Date post: | 30-Dec-2015 |
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Radiation Calculation on a Coarser Grid - Very First Results With LMK
Thorsten Reinhardt, Deutscher [email protected]
Motivation
• Standard calling frequency of radiation scheme: 1 hr, but more frequent calling would be costly
• Column assumption at small grid sizes questionable
• Calling radiation only every hour questionable
Cloud
dx=2.8 km (LMK grid size)assume cloud 7 grid sizes big, moving at v=10.9 m/s
assume cloudmoving at v=10.9 m/s
Cloud
then the cloud has moved 7 gridpoints after 30 min,if dx=2.8 km
assume cloudmoving at v=10.9 m/s
actual cloud
then the cloud has moved 7 gridpoints after 30 min,if dx=2.8 km
But radiative effect is taken into account still at old position!
cloud radiative effect
Therefore:
Calculate radiation scheme on a coarser grid.
Call radiation scheme more frequently.
Approach: calculate radiation on a coarser grid
LMK grid
grid for radiation
Procedure1) Average input variables onto coarser grid
2) Calculate radiation on coarser grid
3) Re-distribute onto LMK grid
4) Smooth output with discrete filter
5) Apply albedo correction
Current implementation: maximal grid size of coarse grid: (nboundlines+1) x LMK gridAveraging (Step 4) and albedo correction (Step 5) can be switched on/off
LMK Testsuite 2.2c for July 2004
Changes compared to Testsuite 2.2:
• Radiation on a coarser (2x2) grid• Call radiation very 15 min instead of every hour
First Results:
First Results:
Overall: nearly neutral impact
• Bottom and top radiative fluxes, averaged: neutral• Verification against 24-h precipitation sums: ok• Eye-inspection of visualized output: ok• Verification against synop data: not yet done• Pointwise, of course, also bigger differences
Outlook:It might be better to vary continously position of coarse grid vs. fine grid.