[1] Global auroral images are used to investigate how specific types of solar wind change relate to the resulting type of auroral-region disturbance, with the goal of determining fundamental response types. For not strongly southward IMF conditions (B z^À 5 nT), we find that IMF changes that are expected to reduce the convection electric field after^30 min of negative IMF B z cause typical substorms, where expansion phase auroral activity initiates within the expected location of the Harang electric field reversal and expands in $10 min to cover $5 hours of MLT. For not strongly southward IMF conditions, solar wind dynamic pressure (P dyn ) enhancements compress the entire magnetosphere, leading to a global auroral enhancement with no evidence for substorm bulge-region aurora or current wedge formation. Following prolonged strongly southward IMF (B z ] À8 nT), an IMF change leading to convection electric field reduction gives a substorm disturbance that is not much different from substorms for less strongly southward IMF conditions, other than the expansion phase auroral bulge region seems to expand somewhat more in azimuth. However, under steady, strongly southward IMF conditions, a P dyn enhancement is found to cause both compressive auroral brightening away from the bulge region and a Harangregion substorm auroral brightening. These two auroral enhancements merge together, leading to a very broad auroral enhancement covering $10-15 hours of MLT. Both current wedge formation and compressive energization in the inner plasma sheet apparently occur for these events. We also find that interplay of effects from a simultaneous IMF and P dyn change can prevent the occurrence of a substorm, leading to what we refer to as null events. Finally, we apply the plasma sheet continuity equation to the IMF and pressure driven substorm responses and the null events. This application suggests that solar wind changes cause substorm onset only if the changes lead to a reduction in the strength of convection within the inner plasma sheet.

[1] Enhancements in relativistic electron fluxes in the outer radiation belt often occur following magnetic storms and have been suggested to result from resonant interactions with enhanced whistler-mode chorus emissions observed on the dawnside. Using observations during a period of persistent high-speed, corotating, solar wind streams, we investigate the aspects of solar wind-magnetosphere coupling that lead to these enhanced chorus emissions. We find that relativistic electron energization occurs in association with large-amplitude Alfvén waves within the high-speed streams. These waves last for multiday periods and cause multiday intervals having intermittent periods of significantly enhanced convection. The enhanced convection periods are followed by repetitive substorm onsets caused by the Alfvén wave related repetitive reductions in convection. We use these substorm onsets, identified using geosynchronous particles and midlatitude H components, as indicators of preceding periods of enhanced convection and of reductions in convection. We use ground-based chorus observations from the Halley station VLF/ ELF Logger Experiment (VELOX) instrument to indicate magnetospheric chorus intensities. These data give evidence that the periods of enhanced convection that precede substorm expansions lead to the enhanced dawnside chorus wave. We also see that the enhanced solar wind densities n sw ahead of high-speed streams are associated with significant energetic electron loss at geosynchronous orbit and that the subsequent flux increases appear to not begin until n sw drops below $5 cm À3 even if the solar wind speed increases earlier. The sequence of loss during the leading interval of high n sw , followed by energization during high-speed streams, occurs whether or not the high n sw interval leads to a magnetic storm.

[1] Satellite observations often show that relativistic electron fluxes that decrease during a geomagnetic storm main phase do not recover their prestorm level even when the storm has substantially recovered. A possible explanation for such sustained flux dropout is that the electrons that move to larger shells (L shells) aided by the disturbance storm time (Dst) effect associated with the main phase geomagnetic field depression may be suffering drift loss to the magnetopause, resulting in irreversible (nonadiabatic) flux decreases during a geomagnetic storm. In this study, we have numerically evaluated the drift loss effect by combining it with the Dst effect and including off-equatorially mirroring electrons for three different storm conditions obtained by averaging 95 geomagnetic storms that occurred from 1997 to 2002. Using the Tsyganenko T02 model and our own simplified method, we estimated the storm time flux changes based on the guiding center orbit dynamics. Assuming that there is no competing source mechanism taking place at the same time, our calculations of the electron fluxes at equatorial midnight suggest that the drift loss when combined with the Dst effect can be responsible for flux dropouts, which can be seen even inside the geosynchronous orbit during storm periods. Specifically, by evaluating omnidirectional flux values at three specific times that correspond to the storm onset time, the time of minimum Dst value, and the end of the Dst recovery, we have obtained the following numerical results. First, for the strong storm with −150 nT < Dst min ≤ −100 nT, the combined drift loss and Dst effect can cause a complete dropout of the electron flux for r ≥ ∼5 R E at the end of the storm recovery. A nearly full recovery of the particle flux by the adiabatic Dst effect is seen only for r < ∼5 R E . For the moderate storm with −100 nT < Dst min ≤ −50 nT, the overall flux decrease level at the end of the storm recovery is less significant compared to that of the strong storm. However, the combined loss effect can still penetrate into r ∼ 5 R E , leading to some partial dropout of the flux. For the severe storm with Dst min ≤ −150 nT, the flux dropout is far more significant than for the other two storms, indicating that the combined drift loss and Dst effect can even reduce the flux level at an inner region of r ∼ 4 R E . But in this case, the solar wind dynamic pressure is so high that the dayside magnetopause can cross the geosynchronous orbit. Consequently, the flux dropouts seen in actual observations can be primarily attributed to a fast and direct loss to the magnetopause at times when the magnetopause crosses the geosynchronous orbit. It is possible that our numerical results may quantitatively change to some extent with different magnetospheric models and assumptions and may also change depending on the validity of the fully adiabatic invariants assumption.Citation: Kim, K. C., D.-Y. Lee, H.-J. Kim, E. S. Lee, and C. R. Choi (2010), Numerical estimates of drift loss and Dst effect for outer rad...

[1] Geosynchronous energetic particle fluxes are used to examine the differences and similarities between the particle disturbances due to an enhancement in solar wind dynamic pressure P dyn and those caused by substorms. Disturbances are also distinguished by IMF conditions. First, for not strongly southward IMF conditions (weakly southward or northward IMF), we find that the magnetospheric compression by a P dyn enhancement usually causes particle fluxes to increase simultaneously at all energy channels. The increase is global around the Earth, but it usually occurs first on the dayside and then propagates to the nightside within a few minutes. We also find that a magnetospheric compression sometimes leads to a flux decrease or no flux change for at least one energy channel at some MLTs, which we attribute to the shape of radial profiles at constant adiabatic invariants. However, we find no evidence for substorm-like injections in our P dyn enhancement events when the IMF is not strongly southward. Following prolonged strongly southward IMF, substorms caused by IMF changes that lead to convection electric field reduction and are not associated with a P dyn change generate flux disturbances that are quite similar to typical substorm flux disturbances for less strongly southward IMF conditions. However, the dispersionless injection front is found over a much wider azimuthal region, sometimes extending to the late afternoonside for protons. We find that under prolonged steady, strongly southward IMF conditions, a P dyn enhancement leads to a two-mode type disturbance. The disturbance due to magnetospheric compression can be clearly identified and is seen primarily on the dayside, and a substorm-like injection associated with current wedge formation is seen on the nightside. The dayside compression effect is seen in both species, but is often more easily identified in the proton fluxes than in the electron fluxes. The substorm-like injection feature is also seen in both species but is usually more evident in the electron fluxes. In the events studied here, the dayside compression disturbance precedes the substorm-like injection on the nightside by a few minutes.