Electron precipitation from the inner radiation belt above Arecibo

Abstract

[1] We examine possible correlations between occurrences of nighttime E-region plasma line (PL) enhancements over Arecibo and 40.75 kHz NAU emissions. On the night of January 1 -2, 2006, the experiments were conducted from 22:00 to 6:00 local time (LT). NAU transmitter was initially turned off until 01:45 LT, when continuous operations resumed for the remainder of the experiments. Enhanced PL events lasting <10 s had central frequencies and bandwidths of about 2.5 and 1.5 MHz, respectively, indicating that Arecibo radar detected 2.3 to 8.5 eV suprathermal electrons streaming along geomagnetic fields. The rate of PL event detections increased by a factor of 2.8 after NAU turn-on. We suggest that 40.75 kHz radiation sporadically leaked though local ionosphere, probably abetted by field-aligned irregularities. The radiation propagated in whistler mode into the L = 1.35 inner radiation belt where gyroresonant interactions with trapped 390 keV electrons increased the precipitation rate. Citation: Pradipta, R

Controlled Studies of Whistler Wave Interactions with Energetic Particles in Radiation Belts

“…Using a simplified slab model of ionospheric plasmas, we can compute the transmission coefficient and, subsequently, estimate that -15% of the incident NAU power can couple into the ionosphere at the altitude of the nighttime F region. As indicated in our earlier experiments [Labno et al, 2007], coupling between NAU transmissions and the ionosphere was enhanced when spread F irregularities were present, while E region irregularities were absent in our nighttime experiments. Gradients at the edges of large field-aligned irregularities can act as waveguides that direct linearly polarized NAU signals along the Earth's magnetic field.…”

“…While the loss of the HF heater renders the controlled creation of ionospheric ducts for NAU whistler-mode wave injection experiments impossible, we began to look into the possibilities of conducting Arecibo experiments using naturally occurring large-scale ionospheric irregularities in the presence of the spread F process. It is reasonable to expect that NAU-generated whistler-mode waves also scatter off and are guided by natural irregularities to propagate into the ionosphere and magnetosphere along Earth's magnetic field [Labno et. al., 2007] Over the past three years we conducted a series of experiments using the Arecibo 430 MHz incoherent scatter radar (ISR) to identify large plasma irregularities and monitor possible ionospheric plasma disturbances induced by NAU transmissions.…”

“…This report focuses on experiments in which the ISR and an ionosonde monitored properties of local ionosphere on the night of January 1-2, 2006 [Pradipta et al, 2007]. Spread F events were monitored continuously by the ionosonde, and they occurred and lasted for several hours during our experiments.…”

Study of the lower hybrid resonance frequency over the regions of gathering earthquakes using DEMETER data

“…For energetic electrons near the loss-cone boundary, this interaction can scatter (or diffuse) them into the loss cone with subsequent precipitation into the atmosphere creating new free electrons (e.g. Karpman and Shklyar, 1977;Imhof et al, 1983;Pradipta et al, 2007). However, as it has been shown by Bell et al (2011) on the basis of DEMETER data, even the most powerful VLF transmitters such as Australian NWC and American NAA do not produce significant large-scale variations of plasma density and temperature in the conjugate region.…”

Mitigation of energetic electrons in the magnetosphere by amplified whistler wave under double cyclotron resonances

“…The motions of energetic electrons are adversely affected by the wave fields which scatter some of them into loss cones (Helliwell et al, 1973). Induced electron precipitation (Voss et al, 1984;Arnoldy and Kintner, 1989;Imhof et al, 1994;Pradipta et al, 2007) by whistler waves has been observed. The Doppler shifted electron cyclotron resonance interaction (Kennel and Petschek, 1966;Villalon and Burke, 1991;Albert, 2000) has been suggested to be a likely electron precipitation mechanism.…”