Characteristics of mid‐latitude whistler ducts as deduced from ground‐based measurements

Propagation characteristics of mid-latitude whistlers, especially whistler duct characteristics, have been investigated based on measurements in August, 1994 at Dunedin, New Zealand(L=2.78) and in August, 1989 at Ceduna, Australia(L=1.93), both during local midnight. Polarization analyses have enabled us to locate whistlers which exited the ionosphere just above the observing station (LDF is defined in this way). The nose extension method was also applied to these whistlers (their Ln is estimated by this method). The following findings have emerged from the analyses; LDF ≃ Ln (at Dunedin) and LDF ≃ Ln-0.43(at Ceduna). Our analysis suggests that mid-latitude ducts are likely to extend down to the ionosphere at L ≈ 2.8. Ray tracing studies for realistic density profiles indicates that a whistler duct terminates at an altitude of about 3,500 ∼ 5,500 km at an L value of ∼1.9 with its enhancement factor being a few percent at least. These results may imply a strong variability of the latitudinal or temporal variations of mid-latitude whistler ducts.