References of "Boakes, P. D"
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See detailA superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures
Boakes, P. D.; Milan, S. E.; Abel, G. A. et al

in Journal of Geophysical Research. Space Physics (2011), 116

We report a superposed epoch analysis of the hemispheric open magnetic flux, maximum nightside auroral intensity, geomagnetic activity, and solar wind and interplanetary magnetic field conditions around ... [more ▼]

We report a superposed epoch analysis of the hemispheric open magnetic flux, maximum nightside auroral intensity, geomagnetic activity, and solar wind and interplanetary magnetic field conditions around the time of substorm onset for three distinct categories of substorms defined by their energetic particle injection signatures. Substorms identified from global auroral imagery are classified into one of three categories based on their energetic particle injection signatures as seen at geosynchronous orbit by the Los Alamos National Laboratory spacecraft. Category 1 events are associated with a “classic” substorm injection, category 2 events show varied activity (i.e., energetic enhancements not following the evolution expected for classic substorms), and category 3 events show no apparent injection activity. The superposed epoch analysis reveals that the three distinct particle injection categories exhibit distinct differences in the level and continuity of magnetospheric driving by the solar wind, such that category 1 events can be described as classic substorm events, category 2 as continuously driven events, and category 3 as weak events. The results of this study suggest that the level and continuity of the dayside solar wind driving of the magnetosphere during substorms have a direct impact on the injection of energetic particles to geosynchronous orbit at substorm onset. These results could have considerable value in empirical predictions of the space weather environment. [less ▲]

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See detailAn initial investigation of the magnetosphere at a system level using auroral oval radius and ring current intensity as state variables
Milan, S. E.; Hutchinson, J.; Boakes, P. D. et al

Conference (2009, December 01)

One approach to understanding the magnetosphere at a system level is to select a number of magnetospheric state variables and to examine statistically their inter-relationships and the temporal evolution ... [more ▼]

One approach to understanding the magnetosphere at a system level is to select a number of magnetospheric state variables and to examine statistically their inter-relationships and the temporal evolution of the magnetosphere through state-space. This talk outlines a first attempt at such a study, using the radius of the auroral oval, a proxy for the open flux content of the magnetosphere, and the Sym-H index, a measure of the intensity of the ring current, as the primary state variables. Using observations from the two-year period June 2000 to May 2002, the response of the state of the magnetosphere to differing solar wind inputs, and the evolution of the system state during geomagnetic storms is investigated. Our main finding is a characteristic evolution of magnetospheric state through the initial, main, and recovery phases of geomagnetic storms. We discuss our findings within the context of the expanding/contracting polar cap paradigm, in terms of a modification of substorm onset conditions by the magnetic perturbation associated with the ring current. [less ▲]

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See detailInfluences on the radius of the auroral oval
Milan, S. E.; Hutchinson, J.; Boakes, P. D. et al

in Annales Geophysicae (2009), 27

We examine the variation in the radius of the auroral oval, as measured from auroral images gathered by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, in response to solar ... [more ▼]

We examine the variation in the radius of the auroral oval, as measured from auroral images gathered by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, in response to solar wind inputs measured by the Advanced Composition Explorer (ACE) spacecraft for the two year interval June 2000 to May 2002. Our main finding is that the oval radius increases when the ring current, as measured by the Sym-H index, is intensified during geomagnetic storms. We discuss our findings within the context of the expanding/contracting polar cap paradigm, in terms of a modification of substorm onset conditions by the magnetic perturbation associated with the ring current. [less ▲]

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See detailA superposed epoch analysis of auroral evolution during substorm growth, onset and recovery: open magnetic flux control of substorm intensity
Milan, S. E.; Grocott, A.; Forsyth, C. et al

in Annales Geophysicae (2009), 27

We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer (IMAGE) spacecraft. The larger of the ... [more ▼]

We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer (IMAGE) spacecraft. The larger of the two studies includes nearly 2000 substorms. We subdivide the substorms by onset latitude, a measure of the open magnetic flux in the magnetosphere, and determine average auroral images before and after substorm onset, for both electron and proton aurora. Our results indicate that substorms are more intense in terms of auroral brightness when the open flux content of the magnetosphere is larger, and that magnetic flux closure is more significant. The increase in auroral brightness at onset is larger for electrons than protons. We also show that there is a dawn-dusk offset in the location of the electron and proton aurora that mirrors the relative locations of the region 1 and region 2 current systems. Superposed epoch analyses of the solar wind, interplanetary magnetic field, and geomagnetic indices for the substorms under study indicate that dayside reconnection is expected to occur at a faster rate prior to low latitude onsets, but also that the ring current is enhanced for these events. [less ▲]

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See detailA statistical study of the open magnetic flux content of the magnetosphere at the time of substorm onset
Boakes, P. D.; Milan, S. E.; Abel, G. A. et al

in Geophysical Research Letters (2009), 36

In this paper we determine the probability of substorm onset as a function of open magnetic flux in the magnetosphere by comparing the occurrence distribution of open flux observed at all times with that ... [more ▼]

In this paper we determine the probability of substorm onset as a function of open magnetic flux in the magnetosphere by comparing the occurrence distribution of open flux observed at all times with that observed at the time of substorm onset. The open magnetic flux is measured in 12735 auroral images of the ionospheric polar cap from the IMAGE WIC detector. The probability of substorm onset is found to be negligible for fluxes below ~0.3 GWb, increases almost linearly until ~0.9 GWb, and is undefined above this. We also demonstrate that those substorms which show a clear particle injection signature at geosynchronous orbit, as measured by the LANL spacecraft, occur, on average, with higher values of open flux than those showing no activity. We discuss these results in the context of various hypotheses for substorm onset. [less ▲]

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See detailResponse of the expanding/contracting polar cap to weak and strong solar wind driving: Implications for substorm onset
Milan, S. E.; Boakes, P. D.; Hubert, Benoît ULg

in Journal of Geophysical Research. Space Physics (2008), 113

We quantify the amount of open magnetic flux in the magnetosphere from observations of the auroral polar cap on a near-continuous basis for a period of 18 days, 20 August to 6 September 2005. This ... [more ▼]

We quantify the amount of open magnetic flux in the magnetosphere from observations of the auroral polar cap on a near-continuous basis for a period of 18 days, 20 August to 6 September 2005. This interval encompasses periods of weak, moderate, and strong solar wind driving, including two geomagnetic storms. We identify 49 substorms during the interval and determine the response of the polar cap to growth and expansion phases of the substorms. We find that the frequency of substorms and the flux closed by substorms both increase during enhanced solar wind driving, each approximately as the square root of the dayside reconnection rate. In addition, the average size of the polar cap increases during intervals when there is strong driving and especially when the SYM-H index indicates that the ring current is enhanced. We suggest that this occurs for two reasons: because there is a delay between substorm onset and the closure of open magnetic flux in the magnetotail (while closed flux is pinched off), during which dayside reconnection can lead to further growth in the size of the polar cap, and also because the magnetotail is more stable to reconnection when the ring current is enhanced. [less ▲]

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See detailOn the use of IMAGE FUV for estimating the latitude of the open/closed magnetic field line boundary in the ionosphere
Boakes, P. D.; Milan, S. E.; Abel, G. A. et al

in Annales Geophysicae (2008), 26

A statistical comparison of the latitude of the open/closed magnetic field line boundary (OCB) as estimated from the three far ultraviolet (FUV) detectors onboard the IMAGE spacecraft (the Wideband ... [more ▼]

A statistical comparison of the latitude of the open/closed magnetic field line boundary (OCB) as estimated from the three far ultraviolet (FUV) detectors onboard the IMAGE spacecraft (the Wideband Imaging camera, WIC, and the Spectrographic Imagers, SI-12 and SI-13) has been carried out over all magnetic local times. A total of over 400 000 OCB estimations were compared from December 2000 and January and December of 2001 2002. The modal latitude difference between the FUV OCB proxies from the three detectors is small, <1°, except in the predawn and evening sectors, where the SI-12 OCB proxy is found to be displaced from both the SI-13 and WIC OCB proxies by up to 2° poleward in the predawn sector and by up to 2° equatorward in the evening sector. Comparing the IMAGE FUV OCB proxies with that determined from particle precipitation measurements by the Defense Meteorological Satellites Program (DMSP) also shows systematic differences. The SI-12 OCB proxy is found to be at higher latitude in the predawn sector, in better agreement with the DMSP OCB proxy. The WIC and SI-13 OCB proxies are found to be in better agreement with the DMSP OCB proxy at most other magnetic local times. These systematic offsets may be used to correct FUV OCB proxies to give a more accurate estimate of the OCB latitude. [less ▲]

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See detailLooking through the oval window
Milan, Steve; Grocott, A.; Forsyth, C. et al

in Astronomy and Geophysics (2008), 49

Space weather is controlled by the dynamic coupling between the solar wind and the magnetosphere, mediated by magnetic reconnection. Data from NASA's IMAGE spacecraft show changes in the auroral oval that ... [more ▼]

Space weather is controlled by the dynamic coupling between the solar wind and the magnetosphere, mediated by magnetic reconnection. Data from NASA's IMAGE spacecraft show changes in the auroral oval that reveal more about substorms, a key manifestation of the reconnection process. In particular, substorm magnitude is determined by the amount of magnetic flux previously stored in the magnetosphere, which may in turn be controlled by the strength of the ring current. This suggests that internal feedback processes modulate the magnetosphere's response to extreme solar wind conditions. [less ▲]

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