Secondary irregularities in the equatorial electrojet

Abstract

Although t h e two-strcam i n s t a b i l i t y t h e o r y [ F a r l e y , 1963a,b] has been q u i t e su-.cessfUl i n accounting for many observed f e a t u r e s of t h e plasma--,;?-:-? 5 y r m~1 7 a r i . t -uies produced i n t h e e q u a t o r i a l e l e c t r o j e t , i n c r e e s e d e m i m~n t z i -* s e n s i t i v i t y and improved ex2erimental techniques of observing ~:~e 11c:er s F c t r a t n of r a d i o echoes from t h e e l e c t r o j e t have r e s u l t e d i n t k x s~l v . t l o n of ve&er i r r e g u l a r i t i e s n o t p r e d i c t e d by t h a t t h e o r y . I n pir~i-ulsr, such h -r e g u l a r i t i e s a r e observed b o t h when a VHF r a d a r l o c a t e d nezr the rnegneiic e q u a t o r i s d i r e c t e d . v e r t i c a l l y , and when t h e r a d a r -is d i r e c t e d o b l l q u e l y i n t h e e q u e t o r i a l plane. I n t h e l a t t e r case, t h e i r r c g u l c t r i t i e s have lower Doppler s h i f t . s t h a n a r e suggested by t h e t h e o r y .E x p e r i n e n t e l s p e c t r a are p r e s e n t e d t h a t demonstrate f e a t u r e s c o n s i s t e n t with :;he f i r s t -o r d e r two-stream t h e o r y for o b s e r v a t i o n s of a well-developed elec'tro;let a t oblique an&s of incidence. However, t h e r e l a t i v e c o n t r i - b u t i o n of t h e weaker i r r e g u l a r i t i e s can be r e s o l v e d i n s p e c t r a f o r i n c ident? zngles approaching t h e z e n i t h or, when t h e e l e c t r o j e t i s comparatively.VCCL, es most tlngles. The s p e c t r a l wldth obtained at v e r t i c a l incidence 5s shorn-t o be narrow for a w e a k e l e c t r o j e t , and t o be broadened as t h e e l e c t r o j e t becomes s t r o n g e r . The weaker i r r e g u l a r i t i e s probably r e s u l t -.-.--irm the n o n -l i n e s r i n t e r a c t i o n among t h e s t r o n g e r i r r e g u l e r i t i e s , as i sJencnszratzd by Dougherty and F a r l e y i19663 i n a companion paper.i v n~% l r 2 s u l t s are p r e s e n t e d t h a t i n d i c a t e and a s y m e t r y n o t p r e d i c t e d by -Lt z r Y~e n r y ; i.-., the upgoin2 i r r e g u l a r i t i e s (observed a t a n g l e s of iiLLic?:nc i t l , > s (L>srr-rvx3 5 : srsles of incidence east o f t h e izni;h). Expert-west of t h e ;enith) are s t r o n g e r tliz 1 t're d~w n g o i n g I r r e g u l a r --

Phase Velocity Analysis of Projected Wave Motion Along Oblique Radar Beams - A Numerical Study of Type-1 Radar Echoes

“…However, it is interesting to note that the statistical analysis for projection phase velocity of 2D modes along radar beams is compatible with radar observations. From the analysis of previous sections, the wavelength dependence of phase velocity at a larger elevation angle are roughly consistent with the observations of multi-frequency HF radar for density gradient effects on FB waves (Hanuise and Crochet 1981), and the phase velocities of shorter wavelength waves approach an isotropic speed near ion acoustic speed that is consistent with saturation features of small-scale FB waves observed by radars (Cohen and Bowles 1967;Kudeki et al 1987;Swartz 1997b). Actually, the radar elevation angle means the angle of radar beam to horizontal ground.…”

“…In principle, the linear theory of FB instability can explain many of the observed behaviors of type-1 radar echoes, but there are many nonlinear features taken from other observations which linear theory cannot account for. For example, the analogous phase velocity spectral peak at different elevation angles (Cohen and Bowles 1967;Hanuise and Crochet 1981), the spectral asymmetry (Cohen and Bowles 1967;Farley et al 1978;Kudeki et al 1985Kudeki et al , 1987Swartz 1997a, b), and echo power drops 0.3 dB/degree as the elevation angle from 0° (horizontal) (Ierkic et al 1980;Swartz 1997b) demonstrates such a discrepancy. To explain these features, one must understand the behavior of nonlinear saturated FB waves, the relevant subject has been studied for four decades (Weinstock and Sleeper 1972;Rogister and Jamin 1975;Sudan 1983a, b;Kudeki et al 1987;Kudeki and Farley 1989;Hamza and St-Maurice 1993a, b;Oppenheim and Otani 1996;Oppenheim 1998, 2006;Kuo 2001, 2009a).…”

Up-down asymmetry of type I plasma waves in the equatorial electrojet region

“…When both are present (in the same Doppler spectrum) the peak power of the up-going waves is greater than that of the down-going waves. During daytime when the electron¯ow (and hence irregularity drift) is westward (corresponding to eastward E y ), the west-oriented beam will be seeing plasma waves with upward inclined propagation vectors along the line-of-sight and the east oriented beam those with downward inclined propagation vectors (Cohen and Bowles, 1967). From Fig.…”

The equatorial E-region and its plasma instabilities: a tutorial

“…Early Doppler spectra observations at Jicamarca at various zenith angles during a strong electrojet showing both type 1 and type 2 echoes. Note that the position of the echo peaks for the oblique echoes is nearly independent of zenith angle (from Cohen and Bowles, 1967). corresponds to radar echoes known as "type 2". These are weaker and have a broader Doppler spectrum with a peak in the vicinity of ω=k plasma ·V d .…”