def _gradient_names(scale, sig_ratio):
    """Return names for the arrays in output of the gradient function"""

    name_dx = f"WE_DERIVATIVE_{scale}M_SIGRATIO{sig_ratio:.3g}"
    name_dy = f"SN_DERIVATIVE_{scale}M_SIGRATIO{sig_ratio:.3g}"
    name_slope = f"SLOPE_{scale}M_SIGRATIO{sig_ratio:.3g}"
    name_aspect = f"ASPECT_{scale}M_SIGRATIO{sig_ratio:.3g}"

    return [name_dx, name_dy, name_slope, name_aspect]