AGU Articles - Query Results

2002-2004 GRL Papers making use of ACE Data in their Investigations. No ACE team members on author list.

(28 Papers)

Polar observations of solitary waves at the Earth's magnetopause Cattell C., J. Crumley, J. Dombeck, J. Wygant, and F. S. Mozer, Polar observations of solitary waves at the Earth's magnetopause, Geophys. Res. Lett., 29 (5), doi:10.1029/2001GL014046, 2002. 2002-03-13 Abstract: Solitary waves have, for the first time, been identified in 3D electric field data at the subsolar, equatorial magnetopause. These nonlinear, bipolar electric field pulses parallel to the magnetic field occur both as individual spikes and as trains of spikes. The solitary waves have amplitudes up to ∼25 mV/m, and velocities from ∼150 km/s to >2000 km/s, with scale sizes the order of a kilometer (comparable to the Debye length). Almost all the observed solitary waves are positive potential structures with potentials of ∼0.1 to 5 Volts. They are often associated with very large amplitude waves in either or both the electric and magnetic fields. Although most of the observed signatures are consistent with an electron hole mode, the events with very low velocities and the few negative potential structures may be indicative of a second type of solitary wave in the magnetopause current layer. The solitary waves may be an important source of dissipation and diffusion at the magnetopause. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Cosmic ray access to Jupiter's magnetosphere Selesnick R. S., Cosmic ray access to Jupiter's magnetosphere, Geophys. Res. Lett., 29 (9), doi:10.1029/2001GL014146, 2002. 2002-05-07 Abstract: Cosmic ray access to Jupiter's magnetosphere is investigated by numerical calculations of cosmic ray trajectories in the combined magnetic fields of the planetary dipole and the magnetospheric current sheet. Entry along the current sheet allows cosmic rays to reach closer to Jupiter than they would in a dipole planetary magnetic field alone. Observations of galactic cosmic rays from Galileo show that the calculations underestimate the true cutoff rigidities at equatorial radial distances >10 R J, but that the calculated ∼14 GV cutoff rigidity at 10 R J is a reasonable estimate. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Saturation of polar cap potential by intense solar wind electric fields Nagatsuma T., Saturation of polar cap potential by intense solar wind electric fields, Geophys. Res. Lett., 29 (10), doi:10.1029/2001GL014202, 2002. 2002-05-24 Abstract: We have examined the statistical relationship between solar wind parameters and the polar cap potential (Φ PC) using data from the Wind and ACE satellites and the northern polar cap index (PCN) as a proxy for Φ PC. We found that PCN tended to be saturated when the value of the merging electric field (E m) was high (greater than 5 mV/m). Furthermore, it was found that the degree of saturation does not depend on the intensity of the interplanetary magnetic field but depends on the value of E m. These results are in quite reasonable agreement with the predictions of the model of Hill et al. [1976]. This fact suggests that the development of magnetospheric convection is not controlled by the efficiency of the dayside merging process itself but is controlled by the coupling among the solar wind, the magnetosphere, and the ionosphere. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Precipitation of auroral protons in detached arcs Immel T. J., S. B. Mende, H. U. Frey, L. M. Peticolas, C. W. Carlson, J.-C. Gerard, B. Hubert, S. A. Fuselier, and J. L. Burch, Precipitation of auroral protons in detached arcs, Geophys. Res. Lett., 29 (11), doi:10.1029/2001GL013847, 2002. 2002-06-11 Abstract: Recent global-scale observations by the IMAGE-FUV instrument demonstrate the existence of regions of particle precipitation at sub-auroral latitudes on the dayside. The signature of this precipitation is seen infrequently, but when so, it is clear in all 3 channels of the FUV instrument. A conjugate hemisphere conjunction with the FAST satellite demonstrates the presence of precipitating protons and the notable absence of precipitating electrons in these arcs. With this knowledge, one can determine the mean energy and energy flux of the precipitating protons by intercomparison of the response in the three FUV channels. Assuming that the protons have a kappa energy distribution, the mean energy is found to be ∼20 keV, with a peak in total energy flux of ∼1 mW/m 2 /sec, consistent with fits to the FAST ion measurements. These phenomena are observed mainly during times of high solar wind dynamic pressure and variable interplanetary magnetic field, and are associated with earlier nightside enhancements in the brightness and latitudinal extent of the proton aurora. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

A telescopic and microscopic view of a magnetospheric substorm on 31 March 2001 Baker D. N., R. E. Ergun, J. L. Burch, J.-M. Jahn, P. W. Daly, R. Friedel, G. D. Reeves, T. A. Fritz, and D. G. Mitchell, A telescopic and microscopic view of a magnetospheric substorm on 31 March 2001, Geophys. Res. Lett., 29 (18), 1862, doi:10.1029/2001GL014491, 2002. 2002-09-19 Abstract: On March 31, 2001 at ∼0635 UT when the CLUSTER constellation was near local midnight and at ∼4 R E geocentric distance, sensors observed an energetic electron injection event associated with a strong (AE ∼ 1200 nT) magnetospheric substorm. Geostationary spacecraft 1991-080 located at ∼20 LT also saw an abrupt electron injection event at ∼0630 UT and FAST spacecraft instruments (∼19 LT) detected a powerful set of magnetic field, electric field, and energetic plasma signatures at ∼0637 UT. The energetic neutral atom imaging experiments onboard the IMAGE spacecraft detected an injection of substorm-produced ions in the pre-midnight sector commencing at ∼0630 UT. Electron injection signatures at the four separate CLUSTER locations allow us to infer the location, speed, and direction of the substorm injection boundary. Hence, the CLUSTER (and IMAGE) telescope-microscope combination is a long-sought realization of a major magnetospheric research objective and shows the power of localized multi-point measurements from CLUSTER. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

A wavy twisted neutral sheet observed by CLUSTER Zhang T. L., W. Baumjohann, R. Nakamura, A. Balogh, and K.-H. Glassmeier, A wavy twisted neutral sheet observed by CLUSTER, Geophys. Res. Lett., 29 (19), 1899, doi:10.1029/2002GL015544, 2002. 2002-10-01 Abstract: From July to October 2001, the Cluster satellites were located within the magnetotail and crossings of the neutral sheet were frequently observed by the FGM instrument [Balogh et al., 2001]. The neutral sheet often appears to be moving relative to the spacecraft. Multiple crossings of the neutral sheet on August 3, 2001 are analysed. These neutral sheet crossings were rather unusual. Spacecraft 2, which is in the northwestern part of the Cluster tetrahedron, leads the crossing from the north to the south lobe which implies a strongly twisted magnetotail on a local scale. Examining the solar wind interplanetary magnetic field conditions, we postulate that a wavy motion in the dawn-dusk direction is superimposed on an extremely twisted and warped neutral sheet. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Coupling of the solar wind to temporal fluctuations in ground magnetic fields Weigle R. S., D. Vassiliadis, and A. J. Klimas, Coupling of the solar wind to temporal fluctuations in ground magnetic fields, Geophys. Res. Lett., 29 (19), 1915, doi:10.1029/2002GL014740, 2002. 2002-10-08 Abstract: A study of the coupling of the solar wind to temporal fluctuations in high–latitude ground magnetic fields is presented. The fluctuation measure considered is the absolute value of the north-south horizontal field time derivative (&mid; dB x / dt &mid;) averaged over a 30–minute interval. The fluctuation level is predicted using a nonlinear mapping of solar wind plasma and field measurements. The predictability of ground magnetic field fluctuations is shown to depend on both local time and latitude. For lower polar cap magnetometer locations, the coupling is highest at the local times that have the highest average fluctuation level and lowest at the local times that have the lowest average fluctuation level. The highest level of coupling is at auroral-zone latitudes in the post-midnight sector. The relative influence of different solar wind inputs is shown to be highly dependent on spatial location. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Timing of magnetic reconnection initiation during a global magnetospheric substorm onset Baker D. N., et al., Timing of magnetic reconnection initiation during a global magnetospheric substorm onset, Geophys. Res. Lett., 29 (24), 2190, doi:10.1029/2002GL015539, 2002. 2002-12-26 Abstract: We have used a unique constellation of Earth-orbiting spacecraft and ground-based measurements in order to study a relatively isolated magnetospheric substorm event on August 27, 2001. Global ultraviolet images of the northern auroral region established the substorm expansion phase onset at 0408:19 (±1 min) UT. Concurrent measurements from the GOES-8, POLAR, LANL, and CLUSTER spacecraft allow us to construct a timeline which is consistent with magnetic reconnection on the closed field lines of the central plasma sheet near X GSM ∼ −18 R E some 7 minutes prior to the near-earth and auroral region times of substorm expansion phase onset. This suggests that magnetic reconnection (i.e., the substorm neutral line) in this case formed in the mid-tail region substantially before current disruption, field dipolarization near geostationary orbit, or auroral substorm onsets occurred. Thus, the magnetic reconnection process is interpreted as the causative driver of dissipation in this well-observed case. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Evidence of periodic (2–3 hour) near-tail magnetic reconnection and plasmoid formation: Geotail observations Huang C.-S., Evidence of periodic (2–3 hour) near-tail magnetic reconnection and plasmoid formation: Geotail observations, Geophys. Res. Lett., 29 (24), 2189, doi:10.1029/2002GL016162, 2002. 2002-12-26 Abstract: During magnetospheric substorms, magnetic reconnection occurs in the near tail and causes the formation of plasmoids. In this paper, we present Geotail observations of periodic magnetic reconnection and plasmoids in the near tail. On April 17–18, 2002, Geotail was located in the northern lobe and detected ten cycles of magnetic field compressions within 24 hours, and southward turnings of the magnetic field B z component or formations of plasmoids were clearly identified in the first seven cycles. The average period of the plasmoids was ∼2.5 hours. A solar wind pressure impulse appeared to trigger the first magnetic compression (or plasmoid). Plasmoids continued to occur for many cycles after the solar wind pressure and interplanetary magnetic field had become stable. The observations suggest that substorms can be periodic and that the periodic substorms can occur without requirement of continuous external triggering. Copyright 2002 by the American Geophysical Union.	[HTML] [PDF]

Testing the Hill model of transpolar potential with Super Dual Auroral Radar Network observations Shepherd S. G., J. M. Ruohoniemi, and R. A. Greenwald, Testing the Hill model of transpolar potential with Super Dual Auroral Radar Network observations, Geophys. Res. Lett., 30 (1), 2237, doi:10.1029/2002GL015426, 2003. 2003-01-02 Abstract: We use a data set consisting of periods for which the transpolar ionospheric potential (Φ $\mathsf{pc}$) is well-determined by Super Dual Auroral Radar Network (SuperDARN) data to test the Hill model. The Hill model, as formulated by Siscoe et al. [2002], specifies Φ $\mathsf{pc}$ as a function of solar wind speed and ram pressure, the interplanetary magnetic field, the reconnection electric field (E $\mathsf{r}$), and the ionospheric conductance (Σ). The periods used in our study were identified as times when the interplanetary electric field was quasi-stable for and SuperDARN coverage was sufficient to determine Φ $\mathsf{pc}$. SuperDARN-determined Φ $\mathsf{pc}$ (Φ $\mathsf{pc}$ $\mathsf{SD}$) is compared to Φ $\mathsf{pc}$ determined using the Hill model (Φ $\mathsf{pc}$ $\mathsf{Hill}$) for 1317 10-min periods. A minimum in the root-mean-square difference between Φ $\mathsf{pc}$ $\mathsf{SD}$ (E $\mathsf{r}$) and Φ $\mathsf{pc}$ $\mathsf{Hill}$ (E $\mathsf{r}$) is achieved when Σ = 23 S and a constant potential, Φ 0 = 17 kV, are used. Some aspects of the data agree very well for these values of Σ and Φ 0, including the mean value of Φ $\mathsf{pc}$ (E $\mathsf{r}$) and that both data sets clearly indicate saturation at higher values of E $\mathsf{r}$. The ram pressure dependence of Φ $\mathsf{pc}$ $\mathsf{Hill}$, however, is inconsistent with that of Φ $\mathsf{pc}$ $\mathsf{SD}$ and suggests that Σ should be lower than 23 S. There is also significantly more variability in Φ $\mathsf{pc}$ $\mathsf{SD}$ for all values of E $\mathsf{r}$ than the Hill model predicts. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Observation of dayside subauroral proton flashes with the IMAGE-FUV imagers Hubert B., J. C. Gérard, S. A. Fuselier, and S. B. Mende, Observation of dayside subauroral proton flashes with the IMAGE-FUV imagers, Geophys. Res. Lett., 30 (3), 1145, doi:10.1029/2002GL016464, 2003. 2003-02-14 Abstract: A detailed description of an intense flash of auroral emissions that occurs equatorward of the dayside auroral oval observed with the IMAGE-FUV imagers is presented. The comparison of simultaneous snapshots of this subauroral flash obtained with the three FUV cameras indicates that proton precipitation is dominant. This transient proton aurora is triggered by the sudden increase of a solar wind dynamic pressure pulse. It occurs on closed field lines mapping to the equatorial plane at distances as small as ∼4 R E. A second similar event is presented, and several other cases are mentioned. These shock induced transcient emissions develop with a time scale of a few minutes (typically ∼5 min), and have a relaxation time on the order of ∼10 minutes. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Effects of plasma sheet variability on the fast initial ring current decay Jordanova V. K., L. M. Kistler, M. F. Thomsen, and C. G. Mouikis, Effects of plasma sheet variability on the fast initial ring current decay, Geophys. Res. Lett., 30 (6), 1311, doi:10.1029/2002GL016576, 2003. 2003-03-25 Abstract: We study the effects of plasma sheet variations on the fast initial ring current (RC) decay during the March 31, 2001 storm. Previous studies have focused on the effects of enhanced plasma sheet density on RC buildup during the main phase of the storms. Using model simulations and energetic particle data from the instruments on CLUSTER and LANL, we demonstrate that the drop of plasma sheet density during the early recovery phase is important for the fast RC decay. In fact, an additional ∼50 nT decrease in Dst index occurs if this drop is not taken into account. We also demonstrate that there is no preconditioning of the RC during this storm period. The second enhancement in the convection electric field is not more effective in building the RC than the first in the case of the same magnetospheric plasma inflow on the nightside. This study shows that the fast initial RC decay is controlled not only by the decreased convection electric field, dayside outflow through the magnetopause, and internal loss processes, but also by the time-varying nightside inflow of plasma from the magnetotail. All factors should be considered for accurate predictions of RC decay timescales and Dst index. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Observed saturation of the ionospheric polar cap potential during the 31 March 2001 storm Hairston M. R., T. W. Hill, and R. A. Heelis, Observed saturation of the ionospheric polar cap potential during the 31 March 2001 storm, Geophys. Res. Lett., 30 (6), 1325, doi:10.1029/2002GL015894, 2003. 2003-03-27 Abstract: Theoretical arguments and MHD simulations have suggested that the potential drop across the polar-cap ionosphere approaches a constant value when the IMF is very large and southward. This idea has been difficult to test because the conditions producing this effect are extremely rare. During the 31 March 2001 storm the IMF was directed southward for over 6 hours with a magnitude of ∼36 nT to ∼20 nT while the DMSP-F13 satellite crossed the polar region, obtaining a good measure of the true polar cap potential drop. The observed potentials are compared with predictions from a theoretical model of the saturation process [Hill et al., 1976 ; Siscoe et al., 2002]. Clear evidence of a non-linear response consistent with the model predictions for height-integrated Pedersen conductivities in the range of 5–10 S are shown. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

The magnetic field in the pile-up region at Mars, and its variation with the solar wind Vennerstrom S., N. Olsen, M. Purucker, M. H. Acuña, and J. C. Cain, The magnetic field in the pile-up region at Mars, and its variation with the solar wind, Geophys. Res. Lett., 30 (7), 1369, doi:10.1029/2003GL016883, 2003. 2003-04-04 Abstract: The magnetic measurements from the Mars Global Surveyor satellite are used to study the magnetic field on the Martian dayside, and its variation with the solar wind. Because of the lack of solar wind measurements near Mars, solar wind measurements near Earth during a period centered on a Mars-Earth conjunction are used. Concurrent variations at Mars and Earth related to the interplanetary sector-structure and dynamic pressure variations are demonstrated. The study is confined to the northern hemisphere of Mars in regions where the crustal anomalies are weak. Here we find a close association between the solar wind dynamic pressure and the magnetic pressure in the pile-up region, and also a strong asymmetry with the Interplanetary magnetic field (IMF) B y -component, probably related to solar wind pick-up of planetary ions. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Bow shock motions observed with CLUSTER Maksimovic M., S. D. Bale, T. S. Horbury, and M. Andre, Bow shock motions observed with CLUSTER, Geophys. Res. Lett., 30 (7), 1393, doi:10.1029/2002GL016761, 2003. 2003-04-09 Abstract: The Cluster mission allows the determination not only of the bow shock crossing position but also, with a simple timing method and a reasonable confidence, the shock normal and the velocity along this normal. We apply this technique to a series of eleven consecutive bow shock crossings which occurred during a time interval of approximatively two and a half hours on 31 March 2001. We fit, on a distance versus time frame, the position of the bow shock subsolar point by imposing that the time derivatives at the crossings be equal to the shock speeds we determine. The curve we obtain this way represents global oscillations of the bow shock with a typical amplitude that compares quite well to the prediction of standard gasdynamic models which take into account the upstream solar wind plasma conditions. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Overshielding event of 28–29 July 2000 Goldstein J., R. W. Spiro, B. R. Sandel, R. A. Wolf, S.-Y. Su, and P. H. Reiff, Overshielding event of 28–29 July 2000, Geophys. Res. Lett., 30 (8), 1421, doi:10.1029/2002GL016644, 2003. 2003-04-17 Abstract: On 29 July 2000, IMAGE EUV observed a shoulder-like bulge on the plasmapause. Goldstein et al. [2002] showed that plasmaspheric shoulders may be caused by a pre-dawn concentration of eastward overshielding electric (E) field triggered by a decrease in magnetospheric convection. A simulation by the Magnetospheric Specification Model (MSM) captures the shoulder formation, reproducing its approximate size and location. ROCSAT-1 ion drift meter data are consistent with the strength, time development and local-time variation of the MSM eastward penetration E-field (and associated radial flows) during the shoulder formation on 28 July. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

An interplanetary cause of large geomagnetic storms: Fast forward shock overtaking preceding magnetic cloud Wang Y. M., P. Z. Ye, S. Wang, X. H. Xue, An interplanetary cause of large geomagnetic storms: Fast forward shock overtaking preceding magnetic cloud, Geophys. Res. Lett., 30 (13), 1700, doi:10.1029/2002GL016861, 2003. 2003-07-10 Abstract: In the event that occurred during October 3–6, 2000, at least one magnetosonic wave and one fast forward shock advanced into the preceding magnetic cloud (MC). By using the field and plasma data from the ACE and WIND spacecraft, we analyze the evolution of this event, including the characteristics and changes of the magnetic fields and plasma. At the rear part of the cloud, a large southward magnetic field is caused by a shock compression. The shock intensified a preexisting southward magnetic field. This increased the geoeffectiveness of this event and produced an intense geomagnetic storm with Dst = −175 nT. We also describe another event with a shock overtaking a MC on Nov. 6, 2001. A great geomagnetic storm of intensity Dst = 292 nT resulted. These observations are used to argue that shock compression of magnetic cloud fields is an important interplanetary cause of large geomagnetic storms. Our analyses suggest that the geoeffectiveness is related to the direction of preexisting magnetic fields, the intensity of overtaking shock, and the amount of shock penetration into the preceding MC. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Dynamics of global scale electron and proton precipitation induced by a solar wind pressure pulse Meurant M., J.-C. Gérard, B. Hubert, V. Coumans, C. Blockx, N. Østgaard, S. B. Mende, Dynamics of global scale electron and proton precipitation induced by a solar wind pressure pulse, Geophys. Res. Lett., 30 (20), 2032, doi:10.1029/2003GL018017, 2003. 2003-10-18 Abstract: 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. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

An empirical formula relating the geomagnetic storm's intensity to the interplanetary parameters: − $\overline{VB_{z}}$ and Δ t Wang Y., C. L. Shen, S. Wang, P. Z. Ye, t, An empirical formula relating the geomagnetic storm's intensity to the interplanetary parameters: − $\overline{VB_{z}}$ and Δ t, Geophys. Res. Lett., 30 (20), 2039, doi:10.1029/2003GL017901, 2003. 2003-10-22 Abstract: We statistically study 105 geomagnetic storms with a Dst peak value ≤ −50 nT during 1998–2001 to examine the influence of the interplanetary parameters − $\overline{VB_{z}}$ and its duration Δ t on the intensity of geomagnetic storms. About 33&percnt; of the events are associated with intense storms with Dst min ≤ −100 nT. It is found that − $\overline{VB_{z}}$ is much more important than Δ t for the formation of geomagnetic storms. A stronger − $\overline{VB_{z}}$ can produce a more intense storm, whereas a longer Δ t can not. A simple empirical formula relating the Dst peak value to − $\overline{VB_{z}}$ and Δ t is obtained, which shows a good correlation (CC = 0.9528) between the estimate value and the observations. This formula suggests that a compressed B s field tends to have a more prominent geoeffectiveness. Moreover, we also identify 33 large − $\overline{VB_{z}}$ intervals with − $\overline{VB_{z}}$ > 5 mV/m and Δ t > 3 hours in the same study interval, and find that they all caused intense storms (Dst min ≤ −100 nT) and 8/9 of the great storms (Dst min ≤ −200 nT) were due to interplanetary compressed structures. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Dependence of the decay phase of solar energetic electron events on the large-scale IMF structure: ACE observations Sarris E. T., O. E. Malandraki, Dependence of the decay phase of solar energetic electron events on the large-scale IMF structure: ACE observations, Geophys. Res. Lett., 30 (21), 2079, doi:10.1029/2003GL017921, 2003. 2003-11-01 Abstract: Using recent measurements of energetic electrons (≥38 keV) by the ACE /EPAM experiment, we examine the dependence of the characteristic decay time of two impulsive solar electron events on the large-scale structure of the Interplanetary Magnetic Field (IMF) within which the electrons are emitted. The technique of mapping the solar wind and extrapolating the frozen-in magnetic field is used to obtain the large-scale IMF structure within and beyond the location of the ACE spacecraft. We find that the electron event that occurred within a converging IMF structure exhibits a remarkably longer decay phase compared to the electron event observed inside a diverging IMF configuration. The observations provide strong evidence for the location of magnetic “barriers” in space beyond 1 AU and their role in determining the decay phase of solar energetic electron events and the establishment and maintenance of particle reservoirs in the heliosphere. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Control of plasmaspheric dynamics by both convection and sub-auroral polarization stream Goldstein J., B. R. Sandel, M. R. Hairston, P. H. Reiff, Control of plasmaspheric dynamics by both convection and sub&hyphen;auroral polarization stream, Geophys. Res. Lett., 30 (24), 2243, doi:10.1029/2003GL018390, 2003. 2003-12-17 Abstract: The long&hyphen;standing hypothesis that plasmaspheric dynamics are described by superposition of corotation and solar&hyphen;wind&hyphen;driven sunward convection is tested via direct comparison between plasmasphere observations and simulation output. The observations consist of global plasmasphere images produced by the IMAGE extreme ultraviolet (EUV) imager during plasmasphere erosion on 2 June 2001. The simulation is a plasmapause evolution model driven by a time&hyphen;varying Volland&hyphen;Stern (VS) electric potential distribution. On the dawnside and much of the nightside the model matches the EUV plasmapause position to within 0.2–0.5 earth radii (R E). Near dusk the model plasmapause is about 0.7–1.2 R E farther out than the EUV plasmapause, suggesting that an improved model should include the duskside flow enhancement known as the sub&hyphen;auroral polarization stream (SAPS). We demonstrate that including a simplified ad&hyphen;hoc SAPS potential can correct the model on the duskside. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Tracking a major interplanetary disturbance with SMEI Tappin S. J., et al. (2004), Tracking a major interplanetary disturbance with SMEI, Geophys. Res. Lett., 31, L02802, doi:10.1029/2003GL018766. 2004-01-22 Abstract: We present the first clear observations of an Earth&hyphen;directed interplanetary disturbance tracked by the Solar Mass Ejection Imager (SMEI). We find that this event can be related to two halo CMEs seen at the Sun about 2 days earlier, and which merged in transit to 1 AU. The disturbance was seen about 16 hours before it reached Earth,and caused a severe geomagnetic storm at the time which would have been predicted had SMEI been operating as a real&hyphen;time monitor. It is concluded that SMEI is capable of giving many hours advance warning of the possible arrival of interplanetary disturbances. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Conditions governing localized high-latitude dayside aurora Korth H., B. J. Anderson, H. U. Frey, T. J. Immel, S. B. Mende (2004), Conditions governing localized high&hyphen;latitude dayside aurora, Geophys. Res. Lett., 31, L04806, doi:10.1029/2003GL018911. 2004-02-24 Abstract: In a recent study of IMAGE FUV data, Frey et al. [2003] examined cases of high&hyphen;latitude dayside aurora (HiLDA) caused by precipitating electrons predominantly during northward IMF with a strongly positive IMF B y component. To determine the conditions that control these auroral emissions, we examine field&hyphen;aligned currents observed by the Iridium constellation for 25 events of prolonged steady IMF orientation with both B z and B y positive. We find that localized FACs are sustained under all observed solar wind conditions, but that the occurrence of HiLDA is generally restricted to solar wind proton densities below 4 cm −3 and peak current densities higher than 0.7 μA/m 2. That the solar wind density orders the occurrence of the auroral emissions indicates that magnetosheath plasma has ready access to the field lines carrying the upward current. Assuming that the magnetosheath plasma density and temperature govern the high&hyphen;altitude conditions on these field lines, we find that the intensity of the HiLDA emissions correlates with an estimate for the particle precipitation energy density based on the Knight relation, using the measured current density and the magnetosheath temperature and density. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

The dependence of Langmuir wave amplitudes on position in Earth's foreshock Sigsbee K., C. A. Kletzing, D. A. Gurnett, J. S. Pickett, A. Balogh, E. Lucek (2004), The dependence of Langmuir wave amplitudes on position in Earth's foreshock, Geophys. Res. Lett., 31, L07805, doi:10.1029/2004GL019413. 2004-04-15 Abstract: We present the first results of Langmuir wave observations in the foreshock from the Cluster WBD Plasma Wave Receiver. When the data were binned by distance to the foreshock boundary, the Langmuir wave amplitude probability distributions followed the log&hyphen;normal statistics predicted by stochastic growth theory for all regions of the foreshock. The Cluster data show for the first time that the centers of the probability distributions shift to lower amplitudes with increasing distance to the boundary, and that a spatially averaged power law distribution results from summing these distributions. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Triple cusps observed by Cluster—Temporal or spatial effect? Zong Q.&hyphen;G., T. A. Fritz, H. Zhang, A. Korth, P. W. Daly, M. W. Dunlop, K.&hyphen;H. Glassmeier, H. Reme, A. Balogh (2004), Triple cusps observed by Cluster—Temporal or spatial effect?, Geophys. Res. Lett., 31, L09810, doi:10.1029/2003GL019128. 2004-05-14 Abstract: On April 18, 2002, the Cluster spacecraft were outbound in the northern hemisphere over the pole and entered the cusp. A cusp&hyphen;like region was observed consecutively three times from 1620 to 1830 UT by all four Cluster Spacecraft although the solar wind dynamic pressure was small and stable. All three cusp encounters were characterized by turbulent magnetic fields, high density plasma and stagnant plasma flow. The cusp region identifications were further confirmed by the clock angle criterion. All three cusps were found to be associated with clear signatures of energetic ions, high He/H and O/H ratios obtained by the RAPID instrument. The observed triple cusps may be either explained as a funnel&hyphen;shaped cusp trifurcated or swiveled into a complicated geometry in space or as a cusp which shifted back and forth three times in a two hour interval. Observational evidence shows that the observed triple cusps were a temporal sequence rather than a spatial effect. We suggest further that the solar wind azimuthal flow was the controlling factor of the cusp position and was stronger factor than the IMF B Y /B Z components. The importance of the solar wind azimuthal and north/south flow as a dynamic driver of the cusp, and even the whole magnetosphere has been more or less neglected or underestimated. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Plasmapause undulation of 17 April 2002 Goldstein J., B. R. Sandel, M. R. Hairston, S. B. Mende (2004), Plasmapause undulation of 17 April 2002, Geophys. Res. Lett., 31, L15801, doi:10.1029/2004GL019959. 2004-08-10 Abstract: We report IMAGE EUV observations of a striking undulatory motion of the plasmapause that occurred on 17 April 2002, in which a large ripple propagated westward across the duskside plasmapause. From the plasmapause motion we infer a peak E-field of ≈3 mV/m associated with the undulation, and estimate the undulation's equatorial azimuthal speed to be 0.9 rad/hr ≈ 4 R E /hr, corresponding to ≈1 km/s in the ionosphere (using an R 3/2 dependence to map from the equator). Because DMSP ion drift data at 850 km altitude show the presence of a subauroral polarization stream (SAPS) flow channel ≈1 km/s at the same location and time as the undulation, we assert that SAPS was responsible for removal of plasma during the undulation. The SAPS apparently formed in response to a 19:00 UT substorm onset. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

The fraction of interplanetary coronal mass ejections that are magnetic clouds: Evidence for a solar cycle variation Richardson I. G., H. V. Cane (2004), The fraction of interplanetary coronal mass ejections that are magnetic clouds: Evidence for a solar cycle variation, Geophys. Res. Lett., 31, L18804, doi:10.1029/2004GL020958. 2004-09-21 Abstract: “Magnetic clouds” (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized by enhanced magnetic fields with an organized rotation in direction, and low plasma β. Though intensely studied, MCs only constitute a fraction of all ICMEs detected in the solar wind. A comprehensive survey of ICMEs in the near-Earth solar wind during the ascending, maximum and early declining phases of solar cycle 23 in 1996–2003 shows that the MC fraction varied with the phase of the solar cycle, from ∼100&percnt; (though with low statistics) at solar minimum to ∼15&percnt; at solar maximum. A similar trend is evident in near-Earth observations during solar cycles 20–21, while Helios 1/2 observations at 0.3–1.0 AU show a weaker trend and larger MC fraction. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Cluster survey of cusp reconnection and its IMF dependence Twitty C., T. D. Phan, G. Paschmann, B. Lavraud, H. Rème, M. Dunlop (2004), Cluster survey of cusp reconnection and its IMF dependence, Geophys. Res. Lett., 31, L19808, doi:10.1029/2004GL020646. 2004-10-12 Abstract: We have surveyed the occurrence of tailward-of-the-cusp reconnection detected by Cluster as a function of the interplanetary magnetic field (IMF) clock angle. The survey covers 3 years (2001–2003) of cusp and magnetopause (MP) crossings and is restricted to periods of relatively stable IMF. Our survey indicates that the reconnection associated plasma flows occur almost exclusively when the IMF has a northward component (or the clock angle is within ∼90° of the GSM +z direction). This finding at first seems inconsistent with the component merging model which should allow reconnection to occur for larger than 90° clock angle (or less than 90° in magnetic shear angle). However, it is possible that this is a geophysical effect. When the IMF has a southward component, reconnection equatorward of the cusp could prevent tailward-of-the-cusp reconnection by (1) creating low-shear condition behind the cusp, and (2) preventing the formation of a plasma depletion layer adjacent to dayside MP, resulting in super-Alfvenic magnetosheath flows at high latitude. No reconnection flows can be detected sunward of the X-line in this regime. Finally, the occurrence rate of tailward-of-the-cusp reconnection flows is ∼90&percnt; when the IMF has a northward component, indicating that simultaneous reconnection in the northern and southern cusps is common during northward IMF. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]