The lidar dark band: An oddity of the radar bright band analogy

The properties of the melting layer in rain showers were studied using polarization lidar and W‐band Doppler radar systems, and supporting research aircraft. The changes in hydrometeor scattering behavior at wavelengths ranging from 0.532 µm to 3.2 mm during the snowflake‐to‐raindrop transition generally conform with the expected features of the bright band phenomenon, except that a narrow lidar returned signal minimum, or dark band, was observed ∼750 m below the freezing level. This new feature is found where Doppler velocity and depolarization data indicate raindrops, and, ironically, also occurs at the position of the W‐band radar reflectivity bright band. Drawing from laboratory laser scattering studies and Mie theory, we conclude that the particles responsible for the lidar dark band are inhomogeneous ice‐containing raindrops formed by the structural collapse of severely melted snowflakes.