Correlation between Lightning Density and Precipitation Amount based on high-resolution Radar Measurements

In order to understand thunderstorms it is necessary to explore the relationship between lightning and precipitation. In recent studies it was found that the amount of precipitation and lightning initiation depend on the size and number of cloud particles as well as on cloud type.

The authors intend to analyse the statistical correlation between lightning density and precipitation amount on small scales. Therefore high-resolution X-Band Radar data are used to verify the results from similar studies as well as to check whether the high resolution offers additional information. The evaluation area is limited to the range of the radar network in the North of Hamburg with a resolution of 250 m and 30 s. The analysis is limited to six hours of one selected thunder storm from June 19th, 2013 featuring high lightning density. Rainfall data are essentially checked for lightning specificity using probability density functions. The overall distribution of precipitation and the lightning-related rainfall distribution are significant different. Considering only grid point radar measurements in the vicinity of lightning results in a strong increase of mean reflectivity from more than 35 up to 50 dBZ and a skewed distribution indicating that detected flashes are more likely at high precipitation reflectivities.

To verify the local mapping, a method of spatial and temporal running mean is applied. Using linear correlation coefficients a negative time lag between the strongest lightning activity and rainfall maximum is determined. For a spatial averaging interval not larger than 10 km x 10 km and an averaging time of up to 10 minutes the time lag is between 6.5 and 8 minutes. Thereby the highest calculated correlation coefficient is 0.59. These results largely confirms the results from previous studies of coarse-scale areas. Interestingly, the correlations are highest at these coarse-scale whereas the statistical relation between precipitation and lightning decreases with higher resolution.