Judy Cumnock

Evolution of the global aurora during positive IMF Bz and varying IMF By conditions

The DE 1 imaging instrumentation provides a full view of the entire auroral 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 z component of the interplanetary magnetic field was positive and the y component was changing sign. Evolution of an expanded auroral emission region into a theta aurora appears to require a change in the sign of By during northward interplanetary magnetic field (IMF). Theta aurora are formed both from expanded duskside emission regions (By changes from positive to negative) and dawnside emission regions (By 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.

Multi‐instrument analysis of the ionospheric signatures of a hot flow anomaly occurring on July 24, 1996

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.

High-latitude ionospheric convection pattern during steady northward interplanetary magnetic field

The DMSP F8 satellites coverage of Earths polar regions provides horizontal ion drift velocities along the dawn-dusk meridian at approximately 835 km altitude in each hemisphere during the ∼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 Bz, the influences on the convection pattern of the IMF Bz/|By| ratio, season, latitude, and solar wind velocity are all considered. The ratio Bz/|By| 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.

Reverse convection potential: A statistical study of the general properties of lobe reconnection and saturation effects during northward IMF

The saturation tendency of the cross-polar potential for southward interplanetary magnetic fields has been the subject of numerous studies, however, the behavior of the reverse convection potentia ...

Evolution in space and time of the quasi‐static acceleration potential of inverted‐V aurora and its interaction with Alfvénic boundary processes

Results are presented from Cluster crossings of the acceleration region of two inverted-V auroras located in the poleward part of an extensive substorm bulge. The particle and field data are used t ...

Response of the ionospheric convection pattern to a rotation of the interplanetary magnetic field on January 14, 1988

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 By and Bz are positive, but By is greater than Bz, strong evidence exists for dayside merging in a manner similar to that expected when Bz is negative. This signature is diminished as By decreases and becomes smaller than Bz resulting in a four-cell convection pattern displaced toward the sunward side of the dawn-dusk meridian. In this case the sign of By affects the relative sizes of the two highest-latitude cells. In the southern hemisphere the duskside high-latitude cell is dominant for By positive and the dawnside high-latitude cell is dominant for By 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.

Occurrence and properties of substorms associated with pseudobreakups

We investigate how substorms with and without growth-phase pseudobreakups are affected by solar wind and ionospheric conditions. The study is based on 874 events identified with Polar UVI. An AE in ...

Statistical analysis of the sources of the cross‐polar potential for southward IMF, based on particle precipitation characteristics

There are several proposed physical processes which may contribute to the cross-polar potential and thus drive ionospheric convection around the polar caps. It is generally believed that magnetic r ...

Response of the ionospheric convection reversal boundary at high latitudes to changes in the interplanetary magnetic field

In this paper we present a systematic study of the location of the convection reversal boundary for southward interplanetary magnetic field by using Defense Meteorological Satellite Program (DMSP) F13 and F15 spacecraft measurements during local summer seasons from 2000 to 2007 for both hemispheres. All the convection reversal boundaries are identified pass bypass by locating the highest-latitude location where the plasma flow shows a large-scale two-cell pattern and reverses direction from sunward to antisunward. The location of the convection reversal boundaries are placed into 10 different categories based on By and the magnitude of southward Bz. Observations suggest that (1) the location of the boundary is well organized by the magnitude of Bz, being at lower latitudes for stronger negative Bz and also organized by the polarity of By, moving toward the dawnside/duskside when By changes from negative to positive in the northern/southern hemisphere; (2) the average latitudinal movement of the boundary associated with By changes is comparable to the average movement of the boundary with Bz changes; (3) an initial reconfiguration of the boundary near local noon is redistributed around the dawnside or duskside dependent on the direction of By; and (4) the boundary has a general spiral shape, which varies depending on Bz and By.

Seasonal dependence and solar wind control of transpolar arc luminosity

[1] The influence of the solar wind and the interplanetary magnetic field (IMF) on the luminosity of transpolar arcs (TPAs) is examined by taking into account seasonal effects. The study focuses on those transpolar arcs that appear after an IMF By sign change during steady northward IMF. It includes 21 northern hemisphere events identified in a previous study from global UV images taken by the Polar spacecraft between 1996 and 2000. Sorting the TPA events by sign of the Earth dipole tilt we find that the TPAs which appear in the dark hemisphere are on average much weaker than TPAs in the sunlit hemisphere. For the dark hemisphere events, no clear correlation between solar wind parameters and TPA luminosity is found. However, in the sunlit hemisphere, a clear dependence on solar wind and IMF conditions is seen. The TPA brightness is strongly influenced by IMF magnitude, northward IMF Bz and solar wind speed. A weak, negative correlation with the ion density is found. The TPA luminosity in the sunlit hemisphere is much more strongly controlled by the magnetic energy flux than by the kinetic energy flux of the solar wind. This explains the absence of transpolar arcs for the two By sign change cases for positive dipole tilts with lowest magnetic energy flux values. The strong influence of the Earth dipole tilt on the transpolar arc luminosity appears due to the dependence of the ionospheric conductivity on solar EUV emissions.