East‐west asymmetries of the equatorial electrojet 8.3 m type‐2 echoes observed over Trivandrum and a possible explanation

Abstract

[1] The east-west asymmetries in the spectral parameters of the type-2 echoes from the equatorial electrojet plasma irregularities observed using a 18 MHz radar from Trivandrum are presented. Observations show that the difference in signal strength, velocity, and spectral width of the type-2 echoes observed in the west and east beam are as high as 15 dB, 60 m s À1 , and 70 m s À1 , respectively. Further, the asymmetry in velocity increases with height, while the asymmetries in signal strength and spectral width decrease with height. While the velocity asymmetry is consistent with the past results, the asymmetries in signal strength and spectral width of the type-2 echoes are significant new results, not reported earlier. Finite vertical drift velocities of the irregularities, associated with the primary wave structures, are found to be responsible for the observed east-west velocity asymmetry. The asymmetries in signal strength and spectral width are attributed to the orientation of kilometer-scale plasma waves present in the equatorial electrojet. Finally, a unified picture is presented to show that the properties of the kilometer-scale waves are the ones that are responsible for all three asymmetries observed in the spectral parameters of the type-2 echoes.

Multiscale equatorial electrojet turbulence:Baseline 2‐D model

“…The large difference between the upward and downward components of the perturbed electric field is common in all phases of simulation and causes an “east‐west” asymmetry in the drift velocity. Patra et al [] reported the first observations verifying the “east‐west” velocity asymmetry found in Type‐II echoes using a 18 MHz radar located at Thumba Equatorial Rocket launching Station (TERLS), Trivandrum, India. Patra et al [] attributed the “east‐west” velocity asymmetry to the large‐scale primary waves that give rise to a large upward plasma drift.…”

“…Patra et al [] reported the first observations verifying the “east‐west” velocity asymmetry found in Type‐II echoes using a 18 MHz radar located at Thumba Equatorial Rocket launching Station (TERLS), Trivandrum, India. Patra et al [] attributed the “east‐west” velocity asymmetry to the large‐scale primary waves that give rise to a large upward plasma drift. However, we find the “east‐west” asymmetry exists even after the breaking‐up of the large‐scale vertical waves into smaller‐scale structures.…”

Combined radar observations of equatorial electrojet irregularities at Jicamarca

“…Likewise, stronger echoes are observed along westward zenith than eastward zeniths. This is also well known and has been termed the "east-west" asymmetry (Bowles et al, 1963;Cohen and Bowles, 1967;Balsley, 1970;Crochet et al, 1976;Fejer et al, 1976;Farley et al, 1978;Tsunoda and Ecklund, 2002;Patra et al, 2005). While the east-west asymmetry was once attributed to local geography, it is now known to be universal (Swartz, 1997).…”

“…Recently, Patra et al (2005) reported on previously unnoticed east-west asymmetries in the power and spectral width of type 2 electrojet echoes, both found to be greater on the westward than the eastward beam. These asymmetries were most discernible at low altitudes.…”

East‐west and vertical spectral asymmetry associated with equatorial type I waves during strong electrojet conditions: 2. Theory

“…East‐west and vertical up‐down spectral asymmetries in equatorial electrojet are now well documented, with several reports over the past 4 decades [ Cohen and Bowles , 1967; Balsley et al , 1976; Hanuise and Crochet , 1978; Kudeki et al , 1985; Swartz , 1997; Tsunoda and Ecklund , 2002; Patra et al , 2005; Denardini et al , 2005]. In a companion paper [ Choudhary et al , 2006, hereinafter referred to as paper 1], we have identified some intriguing new aspects of these asymmetries in Pohnpei radar observations (6.95° north, 158.19° east, 0.7° magnetic dip in the Federated States of Micronesia).…”