Download CMEMS data

Run this once. It fetches the CMEMS subset that the three Cabo Verde notebooks open from disk and writes it to data/cabo_verde_currents_hourly.nc. Re-running it is cheap: if the file is already there and opens, nothing is downloaded.

examples/data/ is gitignored, so the file is never committed and a fresh clone has to run this notebook before the three Cabo Verde ones.

This assumes copernicusmarine has credentials.

from pathlib import Path

import copernicusmarine as cm
import xarray as xr

The subset

Hourly surface velocity (uo, vo) from Global Ocean Physics Analysis and Forecast, GLOBAL_ANALYSISFORECAST_PHY_001_024, doi:10.48670/moi-00016, dataset cmems_mod_glo_phy_anfc_0.083deg_PT1H-m. A box around Cabo Verde, first depth level only. The examples release particles between 2025-08-01 and 2025-08-11 inside a smaller box; the extra day at each end and the margin in longitude and latitude are there so trajectories stay inside the data.

target = Path("data/cabo_verde_currents_hourly.nc")
target.parent.mkdir(parents=True, exist_ok=True)

try:
    xr.open_dataset(target).close()
    have_file = True
except (FileNotFoundError, OSError):
    have_file = False

print(
    f"{target}: already here, skipping the download"
    if have_file
    else f"{target}: missing, downloading it"
)

data/cabo_verde_currents_hourly.nc: already here, skipping the download

if not have_file:
    ds = cm.open_dataset(
        dataset_id="cmems_mod_glo_phy_anfc_0.083deg_PT1H-m",
        variables=["uo", "vo"],
        minimum_longitude=-30.5,
        maximum_longitude=-17.5,
        minimum_latitude=10.0,
        maximum_latitude=22.0,
        minimum_depth=0.0,
        maximum_depth=1.0,
        start_datetime="2025-07-31",
        end_datetime="2025-08-12",
    ).load()
    ds.to_netcdf(target)

print(f"{target}: {target.stat().st_size / 1e6:.0f} MB on disk")

data/cabo_verde_currents_hourly.nc: 53 MB on disk

What landed on disk

currents = xr.open_dataset(target)
currents

<xarray.Dataset> Size: 53MB
Dimensions:    (time: 289, depth: 1, latitude: 145, longitude: 157)
Coordinates:
  * time       (time) datetime64[ns] 2kB 2025-07-31 ... 2025-08-12
  * depth      (depth) float32 4B 0.494
  * latitude   (latitude) float32 580B 10.0 10.08 10.17 ... 21.83 21.92 22.0
  * longitude  (longitude) float32 628B -30.5 -30.42 -30.33 ... -17.58 -17.5
Data variables:
    uo         (time, depth, latitude, longitude) float32 26MB ...
    vo         (time, depth, latitude, longitude) float32 26MB ...
Attributes:
    Conventions:               CF-1.8
    area:                      Global
    contact:                   https://marine.copernicus.eu/contact
    credit:                    E.U. Copernicus Marine Service Information (CM...
    institution:               Mercator Ocean International
    licence:                   http://marine.copernicus.eu/services-portfolio...
    producer:                  CMEMS - Global Monitoring and Forecasting Centre
    references:                http://marine.copernicus.eu
    source:                    MOI GLO12
    title:                     hourly mean fields from Global Ocean Physics A...
    copernicusmarine_version:  2.4.1