The dawn enhancement of the equatorial ionospheric vertical plasma drift

Zhang, Ruilong; Liu, Libo; Chen, Yiding; Le, Huijun

doi:10.1002/2015ja021972

Cited by 22 publications

(55 citation statements)

References 45 publications

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“…1). However, in agreement with our results, a number of studies based mainly on satellite observations have reported anomalous enhancements of eastward electric fields near sunrise in the equatorial ionosphere, seasonally correlated with the sign of the magnetic declination at the point of observation (Aggson et al, 1995;Kelley et al, 2014;Zhang et al, 2015).…”

Section: The Sunrise Effectsupporting

confidence: 93%

“…The enhancement of the integrated zonal electric field related to the proposed dynamo mechanism attains its largest values when the sunrise terminator is aligned with the magnetic meridian. In central South America, this condition prevails during a period close to the December solstice, when there is a seasonal maximum in the intensity of the secondary zonal electric fields associated with the negative magnetic declination (Zhang et al, 2015). This corresponds exactly to the period in which our measurements were taken.…”

Section: The Sunrise Effectmentioning

confidence: 62%

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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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Section: The Sunrise Effectsupporting

confidence: 93%

Section: The Sunrise Effectmentioning

confidence: 62%

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

2020

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“…However, in agreement with our results, a number of studies based mainly on satellite observations have reported anomalous enhancements of eastward electric fields near sunrise in the equatorial ionosphere, seasonally correlated with the sign of the magnetic declination at the point of observation (Aggson et al, 1995;Kelley et al, 2014;Zhang et al, 2015).…”

Section: The Sunrise Effectsupporting

confidence: 93%

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

Silva¹,

Padilha²,

Alves³

2019

Preprint

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Abstract. 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 quiet to moderately disturbed days 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 compressional waves incident vertically 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 result cannot be explained by the ionospheric waveguide model alone and we propose that an alternative propagation model that allows ULF 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 increases the H-to-D 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. The H-component amplification can be explained by enhancements of the zonal electric field near the magnetic equator driven by F-region neutral winds during sunrise.

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“…Among aforementioned abnormal phenomena, the upward drift around dawn, opposite to its climatology, has been observed frequently (Aggson et al, 1995; Kelley et al, 2014; Woodman, 1970). Its occurrence rate reaches as high as ~1/3 (Zhang et al, 2015), and such high occurrence rate is likely associated with the appearance of large day‐to‐day variability since the high occurrence of upward drifts and the large day‐to‐day variability are both caused by frequent day‐to‐day changes of the electric field. In previous investigations, the day‐to‐day variability is generally quantified by standard deviations in one specific time window.…”

Section: Introductionmentioning

confidence: 99%

Quiet‐Time Day‐to‐Day Variability of Equatorial Vertical E × B Drift From Atmosphere Perturbations at Dawn

Zhou

Liu

et al. 2020

JGR Space Physics

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Ionospheric day-to-day variability is ubiquitous, even under undisturbed geomagnetic and solar conditions. In this paper, quiet-time day-to-day variability of equatorial vertical E × B drift is investigated using observations from ROCSAT-1 satellite and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) v2.1 simulations. Both observations and model simulations illustrate that the day-to-day variability reaches the maximum at dawn, and the variability of dawn drift is largest around June solstice at~90-180°W. However, there are significant challenges to reproduce the observed magnitude of the variability and the longitude distributions at other seasons. Using a standalone electro-dynamo model, we find that the day-to-day variability of neutral winds in the E-region (≤~130 km) is the primary driver of the day-to-day variability of dawn drift. Ionospheric conductivity modulates the drift variability responses to the E-region wind variability, thereby determining its strength as well as its seasonal and longitudinal variations. Further, the day-to-day variability of dawn drift induced by individual tidal components of winds in June are examined: DW1, SW2, D0, and SW1 are the most important contributors.Plain Language Summary The ionosphere is different from one day to the next, even under geomagnetic and solar quiet condition. The vertical E × B drift at the geomagnetic equator is a key parameter that influences the state of the ionosphere and atmosphere. In this paper, we study the quiet-time day-to-day variability of the equatorial vertical E × B drift by ROCSAT-1 observations and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) v2.1 simulations. Both observations and WACCM-X show that day-to-day variability is large at dawn and dusk and it also changes with season and longitude. To better study the variability, we carried out numerical experiments with a new standalone electro-dynamo model. We found that wind variability below~130 km is the main contributor, and winds above~130 km plays a secondary role. The ionospheric conductivity mediates the drift variability response to the wind variability and thus affects its strength and seasonal and longitudinal variations. Further, we examine the variability of dawn drifts generated by different tidal components in June and find that DW1, SW2, D0, and SW1 are the most important ones. This work emphasizes the importance of lower atmospheric variability in studying and predicting the day-to-day variations of ionosphere and space environment. Key Points:• We quantify the quiet-time day-to-day variability of equatorial vertical drift as a function of local time, longitude, and season • Both observations and models show the largest variability occurring at LT 06, which is mainly driven by the variability of E-region winds • The variability of dawn drift induced by tidal components are examined,

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The dawn enhancement of the equatorial ionospheric vertical plasma drift

Cited by 22 publications

References 45 publications

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

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

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

Quiet‐Time Day‐to‐Day Variability of Equatorial Vertical E × B Drift From Atmosphere Perturbations at Dawn

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