Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Yamazaki, Yosuke; Maute, Astrid

doi:10.1007/978-94-024-1225-3_12

Cited by 96 publications

(161 citation statements)

References 458 publications

(208 reference statements)

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“…Modeling efforts were also made to simulate different characteristics of EEJ (Anandarao, ; Forbes & Lindzen, ; Richmond, ; Stening, ; Sugiura & Poros, ). Excellent reviews on this topic are available in the literature (Forbes, ; Raghavarao & Anandarao, ; Reddy, ; Stening, ; Yamazaki & Maute, ). The electrojet region is also known to host different types of plasma irregularities as recorded comprehensively by earlier workers (Fejer & Kelley, ; Gupta, ; Kelley, ; Prakash et al, ).…”

Section: Introductionmentioning

confidence: 99%

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

et al. 2018

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Studies made earlier using ground‐based observations of geomagnetic field over the Indian longitudes revealed that the occurrence of equatorial counter electrojet (CEJ) events in afternoon hours is more frequent during June solstice (May‐June‐July‐August) in solar minimum than in other periods. In general, the June solstice solar minimum CEJ events occur between 1500 local time (LT) and 1800 LT with peak strength of about −10 nT at around 1600 LT. In order to understand the frequent occurrence of these CEJ events, an investigation is carried out using an equatorial electrojet model (Anandarao, 1976, https://doi.org/10.1029/GL003i009p00545) and the empirical vertical drift model by Fejer et al. (2008, https://doi.org/10.1029/2007JA012801). The strength, duration, peak value, and the occurrence time of CEJ obtained using electrojet model match remarkably well with the corresponding observation of average geomagnetic field variations. The occurrence of CEJ is found to be due to solar quiet (Sq) electric field in the westward direction which is manifested as downward drift in Fejer et al. (2008, https://doi.org/10.1029/2007JA012801) model output during 1500–1800 LT. Further, the occurrence of afternoon reversal of Sq electric field in this season is shown to be consistent with earlier studies from Indian sector. Therefore, this investigation provides explicit evidence for the role of westward Sq electric field on the generation of afternoon CEJ during June solstice in solar minimum periods over the Indian sector indicating the global nature of these CEJ events.

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Section: Introductionmentioning

confidence: 99%

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

et al. 2018

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“…Since the Sq currents concentrate in a height range of 90–140 km, we can find several signals of long‐term variation in the upper atmosphere from the analysis of long‐term variation in the Sq field. A comprehensive review of advances in understanding of the Sq variation and its origin during the past 75 years has been made by Yamazaki and Maute ().…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Seasonal Variation and Solar Activity Dependence of the Geomagnetic Solar Quiet Daily Variation

et al. 2017

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Characteristics of seasonal variation and solar activity dependence of the X and Y components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in midlatitudes and Guam near the equator have been investigated using long‐term geomagnetic field data with 1 h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq‐X and Sq‐Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq‐X and Sq‐Y. The result of the correlation analysis between the solar F10.7 index and the Sq‐X and Sq‐Y shows an almost linear relationship, but the slope of the linear fitted line varies as a function of local time and month. This implies that the sensitivity of Sq‐X and Sq‐Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq‐Y at Guam shows good agreement with that of a magnetic field produced by interhemispheric field‐aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the prenoon to afternoon sectors. The direction of the interhemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.

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“…The enhanced eastward current flow along the magnetic equator is commonly known as the equatorial electrojet. Spatial and temporal characteristics of the S q current system and equatorial electrojet have been extensively studied on the basis of magnetometer data analysis as well as numerical models (see a review by Yamazaki & Maute, ).…”

Section: Introductionmentioning

confidence: 99%

Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet

et al. 2017

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The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000 to September 2010 and from the two Swarm satellites during November 2013 to February 2017 to determine, for the first time, the complete seasonal‐longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (∼285°E) during the Northern Hemisphere winter and equinoxes, and in the Brazilian sector (∼325°E) during the Northern Hemisphere summer. There are also local amplitude maxima at ∼55°E and ∼120°E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wave number 2 (SW2), with secondary contributions by westward propagating modes with zonal wave numbers 3 (SW3) and 4 (SW4). Eastward propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionospheric conductivities and nonmigrating lunar tides.

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Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Cited by 96 publications

References 458 publications

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

Characteristics of Seasonal Variation and Solar Activity Dependence of the Geomagnetic Solar Quiet Daily Variation

Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet

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