On the relationship between Z-R, the bright band intensity and ZDR in stratiform precipitation

Deposition, riming and aggregation are the dominating processes in snow growth. The balance of these processes determines the density-size relationship of snow and shapes the characteristic drop size distributions (and, thus, Z-R relationships) in the rain region immediately below the melting layer. The density of snow also has an impact on the characteristics of the resulting bright band: large snow aggregates result in much more intense bright bands than dense rimed particles and also give rise to a greater number of large drops, resulting in an overestimation of rain rate using an average Z-R relationship. Similarly, Z_DR provides information about the dominating sizes of drops in rainfall and has widely been used to improve estimates of rainfall together with Z.

In this study, we have used disdrometer observations collocated with a vertically-pointing radar to investigate the functional dependency of the residuals in radar rainfall estimates using a climatological Z-R relationship with the intensity of the melting layer and with Z_DR. The ultimate goal of the study is to quantify the amount of common information in the latter two variables and assess their potential to improve estimation of rainfall at ground.