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 Fractions
The field is called 'VF' for Vegetation Fractions even though it also contains ocean, glaciers, and lakes. The following is a table of GEM input vegetation fractions and corresponding roughness lengths. For CLASS the roughness length is the height of the vegetation divided by 10.
In the geophysical fields the variable is called 'VF' but in model output it is called '2V'.
Instead of having one field name for each surface (vegetation) fraction it was decided to use the same name, 'VF', but different levels to distinguish the different types. The fields themselves contain the fraction of the specific type.
| 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 / bare soil | 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
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