| 726 | 726 | ||[=#PA0503 PA0503] || z0 exceeds surface-layer height at horizontal/vertical natural/urban surface and is decreased appropriately || In PALM, Monin-Obukhov similarity is assumed between the surface and the first computational grid point normal to the surface. Because of the staggered grid, the distance between these two points is half of the grid spacing in the respective direction, i.e. dz/2 in vertical direction. The height z = dz/2 defines the top of the (analytical) logarithmic layer zs, which is called the surface layer height here. Now functions like {{{ln(zs/z0)}}}, where z0 is the roughness length, are used to calculate characteristic surface layer variables like u* or theta*. This mathematically requires that {{{zs > z0}}}, or in other words, that {{{z0 < dz/2}}}. In case you have run into this error, you either need to reduce the roughness length z0 or increase the grid spacing dz. \\ '''Attention:''' This message is given only once (for the first grid point where the exceedance has been detected). Be aware that there might be more grid points where z0 exceeds the surface-layer height. || |
