Latitude and local time variations of topside magnetic field-aligned ion drifts at solar minimum

Burrell, A. G.; Heelis, R. A.; Stoneback, R.

doi:10.1029/2011ja016715

Cited by 15 publications

(28 citation statements)

References 20 publications

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“…The ranges of these orbital swaths were chosen to encompass the usable ion flow data from CINDI during this time period. During the extended solar minimum starting in 2008 only the cross track ion flow data below 550 km were usable because the percentage of O+ above that altitude was too small for the ion drift meter to function accurately Burrell et al, 2011). But by September 2011, the increased solar activity had increased the percentage of O+ at all altitudes so that the quality of the cross track ion flow data were good up to 750 km.…”

Section: Analytical Approachmentioning

confidence: 96%

Storm-time meridional flows: a comparison of CINDI observations and model results

et al. 2014

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Abstract. During a large geomagnetic storm, the electric field from the polar ionosphere can expand far enough to affect the mid-latitude and equatorial electric fields. These changes in the equatorial zonal electric field, called the penetration field, will cause changes in the meridional ion flows that can be observed by radars and spacecraft. In general this E × B ion flow near the equator caused by the penetration field during undershielding conditions will be upward on the dayside and downward on the nightside of the Earth. Previous analysis of the equatorial meridional flows observed by CINDI instrument on the C/NOFS spacecraft during the 26 September 2011 storm showed that all of the response flows on the dayside were excess downward flows instead of the expected upward flows. These observed storm-time responses are compared to a prediction from a physics-based coupled model of thermosphere-ionosphereinner-magnetosphere in an effort to explain these observations. The model results suggest that the equatorial downward flow could be attributed to a combined effect of the overshielding and disturbance dynamo processes. However, some discrepancy between the model and observation indicates a need for improving our understanding of how sensitive the equatorial electric field is to various model input parameters that describe the magnetosphere-ionosphere coupling processes.

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Section: Analytical Approachmentioning

confidence: 96%

Storm-time meridional flows: a comparison of CINDI observations and model results

et al. 2014

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“…The longitude regions separate the observations into regions of common magnetic declination and offset between geomagnetic and geographic equators while the local time regions consider morning, day, dusk and nighttimes. The longitude divisions are the same as those used by West et al [1997] and are shown in Table 1 along with the seasonal and local time divisions, which were previously used by Burrell et al [2011]. When considering the explicit dependence of the field‐aligned drift on longitude or local time the corrected magnetic latitude is constrained to ±5°.…”

Section: Datamentioning

confidence: 99%

“…These cadences were determined by the sample rate. Further data processing details may be found in the work of Burrell et al [2011].…”

Section: Datamentioning

confidence: 99%

“…These movements can produce hemispheric asymmetries in the plasma density, resulting in field‐aligned motions. As was done by Burrell et al [2011], the Horizontal Wind Model (HWM07) [ Drob et al , 2008] is used to obtain an estimate of the neutral winds along the magnetic meridian below the h m F 2 . For the year under consideration, HWM07 was run at a 30 min universal time cadence at 250 km.…”

Section: Datamentioning

confidence: 99%

“…Many inferred characteristics have been successfully confirmed using direct measurements of the field‐aligned plasma drift. Seasonal, local time, and magnetic latitude variations were explored in a case study by Venkatraman and Heelis [2000] and more systematically by Burrell et al [2011]. Another case study by Chao et al [2004] related direct measurements of the morning equatorial field‐aligned plasma drifts at solar maximum to the previously inferred seasonal and spatial variations.…”

Section: Introductionmentioning

confidence: 99%

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Equatorial longitude and local time variations of topside magnetic field‐aligned ion drifts at solar minimum

2012

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[1] In the topside ionosphere, the high mobility of the plasma along the magnetic field allows field-aligned ion drifts to occur readily as a result of field-aligned gravitational forces, collisional forces, or pressure gradients. Therefore, variations in the field-aligned ion drifts can be used to explore the influence of thermospheric, electrodynamic, and chemical processes on the ionosphere. Longitude and local time variations in the field-aligned ion drifts near the magnetic equator are presented using observations from the Coupled Ion Neutral Dynamics Investigation on board the Communications/Navigation Outage Forecast System satellite. These observations were obtained during the period of extremely low solar activity present in 2008 and 2009, allowing the seasonal, local time, and longitudinal variations to reveal the relative importance of the processes responsible for topside field-aligned plasma drifts during solar minimum. This investigation found that the low-altitude winds and tides, the net ionization or loss, and the meridional EÂB drift were all influential in creating longitudinal and local time variations in the field-aligned drift, though the strength of the influence seen by each driver was found to vary with season, local time, and longitude.

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Formation of the equatorial thermosphere anomaly trough: Local time and solar cycle variations

et al. 2014

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Key Points:• ETA trough is a hydrodynamic response to field-aligned ion drag • EIA and ETA are tightly coupled leading to local time and solar cycle variations • Neutral-ion collisions strongly control ETA trough formation Abstract This paper evaluates the formation and behavior of the equatorial thermosphere anomaly (ETA) trough in neutral temperature and mass density using the National Center for Atmospheric Research thermosphere-ionosphere electrodynamics general circulation model under quiet geomagnetic activity and March equinox conditions. The driving mechanism for the generation of the ETA trough in the model is field-aligned ion drag. In our simulations, during the daytime, field-aligned ion drag on the north-south flanks of the magnetic equator causes a divergence in meridional winds, leading to an upward change in vertical winds, adiabatic cooling, and a reduction in neutral temperature of about 30 K over the magnetic equator near 400 km. This response closely links ETA behavior to variations in the equatorial ionosphere anomaly (EIA) associated with local time and solar cycle. As the EIA begins to disappear in the evening, the processes in the ETA mechanism recede, causing the ETA trough to subside. The ETA trough is not completely eliminated until about after 23:00 LT. In our simulations, the trough becomes more prominent as the solar cycle progresses from low (F 10.7 = 80) to high (F 10.7 = 180), in agreement with observations. The neutral-ion collision frequency (proportional to variations in electron density) controls ETA day-to-night and solar cycle variations, while plasma scale height and gradients in electron number density and plasma temperature produce a secondary structure in ETA local time behavior that varies with solar cycle levels.

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Latitude and local time variations of topside magnetic field-aligned ion drifts at solar minimum

Cited by 15 publications

References 20 publications

Storm-time meridional flows: a comparison of CINDI observations and model results

Storm-time meridional flows: a comparison of CINDI observations and model results

Equatorial longitude and local time variations of topside magnetic field‐aligned ion drifts at solar minimum

Formation of the equatorial thermosphere anomaly trough: Local time and solar cycle variations

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