Abstract
Whether the size distribution change due to coalescence or breakup of melting snowflakes and raindrops occur significantly in the lower-half region of the melting layer and the raindrop region is investigated by the two wavelength radar observation together with model calculation. This observational technique is based on a fact that response of radar reflectivity factor to size distribution transition between two altitudes is dependent on theradar wavelength. We use two radars with wavelength of 3.2cm (X-band) and 0.86cm (K-band) since the two wavelengths give a significant difference of the radar reflectivity factor within a size range of observing particles.
The comparison of the observed and calculated results reveals a strong evidence of particle size distribution transition equivalent to coalescence in the lower-half region of the melting layer for stably uniform precipitations, i.e., typical stratiform precipitation. The activity of the distribution transition does not strongly depend on the precipitation intensity. For the same type of the precipitation, when the precipitation rate is relatively large, increase of medium-sized particles (0.1-0.25cm in diameter) is likely to be predominant in the raindrop region just below the melting layer. Any distinguishable evidences cannot be found for less-uniform precipitations with weak cellular structures.
