Radar Observations of 8.3-m scale equatorial spread F irregularities over Trivandrum

Abstract

Abstract. In this paper, we present observations of equatorial spread F (ESF) irregularities made using a newly installed 18MHz radar located at Trivandrum. We characterize the morphology and the spectral parameters of the 8.3-m ESF irregularities which are found to be remarkably different from that observed so extensively at the 3-m scale size. We also present statistical results of the irregularities in the form of percentage occurrence of the echoes and spectral parameters (SNR, Doppler velocity, Spectral width). The Doppler spectra are narrower, less structured and less variable in time as compared to those observed for 3-m scale size. We have never observed the ESF irregularity velocities to be supersonic here unlike those at Jicamarca, and the velocities are found to be within ±200ms–1. The spectral widths are found to be less than 150ms–1. Hence, the velocities and spectral width both are smaller than those reported for 3-m scale size. The velocities and spectral widths are further found to be much smaller than those of the American sector. These observations are compared with those reported elsewhere and discussed in the light of present understanding on the ESF irregularities at different wavelengths. Key words. Ionoshphere (equatorial ionosphere, plasma waves and instabilities; ionospheric irregularities)

Simultaneous radar observations of meter‐scale F region irregularities at and off the magnetic equator over India

“…Further, the occurrence of high‐altitude plume structures after ∼21 LT and the irregularities, in general, after 23 LT are very infrequent at Trivandrum. Similar observations have been reported by Tiwari et al [2004]. In contrast, irregularities extending to higher altitudes are observed at Gadanki on quite a few occasions even after midnight.…”

“…They have been observed at Gadanki also. The present database as well as that reported by Tiwari et al [2004] suggests that the postmidnight 8.3 m spread F irregularities possibly are too weak to be detected by the existing 18 MHz radar at Trivandrum. In this context, the observations on ESF irregularities reported by Clemesha [1964] using a 18 MHz radar and by Kelleher and Skinner [1971] using a 27.8 MHz radar are relevant.…”

Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities

“…A high degree of correlation found between spaced receiver records of scintillations have been shown to arise from the bottomside equatorial F-region irregularities layers, indicating the absence of random changes in these irregularities or their drift velocities, which would imply that the steady, nonlinear states reached are stable in this case (Bhattacharyya et al, 2001;Bhattacharyya, 2004). Some of the weaker echoes associated with bottomside structures have not been detected regularly using the 18-MHz radar system, due to low sensitivity of the system (Tiwari et al, 2004). These echoes have been observed regularly using the Jicamarca radar with SNR exceeding 30 dB (Woodman and La Hoz, 1976).…”

“…Spectral characteristics of the signal backscattered by 8.3-m scale size ESF irregularities, which have been obtained using this radar, have been studied by Tiwari et al (2004). The radar specifications and other important parameters used for ESF studies are given in Table 1.…”

On the nature of low‐latitude Es influencing the genesis of equatorial plasma bubble

“…One can note that the lower part of the F region (200-250 km) over the magnetic equator is connected via magnetic field line to the E region (100-150 km) over 6.5 magnetic latitude, where Gadanki and Sriharikota are located. Because the typical altitude from where the radar plumes, representing EPB, as observed by coherent backscatter radar is 300-350 km in the Indian longitude [Tiwari et al, 2004], the seeding is expected to occur somewhere below 300 km. Thus, the E s observations from Sriharikota may prove to be relevant in studying the low-latitude E s affect on the growth of EPB.…”