Evaluation of vertically resolved longwave radiation in SPARTACUS-Urban 0.7.3 and the sensitivity to urban surface temperatures

Cities' materials and urban form impact radiative exchanges and surface and air temperatures. Here, the SPARTACUS (Speedy Algorithm for Radiative Transfer through Cloud Sides) multi-layer approach to modelling longwave radiation in urban areas (SPARTACUS-Urban) is evaluated using the explicit DART (Discrete Anisotropic Radiative Transfer) model. SPARTACUS-Urban describes realistic 3D urban geometry statistically rather than assuming an infinite street canyon. Longwave flux profiles are compared across an August day for a 2 km × 2 km domain in central London. Simulations are conducted with multiple temperature configurations, including realistic temperature profiles derived from thermal camera observations. The SPARTACUS-Urban model performs well (cf. DART, 2022) when all facets are prescribed a single temperature, with normalised bias errors (nBEs)