Vertical radar reflectivity profiles in Slovenia

Summary Radar reflectivity from hydrometeors is used for the estimation of the precipitation rate at ground level. If the vertical reflectivity profile is taken into account, the estimate can be improved considerably. In the first part of the article some theoretical explanations are given for the two most pronounced characteristic of the vertical radar reflectivity profile from clouds. In general, the observed values decrease with height in the upper part of the radar echo due to the growth of precipitation particles by collision and coalescence. The effect of the bright band, especially in more stratiform types of precipitation, adds a significant strong peak to the profile, at the approximate height of the 0 °C isotherm. These explanations, although being simplified, also provide a quantitative explanation of the two characteristics mentioned previously. Averaged seasonal characteristics of vertical profiles in Slovenia are used as the climatological basis for the construction of an idealised profile for correcting the precipitation estimate. For individual cases, and also after averaging, a maximum in the profiles can clearly be detected. This maximum is much sharper if the profiles are normalised. When looking at time changes, it is shown that most of the changes in radar reflectivity, on average, occur during a roughly 6-hour time-lag between the two measurements. With greater time-lags, the differences are smaller on average. This is caused by the local natural evolution of the precipitation field and indicates that a 6-hour to 12-hour accumulating and averaging of data could diminish much of the error due to the time variation in radar estimated precipitation.With 5 Figures