Neutral‐ion interaction in the auroral E region obtained from coordinated Fabry‐Perot imager and VHF radar observations

Abstract

[1] It is important to investigate the small-scale dynamics of thermospheric neutrals and ionospheric plasmas at high latitudes since there are local and temporal variations in energy input and transfer processes associated with auroral activities. To clarify these ionosphere-thermosphere interactions in the auroral E region, we examined neutral winds and plasma motions obtained by coordinated Fabry-Perot imager and VHF radar observations at Syowa Station, Antarctica. From case studies on 11 and 12 September 1996, we found a good correlation between temporal variation (period < 1 hr) of E region neutral winds measured by the Fabry-Perot imager and the Doppler velocities of plasmas obtained from the VHF radar echoes. On the other hand, the absolute mean values of the neutral winds were around zero whereas the plasma Doppler velocities were 350-400 m/s, showing a significant discrepancy. Considering that the neutral-ion and ion-neutral momentum transfer collision frequencies in the E region are $10 À6 Hz and $10 2 Hz, respectively, these good correlations are probably due to ion motions driven by neutral drag force, suggesting a strong coupling between neutrals and ions in the E region. The observed correlation and discrepancy between the radar Doppler velocity and the neutral wind velocity are consistent with the linear theory of E region irregularities that shows the radar Doppler velocity is the sum of two components; one is the E Â B drift speed, and another is proportional to the neutral wind velocity.Citation: Sakanoi, T., H. Fukunishi, K. Igarashi, S. Okano, and N. Nishitani (2009), Neutral-ion interaction in the auroral E region obtained from coordinated Fabry-Perot imager and VHF radar observations,

High‐latitudeEregion ionosphere‐thermosphere coupling: A comparative study using in situ and incoherent scatter radar observations

“…Collisions determine where field‐aligned currents in the high latitude ionosphere close and thus where magnetospheric energy is deposited [e.g., Thayer , 2000]. Numerous satellite observations have indirectly demonstrated that the neutral atmosphere responds to ionospheric forcing at high latitudes, especially in the auroral and magnetic cusp regions [ Emery et al , 1985; Heelis , 1987; Knowles et al , 2001; Lühr et al , 2004; Clemmons et al , 2008; Prölss , 2008; Sakanoi et al , 2009; Ritter et al , 2010]. The resulting variations in neutral density affect low‐perigee satellite orbits and consequently impact the accuracy of satellite orbit prediction and tracking operations [e.g., Storz et al , 2005].…”

A Tiny Fabry-Perot Interferometer with Postpositional Filter for Measurement of the Thermospheric Wind

“…To date, wind measurements using Fabry-Perot interferometers from the ground have been made for several decades by many scientists. Various investigations and improvements have been reported for FPIs, for example, studies featuring long-term measurements (Hernandez andRoble 1995, Biondi et al 1999), use of cooled CCD detectors (Biondi et al 1995, Shiokawa et al 2001, 2003, two-dimensional imaging capability (Rees et al 1984, Niciejewski et al 1994, Nakajima et al 1995, Ishii et al 1997, Conde et al 2001, Sakanoi et al 2009, Kosch et al 2010, and daytime measurement (Gerrard and Meriwether 2011, Wu et al 2012). Most of these instruments are designed using large-aperture etalons and filters.…”

Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies

“…These instruments have a throughput that is large when compared with the performance of grating spectrometers. Various investigations and improvements have been reported for these interferometers, for example, studies featuring long-term (solar cycle) measurements (e.g., Hernandez and Roble, 1995;Biondi et al, 1999), satellite-borne instruments (DE2: Killeen and Roble, 1988; UARS/HRDI: Hays et al, 1993;and TIMED/TIDI: Killeen et al, 1999), use of cooled-CCD detectors (e.g., Biondi et al, 1995;Shiokawa et al, 2001Shiokawa et al, , 2003, two-dimensional imaging capability (e.g., Rees et al, 1984;Nakajima et al, 1995;Ishii et al, 1997;Conde et al, 2001;Sakanoi et al, 2009;Kosch et al, 2010), and tristatic measurements of the auroral thermosphere (e.g., Aruliah et al, 2004). The recent development of robust thermoelectric-cooled CCD detectors combined with a computer control system makes it possible to fully automate the operation of these Fabry-Perot interferometers (FPIs).…”