An empirical model of the auroral oval derived from CHAMP field-aligned current signatures – Part 2

Xiong, Chao; Lühr, Hermann

doi:10.5194/angeo-32-623-2014

Cited by 34 publications

(61 citation statements)

References 14 publications

(20 reference statements)

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“…According to previous studies, the time‐integrated merging electric field ( E m ) can be expressed as

E_{m} (t, τ) = \frac{\int_{t_{1}}^{t} E_{m}^{^{'}} (t^{^{'}}) e^{(t^{^{'}} - t) / τ} d t^{^{'}}}{\int_{t_{1}}^{t} e^{(t^{^{'}} - t) / τ} d t^{^{'}}},

where

E_{m}^{^{'}}

is treated as a continuous function of time

t^{^{'}}

, t 1 is chosen 3 h before the actual epoch, and τ is the e ‐folding time of the weighting function in the integrands, with a value τ = 0.5 h. Richmond et al [] found that it is appropriate to consider the past 3 h of solar wind variations. An e ‐folding time of 0.5 h was also found suitable for calculating the merging electric field in previous ionospheric studies [ Xiong et al , ; Xiong and Lühr , ; Xiong et al , ].…”

Section: Resultsmentioning

confidence: 84%

The response of equatorial electrojet, vertical plasma drift, and thermospheric zonal wind to enhanced solar wind input

2016

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In this study we used observations from the CHAMP and ROCSAT‐1 satellites to investigate the solar wind effects on the equatorial electrojet (EEJ), vertical plasma drift, and thermospheric zonal wind. We show that an abrupt increase in solar wind input has a significant effect on the low‐latitude ionosphere‐thermosphere system, which can last for more than 24 h. The disturbance EEJ and zonal wind are mainly westward for all local times and show most prominent responses during 07–12 and 00–06 magnetic local time (MLT), respectively. The equatorial disturbance electric field is mainly eastward at night (most prominent for 00–05 MLT) and westward at daytime with small amplitudes. In this study we show for the first time that the penetration electric field is little dependent on longitude at both the day and night sides, while the disturbance zonal wind is quite different at different longitude sectors, implying a significant longitudinal dependence of the ionospheric disturbance dynamo. Our result also indicates that the F region equatorial zonal electric field reacts faster than E region dynamo, to the enhanced solar wind input.

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“…According to previous studies, the time‐integrated merging electric field ( E m ) can be expressed as

E_{m} (t, τ) = \frac{\int_{t_{1}}^{t} E_{m}^{^{'}} (t^{^{'}}) e^{(t^{^{'}} - t) / τ} d t^{^{'}}}{\int_{t_{1}}^{t} e^{(t^{^{'}} - t) / τ} d t^{^{'}}},

where

E_{m}^{^{'}}

is treated as a continuous function of time

t^{^{'}}

Section: Resultsmentioning

confidence: 84%

The response of equatorial electrojet, vertical plasma drift, and thermospheric zonal wind to enhanced solar wind input

2016

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“…Compared to the work by Gussenhoven et al (), the deviation between the model and the empirical data is small. The radius for Kp = 0 can easily be compared to the radius from Xiong & Lühr () when using the values for E m = 0. From the presented parameters, we calculated the radius of the ellipse by using eq.…”

Section: Resultsmentioning

confidence: 99%

“…From the presented parameters, we calculated the radius of the ellipse by using eq. 3 in Xiong & Lühr (). The radius for each boundary on both hemispheres was calculated in 24 magnetic local time bins.…”

Section: Resultsmentioning

confidence: 99%

Variation of the auroral oval size and offset for different magnetic activity levels described by the Kp‐index

Wagner¹,

Neuhäuser²

2019

Astron Nachr

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The understanding of the behavior of the auroral oval is crucial for the correct reconstruction of its size and location during past centuries by using historical aurora sightings. Therefore, we investigated the radius of the intensity maximum of the oval as well as the offset from the geomagnetic poles for different magnetic activity levels described by the Kp‐index. The Spin‐Scan Auroral Imager mounted on the Dynamics Explorer 1 satellite provides image data from 1981 to 1991, which were used for this purpose. Geometrical analysis of the oval's intensity maximum for each image, transformed into quasi‐dipole coordinates, gives the center of the oval and its radius. The results show a linear dependence between the Kp‐index and radius and a nearly constant shift of the oval center toward the midnight sector of around 4.5°. Furthermore, the images show that the Holzworth mathematical model underestimates the size of the auroral oval in the dawn and dusk sector especially for high magnetic activities.

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“…where

E_{m}^{^{'}}

is treated as a continuous function of time

t^{^{'}}

, t 1 is chosen 3 h before the actual epoch, and τ is the e ‐folding time of the weighting function in the integrands, with a value τ = 0.5 h. A similar approach for calculating the merging electric field has been used in our previous studies [ Xiong et al , ; Xiong and Lühr , ].…”

Section: Resultsmentioning

confidence: 99%

Global features of the disturbance winds during storm time deduced from CHAMP observations

2015

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A wind‐driven disturbance dynamo has been postulated many decades ago. But due to the sparseness of thermospheric wind measurements, details of the phenomena could not be investigated. In this study we use the CHAMP zonal wind observations from 2001 to 2005 to investigate the global features of the disturbance winds during magnetically disturbed periods. The disturbance zonal wind is mainly westward, which increases with magnetic activity and latitude. At subauroral region, the westward zonal wind is strongly enhanced in the magnetic local time (MLT) sector from afternoon to midnight, which we relate to the plasma drift within the subauroral polarization streams. At middle and low latitudes, the disturbance zonal wind is largely independent of season. Peak values of the disturbance zonal wind occur at different MLTs for different latitudes. That is around 1800 MLT at subauroal region, with average values of about 200 m/s; around 2300 MLT at middle latitudes, with average values of about 80 m/s; and around 0300 MLT at low latitudes, with average values up to 50 m/s. The shift of the peak values of the westward disturbance zonal wind in local time at different latitudes could be considered as a response of the disturbance wind when it propagates from high to low latitudes. Further by applying for the first time a superposed epoch analysis, we show that the disturbance zonal wind responds with a delay to the sudden changes of solar wind input, which is different for the various latitudinal ranges. The propagation time of disturbance wind from the auroral region to the equator is about 3–4 h. This is consistent with the speed of traveling atmospheric disturbances. Based on CHAMP observations, we try to illustrate the whole chain of processes from the solar wind driving to the ionospheric effects at lower latitudes.

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An empirical model of the auroral oval derived from CHAMP field-aligned current signatures – Part 2

Cited by 34 publications

References 14 publications

The response of equatorial electrojet, vertical plasma drift, and thermospheric zonal wind to enhanced solar wind input

The response of equatorial electrojet, vertical plasma drift, and thermospheric zonal wind to enhanced solar wind input

Variation of the auroral oval size and offset for different magnetic activity levels described by the Kp‐index

Global features of the disturbance winds during storm time deduced from CHAMP observations

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