Southern boundaries of ultraenergetic relativistic electron precipitations in several cases from 1982 to 1986 years

We analyze the rare phenomenon of ultraenergetic relativistic electron (∼100 MeV) precipitation into the middle polar atmosphere prevalent under quiescent geophysical conditions. Such events have been established previously from ground‐based radio wave measurements for two radio paths—one is purely auroral and the other is partly auroral—that have a mutual point of signal reception. We solve an inverse very low frequency wave problem of the second type using these particular paths. The solution gives a linear scale of the northern part of radio path, which has been disturbed by the ultraenergetic relativistic electron precipitations. By such a way the effective latitudes of southern boundaries for several precipitation events, published earlier, were determined. Nearly circular shape of equatorward cutoff at ∼61°magnetic latitude without day‐night asymmetry supports that ultraenergetic relativistic electron precipitation is due to precipitation of very high energy electrons coming from outer space. Key Points South boundary of URE precipitation was determined Precipitation boundary did not exceed 65 degrees of latitude VLF inverse radio problems were solved