Weather

The 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;

  • valid_time coordinate: required when the configured data_resolution is finer than the configured file_resolution (i.e., a single file holds multiple time steps). In that case valid_time is sliced via xarray.Dataset.sel(method='nearest', tolerance=1h) for the requested timestamp. If data_resolution equals file_resolution, valid_time is absent or length-1 and no slicing is performed.

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:

import pandas as pd

from AEIC.config import Config
from AEIC.config.weather import TemporalResolution
from AEIC.trajectories.ground_track import GroundTrack
from AEIC.types.spatial import Location
from AEIC.weather import Weather

Config.load()

# Construct a Weather instance pointing at a directory of daily ERA5
# NetCDF files (one file per UTC day, named YYYY-MM-DD.nc by default).
weather = Weather('data/weather', file_resolution=TemporalResolution.DAILY)

# Build a great-circle track between two locations.
track = GroundTrack.great_circle(
    Location(longitude=-71.0, latitude=42.4),   # origin
    Location(longitude=-0.5, latitude=51.5),    # destination
)

ground_speed = weather.get_ground_speed(
    time=pd.Timestamp('2024-09-01 12:00:00', tz='UTC'),
    gt_point=track.location(5000.0),  # 5 km along the track
    altitude=10000.0,                  # meters above sea level
    true_airspeed=230.0,               # m/s
)

Class members

class AEIC.weather.Weather(data_dir, file_resolution, data_resolution=None, file_format=None)

A class to query weather data variables and ground speed along ground track points.

Parameters:

  • data_dir (str | Path) – Path to directory containing ERA5 weather data NetCDF files. The filename for a given timestamp is resolved via file_format. Files should contain variables t, u, v with coordinates pressure_level, latitude, longitude. A valid_time coord is required when data_resolution is finer than file_resolution and is otherwise either absent or length-1.

  • file_resolution (TemporalResolution) – Temporal layout of files on disk: one file per file_resolution period. Must be annual, monthly, or daily.

  • data_resolution (TemporalResolution, optional) – Temporal resolution of the data within each file. Defaults to file_resolution (one period-mean per file). Must satisfy data_resolution <= file_resolution.

  • file_format (str, optional) – strftime-style pattern (relative to data_dir) for mapping a timestamp to a filename. Defaults are derived from file_resolution: %Y.nc (annual), %Y-%m.nc (monthly), %Y-%m-%d.nc (daily).

get_ground_speed(time, gt_point, altitude, true_airspeed, azimuth=None)

Compute ground speed at a point along the mission.

Parameters:

  • time (pd.Timestamp) – Time at the ground track point. Interpreted as UTC; tz-aware timestamps are converted to UTC, tz-naive timestamps are assumed UTC.

  • gt_point (GroundTrack.Point) – Spatial point along the ground track from the origin.

  • altitude (float) – Altitude above sea level [meters].

  • true_airspeed (float) – True airspeed [m/s].

  • azimuth (float, optional) – Azimuth [degrees]. If omitted, use the precomputed ground-track azimuth.

Returns:

ground_speed – Ground speed [m/s]

Return type:

float