Phase velocities of irregularities in the equatorial electrojet

Abstract

Spectral decomposition of the power spectrum of radar echoes at 50 MHz from the equatorial electrojet reveals information as to the phase velocities of several classes of electron density irregularities and permits inferences as to the electron drift velocity and the electron and ion temperatures in the electrojet. In particular, it is shown that the phase velocity of two-stream irregularities is comparable to the ion-acoustic speed and independent of the horizontal phase velocity of coexistent non-two-stream irregularities. The latter can exceed the ion-acoustic speed and is probably a measure of the electron drift velocity. Thus a probable inference is that the electron drift velocity can itself be supersonic, contrary to some existing theoretical opinions. The resttits suggest that there are frequently two or more strata containing non-two-stream irregularities moving at different mean phase velocities. Identification of the phase velocity of the two-stream irregularities with the ion acoustic speed leads to the conclusion that the electron and ion temperatures in the electrojet are comparable, in agreement with incoherent scatter observations of the E region at other latitudes. Thus, these results tend to refute rocket measurements made by Langmuir probes in the electrojet.The equatorial electrojet is a strong current The physical explanation for selection of this embedded in a slightly ionized ionospheric plasma height region relates to the maximization of (the E layer near the magnetic equator). This ionospheric conductivities there [cf. Hanson, current is a flow of electrons across geomagnetic 1965]. The important feature of this height field lines through ions and neutrals that are for region to note for our purposes is that the many purposes considered to be at rest. This electrons are mainly controlled by the geomagflow is characterized as a drift, since an electric netic field, and not by collisions with neutrals, field is required to propel the electrons. A global whereas the reverse is true for ions. Hence in electric field (resulting from tidal forces)known this region the electrons are subject to drift as the dynamo field [Fejer, 1953] is the driving forces but not the ions. Thus the unusual charforce.acteristics of the electrojet result from the Although the dynamo field is present at other combination of the electric field magnification latitudes, its effects are emphasized near the stemming from the special equatorial magnetic magnetic equator, where the east-west dynamo geometry and the existence of an altitude region field sets up a large vertical polarization field. in which the electrons drift through the ions. This vertical electric field, or Hall field, is muchA phenomenon closely related to the electron stronger than the originally imposed east-west drifts is the production of ionospheric irregudynamo field. This electric field E and the larities. Experiments with radar (until recently ambient magnetic field B cause (through E xB mainly at 50 MHz) have distinguished two forces) east-west ...

Climatological study of the daytime occurrence of the 3-meter EEJ plasma irregularities over Jicamarca close to the solar minimum (2007 and 2008)

“…The Jicamarca radar system has already been described in some publications, e.g., Cohen (1967) and Woodman (1971). Therefore, we will restrict ourselves to briefly recalling some of its most important features that impact on the data we used.…”

“…Experimental investigations of the equatorial plasma irregularities using VHF coherent and incoherent scatter radars were also carried out over Jicamarca by Cohen (1967), Fejer et al (1975), Farley and Fejer (1975), and many others.…”

Influence of uncertainties of the empirical models for inferring the E-region electric fields at the dip equator

“…The Doppler velocities of type II irregularities are proportional to Ez, as given in Eq. 3 (Cohen 1973;Reddy 1977): where Θ is the zenith angle of the radar beam and H is the horizontal component of the geomagnetic field. Physical features of the EEJ were examined by Richmond (1973) using a numerical model, which includes the two-stream instability.…”

“…Type II echoes are observed whenever the density gradient has a positive projection along Ez. The Doppler frequency of type II echoes is proportional to Ez, which is related to Ey through the ionospheric conductivities (Cohen 1973;Reddy 1977).…”

Variance Analysis of Incoherent Integration Applied to Simulated Equatorial Electrojet Irregularities Radar Power Spectra

“…These studies showed distinct spectral signatures of two types of irregularities, called Type 1 and Type 2, explained by a modified two-stream (Farley, 1963;Buneman, 1963) and the gradient drift (Rogister and D'Angelo, 1970) instabilities, respectively. Several experiments have been done to investigate the EEJ irregularities in order to characterize its spectra and explain the phenomenology in many sectors, such as Peruvian (Cohen and Bowles, 1967;Balsley, 1969;Cohen, 1973;Fejer et al, 1975;Farley and Fejer, 1975), Indian (Prakash et al, 1971;Reddy and Devasia, 1981), and Brazilian (Abdu et al, 2002;Abdu et al, 2003;de Paula and Hysell, 2004;Denardini et al, 2004;Denardini et al, 2005).…”