Analysis of magnetospheric ELF/VLF wave amplification from the Siple Transmitter experiment

Abstract

Controlled experiments with dedicated ground-based ELF/VLF (0.3-30 kHz) transmitters are invaluable in investigating nonlinear whistler mode wave-particle interactions in the Earth's magnetosphere.The most productive such experiment operated between 1973 and 1988 near L = 4 at Siple Station, Antarctica. A major effort has been undertaken to digitize and preserve a significant portion of the historical data set from the original magnetic tapes, and we describe here the data set and the processing techniques used to remove artifacts introduced during recording and playback. We analyze a commonly transmitted diagnostic format from 1986 and present statistics on the occurrence and properties of amplified ELF/VLF waves received by a ground-based receiver at the geomagnetic conjugate location to Siple at Lake Mistissini, Quebec. For the interval examined, only 11% of Siple transmissions are successfully received in the conjugate hemisphere with quiet geomagnetic conditions being significantly more conducive to successful reception. The total growth for the events examined is estimated to be 5-40 dB, and nonlinear growth rates are in the range of 20-350 dB/s. The observations show that as the nonlinear growth rate increases, the duration of nonlinear growth decreases. Significant linear correlation is found between the noise floor and the saturation level, with higher noise floors resulting from increases in natural magnetospheric emissions. Finally, we find a lack of correlation between the nonlinear growth rate and the noise, threshold, and saturation levels.

Predicting conditions for the reception of one‐hop signals from the Siple transmitter experiment using the Kp index

“…The use of these larger number of MDIAG transmissions provides an improved statistical understanding of wave amplification behavior of injected whistler mode waves, as presented in Figures c–e. This improves on the results presented in Li et al [] and even more so on statistics from earlier work such as Helliwell and Katsufrakis [] and Helliwell et al []. Figure c shows a histogram of the nonlinear growth rates, which ranges from 3 dB/s to 270 dB/s with a median growth rate of 68 dB/s.…”

“…In order for Siple signals to be observed in the conjugate hemisphere, they must propagate in the magnetosphere within field‐aligned density irregularities known as ducts [ Angerami , ]. The reception of signals transmitted from Siple is more likely when geomagnetic conditions are less disturbed [ Carpenter and Bao , ; Li et al , ]. This requirement for quieting in Kp was also observed in wave injection experiments using the HAARP ionospheric heater [ Golkowski et al , ] and was attributed to the formation of stable ducts.…”

“…(b) The p values for a two‐sample Kolmogorov‐Smirnov statistical significance test are plotted for each 3 h interval, and the y axis is inverted so that the more significant p values are better highlighted. This figure is an updated version considering a larger number of transmissions from Figure 4 in Li et al [].…”

Preferential amplification of rising versus falling frequency whistler mode signals

“…The correlation coefficient between noise power and amplification ratio in that range of r is −0.46( p < 0.01). Li et al [] reported that the primary contribution to the increase in noise power for Siple receptions is the occurrence of natural emissions such as hiss, as seen in Figure c, and as such, intervals of higher noise power likely indicate when the conditions for linear growth are enhanced. As applied to Figure c, lower noise power suggests lower linear growth rates which are then associated with higher amplification ratios.…”

Modulation Analysis of Whistler Mode Sidebands in VLF‐Triggered Emissions and Implications for Conditions of Nonlinear Growth

“…The experiment yielded a vast amount of data, most of which continue to lack satisfactory theoretical explanation. Fortunately, the data from the experiment have been diligently digitized and are available for further study (Li et al, ).…”