.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/geophysics/plot_08_brunhes_reversed_magnetization.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_geophysics_plot_08_brunhes_reversed_magnetization.py>`
        to download the full example code or to run this example in your browser via JupyterLite.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_geophysics_plot_08_brunhes_reversed_magnetization.py:


Brunhes's reversed magnetization (1906)
=======================================

Bernard Brunhes studied a lava flow at Pontfarein in the Massif Central and
the clay it had baked as it flowed over it. Both were magnetized in the same
direction, nearly opposite to today's field: pointing south and up. The clay
could only have taken its magnetization from the field as it cooled, so the
field itself had pointed the other way. A reversed dipole at the site's
latitude of 45 degrees gives a declination of 180 degrees and an inclination of
-63 degrees.

.. GENERATED FROM PYTHON SOURCE LINES 13-47



.. image-sg:: /api/gallery/geophysics/images/sphx_glr_plot_08_brunhes_reversed_magnetization_001.png
   :alt: Lava and baked clay point south and up
   :srcset: /api/gallery/geophysics/images/sphx_glr_plot_08_brunhes_reversed_magnetization_001.png
   :class: sphx-glr-single-img





.. code-block:: Python


    import matplotlib.pyplot as plt
    import numpy as np

    from earthsciencekit.geophysics import dipole_field, direction_angle, field_elements
    from earthsciencekit.units import convert

    latitude = np.radians(45.0)
    normal = field_elements(*np.insert(dipole_field(latitude, 6.371e6, 8e22), 1, 0))
    reversed_field = field_elements(*np.insert(dipole_field(latitude, 6.371e6, -8e22), 1, 0))
    assert np.isclose(abs(reversed_field[0]), np.pi) and np.isclose(reversed_field[1], -normal[1])
    assert np.isclose(convert(reversed_field[1], "rad", "degree"), -np.degrees(np.arctan(2)))

    rng = np.random.default_rng(1906)
    scatter = rng.normal(0, 0.04, size=(2, 12, 3))
    samples = {}
    for k, name in enumerate(["lava", "baked clay"]):
        vectors = np.insert(dipole_field(latitude, 6.371e6, -8e22), 1, 0) / 3e-5 + scatter[k]
        samples[name] = field_elements(vectors[:, 0], vectors[:, 1], vectors[:, 2])
        assert np.all(direction_angle(samples[name][:, 0], samples[name][:, 1], reversed_field[0], reversed_field[1]) < np.radians(10))

    fig = plt.figure(figsize=(5, 5))
    ax = fig.add_subplot(projection="polar")
    ax.set_theta_zero_location("N")
    ax.set_theta_direction(-1)
    for name, marker in [("lava", "o"), ("baked clay", "s")]:
        ax.plot(samples[name][:, 0], 90 - np.abs(np.degrees(samples[name][:, 1])), marker, mfc="none", ls="", label=f"{name} (upward)")
    ax.plot(normal[0], 90 - np.degrees(normal[1]), "k*", ms=12, label="today's field (downward)")
    ax.set_rlim(0, 90)
    ax.set_yticklabels([])
    ax.set_title("Lava and baked clay point south and up")
    ax.legend(loc="lower left", fontsize="small")

    plt.show()


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.101 seconds)


.. _sphx_glr_download_api_gallery_geophysics_plot_08_brunhes_reversed_magnetization.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: lite-badge

      .. image:: images/jupyterlite_badge_logo.svg
        :target: ../../../lite/lab/index.html?path=api/gallery/geophysics/plot_08_brunhes_reversed_magnetization.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_08_brunhes_reversed_magnetization.ipynb <plot_08_brunhes_reversed_magnetization.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_08_brunhes_reversed_magnetization.py <plot_08_brunhes_reversed_magnetization.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_08_brunhes_reversed_magnetization.zip <plot_08_brunhes_reversed_magnetization.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_