...

Fields and observations can often contain missing values - it can be important to understand the implications of these, and also how to use them to remove unwanted data points. Using a mask of missing values can enable Metview to perform computations on a specific subset of points.

XXXX Download data

Computing the mean surface temperature over land

...

The variable lsm has been replaced with a stricter mask. Applying boolean operators such as < and > returns a result consisting entirely of 1s (where the grid values pass the test) and 0s (where the grid values fail the test). Visualise Plot the result with gridvals to confirm this change.

Now we want to read t2m.grib and 'deactivate' the points where the land-sea mask is 0 (the sea points).

...