TY  - JOUR
A1  - Klinger, Carolin
A1  - Mayer, Bernhard
T1  - Neighboring Column Approximation—An Improved 3D Thermal Radiative Transfer Approximation for Non-Rectangular Grids
Y1  - 2020
VL  - 12
IS  - 1
JF  - Journal of Advances in Modeling Earth Systems
DO  - 10.1029/2019MS001843
DO  - 10.23689/fidgeo-4934
N2  - We present a significantly improved version of the Neighboring Column Approximation (NCA 2.0), a fast 3D approximation for the calculation of thermal heating and cooling rates in cloudy atmospheres for large eddy simulation models. The method can now be used on non-rectangular grids, and the heating rate bias in cloudy atmospheres is substantially reduced compared to a 1D solution and the original version of the NCA (NCA 1.0). For different cloud fields the bias is in the range of −5–30% in the 1D case and −2–7% for the NCA 2.0. The calculation of 3D radiative transfer quantities requires horizontal transport of radiation which causes difficulties in the parallelization of numerical models and is computationally expensive. The NCA overcomes this problem and can calculate 3D thermal heating rates at the expense of only a factor 1.5 to 2 higher compared to a 1D radiative transfer approximation. The method uses the fluxes calculated by a 1D radiation scheme and estimates horizontal fluxes using results from neighboring columns. For the estimation of the heating rates from the before estimated fluxes pre-calculated lookup tables of emissivities are used. For the calculation of the heating rates we neglect scattering (independent of the fact if the incoming fluxes consider scattering or not). Inconsistencies made by assumptions for the method are corrected by a correction factor.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9280
ER  -