characterization of the RPAS based turbulence sensors through laboratory experiments and a validation campaign at DWD observatory in Lindenberg. Three different RPAS systems, the Multipurpose Atmospheric Sensor Carrier (MASC, for long-range horizontal turbulence measurements), the Small Unmanned Meteorological Observer (SUMO, for turbulence measurements and vertical profiles) and the Advanced Mission and Operation Research (AMOR) multicopter system (for vertical profiles of the Surface Layer and fixed-location turbulence measurements) will be applied during two four-week long campaigns. These campaigns will focus on the SBL over homogeneous sea-ice (Arctic Ocean around Svalbard, winter/spring 2017) and surface heterogeneities due to partially open water (western fjords of Svalbard, winter/spring 2018). Collocated and coordinated measurements by a large number of RPAS (2 MASC, 7 SUMO, 2-4 AMOR) will provide a unique opportunity to sample the relevant data with so far unreached resolution. Supported by Single Column Model and Large-Eddy Simulation experiments we will use the collected data sets to develop new SBL parameterization schemes and implement them in the state-of-the-art Weather and Research Forecasting model (WRF)