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Abstract: Auroral forms (“crewcuts”) that extend equatorward from the geomagnetically east–west aligned persistent midday aurora have been characterized based on a survey of Svalbard 630.0-nm all-sky images from eight December solstice seasons. The 630.0-nm forms are directly related to a mix of precipitating magnetosheath and plasma sheet electrons embedded in a population of boundary layer ions, as observed by NOAA 6. The associated midday aurora lies at the equatorward edge of poleward velocity-dispersed cusp ‘ion plumes’ observed by DMSP F7 at 1000 magnetic local time. In this survey, crewcuts are found to occur for Kp≤3. Distinct in many salient ways (including dynamics, orientation and associated IMF polarity) from the poleward-moving auroral forms (PMAFs) associated with transient dayside merging, crewcuts represent a solar wind-magnetosphere interaction that is more characteristic of quiet geomagnetic conditions. Crewcuts are present on 44% of the days for which all-sky images are complete and observing conditions are clear ±1.5h around geomagnetic noon. During these periods, crewcuts are observed during 10.6% of the minutes for which IMF data from ISEE 2 or IMP 8 are available. We derive from the data a simple set of IMF “search criteria” that maximize the likelihood of observing crewcuts around the December solstice. The IMF magnitude range for which crewcuts are most commonly observed is 3.5±0.5nT (36%). The IMF GSM component ranges in which crewcuts are most commonly observed are: B x =−3.5±0.5nT (27%), B y =−1.5±0.5nT (25%), and B z =0.5±0.5nT (26%). The IMF clock angular ranges for which crewcuts are most commonly observed are −70°±10° and 90°±10° (both 21%). The IMF cone angular range for which crewcuts are most commonly observed is 12.5°±2.5° (28%). Considering these observations in the context of magnetic merging topologies, we suggest crewcuts observed at Svalbard are most likely to lie at the foot of overdraped field lines recently opened by spatially patchy, quasi-steady merging in the southern hemisphere. [Copyright &y& Elsevier]

Abstract: A novel procedure to derive the daily varying quiet level for polar geomagnetic data is presented. Recorded data from selected quiet intervals are weighted and superposed to form the basis for an estimate of the quiet daily curve (QDC) for the variation in each of the recorded components on any selected day. The quiet daily variation is controlled by the level of solar UV and X-ray emissions, and parameters in the solar wind in combination with the actual season and the location of the observatory. The procedure uses the variability in the recorded geomagnetic data rather than international magnetic indices like Kp to determine the quiet intervals in accordance with the concept proposed by . A special problem for the estimation of the QDC in polar regions is the influence from the solar wind sector structure acting particularly through the azimuthal component, IMF By, of the interplanetary magnetic field. In the superposition of recordings to estimate the QDC for any given day, the present procedure uses weighting functions to give preference to intervals with quietest conditions, closest to the day in question, exposed to the same face of the sun, and within the same sector of the solar wind. The effects of control parameters for the selection of quiet intervals and smoothing of the initial QDC values are carefully controlled. The procedure is fully automated and delivers quality control parameters in addition to the QDC values. It is considered a further step forward in the processing of geomagnetic data to derive reliable and reproducible QDCs for the difficult high-latitude regions. [Copyright &y& Elsevier]

Abstract: Sudden impulses of the magnetospheric and geomagnetic field are caused by sudden increases in the dynamic pressure of the solar wind, generally associated with the Earth’s arrival of interplanetary shock waves or discontinuities. We compared the observed field jumps, at geosynchronous orbit and at ground, with those predicted by a theoretical model (T04, Tsyganenko and Sitnov, 2005) for transitions between two steady states representations of the magnetosphere under different solar wind conditions. The geosynchronous response (mostly along the northward component, B z) in the dayside hemisphere is basically consistent with the magnetic field jump expected for changes of the magnetopause current alone. A similar conclusion holds for the positive changes observed in the nightside hemisphere; by contrast, the competing contributions of several current systems (from the magnetopause, cross-tail current, ring current, field aligned currents) determine in this time sector a large variety of small amplitude and negative responses that cannot be univocally interpreted. A different situation emerges in ground observations, at low latitudes. Here the observed responses along the northward component, H, in the dawn sector are consistent with changes of the magnetopause current; by contrast, in the entire postnoon hemisphere, they are greater than expected. The H variations are also typically accompanied by a significant change of the eastward component, D. These aspects reveal additional ionospheric contributions which determine a negative change of the D component through the entire day and a remarkable enhancement (≈50%) of the H component in the postnoon sector. The comparison between observations and model representations in several cases allows to discriminate between the roles of the current systems which compete in determining the field variations. Occasionally, SI manifestations are accompanied by trains of ULF fluctuations (f≈1–100mHz); we present a case in which the experimental observations suggest evidence for a cavity/waveguide oscillation at f≈3.2mHz. [Copyright &y& Elsevier]

Abstract: Volume currents in the magnetosheath region are calculated within the framework of a new analytical model. Magnetic field structure in the region is found, satisfying boundary conditions on the bow shock and the magnetopause, and then volume currents are calculated using the Maxwell equation. Surface bow shock and magnetopause currents are calculated, too. Free parameters of the model are interplanetary magnetic field, Mach number of the solar wind flow, distances to the bow shock and to the magnetopause, and field compression at the magnetopause. [ABSTRACT FROM AUTHOR]

Abstract: The superdense plasma sheet in the Earth''s magnetosphere is studied via a superposition of multispacecraft data collected during 124 high-speed-stream-driven storms. The storm onsets tend to occur after the passage of the IMF sector reversal and before the passage of the stream interface, and the storms continue on for days during the passage of the high-speed stream. The superdense phase of the plasma sheet is found to be a common feature of high-speed-stream-driven storms, commencing before the onset of the storm and persisting for about 1 day into the storm. A separate phenomenon, the extra-hot phase of the plasma sheet, commences at storm onset and persists for several days during the storm. The superdense plasma sheet originates from the high-density compressed slow and fast solar wind of the corotating interaction region on the leading edge of the high-speed stream. Tracking the motion of this dense plasma into and through the magnetosphere, plasma transport times are estimated. Transport from the nightside of the dipole to the dayside requires about 10h. The occurrences of both the superdense plasma sheet and the extra-hot plasma sheet have broad implications for the physics of geomagnetic storms. [Copyright &y& Elsevier]

Abstract: The average plasmapause radial position is highly dependent on the electric field convection pattern in the inner magnetosphere. We present correlations relating the plasmapause position directly to interplanetary parameters. The plasmapause position is found to be strongly correlated with the interplanetary magnetic field (IMF) component, IMF clock angle, and , a merging proxy. Delay in the plasmapause response to the arrival of both IMF and IMF clock angle at Earth is found to be while the delay to the arrival of is found to be . A relation is derived between IMF , , and the plasmapause position. Avoiding the use of geomagnetic indices removes any requirement of knowledge of the current state or response of the magnetosphere. [Copyright &y& Elsevier]

Abstract: In the first place, this work will demonstrate that there are at least several cases for which the magnetosphere–ionosphere system “does not behave as a low-pass filter”, or better it transmits high frequencies. In one selected case study, a monochromatic solar wind pressure wave in the Pc5 band directly excites the same frequency of ground pulsations. The other two case studies are composed of repetitive solar wind pressure pulses, like quasi-periodic solar wind pressure waves, which are associated to ionospheric currents in a one-to-one correspondence. Our most interesting case shows that the magnetosphere sometimes has the ability to respond in such small timescales as 2.7min. The same case provides strong evidence that the successive solar wind pressure pulses excite a global mode wave in the magnetosphere. We further discuss these events under the perspective established by the three recent papers of Sarafopoulos (2004a. Distinct solar wind pressure pulses producing convection twin-vortex systems in the ionosphere. Annales Geophysicae 22, 2201–2211; 2004b. Repetitive X-line Hall current structures over the dawnside ionosphere induced by successive exo-magnetosphere pressure pulses. Annales Geophysicae 22, 4153–4163; 2005. Pseudo-field line resonances in ground Pc5 pulsation events. Annales Geophysicae 23, 593–608) that the solar wind pressure pulses produce pseudo-field-line resonances on the ground station data; and this result certainly do not support the cavity mode model. Previously, many researchers have suggested that the magnetosphere acts as low-pass filter with a threshold separating the driven from the loading–unloading processes that are based on the inherent system dynamics. Essentially, their works are based on the AE (or AL) index. Our suggestion here is that the methodology whereby the AE index was introduced may eliminate the power density in high frequencies. The AE index may fail to carry the high-frequency part of input information. Neighboring ground stations with a phase-shift in their recorded waveforms may produce a no fluctuating AE index. The research efforts using AE may result in an error estimate of the cutoff frequency for the magnetosphere considered as a low-pass filter. Additionally, these works are not able to capture high-frequency couplings between the solar wind and the magnetosphere because they use low-resolution measurements. The presented high-frequency couplings emphasize the complementary character of this work. We shall not search special mechanisms or conditions permitting or preventing the direct entry of Pc5 frequency activity on Earth and any statistical approach is beyond the scope of this paper. [Copyright &y& Elsevier]

Abstract: The prompt trapping of solar energetic particles (SEPs) in the inner magnetosphere around –2.5, including protons and heavier ions, has been observed at both the Cycle 22 and 23 solar maxima, in association with high-speed interplanetary shocks and storm sudden commencements (SSCs). Recent observations include the Bastille Day 2000 CME-driven storm as well as two in November 2001, which produced a long-lived new proton belt, as well as trapping of heavy ions up to Fe in all three cases. A survey of such events around the most recent solar maximum, including high altitude measurements from Polar and HEO satellites along with low altitude measurements from `the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX)'', indicates similarities to the well-studied March 24, 1991 SSC event. In this event, electrons and protons in drift resonance with a magnetosonic impulse were transported radially inward. A requirement for such shock-induced acceleration is a high-speed CME-shock at 1AU, which launches a perturbation with comparable velocity inside the magnetosphere. Secondly, there must be a source population which is drift-resonant with the impulse. The CME-shock itself is a source of solar energetic particles, both protons and heavy ions, with higher fluxes and harder spectra associated with faster moving CMEs. Arrival of the interplanetary shock compresses and changes the magnetosphere topology, leading to a reduction of the geomagnetic cutoff, initially around for SEP protons. This effect is modeled using a 3D Lorentz integration of SEP trajectories in electric and magnetic fields taken from the Lyon–Fedder–Mobarry (LFM) global MHD code, with solar wind input parameters taken from spacecraft measurements upstream from the bow shock, carried out for the November 24, 2001 SEP event. The results indicate that an enhancement in solar wind dynamic pressure for this event plays a role in the observed injection of ions to low L-values, to form a new proton belt which has lasted for more than 2 years. [Copyright &y& Elsevier]

Abstract: High fluxes of relativistic electrons in the inner magnetosphere have been associated with a range of spacecraft anomalies, and therefore the modeling of the flux is of direct relevance to the development of space weather applications. Time variations of the electron flux at a given shell are ultimately functions of interplanetary parameters as well as of internal magnetospheric dynamics. It is important to resolve which one of the two elements is important for modeling and to what extent. To that end we compare two models of the magnetospheric relativistic electron flux at 2–6MeV spanning the range –10 and driven by the solar wind plasma velocity, . The finite-impulse-response (FIR) model represents the coupling of the flux to the solar wind velocity. It is part of an empirical model chain currently in development at the Center for Integrated Space Weather Modeling. The autoregressive moving-average (ARMA) model also includes a representation of the internal flux dynamics. The comparison is quantified in terms of the prediction accuracy, its variation with season and solar cycle phase, and its dependence on activity level. We find that the FIR model is more accurate than the ARMA model in most radial regions of the radiation belts, including the geosynchronous orbit. The results indicate that the long memory of the FIR model to past solar wind velocity inputs is more important in representing the effective coupling than ARMA''s additional internal dynamics. [Copyright &y& Elsevier]