bluuebunny/crossref_metadata_2025 huggingface dataset:
Field-aligned currents and ionospheric parameters deduced from EISCAT radar measurements in the post-midnight sector
Authors: Sugino M. , Fujii R. , Nozawa S. , Nagatsuma T. , Buchert S. C. , Gjerloev J. W. , Kosch M. J.
Published: June 2010

Abstract. Attempting to derive the field-aligned current (FAC) density using the EISCAT radar and to understand the role of the ionosphere on closing FACs, we conducted special radar experiments with the EISCAT radar on 9 October 1999. In order to derive the gradient of the ionospheric conductivity (grad S) and the divergence of the electric field (div E) nearly simultaneously, a special experiment employed an EISCAT radar mode which let the transmitting antenna sequentially point to four directions within 10 min; two pairs of the four directions formed two orthogonal diagonals of a square.  Our analysis of the EISCAT radar data disclosed that SP div E and E · grad SP produced FACs with the same direction inside a stable broad arc around 05:00 MLT, when the EISCAT radar presumably crossed the boundary between the large-scale upward and downward current regions. In the most successfully observed case, in which the conductances and the electric field were spatially varying with little temporal variations, the contribution of SP div E was nearly twice as large as that of E · grad SP . On the other hand, the contribution of (b × E) · grad SH was small and not effective in closing FACs. The present EISCAT radar mode along with auroral images also enables us to focus on the temporal or spatial variation of high electric fields associated with auroral arcs. In the present experiment, the electric field associated with a stable arc was confined in a spatially restricted region, within ~ 100 km from the arc, with no distinct depletion of electron density. We also detected a region of the high arc-associated electric field, accompanied by the depletion of electron density above 110 km. Using auroral images, this region was identified as a dark spot with a spatial scale of over 150 × 150 km. The dark spot and the electron depletion were likely in existence for a limited time of a few minutes.Key words. Ionosphere (auroral ionosphere; electric fields and currents; particle precipitation)
Positive storm effects in the dayside polar ionospheric F-region observed by EISCAT and ESR during the magnetic storm of 15 May 1997
Authors: Ma S. Y. , Cai H. T. , Liu H. X. , Schlegel K. , Lu G.
Published: June 2010

Abstract. EISCAT/ESR radar data and in situ FAST and POLAR satellite observations are coordinately analyzed to investigate positive ionospheric storm effects in the dayside upper F-region in both the polar cap and the auroral oval during the magnetic storm of 15 May 1997. An ionization enhancement, lasting for about 2.5 h, appeared first over the EISCAT site around magnetic noon; about one hour later, a similar ionization enhancement was also seen over ESR. During the concerned time period ion energy spectra measured on board FAST show clearly continuous energy-latitude dispersion when the satellite passed by over the EISCAT latitude. This implies that EISCAT was located under the polar cusp region which was highly active, and expanded greatly equatorwards due to magnetopause reconnections during long-lasting southward IMF. Simultaneously, soft particles of the magnetosheath precipitated into the F-region ionosphere and caused the positive storm effects over EISCAT. The coincident increase in electron temperature at EISCAT gives additional evidence for soft particle precipitation. Consistently, POLAR UV images show strong dayside aurora extending to as low as 62° N magnetic latitude. The ionization enhancement over ESR, however, seems not to be caused by local particle precipitation, evidenced by a lack of enhanced electron temperature. The observed plasma convection velocity and data-fitted convection patterns by AMIE suggested that it is likely to be a polar patch originating from the cusp region and traveling to the ESR site.Key words. Ionosphere (auroral ionosphere; particle percipitation) Magnetospheric physics (storms and substorms)
Nightside studies of coherent HF Radar spectral width behaviour
Authors: Woodfield E. E. , Davies J. A. , Lester M. , Yeoman T. K. , Eglitis P. , Lockwood M.
Published: June 2010

Abstract. A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1) exists poleward of a region of low HF spectral width (<200 ms-1). Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT) on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1) have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to the data presented here. Since the regions of high spectral width are observed both on closed and open field lines the use of the boundary between low and high spectral width as an ionospheric proxy for the open/closed field line boundary is not a simple matter, if indeed it is possible at all.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities)
Electron acceleration observed by the FAST satellite within the IAR during a 3 Hz modulated EISCAT heater experiment
Authors: Cash S. R. , Davies J. A. , Kolesnikova E. , Robinson T. R. , Wright D. M. , Yeoman T. K. , Strangeway R. J.
Published: June 2010

Abstract. A quantitative analysis is presented of the FAST satellite electric field and particle flux data during an EISCAT heating experiment run on 8 October 1998. Radio frequency heating, modulated at 3 Hz, launched ULF waves from the ionosphere into the lower magnetosphere. The ULF waves were observed in FAST data and constituted the first satellite detection of artificially excited Alfvénic ULF waves. The downward electron flux data for this event contain the first observations of electrons undergoing acceleration within the Ionospheric Alfvén Resonator (IAR) due to parallel electric fields associated with an artificially stimulated Alfvén wave. The time history and spectral content of the observed down-ward electron fluxes is investigated by considering the effects of a localised parallel electric field. Furthermore, it is demonstrated that a power law electron energy distribution describes the time-variable observed fluxes better than a Maxwellian distribution.Key words. Ionosphere (active experiments; particle acceleration) – Magnetospheric physics (electric fields)
Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm
Authors: Grocott A. , Cowley S. W. H. , Sigwarth J. B. , Watermann J. F. , Yeoman T. K.
Published: June 2010

Abstract. We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ~40 kV prior to expansion phase onset, grew to ~80 kV over a ~15 min interval during the expansion phase, and then decayed to ~35 kV over ~10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ~65– 75 kV, compared with continuing dayside reconnection rates of ~30–45 kV. The net closure of open flux during the sub-storm was thus ~0.4–0.6 × 108 Wb, representing ~15–20% of the open flux present at onset, and corresponding to an overall contraction of the open-closed field line boundary by ~1° latitude.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection)
Ionospheric cusp flows pulsed by solar wind Alfvén waves
Authors: Prikryl P. , Provan G. , McWilliams K. A. , Yeoman T. K.
Published: June 2010

Abstract. Pulsed ionospheric flows (PIFs) in the cusp foot-print have been observed by the SuperDARN radars with periods between a few minutes and several tens of minutes. PIFs are believed to be a consequence of the interplanetary magnetic field (IMF) reconnection with the magnetospheric magnetic field on the dayside magnetopause, ionospheric signatures of flux transfer events (FTEs). The quasiperiodic PIFs are correlated with Alfvénic fluctuations observed in the upstream solar wind. It is concluded that on these occasions, the FTEs were driven by Alfvén waves coupling to the day-side magnetosphere. Case studies are presented in which the dawn-dusk component of the Alfvén wave electric field modulates the reconnection rate as evidenced by the radar observations of the ionospheric cusp flows. The arrival of the IMF southward turning at the magnetopause is determined from multipoint solar wind magnetic field and/or plasma measurements, assuming plane phase fronts in solar wind. The cross-correlation lag between the solar wind data and ground magnetograms that were obtained near the cusp footprint exceeded the estimated spacecraft-to-magnetopause propagation time by up to several minutes. The difference can account for and/or exceeds the Alfvén propagation time between the magnetopause and ionosphere. For the case of short period ( < 13 min) PIFs, the onset times of the flow transients appear to be further delayed by at most a few more minutes after the IMF southward turning arrived at the magnetopause. For the case of long period (30 – 40 min) PIFs, the observed additional delays were 10–20 min. We interpret the excess delay in terms of an intrinsic time scale for reconnection (Russell et al., 1997) which can be explained by the surface-wave induced magnetic reconnection mechanism (Uberoi et al., 1999). Here, surface waves with wavelengths larger than the thickness of the neutral layer induce a tearing-mode instability whose rise time explains the observed delay of the reconnection onset. The compressional fluctuations in solar wind and those generated in the magnetosheath through the interaction between the solar wind Alfvén waves and the bow shock were the source of magnetopause surface waves inducing reconnection.Key words. Interplanetary physics (MHD waves and turbulence) – Magnetospheric physics (magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)
Letter to the Editor UHF electromagnetic emission stimulated by HF pumping of the ionosphere
Authors: Grach S. M. , Fridman V. M. , Lifshits L. M. , Podstrigach T. S. , Sergeev E. N. , Snegirev S. D.
Published: June 2010

Abstract. UHF electromagnetic emission (with a frequency near 600 MHz) from the F-region of the ionosphere pumped by an HF powerful radio wave is revealed. Possible mechanisms of the emission excitation, such as plasma mode con-version, scattering or Earth thermal noise emission off the plasma density irregularities, bremsstrahlung and excitation of high Rydberg states of the neutral particles by the accelerated electrons are discussed.Key words. Ionosphere (active experiments; wave-particle interactions) – Solar physics, astrophysics, and astronomy (radio emissions)
Global morphology of night-time NmF2 enhancements
Authors: Farelo A. F. , Herraiz M. , Mikhailov A. V.
Published: June 2010

Abstract. An overall statistical study of night-time enhancements of NmF2 has been carried out. All available foF2 observations since 1955 at 53 ionosonde stations distributed worldwide in the latitude range fgeom = 15° - 60° were used in the analysis. More than 200 000 station-nights of data were analysed. This large data base allowed us to study seasonal, solar cycle and spatial variations of the NmF2 nighttime enhancements. Both pre-midnight and post-midnight NmF2 peaks demonstrate distinct variations with geophysical conditions, indicating different physical mechanisms responsible for their formation.Key words. Ionosphere (mid-latitude ionosphere, ionosphere-magnetosphere interactions) Radio science (ionospheric physics)
An assessment of the "map-potential" and "beam-swinging" techniques for measuring the ionospheric convection pattern using data from the SuperDARN radars
Authors: Provan G. , Yeoman T. K. , Milan S. E. , Ruohoniemi J. M. , Barnes R.
Published: June 2010

Abstract. The SuperDARN HF coherent scatter radars (Greenwald et al., 1995) provide line-of-sight (l-o-s) velocity measurements of ionospheric convection flow over the polar regions of the northern and southern hemispheres. A number of techniques have been developed in order to obtain 2-D plasma flow vectors from these l-o-s observations. This study entails a comparison of the ionospheric flow vectors derived using the "map-potential", and "beam-swinging" techniques with the vectors derived using the "merging" technique. The merging technique is assumed to be the most accurate method of deriving local flow vectors from l-o-s velocities. We can conclude that the map-potential model is significantly more successful than the beam-swinging technique at estimating both the magnitude and the direction of the large-scale ionospheric convection flow vectors. The quality of the fit is dependent on time of day, with vectors observed at low latitudes in the dawn sector agreeing most closely with the merged vector flow pattern.Key words. Ionosphere (plasma convection; instruments and techniques) – Radio science (instruments and techniques)
Estimating the contribution from different ionospheric regions to the TEC response to the solar flares using data from the international GPS network
Authors: Leonovich L. A. , Afraimovich E. L. , Romanova E. B. , Taschilin A. V.
Published: June 2010

Abstract. This paper proposes a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare, based on data from the international network of two-frequency multichannel receivers of the navigation GPS system. The method uses the effect of partial "shadowing" of the atmosphere by the terrestrial globe. The study of the solar flare influence on the atmosphere uses GPS stations located near the boundary of the shadow on the ground in the nightside hemisphere. The beams between the satellite-borne transmitter and the receiver on the ground for these stations pass partially through the atmosphere lying in the region of total shadow, and partially through the illuminated atmosphere. The analysis of the ionospheric effect of a powerful solar flare of class X5.7/3B that was recorded on 14 July 2000 (10:24 UT, N22 W07) in quiet geomagnetic conditions (Dst = -10 nT) has shown that about 75% of the TEC increase corresponds to the ionospheric region lying below 300 km and about 25% to regions lying above 300 km.Key words. Ionosphere (solar radiation and cosmic ray effects; instruments and techniques) – Solar physics, astrophysics and astronomy (ultraviolet emissions)
A statistical study of ion energization at 1700 km in the auroral region
Authors: Hamrin M. , Norqvist P. , Hellström T. , André M. , Eriksson A. I.
Published: June 2010

Abstract. We present a comprehensive overview of several potentially relevant causes for the oxygen energization in the auroral region. Data from the Freja satellite near 1700 km altitude are used for an unconditional statistical investigation. The data are obtained in the Northern Hemisphere during 21 months in the declining phase of the solar cycle. The importance of various wave types for the ion energization is statistically studied. We also investigate the correlation of ion heating with precipitating protons, accelerated auroral electrons, suprathermal electron bursts, the electron density variations, Kp index and solar illumination of the nearest conjugate ionosphere. We find that sufficiently strong broad-band ELF waves, electromagnetic ion cyclotron waves, and waves around the lower hybrid frequency are foremost associated with the ion heating. However, magnetosonic waves, with a sharp, lower frequency cutoff just below the proton gyrofrequency, are not found to contribute to the ion heating. In the absence of the first three wave emissions, transversely energized ions are rare. These wave types are approximately equally efficient in heating the ions, but we find that the main source for the heating is broadband ELF waves, since they are most common in the auroral region. We have also observed that the conditions for ion heating are more favourable for smaller ratios of the spectral densities SE /SB of the broadband ELF waves at the oxygen gyrofrequency.Key words. Ionosphere (auroral ionosphere; wave propogation) Magnetospheric physics (electric fields)
Effects of temperature dependence of reaction N2(A3 S+u) + O ongreenline dayglow emission
Authors: Upadhayaya A. K. , Singh V.
Published: June 2010

Abstract. The greenline dayglow emission profiles measured by the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) are modelled using recently proposed revisions to the temperature dependent rate coefficient of the reaction N2 (A3 S+u ) + O in the glow model. The volume emission rates of greenline dayglow emissions are calculated using the Hinteregger et al. (1981) and Tobiska (1991) solar flux models. It is found that the average modelled profiles obtained using the Hinteregger et al. (1981) solar flux model with the temperature dependent rate coefficient and a quantum yield of 0.36 for the reaction N2 (A3 S+u ) + O agree to within 8% of the observed profiles in the thermospheric peak region, which shows significant improvement over the earlier results (20% smaller than WINDII results) obtained using the temperature independent reaction rate coefficient. On the other hand, the average modelled profiles obtained with a temperature dependent rate coefficient in the Tobiska (1991) solar flux model are about 12% higher than the WINDII results, whereas with the temperature independent rate coefficient the results are about 10% smaller than the WINDII results in the thermospheric peak region. The present study reveals that the emission profiles obtained using the Hinteregger et al. (1981) solar flux model, along with the temperature dependent rate coefficient and a quantum yield of 0.36 for the reaction N2 (A3 S+u ) + O in glow model, reproduce the thermospheric emission peak as observed by WINDII, a capability which eluded earlier models. These findings support the newly discovered temperature dependence of the rate coefficient of re-action N2 (A3 S+u ) with O.Key words. Ionosphere (ionization mechanisms; modeling and forecasting; general or miscellaneous)
Letter to the Editor Simultaneous observations of the ionospheric footprint of flux transfer events and dispersed ion signatures
Authors: Provan G. , Milan S. E. , Lester M. , Yeoman T. K. , Khan H.
Published: June 2010

Abstract. We perform a case study of a favourable conjunction of overpasses of the DMSP F11 and F13 spacecraft with the field of view of the Hankasalmi HF coherent scatter. At the time, pulsed ionospheric flows (PIFs) were clearly observed at a high-latitude in the radar field of view. The PIFs were associated with medium spectral width values and were identified as the fossilized signatures of pulsed dayside reconnection. Simultaneously, DMSP spectrograms from the two spacecraft showed dispersed ion signatures, observed equatorwards of the PIF signatures. We identified dayside high-latitude magnetosphere boundaries; these boundaries agreed well with those defined using the algorithm on the JHU/APL auroral particle website (Haerendel et al., 1978; Newell and Meng, 1988, 1995; Newell et al., 1991a, 1991b, 1991c; Traver et al., 1991). We conclude that in this case study the dispersed ion signatures map to regions of very newly-opened flux. It is only when this flux has convected polewards that the signatures of the PIFs with medium spectral widths are observed by the HF radars. These particular PIF signatures map to regions of mantle precipitation, i.e. recently reconnected flux.Key words. Ionosphere (ionosphere-magnetosphere interaction) – Magnetospheric physics (magnetopause, cusp and boundary layers; plasma convection)
A case study of HF radar spectral width in the post midnight magnetic local time sector and its relationship to the polar cap boundary
Authors: Woodfield E. E. , Davies J. A. , Eglitis P. , Lester M.
Published: June 2010

Abstract. The aim of this paper is to advance the current understanding of the spectral width parameter observed by coherent high frequency (HF) radars. In particular, we address the relationship of a frequently observed gradient, between low ( < 200 m/s) and high ( > 200 m/s) spectral width, to magnetospheric boundaries. Previous work has linked this gradient in the spectral width, in the nightside sector of magnetic local time, to the Polar Cap Boundary (PCB), and also to the boundary between the Central Plasma Sheet (CPS) and the Plasma Sheet Boundary Layer (PSBL). The present case study investigates the former by comparison with the 630.0 nm optical emission. No suitable data were available to test the second of the two hypotheses. It is found that during the interval in question the spectral width gradient is within the region of the 630.0 nm optical emission. A comparison of coherent and incoherent scatter radar data is also conducted, which indicates that values of high spectral width are typically collocated with elevated F-region electron temperatures. We conclude that the high spectral width region in the interval under study is associated with particle precipitation and also that the spectral width gradient is not a reliable method for locating the PCB.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities)
The spectral characteristics of E-region radar echoes co-located with and adjacent to visual auroral arcs
Authors: Milan S. E. , Sato N. , Lester M. , Yeoman T. K. , Murata Y. , Doi H. , Saemundsson T.
Published: June 2010

Abstract. Simultaneous all-sky camera and HF radar observations of the visual and E-region radar aurora in the west-ward electrojet suggest a close relationship between a pair of parallel east-west-aligned auroral arcs, separated by ~ 30 km, and a region of strong radar backscatter. Poleward of this a broader region of radar backscatter is observed, though the spectral characteristics of the echoes in these two regions differ considerably. We suggest that the visual aurorae and their radar counterparts are produced in a region of upward field-aligned current (FAC), whereas the backscatter poleward of this is associated with downward FAC. Relatively low electric fields ( ~ 10 mV m-1) are observed in the vicinity of the arc system, suggesting that in this case, two-stream waves are not directly generated through the electrodynamics of the arc. Rather, the generation of irregularities is most probably associated with the gradient drift instability operating within horizontal electron density gradients produced by the filamentary nature of the arc FAC system. The observation of high Doppler shift echoes superimposed on slow background flow within the region of backscatter poleward of the visual aurora is argued to be consistent with previous suggestions that the ion-acoustic instability threshold is reduced in the presence of upwelling thermal electrons carrying downward FAC.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; particle precipitation)
Modelling interplanetary CMEs using magnetohydrodynamic simulations
Authors: Cargill P. J. , Schmidt J. M.
Published: June 2010

Abstract. The dynamics of Interplanetary Coronal Mass Ejections (ICMEs) are discussed from the viewpoint of numerical modelling. Hydrodynamic models are shown to give a good zero-order picture of the plasma properties of ICMEs, but they cannot model the important magnetic field effects. Results from MHD simulations are shown for a number of cases of interest. It is demonstrated that the strong interaction of the ICME with the solar wind leads to the ICME and solar wind velocities being close to each other at 1 AU, despite their having very different speeds near the Sun. It is also pointed out that this interaction leads to a distortion of the ICME geometry, making cylindrical symmetry a dubious assumption for the CME field at 1 AU. In the presence of a significant solar wind magnetic field, the magnetic fields of the ICME and solar wind can reconnect with each other, leading to an ICME that has solar wind-like field lines. This effect is especially important when an ICME with the right sense of rotation propagates down the heliospheric current sheet. It is also noted that a lack of knowledge of the coronal magnetic field makes such simulations of little use in space weather forecasts that require knowledge of the ICME magnetic field strength.Key words. Interplanetary physics (interplanetary magnetic fields) Solar physics, astrophysics, and astronomy (flares and mass ejections) Space plasma physics (numerical simulation studies)
Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations
Authors: McKenna-Lawlor S. M. P. , Dryer M. , Smith Z. , Kecskemety K. , Fry C. D. , Sun W. , Deehr C. S. , Berdichevsky D. , Kudela K. , Zastenker G.
Published: June 2010

Abstract. The arrival times at L1 of eleven travelling shocks associated both with X-ray flaring and with halo CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the velocities of these events were estimated using either Type II radio records or CME speeds. Close to the Earth the shocks were detected in the data of various solar wind plasma, interplanetary magnetic field (IMF) and energetic particle experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock arrival predictions of three numerical models, namely the Shock Time of Arrival Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these observations. This is the first time that energetic protons (tens of keV to a few MeV) have been used to complement plasma and IMF data in validating shock propagation models. The models were all generally successful in predicting shock arrivals. STOA provided the smallest values of the "predicted minus measured" arrival times and displayed a typical predictive precision better than about 8 h. The ratio of the calculated standard deviation of the transit times to Earth to the standard deviation of the measurements was estimated for each model (treating interacting events as composite shocks) and these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2, respectively. If an event in the sample for which the shock velocity was not well known is omitted from consideration, these ratios become 0.36, 0.76 and 0.81, respectively. Larger statistical samples should now be tested. The ratio of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh /Vtr) was in the range of 0.7–0.9 for individual, non-interacting, shock events. HAFv.2 uniquely provided information on those changes in the COBpoint (the moving Connection point on the shock along the IMF to the OBserver) which directly influenced energetic particle rise times. This model also illustrated the non-uniform upstream conditions through which the various shocks propagated; furthermore it simulated shock deformation on a scale of fractions of an AU. On the spatial scale (300 RE ), where near-Earth spacecraft are located, the passing shocks, in conformity with the models, were found to be locally planar. The shocks also showed tilting relative to the Sun-Earth line, probably reflecting the inherent directionality associated with their solar origin. Key words. Interplanetary physics (energetic particles; interplanetary shocks; solar wind plasma)
Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99
Authors: Blagoveshchensky D. V. , Maltseva O. A. , Rodger A. S.
Published: June 2010

Abstract. The temporal and spatial behaviour of the ionospheric parameters foF2 and h'F during isolated substorms are examined using data from ionospheric stations distributed across Europe and western Asia. The main purpose is finding the forerunners of the substorm disturbances and a possible prediction of these disturbances. During the period from March 1998 to March 1999, 41 isolated substorms with intensities I = 60 - 400 nT were identified and studied. The study separated occasions when the local magnetometers were affected by the eastward electrojet (positive substorms) from those influenced by the westward electrojet (negative substorms). The deviations of the ionospheric parameters from their monthly medians (DfoF2 and Dh'F) have been used to determine the variations through the substorm. Substorm effects occurred simultaneously (< 1 h) across the entire observatory network. For negative substorms, DfoF2-values increase > 6 h before substorm onset, To, reaching a maximum 2–3 h before To. A second maximum occurs 1–2 h after the end of the substorm. The Dh'F values 3–4 h before To have a small minimum but then increase to a maximum at To. There is a second maximum at the end of the expansion phase before dh'F drops to a minimum 2–3 h after ending the expansion phase. For positive substorms, the timing of the first maximum of the dfoF2 and dh'F values depends on the substorm length – if it is longer, the position is closer to To. The effects on the ionosphere are significant: DfoF2 and Dh'F reach 2–3 MHz (dfoF2 = 50–70% from median value) and 50–70 km (D h'F = 20–30% from median value), respectively. Regular patterns of occurrence ahead of the first substorm signature on the magnetometer offer an excellent possibility to improve short-term forecasting of radio wave propagation conditions.Key words. Ionosphere (ionospheric disturbances) – Magnetospheric physics (storms and substorms) Radio science (ionospheric physics)
Reconstruction of the ion plasma parameters from the current measurements: mathematical tool
Authors: Séran E.
Published: June 2010

Abstract. Instrument d’Analyse du Plasma (IAP) is one of the instruments of the newly prepared ionospheric mission Demeter. This analyser was developed to measure flows of thermal ions at the altitude of ~ 750 km and consists of two parts: (i) retarding potential analyser (APR), which is utilised to measure the energy distribution of the ion plasma along the sensor look direction, and (ii) velocity direction analyser (ADV), which is used to measure the arrival angle of the ion flow with respect to the analyser axis. The necessity to obtain quick and precise estimates of the ion plasma parameters has prompted us to revise the existing mathematical tool and to investigate different instrumental limitations, such as (i) finite angular aperture, (ii) grid transparency, (iii) potential depression in the space between the grid wires, (iv) losses of ions during their passage between the entrance diaphragm and the collector. Simple analytical expressions are found to fit the currents, which are measured by the APR and ADV collectors, and show a very good agreement with the numerical solutions. It was proven that the fitting of the current with the model functions gives a possibility to properly resolve even minor ion concentrations and to find the arrival angles of the ion flow in the multi-species plasma. The discussion is illustrated by an analysis of the instrument response in the ionospheric conditions which are predicted by the International Reference Ionosphere (IRI) model.Key words. Ionosphere (plasma convection; instruments and techniques) – Space plasma physics (experimental and mathematical techniques)
How did the solar wind structure change around the solar maximum? From interplanetary scintillation observation
Authors: Fujiki K. , Kojima M. , Tokumaru M. , Ohmi T. , Yokobe A. , Hayashi K. , McComas D. J. , Elliott H. A.
Published: June 2010

Abstract. Observations from the second Ulysses fast latitude scan show that the global structure of solar wind near solar maximum is much more complex than at solar minimum. Soon after solar maximum, Ulysses observed a polar coronal hole (high speed) plasma with magnetic polarity of the new solar cycle in the Northern Hemisphere. We analyze the solar wind structure at and near solar maximum using interplanetary scintillation (IPS) measurements. To do this, we have developed a new tomographic technique, which improves our ability to examine the complex structure of the solar wind at solar maximum. Our IPS results show that in 1999 and 2000 the total area with speed greater than 700 km s-1 is significantly reduced first in the Northern Hemisphere and then in the Southern Hemisphere. For year 2001, we find that the formation of large areas of fast solar wind around the north pole precedes the formation of large polar coronal holes around the southern pole by several months. The IPS observations show a high level agreement to the Ulysses observation, particularly in coronal holes.Key words. Interplanetary physics (solar wind plasma) – Radio science (remote sensing)
The charge-exchange induced coupling between plasma-gas counterflows in the heliosheath
Authors: Fahr H. J.
Published: June 2010

Abstract. Many hydrodynamic models have been presented which give similar views of the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In the more recent of these models it is taken into account that the solar and interstellar hydrodynamic flows of neutral atoms and protons are coupled by mass-, momentum-, and energy-exchange terms due to charge exchange processes. We shall reinvestigate the theoretical basis of this coupling here by use of a simplified description of the heliospheric interface and describe the main physics of the H-atom penetration through the more or less standing well-known plasma wall ahead of the heliopause. Thereby we can show that the type of charge exchange coupling terms used in up-to-now hydrodynamic treatments unavoidably leads to an O-type critical point at the sonic point of the H-atom flow, thus not allowing for a continuation of the integration of the hydrodynamic set of differential equations. The remedy for this problem is given by a more accurate formulation of the momentum exchange term for quasi-and sub-sonic H-atom flows. With a refined momentum exchange term derived from basic kinetic Boltzmann principles, we instead arrive at a characteristic equation with an X-type critical point, allowing for a continuous solution from supersonic to subsonic flow conditions. This necessitates that the often treated problem of the propagation of inter-stellar H-atoms through the heliosheath has to be solved using these newly derived, differently effective plasma – gas friction forces. Substantially different results are to be expected from this context for the filtration efficiency of the heliospheric interface.Key words. Interplanetary physics (heliopause and solar wind termination; interstellar gas) – Ionosphere (plasma temperature and density)
The location and rate of dayside reconnection during an interval of southward interplanetary magnetic field
Authors: Pinnock M. , Chisham G. , Coleman I. J. , Freeman M. P. , Hairston M. , Villain J.-P.
Published: June 2010

Abstract. Using ionospheric data from the SuperDARN radar network and a DMSP satellite we obtain a comprehensive description of the spatial and temporal pattern of day-side reconnection. During a period of southward interplanetary magnetic field (IMF), the data are used to determine the location of the ionospheric projection of the dayside magnetopause reconnection X-line. From the flow of plasma across the projected X-line, we derive the reconnection rate across 7 h of longitude and estimate it for the total length of the X-line footprint, which was found to be 10 h of longitude. Using the Tsyganenko 96 magnetic field model, the ionospheric data are mapped to the magnetopause, in order to provide an estimate of the extent of the reconnection X-line. This is found to be ~ 38 RE in extent, spanning the whole dayside magnetopause from dawn to dusk flank. Our results are compared with previously reported encounters by the Equator-S and Geotail spacecraft with a reconnecting magnetopause, near the dawn flank, for the same period. The SuperDARN observations allow the satellite data to be set in the context of the whole magnetopause reconnection X-line. The total potential associated with dayside reconnection was ~ 150 kV. The reconnection signatures detected by the Equator-S satellite mapped to a region in the ionosphere showing continuous flow across the polar cap boundary, but the reconnection rate was variable and showed a clear spatial variation, with a distinct minimum at 14:00 magnetic local time which was present throughout the 30-min study period.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionoshere interactions) – Space plasma physics (magnetic reconnection)
E-region echo characteristics governed by auroral arc electrodynamics
Authors: Milan S. E. , Sato N. , Lester M. , Murata Y. , Shinkai Y. , Doi H. , Frey H. U. , Saemundsson T.
Published: June 2010

Abstract. Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.Key words. Ionosphere (ionospheric irregularities; electric fields and currents)
Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications
Authors: Bouhram M. , Malingre M. , Jasperse J. R. , Dubouloz N. , Sauvaud J.-A.
Published: June 2010

Abstract. In this paper, we consider major ion energization mechanisms in the dayside cusp/cleft region. This includes transverse ion heating by ion cyclotron resonance (ICR), ion energization through structures of field-aligned electric potential drops, and transverse heating by lower hybrid (LH) waves. First, we present and discuss three typical cusp/cleft crossings associated with one of the first two mechanisms mentioned above. Then, we develop a procedure for finding the altitude dependence of ICR heating for any data set in the high-altitude cusp/cleft under the absence of field-aligned potential drops. This has been accomplished using a large set of numerical simulations from a two-dimensional, steady-state, Monte Carlo, trajectory-based code, as discussed in detail in the first companion paper (Bouhram et al., 2003). The procedure is applied and tested successfully for the first two events, by using patterns of ion moments along the satellite track as constraints. Then, we present a statistical study that uses 25 cusp/cleft crossings associated with steady IMF conditions, where ICR heating is expected to occur alone. It is pointed out that the ICR heating increases gradually versus geocentric distance as s 3.3 ± 1.8 . The inferred values of the wave power and the spectral index associated with the component responsible for ICR heating are lower than those characterizing the broad-band, extremely low-frequency (BBELF) turbulence usually observed in the cusp/cleft. This strengthens the idea that more than one wave-mode is contained in the BBELF turbulence, and only a small fraction of the observed turbulence is responsible for ICR heating. Then, we study the occurrence versus magnetic local time (MLT) of field-aligned potential drops. According to previous statistical studies, such structures are not common in the cusp and tend to be associated with the cleft region. We also discuss the effects of LH heating in the cusp on the observed ion distributions. However, this mechanism turns out to be of less importance than ICR heating.Key words. Magnetospheric physics (Auroral phenomena) – Space plasma physics (charged particle motion and acceleration; wave-particle interactions)
The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data
Authors: Janhunen P. , Olsson A. , Peterson W. K.
Published: June 2010

Abstract. We study the occurrence frequency of upward auroral ion beams as a function of altitude using three years of  Polar/TIMAS ion data combined with 11 years of DE-1/ EICS ion data, in order to reach a complete altitude coverage between 5000 and 30 000 km. The most interesting result is that there is a peak in ion beam occurrence frequency and invariant energy flux and invariant particle flux at ¢ 3 RE radial distance. The peak exists at about the same altitude in both the evening and midnight MLT sectors. No solar cycle effects are found. We suggest that the peak could be due to a preferred altitude of auroral potential structures at ¢ 3 RE . To substantiate the suggestion, we also present a simple Monte Carlo simulation of ion beams. Another result is that the ion beam occurrence frequency and invariant (mapped to ionospheric altitude) energy and particle fluxes increase in the radial distance range 4–6 RE , suggesting that wave heating processes may take place in this altitude range.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) – Space plasma physics (charged particle motion and acceleration)
High-resolution nested model simulations of the climatological circulation in the southeastern Mediterranean Sea
Authors: Brenner S.
Published: June 2010

Abstract. As part of the Mediterranean Forecasting System Pilot Project (MFSPP) we have implemented a high-resolution (2 km horizontal grid, 30 sigma levels) version of the Princeton Ocean Model for the southeastern corner of the Mediterranean Sea. The domain extends 200 km offshore and includes the continental shelf and slope, and part of the open sea. The model is nested in an intermediate resolution (5.5 km grid) model that covers the entire Levantine, Ionian, and Aegean Sea. The nesting is one way so that velocity, temperature, and salinity along the boundaries are interpolated from the relevant intermediate model variables. An integral constraint is applied so that the net mass flux across the open boundaries is identical to the net flux in the intermediate model. The model is integrated for three perpetual years with surface forcing specified from monthly mean climatological wind stress and heat fluxes. The model is stable and spins up within the first year to produce a repeating seasonal cycle throughout the three-year integration period. While there is some internal variability evident in the results, it is clear that, due to the relatively small domain, the results are strongly influenced by the imposed lateral boundary conditions. The results closely follow the simulation of the intermediate model. The main improvement is in the simulation over the narrow shelf region, which is not adequately resolved by the coarser grid model. Comparisons with direct current measurements over the shelf and slope show reasonable agreement despite the limitations of the climatological forcing. The model correctly simulates the direction and the typical speeds of the flow over the shelf and slope, but has difficulty properly re-producing the seasonal cycle in the speed.Key words. Oceanography: general (continental shelf processes; numerical modelling; ocean prediction)
A singular evolutive extended Kalman filter to assimilate real in situ data in a 1-D marine ecosystem model
Authors: Hoteit I. , Triantafyllou G. , Petihakis G. , Allen J. I.
Published: June 2010

Abstract. A singular evolutive extended Kalman (SEEK) filter is used to assimilate real in situ data in a water column marine ecosystem model. The biogeochemistry of the ecosystem is described by the European Regional Sea Ecosystem Model (ERSEM), while the physical forcing is described by the Princeton Ocean Model (POM). In the SEEK filter, the error statistics are parameterized by means of a suitable basis of empirical orthogonal functions (EOFs). The purpose of this contribution is to track the possibility of using data assimilation techniques for state estimation in marine ecosystem models. In the experiments, real oxygen and nitrate data are used and the results evaluated against independent chlorophyll data. These data were collected from an offshore station at three different depths for the needs of the MFSPP project. The assimilation results show a continuous decrease in the estimation error and a clear improvement in the model behavior. Key words. Oceanography: general (ocean prediction; numerical modelling) – Oceanography: biological and chemical (ecosystems and ecology)