Modulation of ionospheric conductance and electric field associated with pulsating aurora

Abstract

[1] We present, for the first time, a quasiperiodic modulation of ionospheric parameters, associated with the occurrence of pulsating auroras, such as electron density, conductance, and electric field. In March 2008, simultaneous campaign-based measurements of pulsating auroras were conducted over Tromsø (69.60°N, 19.20°E), Norway, using an all-sky TV camera (ATV) and the European Incoherent Scatter (EISCAT) UHF system. During an interval within this campaign period, pulsating auroras, with periods of 8-17 s, were observed by the ATV in the morning local time sector (∼0500 MLT). In this interval, quasiperiodic oscillations were identified in the raw electron density obtained by EISCAT. The electron density at lower altitudes in the E region (95-115 km) was enhanced by a factor of 3-4 immediately after the optical pulsation became "on."The height-integrated Hall conductance was also elevated, by a factor of 1.5-2, almost in harmony with the electron density variation. The response of the electron density and Hall conductance to the appearance of the pulsating aurora was almost immediate. However, both did not decrease to the background level promptly after optical pulsation ceased. This was primarily because it took a few seconds for the electron density to decrease through recombination with ambient ions at these altitudes. Interestingly, electric field measurements performed by the remote antenna at Kiruna showed that redirection of the electric field occurred when the pulsating aurora was "on." We propose a model in which the enhancement of Hall conductance within patches of the pulsating aurora caused charge accumulation at the edges of the patches, and the electric field was then modified by the resulting polarization electric field. An estimation of the electric field modulation with this model well reproduced the actual electric field observations carried out by EISCAT, which confirmed the validity of the model. These results imply that the ionization caused by high-energy electron precipitation associated with a pulsating aurora has a significant effect on the ionospheric conductivity and current system. This modification of the ionosphere may facilitate characterization of the morphological features of pulsating auroras. In particular, modification of the electric field would affect the spatial structure of pulsating aurora patches, such as their motion and shapes.

Low‐altitude satellite measurements of pulsating auroral electrons

“…The pronounced temporal modulations (few seconds to few tens of second periods) are likely caused by groups of closely spaced individual chorus elements (lower band scattering the high-energy primaries), and these distinct patches may also be associated with field-aligned currents [Arnoldy et al, 1982;Oguti and Hayashi, 1984;Fujii et al, 1985;Hosokawa et al, 2010]. Therefore, the strong temporal modulations within distinct patches likely have upward field-aligned currents associated with them and therefore parallel potential drops which would be preventing the secondaries from leaving both the Southern and Northern Hemispheres, if the potential structure is symmetric.…”

Fine scale structures of pulsating auroras in the early recovery phase of substorm using ground‐based EMCCD camera

“…On the other hand, the characteristics of PAs in the early recovery phase of substorm that we presented here are still unknown for the most part, including the generation mechanisms and morphology. For example, one of the causes for the morphology was suggested to be the modification of the electric field in the ionosphere [ Hosokawa et al , 2010]. In addition to the ionospheric feedback, highly structured diffuse auroras in the non‐patch shape were suggested to be a result of interchange instability in the magnetosphere [ Ebihara et al , 2010].…”

Plasma irregularities adjacent to auroral patches in the postmidnight sector

“…The Hall conductance was elevated from 5 to 8 mho to 15–20 mho when the auroral patches appeared at the zenith of Tjörnes. Recently, Hosokawa et al [2010] used the EISCAT radar to measure variations in the ionospheric conductance associated with the occurrence of pulsating aurora. They demonstrated that the Hall conductance was elevated by a factor of 2 or more when patches of pulsating aurora appeared at the sensing area of EISCAT, which suggests that the Hall conductance enhancement assumed here is reasonable.…”