| 1. |
|
|
| 2. |
- Sitar, R J, et al.
(författare)
-
Multi-instrument analysis of the ionospheric signatures of a hot flow anomaly occurring on July 24, 1996
- 1998
-
Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. ; 103, s. 23357-23372
-
Tidskriftsartikel (refereegranskat)abstract
- We present the analysis of a coordinated set of observations from the POLAR ultraviolet imager (UVI), ground magnetometers, incoherent scatter radar, solar wind monitors, and the DMSP satellite, focused on a traveling convection vortex (TCV) event on July 24, 1996. Starting at approximately 1036 UT, ground magnetometers in Greenland and eastern Canada observe pulsations consistent with the passing overhead of a series of TCV field-aligned current pairs. Azimuthal scans by the Sondrestrom incoherent scatter radar located near Kangerlussuaq (formerly Sondrestrom), Greenland, at this time show strong modulation in the strength and direction of ionospheric plasma flow. The magnetometer pulsations grow in magnitude over the next hour, peaking in intensity at 1137 UT. Images from the UVI instrument show a localized intensification of auroral emissions over central and western Greenland at 1139 UT. Subsequent images show the intensification grow in strength and propagate westward (tailward) until approximately 1158 UT, at which time the intensification fades, These observations are consistent with the westward passage of four pairs of TCVs over central Greenland. The intensification of auroral emissions at 1139 UT is associated with the leading vortex of the fourth TCV pair, thought to be the result of an upward field-aligned current. The modulated flow observed by the radar is the result of the strong electric fields associated with the field-aligned current systems responsible for the impulsive TCV as they pass through the field of view of the radar. Measurements taken in the solar wind by the Wind spacecraft suggest that a pressure change triggers the onset of TCV activity. A subsequent sudden change in the orientation of the interplanetary magnetic field produces a hot flow anomaly which forms at the bow shock. We believe that the interaction of the hot flow anomaly with the magnetopause intensified the fourth TCV pair and. produced the associated auroral brightening. DMSP particle data indicate that the TCVs occur on field lines which map to the boundary plasma sheet-low latitude boundary layer interface. The ground observations associated with the hot flow anomaly are the first of their kind and provide a mechanism to tie an interplanetary magnetic field orientation change into the existing theory that TCVs result from a deformation of the magnetopause.
|
|
| 3. |
- Cumnock, Judy, et al.
(författare)
-
POLAR UVI Observations of Auroral Oval Intensifications During a Transpolar Arc Event on December 7, 1996
- 2000
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The evolution of the northern hemisphere aurora is examined during a time when the IMF makes three brief southward excursions after a change in the sign of By during an extended period of northward IMF. POLAR UVI provides images of the aurora while DMSP F13 and F14 provide in situ measurements of precipitating particles, ionospheric plasma flows and ion density. Three different intensifications located in the nightside auroral oval occur during northward turnings of the IMF after brief periods of southward IMF. Spatial expansion, intensity of emissions and their duration are related to the length of time the IMF is southward prior to the northward turning. Thus the longer the period of enhanced magnetospheric convection the more intense the ionospheric response. Observations of a transpolar arc indicate that when the transpolar arc reaches highest latitudes it is located on a spatially narrow region of closed field lines, which extends along the noon-midnight meridian. UV observations indicate a connection between the transpolar arc and the nightside auroral enhancements. Precipitating particles associated with both features are attributed to a plasma sheet boundary layer source in the magnetotail implying a magnetospheric connection between the transpolar arc and the nightside auroral oval intensification.
|
|
| 4. |
|
|
| 5. |
- Germany, G A, et al.
(författare)
-
Remote determination of auroral energy characteristics during substorm activity
- 1997
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 24, s. 995-998
-
Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet auroral images from the Ultraviolet Imager (UVI) onboard the POLAR satellite can be used as quantitative remote diagnostics of the auroral regions, yielding estimates of incident energy characteristics, compositional changes, and other higher order data products. Here incident energy estimates derived from UVI are compared with in situ measurements of the same parameters from an overflight by the DMSP F12 satellite coincident with the UVI image times during substorm activity occurring on May 19, 1996. This event was simultaneously observed by WIND, GEOTAIL, INTERBALL, DMSP and NOAA spacecraft as well as by POLAR.
|
|
| 6. |
- Kullen, A., et al.
(författare)
-
Solar wind dependence of the occurrence and motion of polar auroral arcs : A statistical study
- 2002
-
Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 107:A11
-
Tidskriftsartikel (refereegranskat)abstract
- [1] Polar UV images from a 3-month period in winter 1998-1999 are used for a statistical study of polar arcs. The study covers all auroral arcs that are located poleward of the northern auroral oval, and which are detectable by the UV imager. The arcs are examined with respect to their spatial and temporal behavior as well as to a possible connection to solar wind parameters using ACE satellite data. It is found that the majority of polar arcs appear during northward IMF, strong IMF magnitude, and high solar wind speed. A modified Akasofu-Perreault epsilon parameter with a cosine function instead of a sine function (nuB(2) cos(4) (theta/2)(l(0)(2)/mu(0))) combines these results. It correlates well with the occurrence frequency of polar arcs for long timescales. The location of polar arcs is strongly dependent on the sign of the IMF B-y component. Static polar arcs occur in the Northern Hemisphere on the dawn (dusk) side of the oval for negative (positive) IMF B-y, whereas poleward-moving arcs separate from the opposite side of the oval, and then move in the direction of IMF B-y. All polar arcs are sorted into five different categories according to their spatial structure and evolution: oval-aligned, bending, moving, midnight, and multiple arcs. Each polar arc type occurs for a characteristic combination of solar wind parameters. IMF clock angle changes seem to have a strong influence on what type of arc occurs. Oval-aligned arcs appear mainly during steady IMF, bending arcs after an IMF B-z sign change, and moving arcs after an IMF B-y sign change. For the rare midnight and multiple arc events, no characteristic IMF clock angle dependence has been found. The different types of clear polar arcs are discussed in the context of existing observational studies and transpolar arc models.
|
|
