# Weather

The {py:mod}`AEIC.weather` module loads ERA5-style NetCDF files and provides
wind-aware ground speeds along a mission's ground track.

The dataset is read from disk (no pre-processing required) and must contain:

 * variables: temperature `t` [K], eastward wind `u` [m/s], northward wind `v`
   [m/s];
 * coordinates: `pressure_level` [hPa], `latitude`, `longitude`;
 * optional dimension: `valid_time` (sliced using `mission.departure.hour` if
  present).

During a ground-speed query, altitude is converted to a pressure level using a
standard-atmosphere approximation, winds are interpolated at the requested
longitude/latitude, and those winds are combined with the aircraft heading
derived from the ground track (or an override supplied via `azimuth`).

Example::

```python
   mission = Mission(...)
   track = GroundTrack.great_circle(
       mission.origin_position.location,
       mission.destination_position.location,
   )

   weather = Weather('data/weather/sample_weather_subset.nc', mission, track)
   ground_speed = weather.get_ground_speed(
       ground_distance=5000.0,  # meters from departure
       altitude=10000.0,        # meters
       true_airspeed=230.0,      # m/s
   )
```

## Class members

```{eval-rst}
.. autoclass:: AEIC.weather.weather.Weather
   :members:
```