Area average plots

[mo-tomosevans]

What problem does your feature request solve?

Generates area-weighted averages of a field over a defined region, as is available in the UK trialling branch of the RES toolbox.

Describe the solution you'd like

A clear process to calculating area average for a model. A provisional process could be as follows:

• Identify region
• Read model field
• Mask to region (if required)
• Remove missing data
• Apply area weighting
• Compute the mean
• Plot

Observations should be an option for the plots once available, see #403.

Describe alternatives you've considered

[mo-tomosevans]

The toolbox uses cube_statistics.area_average to calculate the area average of an iris cube. Within this function cube_utils.guess_bounds is called to check bounds, and add them if necessary. This is because iris.analysis.cartography.area_weights is later used to calculate the weighting, which requires bounds on all the coordinates.
The computation of the area-weighted average then uses iris.analysis.MEAN operation over the latitudes and longitudes for a spatial average.

[mo-tomosevans]

RES options
Fields: 1 hr precip rate (total), 10m wind speed, Low/Med/High cloud amount, RelHum at 1.5m, Temp at 1.5m
Obs: None, GPM
Time grouping: Forecast period, Hour, Time

[mo-tomosevans]

Further to this, there needs to be steps when the file path points towards multiple files. Perhaps the option should be there to plot each individual file as its own timeseries but not by default.
The toolbox has a process for this in area_average.area_average. It loads all files and performs extract_overlapping and identify_unique_times functions, then aggregates and produces a single cube to plot.

[mo-tomosevans]

Keep an eye on cell stats development (#1716, amongst others to come) - could be overlap of useful utility functions

[SGallagherMet]

RES options Fields: 1 hr precip rate (total), 10m wind speed, Low/Med/High cloud amount, RelHum at 1.5m, Temp at 1.5m Obs: None, GPM Time grouping: Forecast period, Hour, Time

Just to note that the RES uses Radar over the UK for Precipitation observations.