Abstract
AbstractThe impact of model grid spacing and land‐surface resolution (LSR) on convective precipitation are investigated for areas with different orographic complexities. ICOsahedral Nonhydrostatic (ICON) model simulations were performed for six days having weak large‐scale forcing using six model grid spacings (in metres): Numerical Weather Prediction (NWP) (, ) and Large‐Eddy Simulation (LES) physics simulations (, , , and ) in a nested set‐up. Concerning LSR, we focused on simulations with LSRs of 1,250 and 5,000 m, keeping the model grid spacing at 156 m. The onset of precipitation in is earlier by 0.5–2 hr, while LSR modifications show a similar onset compared with . The relative percentage difference (RPD) of areal mean daily precipitation across LES physics simulations decreases consistently with model grid spacing for most of the cases. The RPD of precipitation in is considerably higher (75th percentile: ≈155%) than that of the LSR runs at resolutions of both 1,250 and 5,000 m, with 75th percentiles of ≈7% and ≈22%, respectively. To investigate the processes causing the differences in precipitation characteristics, like onset time and amount, the heat and moisture budgets of and were compared. The results show that, at the initial stage of cloud formation, a higher number of smaller clouds are formed in compared with . The small clouds in are subject to considerable evaporative cooling at their edges and shell regions, due to entrainment processes. As a result, these clouds often dissolve before they can grow deep. Later on, cloud aggregation in also enables precipitation. The delayed onset of precipitation and reduced areas of aggregated clouds having low precipitation rates are the main reasons for less precipitation in than in .
Highlights
Convective precipitation is one of the more difficult phenomena to forecast in model simulations, as the processes involved range over the spatiotemporal micro- and mesoscales
We investigated the impact of model grid spacing and land-surface resolution (LSR) on clouds and convective precipitation for areas of different orographic complexities, that is, flat terrain, an isolated mountain range, and mountainous terrain
The impact of LSR on precipitation was deduced by using resolutions of land-surface properties and/or orography of 1,250 and 5,000 m, keeping the model grid spacing at 156 m
Summary
Convective precipitation is one of the more difficult phenomena to forecast in model simulations, as the processes involved range over the spatiotemporal micro- and mesoscales. The simulated precipitation depends on, for example, the model grid spacing, turbulence parameterization scheme, initial and boundary conditions, and land-surface resolution (LSR). It is important to know how moist convection and precipitation depend on model grid spacing and LSR in the grey zone, as initiation and evolution of moist convection is coupled with land-surface parameters (Avissar and Chen, 1993) and their resolution (Banta, 1990; Weckwerth, 2000). It is interesting to know how the impacts of model grid spacing and LSR compare with respect to triggering of convection, onset, and spatial distribution of clouds and precipitation, as well as precipitation intensity.
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