def stabilityParam(L_m, siteConf):
    """
    Calculates the Monin-Obukhov Similarity Variable
    defined as

    zeta = (z-d)/Lo
    where d is the displacement height or zero-plane displacement
    and L_m is the Monin-Obukhov Length.
    """
    z = siteConf.measurement_height
    d = siteConf.displacement_height
    zeta = (z - d) / L_m
    return zeta
