27 Sep 2022
27 Sep 2022

Effects of complex terrain on the shortwave radiative balance: A sub–grid scale parameterization for the GFDL Land Model version 4.2

Enrico Zorzetto1, Sergey Malyshev2, Nathaniel Chaney3, David Paynter2, Raymond Menzel2,4, and Elena Shevliakova2 Enrico Zorzetto et al.
  • 1Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
  • 2NOAA OAR Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 3Department of Civil and Environmental Engineering, Duke University, Durham, NC, USA
  • 4University Corporation for Atmospheric Research, Princeton, NJ, USA

Abstract. Parameterizing incident solar radiation over complex topography regions in Earth System Models (ESMs) remains a challenging task. In ESMs, downward solar radiative fluxes at the surface are typically computed using plane parallel radiative transfer schemes, which do not explicitly account for the effects of a three-dimensional topography, such as shading and reflections. To improve the representation of these processes, we introduce and test a parameterization of radiation-topography interactions tailored to the Geophysical Fluid Dynamics Laboratory (GFDL) ESM land model. The approach presented here builds on an existing correction scheme for direct, diffuse and reflected solar irradiance terms over three-dimensional terrain. Here we combine this correction with a novel hierarchical multivariate clustering algorithm which explicitly describes the spatially varying downward irradiance over mountainous terrain. Based on a high-resolution digital elevation model, this combined method first defines a set of sub–grid land units ("tiles") by clustering together sites characterized by similar terrain-radiation interactions (e.g., areas with similar slope orientation, terrain and sky view factors). Then, based on terrain parameters characteristic for each tile, correction terms are computed to account for the effects of local 3-D topography on shortwave radiation over each land unit. We develop and test this procedure based on a set of Monte Carlo ray tracing simulations approximating the true radiative transfer process over three dimensional topography. Domains located in three distinct geographic regions (Alps, Andes, and Himalaya) are included in this study to allow for independent testing of the methodology over surfaces with differing topographic features. We find that accounting for the sub–grid spatial variability of solar irradiance originating from interactions with complex topography is important as these effects lead to significant local differences with respect to the plane-parallel case, as well as with respect to grid–cell scale average topographic corrections. Finally, we quantify the importance of the topographic correction for a varying number of terrain clusters and for different radiation terms (direct, diffuse, and reflected radiative fluxes) in order to inform the application of this methodology in different ESMs with varying sub-grid tile structure.

Enrico Zorzetto et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on egusphere-2022-770', Astrid Kerkweg, 07 Oct 2022
    • AC1: 'Reply on CEC1', Enrico Zorzetto, 10 Oct 2022
  • RC1: 'Comment on egusphere-2022-770', Anonymous Referee #1, 06 Nov 2022
  • RC2: 'Comment on egusphere-2022-770', Anonymous Referee #2, 21 Nov 2022

Enrico Zorzetto et al.

Data sets

Data used for developing a parameterization for spatial distribution of solar irradiance over rugged terrain Enrico Zorzetto

Model code and software

Code for analyzing the sub–grid distribution of shortwave radiation over mountainous terrain. Enrico Zorzetto

Enrico Zorzetto et al.


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Short summary
In this paper we develop a methodology to model the spatial distribution of solar radiation received by land over mountainous terrain. The approach is designed to be used in Earth System Models, where coarse grid cells hinder the description of fine scale land-atmosphere interactions. We adopt a clustering algorithm to partiton land domain in a set of homogeneous sub-grid “tiles”, and for each evaluate solar radiation receive by land based on terrain properties.