| 1. |
- Cumnock, J. A., et al.
(author)
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Interplanetary magnetic field control of theta aurora development
- 2002
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In: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 107:A7
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Journal article (peer-reviewed)abstract
- [1] We ascertain the influence of the B-y component of the interplanetary magnetic field (IMF) on theta aurora evolution. During most cases where a transpolar arc is observed to move across the polar region, and form a theta aurora, there are brief (minutes) southward excursions of IMF B-z, however northward IMF is required prior to theta aurora formation. Observations show that theta aurora can form during strictly northward IMF with its motion consistent with a change in sign of IMF B-y. It is important to note that since transpolar arcs can persist for 20-30 min after the IMF turns southward, errors will occur in assigning instantaneous IMF conditions to snapshots'' of particular auroral patterns. We consider the entire evolution of the theta aurora and the changing IMF conditions. The influence of IMF B-y is best illustrated by examples which occur during steady northward IMF as compared to times when the IMF is northward on average. We show examples, provided by the Polar UV imager, when the IMF is steady northward. For one case, DMSP F13 and F14 provide in situ measurements of precipitating particles, ionospheric plasma flows and ion density. This unique data set enables us to analyze in detail the evolution of a theta aurora, in one case crossing the entire polar region. No sign change in B-z is needed for theta aurora formation.
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| 2. |
- Cumnock, Judy, et al.
(author)
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Evolution of the global aurora during positive IMF B-z and varying IMF B-y conditions
- 1997
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In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. ; 102, s. 17489-17497
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Journal article (peer-reviewed)abstract
- The DE 1 imaging instrumentation provides a full view of the entire amoral oval every 12 min for several hours during each orbit. We examined five examples of global evolution of the aurora that occurred during the northern hemisphere winter of 1981-1982 when the a component of the interplanetary magnetic field was positive and the y component was changing sign. Evolution of an expanded amoral emission region into a theta aurora appears to require a change in the sign of B-y during northward interplanetary magnetic field (IMF). Theta aurora are formed both from expanded duskside emission regions (B-y changes from positive to negative) and dawnside emission regions (B-y changes from negative to positive), however the dawnside-originating and duskside-originating evolutions are not mirror images. The persistence of a theta aurora after its formation suggests that there may be no clear relationship between the theta aurora pattern and the instantaneous configuration of the IMF.
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| 3. |
- Cumnock, Judy, et al.
(author)
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High-Latitude Ionospheric Convection Pattern During Steady Northward Interplanetary Magnetic Field
- 1995
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 100, s. 14537-14555
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Journal article (peer-reviewed)abstract
- The DMSP F8 satellite’s coverage of Earth’s polar regions provides horizontal ion drift velocities along the dawn-dusk meridian at approximately 835 km altitude in each hemisphere during the similar to 100 min orbital period. We examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field (IMF) is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass. These convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions. Here we describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward IMF conditions. In addition to IMF B-z, the influences on the convection pattern of the IMF B-z/\textbackslashB-y\textbackslash ratio, season, latitude, and solar wind velocity are all considered. The ratio B-z/\textbackslashB-y\textbackslash provides a first order organization of the signatures that occur on the dayside of the dawn-dusk meridian. Sunward flow at highest latitudes on the dayside of the dawn-dusk meridian is the dominant feature seen in the large-scale convection signature during steady northward IMF; however, sunward flow at highest latitudes does not imply the existence of a particular number of convection cells.
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| 4. |
- Cumnock, Judy, et al.
(author)
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Response of the Ionospheric Convection Pattern to a Rotation of the Interplanetary Magnetic Field on January 14, 1988
- 1992
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 97, s. 19449-19460
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Journal article (peer-reviewed)abstract
- Ionospheric convection signatures observed over the polar regions are provided by the DMSP F8 satellite. We consider five passes over the southern summer hemisphere during a time when the z component of the interplanetary magnetic field was stable and positive and the y component changed slowly from positive to negative. Large-scale regions of sunward flow are observed at very high latitudes consistent with a strong z component. When B(y) and B(z) are positive, but B(y) is greater than B(z), strong evidence exists for dayside merging in a manner similar to that expected when B(z) is negative. This signature is diminished as B(y) decreases and becomes smaller than B(z) resulting in a four-cell convection pattern displaced toward the sunward side of the dawn-dusk meridian. In this case the sign of B(y) affects the relative sizes of the two highest-latitude cells. In the southern hemisphere the dusk side high-latitude cell is dominant for B(y) positive and the dawnside high-latitude cell is dominant for B(y) negative. The relative importance of possible electric field sources in the low-latitude boundary layer, the dayside cusp, and the lobe all need to be considered to adequately explain the observed evolution of the convection pattern.
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