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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Global morphology of substorm growth phases observed by the IMAGE‐SI12 imager
TL;DR: In this article, the authors present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases, based on observations of the Doppler-shifted Lyman-α auroral emission obtained with the SI12 Spectrographic Imager.
Journal ArticleDOI
Comparison of the open-closed separatrix in a global magnetospheric simulation with observations: The role of the ring current
I. J. Rae,K. Kabin,Jianyong Lu,Robert Rankin,Steve Milan,F. R. Fenrich,Clare E. J. Watt,Jichun Zhang,Aaron J. Ridley,Tamas I. Gombosi,C. R. Clauer,Gabor Toth,Darren L. DeZeeuw +12 more
TL;DR: In this paper, the location of the polar cap boundary, or open-closed field line boundary (OCB), can be determined in the ionosphere using a combination of instruments during a period encompassing a sharp northward to southward interplanetary field turning.
Evolution of asymmetrically displaced footpoints during substorms
Anders Ohma,Nikolai Østgaard,Karl Magnus Laundal,Jone Peter Reistad,Paul Tenfjord,Kristian Snekvik,Matthew Fillingim +6 more
Journal ArticleDOI
Real-time determination and monitoring of the auroral electrojet boundaries
TL;DR: In this paper, a method for nowcasting of the auroral electrojet location from real-time geomagnetic data in the European sector is presented, where the relationship between the electrojet and the diffuse auroral oval is discussed, and it is concluded that although there may exist timedependent differences in boundary locations, there exists a general coincidence.
Journal ArticleDOI
Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight
Anita Aikio,Heikki Vanhamäki,Heikki Vanhamäki,Abiyot Workayehu,Ilkka Virtanen,Kirsti Kauristie,Liisa Juusola,Stephan Buchert,David J. Knudsen +8 more
TL;DR: In this paper, Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes were presented, and the most striking feature is a plasma flow channel located equatorward.
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.