Features of positive ground flashes observed in Kathmandu Nepal

• The positive ground flashes over Nepal is found to be proportionally higher than other geographical regions.
• Electric field signatures of the positive ground flashes were recorded at a measuring station in Kathmandu, at an altitude of about 1300 m above the average sea level and analyzed.
• This is the first time that the fine structure of electric field signatures pertinent to the positive return stroke; have been analyzed and presented from Nepal.
• It is observed that the occurrence of the positive ground flashes is predominant on some of the thunder days with multiplicity of 1.1.
• Features of the positive ground flashes were found to be similar to those observed in other geographical locations, with the average rise time found to be longer than those observed in other geographical locations.

Lightning vertical electric fields pertinent to the subtropical thunderstorms occurring over the rugged terrain have been measured and recorded at a hilly station Kathmandu, Nepal. In the present work, waveforms of the positive ground flashes have been selected from all the records and were analyzed. To the best of our knowledge, this is the first time that fine structure of electric field signature pertinent to the positive return stroke; have been analyzed and presented from Nepal. One hundred and thirty three (133) of the total of four hundred twenty-five (425) flashes were selected from seven thunderstorm days and analyzed. Of the data recorded for seven days, 133 flashes (31.3%) were positive flashes and 276 flashes (64.9%) were cloud flashes. Majority of the positive ground flashes were found to be single stroke ones, whereas, the average number of strokes per flash is found to be 1.1 with a maximum value of 4. Majority of the positive ground flashes were found either lacking the initial breakdown process and the leader stage or these processes could not be detected. The return strokes are found to be succeeded by large in cloud activity in the continuing current portion of the flash. The average zero-crossing time of the positive return strokes was found to be 60.45 µs with a range of 447.81 µs and the average rise time was found to be 9.44 µs with a range of 42.56 µs.