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Oceanic transport toward the Arctic Ocean consists mostly of Atlantic Water (AW hereafter) being transported by the Norwegian Atlantic Current toward higher latitudes (Helland-Hansen & Nansen, 1909). At the entrance of the Barents Sea, the AW flow divides in two branches. One branch enters the Barents Sea where it can either be transformed into dense water and exits at depths as so-called Arctic Intermediate Water (Schauer et al., 1997), or melt ice and become part of the "estuarine" component of the Arctic Ocean (Eldevik & Nilsen, 2013;Rudels, 2016;Stigebrandt, 1981). The other AW branch forms the West Spitsbergen Current which further splits into two branches. One of these recirculates and heads South, and merges with the East Greenland Current, and the other enters the Arctic through Fram Strait. The latter branch can either melt ice, or subduct below the lighter colder and fresher layer of Arctic Water. This latter branch then follows a pathway along the continental slope North of Svalbard and Franz Josef Land toward the eastern Nansen Basin, slowly losing its properties (Bluhm et al., 2020;Timmermans & Marshall, 2020).

This paper describes the developing theory and underlying processes of the microscale obstacle-resolving model MITRAS version 2. MITRAS calculates wind, temperature, humidity, and precipitation fields, as well as transport within the obstacle layer using Reynolds averaging. It explicitly resolves obstacles, including buildings and overhanging obstacles, to consider their aerodynamic and thermodynamic effects. Buildings are represented by impermeable grid cells at the building positions so that the wind speed vanishes in these grid cells. Wall functions are used to calculate appropriate turbulent fluxes. Most exchange processes at the obstacle surfaces are considered in MITRAS, including turbulent and radiative processes, in order to obtain an accurate surface temperature. MITRAS is also able to simulate the effect of wind turbines. They are parameterized using the actuator-disk concept to account for the reduction in wind speed. The turbulence generation in the wake of a wind turbine is parameterized by adding an additional part to the turbulence mechanical production term in the turbulent kinetic energy equation. Effects of trees are considered explicitly, including the wind speed reduction, turbulence production, and dissipation due to drag forces from plant foliage elements, as well as the radiation absorption and shading. The paper provides not only documentation of the model dynamics and numerical framework but also a solid foundation for future microscale model extensions.Published by Copernicus Publications on behalf of the European Geosciences Union.

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