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Planet with auroral oval and two pythons representing closed and open magnetic field lines Overview

OCBpy is a Python module that converts between AACGM coordinates and a magnetic coordinate system that adjusts latitude and local time relative to the Open Closed field line Boundary (OCB). This is particulary useful for statistical studies of the poles, where gridding relative to a fixed magnetic coordinate system would cause averaging of different physical regions, such as auroral and polar cap measurements. This coordinate system is described in:

  • Chisham, G. (2017), A new methodology for the development of high‐latitude ionospheric climatologies and empirical models, Journal of Geophysical Research: Space Physics, doi:10.1002/2016JA023235.

  • Full documentation

OCBs must be obtained from observations for this coordinate transformation. In the British Antarctic Survey's IMAGE Auroral Boundary data project from three auroral instruments provide northern hemisphere OCB locations for 3 May 2000 03:01:42 UT - 22 Aug 2002 00:01:28, though not all of the times included in these files contain high-quality estimations of the OCB. Recommended selection criteria are included as defaults in the OCBoundary class. OCBpy also supports boundaries provided by AMPERE and DMSP:

Currently, support is included for files from the following datasets:

These routines may be used as a guide to write routines for other datasets.

Python versions

This module has been tested on python version 2.7, 3.5 - 3.8. Support for 2.7 will be dropped in 2020.


The listed dependecies were tested with the following versions:

  • numpy
  • aacgmv2
  • pysat (2.0.0+)
  • ssj_auroral_boundary

Testing is performed using the python module, unittest. To limit dependency issues, pysat (>=2.0.0) and ssj_auroral_boundary are optional dependencies.


Installation is now available through pypi

    $ pip install ocbpy

You may also checkout the repository and install it yourself:

    $ git clone git://;

Change directories into the repository folder and run the file. For a local install use the "--user" flag after "install".

    $ cd ocbpy/
    $ python install

To run the unit tests,

    $ python -m unittest discover


In iPython, run:

import numpy as np
import ocbpy

Then initialise an OCB class object. This uses the default IMAGE FUV file and will take a few minutes to load.

ocb = ocbpy.ocboundary.OCBoundary()

The output should be as follows:

Open-Closed Boundary file: ~/ocbpy/ocbpy/boundaries/si13_north_circle
Source instrument: IMAGE
Open-Closed Boundary reference latitude: 74.0 degrees

219927 records from 2000-05-05 11:35:27 to 2002-08-22 00:01:28

YYYY-MM-DD HH:MM:SS Phi_Centre R_Centre R
2000-05-05 11:35:27 356.93 8.74 9.69
2000-05-05 11:37:23 202.97 13.23 22.23
2002-08-21 23:55:20 322.60 5.49 15.36
2002-08-22 00:01:28 179.02 2.32 19.52

Uses scaling function(s):

Get the first good OCB record, which will be record index 27.



To get the OCB record closest to a specified time, use ocbpy.match_data_ocb

first_good_time = ocb.dtime[ocb.rec_ind]
test_times = [first_good_time + dt.timedelta(minutes=5 * (i + 1))
              for i in range(5)]
itest = ocbpy.match_data_ocb(ocb, test_times, idat=0)
print(itest, ocb.rec_ind, test_times[itest], ocb.dtime[ocb.rec_ind])

0 31 2000-05-05 13:45:30 2000-05-05 13:50:29

More examples are available in the documentation.