Proton Whistlers Research Articles

Experimental observations of proton whistlers from Injun 3 VLF data

A new VLF phenomenon named a proton whistler has been identified in the VLF data from Alouette 1 and Injun 3 satellites. Two independent analyses on 12% of the proton whistler Injun 3 data were conducted: a semimonthly sample of data for Injun 3's 10-month lifetime to determine the gross features of proton whistlers; and a local nighttime and local daytime study of proton whistlers. Six assertions are made from these experimental observations: (1) Proton whistlers are observed only after the reception of an upward-propagating electron whistler. (2) At a frequency termed the crossover frequency (ω12), the initial electron whistler frequency-time trace and the proton whistler trace are coincident in time. (3) Proton whistler traces show initially a rapid rise in frequency which starts at ω12 and which asymptotically approaches the proton gyrofrequency Ω1 (200–650 cps for altitudes of 2700–400 km). (4) Proton whistlers occur more frequently during local nighttime than during local daytime, and they have not been observed to occur below 442 km during local nighttime or below 640 km during local daytime. (5) The ratio of the crossover frequency to the proton gyrofrequency increases with decreasing altitude and approaches unity at an altitude of approximately 440 km around local midnight and approximately 640 km around local noon. (6) There is an apparent northern hemisphere-southern hemisphere asymmetry in the occurrence of proton whistlers; they occur 3 times more frequently in the northern than in the southern hemisphere. Also, there is a high-latitude boundary in the occurrence of proton whistlers that seems to correspond with the auroral zone. The theory describing proton whistlers due to Gurnett is summarized.

Fractional concentration of hydrogen ions in the ionosphere from VLF proton whistler measurement

The derivation and the accuracy of an expression relating the fractional concentration of H+, α1 = n(H+)/ne, to the crossover frequency ω12 for a VLF proton whistler are discussed. To an accuracy of ±3½% it is found that α1 = (264/255) (1 - Λ122), where Λ12 = ω12/Ω1 and Ω1 is the proton gyrofrequency. Values of α1 have been deduced from measurement of proton whistler spectrograms for some of the satellite Injun 3 VLF data and plotted against altitude (400–2600 km) and against invariant latitude (20°–63°) for summer daytime and winter nighttime of 1963. The fractional concentration of H+ is found to be higher for winter nighttime than for summer daytime at all altitudes and latitudes; the ratio was approximately 3:1 at 1000 km. At 1000 km the value of α1 dropped from 0.43 in the 20°–30° invariant latitude range to 0.27 in the 40°–45° range for summer daytime. For winter nighttime α1 was nearly constant at 0.82 for 1000 km from 30° to 50° latitude, but dropped to 0.75 in the 50°–63° latitude range. Near 2400 km for summer daytime, α1 drops from 0.65 at 46° latitude to 0.20 at 56° latitude. This same tendency is observed for winter nighttime, apparently being due to auroral-zone heating. These observations are consistent with the assumption that the heavier ions tend to predominate with increasing latitude for a given altitude. Comparison of these VLF proton whistler results for α1 is made with reasonably good agreement to rocket ion mass spectrometer results of NASA 8.23 and to Alouette 1 VLF results deduced from lower hybrid resonance frequency. This general agreement establishes the VLF radio technique as an independent method for determining ion concentrations in the ionosphere. The general equations for uniquely determining the concentration of O+, He+, and H+ from observation of the critical frequencies (crossovers, hybrid resonances, and cutoffs) due to the presence of ions are presented, and their usage is discussed.

Ion cyclotron whistlers

Proton whistler /VLF phenomenon observed in satellite data/ discussing propagation in multicomponent plasma and ion cyclotron mode