Spatial and temporal distribution of lightning activity around Java

Cloud-to-ground lightning flashes on and around the island of Java, Indonesia, in the tropical maritime continent region, were observed continuously by a magnetic direction-finder network for lightning location from December 1994 to January 1996. The annual ground flash density, estimated by correcting the raw data by using the detection efficiency of the network, ranged from less than 2 to about 16 flashes/y/km 2 on the island. The average annual ground flash density over the entire island was 3.2 flashes/y/km 2 , as opposed to 0.24 flashes/y/km 2 on the Indian Ocean about 100 km south of the island. The majority of the flashes on the land occurred during November to April in the rainy season. In the dry season, lightning was active only in the western part of the island. The amount of monthly precipitation over the island was related to the monthly number of ground flashes, but the ratio of the precipitation to the ground flash density differed from season to season, from 4 × 10 8 kg/flash in the rainy season to 1.3 × 10 9 kg/flash for other months. The ratio observed in the rainy season is equal to that for the break period in the rainy season observed at Darwin, Australia, in the same maritime continent region. The annual ratio for the entire island was 6 × 10 8 kg/flash. The diurnal variation of the lightning activity averaged over the island in the set season showed a single peak in the afternoon with the peak time of about 1530 LT, similar to those reported for land stations in the tropics. The diurnal variation over the ocean had a peak in the early morning, showing the same characteristic observed in the western Pacific. The diurnal variation of the lightning activity on the sea of offshore regions around Java showed an almost out-of-phase pattern to the variation on the land, indicating the influence of the land-sea effect.