bluuebunny/crossref_metadata_2025 huggingface dataset:
Concerning long-term geomagnetic variations and space climatology
Authors: Glassmeier K.-H. , Vogt J. , Stadelmann A. , Buchert S.
Published: June 2010

Abstract. During geomagnetic polarity transitions the surface magnetic field of the Earth decays to about 25% and less of its present value. This implies a shrinking of the terrestrial magnetosphere and posses the question of whether magnetospheric magnetic field variations scale in the same manner. Furthermore, the geomagnetic main field also controls the magnetospheric magnetic field and space weather conditions. Long-term geomagnetic variations are thus intimately related to space climate. We critically assess existing scaling relations and derive new ones for various magnetospheric parameters. For example, we find that ring current perturbations do not increase with decreasing dipole moment. And we derive a scaling relation for the polar electrojet contribution, indicating a weak increase with increasing internal field. From this we infer that the ratio between external and internal field contributions may be weakly enhanced during polarity transitions. Our scaling relations also provide more insight on the importance of the internal geomagnetic field contribution for space climate.
Evolutionary signatures in complex ejecta and their driven shocks
Authors: Farrugia C. J. , Berdichevsky D. B.
Published: June 2010

Abstract. We examine interplanetary signatures of ejecta-ejecta interactions. To this end, two time intervals of inner-heliospheric (≤1AU) observations separated by 2 solar cycles are chosen where ejecta/magnetic clouds are in the process of interacting to form complex ejecta. At the Sun, both intervals are characterized by many coronal mass ejections (CMEs) and flares. In each case, a complement of observations from various instruments on two spacecraft are examined in order to bring out the in-situ signatures of ejecta-ejecta interactions and their relation to solar observations. In the first interval (April 1979), data are shown from Helios-2 and ISEE-3, separated by ~0.33AU in radial distance and 28° in heliographic longitude. In the second interval (March-April 2001), data from the SOHO and Wind probes are combined, relating effects at the Sun and their manifestations at 1AU on one of Wind's distant prograde orbits. At ~0.67AU, Helios-2 observes two individual ejecta which have merged by the time they are observed at 1AU by ISEE-3. In March 2001, two distinct Halo CMEs (H-CMEs) are observed on SOHO on 28-29 March approaching each other with a relative speed of 500kms-1 within 30 solar radii. In order to isolate signatures of ejecta-ejecta interactions, the two event intervals are compared with expectations for pristine (isolated) ejecta near the last solar minimum, extensive observations on which were given by Berdichevsky et al. (2002). The observations from these two event sequences are then intercompared. In both event sequences, coalescence/merging was accompanied by the following signatures: heating of the plasma, acceleration of the leading ejecta and deceleration of the trailing ejecta, compressed field and plasma in the leading ejecta, disappearance of shocks and the strengthening of shocks driven by the accelerated ejecta. A search for reconnection signatures at the interface between the two ejecta in the March 2001 event was inconclusive because the measured changes in the plasma velocity tangential to the interface (Δνt) were not correlated with Δ(Bt /ρ). This was possibly due to lack of sufficient magnetic shear across the interface. The ejecta mergers altered interplanetary parameters considerably, leading to contrasting geoeffects despite broadly similar solar activity. The complex ejecta on 31 March 2001 caused a double-dip ring current enhancement, resulting in two great storms (Dst, corrected for the effect of magnetopause currents, <-450nT), while the merger on 5 April 1979 produced only a corrected Dst of ~-100nT, mainly due to effects of magnetopause currents.
Solar wind velocity at solar maximum: A search for latitudinal effects
Authors: Bavassano B. , D'Amicis R. , Bruno R.
Published: June 2010

Abstract. Observations by Ulysses during its second out-of-ecliptic orbit have shown that near the solar activity maximum the solar wind appears as a highly variable flow at all heliolatitudes. In the present study Ulysses data from polar latitudes are compared to contemporary ACE data in the ecliptic plane to search for the presence of latitudinal effects in the large-scale structure of the solar wind velocity. The investigated period roughly covers the Sun's magnetic polarity reversal. The Ulysses-ACE comparison is performed through a multi-scale statistical analysis of the velocity fluctuations at scales from 1 to 64 days. The results indicate that, from a statistical point of view, the character of the wind velocity structure does not appear to change remarkably with latitude. It is likely that this result is characteristic of the particular phase of the solar magnetic cycle.
Numerical and the MU radar estimations of gravity wave enhancement and turbulent ozone fluxes near the tropopause
Authors: Gavrilov N. M. , Fukao S.
Published: June 2010

Abstract. It is shown with a numerical simulation that a sharp increase in the vertical temperature gradient and Brunt-Väisälä frequency near the tropopause may produce an increase in the amplitudes of internal gravity waves (IGWs) propagating upward from the troposphere, wave breaking and generation of stronger turbulence. This may enhance the transport of admixtures between the troposphere and stratosphere in the middle latitudes. Turbulent diffusion coefficient calculated numerically and measured with the MU radar are of 1-10m2/s in different seasons in Shigaraki, Japan (35° N, 136° E). These values lead to the estimation of vertical ozone flux from the stratosphere to the troposphere of (1-10)x1014, which may substantially add to the usually supposed ozone downward transport with the general atmospheric circulation. Therefore, local enhancements of IGW intensity and turbulence at tropospheric altitudes over mountains due to their orographic excitation and due to other wave sources may lead to the changes in tropospheric and total ozone over different regions.
The atmospheric circulation associated with extreme rainfall events in Piura, Peru, during the 1997--1998 and 2002 El Niño events
Authors: Takahashi K.
Published: June 2010

Abstract. The lowland of Piura, in northwestern Peru, is very strongly impacted by El Niño. Its climate is arid but can experience very heavy rainfall associated with the high nearby sea surface temperature (SST) during El Niño events. Rainfall, however, tends to occur in discrete, intense events and an understanding of the physical conditions favoring a particular day with heavy rainfall over others is of both scientific and practical interest. In this work, we consider the rainy periods of December 1997 to April 1998 and March to April 2002, corresponding to very strong and weak to moderate El Niño conditions, respectively, and search for systematic differences in the atmospheric circulation that may account for the day-to-day variability of rainfall in Piura. Composites of vertical profiles of winds measured by wind profiling radars in Piura, as well as composites of NCEP/NCAR Reanalysis wind fields, suggest that rainy days are associated with an enhanced onshore westerly low-level flow, which may help the triggering of convection by orographic lifting over the western slope of the Andes. Synoptic control was evident in the rainfall record for 1997-1998 but was not as clear in that of 2002. However, in both periods of study the low-level flow over Piura, which we found to be important for the triggering of rainfall, was modulated by tropical synoptic scale disturbances. The structures of the composited wind differences suggest that they may be related to equatorially trapped tropospheric waves, particularly Kelvin and n=1 Rossby waves.
Vertical velocity and turbulence aspects during Mistral events as observed by UHF wind profilers
Authors: Caccia J.-L. , Guénard V. , Benech B. , Campistron B. , Drobinski P.
Published: June 2010

Abstract. The general purpose of this paper is to experimentally study mesoscale dynamical aspects of the Mistral in the coastal area located at the exit of the Rhône-valley. The Mistral is a northerly low-level flow blowing in southern France along the Rhône-valley axis, located between the French Alps and the Massif Central, towards the Mediterranean Sea. The experimental data are obtained by UHF wind profilers deployed during two major field campaigns, MAP (Mesoscale Alpine Program) in autumn 1999, and ESCOMPTE (Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transports d'Emission) in summer 2001. Thanks to the use of the time evolution of the vertical profile of the horizontal wind vector, recent works have shown that the dynamics of the Mistral is highly dependent on the season because of the occurrence of specific synoptic patterns. In addition, during summer, thermal forcing leads to a combination of sea breeze with Mistral and weaker Mistral due to the enhanced friction while, during autumn, absence of convective turbulence leads to substantial acceleration as low-level jets are generated in the stably stratified planetary boundary layer. At the exit of the Rhône valley, the gap flow dynamics dominates, whereas at the lee of the Alps, the dynamics is driven by the relative contribution of "flow around" and "flow over" mechanisms, upstream of the Alps. This paper analyses vertical velocity and turbulence, i.e. turbulent dissipation rate, with data obtained by the same UHF wind profilers during the same Mistral events. In autumn, the motions are found to be globally and significantly subsident, which is coherent for a dry, cold and stable flow approaching the sea, and the turbulence is found to be of pure dynamical origin (wind shears and mountain/lee wave breaking), which is coherent with non-convective situations. In summer, due to the ground heating and to the interactions with thermal circulation, the vertical motions are less pronounced and no longer have systematic subsident charateristics. In addition, those vertical motions are found to be much less developed during the nighttimes because of the stabilization of the nocturnal planetary boundary layer due to a ground cooling. The enhanced turbulent dissipation-rate values found at lower levels during the afternoons of weak Mistral cases are consistent with the installation of the summer convective boundary layer and show that, as expected in weaker Mistral events, the convection is the preponderant factor for the turbulence generation. On the other hand, for stronger cases, such a convective boundary layer installation is perturbed by the Mistral.
The effect of precipitation on wind-profiler clear air returns
Authors: McDonald A. J. , Carey-Smith T. K. , Hooper D. A. , Fraser G. J. , Lublow B. P.
Published: June 2010

Abstract. A small number of studies have indicated that reductions in the signal strength of clear air returns can be observed at low altitudes in regions of precipitation. This study uses data from the NERC MST radar facility in Aberystwyth (52.4° N, 4.1° W) and co-located tipping bucket rain gauge data to determine whether this effect can be observed for all periods where high rainfall rates were observed at the ground. The period selected for examination includes all of the days where a peak rainfall rate of 6mm h-1 was exceeded in 2001. A statistical examination of VHF radar signal power during periods with and without surface rainfall suggests that the returned power is reduced by the presence of precipitating clouds. The corrected spectral width of the Doppler spectra is also significantly wider during periods of precipitation. The process which causes the decrease in the VHF signal power seems to be associated with a reduction in Fresnel reflection within precipitating clouds. This, in turn, may be due to a reduction of humidity gradients in clouds. UHF wind profiler data is also used to show that there is a relationship between enhanced UHF returns (signifying precipitation) and reduced VHF returns. To clarify the processes and effects observed we examine three case studies which show typical relationships between the VHF signal power and surface rainfall or enhanced UHF signal-to-noise ratios. The effect of precipitation on the signal processing scheme's derivation of signal power and spectral width is explored using individual Doppler spectra.
Multitaper spectral analysis of atmospheric radar signals
Authors: Anandan V. K. , Pan C. J. , Rajalakshmi T. , Ramachandra Reddy G.
Published: June 2010

Abstract. Multitaper spectral analysis using sinusoidal taper has been carried out on the backscattered signals received from the troposphere and lower stratosphere by the Gadanki Mesosphere-Stratosphere-Troposphere (MST) radar under various conditions of the signal-to-noise ratio. Comparison of study is made with sinusoidal taper of the order of three and single tapers of Hanning and rectangular tapers, to understand the relative merits of processing under the scheme. Power spectra plots show that echoes are better identified in the case of multitaper estimation, especially in the region of a weak signal-to-noise ratio. Further analysis is carried out to obtain three lower order moments from three estimation techniques. The results show that multitaper analysis gives a better signal-to-noise ratio or higher detectability. The spectral analysis through multitaper and single tapers is subjected to study of consistency in measurements. Results show that the multitaper estimate is better consistent in Doppler measurements compared to single taper estimates. Doppler width measurements with different approaches were studied and the results show that the estimation was better in the multitaper technique in terms of temporal resolution and estimation accuracy.
Surface winds in the Euro-Mediterranean area: the real resolution of numerical grids
Authors: Chèruy F. , Speranza A. , Sutera A. , Tartaglione N.
Published: June 2010

Abstract. Surface wind is a variable of great importance in forcing marine waves and circulations, modulating surface fluxes, etc. Surface wind defined on numerical grids is currently used in forecast-analysis, as well as in climatology. Gridded fields, however, suffer for systematic errors associated with the numerical procedures adopted in computing them. In this paper the climatology of surface wind produced by three different numerical models in the European-Mediterranean area is analyzed. The systematic loss of power at the smallest grid-scales appears in the power spectrum of all the different models. Some prototype numerical integrations show that this systematic over-smoothing is due to numerical stabilization operators that represent the main source of the diagnosed error; the error progression in space and time is also analyzed. Key words. Meteorology and atmospheric dynamics (Mesoscale meteorology; Ocean-atmosphere interaction; Climatology)
Variations of the ionospheric electron density during the Bhuj seismic event
Authors: Trigunait A. , Parrot M. , Pulinets S. , Li F.
Published: June 2010

Abstract. Ionospheric perturbations by natural geophysical activity, such as volcanic eruptions and earthquakes, have been studied since the great Alaskan earthquake in 1964. Measurements made from the ground show a variation of the critical frequency of the ionosphere layers before and after the shock. In this paper, we present an experimental investigation of the electron density variations around the time of the Bhuj earthquake in Gujarat, India. Several experiments have been used to survey the ionosphere. Measurements of fluctuations in the integrated electron density or TEC (Total Electron Content) between three satellites (TOPEX-POSEIDON, SPOT2, SPOT4) and the ground have been done using the DORIS beacons. TEC has been also evaluated from a ground-based station using GPS satellites, and finally, ionospheric data from a classical ionospheric sounder located close to the earthquake epicenter are utilized. Anomalous electron density variations are detected both in day and night times before the quake. The generation mechanism of these perturbations is explained by a modification of the electric field in the global electric circuit induced during the earthquake preparation. Key words. Ionosphere (ionospheric disturbances) – Radio Science (ionospheric physics) – History of geophysics (seismology)
Radial dependence of foreshock cavities: a case study
Authors: Sibeck D. G. , Kudela K. , Mukai T. , Nemecek Z. , Safrankova J.
Published: June 2010

Abstract. We present a case study of Geotail, Interball-1, IMP-8, and Wind observations of density and magnetic field strength cavities excavated by the enhanced pressures associated with bursts of energetic ions in the foreshock. Consistent with theoretical predictions, the pressure of the energetic ions diminishes rapidly with upstream distance due to a decrease in the flux of energetic ions and a transition from near-isotropic to streaming pitch angle distributions. Consequently, the cavities can only be observed immediately upstream from the bow shock. A comparison of conditions upstream from the pre- and post-noon bow shock demonstrates that foreshock cavities introduce perturbations into the oncoming solar wind flow with dimensions smaller than those of the magnetosphere. Dayside geosynchronous magnetic field strength variations observed by GOES-8 do not track the density variations seen by any of the spacecraft upstream from the bow shock in a one-to-one manner, indicating that none of these spacecraft observed the precise sequence of density variations that actually struck the subsolar magnetopause. Key words. Interplanetary physics (energetic particles; planetary bow shocks) – Magnetospheric physics (solar wind-magnetosphere interactions)
Thinning and expansion of the substorm plasma sheet: Cluster PEACE timing analysis
Authors: Dewhurst J. P. , Owen C. J. , Fazakerley A. N. , Balogh A.
Published: June 2010

Abstract. The storage and subsequent removal of magnetic flux in the magnetotail during a geomagnetic substorm has a dramatic effect on the thickness of the cross-tail plasma sheet. The near-Earth plasma sheet is thought to thin during the growth phase and then rapidly expand after onset of the substorm. The direction of propagation, whether earthward or tailward along the GSM-X direction in the near-Earth tail, may suggest the time ordering of current-disruption and near-Earth reconnection, both of which are key to the substorm process. Cluster's Plasma Electron And Current Experiment (PEACE) allows 4-point observations of electrons at the plasma sheet - lobe boundary as this interface passes over the Cluster tetrahedron. The relative timings of the boundary passage at each spacecraft allow a determination of this boundary's speed and direction of motion, assuming this is planar on the scale of the Cluster separation scale. For those boundaries corresponding to the expansion of the plasma sheet, this direction is fundamental to determining the direction of expansion. We present an example of isolated thinning and expansion of the plasma sheet, as well as a multiple thinning-expansion event that occurs during a more active substorm. Data from the 2001 and 2002 tail passes have been analysed and the average plasma sheet – lobe boundary normal vectors and normal component velocities have been calculated. A total of 77 crossings, typically between 10 and 20 RE downtail, correspond to substorm associated expansion of the plasma sheet over the spacecraft. These had normal vectors predominantly in the GSM-YZ plane and provided no clear evidence for the formation of the near-Earth neutral line occurring before current disruption or vice versa. The expansions of the plasma sheet generally exhibit the appropriate GSM-Z direction expected for the given lobe, and tend to have GSM-Y components that support onset occurring near the origin of the GSM-YZ plane. This result is noteworthy in that it indicates a homogeneous plasma sheet expansion. These expansions have an average velocity along their normal of 60±37kms–1. Conversely we find an average thinning velocity of 43±32kms–1 from 66 substorm-associated thinnings. The normal vectors of the thinning plasma sheet vary considerably in the GSM-YZ plane across the entire magnetotail, suggesting that more complex dynamics govern this process.Key words. Magnetospheric physics (Magnetotail; Plasma sheet; Storms and substorms)bk\\rasphone.
Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes
Authors: Ritter P. , Lühr H. , Viljanen A. , Amm O. , Pulkkinen A. , Sillanpää I.
Published: June 2010

Abstract. One important contribution to the magnetic field measured at satellite altitude and at ground level comes from the external currents. We used the total field data sampled by the Overhauser Magnetometer on CHAMP and the horizontal magnetic field measurements of the IMAGE ground-based magnetometer network to study the ionospheric Hall current system in the auroral regions. For the CHAMP data a current model consisting of a series of lines and placed at a height of 110km is fitted to the magnetic field signature sampled on the passage across the polar region. The derived current distributions depend, among others, on season and on the local time of the satellite track. At dawn/dusk the auroral electrojets can be detected most clearly in the auroral regions. Their intensity and location are evidently correlated with the A E activity index. For a period of almost two years the results obtained from space and the currents determined from ground-based observations are studied. For the full IMAGE station array a newly-developed method of spherical elementary current systems (SECS) is employed to compute the 2-D equivalent current distribution, which gives a detailed picture of an area covering latitudes 60° – 80° N and 10° – 30° E in the auroral region. Generally, the current estimates from satellite and ground are in good agreement. The results of this survey clearly show the average dependence of the auroral electrojet on season and local time. This is particularly true during periods of increased auroral activity. The correlation coefficient of the results is close to one in the region of sizeable ionospheric current densities. Also the ratio of the current densities, as determined from above and below the ionosphere, is close to unity. It is the first time that the method of Hall current estimate from a satellite has been validated quantitatively by ground-based observations. Among others, this result is of interest for magnetic main field modelling, since it demonstrates that ground-based observations can be used to predict electrojet signatures in satellite magnetic field scalar data. Key words. Ionosphere (auroral Ionosphere; electric fields and currents; ionosphere-magnetosphere interactions)
Interplanetary magnetic field control of dayside transient event occurrence and motion in the ionosphere and magnetosphere
Authors: Korotova G. I. , Sibeck D. G. , Singer H. J. , Rosenberg T. J. , Engebretson M. J.
Published: June 2010

Abstract. The pressure pulse model for dayside transient ionospheric events predicts dawnward moving events at and prior to local noon during periods of spiral interplanetary magnetic field (IMF) orientation, but duskward moving events at and after local noon during rarer periods of orthospiral IMF orientation. We use this model to interpret ground and geosynchronous magnetometer observations of a duskward-moving transient event that occurred on 10 August 1995 during a period of orthospiral IMF orientation.  We then survey geosynchronous GOES-8, 9, and 10 magnetometer observations to determine the directions of motion for 67 isolated magnetic impulse events seen in South Pole magnetograms from 1995-1999. The occurrence patterns and directions of motion inferred from both case and statistical studies are consistent with pressure pulse model predictions. Key words. Interplanetary physics (Interplanetary magnetic fields; discontinuities) – Magnetospheric physics (Magnetosphere-ionosphere interactions)
Identification of broad-band waves above the auroral acceleration region: Cluster observations
Authors: Backrud M. , André M. , Balogh A. , Buchert S. , Cornilleau-Wehrlin N. , Vaivads A.
Published: June 2010

Abstract. We investigate broad-band emissions at frequencies above the ion gyrofrequency on auroral field lines at geocentric distances of about 4.5 Earth radii. Observations by the Cluster satellites are used to study the wave characteristics and to determine the wave modes involved. All events include some bursts of broad-band emissions with a substantial component of the electric field parallel to the geomagnetic field. Studying the polarization of the emissions we find that linear waves in a homogeneous plasma can be used to theoretically describe the observations. The broad-band emissions include short bursts of ion acoustic waves, and longer periods of ion Bernstein and Electrostatic Ion Cyclotron (EIC) waves. All waves occur during the same event within a few seconds, with EIC waves as the most common. Theoretically, there is no sharp limit between these wave modes and they can be described by the same dispersion surface. These emissions are closely associated with low-frequency Alfvén waves, indicating a possible generation mechanism. Key words. Magnetospheric physics (auroral phenomena; electric fields; plasma waves and instabilities)
Plasma depletion layer: the role of the slow mode waves
Authors: Wang Y. L. , Raeder J. , Russell C. T.
Published: June 2010

Abstract. The plasma depletion layer (PDL) is a layer on the sunward side of the magnetopause with lower plasma density and higher magnetic field compared to their corresponding values in the upstream magnetosheath. The depletion layer usually occurs during northward (IMF) conditions with low magnetic shear across the magnetopause. We have previously validated the Raeder global model by comparing the computed formation of a magnetosheath density depletion with in-situ observations. We also have performed a detailed force analysis and found the varying roles that different MHD forces play along the path of a plasma parcel flowing around the magnetopause. That study resulted in a new description of the behavior of magnetosheath magnetic flux tubes which better explains the plasma depletion along a flux tube. The slow mode waves have been observed in the magnetosheath and have been used to explain the formation of the PDL in some of the important PDL models. In this study, we extend our former work by investigating the possible role of the slow mode waves for the formation of the PDL, using global MHD model simulations. We propose a new technique to test where a possible slow mode front may occur in the magnetosheath by comparing the slow mode group velocity with the local flow velocity. We find that the slow mode fronts can exist in certain regions in the magnetosheath under certain solar wind conditions. The existence and location of such fronts clearly depend on the IMF. We do not see from our global simulation results either the sharpening of the slow mode front into a slow mode shock or noticeable changes of the flow and field in the magnetosheath across the slow mode front, which implies that the slow mode front is not likely responsible for the formation of the PDL, at least for the stable solar wind conditions used in these simulations. Also, we do not see the two-layered slow mode structures shown in some observations and proposed in certain PDL models. Instead, we see only a one-layered spatial PDL structure under the stable solar wind conditions used in this study.
The Plasmasphere Boundary Layer
Authors: Carpenter D. L. , Lemaire J.
Published: June 2010

Abstract. As an inner magnetospheric phenomenon the plasmapause region is of interest for a number of reasons, one being the occurrence there of geophysically important interactions between the plasmas of the hot plasma sheet and of the cool plasmasphere. There is a need for a conceptual framework within which to examine and discuss these interactions and their consequences, and we therefore suggest that the plasmapause region be called the Plasmasphere Boundary Layer, or PBL. Such a term has been slow to emerge because of the complexity and variability of the plasma populations that can exist near the plasmapause and because of the variety of criteria used to identify the plasmapause in experimental data. Furthermore, and quite importantly in our view, a substantial obstacle to the consideration of the plasmapause region as a boundary layer has been the longstanding tendency of textbooks on space physics to limit introductory material on the plasmapause phenomenon to zeroth order descriptions in terms of ideal MHD theory, thus implying that the plasmasphere is relatively well understood. A textbook may introduce the concept of shielding of the inner magnetosphere from perturbing convection electric fields, but attention is not usually paid to the variety of physical processes reported to occur in the PBL, such as heating, instabilities, and fast longitudinal flows, processes which must play roles in plasmasphere dynamics in concert with the flow regimes associated with the major dynamo sources of electric fields. We believe that through the use of the PBL concept in future textbook discussions of the plasmasphere and in scientific communications, much progress can be made on longstanding questions about the physics involved in the formation of the plasmapause and in the cycles of erosion and recovery of the plasmasphere. Key words. Magnetospheric physics (plasmasphere; plasma convection; MHD waves and instabilities)
Anomalous nighttime electron temperatures over Millstone Hill: a statistical study
Authors: Lobzin V. V. , Pavlov A. V.
Published: June 2010

Abstract. A statistical study of anomalous nighttime electron temperature enhancements, NETEs, observed on 336 nights during Millstone Hill radar measurements on 730 nights from 1976 to 2001 is carried out. NETEs are most frequent in winter and in autumn. The NETE occurrence has a maximum probability in February and a minimum probability in July. The asymmetry between spring and autumn NETE occurrences is found for NETEs, which are observed during geomagnetially quiet time periods. The calculated value of the NETE occurrence probability is decreased with the solar activity index F10.7 increase. The increase in a 3-h geomagnetic index Kp or the decrease in a 1-h geomagnetic index Dst leads to the increase in the NETE occurrence probability. This tendency is more pronounced for current values of Kp or Dst rather than for delayed ones and becomes more weak with the delay increase. The NETEs are most likely to begin between 19:00 and 20:00 UT. The studied NETEs are characterized by the most typical duration from 1 to 3h with the percentage peak between 1 and 2h. The electron temperature increases are predominately between 100K and 300K. We did not find any relationship between the amplitude and duration of the NETEs studied. It is shown that there is a tendency for the NETE amplitude to increase if the value of Kp or ∣Dst∣ increases. To determine whether there exists a difference between NETEs observed during different solar cycles, we chose the data subsets corresponding to 21 and 22solar cycles and performed the statistical studies for each subset. It was found that, within the errors, the corresponding dependencies are the same for the cycles considered and for the entire data set. Key words. Ionosphere (plasma temperature and density; ionospheric disturbances; modeling and forecasting)
Oscillations in the open solar magnetic flux with a period of 1.68 years: imprint on galactic cosmic rays and implications for heliospheric shielding
Authors: Rouillard A. , Lockwood M.
Published: June 2010

Abstract. An understanding of how the heliosphere modulates galactic cosmic ray (GCR) fluxes and spectra is important, not only for studies of their origin, acceleration and propagation in our galaxy, but also for predicting their effects (on technology and on the Earth's environment and organisms) and for interpreting abundances of cosmogenic isotopes in meteorites and terrestrial reservoirs. In contrast to the early interplanetary measurements, there is growing evidence for a dominant role in GCR shielding of the total open magnetic flux, which emerges from the solar atmosphere and enters the heliosphere. In this paper, we relate a strong 1.68-year oscillation in GCR fluxes to a corresponding oscillation in the open solar magnetic flux and infer cosmic-ray propagation paths confirming the predictions of theories in which drift is important in modulating the cosmic ray flux. Key words. Interplanetary physics (Cosmic rays, Interplanetary magnetic fields)
Variations of thermospheric composition according to AE-C data and CTIP modelling
Authors: Rishbeth H. , Heelis R. A. , Müller-Wodarg I. C. F.
Published: June 2010

Abstract. Data from the Atmospheric Explorer C satellite, taken at middle and low latitudes in 1975-1978, are used to study latitudinal and month-by-month variations of thermospheric composition. The parameter used is the "compositional Ρ-parameter", related to the neutral atomic oxygen/molecular nitrogen concentration ratio. The midlatitude data show strong winter maxima of the atomic/molecular ratio, which account for the "seasonal anomaly" of the ionospheric F2-layer. When the AE-C data are compared with the empirical MSIS model and the computational CTIP ionosphere-thermosphere model, broadly similar features are found, but the AE-C data give a more molecular thermosphere than do the models, especially CTIP. In particular, CTIP badly overestimates the winter/summer change of composition, more so in the south than in the north. The semiannual variations at the equator and in southern latitudes, shown by CTIP and MSIS, appear more weakly in the AE-C data. Magnetic activity produces a more molecular thermosphere at high latitudes, and at mid-latitudes in summer. Key words. Atmospheric composition and structure (thermosphere – composition and chemistry)
Stereo CUTLASS - A new capability for the SuperDARN HF radars
Authors: Lester M. , Chapman P. J. , Cowley S. W. H. , Crooks S. J. , Davies J. A. , Hamadyk P. , McWilliams K. A. , Milan S. E. , Parsons M. J. , Payne D. B. , Thomas E. C. , Thornhill J. D. , Wade N. M. , Yeoman T. K. , Barnes R. J.
Published: June 2010

Abstract. The Super Dual Auroral Radar Network (SuperDARN), which consists of networks of HF radars surrounding the northern and southern poles, has proven to be an extremely successful experimental technique in a wide range of scientific areas. The basic design of the radars, which contributes to SuperDARN, has remained virtually unchanged since the first radar was built in the early 1980s. This paper presents the first results of a significant new development of the basic system. Termed "Stereo", this development involves the addition of a duplicate receive channel and makes use of the spare duty cycle available in the current transmitters. The Stereo system has been implemented on the two radars that form the Co-operative UK Twin Located Auroral Sounding System (CUTLASS), which are the easternmost pair of radars in the Northern Hemisphere SuperDARN chain. Instead of the standard 7 pulse sequence normally employed by the radars, two such pulse sequences are interleaved and transmitted at different frequencies separated by more than 15kHz. This development allows for the radar to run two entirely different experimental modes simultaneously. Here we describe the basic Stereo system and some of the early results. We also identify potential new experiments which could be run with Stereo to complement the existing standard SuperDARN radar. Key words. Ionosphere (ionosphere-magnetosphere interactions; ionospheric irregularities; instruments and techniques)
Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: signatures of boundary layer processes in the cusp
Authors: Oksavik K. , Søraas F. , Moen J. , Pfaff R. , Davies J. A. , Lester M.
Published: June 2010

Abstract. In this paper we discuss counterstreaming electrons, electric field turbulence, HF radar spectral width enhancements, and field-aligned currents in the southward IMF cusp region. Electric field and particle observations from the FAST spacecraft are compared with CUTLASS Finland spectral width enhancements and ground-based optical data from Svalbard during a meridional crossing of the cusp. The observed 630nm rayed arc (Type-1 cusp aurora) is associated with stepped cusp ion signatures. Simultaneous counterstreaming low-energy electrons on open magnetic field lines lead us to propose that such electrons may be an important source for rayed red arcs through pitch angle scattering in collisions with the upper atmosphere. The observed particle precipitation and electric field turbulence are found to be nearly collocated with the equatorward edge of the optical cusp, in a region where CUTLASS Finland also observed enhanced spectral width. The electric field turbulence is observed to extend far poleward of the optical cusp. The broad-band electric field turbulence corresponds to spatial scale lengths down to 5m. Therefore, we suggest that electric field irregularities are directly responsible for the formation of HF radar backscatter targets and may also explain the observed wide spectra. FAST also encountered two narrow highly structured field-aligned current pairs flowing near the edges of cusp ion steps. Key words. Ionosphere (electric fields and currents). Magnetosphere physics (magnetopause, cusp, and boundary layers; auroral phenomena)
Ionospheric control of the magnetosphere: conductance
Authors: Ridley A. J. , Gombosi T. I. , DeZeeuw D. L.
Published: June 2010

Abstract. It is well known that the ionosphere plays a role in determining the global state of the magnetosphere. The ionosphere allows magnetospheric currents to close, thereby allowing magnetospheric convection to occur. The amount of current which can be carried through the ionosphere is mainly determined by the ionospheric conductivity. This paper starts to quantify the nonlinear relationship between the ionospheric conductivity and the global state of the magnetosphere. It is found that the steady-state magnetosphere acts neither as a current nor as a voltage generator; a uniform Hall conductance can influence the potential pattern at low latitudes, but not at high latitude; the EUV generated conductance forces the currents to close in the sunlight, while the potential is large on the nightside; the solar generated Hall conductances cause a large asymmetry between the dawn and dusk potential, which effects the pressure distribution in the magnetosphere; a uniform polar cap potential removes some of this asymmetry; the potential difference between solar minimum and maximum is ∼11%; and the auroral precipitation can be related to the local field-aligned current through an exponential function. Key words. Ionosphere (ionosphere-magnetosphere interactions; modelling and forecasting; polar ionosphere)
Correlation of Pc5 wave power inside and outside themagnetosphere during high speed streams
Authors: Kessel R. L. , Mann I. R. , Fung S. F. , Milling D. K. , O'Connell N.
Published: June 2010

Abstract. We show a clear correlation between the ULF wave power (Pc5 range) inside and outside the Earth's magnetosphere during high speed streams in 1995. We trace fluctuations beginning 200RE upstream using Wind data, to fluctuations just upstream from Earth's bow shock and in the magnetosheath using Geotail data and compare to pulsations on the ground at the Kilpisjarvi ground station. With our 5-month data set we draw the following conclusions. ULF fluctuations in the Pc5 range are found in high speed streams; they are non-Alfvénic at the leading edge and Alfvénic in the central region. Compressional and Alfvénic fluctuations are modulated at the bow shock, some features of the waveforms are preserved in the magnetosheath, but overall turbulence and wave power is enhanced by about a factor of 10. Parallel (compressional) and perpendicular (transverse) power are at comparable levels in the solar wind and magnetosheath, both in the compression region and in the central region of high speed streams. Both the total parallel and perpendicular Pc5 power in the solar wind (and to a lesser extent in the magnetosheath) correlate well with the total Pc5 power of the ground-based H-component magnetic field. ULF fluctuations in the magnetosheath during high speed streams are common at frequencies from 1–4mHz and can coincide with the cavity eigenfrequencies of 1.3, 1.9, 2.6, and 3.4mHz, though other discrete frequencies are also often seen. Key words. Interplanetary physics (MHD waves and turbulence) – Magnetospheric physics (solar wind-magnetosphere interactions; MHD waves and instabilities)
Modelling of the ring current in Saturn's magnetosphere
Authors: Giampieri G. , Dougherty M. K.
Published: June 2010

Abstract. The existence of a ring current inside Saturn's magnetosphere was first suggested by Smith et al. (1980) and Ness et al. (1981, 1982), in order to explain various features in the magnetic field observations from the Pioneer 11 and Voyager 1 and 2 spacecraft. Connerney et al. (1983) formalized the equatorial current model, based on previous modelling work of Jupiter's current sheet and estimated its parameters from the two Voyager data sets. Here, we investigate the model further, by reconsidering the data from the two Voyager spacecraft, as well as including the Pioneer 11 flyby data set. First, we obtain, in closed form, an analytic expression for the magnetic field produced by the ring current. We then fit the model to the external field, that is the difference between the observed field and the internal magnetic field, considering all the available data. In general, through our global fit we obtain more accurate parameters, compared to previous models. We point out differences between the model's parameters for the three flybys, and also investigate possible deviations from the axial and planar symmetries assumed in the model. We conclude that an accurate modelling of the Saturnian disk current will require taking into account both of the temporal variations related to the condition of the magnetosphere, as well as non-axisymmetric contributions due to local time effects. Key words. Magnetospheric physics (current systems; planetary magnetospheres; plasma sheet)
Formation of a strong southward IMF near the solar maximum of cycle 23
Authors: Watari S. , Vandas M. , Watanabe T.
Published: June 2010

Abstract. We analyzed observations of the solar activities and the solar wind parameters associated with large geomagnetic storms near the maximum of solar cycle 23. This analysis showed that strong southward interplanetary magnetic fields (IMFs), formed through interaction between an interplanetary disturbance, and background solar wind or between interplanetary disturbances are an important factor in the occurrence of intense geomagnetic storms. Based on our analysis, we seek to improve our understanding of the physical processes in which large negative Bz's are created which will lead to improving predictions of space weather. Key words. Interplanetary physics (Flare and stream dynamics; Interplanetary magnetic fields; Interplanetary shocks)
Long-term changes in hydrographic conditions in northern Adriatic and its relationship to hydrological and atmospheric processes
Authors: Supić N. , Grbec B. , Vilibić I. , Ivančić I.
Published: June 2010

Abstract. A very long data series (1921–2000) of hydrographic parameters (temperature, salinity and density) collected in surface and bottom layers at a station in the coastal zone in the northeastern Adriatic was analyzed. Seasonal and interannual variability of the three parameters is described on the basis of monthly and yearly averages. The seasonal cycles obtained were found to be typical for the northern Adriatic. Interannual analysis showed that there was no trend in temperature, salinity and density in the region during the interval analyzed. The long-term series of yearly means of hydrographic parameters were related to the long-term series of yearly means of several hydrological/atmospheric parameters using different time lags of between 0 and 4 years. These parameters are surface heat flux gained by insolation Qs computed for Trieste, precipitation P in Trieste, Po River discharge rate R and two atmospheric oscillation indexes, a Mediterranean Oscillation (MO) index and North Atlantic Oscillation (NAO) index. At zero time lag the interannual changes at the surface were found to be significantly related to changes in the Qs and NAO index (temperature) and R (salinity and density). At the same time lag the changes in the bottom were found to be related to the MO index (temperature, salinity and density). Additionally, bottom salinity and density were significantly related to R at a time lag of 1 year. Key words. Oceanography: Physical (air-sea interactions; hydrography)
Location accuracy of long distance VLF lightning locationnetwork
Authors: Rodger C. J. , Brundell J. B. , Dowden R. L. , Thomson N. R.
Published: June 2010

Abstract. An experimental VLF WorldWide Lightning Location (WWLL) network is being developed to provide realtime locations of cloud to ground lightning discharges occurring throughout the globe. This network has expanded from a limited number of stations in the Western Pacific to its current state of 11 stations, in most longitude sectors, with additional stations planned in the near future. As part of the initial testing phase of the WWLL the network has operated in a simple mode, sending the station trigger times into a central processing point rather than using the sferic Time of Group Arrival (TOGA). During this initial stage, a significant quantity of lightning location data has been collected, some of which is being applied to research questions. In this paper the operation of the WWLL network is described, and the location accuracy of the pre-TOGA WWLL network is characterised. This is performed by contrasting commercial lightning location data from an Australian network, Kattron, over 2 days in January 2002, with 4 WWLL stations covering the same region. It was found that there were 426 matched lightning events, corresponding to lightning discharges with large lightning return stroke peak currents (mean absolute peak current of ~26kA compared with ~12kA for all Kattron events). By considering the random errors in the difference locations between the matching lightning events, an appropriate Gaussian timing error for the WWLL network of receiving stations is determined, and hence an estimate for the global location errors for the existing 11-station network is found. The "worst-case" global location error for the existing network ranges spatially from 7.5–100km, with the global median being 15km, and the global mean 30km. When the TOGA method is implemented, the station timing errors will decrease, allowing for an increase in the location accuracies. Hence, the location accuracy estimates determined in this paper will be very conservative for the future WWLL network employing the TOGA technique. Key words. Meteorology and atmospheric dynamics (lightning, atmospheric electricity, instruments and techniques)