Whistler Precursors

A study has been made of the whistler precursor events that have been observed at the “Whistlers‐East” network of Dartmouth College in the period from IGY through IQSY. The results confirm the earlier reports that precursors are associated only with two‐hop whistlers. Other results are presented to illustrate some of the common features of precursor events, such as the absence of one‐hop hybrid components, the relatively high intensity of precursors, and the repeatability of the patterns of precursor events over time periods as long as a day. It is concluded that while the exact nature of the mechanism of precursor generation is not yet clear, we are probably dealing with triggering involving an instability process in a fairly limited region of space. The mechanism must, however, differ in some significant respect from the type of forward‐triggering that has been discussed in some detail in the literature.