Topside sounder proton‐cyclotron echo generation from a plasma memory process and electron Bernstein‐wave propagation

Abstract

Abstract. Evidence is presented for the radiation of an electron Bernstein wave from a radio frequency pulse simulated by proton-cyclotron motion. The protons are energized by an ionospheric topside sounder transmitter pulse and take part in a plasma memory process that simulates the original transmitter pulse. These echoes appear on topside ionograms as thin traces. At frequencies below the electron cyclotron frequency f•, the proton echo delay is a multiple of the proton-cyclotron period t•. At frequencies above f•, there can be an additional delay to t• depending on two factors: 1) the antenna orientation

Advances in Plasmaspheric Wave Research with CLUSTER and IMAGE Observations

“…Also in contrast to WM echoes, f + ce echoes appeared to replicate the sounder pulse frequency and in so doing experienced large frequency-dependent increases in travel time as f ce was approached from above. This dispersion as well as a year-to-year decrease in f + ce echo activity with increasing separation of the antenna from the "excited" field lines, is consistent with an explanation of f + ce echoes observed in the ISIS satellites in terms of thermal-mode propagation from a perturbed proton distribution (Muldrew 1998). A possible source of energy for the comparatively weak f + ce echoes is the quasi-static electric field that exists in the ion sheath that surrounds each antenna element in the immediate aftermath of an rf pulse, as discussed in Carpenter et al (2007).…”

“…The coupling to protons is revealed in echoes that arrive at multiples of the local proton gyroperiod t p . Lower-altitude (<4000 km) versions of several of these proton cyclotron (PC) echo forms were observed in the topside ionosphere by sounders in the ISIS satellite era, among them discrete echoes in the WM domain below f ce and in the nominally nonelectromagnetically propagating domain above f ce (e.g., Oya 1978;Horita 1987;Muldrew 1998). Also seen on ISIS satellites were spur-like broadenings of resonances such as the one at f pe (e.g., King and Preece 1967;Benson 1975;Horita 1987).…”

“…Previously suggested processes that were considered relevant to PC echoes above f ce and to the new resonance include: (i) coupling between an excited Z-mode wave and longitudinal plasma waves (Benson 1975), (ii) accumulation of negative charge on an electric antenna during an rf pulse (Oya 1978), and (iii) Bernstein-mode propagation to an antenna from an excited proton population (Muldrew 1998). …”

The Poynting vector applied to the complex refractive index in a hot plasma near the electron cyclotron frequency and to the cyclotron resonance observed on topside ionograms

“…The reason that direct radiation from the antenna is not observed is uncertain but it could be due to extremely high electron temperatures near the antenna during pulse transmission that affect the propagation. Muldrew [1998] (hereinafter referred to as M98) found the minimum delay time of fixed‐frequency proton echoes to occur for the same coplanar condition of these three vectors, implying that aspects of the proton echo theory are fundamental to the explanation of the electron cyclotron theory presented here. In the correction to Muldrew [1998], a slightly improved agreement between theory and observation, is presented.…”

New satellite mission with old data: Rescuing a unique data set

“…Rather, our intent is to highlight a number of more recent publications indicating a resurgence of international interest in the ISIS topside sounder data based on the new digital ionograms. These publications have (1) presented evidence of extremely low altitude ionospheric peak densities at high latitudes [ Benson and Grebowsky , 2001], (2) improved the IRI model for the topside ionosphere [ Bilitza , 2004, 2009; Bilitza et al , 2006], (3) presented new models for the topside scale height and ion transition height [ Kutiev and Marinov , 2007; Kutiev et al , 2006; Marinov et al , 2004], (4) investigated transionospheric HF propagation [ James , 2006], (5) presented convincing new interpretations of the plasma resonance stimulated at f H (which has challenged theorists for decades) [ Muldrew , 2006] and of ion emissions stimulated by topside sounders and responsible for proton echoes [ Muldrew , 1998, 2000], (6) connected magnetospheric N e profiles to the high‐latitude topside ionosphere [ Reinisch et al , 2007], and (7) provided a new approach to modeling the F2 peak height hmF2 [ Gulyaeva et al , 2008]. In addition, the data have been used in a M.Sc.…”