22 Aug 2023
 | 22 Aug 2023
Status: this preprint is open for discussion.

Effects of vertical grid spacing on the climate simulated in the ICON-Sapphire global storm-resolving model

Hauke Schmidt, Sebastian Rast, Jiawei Bao, Shih-Wei Fang, Diego Jimenez-de la Cuesta, Paul Keil, Lukas Kluft, Clarissa Kroll, Theresa Lang, Ulrike Niemeier, Andrea Schneidereit, Andrew I. L. Williams, and Bjorn Stevens

Abstract. Global storm-resolving models (GSRM) use strongly refined horizontal grids in comparison to climate models typically used in the Coupled Model Intercomparison Project (CMIP) but comparable vertical grid spacings. Here, we study how changes in vertical grid spacing and adjustments of the integration time step affect basic climate quantities simulated by the ICON-Sapphire atmospheric GSRM. Simulations are performed over a 45-day period for five different vertical grids having between 55 and 540 vertical layers and maximum tropospheric vertical grid spacings between 800 and 50 m. The effects of changes in vertical grid spacing are compared to differences between simulations with horizontal grid spacings of 5 and 2.5 km. For most quantities considered, halving vertical grid spacing has smaller effects than halving horizontal grid spacing but is not negligible. Every halving of the vertical grid spacing jointly with the necessary reductions of the time step length increases cloud liquid water by about 7 %, compared to about 16 % decrease for halving the horizontal grid spacing. The effect is due to both vertical grid refinement and time step reduction. There is no tendency of convergence in the range of grid spacings tested here. The cloud ice amount also increases with a refinement of the vertical grid but is hardly affected by the time step length and does show a tendency of convergence. While the effect on shortwave radiation is globally dominated by the changed reflection due to the changed cloud liquid water content, effects on longwave radiation are more difficult to interpret because changes in cloud ice concentration and cloud fraction are anticorrelated in some regions.

Hauke Schmidt et al.

Status: open (until 17 Oct 2023)

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Hauke Schmidt et al.

Hauke Schmidt et al.


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Short summary
A recent development in numerical models of the global atmosphere is the increase of horizontal resolution from the order of hundred to a few kilometers grid spacing. However, the vertical grid spacing of these models has not been reduced at the same rate as the horizontal grid spacing. Here we assess effects of much finer vertical grid spacings in particular on cloud quantities and the atmospheric energy balance.