Abstract
General characteristics of K-changes, including their duration and probability of occurrence associated with ground flashes in Sri Lanka in the tropics, together with their fine structure, are presented. In 98 ground flashes where the small step changes associated with K-changes are clearly visible, there were about two K-changes per flash on average. The mean K-change time duration observed in this study is 0.38 ms. In 53 of the ground flashes, there were 120 consecutive K-changes. In these cases, the geometric mean of the time interval between K-changes was 12 ms. Analysis of the fine structure of the K-changes reveals the K-changes are always associated with either a chaotic pulse train or a combination of chaotic and regular pulse trains. The results suggest that the small step-like static electric fields identified in the literature as K-changes are the step-like static fields associated with the processes that generate chaotic or a combination of chaotic and regular pulse trains. Thus, at larger distances where the static fields are negligible, K-changes may appear as a chaotic pulse train or a combination of chaotic and regular pulse trains.
Highlights
Kitagawa [1] and Kitagawa and Kobayashi [2] were the first scientists to identify and study theK-changes in lightning flashes
Our study indicates the fine structure associated with the K-change is either a chaotic pulse train (CPT)
Observations in this study suggest that the K-changes are associated with the physical activity in the cloud that gives rise to either chaotic pulse train or a combination of chaotic chaotic pulse trains
Summary
The term K-change is used today to denote relatively small step-like static field changes that occur in between and after return strokes, and during intra-cloud flashes. By analyzing how the polarity of the K-changes vary with the distance, they concluded that they are produced by electrical activity inside the cloud. Kitagawa and Brook [3] analyzed the signature of these pulses, both for cloud and ground flashes in detail, and concluded that there is no difference between the K-changes produced during cloud and ground flashes. Brook and Kitagawa [4] observed strong electromagnetic emissions within 400 MHz to 1000 MHz during K-changes, and Ogawa and. Brook [5] proposed that K-changes were produced by return stroke-like discharges that travel along positive leaders when they encounter negatively-charged regions.
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