CHARACTERISTICS OF MIDLATITUDE WHISTLER DUCTS AS DEDUCED FROM GROUND-BASED MEASUREMENTS

Propagation characteristics of mid-latitude whistlers, especially whis tler duct characteristics, have been investigated based on measurement s in August, 1994 at Dunedin, New Zealand(L = 2.78) and in August, 198 9 at Ceduna, Australia(L = 1.93), both during local midnight. Polariza tion analyses have enabled us to locate whistlers which exited the ion osphere just above the observing station (L(DF) is defined in this way ). The nose extension method was also applied to these whistlers (thei r L(n) is estimated by this method). The following findings have emerg ed from the analyses; L(DF) similar or equal to L(n) (at Dunedin) and L(DF) similar or equal to L(n)-0.43(at Ceduna). Our analysis suggests that mid-latitude ducts are likely to extend down to the ionosphere at L approximate to 2.8. Ray tracing studies for realistic density profi les indicates that a whistler duct terminates at an altitude of about 3, 500 similar to 5, 500 km at an L value of similar to 1.9 with its e nhancement factor being a few percent at least. These results may impl y a strong variability of the latitudinal or temporal variations of mi d-latitude whistler ducts.