Cavitation of lower hybrid waves in the Earth's ionosphere: A model analysis

Abstract

Abstract. Lower hybrid wave cavities detected by the Freja satellite are analyzed. On the basis of simple statistical arguments by use of signals from two density probes, it is possible to obtain rather general results concerning the individual shapes of these cavities. In particular, it is demonstrated that a cylindrically symmetric Gaussian density depletion seems to give a very good fit for a vast majority of cases. The validity of this model is shown to give a great simplification in the interpretation of the data. As a result, a number of well-defined characteristics are obtained which have to be accommodated within an ultimate theory describing the observed wave phenomena.

Evolution of electron beam generated waves resulting in transverse ion heating and filamentation of the plasma

“…The spatial structure of the plasma density associated with these oscillations is like filaments, which extend all along the length of the simulation plasma parallel to Bo, but they are quite thin transverse to Bo. We have shown that the major features of Freja data on LHSS [see Hoymork et al, 2000] are explainable in terms of the electrostatic ELF wave structure, including the upper and lower bounds on the perpendicular scale length and their perpendicular motion.…”

Localization of wave fields in lower hybrid cavities

“…It has been shown by Høymork et al (2000) that the measured density profiles of the lower hybrid cavities agree well with a Gaussian shape. We may then write a typical profile of a density depletion as…”

“…The data in Fig. 3 are taken from Høymork et al (2000) and show the widths and depths of the cavities. We have superimposed contours of maximum k z (in units of m −1 ), for different b (1/e-width) and (relative depth), from relation (41).…”

“…How well are trapped modes confined in a general density cavity? How does the results obtained for parabolic profiles apply to other profiles, for example, the Gaussian profiles reported from observations by Høymork et al (2000)? What can be said in general terms about the frequency and wave number of trapped modes and their relation to the depth and gradients of density cavities?…”

“…Vago et al, 1992;Pinçon et al, 1997;Lynch et al, 1999;Knudsen et al, 1999), and the Freja satellite (e.g. Eriksson et al, 1994;Pécseli et al, 1996;Dovner et al, 1997;Høymork et al, 2000) at altitudes up to about 2000 km. Recently, LHCs have been identified further out in the magnetosphere in the Viking and Cluster data sets (Tjulin et al, 2003) at altitudes up to above 20 000 km.…”