Variations in the polar cap area during two substorm cycles
Steve Milan,Mark Lester,Stanley W. H. Cowley,Kjellmar Oksavik,Mitchell J. Brittnacher,R. A. Greenwald,George J. Sofko,Jean-Paul Villain +7 more
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In this article, the authors employed observations from several sources to determine the location of the polar cap bound-ary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified.Abstract:
This study employs observations from several sources to determine the location of the polar cap bound- ary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral im- ages from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the mag- netosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, al- lowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and de- creases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to de- crease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap bound- ary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times sup- ports this finding.read more
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Journal ArticleDOI
Polar Cap Boundary Identification Using Redline Optical Data and DMSP Satellite Particle Data
TL;DR: In this paper , the authors used data from the Defense Meteorological Satellite Program satellites in conjunction with the University of Calgary's Redline Emission Geospace Observatory (630.0 nm) data to assess the viability of automated detection of the 2D polar cap boundary.
Multi‐Instrument Observations of the Effects of a Solar Wind Pressure Pulse on the High Latitude Ionosphere: A Detailed Case Study of a Geomagnetic Sudden Impulse
Alexandra Ruth Fogg,Mark Tester,Tim K. Yeoman,J. A. Carter,Steve Milan,Harneet K. Sangha,T. Elsden,S. J. Wharton,Matthew K. James,John Malone-Leigh,Larry J. Paxton,K. J. Anderson,Sarah K. Vines +12 more
TL;DR: In this article , a superposition of Alfvén and compressional propagation modes are observed in magnetometer signatures, with the dominance of these signatures varying with latitude, and collocated lobe reconnection convection vortices and region 0 field aligned currents are observed preceding the positive geomagnetic sudden impulse (+SI) onset.
Journal ArticleDOI
Auroral Oval Morphology: Dawn‐Dusk Asymmetry Partially Induced by Earth's Rotation
TL;DR: In this paper , the authors developed a statistical method to characterize the auroral oval morphology by using 20 years of electron energy flux measurements from the Defense Meteorological Satellite Program/Special Sensor J (DMSP/SSJ); instead of relying on auroral boundary boundaries, they derived the probability of observing aurora from a threshold of 2.109 eV/cm2/s/sr above which the total energy flux of electrons (in the energy range 1-30 keV) is defined as aurora.
Journal ArticleDOI
Cluster Observation of Ion Outflow in Middle Altitude LLBL/Cusp from Different Origins
Bin Li,Huigen Yang,Jicheng Sun,Zejun Hu,Jianjun Liu,Xiangcai Chen,Yong Wang,Jie Ren,Chao Yue,C. P. Escoubet,Qian Wang,Qiugang Zong +11 more
TL;DR: In this article , two different origins of the outflowing particles were determined based on the Cluster observation in the magnetospheric cusp region, and their unique mechanisms of formation were discussed.
Journal ArticleDOI
Multi‐Instrument Observations of the Effects of a Solar Wind Pressure Pulse on the High Latitude Ionosphere: A Detailed Case Study of a Geomagnetic Sudden Impulse
TL;DR: In this paper , a superposition of Alfvén and compressional propagation modes are observed in magnetometer signatures, with the dominance of these signatures varying with latitude, and collocated lobe reconnection convection vortices and region 0 field aligned currents are observed preceding the positive geomagnetic sudden impulse (+SI) onset.
References
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Journal ArticleDOI
Empirical high-latitude electric field models
J. P. Heppner,N. C. Maynard +1 more
TL;DR: In this paper, large-scale revisions of the OGO 6 dawn-dusk measurement models are made, showing that the deformations of the two-cell patterns lead to sunward convection in dayside polar regions, while maintaining the integrity of the night-side convection pattern.
Journal ArticleDOI
DARN/SUPERDARN : A global view of the dynamics of high-latitude convection
R. A. Greenwald,K. B. Baker,J. R. Dudeney,Michael Pinnock,T. B. Jones,E. C. Thomas,Jean-Paul Villain,Jean-Claude Cerisier,C. Senior,C. Hanuise,R. D. Hunsucker,George J. Sofko,James A. Koehler,Erling Nielsen,R. J. Pellinen,Anthony Walker,N. Saot,H. Yamagishi +17 more
TL;DR: The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere as mentioned in this paper.
Journal ArticleDOI
Initial ISEE Magnetometer Results: Magnetopause Observations (Article published in the special issues: Advances in Magnetospheric Physics with GEOS- 1 and ISEE - 1 and 2.)
C. T. Russell,R. C. Elphic +1 more
Abstract: The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes. During one of these passes the magnetosheath field was northward, during one it was slightly southward, and in two it was strongly southward. The velocity of the magnetopause is found to be highly irregular ranging from 4 to over 40 km s-1 and varying in less time than it takes for a spacecraft to cross the boundary. Thicknesses ranged from 500 to over 1000 km.Clear evidence for reconnection is found in the data when the magnetosheath field is southward. However, this evidence is not in the form of classic rotational discontinuity signatures. Rather, it is in the form of flux transfer events, in which reconnection starts and stops in a matter of minutes or less, resulting in the ripping off of flux tubes from the magnetosphere. Evidence for flux transfer events can be found both in the magnetosheath and the outer magnetosphere due to their alteration of the boundary normal. In particular, their presence at the time of magnetopause crossings invalidates the usual 2-dimensional analysis of magnetopause structure. Not only are these flux transfer events probably the dominant means of reconnection on the magnetopause, but they may also serve as an important source of magnetopause oscillations, and hence of pulsations in the outer magnetosphere. On two days the flux transfer rate was estimated to be of the order of 2 × 1012 Maxwells per second by the flux transfer events detected at ISEE. Events not detectable at ISEE and continued reconnection after passage of an FTE past ISEE could have resulted in an even greater reconnection rate at these times.
Book ChapterDOI
Initial ISEE magnetometer results - Magnetopause observations
TL;DR: The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes as discussed by the authors, during which the magnetosheath field was northward, during one pass it was slightly southward, and in two it was strongly southward.
Journal ArticleDOI
ISEE observations of flux transfer events at the dayside magnetopause
TL;DR: In this paper, the authors examined magnetic field measurements from the ISEE 1 and 2 spacecraft in the vicinity of the magnetopause near local noon on a typical pass when the magnetosheath field is southward.