Methods of determining whistler nose-frequency and minimum group delay

The optimization of the method whereby the key whistler parameters, nose-frequency (fn) and minimum group delay (tn) are determined is important for the efficient reduction of whistler recordings to yield magnetospheric electric field data (from the motion of whistler ducts) and electron tube content. Various methods proposed in the literature, together with a new iteration method based on that of Dowden and Allcock, are applied to 1. (i) theoretical whistler profiles 2. (ii) single whistlers for which fn may be measured directly, 3. (iii) single whistlers for which neither fn nor the sferic time may be measured directly 4. (iv) multi-component groups of whistlers. This critical comparison of the different methods using some two hundred whistlers, with nose-frequencies lying in the range 3 < fn < 7 kHz, leads us to the conclusion that, for the location of Halley Bay, no significant gain in accuracy is obtained by taking more than three points on a whistler profile. The deviation of an observed profile from that theoretically calculated is discussed in terms of the normalized profile ( ffnvs.ttn ). The deviations cannot be attributed simply to scaling errors and are non-random in nature. The sonagrams indicate that they are related to variation in the whistler signal intensity along its profile, indicative of wave-amplification and the triggering of ELF/VLF emissions. Ariel 4 studies have shown that wave-particle interactions are most prevalent in this longitude sector which is to the west of the South Atlantic Anomaly.

Details