Publication Date:
2019
Description:
A sub‐grid parameterization scheme representing the enhancement of precipitation due to sub‐grid orography via the seeder‐feeder effect has been modified to account for flow blocking in small Froude number situations. The scheme was validated in a set of Limited Area Model simulations with a 1.5~km grid spacing, in which the orography was degraded by varying amounts. For simulations in which the largest orographic scales are still fairly well represented, the Seeder Feeder scheme was able to reduce the precipitation deficit by 30% to 70%. For simulations where the hills were completely sub‐grid, the Seeder Feeder scheme was still able to reduce the precipitation deficit by 10% to 30%. As well as increasing the integrated precipitation in global simulations with various grid spacings, some of the precipitation production was shifted from the convection scheme, with its very simple microphysical representation, to the microphysics scheme.
In a long‐duration climate simulation, Seeder Feeder scheme enhancements of orographic precipitation perturb the large‐scale hydrological cycle, as evidenced by the far‐field changes in both microphysical and convective precipitation. Changes over major mountain ranges were similar to those described for the case studies, so long as the upstream precipitation impinging on the mountains was not reduced by these changes in the global hydrological cycle.
Increased atmospheric drying reduces column‐integrated resolved cloud water mixing ratios over mountains, reducing a positive bias in the amount of optically thick cloud with low to mid‐level tops compared to ISCCP satellite observations. The associated reductions in cloud albedo slightly reduced the RMS error in the TOA outgoing shortwave radiative fluxes over mountains compared to CERES satellite observations.
Print ISSN:
0035-9009
Electronic ISSN:
1477-870X
Topics:
Geography
,
Physics
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