The Polar Ultraviolet Imager (UVI) observes auroral responses to incident solar wind pressure pulses and interplanetary shocks such as those associated with coronal mass ejections. The arrival of a CME pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside auroral precipitation. Our observations show a simultaneous brightening over broad areas of the dayside and nightside aurora in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolated substorms. We estimate the average energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has average energies greater than 10 keV and is structured both in local time and magnetic latitude. For auroral intensifications following the arrival of a pressure pulse or interplanetary shock, electron precipitation is less spatially structured and has greater ux of lower energy electrons (Eave _ 7 keV) than during isolated substorm, onsets. The average energies of the precipitating electrons inferred from UVI are consistent with those measured in-situ by the FAST spacecraft. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.
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"Within a few minutes, the region of auroral emission expands longitudinally, reaches the dawn and dusk sectors and eventually the nightside. The delay between the arrival of the shock on the front of the magnetosphere and the auroral response is shorter than the convection timescale [Chua et al., 2001]. Due to the short rise time, the magnetosphere does not have time to equilibrate with the new magnetic field configuration and strong transient perturbations are observed everywhere in the magnetosphere [Boudouridis et al., 2003]. "
[Show abstract][Hide abstract] ABSTRACT: 1] On April 28 2001, simultaneous global images of electron and proton aurora were obtained by IMAGE-FUV following a sudden increase of solar wind dynamic pressure. The local time and intensity distribution of both types of precipitation are examined and compared. It is found that the electron and the proton precipitation both start in the post noon sector and expand concurrently, but the expansion into the nightside starts sooner for the protons than for the electrons. The characteristic rise time in the onset sector is on the order of 6 minutes. A distinct dynamics and morphology of electron and proton precipitation is observed in the nightside sector. DMSP electron measurements in the afternoon sector indicate that the shock has a significant effect on the electron spectral characteristics. It is suggested that the various Alfven frequencies generated by the shock account for the two different speeds of propagation of the disturbance.
"Some case studies have been carried out to investigate the quick response of the dayside auroral illumination during extreme changes of interplanetary shocks and pressure pulses [e.g., Zhou and Tsurutani, 1999, 2004; Liou, 2006]. On the nightside, the compression-induced aurora is more intense than that on the dayside, especially under southward IMF Bz conditions and often leads to the widening of the auroral oval and the closure of the polar cap [e.g., Chua et al., 2001; Zhou and Tsurutani, 2001; Boudouridis et al., 2003; Liou et al., 2003; Liou, 2006]. In addition, the majority of the auroral power is usually deposited on the nightside [Luan et al., 2010]. "
[Show abstract][Hide abstract] ABSTRACT: superposed epoch analysis is performed to investigate the relative
impact of the solar wind/interplanetary magnetic field (IMF) on
geomagnetic activity, auroral hemispheric power, and auroral morphology
during corotating interaction regions (CIRs) events between 2002 and
2007, when auroral images from Thermosphere Ionosphere Mesosphere
Energetics and Dynamics/Global Ultraviolet Imager were available. Four
categories of CIRs have been compared. These were classified by the
averaged IMF Bz and the time of maximum solar wind dynamic pressure
around the CIR stream interface or onset time. It is found that during
CIR events: (1) The peaks of auroral power and Kp were largely
associated with dominant southward Bz, whereas auroral activity also
became stronger with increases of solar wind speed, density, and dynamic
pressure. (2) The percentage and absolute increases of auroral
hemispheric power with solar wind speed were much greater under
dominantly northward Bz conditions than under dominantly southward Bz
conditions. (3) The enhancement of the auroral power and Kp with
increasing solar wind speed followed the same pattern, for both
dominantly southward and northward Bz conditions, regardless of the
behavior of solar wind density and dynamic pressure. These results
suggest that, during CIR events, southward Bz played the most critical
role in determining geomagnetic and auroral activity, whereas solar wind
speed was the next most important contributor. The solar wind dynamic
pressure was the less important factor, as compared with Bz and solar
wind speed. Relatively strong auroral precipitation energy flux (> ~3
mW/m2) occurred in a wider auroral oval region after the
stream interface than before it for both dominantly northward and
southward Bz conditions. These conditions enhanced the auroral
hemispheric power after the stream interface. Intense auroral
precipitation (> ~4 mW/m2) generally occurred widely at
night under dominantly southward Bz conditions, but the location of this
precipitation in the auroral oval was different when it was associated
with different solar wind density and speed conditions.
Full-text · Article · Mar 2013 · Journal of Geophysical Research Atmospheres
"suggests that magnetic bays associated with dynamic pressure pulses frequently do not progress to auroral breakup calling into question the effectiveness of dynamic pressure disturbances as substorm triggers. Other studies indicate that some nightside shock-triggered auroral activity are not substorm activity at all but are more global in nature (c.f., Chua et al., 2001; Lyons, 2000; Zesta, 2000 "
[Show abstract][Hide abstract] ABSTRACT: The seven CAWSES interplanetary fast forward shocks and their geomagnetic effects during 2004–2005 have been analyzed. It is found that the arrival time of the shocks at Earth can be estimated within an accuracy of ∼5 min. Furthermore, AL decreases are found to occur within 10 min of shock impingement on the magnetopause. It was also determined that there is a direct correlation between the interplanetary magnetic field southward directed (IMF Bs) prior to shock arrival and substorms triggered by the shocks. If the IMF is northward prior to shock arrival, the geomagnetic activity is present but is low. One interpretation of this result is that the preconditioning energy stored in the magnetotail leaks away rapidly. A correlation between substorm peak AL and shock strength (Mach number) has also been noted, which could imply that shock strength is important for the amount of energy released into the magnetosphere/ionosphere.Research Highlights►AL decreases occur within 10 min of shock impingement on the magnetopause. ►There is a direct correlation between IMF Bs prior to shock arrival and substorms. ►A correlation between substorm peak AL and shock Mach number was noted.
Full-text · Article · Jul 2011 · Journal of Atmospheric and Solar-Terrestrial Physics