Observations of ULF wave related equatorial electrojet and density fluctuations

Yizengaw, E.; Zesta, E.; Biouele, César Mbane; Moldwin, M. B.; Boudouridis, A.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.; Hartinger, M.

doi:10.1016/j.jastp.2013.03.015

Cited by 10 publications

(12 citation statements)

References 34 publications

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“…It is worth mentioning about the small‐scale fluctuation embedded in the large quasiperiodic EEJ variation, e.g., shown in between 16:45 and 17:50 UT in Figure . Yizengaw et al [] reported that the ULF wave in the Pc 5 range is the possible cause for the formation of those small‐scale EEJ fluctuations that are predominantly visible in Figure compared to that of Figure where these fluctuations are visible only at the eastward peaks of EEJ.…”

Section: Discussionmentioning

confidence: 99%

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

Yizengaw

Moldwin

Zesta

et al. 2016

Geophysical Research Letters

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The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground‐based multiinstrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP 2 current system. The quasiperiodic DP 2 current system, which fluctuates coherently with fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high‐latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

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Section: Discussionmentioning

confidence: 99%

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

Yizengaw

Moldwin

Zesta

et al. 2016

Geophysical Research Letters

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“…The question is what is the physical mechanism that the ULF wave can cause strong east‐west electric field oscillation at the equatorial region and lead to the formation of such strong density irregularity and thus scintillation? It is obvious that ULF wave causes electric field perturbation in the ionospheric dynamo region at all latitudes when mapped along the field lines (Hughes, ; Reddy et al, ; Yizengaw et al, ). However, this conclusion may not be true all the time due to a simple factual difference between ionospheric region in the high latitude and equatorial region.…”

Section: Discussionmentioning

confidence: 99%

“…We use data from magnetometers that are operated under the umbrella of African Meridian B-field Education and Research (Yizengaw & Moldwin, 2009) and International Real-time Magnetic Observatory Network (INTERMAGNET) (Love & Chulliat, 2013). Detailed description of the technique that we used to identify ULF wave pulsation and to estimate the EEJ from the magnetometer observation can be found in Yizengaw et al (2013) and Yizengaw et al (2014), respectively. We also used the GNSS and the 250 MHz VHF receivers, operated as part of the Air Force Research Laboratory's Scintillation Network Decision Aid project (Groves et al, 1997) to observe density irregularity and scintillation during the presence and absence of ULF magnetic pulsations.…”

Section: Experimental Data Analysismentioning

confidence: 99%

“…Especially, pulsations in the range of ULF Pc5 frequency (f ≈ 1.5-7 mHz) are the most easily observed ULF wave, due to its large amplitude (up to some 100 nT) and long period (several minutes) compared to other higher-frequency ULF wave bands. The Pc5 pulsations are not only regularly observed near auroral latitudes (e.g., Pilipenko, Belakhovsky, Kozlovsky, et al, 2014;Pilipenko, Belakhovsky, Murr, et al, 2014) but also penetrate to lower latitudes and can be detected at middle and low latitudes (e.g., Liu et al, 1993;Motoba et al, 2002) and even equatorial latitudes (e.g., Reddy et al, 1994;Vorontsova et al, 2016;Yeoman et al, 1990;Yizengaw et al, 2013). Different mechanisms have been proposed to explain ULF wave penetration to lower latitudes (Chi et al, 2001;Kikuchi & Araki, 1979 ULF wave-related perturbations at low latitudes are extremely limited, due to the lack of instrumentation in the region, and its impact at this region remains far from understood.…”

Section: Introductionmentioning

confidence: 99%

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ULF Wave‐Associated Density Irregularities and Scintillation at the Equator

Yizengaw

Zesta

Moldwin

et al. 2018

Geophysical Research Letters

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This paper presents independent multi‐instrument observations that address the physical mechanisms of how ultralow‐frequency (ULF) wave‐associated electric fields initiate ionospheric density fluctuation and scintillation at the equator. Since the magnetic field at the equator is entirely embedded in a relatively high‐collision and high‐conductivity medium, the condition may not be possible for the geomagnetic field to fluctuate due to ULF wave activity. This implies that the fluctuating electric field at the equator may not be produced through equatorial dynamo action due to fluctuating magnetic fields. Instead, the electric field penetrates from high latitudes and produces fluctuating magnetic field as well as modulates the vertical drift and hence causes the density to fluctuate at the equatorial region. We demonstrate this by estimating the ULF associated fluctuating electric field at high latitudes and at the equatorial region by applying the appropriate attenuation factor as it penetrates to lower latitudes. The periodicity of both electric field and density fluctuations appears to be between 6 and 9 min, which is a typical period of ULF waves in the Pc5 range. Because of its large amplitude and long periods compared to other ULF wave frequency bands, the Pc5 wave‐associated electric field, which can even be estimated using magnetograms with low sensitivity and low sampling rate (e.g., 1 min), can easily penetrate to the lower latitude region and produce significant ionospheric density fluctuations that can be strong enough to create scintillation at the equatorial region.

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“…The mechanisms involved in the generation, propagation, and amplification of equatorial pulsations have not yet been clearly identified. At very low latitudes, a significant portion of the geomagnetic field lines lies within the ionosphere, and therefore the field line resonance theory that explained numerous observations at middle and high latitudes cannot be applied (Yumoto, 1986). Generally, two models are proposed as the possible mechanisms for the generation and propagation of magnetic pulsations near the ground magnetic equator.…”

Section: Introductionmentioning

confidence: 99%

Latitudinal variation of Pc3–Pc5 geomagnetic pulsation amplitude across the dip equator in central South America

2020

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In order to clarify the equatorial electrojet effects on ground magnetic pulsations in central South America, we statistically analyzed the amplitude structure of Pc3 and Pc5 pulsations recorded during days considered quiet to moderately disturbed at multiple equatorial stations nearly aligned along the 10 • magnetic meridian. It was observed that Pc3 amplitudes are attenuated around noon at the dip equator for periods shorter than ∼ 35 s. It is proposed that daytime Pc3s are related to MHD (magnetohydrodynamic) compressional wave vertically incident on the ionosphere, with the screening effect induced by enhanced conductivity in the dip equator causing wave attenuation. Daytime Pc5s showed amplitude enhancement at all equatorial stations, which can be explained by the model of waves excited at higher latitudes and propagating equatorward in an Earth-ionosphere waveguide. However, a slight depression in Pc5 amplitude compared to neighboring equatorial stations and a phase lag in relation to an off-equatorial station were detected at the dip equator. This wave amplitude depression in the Pc5 frequency band cannot be explained by the ionospheric waveguide model alone, and we propose that an alternative propagation model that allows ULF (ultra-low-frequency) waves to penetrate directly from the magnetosphere to low latitudes could be operating simultaneously to produce these features at the dip equator. Significant effects of the sunrise terminator on Pc3 pulsations were also observed at the stations closest to the dip equator. Contrary to what is reported at other longitudes, in central South America the sunrise effect decreases the D/H amplitude ratio. We suggest that these differences may arise from the unique characteristics of this sector, with a strong longitudinal variation in the magnetic declination and precipitation of energetic particles due to the presence of the South Atlantic Magnetic Anomaly (SAMA). The Hcomponent amplification can be explained by enhancements of the zonal electric field near the magnetic equator driven by F-region neutral winds and waves in the fast-mode of propagation during sunrise.

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Observations of ULF wave related equatorial electrojet and density fluctuations

Cited by 10 publications

References 34 publications

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

Response of the equatorial ionosphere to the geomagnetic DP 2 current system

ULF Wave‐Associated Density Irregularities and Scintillation at the Equator

Latitudinal variation of Pc3–Pc5 geomagnetic pulsation amplitude across the dip equator in central South America

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