Geophysical fields are time invariant fields provided to GEM at the beginning of a simulation.
They get created from different geophysical field databases.
Geophysical fields should always match your model grid. They can be larger but should match every model grid point one-to-one.
Dictionary of geophysical fields
| variable name | description | units / range |
|---|---|---|
| ME, MENF | topography elevation | m (may be negative, if below sea-level) |
| MG | land fraction (“land-sea mask”) | 0.0 – 1.0 (no unit) |
| VF ('2V' in output files) | vegetation fraction per class (26 classes) | 0.0 – 1.0 (no unit) |
| VG | class number of dominant vegetation type of above classes | 1 – 26 (integer, no unit) |
| GA | glacier fraction ( same as VF(2) ) | 0.0 – 1.0 (no unit) |
| J1/J2 (ISBA) SAND/CLAY (CLASS) | percentage of sand/clay per layer J1/J2: 5 layers; SAND/CLAY : 1-n layers | 0.0 – 100.0 % |
| DPTH (CLASS) | depth to dedrock | m |
| LDPT (FLake) | lake depth | m |
| Z0 | (effective) total roughness length for momentum | m |
| ZP | ln(Z0) | no unit |
| ZTOP | orographic roughness length for momentum | m |
| ZVG2 | vegetation roughness length for momentum | m |
| SSS | subgrid orography SD (small scale) | m |
| LH | launching height | m |
| Y7,Y8,Y9 | subgrid topography gradient correlations | no unit |
Table of vegetation classes
and corresponding roughness lengths. For CLASS the roughness length is the height of the vegetation divided by 10.
| Arbitrary level # | Description | Z0 [m] |
|---|---|---|
| 1 | salt water, ocean | 0.001 |
| 2 | glacier | 0.0003 |
| 3 | inland lake | 0.001 |
| 4 | evergreen needle-leaf trees | 1.5 |
| 5 | evergreen broadleaf trees | 3.5 |
| 6 | deciduous needle-leaf trees | 1.0 |
| 7 | deciduous broadleaf trees | 2.0 |
| 8 | tropical broadleaf trees | 3.0 |
| 9 | drought deciduous trees | 0.8 |
| 10 | evergreen broadleaf shrubs | 0.05 |
| 11 | deciduous shrubs | 0.15 |
| 12 | thorn shrubs | 0.15 |
| 13 | short grass and forbs | 0.02 |
| 14 | long grass | 0.08 |
| 15 | crops | 0.08 |
| 16 | rice | 0.08 |
| 17 | sugar | 0.35 |
| 18 | maize | 0.25 |
| 19 | cotton | 0.1 |
| 20 | irrigated crops | 0.08 |
| 21 | urban | 1.35 |
| 22 | tundra | 0.01 |
| 23 | swamp | 0.05 |
| 24 | desert | 0.05 |
| 25 | mixed wood forests | 1.5 |
| 26 | mixed shrubs | 0.05 |
Creation of geophysical fields
Geophysical fields for GEM can get created with GenPhysX.
Processing of “vegetation” fields in GenPhysX -> GEM -> CLASS
Click on the following link to learn about the : Processing of “vegetation” fields