HF Doppler observations of vector plasma drifts in the evening F-region at the magnetic equator

Balan, N.; Jayachandran, B.; Nair, R. Balachandran; Namboothiri, S. P.; Bailey, G. J.; Rao, P. B.

doi:10.1016/0021-9169(92)90162-e

Cited by 34 publications

(27 citation statements)

References 48 publications

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“…The threshold height was found to depend largely on solar activity. As observed by a HF Doppler radar at 5.5 MHz (Balan et al, ), the virtual threshold height (Figure ) decreases from about 450 km in 1984 to 350 km in 1985 due to the decrease in ν in (Jayachandran et al, ).…”

Section: Ionospheric Irregularitiesmentioning

confidence: 74%

A brief review of equatorial ionization anomaly and ionospheric irregularities

Balan

Liu

2018

Earth and Planetary Physics

166

124

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Following a brief history and progress of ionospheric research, this paper presents a brief review of the recent developments in the understanding of two major phenomena in low and mid latitude ionosphere—the equatorial ionization anomaly (EIA) and involved equatorial plasma fountain (EPF) and ionospheric irregularities. Unlike the easy‐to‐understand misinterpretations, the EPF involves field perpendicularE×B plasma drift and field‐aligned plasma diffusion acting together and plasma flowing in the direction of the resultant at all points along the field lines at all altitudes. The EIA is formed mainly from the removal of plasma from around the equator by the upward E×B drift creating the trough and consequently the crests with small accumulation of plasma at the crests when the crests are within ~±20° magnetic latitudes and no accumulation when they are beyond ~±25° magnetic latitudes. The strong EIA under magnetically active conditions arises from the simultaneous impulsive action of eastward prompt penetration electric field and equatorward neutral wind. Intense ionospheric irregularities develop in the post‐sunset bottom‐side equatorial ionosphere when it rises to high altitudes, and evolve nonlinearly into the topside. Pre‐reversal enhancement (PRE) of the vertical upward E×B drift and its fluctuations amplified during PRE provide the driving force and seed, with neutral wind and gravity waves being the primary sources. At low solar activity especially in summer when fast varying PRE is absent, the slow varying gravity waves including large scale waves (LSW) seem to act as both driver and seed for weak irregularities. At mid latitudes, the irregularities are weak and associated with medium scale traveling ionospheric disturbances (MSTIDs). A low latitude minimum in the occurrence of the irregularities at March equinox predicted by theoretical models is identified. The minimum occurs on the poleward side of the EIA crest and shifts equatorward from ~25° magnetic latitudes at high solar activity to below 17° at low solar activity.

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Section: Ionospheric Irregularitiesmentioning

confidence: 74%

A brief review of equatorial ionization anomaly and ionospheric irregularities

Balan

Liu

2018

Earth and Planetary Physics

166

124

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“…In addition, there are second hop traces which could be due to multiple reflections from the ground and ionosphere [e.g., Bhaneja et al ., ]. In the recent past, several investigations have been made by using satellite traces over equatorial sites during ESF or non‐ESF nights and their relation to occurrence of plasma density irregularities including Tirunelveli station [e.g., Narayanan et al ., ]. As observations belong to the March period which is the season for strong spread F over India, we may be seeing several satellite traces in the ionogram prior to spread F .…”

Section: Cadi System Descriptionmentioning

confidence: 99%

Characteristics of the equatorial plasma drifts as obtained by using Canadian Doppler ionosonde over southern tip of India

et al. 2016

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We present here characteristics of the Doppler drift measurements over Tirunelveli (8.73°N, 77.70°E; dip 0.5°N), an equatorial site over Southern India using Doppler interferometry technique of Canadian ionosonde. Three‐dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using Doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic E‐W and N‐S directions. After having compared with Lowell's digisonde drifts at Trivandrum, we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012. The observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons. The comparison of Doppler vertical drifts with the drifts obtained from (a) virtual height and (b) Fejer drift model suggests that Doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods. Further, it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread F in the ionograms and GPS L band scintillations. The zonal drifts, on the other hand, showed westward during daytime with mean drifts of ~150–200 m/s and correlated well with equatorial electrojet strength indicating the role of E region dynamo during daytime, while they are eastward during nighttime with mean drifts of ~100 m/s resembling F region dynamo process. Also, zonal drifts showed large westward prior to the spread F onset during autumn equinox than vernal equinox, suggesting strong zonal shears which might cause equinoctial asymmetry in spread F.

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“…The equatorial ionosphere has been extensively studied with incoherent scatter radar, ionosonde and spaced receiver HF Doppler radar techniques (Woodman, 1970;Abdu et al, 1993;Nair et al, 1992;Subbarao and Murthy, 1994;Fejer et al, 1979;Balan et al, 1992;Nayar and Sreehari, 2004;Nayar et al, 2009). These observations have provided a wealth of information on the equatorial ionospheric plasma dynamics.…”

Section: Introductionmentioning

confidence: 98%