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

Abstract: 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) <2.5 % for downwelling fluxes, and <0.5 % for top-of-canopy upwelling fluxes. Errors are larger (nBE <8 %) for net longwave fluxes from walls and roofs. Using more realistic surface temperatures, varying depending on surface shading, the nBE in upwelling longwave increases to ∼2 %. Errors in roof and wall net longwave fluxes increase through the day, but nBEs are still 8 %–11 %. This increase in nBE occurs because SPARTACUS-Urban represents vertical but not horizontal surface temperature variation within a domain. Additionally, SPARTACUS-Urban outperforms the Harman single-layer canyon approach, particularly in the longwave interception by roofs. We conclude that SPARTACUS-Urban accurately predicts longwave fluxes, requiring less computational time (cf. DART, 2022) but with larger errors when surface temperatures vary due to shading. SPARTACUS-Urban could enhance multi-layer urban energy balance scheme prediction of within-canopy temperatures and fluxes

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: ISSN: 1991-9603

Classification and Topics

• Classification: Architektur
• Keyword: Strahlung ; Wärmestrahlung ; Oberflächentemperatur ; Stadtklima

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2023
• Creator: Stretton, Megan A. ; Morrison, William ; Hogan, Robin J. ; Grimmond, Sue

Further information

• DOI: 10.5194/gmd-16-5931-2023
• URN: urn:nbn:de:bsz:25-freidok-2406796
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:49 AM CEST