On the occurrence and spatial extent of electron precipitation induced by oblique nonducted whistler waves

Abstract

[1] Two different 4-hour sequences of subionospheric Very Low Frequency (VLF) signal perturbations are examined to characterize electron precipitation induced by nonducted obliquely propagating whistlers. These lightning-induced electron precipitation (LEP) events are typically associated with cloud-to-ground lightning discharges. The temporal and spatial signatures of LEP events associated with two disparate storms occurring over two 4-hour periods are examined. A distributed set of VLF observing sites, known as the Holographic Array for Ionospheric and Lightning Research (HAIL), captures the full latitudinal extent of the events, providing evidence that 90% of the precipitation occurs over a region 8°± 1°and 9°± 1°in latitudinal extent for the two time periods. The measured peak of the precipitation is poleward displaced (6°45 0 ± 30 0 and 7°45 0 ± 30 0 for the two case studies) from the causative discharge. Analysis indicates that the onset delay and the duration of precipitation steadily increase with increasing L-value, while the signal recovery time is independent of L-value for the LEP events associated with both storms. The causative lightning discharges associated with the two storms were located at different latitudes. For lightning occurring in the storm at higher latitudes, the associated LEP events are of longer duration and exhibit precipitation in a smaller area displaced less from the causative discharge. The onset delays and event durations increase more rapidly with increasing L-value for events associated with lightning occurring in the storm at higher latitudes. The general spatial and temporal signatures are consistent with those expected for LEP events induced by nonducted whistlers.

Study of Antarctic-South America Connectivity From Ionospheric Radio Soundings

“…helliwell et al 1973, Inan et al 1978, Inan & Carpenter 1987. But, statistical analysis of these bursts had shown they occur mostly during the equinoxes (Fernandez et al 2003) in close association with the occurrence of geomagnetic storms (Peter & Inan 2004, Peter et al 2005, suggesting a connection with magnetospheric phenomena.…”

“…This region is maintained by the solar Lymanalpha radiation (Nicolet & Aikin 1960) during quiet periods, but can be highly disturbed by enhancements of X-ray emission during solar flares (McRae & Thomson 2004, Raulin et al 2010, as well by electron precipitation events from the radiation belts (helliwell et al 1973, Inan et al 1982, Fernandez et al 2003, Peter & Inan 2004, Correia et al 2007, Correia et al 2010b. These disturbances produce changes in the electron density of the D-region that affects the conductivity gradient and/ or the reference height, which govern the refractive index (Wait & Spies 1964).…”

A statistical study over Europe of the relative locations of lightning and associated energetic burst of electrons from the radiation belt

“…3). Considering the large number of LEPs at times characterized via subionospheric VLF signal perturbations (e.g., 80 and 81 LEPs for two 4 h periods; Peter and Inan, 2004), the number of events presented here is relatively small. This is mostly due to the strict rules used during the selection process and the limitation of the IDP, which cannot detect energies lower than 90 keV.…”

“…Note that a 0.4-0.6 s time delay represents the expected duration between the lightning-generated whistler and the interaction with radiation belt electrons, which precipitate into the ionosphere (Peter and Inan, 2004). LEP events, in which several distant and simultaneous thunderstorms and the causative lightning position could not be clearly determined, have been excluded.…”

“…-On board DEMETER, the time occurrence of the electron burst (minimum recorded duration of 1 s in burst mode) has to follow the time occurrence of whistlers within 0.6 s (see Peter and Inan, 2004). …”