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
Reads0
Chats0
TLDR
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
Citations
More filters
Journal ArticleDOI
Comparative study of large-scale auroral signatures of substorms, steady magnetospheric convection events, and sawtooth events
M.-T. Walach,M.-T. Walach,Steve Milan,Kyle R. Murphy,J. A. Carter,Benoît Hubert,Adrian Grocott +6 more
TL;DR: In this article, a superposed epoch analysis using data from the Imager for Magnetopause-to-Aurora Global Exploration Far Ultraviolet spectrographic imager and wideband imaging camera for each of these event types was conducted.
Journal ArticleDOI
Interaction evidence between Enceladus' atmosphere and Saturn's magnetosphere
TL;DR: In this paper, a search for Enceladus' auroral footprint using series of UV images of Saturn's aurora taken by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) in January 2004 and the Advanced Camera for Surveys (ACS) between February 2005 and January 2007 was conducted.
Journal ArticleDOI
What controls the local time extent of flux transfer events
TL;DR: In this paper, the authors compare two sequences of the ionospheric signatures of flux transfer events observed in global auroral imagery and coherent ionosphere radar measurements, and discuss the ramifications of these differences for solar wind-magnetosphere coupling.
Journal ArticleDOI
Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 2. Persistence of ionospheric convection
Mike Lockwood,Mike Lockwood,Betty Lanchester,Steven K. Morley,K. Throp,Steve Milan,Mark Lester,Harald U. Frey +7 more
TL;DR: In this paper, the Enosin 4 (q/2) model was used to estimate the peak value of Eno,b y matching observed and modeled variations of both the latitude, LOCB, of the dayside OCB, as inferred from the equatorward edge of cusp proton emissions seen by FUV and the transpolar voltage FPC (as derived using the mapped potential technique from SuperDARN HF radar data).
References
More filters
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.