def normal_curl_evar(curl_evar, unscaled_r, scaled_r):
    """ Normalise a variable proportional to the curl of the electric field

    Parameters
    -----------
    curl_evar : (float)
        Variable related to electric field (e.g. vorticity)
    unscaled_r : (float)
        Radius of polar cap in degrees
    scaled_r : (float)
        Radius of normalised OCB polar cap in degrees

    Returns
    --------
    nvar : (float)
        Normalised variable

    Notes
    -------
    Assumes that the cross polar cap potential is fixed across the polar cap
    regardless of the radius of the Open Closed field line Boundary.  This is
    commonly assumed when looking at statistical patterns that control the IMF
    (which accounts for dayside reconnection) and assume that the nightside
    reconnection influence is averaged out over the averaged period.

    References
    -----------
    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.
    """
    nvar = curl_evar * (unscaled_r / scaled_r) ** 2
    return nvar
