Vector data - plotting wind flags

This notebook introduces how to plot vector data, such as wind fields, as flags/barbs.

Example: Wind from Storm Ophelia (October 2017)

In this example, we will use sample wind data from Storm Ophelia, which impacted the UK in October 2017.

import earthkit.data as ekd

import earthkit.plots as ekp

data = ekd.from_source("sample", "storm_ophelia_wind_850.grib").to_fieldlist()
data.ls()

	parameter.variable	time.valid_datetime	time.base_datetime	time.step	vertical.level	vertical.level_type	ensemble.member	geography.grid_type
0	u	2017-10-16	2017-10-16	0 days	850	pressure	0	regular_ll
1	v	2017-10-16	2017-10-16	0 days	850	pressure	0	regular_ll

This dataset contains U (zonal wind) and V (meridional wind) components, which earthkit-plots can automatically detect and extract. To plot this data as wind flags, we can use the barbs method:

# Create a map of the region around the UK
chart = ekp.Map(domain=[-20, 5, 40, 60])

# Automatically detect U and V fields and plot vectors
chart.barbs(data)

# Add map features
chart.coastlines()
chart.land()
chart.gridlines()

chart.legend()

# Show the plot
chart.show()

Or using the high-level API:

ekp.geo.barbs(data, domain=[-20, 5, 40, 60])

<earthkit.plots.components.maps.Map at 0x156d74f10>

Alternatively, you can explicitly provide U and V components as u and v arguments. This can be useful when working with datasets that store U and V components separately or which use non-standard metadata.

# Create a map of the region around the UK
chart = ekp.Map(domain=[-20, 5, 40, 60])

# Pass U and V components separately
chart.barbs(u=data.sel({"parameter.variable": "u"}), v=data.sel({"parameter.variable": "v"}))

# Add map features
chart.coastlines()
chart.land()
chart.gridlines()

# Show the plot
chart.show()

Next Steps

Continue exploring the topics in this section to expand your knowledge of vector plotting, including:

• Wind arrows: Learn how to plot vectors using wind arows.

• Resampling and Regridding: Discover how to manage vector density for clearer plots.

• Applying Styles: Customise vector colours, lengths, and arrow styles.