Table 4. Values of relevant PRISM interpolation parameters.
Name | Description | T dmean | VPD min | VPD max |
---|---|---|---|---|
Regression Function | ||||
R | Radius of influence | 20 km* | 20 km* | 20 km* |
s t | Minimum number of total stations desired in regression | 25 stations | 25 stations | 25 stations |
β 1ma | Min valid regression slope, layer 1 | -0.5 + | -10/-1/-1.5 # | 0.99/0/0 # |
β 1xa | Max valid regression slope, layer 1 | 2.5 + | 10/2/1 # | 1.01/1.5/1.5 |
β 1da | Default regression slope, layer 1 | 0.5 + | 1/0.5/0.5 # | 1/1/1 # |
β 1mb | Min valid regression slope, layer 2 | -0.5 + | -10/-1/-1 # | 0.99/0/0 # |
β 1xb | Max valid regression slope, layer 2 | 2.5 + | 10/2/1 # | 1.01/1.5/1.5 # |
β 1db | Default regression slope, layer 2 | 0.5 + | 1/1/0.5 # | 1/1/1 # |
Distance Weighting | ||||
A | Weighting exponent | 1.5 | 1.5 | 1.5 |
F d | Importance factor | 0.5 | 0.5 | 0.5 |
D m | Minimum allowable distance | 0 km | 0 km | 0 km |
Elevation Weighting | ||||
B | Weighting exponent | 1.5 | 1.5 | 0.5 |
F z | Importance factor | 0.5 | 0.5 | 0.5 |
Δz m | Station-grid cell elev difference below which weight is maximum | 100 m | 100 m | 100 m |
Δz x | Station-grid cell elev difference above which weight is zero | 5000 m | 5000 m | 5000 m |
Coastal Proximity Weighting | ||||
v | Weighting exponent | 1.0 | 1.0 | 1.0 |
Δp m | Station-grid cell proximity difference below which weight is maximum | 100 $ | 100 $ | 100 $ |
Δp x | Station-grid cell proximity difference above which weight is zero | 300 $ | 300 $ | 300 $ |
Vertical Layer Weighting | ||||
y | Weighting exponent | 0.5 | 0.5 | 0.5 |
Δl m | Station-grid cell distance to adjacent layer below which weight is maximum | 100 m | 100 m | 100 m |
Δl x | Station-grid cell distance to adjacent layer above which weight is zero | N/A | N/A | N/A |
Topographic Position Weighting | ||||
μ | Weighting exponent | 1.5 | 1.5 | 1.5 |
Δt m | Station-grid cell topo difference below which weight is maximum | 50 m | 50 m | 50 m |
Δt x | Station-grid cell topo difference above which weight is zero | 900 m | 900 m | 900 m |
* Expands as needed to encompass minimum number of total stations desired in regression (s t).
+ Slope is expressed as the change in dew point depression (DPD) per unit Tmin from the predictor grid
# Slope is expressed as the change in VPD per unit first-guess VPD from the predictor grid
$ Units are effective distance in grid cells from the coast, incorporating terrain barriers