Gradient

Gridpp supports several ways to downscale fields by using an elevation gradient. The constant lapse rate method prescribes a fixed elevation gradient that is used across the whole field. A more advanced approach is to let gridpp compute a local elevation gradient by looking in a neighbourhood surounding a given gridpoint. Gradients can also occur due to land-sea differences.

Meteorological variables change predictably with elevation. When a high resolution topography is available, coarse resolution models can be downscaled by fitting the variable to the new topography.

In v0.3.0, a combined coastal and elevation gradient approach is implemented. The method first computes an elevation gradient based on land points only, and then computes a land-sea gradient after correcting points in a neighbourhood with the elevation gradient.

The two gradients are then added.

Library example

Currently, only a fixed elevation gradient is supported in the library:

import gridpp
ovalues = gridpp.simple_gradient(igrid, ogrid, temp_analysis[:, :, 0], -0.0065)

Command-line example

The following applies a 6.5°C/km lapse rate:

gridpp input.nc output.nc -v air_temperature_2m -d gradient constantGradient=-0.0065

The following uses a local gradient based on a neighbourhood with radius of 3 gridpoints:

gridpp input.nc output.nc -v air_temperature_2m -d gradient radius=3