def harris(f, sigma2, **kwargs):
    """ one-side Harris spectra, adopted in Austrilia code

    Args:
        f (1d-ndarray): freqency, unit: Hz
        sigma2 (float): variance, (Iu * vz) ** 2

        **kwargs: spectrum propeteries
        v10 (float): mean wind speed at 10m height, unit: m/s
    """
    v10 = kwargs["v10"]
    x = f * 1800 / v10
    ret = sigma2 / f * 0.6 * x / ((2 + x * x) ** (5.0 / 6))
    return ret