Characteristics of Lightning Electric Fields Over Land and Sea Observed in Sarawak, Malaysia
Abstract
Many researchers around the world have investigated the lightning electric field characteristics of return strokes occurring over the sea and land. However, such studies are never carried out in East Malaysia, which is surrounded by the South China Sea. Therefore, this paper presents the characteristics of lightning electric fields overland and at sea observed in Sibu, Sarawak. In this measurement, a total of 42 negative cloud-to-ground lightnings (24 from over the land and 18 from over the sea) were considered for further analysis. The samples were collected at distances ranging from 26 to 100 km using a parallel plate antenna. Four parameters of the first return strokes were measured, namely, normal electric field (En), zero crossing time (Tzc), zero-to-peak rise time (Tzp), and 10-90% rise time (T10−90). The lightning that was captured over the sea in Sarawak had an En value that was 2% lower, Tzc that was more than twice longer, Tzp, and T10−90 that were 7% and 23% shorter, respectively, when it was on land. The results obtained in Sarawak (East Malaysia) compared with those from Kuala Perlis (West Malaysia) revealed the attribution of roughness to variations in lightning parameters. It has been observed that when the roughness of the propagation medium increases, En and Tzp decrease. Whereas, T10−90 increases with increasing propagation medium roughness. On the contrary, Tzc is independent of the roughness of the propagation medium due to its strong negative correlation with En. In terms of correlations between lightning parameters and propagation distance, En measured at both sea and land in Sarawak has a negative correlation with propagation distance. Meanwhile, Tzc, Tzp and T10−90 observed from the land show a positive correlation with propagation distance. In contrast, the same three parameters observed from the sea have a negative correlation with propagation distance. In summary, the patterns of lightning characteristics mentioned above are very useful in identifying the origin of the lightning event.
