A Study of E-field Peaks Associated with Maritime Negative First Return Strokes

Cummins et al. have clarified that the maritime return-stroke current on the Gulf of Mexico is higher than the inland return-stroke current by using the current obtained by NLDN. In this report, the authors compare the inland and the maritime negative first return-stroke current in southern part of Kyusyu locating in the south of Japan by using the data obtained by JLDN. The 50% value of the peaks of the maritime return strokes are higher than those of the inland return strokes. This tendency is the same as is shown by Cummins et al. by using the data obtained by NLDN. Murray et al. categorized the time derivative of the E-Field waveforms sampled every 10ns with respect to the peak in the time range from -4 to 1 microseconds of the main peak. Therefore, the authors calculated the time derivative of the E-Field waveform associated with maritime negative first return strokes, measured at a seashore station with the sampling interval of 40ns in south Kyusyu. The number of data subject to analysis is 268, and the propagation distance over land for these waves, influential on the high frequency components, is less than 385m. The frequency of occurrence for the three type agrees with that reported by Murray et al. with the discrepancy of less than 6percents. The authors found some difference in the distribution of the field peaks, and attribute them mainly to the difference of the sampling interval of the recording system and the frequency range in the measurement.