CUSP/CLEFT Auroral Activity in Relation to Solar Wind Dynamic Pressure, IMF BZ and BY

Sandholt, P. E.; Farrugia, C. J.; Burlaga, L. F.; Holtet, J. A.; Moen, J.; Lybekk, B.; Jacobsen, B.; Opsvik, D.; Egeland, Alv; Lepping, R. P.; Lazarus, A. J.; Hansen, Truls Lynne; Brekke, A.; Friis‐Christensen, E.

doi:10.1007/978-94-011-1052-5_12

Cited by 29 publications

(59 citation statements)

References 30 publications

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“…Optical observations made from Svalbard do not show any evidence of such large or rapid equatorward motion of the 630 nm cusp precipitation region, e.g. Sandholt et al (1994). Fig.…”

Section: High Time Resolution Datamentioning

confidence: 90%

The ionospheric response to flux transfer events: the first few minutes

Rodger

Pinnock

1997

Ann. Geophys.

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Abstract. We utilise high-time resolution measurements from the PACE HF radar at Halley, Antarctica to explore the evolution of the ionospheric response during the ®rst few minutes after enhanced reconnection occurs at the magnetopause. We show that the plasma velocity increases associated with¯ux transfer events (FTEs) occur ®rst $100±200 km equatorward of the region to which magnetosheath (cusp) precipitation maps to the ionosphere. We suggest that these velocity variations start near the ionospheric footprint of the boundary between open and closed magnetic ®eld lines. We show that these velocity variations have rise times $100 s and fall times of $10 s. When these velocity transients reach the latitude of the cusp precipitation, sometimes the equatorward boundary of the precipitation begins to move equatorward, the expected and previously reported ionospheric signature of enhanced reconnection. A hypothesis is proposed to explain the velocity variations. It involves the rapid out¯ow of magnetospheric electrons into the magnetosheath along the most recently reconnected ®eld lines. Several predictions are made arising from the proposed explanation which could be tested with ground-based and space-based observations.

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“…Optical observations made from Svalbard do not show any evidence of such large or rapid equatorward motion of the 630 nm cusp precipitation region, e.g. Sandholt et al (1994). Fig.…”

Section: High Time Resolution Datamentioning

confidence: 90%

The ionospheric response to flux transfer events: the first few minutes

Rodger

Pinnock

1997

Ann. Geophys.

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“…The motion of the magnetopause may lead to ionospheric forms consistent with the spatial/temporal scale and location of PMAFs. Using case studies, Lui and Sibeck [1991] and Sandholt et al [1994] found a correlation between PMAFs and transient pressure pulses. However, Lockwood et al [1990] found no correlation between PMAFs and dynamic pressure pulses in their case study.…”

Section: Introductionmentioning

confidence: 99%

“…The mechanisms of solar wind energy and momentum transfer to the magnetosphere can be studied in the dayside cusp/cleft ionosphere where field lines map directly to the dayside magnetopause and boundary layers. Poleward moving auroral forms (PMAFs) are one of the most common features of the dynamic dayside cusp [ Horwitz and Akasofu , 1977; Rairden and Mende , 1989; Fasel et al , 1992; Fasel , 1995; Sandholt et al , 1986, 1990, 1994, 1998a, 1998b; Sandholt and Farrugia , 1999]. These transient forms are initiated by a brightening at the equatorward boundary of the dayside auroral oval, then separate, and move antisunward (tailward), subsequently fading and disappearing several degrees from the auroral oval in the polar cap [ Fasel et al , 1992].…”

Section: Introductionmentioning

confidence: 99%

Southern Hemisphere poleward moving auroral forms

et al. 2003

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This paper presents a statistical study of Southern Hemisphere poleward moving auroral forms (PMAFs) using optical data from the US Automatic Geophysical Observatory network in Antarctica. These Southern Hemisphere events are compared with Northern Hemisphere PMAFs, which have previously been observed during varied interplanetary magnetic field (IMF) configurations. The frequency of PMAF occurrence is studied as a function of IMF orientation and magnetic local time. Southern Hemisphere PMAFs are biased to Bz < 0 constituting 62% of events, but are frequently observed during conditions of Bz > 0 constituting 38% of events. Southern Hemisphere PMAFs share a similar IMF Bz dependence with Northern Hemisphere events [e.g., Fasel, 1995]. The primary modulator of PMAFs was found to be IMF By, which was negative for 81% of events. Although the average background IMF was biased to By < 0, we find significant enhancement during By < 0 after this bias was removed. In a statistical study of Northern Hemisphere events, Fasel [1995] found 77% of events occur during positive By. PMAFs appear to have an antisymmetric By dependence between hemispheres. We find By < 0 (By > 0) enhances the observation of PMAFs in the prenoon (postnoon) region, consistent with the release of magnetic stress. A morning bias of Southern Hemisphere PMAFs is observed, consistent with Northern Hemisphere events.

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“…l e) in¯uences the position of the separatrix, although observable eects may only occur for Dp/p ³ 0.5 (Sandholt et al, 1994). We have estimated the eect of the solar wind pressure variations on our data by assuming a simple pressure balance condition and estimating the position of the magnetopause (e.g., Kivelson and Russell, 1995, p172).…”

Section: Response To Solar Wind Dynamic Pressure Variationsmentioning

confidence: 99%

Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

et al. 1999

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Abstract. Data from HF-radars are used to make the ®rst simultaneous conjugate measurements of the dayside reconnection electric ®eld. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic ®eld (IMF) was southward whilst the eastward component (By) was variable. The¯ow patterns derived from the radar data show the expected conjugate asymmetries associated with IMF jByj > 0. High-time resolution data (50 and 100 s) enable the¯ow of plasma across the open/closed ®eld line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical dierence of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s A1 ) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively ®ts that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be signi®cantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat¯ow occurs is dierent in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric ®eld values are largest when the radar's meridian is in the throat ow or early afternoon¯ow regions. In the morning or afternoon convection cells, the reconnection electric ®eld tends to zero away from the throat¯ow region. The reconnection electric ®eld observed in the throat¯ow region is bursty in nature.

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CUSP/CLEFT Auroral Activity in Relation to Solar Wind Dynamic Pressure, IMF BZ and BY

Cited by 29 publications

References 30 publications

The ionospheric response to flux transfer events: the first few minutes

The ionospheric response to flux transfer events: the first few minutes

Southern Hemisphere poleward moving auroral forms

Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

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