Dynamical polar cap: A unifying approach

Newell, P. T.; Xu, Dingan; Meng, C.‐I.; Kivelson, M. G.

doi:10.1029/96ja03045

Cited by 65 publications

(50 citation statements)

References 22 publications

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“…By contrast, polar cap fluxes 50% greater than the mode were still fairly common in 1992 (the active year). The reason for this asymmetry is that the polar cap only loses open magnetic flux slowly during quiet times; hence it rarely drops to very low values (Newell et al, 1997). At very small polar cap flux levels (below, say, 100 MWb), there is typically a difficulty in accurately measuring the size from DMSP measurements.…”

Section: Solar Cycle Variation Of Pcmentioning

confidence: 99%

OVATION: Oval variation, assessment, tracking, intensity, and online nowcasting

et al. 2002

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Abstract. The location of the auroral oval and the intensity of the auroral precipitation within it are basic elements in any adequate characterization of the state of the magnetosphere. Yet despite the many ground-based and spacecraftborne instruments monitoring various aspects of auroral behavior, there are no clear and consistent answers available to those wishing to locate the auroral oval or to quantify its intensity. The purpose of OVATION is to create a tool which does so. OVATION is useful both for archival purposes and for space weather nowcasting. The long-running DMSP particle data set, which covers both hemispheres, and has operated since the early 1980s, and which will continue to operate well into the next decade, is chosen as a calibration standard. Other data sets, including global images from Polar UVI, SuperDARN boundaries, and meridian scanning photometer images, are cross-calibrated to the DMSP standard. Each incorporated instrument has its average offset from the DMSP standard determined as a function of MLT, along with the standard deviations. The various data can, therefore, be combined in a meaningful manner, with the weight attached to a given boundary measurement varying inversely with the variance (square of the standard deviation). OVATION currently spans from December 1983 through the present, including real-time data. Participation of additional experimenters is highly welcomed. The only prerequisites are a willingness to conduct the prescribed cross-calibration procedure, and to make the data available online. The real-time auroral oval location can be found here: http://sd-www.jhuapl.edu/Aurora/ ovation live/north display.html.

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Section: Solar Cycle Variation Of Pcmentioning

confidence: 99%

OVATION: Oval variation, assessment, tracking, intensity, and online nowcasting

et al. 2002

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“…No explicit distinction is made between a double oval and other auroral features that may appear poleward of the main oval, such as high-latitude sun-aligned arcs. When present, high-latitude sun-aligned arcs can be suggestive of a configuration of multiple regions of open and closed magnetic flux rather than a single open polar cap (e.g., Newell et al, 1997;Brittnacher et al, 1999;Newell et al, 2009). For each MLT sector, only a single PALB is assumed to be a proxy for the OCB and, hence, polar caps with multiple open field line regions will not be well modelled.…”

Section: Technique Limitationsmentioning

confidence: 99%

Estimating the location of the open-closed magnetic field line boundary from auroral images

et al. 2010

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Abstract. The open-closed magnetic field line boundary (OCB) delimits the region of open magnetic flux forming the polar cap in the Earth's ionosphere. We present a reliable, automated method for determining the location of the poleward auroral luminosity boundary (PALB) from far ultraviolet (FUV) images of the aurora, which we use as a proxy for the OCB. This technique models latitudinal profiles of auroral luminosity as both a single and double Gaussian function with a quadratic background to produce estimates of the PALB without prior knowledge of the level of auroral activity or of the presence of bifurcation in the auroral oval. We have applied this technique to FUV images recorded by the IMAGE satellite from May 2000 until August 2002 to produce a database of over a million PALB location estimates, which is freely available to download. From this database, we assess and illustrate the accuracy and reliability of this technique during varying geomagnetic conditions. We find that up to 35% of our PALB estimates are made from double Gaussian fits to latitudinal intensity profiles, in preference to single Gaussian fits, in nightside magnetic local time (MLT) sectors. The accuracy of our PALBs as a proxy for the location of the OCB is evaluated by comparison with particle precipitation boundary (PPB) proxies from the DMSP satellites. We demonstrate the value of this technique in estimating the total rate of magnetic reconnection from the time variation of the polar cap area calculated from our OCB estimates.

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“…A polar arc model that became widely accepted in recent years has been developed by Newell et al (1997) and Chang et al (1998). It explains the creation of a new region of open field lines dawnward (or duskward) of the main polar cap near noon with an abrupt jump in the dayside merging line.…”

Section: Polar Arc Modelsmentioning

confidence: 99%

Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study

2004

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Abstract. We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF B y sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results.The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF B y . The tail becomes longer and at its tailward end stronger twisted for IMF B z >|B y | than for IMF B z <|B y |. The field lines originating in the high-latitude flank of the far-tail plasma sheet map into the near-Earth tail lobes and to a strongly poleward displaced polar cap boundary. A comparison with observations suggests that an ovalaligned arc may occur on the high-latitude part of the polar cap boundary.An IMF B y sign change causes large deformations of the tail. After the IMF B y flip the near-Earth and far-tail plasma sheet regions are oppositely twisted which causes in the nearEarth tail a bifurcation of the closed field line region that moves from one flank to the other. The bifurcated part of the closed field line region maps to a bridge of closed field lines moving over the entire polar cap. This moving bridge may be interpreted as the mapped region of a moving transpolar arc. Based on earlier observations, such a type of polar arcs is expected to occur after an IMF B y sign change.

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Dynamical polar cap: A unifying approach

Cited by 65 publications

References 22 publications

OVATION: Oval variation, assessment, tracking, intensity, and online nowcasting

OVATION: Oval variation, assessment, tracking, intensity, and online nowcasting

Estimating the location of the open-closed magnetic field line boundary from auroral images

Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study

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