Coordinated observations of F region 3 m field‐aligned plasma irregularities associated with medium‐scale traveling ionospheric disturbances

Abstract

Three meter field‐aligned irregularities (3 m FAIs) associated with medium‐scale traveling ionospheric disturbances (MSTIDs) that occurred on 5 February 2008 were observed by using the Chung‐Li 52 MHz coherent scatter radar. Interferometry measurements show that the plasma structures responsible for the 3 m FAI echoes are in a clumpy shape with a horizontal dimension of about 10–78 km in a height range of 220–300 km. In order to investigate the dynamic behaviors of the plasma irregularities at different scales in the bottomside of F region, the VHF radar echo structures from the 3 m FAIs combined with the 630 nm airglow images provided by the Yonaguni all‐sky imager are compared and analyzed. The results show that the radar echoes were located at the west edge of the depletion zones of the 630 nm airglow image of the MSTIDs. The bulk echo structures of the 3 m FAIs drifted eastward at a mean trace velocity of about 30 m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630 nm airglow images. These results suggest that the observed F region 3 m FAIs for the present case can be regarded as the targets that are frozen in the local region of the MSTIDs. In addition, the radar‐observed 3 m FAI echo intensity and spectral width bear high correlations to the percentage variations of the 630 nm emission intensity. These results seem to suggest that through the nonlinear turbulence cascade process, the MSTID‐associated 3 m FAIs are very likely generated from the kilometer‐scale plasma irregularities with large amplitude excited by the gradient drift instability.

Low‐latitude daytime F region irregularities observed in two geomagnetically quiet days by the Hainan coherent scatter phased array radar (HCOPAR)

“…While the prereversal enhancement occurs, the enhanced eastward electric field will raise the height of ionosphere, steepen the density gradient in the bottomside F region, and so create the favorable conditions for RT instability [ Chiu and Straus , ; Ossakow , ]. Another is attributed to the gradient drift instability associated with the medium‐scale traveling ionospheric disturbances (TIDs) [ Lin et al ., ]. The SpreadF Experiment carried out in Brazil indicated that the gravity wave‐induced TIDs have the ability to seed the RT instability and the following plasma bubbles extending to higher altitudes [ Abdu et al ., ; Fritts et al ., ].…”

“…The strong photoionization after sunrise is unfavorable for the formation of steep electron density gradient and polarized electric fields. It is very difficult for the plasma bubbles to be produced in the sunlit ionosphere, whether the RT instability, the gravity waves, the transequatorial wind, or the collisional shear instability is working [ Maruyama , ; Hysell et al ., , ; Saito et al ., ; Abdu et al ., ; Li et al ., ; Tsunoda , ; Lin et al ., ]. However, once the nighttime plasma bubbles are produced, they can survive in the sunshine for a relatively long period.…”

Radar phase offset estimate using ionospheric field-aligned irregularities and aircraft

“…present in this region can be detected by the radar. In light of the fact that the measured phase differences between different receiving channels contain the system phase bias, a comparison of the radar-measured phase differences and IGRF-12-calculated phase differences can deduce the radar system phase offsets (Chu and Wang 1997;Wang 1999;Lin et al 2016). Figure 2 shows its expected echoing regions for the years of 1986 and 2018, in which the FAI height range of 100 -110 km and aspect angle of 0.1° are given to calculate the echoing region from IGRF-12 model.…”

“…The locations of the 3-m FAIs in the echoing region can be identified and positioned from their echoes by using interferometry technique. The elevation angle i and azimuth angle z can be estimated from the phase differences of the FAI echoes detected by different receiving channel pairs in accordance with following equations (Chu and Wang 1997;Lin et al 2016)…”

Measurement of Aspect Angle of Field-Aligned Plasma Irregularities in Mid-Latitude E Region Using VHF Atmospheric Radar Imaging and Interferometry Techniques

“…Radar interferometry (RI) has been widely used in atmospheric studies such as mean angle of arrival of radar echoes [26], lightning detection [27], meteor radar wind [28], among others. Use of RI in measurement of the aspect angle of FAIs was first reported by Kudeki and Farley in 1989 [3] for the equatorial electrojet region.…”