Abstruct-A melting layer model related to the physical constants and meteorological parameters is employed in this investigation. The specific phase shift, together with the specific attenuation, is computed at 1-100 GHz by using the Mie theory. The additional zenith attenuation, which is the difference between zenith attenuation due to the melting layer and attenuation due to the same thickness of the resulting rain, is comprehensively studied. The ratio of the difference to rain zenith attenuation may be over 1 at 1-5 GHz although the difference is much less than 1 dB. The difference can be over 1 dB at frequencies above 20 GHz. A minimum of the ratio is below 0.05 at frequencies about 40-60 GHz but the ratio can become a value of about 0.1 at 100 GHz. The additional attenuation should be taken into account in satellite-earth communications and radar remote sensing. The power law parameters of the average specific attenuation of the melting layer and rain specific attenuation are tabulated for three raindrop size distributions at rain rates of below 25 mm/h. The power law method could be utilized in the additional attenuation calculation. It is a good approximation of the Mie theory results at 1-50 GHz and a useful estimate at 50-100 GHz.