SM53A-1648
Properties of low frequency waves inside hot flow anomaly cavities
Hot flow anomalies (HFAs) are regions of hot and highly deflected ion flow near the bow shock. They are believed to come from interaction between the bow shock and tangential discontinuities in the interplanetary magnetic field. This study is focused on the low frequency wave properties inside two HFAs at different stages of evolution, observed by the Cluster spacecraft on 2. April 2002. The k-filtering technique could applied in this study thanks to the simultaneous multi-point measurements of the Cluster satellites. In the HFA that was in an early stage of its evolution, the observed wave activity was interpreted as a combination of inherent fluctuation in the solar wind and those of a plasma component that had been specularly reflected at the Earth's bow shock. The amplitude of these fluctuations had been increased which probably was the effect of a plasma beam instability. In the more evolved HFA, the wave field was found to be less complex in terms of the number of wave modes. Instead a periodicity was found in the wave number distribution, and it had a period that suggests that it came from the geometrical properties of the HFA cavity.
SM53A-1649
Polar UVI and THEMIS GBO Observations of the Ionospheric and Magnetospheric Response to a Hot Flow Anomaly
We present observations of the ionospheric response to a hot flow anomaly (HFA) interacting with the
magnetosphere. On 4 July 2007, the THEMIS spacecraft observed a HFA on both sides of the bow shock.
The ionospheric response was measured by global auroral images taken over the southern hemisphere by
Polar UVI, by ground based magnetometers and photometers in Antarctica, and by the THEMIS Ground
Based Observatories (GBOs) in the northern hemisphere. Polar UVI observations show a region of
enhanced auroral emission in the morning sector about 10 minutes after the THEMIS spacecraft observed
the HFA. This region of enhanced emission was located above South Pole station which observed an
increase in the auroral luminosity and magnetic perturbations. The THEMIS GBOs in the conjugate
hemisphere also observed magnetic perturbations consistent with a traveling convection vortex. Polar UVI
tracked the spatial and temporal development of the region of enhanced emission. Slow anti-sunward motion
was observed as the emission weakened and then re-brightened over the course of about 10 minutes.
Simultaneously, the THEMIS GBO array observed anti-sunward motion of the magnetic impulse with a velocity
much greater than that of the auroral emission. The origin of the magnetic perturbation and resulting
auroral emission is suggested to be the deformation of the magnetopause due to the HFA-magnetosphere
interaction. The different propagation speeds of the auroral emission in the southern hemisphere and the
magnetic perturbation in the northern hemisphere imply either 1) a decoupling of the auroral emission and
field-aligned current signature or 2) a decoupling of these processes between the two hemispheres. The
large difference in the ionospheric conductivity between the northern (summer) and southern (winter)
hemispheres may be an important factor in this decoupling.
http://sprg.ssl.berkeley.edu/matt/AGU2008/
SM53A-1650
3-D Hybrid Simulation of Interaction Between Solar Wind Discontinuity and Magnetosphere
Previous simulations and observations indicate that interaction of interplanetary directional tangential discontinuities (TD), across which only the direction of magnetic field changes,with the bow shock may initiate magnetic reconnection as the TD is transmitted into the magnetosheath. We employ a 3-D electromagnetic, hybrid simulation to study such interaction between the TD and the bow shock-magnetosheath-magnetopause system, while the hybrid model treats the ions kinetically via particle-in-cell methods and the electrons as a massless fluid. We present results corresponding to different orientations of the initial IMF, TDs with various thicknesses ranging from 10 to 30 ion skin depths, and polarizations of magnetic field and senses of field rotation across the TD. Our results indicate that the reconnection rate and structure can be influenced by the width and the structure of the TD. The kinetic structure and evolution of FTEs produced by the magnetosheath reconnection, as they propagate to the magnetopause, will be studied.
SM53A-1651
MHD simulation of a fast forward shock event
Following the propagation of interplanetary shocks (IPS) in the solar wind and throughout the Earth's magnetosphere is vital to understand the processes associated with their interaction with the magnetosphere. A case study using multiple spacecraft analysis and GUMICS-4 global MHD simulation shows that stronger fast forward shocks with a higher shock speed cause a greater response in the magnetosphere. Additionally, a statistical analysis of a set of fast forward shock events shows that the solar wind speed and dynamic pressure play an important role in the geomagnetic activity: Our results show that higher interplanetary shock speeds cause a higher response in the AE index. Furthermore, we have used the GUMICS-4 global MHD simulation results to interpret the unusual double step structure observed at geostationary orbit. The temporal variations in the velocity and electric field in the dayside magnetosphere near geostationary orbit strongly suggest that the second part of the double step structure is a reflected disturbance from the inner boundary of the magnetosphere.
SM53A-1652
Dynamic Motion of the Bow Shock and the Magnetopause and the Magnetospheric Response - THEMIS Observations
We present an observational study of the dynamic motion of the bow shock and the magnetopause and suggest that the dynamic motion is due to the interaction of an interplanetary shock with the Earth's bow shock. THEMIS B spacecraft crossed the magnetopause, a discontinuity and the bow shock successively in 5 minutes during its outbound journey on July 10, 2007. Following THEMIS B, THEMIS C, D, E and A consecutively crossed the magnetopause and the discontinuity but not the bow shock. Timing analysis shows that the magnetopause and the discontinuity were moving earthward with speeds of ~47 km/s and ~90 km/s respectively. There is a trend that the discontinuity decelerates as it propagates towards the magnetopause. We suggest that the dynamic motion and the discontinuity are results of the interaction of a weak (MA=1.2) interplanetary shock with the Earth's bow shock. After the interaction, the transmitted interplanetary shock took the form of a discontinuity where total magnetic field and density increase and the temperature decreases. The rotation of the magnetic field across this discontinuity was similar to that of the interplanetary shock. The expected fast shock ahead of the discontinuity for shock-shock interaction was not observed. Ground stations recorded compression over a wide range of MLT and latitudes.
SM53A-1653
Control of the Polarity of the Interplanetary Magnetic Field on the Dawn-Dusk Symmetry of the Magnetopause
The solar wind dynamic pressure is reduced when the solar wind flows around the magnetosphere due to the diversion of the flows. The magnetopause is the boundary where the reduced dynamic pressure is balanced with the magnetic pressure of the compressed magnetosphere by the solar wind. The size and shape of the magnetopause have long been considered among the most important parameters in Solar Terrestrial physics. Previous models of the size and shape of the magnetopause often assumed the axis- symmetry of the magnetopause with respect to the Sun-Earth line. With a large number of magnetopause crossings by ISEE-1 and -2, AMPTE/IRM, Hawkeye, Geotail, Interball-1, and Magion-4, we are able to consider the asymmetry of the magnetopuase. In the Shue et al. [1997] model, the magnetopause was modeled by two parameters, r0 and alpha, representing the subsolar standoff distance and the flaring level of the magnetopause, respectively. Parameter alpha was assumed to be independent of phi in the Shue et al. [1997] model, where phi is the angle between the Z axis and the mapping of the radial vector of the magnetopause on the YZ plane. In the present study we allow alpha to be a function of phi. We separate crossings with different phis and fit them in each bin to the new functional form proposed by Shue et al. [1997]. We find that the magnetopause is symmetric in the dawn-dusk direction for northward IMF. However, its size on the dawnside becomes larger when the IMF is southward. The function of alpha in terms of phi can be combined with the 2-D Shue et al. [1997] model into a 3-D magnetopause model. (Shue, J.-H., J. K. Chao, H. C. Fu, C. T. Russell, P. Song, K. K. Khurana, and H. J. Singer, A new functional form to study the solar wind control of the magnetopause size and shape, J. Geophys. Res., 102, 9497, 1997.)
SM53A-1654
Statistical Study of Magnetopause Boundary Region Vortices Observed During Modeled Solar Wind Conditions
With MHD simulations using fixed solar wind speeds and a step function in IMF direction we have found vortices on the magnetopause flanks near the ecliptic plane. We compare and contrast a case of nominal solar wind speed, around 360 km/s, and a higher solar wind speed, 700 km/s, both starting with southward IMF, -5 nT, for 15 minutes, and then turning northward, +5 nT for two hours. A total of 11 vortices were found for the case with nominal solar wind speed. Most of these vortices evolved into more complex or more defined vortices during their one-hour duration. They exhibited peculiar characteristics; their rotation axis were primarily in the x or y direction even though the IMF was predominantly in the z direction. Most of them were large in scale (6-10 RE) and also appeared to have a symmetry in which dawn and dusk vortices would develop simultaneously on the magnetopause flanks with the same rotation direction. Curiously, vortices would also develop simultaneously at the same x-y location but with a different z coordinate, and these would always rotate in the opposite sense to those in the ecliptic plane, i.e, ones at z=0 rotated clockwise and ones at z=-8 rotated counterclockwise. For the case with higher solar wind speed, 700 km/s, around 25 vortices were found exhibiting the same characteristics, but with longer durations. In a previous study we presented a total of 304 vortices found near the ecliptic plane on the magnetopause flanks using simulated MHD data driven by real solar wind conditions. Comparison of these results to our recent simulations with fixed conditions will also be presented.
SM53A-1655
Dayside Magnetosphere-Ionosphere Solar Wind Driven Dynamics
oDynamical equations are derived for the dayside region 1, region 2, and magnetopause current loops associated with solar wind compressions of the magnetopause stand off distance. The geometry for the loops is determined first with analytical models and then compared with the Tsyganenko 2005 model. The model predicts from solar wind plasma data the motion of the magnetopause standoff distance Rmp(t) and the the upper auroral index AU from the eastward auroral electrojet current in the auroral oval. The dynamical frequencies are in the range to drive ULF and VLF waves in the magnetosphere. The addition of the Chapman-Ferraro currents to the WINDMI model allows the prediction of the sudden commencement peaks of positive Dst that occur when the magnetopuase is pushed Earthward by a strong pressure pulse. The first runs show a sudden commencement signal typical of the data. The work is supported by NSF grant ATM-0638480.
SM53A-1656
Effects of the solar-wind dynamic pressure on the Region-2 field-aligned current intensity
The relationship between the Region-2 field-aligned currents and the solar-wind dynamic pressure is investigated using magnetic-field data from Defense Meteorological Satellite Program-F13 (DMSP-F13). The Region-2 currents are generated if gradients of the thermal and magnetic pressure are neither parallel nor anti-parallel to each other. In the Earth's magnetosphere, the magnetic pressure is generally larger on the dayside than on the nightside while the thermal pressure is not. Thus, the gradient of the magnetic pressure deviates from that of the thermal pressure, which should cause the generation of the Region-2 currents. Past studies have suggested that the day-night asymmetry in the magnetic-pressure gradients in the magnetosphere highly depends on the solar-wind dynamic pressure. We can then expect that the Region-2 currents might also depend on the solar-wind dynamic pressure. This study compares the Region-2 field- aligned current intensity at the altitude of the ionosphere, as derived using magnetic-field data from DMSP- F13, with the solar-wind dynamic pressure derived from OMNI2 hourly data. It was confirmed that the Region- 2 current intensity depends on the solar-wind dynamic pressure during magnetic storms. During non-storm times, however, a correlation between the Region-2 currents and the solar-wind dynamic pressure becomes weak. This finding indicates that the condition of the thermal pressure in the ring-current region could also be essential for the generation of Region-2 currents.
SM53A-1657
Response of the Magnetosphere and Ionosphere to Solar Wind Dynamic Pressure Pulse
The interaction of the solar wind with Earth's magnetosphere produces various phenomena, such as substorms and aurora, in polar region. When the IMF turns southward, the energy of the solar wind is efficiently transferred to the magnetosphere by reconnection, and convection and currents within in the magnetosphere increase. Some of observation results show that the polar cap potential are saturated and dayside magnetic reconnection are enhanced due to the increase of solar wind dynamic pressure. However, the effects of solar wind dynamic pressure variation were not systematically studied by using a global simulation. We have investigated the effects of sudden enhancement of dynamic pressure with a constant IMF value in the ideal case on the magnetosphere and ionosphere by using a global MHD simulation. For sudden enhancement of the density (from 5 /cc to 10 /cc) with a small value of Bz (-2 nT), large viscous cells appear near the magnetopause region but the convection is very small in the tail. The location of dayside magnetopause is at 14 Re. Tail reconnection occurs after 20 min of the pulse arrival with earthward flow (~40 km/s). For case with a strong IMF Bz (= -10 nT), the location of the dayside magnetopause is at 13 Re. Tail reconnection occurs at 11 Re with a strong earthward flow (~300 km/s) after 10 min and tail current increases about 3 times. In addition, pressure gradient is very high near the inner magnetopause in the tail.
SM53A-1658
Ionospheric response to solar wind discontinuities
We investigate the ionospheric response to solar wind discontinuities as shown by the solar wind - magnetosphere coupling efficiency and other ionospheric activity. We carry out a superposed epoch analysis of 236 pressure impulses and 171 sudden decompressions of the magnetosphere from the years 1998- 2002, detected by the ACE/SWEPAM instrument. The data set includes events mimicking fast, slow and reverse slow shocks that we define as fast-type, slow-type and reverse slow-type discontinuities. We find that the coupling efficiency, defined as the ratio between the polar cap and magnetospheric potential, to sudden compressions depends on the internal structure of the impulse. Ionospheric activity as measured by the IMAGE magnetometer chain increseas (decreases) after sudden impulses (decompressions). The coupling efficiency increases (decreases) for slow-type (fast-type) discontinuities. However, the coupling energy estimated from the IMAGE magnetometer chain is larger for the fast-type events and stronger drivers. Hence, our results indicate that the magnetosphere uses the energy from the weaker driver more geoeffectively, while the energy associated with stronger drivers is partly transmitted through the system.
SM53A-1659
Heavy Ion Effects on Geomagnetic Field Line Resonance Calculations
Field-aligned eigenmodes can be excited by mode conversion of compressional waves propagating across magnetospheric field lines. At low frequencies, the mode conversion occurs at the Alfven resonance, but mode conversion may also occur for higher frequencies at the ion-ion hybrid resonance when multiple ions are present. The mode-converted waves propagate along the magnetic field and set up a field-aligned eigenmode between the ionospheres. We examine the spectrum of field-aligned eigenmodes and their eigenfrequencies using numerical and analytical techniques based on an extension of the low frequency Alfvenic field-line resonance theory. For the computations, we use an a axisymmetric dipole magnetic field along with an accurate model for electron number density data between 3 and 9 Earth radii L shells. The eigenvalue problem is solved using a shooting code combined with an analytic continuation into the complex plane around the singularities at ion cyclotron resonances. We examine the dependence of the eigenmodes, which can be global or spatially localized along the field line, on the concentration of heavy ions. Some modes are also damped because of wave absorption at the cyclotron frequency. We discuss implications of the solutions for observed Pc1 pulsations and discuss the localization of eigenmodes in the equatorial magnetosphere.
SM53A-1660
Variations in geomagnetic shielding of solar energetic particles associated with the arrival of an interplanetary shock at the Earth's magnetosphere
The Earth's magnetic field usually shields latitudes below approximately 60 degrees from direct penetration by solar energetic particles (SEPs). Geomagnetic storms suppress geomagnetic shielding and lower the cutoff latitude up to ~15 degrees, predominantly due to a reduction in field strength in the inner magnetosphere caused by ring current buildup. Significant variations in SEP cutoffs may also occur during storm onset with the arrival of an interplanetary shock. In this work we examine how sudden increases in solar wind dynamic pressure affect geomagnetic cutoffs. SAMPEX energetic particle observations and numerical model results will be presented and directly compared. In most cases, large increases in solar wind dynamic pressure are found to increase the cutoff near local noon and suppress the cutoff at dawn, dusk and midnight local times. An application of the numerical cutoff model used for this work will also be discussed, involving a nowcast prediction of radiation exposure on high altitude polar flights for the safety of airline crews and passengers.
SM53A-1661
Geomagnetic Cutoff Variations Due to Interplanetary Shocks
Geomagnetic storms can significantly suppress geomagnetic shielding of solar energetic particles (SEPs). This is caused by a reduction in field strength in the inner magnetosphere due to ring current buildup and is correlated with the depression and recovery of the disturbance storm time index (Leske et al., JGR, Vol. 106, No. A12, Pages 30,011-30,022 2001). Observations and model results also show that changes in solar wind dynamic pressure significantly modifies SEP cutoffs on a timescale of minutes well before the main phase of a storm (Kress et al., GRL, Vol. 31, L04808, 2004). In this work, we examined SEP cutoff variations due to the arrival of interplanetary shocks at the Earth's magnetosphere, and observed a characteristic pattern as a function of local-time. Increases in solar wind dynamic pressure are found to increase the cutoff near local noon and suppress the cutoff at dawn, dusk and midnight local times.
SM53A-1662
Radial gradients of phase space density of the outer radiation belt electrons prior to sudden solar wind pressure enhancements
When sudden solar wind pressure enhancements impact Earth's magnetosphere, dayside trapped electrons are transported radially inwards, conserving their first and second adiabatic invariants (μ and K). Using measurements from geosynchronous spacecraft immediately before and after these events, the direction of the phase space density (PSD) radial gradient can be determined. Here we describe this method and discuss our results from over fifty events. These results suggest that the PSD radial gradients are μ (or energy) dependent; the gradients for low energy electrons, with energy less than a couple of hundred keV, tend to be flat or slightly increasing (positive gradient), while the gradient for higher energy electrons, with energies of several hundred keV to MeV, decreases (negative gradient) in the majority of cases. This implies that a local heating occurs inside GEO for the high energy electrons in the majority of cases examined. We also discuss a superposed epoch analysis studying the differences prior to events where the PSD gradient for high energy electrons is positive and negative.
SM53A-1663
Electron Spectral Changes Observed Near L=4.2 by 9 CXD Instruments During a Recent Small Magnetic Storm
The current phase of the solar cycle is characterized by long intervals between significant magnetic storms during which the trapped electron population decays and electron spectra harden significantly. Indeed, during the long recovery phase between storms a characteristic lower-energy (0.1 to 1.5 MeV) feature develops systematically as the magnetic equator is approached and is most significant at the lowest L-shell visited along the orbit of GPS satellites; such features have been reported previously for this region of the magnetosphere.1-4 Following the main phase of a magnetic storm a smooth featureless increase below about 1.5 MeV replaces the low-energy structure mentioned above -- a spectral characteristic of the electron population near the geostationary orbit. Electron spectral results at the magnetic equator from 9 Combined X-ray senor and Dosimeter instruments will be presented here for the small (55 nT) storm of 4 September 2008. 1. A. L. Vampola, J. B. Blake, and G. A. Paulikas, "A New Study of the Magentospheric Electron Environment," Journal of Spacecraft and Rockets 14, 690 (1977). 2. J. B. Reagan, R. W. Nightingale, E. E. Gaines, W. L. Imhof, and E. G. Stassinopoulos, "Outer Zone Energetic Electron Spectral Measurements," Journal of Spacecraft and Rockets 18, 83 (1981). 3. A. L. Vampola, "Solar Cycle Effects on Trapped Energetic Particles," Journal of Spacecraft and Rockets 26, 416 (1989). 4. W. D. Pesnell, "Fluxes of Relativistic Electrons in Low-Earth Orbit during the Decline of Solar Cycle 22," IEEE Transactions on Nuclear Science 48, 2016 (2001).
SM53A-1664
Comparison of LFM-test particle simulations and radial diffusion models of radiation belt electron injection into the slot region
The physics-based Lyon-Fedder-Mobarry (LFM) code simulates Earth's magnetospheric topology and dynamics by solving the equations of ideal MHD using input solar wind parameters at the upstream boundary. Comparison with electron phase space density evolution during storms using a radial diffusion code, as well as spacecraft measurements where available, will tell us when diffusion is insufficiently accurate for radiation belt simulation, for example, during CME-shock injection events like March 24, 1991, which occurred on MeV electron drift time scales of minutes (Li et al., 1993). The 2004 July and 2004 November storms, comparable in depth of penetration into the slot region to the Halloween 2003 storm, have been modeled with both approaches. The November 8, 2004 storm was preceded by a Storm Sudden Commencement produced by a CME-shock followed by minimum Dst = -373 nT, while the July 23 to July 28 storm interval had milder consecutive drops in Dst, corresponding to multiple CME shocks and southward IMF Bz turnings. We have run the November and July storms with LFM using ACE data as upstream input, running the July storm with lower temporal resolution over a longer time interval. The November storm was different because the SCC shock was unusually intense, therefore the possibility of drift time scale acceleration by the associated magnetosonic impulse produced by the shock exists, as in March 1991 and also Halloween 2003 events (Kress et al., 2007). It can then take a short time (minutes) for electrons to be transported to low L shell while conserving their first invariant, resulting in a peak in energy and phase space density in the slot region. Radial diffusion suffices for some storm periods like the July 2004 sequence of three storms, while the guiding center test particle simulation in MHD fields is necessary to describe prompt injections which occur faster than diffusive time scales, for which November 2004 is a likely candidate. Earlier examples have been studied, including the Kress et al., 2007 study of the Halloween 2003 storm and Li et al., 1993 study of the March 24, 1991 injection event with MHD simulation carried out by Elkington et al. (2002) for this event. Radial diffusion remains the best approach for extended relatively quiet periods like the two month interval following the March 1991 prompt injection. Strong shocks will inject particles into lower L shell within a few minutes violating the third adiabatic invariant, so the diffusion mechanism cannot be adopted for sudden commencements, when Dst increases then decreases drastically; however particle tracing in time-dependent MHD fields will give an accurate estimation, so radial diffusion and particle tracing in MHD fields complement each other in radiation belt studies. Elkington, S. R., M.K. Hudson, M.J. Wiltberger, J.G. Lyon (2002) JASTP, 64, p. 607-615; Kress B. T., M. K. Hudson, M. D. Looper, J. Albert, J. G. Lyon, C. C. Goodrich (2007), J. Geophys. Res., 112, A09215, doi:10.1029/2006JA012218; Li, X., I. Roth, M. Temerin, J. R. Wygant, M. K. Hudson, and J. B. Blake (1993), Geophys. Res. Lett., 20, p. 2423–2426.
SM53A-1665
Statistical Study of the Response of the Transpolar Potential to Solar Wind Dynamic Pressure Fronts as a Function of their Pressure Change and Accompanying IMF
The significant effect of solar wind dynamic pressure fronts on the state on the magnetosphere has been amply demonstrated in recent years. Sudden enhancements in solar wind dynamic pressure have been shown to lead to increased ionospheric convection at high latitudes. Defense Meteorological Satellite Program (DMSP) measurements have shown that solar wind dynamic pressure enhancements significantly increase the transpolar potential and the solar wind/magnetosphere coupling efficiency. Case studies of long-duration solar wind pressure steps indicate that the potential first rises in response to the increase in pressure, but gradually subsides a few hours later despite the solar wind pressure remaining high. It has also been shown in the past that the geoeffectiveness of solar wind pressure fronts depends on the background Interplanetary Magnetic Field (IMF) conditions. Another factor that can affect their geoeffectiveness is the magnitude of pressure change (absolute or relative). We use DMSP flow observations to conduct a statistical study of the effect of solar wind dynamic pressure fronts on the transpolar potential as a function of the pressure change and accompanying IMF. Our results, consistent with the individual case studies, show that the transpolar potential increases after the increase in pressure, reaching a maximum 2-3 hours after impact. It then falls again within one hour perhaps to slightly higher values than before the pressure enhancement. The potential response is faster under southward IMF conditions. The potential changes also seem to be slightly larger but slower to occur for larger absolute magnitude of the pressure increase.
SM53A-1666
Role of Saturation of the Polar Cap in Regulating Energy Coupling Efficiency in Magnetic Storms
Energy coupling in magnetic storms is a fundamental issue in magnetospheric physics. While not completely understood, there have been hints regarding coupling mechanisms and their limitations. For example, magnetic storms due to Corotating Interaction Regions (CIRs) have been shown to elicit different responses in the magnetosphere than those prompted by other types of solar wind driving conditions such as CMEs. In particular, CIR-driven storms are more geoefficient, coupling more energy into the magnetosphere- ionosphere system per input energy from the solar wind than storms driven by CMEs. In this work, we present analysis concerning why this is the case. In particular, we show analysis of the role of polar cap saturation in mediating the energy coupling capability of the solar wind to the magnetosphere in storm events. We generalize our findings to all storms regardess of the type of storm driver.
SM53A-1667
Modeled cross-polar cap potential response after sudden IMF changes
This paper presents an in-depth study of the response of the cross-polar-cap potential (CPCP) modeled by the Space Weather Modeling Framework (SWMF) when there are sudden changes in the interplanetary magnetic field (IMF). We study the model response to answer how the level of conductance (and other, numerical, parameters) in a model affects the response time after a sudden change of the IMF. In this study we present simulation runs of the global geomagnetic models BATSRUS as part of SWMF with solar wind magnetic field Bz level of 10nT (switching from negative to positive and back to negative) and average solar wind density and solar wind conditions. We use uniform ionospheric Pedersen conductances between 2 and 20 mho and vary a few numerical parameters inside the magnetosphere as well. We generally find that lower conductances and higher numerical resolution combined with a less diffusive numerical scheme give rise to higher levels of oscillations in the magnetosphere-ionosphere system after the IMF change. We also see an increase of the elapsed time until the new level of the CPCP is reached. This study is performed as a model validation at the Community Coordinated Modeling Center.
SM53A-1668
Global Mapping of Magnetic Field Variations During Typical and Atypical Sudden Magnetospheric Compressions
The sudden compression of the magnetosphere in response to a sharp increase in the solar wind dynamic pressure typically produces a world-wide enhancement of the northward ground magnetic field at low latitudes, with a slightly larger enhancement on the day side. A few events produce "atypical" signatures where the low-latitude field enhancements are asymmetric, with the largest field enhancement seen on the night side and little or no field increase near local noon. In most cases the atypical response has been seen in conjunction with a simultaneous Northward turning of the IMF, and has been explained by a transition current system that develops in the high-latitude magnetosphere. However, in at least one atypical instance the IMF has remained Southward but smoothly increasing, and an additional theory involving polar electrojets had been proposed to explain this response. Previously these compression events had been studied by mapping contours of the magnetic variation, with Universal Time on one axis and Magnetic Local Time on the other. In order to validate the models of typical or atypical magnetospheric response to sudden compressions, there is a need to observe the response at all latitudes. We will present the results of constructing maps of the geomagnetic variations from equator to pole, at sequential time steps during the course of both typical and atypical compression events.
SM53A-1669
Response of the Equatorward Boundary of the Ion Auroral Oval to the Southward turning of the Interplanetary Magnetic Field
The response of the equatorward boundary of the ion aural oval in the dusk-midnight sector to the southward turning of the Interplanetary Magnetic Field (IMF), using ground based SuperDARN radars, is detailed in this paper. The equatorward boundary moves equatorward in response to the southward turning of the IMF. The equatorward motion is always delayed with respect to the southward turning of the IMF. We have estimated the boundary response delay using two methods. In the first method, we have directly used the measurement of the IMF by an upstream solar wind monitor and corrected for the propagation delay of the IMF change from the satellite to the ionosphere and estimated delay of the boundary response. This method yielded an average delay of ~37 minutes. In the second method, in order to avoid the uncertainty in the estimation of the propagation delay from the IMF monitor to the ionosphere, we have used changes in the polar cap convection as a indicator of the arrival of the change in the IMF at the ionosphere and estimated the boundary response delay from the time of the polar cap convection change. This method yielded an average delay of ~28 minutes. This confirms that the boundary response is always delayed with respect to the changes in the IMF and suggests the boundary response is consistent with the progressive propagating scenario of the changes associated with the transitions of the IMF.
SM53A-1670
Multi-Satellite Low-Altitude Observations of a Magnetopause Merging Burst
A fortuitous combination of DMSP F12 and F13 observations of a dayside merging event driven by a sudden sharp southward interplanetary magnetic field (IMF) turning illuminates several facets of the ionospheric particle and auroral signatures of reconnection. Nearly coincident with the sharp southward IMF turning (as propagated from ACE), DMSP F13 observed a region equatorward of the cusp apparently emptied of magnetospheric ions (of tens of keV energy), and bounded by two sharp intensifications of electron energy flux. The equatorward electron intensification occurred at 74.3xxx MLAT, which is both the boundary to which magnetospheric ions were depleted, and the boundary to which magnetosheath energy ions reached in the F12 satellite pass 4 minutes later (these latter ions evinced a low-energy cutoff corresponding to xxx minutes elapsed since merging). The equatorward electron burst observed by F13, reaching to 5xxx ergs/cm2 s, had a striking and hitherto unreported signature, which suggests recent disconnection from the x-line merging site. To wit, these very high electron fluxes had a spectacularly clear high energy cutoff corresponding to a transit time from the nose of the magnetospause of from 5-6 seconds. The more poleward electron burst observed by F13, occurring at the equatorward edge of the old cusp, had a more conventional signature suggesting wave aurora. Drift meter data on F13 indicates that the merging burst resulted in ionospheric flow speeds above 1 km/s, and a xxx kV cusp contribution to the cross polar cap potential. Simultaneous observations by Polar UVI suggest a large-scale auroral transient at cusp latitudes, while magnetometer observations suggest sheet currents rather than filamentary currents, also indicative of the broad scale of the event. Taken together, these observations suggest the ability to recognize newly opened dayside regions even prior to the arrival of magnetosheath (cusp) plasma from low-altitude observations.
SM53A-1671
Magnetic Latitude and Local Time Dependence of the Amplitude of Geomagnetic Sudden Commencements
Statistical analysis of the main impulse (MI) amplitude of geomagnetic sudden commencements (SCs) observed from the dip equator to middle latitude has been made using the long-term geomagnetic field data obtained from the Yap (geomagnetic latitude, 0.38 degree), Gaum (5.22 degree), Okinawa (16.54 degree), Kakioka (27.18 degree), Memanbetsu (35.16 degree), and St. Paratunka (45.58 degree) stations. The magnetic local time (MLT) dependence of SC amplitude in the middle latitude showed the DP2-type magnetic field variations with its strong dawn-dusk asymmetry produced by ionospheric Hall currents which are driven by the dawn-to-dusk electric field accompanying a pair of field-aligned currents (FACs). The difference between the minimum and maximum values tends to become larger with increasing of magnetic latitude. In the low latitude, the maximum of the SC amplitude appears around noon (11:30, MLT), which means that the DL part of SC produced by the Chapman-Ferraro currents can be dominant in this region. However, the DP part of SC contaminated 5 percent of the DL one even in the low-latitude (16.54 degree). On the other hand, at the dip equator of the daytime sector between 8:00 and 16:00 (MLT), the equatorial enhancement of SC amplitude clearly appeared with its maximum amplitude of 3.24 (normalized SYM-H value) around 11:00 (MLT). Another interesting point is that the SC amplitude in the nighttime sector was enhanced at all the stations again, and its peak value increases with increasing of magnetic latitude. The nighttime enhancement is caused by the magnetic effects produced by the FACs associated with the MI phase of SC.
SM53A-1672
Storm-time electric fields in the mid-latitude ionosphere observed by ground magnetometers and the Akebono satellite
The mid-latitude ionosphere electromagnetically connected to the inner magnetosphere via magnetic field lines is an important region for understanding storm-time magnetosphere-ionosphere coupling processes. In order to clarify distributions of electric fields and currents in the mid- and low-latitude ionosphere during storms, we investigated latitudinal and local time dependence of magnetic field variations for six storms using a ground magnetometer network covering from high to equatorial latitudes. The analysis results suggested that competition between convection and shielding electric fields controlled characteristics of magnetic disturbances caused by mid-latitude ionospheric currents. However, a quantitative relationship between ground magnetic disturbances and in-situ ionospheric electric fields has not been clarified yet because of difficulties in deducing electric fields from magnetic field variations. Therefore, in this study, we analyzed ground magnetic disturbances and electric field mapped onto the ionosphere observed by the Akebono satellite during the storm occurred on February 21-22, 1994, with a minimum SYM-H value of -152 nT. During the main phase of the storm, the satellite passed through a region from 73 degrees invariant latitude (ILAT) and 10 magnetic local time (MLT) to 49 degrees ILAT and 18 MLT from 0055 to 0148 UT. The poleward electric field changed negative to positive values at 65.5 degrees ILAT (15 MLT). The electric field signature indicates that the center of region-1 field-aligned currents (R-1 FACs) was located at this latitude. Subsequently, the electric field profile showed two peaks at 62-63 degrees ILAT (15.5 MLT) and 55 degrees ILAT (17 MLT). The former corresponds to the auroral oval identified by the lower energy particle instrument of the Akebono. On the other hand, during the same period, we also investigated the latitudinal distribution of the northward magnetic field variation measured on the ground (16.5-19.5 MLT). The analysis result shows centers of R-1 FACs and auroral electrojet were located at 67.5 and 62.5 degrees in corrected geomagnetic latitude, respectively. This is consistent with each current position deduced from the electric field observed by the Akebono satellite. This fact indicates that there is a possibility of quantitative derivations of ionospheric electric fields using magnetic field variations measured on the ground.
SM53A-1673
Multifractal analysis of geomagnetic storm and solar flare indices and their class dependence
The multifractal properties and correlation of two indices of geomagnetic activity - Dst , representative of low latitudes and ap, representative of the global geomagnetic activity - with the solar X-ray brightness, Xl, during the period from 1 March 1995 to 17 June 2003 are examined using the detrended fluctuation analysis (DFA) and multifractal detrended fluctuation analysis (MF-DFA) techniques. The DFA results show that the Dst and ap time series are non-stationary and anti-persistent, while the Xl time series is stationary and persistent. The h(q) curves of Dst and ap in the MF- DFA are similar to each other, but they are different from that of Xl, indicating that the scaling properties of Xl are different from those of Dst and ap. Hence, one should not predict the magnitude of magnetic storms directly from solar X-ray observations. However, a strong relationship exists between the classes of the solar X-ray irradiance (the irradiance classes used separate solar flares of class X-M, class C, and class B or less, including no flares) in hourly measurements and the geomagnetic disturbances (large to moderate, small, or quiet) seen in Dst and ap during the active period. Each time series was converted into a symbolic sequence using 3 classes. The frequency, yielding the measure representations, of the substrings in the symbolic sequences then characterizes the pattern of space weather events. Using the MF-DFA method and traditional multifractal analysis, we calculate the h(q), D(q) and τ(q) curves of the measure representations. The τ(q) curves indicate that the measure representations of these three indices are multifractal. Based on this 3-class clustering, we find that the h(q), D(q) and τ(q) curves of the measure representations of Xl and Dst are similar to each other for positive values of q. This confirms a positive flare-storm class dependence reflected in the scaling exponents h(q) in the MF-DFA and the multifractal exponents D(q) and τ(q). This finding indicates that the solar flare classes can be used to improve the prediction of Dst.