bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences
Authors: Chakrabarty D. , Sekar R. , Chandra H. , Narayanan R. , Pathan B. M. , Subbarao K. S. V.
Published: June 2010

Abstract. Measurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6° N, 73.7° E, dip lat 19.09° N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00–15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind.Key words. Ionosphere (equatorial ionosphere; ionosphere – atmosphere interactions; ionospheric disturbances)
First observation of one noctilucent cloud by a twin lidar in two different directions
Authors: Baumgarten G. , Lübken F.-J. , Fricke K. H.
Published: June 2010

Abstract. In the early morning hours of 14 July 1999, a noctilucent cloud (NLC) was observed simultaneously by the two branches of a twin lidar system located at the ALOMAR observatory in northern Norway (69° N). The telescopes of the two lidars were pointing vertical (L^) and off the zenith by 30° (L30°). The two lidars detected an enhancement in the altitude profile of backscattered light (relative to the molecular background) for more than 5 h, starting approximately at 01:00 UT. These measurements constitute the detection of one NLC by two lidars under different directions and allow for a detailed study of the morphology of the NLC layer. A cross-correlation analysis of the NLC signals demonstrates that the main structures seen by both lidars are practically identical. This implies that a temporal evolution of the microphysics within the NLC during its drift from one lidar beam to the other is negligible. From the time delay of the NLC structures, a drift velocity of 55–65 m/s is derived which agrees nicely with radar wind measurements. During the observation period, the mean NLC altitude decreases by ~0.5 km/h (=14 cm/s) at both observation volumes. Further-more, the NLC is consistently observed approximately 500 m lower in altitude at L30° compared to L^. Supplementing these data by observations from rocket-borne and ground-based instruments, we show that the general downward progression of the NLC layer through the night, as seen by both lidars, is caused by a combination of particle sedimentation by 4–5 cm/s and a downward directed vertical wind by 9–10 cm/s, whereas a tilt of the layer in drift direction can be excluded.Key words. Atmospheric composition and structure (cloud physics and chemistry; aerosols and particles) Meteorology and atmospheric dynamics (middle atmosphere dynamics)
Observations on Stratospheric-Mesospheric-Thermospheric temperatures using Indian MST radar and co-located LIDAR during Leonid Meteor Shower (LMS)
Authors: Selvamurugan R. , Devasia C. V. , Jain A. R. , Raghava Reddi C. , Rao P. B. , Sridharan R.
Published: June 2010

Abstract. The temporal and height statistics of the occurrence of meteor trails during the Leonid meteor shower revealed the capability of the Indian MST radar to record large numbers of meteor trails. The distribution of radio meteor trails due to a Leonid meteor shower in space and time provided a unique opportunity to construct the height profiles of lower thermospheric temperatures and winds, with good time and height resolution. There was a four-fold increase in the meteor trails observed during the LMS compared to a typical non-shower day. The temperatures were found to be in excellent continuity with the temperature profiles below the radio meteor region derived from the co-located Nd-Yag LIDAR and the maximum height of the temperature profile was extended from the LIDAR to ~110 km. There are, how-ever, some significant differences between the observed profiles and the CIRA-86 model profiles. The first results on the meteor statistics and neutral temperature are presented and discussed below.  Key words. Atmospheric composition and structure (pres-sure, density, and temperature) History of geophysics (at-mospheric sciences) Meteorology and atmospheric dynamics (middle atmosphere dynamics)
Cloud microphysical characteristics versus temperature for three Canadian field projects
Authors: Gultepe I. , Isaac G. A. , Cober S. G.
Published: June 2010

Abstract. The purpose of this study is to better understand how cloud microphysical characteristics such as liquid water content (LWC) and droplet number concentration (Nd) change with temperature (T). The in situ observations were collected during three research projects including: the Radiation, Aerosol, and Cloud Experiment (RACE) which took place over the Bay of Fundy and Central Ontario during August 1995, the First International Regional Arctic Cloud Experiment (FIRE.ACE) which took place in the Arctic Ocean during April 1998, and the Alliance Icing Research Study (AIRS) which took place in the Ontario region during the winter of 1999–2000. The RACE, FIRE.ACE, and AIRS projects represent summer mid-latitude clouds, Arctic clouds, and mid-latitude winter clouds, respectively. A LWC threshold of 0.005 g m-3 was used for this study. Similar to other studies, LWC was observed to decrease with decreasing T. The LWC-T relationship was similar for all projects, although the range of T conditions for each project was substantially different, and the variability of LWC within each project was considerable. Nd also decreased with decreasing T, and a parameterization for Nd versus T is suggested that may be useful for modeling studies.Key words. Atmospheric composition and structure (cloud physics and chemistry) – Meteorology and atmospheric dynamics (climatology; general circulation)
SuperDARN E-region backscatter boundary in the dusk-midnight sector – tracer of equatorward boundary of the auroral oval
Authors: Jayachandran P. T. , Donovan E. F. , MacDougall J. W. , Moorcroft D. R. , St. Maurice J.-P. , Prikryl P.
Published: June 2010

Abstract. We compare the locations of the equatorward boundaries of SuperDARN E-region backscatter and Hb  emissions, focusing on the dusk-midnight sector of the auroral oval where the proton aurora is statistically located equatorward of the discrete electron aurora. We show that, whenever both boundaries can be simultaneously identified, they are coincident. Our result complements earlier studies, which demonstrated the correspondence between the DMSP b2i boundary and both the equatorward boundary of the proton auroral oval (Donovan et al., 2002), and the equatorward boundary of SuperDARN E-region echoes (Jayachandran et al., 2002). Further, our result shows that, provided there is sufficient precipitating proton energy flux, the SuperDARN radars can be used to monitor the equatorward edge of the proton auroral oval.Key words. Ionosphere (auroral ionosphere; particle precipitation; ionospheric irregularities)
A multi-instrument approach to mapping the global dayside merging rate
Authors: Provan G. , Yeoman T. K. , Lester M. , Milan S. E.
Published: June 2010

Abstract. For the first time three different methods have been used to calculate the global merging rate during the same substorm growth phase. The ionospheric plasma drift was monitored by six of the Northern Hemisphere SuperDARN radars, allowing the convection pattern to be studied over 12 h of magnetic local time. The radars observed reconnection signatures on the dayside simultaneously with substorm signatures on the nightside. The three methods to calculate the global merging rate are: (i) the equatorward expansion of radar backscatter on the nightside, which provides an estimate of the rate of polar cap expansion, while upstream WIND measurements gave an estimate of the reconnection electric fields; (ii) the derivation of the dayside boundary normal plasma flow velocity and an estimate of the extent of the ionospheric merging gap, from radar observation of dayside reconnection; (iii) utilizing the map-potential technique to map the high-latitude plasma flow and cross polar cap potential (Ruohoniemi and Baker, 1998), allowing the global dayside merging rate to be calculated. The three methods support an extensive magnetopause X-line length of between 30 ± 12RE and 35 ± 15 RE (assuming a single X-line and constant merging rate). Such close agreement between the different methods of calculation are unexpected, especially as the length of the magnetopause X-line is not well known.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere – ionosphere interactions; solar-wind magnetosphere interactions)
Theoretical simulation of O+ and H+ densities in the Indian low latitude F-region and comparison with observations
Authors: Bhuyan P. K. , Kakoty P. K. , Singh S. B.
Published: June 2010

Abstract. The O+ and H+ ion density distributions in the Indian low latitude F-region, within ± 15° magnetic latitudes, are simulated using a time dependent model developed on the basis of solution of the plasma continuity equation. The simulated ion densities for solar minimum June and December solstices are then compared with ionosonde observations from the period 1959–1979 and measurements made by the Indian SROSS C2 satellite during 1995–1996 at an altitude of ~ 500 km. The simulated O+ density has a minimum around pre-sunrise hours and a maximum during noontime. H+ density is higher at nighttime and lower during the day. The simulations reproduced the well-known equatorial ionization anomaly (EIA) observed in electron density at the peak of the F2-region in the Indian low latitude sector during solar minimum. In situ measurement of O+ density by the SROSS C2, however, showed a single peak of ionization around the equator.Key words. Ionosphere (equatorial ionosphere; modeling and forecasting)
Modelling the effects of the October 1989 solar proton event on mesospheric odd nitrogen using a detailed ion and neutral chemistry model
Authors: Verronen P. T. , Turunen E. , Ulich Th. , Kyrölä E.
Published: June 2010

Abstract. Solar proton events and electron precipitation affect the concentrations of middle atmospheric constituents. Ionization caused by precipitating particles enhances the production of important minor neutral constituents, such as nitric oxide, through reaction chains in which ionic reactions play an important role. The Sodankylä Ion Chemistry model (SIC) has been modified and extended into a detailed ion and neutral chemistry model of the mesosphere. Our steady-state model (containing 55 ion species, 8 neutral species, and several hundred chemical reactions) is used to investigate the effect of the October 1989 solar proton event on odd nitrogen at altitudes between 50–90 km. The modelling results show that the NO concentration is significantly enhanced due to the proton precipitation, reaching 107 –108 cm-3 throughout the mesosphere on the 20 October when the proton forcing was most severe. A comparison between the chemical production channels of odd nitrogen indicates that ion chemical reactions are an important factor in the total odd nitrogen production during intense ionization. The modelled electron concentration for the 23 October is compared with EISCAT incoherent scatter radar measurements and a reasonable agreement is found.Key words. Atmospheric composition and structure (Middle atmosphere – composition and chemistry); Ionosphere (Particle precipitation)
Thermospheric vertical winds in the auroral oval/polar cap region
Authors: Greet P. A. , Innis J. L. , Dyson P. L.
Published: June 2010

Abstract. Thermospheric mean vertical winds from high-resolution Fabry-Perot Spectrometer observations of the l630 nm emission (from ~ 240 km altitude), over a four year interval 1997–2000, from Mawson (67.6° S, 62.9° E, Inv 70.5° S) and Davis (68.6° S, 78.0° E, Inv 74.6° S) are presented. Combining the four years of data shows Mawson mean hourly vertical winds vary between -10 ms-1 and +4 ms-1, while Davis mean hourly vertical winds vary between - 0 ms-1 and +10 ms-1. Mean hourly vertical winds from Mawson show little change with Kp, while at Davis the range of variation increases with increasing geomagnetic activity. Histograms of frequency distributions of such winds, and their variations with Kp and l630 nm emission intensity, are presented and discussed. Variations in mean hourly thermospheric winds and l630 nm emission intensities show at least three significant associations between mean vertical winds and the auroral oval. Mean vertical winds within the auroral oval are smaller than those outside the oval, particularly those in the polar cap. A downward wind associated with entry of the observing region into the auroral oval can be seen in both Mawson and Davis hourly mean vertical winds. Large vertical winds are seen poleward of the auroral oval/polar cap boundary, most significantly upward winds occur within ± 2 hr of magnetic midnight. Under moderately quiet geomagnetic conditions Davis passes through the auroral oval into the polar cap in the evening, but at higher Kp it passes into the polar cap earlier and larger, and more sustained mean vertical winds are observed.Key words. Meteorology and atmospheric dynamics (thermospheric dynamics)
New insights from a nonlocal generalization of the Farley-Buneman instability problem at high latitudes
Authors: Drexler J. , St.-Maurice J.-P. , Chen D. , Moorcroft D. R.
Published: June 2010

Abstract. When their growth rate becomes too small, the E-region Farley-Buneman and gradient-drift instabilities switch from absolute to convective. The neutral density gradient is what gives the instabilities their convective character. At high latitudes, the orientation of the neutral density gradient is close to the geomagnetic field direction. We show that this causes the wave-vector component along the geomagnetic field to increase with time. This in turn leads to wave stabilization, since the increase goes hand-in-hand with an increase in parallel electric fields that ultimately short-circuits the irregularities. We show that from an equivalent point of view, the increase in the parallel wave vector is accompanied by a large upward group velocity that limits the time during which the perturbations are allowed to grow before escaping the unstable region. The goal of the present work is to develop a systematic formalism to account for the propagation and the growth/decay of high-latitude Farley-Buneman and gradient-drift waves through vertical convective effects. We note that our new formalism shies away from a plane wave decomposition along the magnetic field direction. A study of the solution to the resulting nonlinear aspect angle equation shows that, for a host of initial conditions, jump conditions are often triggered in the parallel wave-vector (defined here as the vertical derivative of the phase). When these jump conditions occur, the waves turn into strongly damped ion-acoustic modes, and their evolution is quickly terminated. We have limited this first study to Farley-Buneman modes and to a flow direction parallel to the electron E × B drift. Our initial findings indicate that, irrespective of whether or not a jump in aspect angle is triggered by initial conditions, the largest amplitude modes are usually near the ion-acoustic speed of the medium (although Doppler shifted by the ion motion), unless the growth rates are small, in which case the waves tend to move at the same drift as the ambient electrons.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; plasma waves and instabilities)
The 16-day variation in the mean flow at Grahamstown (33.3° S, 26.5° E)
Authors: Malinga S. B. , Poole L. M. G.
Published: June 2010

Abstract. Data from the Grahamstown (33.3° S, 26.5° E) meteor radar have been used to study the short-term variations of the mean flow at ~ 90 km altitude. The results show considerable variation characterised by a superposition of fluctuations on different planetary time scales. Wavelet multi-resolution and spectral techniques reveal that the quasi-16-day oscillation dominates the wave spectrum in the ~ 2–20-day period range. This quasi-16-day oscillation, which is thought to be related to a similar oscillation in the lower atmosphere, is found to be dominant in winter and the equinoxes. However, it is sometimes significant in summer, which could be due to cross-equatorial ducting and the selective transmissivity of gravity waves.Key words. Meteorology and atmospheric dynamics (waves and tides)
Atmospheric and oceanic dust fluxes in the northeastern tropical Atlantic Ocean: how close a coupling?
Authors: Bory A. , Dulac F. , Moulin C. , Chiapello I. , Newton P. P. , Guelle W. , Lambert C. E. , Bergametti G.
Published: June 2010

Abstract. Atmospheric inputs to the ocean of dust originating from Africa are compared with downward dust flux in the oceanic water column. Atmospheric fluxes were estimated using remote-sensing-derived dust optical thickness and parameters from a transport/deposition model (TM2z). Oceanic fluxes were measured directly over/in two regions of contrasting primary productivity of the northeastern tropical Atlantic (one mesotrophic and one oligotrophic, located at about 500 and 1500 km off Mauritania) underlying the offshore dust plume. In both regions, estimates of annual atmospheric dust inputs to the ocean surface are lower than, but of the same order of magnitude as, oceanic fluxes (49.5 and 8.8 mg.m-2 .d-1 in the mesotrophic and oligotrophic regions). Part of this mismatch may reflect both a general flaw in the dust grain size distribution used in transport models, which likely underestimates large particles, and/or lateral advection to each region of dustier surface waters from upstream, where dust deposition is higher. Higher-frequency temporal coupling between atmospheric and oceanic fluxes seems to be primary-productivity dependent, as hypothesized in previously reported studies.Key words. Atmospheric composition and structure (aerosols and particles; geochemical cycles) Oceanography: biological and chemical (geochemistry)
Transformation and disintegration of strongly nonlinear internal waves by topography in stratified lakes
Authors: Vlasenko V. I. , Hutter K.
Published: June 2010

Abstract. For many lakes the nonlinear transfer of energy from basin-scale internal waves to short-period motions, such as solitary internal waves (SIW) and wave trains, their successive interaction with lake boundaries, as well as over-turning and breaking are important mechanisms for an enhanced mixing of the turbulent benthic boundary layer. In the present paper, the evolution of plane SIWs in a variable depth channel, typical of a lake of variable depth, is considered, with the basis being the Reynolds equations. The vertical fluid stratification, wave amplitudes and bottom parameters are taken close to those observed in Lake Constance, a typical mountain lake. The problem is solved numerically. Three different scenarios of a wave evolution over variable bottom topography are examined. It is found that the basic parameter controlling the mechanism of wave evolution is the ratio of the wave amplitude to the distance from the metalimnion to the bottom d. At sites with a gentle sloping bottom, where d is small, propagating (weak or strong) internal waves adjust to the local ambient conditions and preserve their form. No secondary waves or wave trains arise during wave propagation from the deep part to the shallow water. If the amplitude of the propagating waves is comparable with the distance between the metalimnion and the top of the underwater obstacle ( d ~ 1), nonlinear dispersion plays a key role. A wave approaching the bottom feature splits into a sequence of secondary waves (solitary internal waves and an attached oscillating wave tail). The energy of the SIWs above the underwater obstacle is transmitted in parts from the first baroclinic mode, to the higher modes. Most crucially, when the internal wave propagates from the deep part of a basin to the shallow boundary, a breaking event can arise. The cumulative effects of the nonlinearity lead to a steepening and overturning of the rear wave face over the inclined bottom and to the formation of a turbulent jet propagating upslope. Some time later, after the breaking event, a new stable stratification is formed at the site of wave destruction. The breaking criterion of ISWs is discussed.Key words. Oceanography: general (limnology; numerical modeling) – Oceanography: physical (internal and inertial waves)
Aspect sensitivity measurements of polar mesosphere summer echoes using coherent radar imaging
Authors: Chilson P. B. , Yu T.-Y. , Palmer R. D. , Kirkwood S.
Published: June 2010

Abstract. The Esrange VHF radar (ESRAD), located in northern Sweden (67.88° N, 21.10° E), has been used to investigate polar mesosphere summer echoes (PMSE). During July and August of 1998, coherent radar imaging (CRI) was used to study the dynamic evolution of PMSE with high temporal and spatial resolution. A CRI analysis provides an estimate of the angular brightness distribution within the radar’s probing volume. The brightness distribution is directly related to the radar reflectivity. Consequently, these data are used to investigate the aspect sensitivity of PMSE. In addition to the CRI analysis, the full correlation analysis (FCA) is used to derive estimates of the prevailing three-dimensional wind associated with the observed PMSE. It is shown that regions within the PMSE with enhanced aspect sensitivity have a correspondingly high signal-to-noise ratio (SNR). Although this relationship has been investigated in the past, the present study allows for an estimation of the aspect sensitivity independent of the assumed scattering models and avoids the complications of comparing echo strengths from vertical and off-vertical beams over large horizontal separations, as in the Doppler Beam Swinging (DBS) method. Regions of enhanced aspect sensitivity were additionally shown to correlate with the wave-perturbation induced downward motions of air parcels embedded in the PMSE.Key words. Ionosphere (polar ionosphere) Meteorology and Atmospheric Dynamics (middle atmosphere dynamics) Radio Science (Interferometry)
Synoptic conditions leading to extremely high temperatures in Madrid
Authors: García R. , Prieto L. , Díaz J. , Hernández E. , del Teso T.
Published: June 2010

Abstract. Extremely hot days (EHD) in Madrid have been analysed to determine the synoptic patterns that produce EHDs during the period of 1955–1998. An EHD is defined as a day with maximum temperature higher than 36.5°C, a value which is the threshold for the intense effects on mortatility and it coincides with the 95 percentile of the series. Two different situations have been detected as being responsible for an EHD occurrence, one more dynamical, produced by southern fluxes, and another associated with a stagnation situation over Iberia of a longer duration. Both account for 92% of the total number of days, thus providing an efficient classification framework. A circulation index has been derived to characterise and forecast an EHD occurrence. This paper shows that EHD occur in Madrid during short duration events, and no long heat waves, like those recorded in other cities, are present. Additionally, no clear pattern can be detected in the EHD frequency; the occurrence is tied to changes in the summer location of the Azores high.Key words. Meteorology and atmospheric dynamics (Climatology; synoptic-scale meteorology; general or miscellaneous)
Confluence and redistribution of Atlantic water in the Nansen, Amundsen and Makarov basins
Authors: Schauer U. , Rudels B. , Jones E. P. , Anderson L. G. , Muench R. D. , Björk G. , Swift J. H. , Ivanov V. , Larsson A.-M.
Published: June 2010

Abstract. The waters in the Eurasian Basin are conditioned by the confluence of the boundary flow of warm, saline Fram Strait water and cold low salinity water from the Barents Sea entering through the St. Anna Trough. Hydrographic sections obtained from RV Polarstern during the summer of 1996 (ACSYS 96) across the St. Anna Trough and the Voronin Trough in the northern Kara Sea and across the Nansen, Amundsen and Makarov basins allow for the determination of the water mass properties of the two components and the construction of a qualitative picture of the circulation both within the Eurasian Basin and towards the Canadian Basin. At the confluence north of the Kara Sea, the Fram Strait branch is displaced from the upper to the lower slope and it forms a sharp front to the Barents Sea water at depths between 100 m and greater than 1000 m. This front disintegrates downstream along the basin margin and the two components are largely mixed before the boundary current reaches the Lomonosov Ridge. Away from the continental slope, the presence of interleaving structures coherent over wide distances is consistent with low lateral shear. The return flow along the Nansen Gakkel Ridge, if present at all, seems to be slow and the cold water below a deep mixed layer there indicates that the Fram Strait Atlantic water was not covered with a halocline for about a decade. Anomalous water mass properties in the interior of the Eurasian Basin can be attributed to isolated lenses rather than to baroclinic flow cores. Eddies have probably detached from the front at the confluence and migrated into the interior of the basin. One deep (2500 m) lens of Canadian Basin water, with an anticyclonic eddy signature, must have spilled through a gap of the Lomonosov Ridge. During ACSYS 96, no clear fronts between Eurasian and Canadian intermediate waters, such as those observed further north in 1991 and 1994, were found at the Siberian side of the Lomonosov Ridge. This indicates that the Eurasian Basin waters enter the Canadian Basin not only along the continental slope but they may also cross the Lomonosov Ridge at other topographic irregularities. A decrease in salinity around 1000 m in depth in the Amundsen Basin probably originates from a larger input of fresh water to the Barents Sea. The inherent density changes may affect the flow towards the Canadian Basin.Key words. Oceanography: general (Artic and Antartic oceanography; descriptive and regional oceanography) Oceanography: physical (hydrography)
Interball-tail observations of vertical plasma motions in the magnetotail
Authors: Petrukovich A. A. , Yermolaev Y. I.
Published: June 2010

Abstract. The Interball spacecraft configuration favors, in contrast to previous experiments, investigation of vertical ion flows (GSM Vz ). We use measurements of the CORALL instrument for the statistical study of Vz and Vy plasma flows in the mid-tail plasma sheet. In agreement with the previous observations, the mean Vy was positive on the dusk side and negative on the dawn side. When IMF was southward, the mean Vz consisted of the convection flow towards the equatorial plane ~ 7 km/s and the northward flow ~ 8 km/s. When IMF was northward, both components nearly vanished. The velocity variance was much larger than the mean values. The Vz variance maximized on the dawn flank and was always 15–20% smaller than the Vy one. The Vy variance maximized in the pre-midnight sector closer to the neutral sheet. We conclude that velocity fluctuations are composed with the inherent high-beta plasma turbulence contributing to all components, and the BBF-related activity contributing mainly to Vy in the pre-midnight plasma sheet.Key words. Magnetospheric physics (magnetotail; plasma sheet; plasma convection)
Statistical study of transient plasma structures in magnetotail lobes and plasma sheet boundary layer: Interball-1 observations
Authors: Grigorenko E. E. , Fedorov A. , Zelenyi L. M.
Published: June 2010

Abstract. The present paper is devoted to the statistical study of plasma structures observed at the interface between magnetospheric lobes and the plasma sheet at distances of 15–25 RE . The majority of the registered structures are bursty earthward ion streams with energies about 10–30 keV known as "beamlets". The paper describes the results of beamlet statistical analysis for different interplanetary magnetic fields (IMF), clock-angles and various magnetospheric conditions. It is shown that the energy of beamlets increases monotonously with a distance from the neutral sheet (NS) during slightly southward IMF and quiet magnetospheric conditions. Under these conditions, beamlets are observed up to 5–6 RE over the NS. In contrast, the beamlet energy decreases with increasing distance from the NS if the IMF is northward, and the region of beamlet observation becomes much wider up to 12 RE above the NS. The same (inverse) beamlet energy dependence on the distance from the NS is also registered during active magnetospheric periods. Yet, the plasma structures of various duration with quasi-isotropic ion velocity distributions resembling the plasma of the plasma sheet (PS) were observed in the same region. Statistical study performed for various IMF clock-angles demonstrates the clear difference in the spatial distributions of such plasma structures for two extreme IMF directions. When IMF is primarily northward, PS-like plasma fills the lobe region almost entirely and could be associated with the PS expansions. For primarily southward IMF time intervals, the probability of observing PS-like structures of long duration sharply decreases with the increasing distance from the NS, but PS-like structures of short durations (< 500 s) are distributed almost uniformly up to 12 RE above the NS. This feature cannot be described in terms of the PS flapping motions and requires another explanation. Relevance and limitations of the existing models attempting to explain the generation mechanisms of these transient structures are briefly discussed in the concluding part of the paper.Key words. Magnetospheric physics (magnetotail; magnetotail boundary layers; plasma sheet)
Plasma sheet fast flows and auroral dynamics during substorm: a case study
Authors: Borodkova N. L. , Yahnin A. G. , Liou K. , Sauvaud J.-A. , Fedorov A. O. , Lutsenko V. N. , Nozdrachev M. N. , Lyubchich A. A.
Published: June 2010

Abstract. Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL). It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region) is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs), described by Angelopolous et al. (1992). These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i) tailward/earthward flows were superimposed on a very strong duskward flow, and (ii) wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.Key words. Magnetospheric physics (auroral phenomena; plasma sheet; storms and substorms)
Polarization Jet: characteristics and a model
Authors: Galperin Y. I.
Published: June 2010

Abstract. Recent analysis of the ground-based observations of the Polarization Jet (PJ) effects in the subauroral ionosphere has shown that PJ can rapidly develop in the near-midnight sector near the Harang Discontinuity (HD). Based on these observations, a simple, semi-quantitative theory of the PJ formation and its main characteristics is constructed. According to the model, PJ starts to develop, as proposed by Southwood and Wolf, 1978, due to the penetration of the injected energetic ions to the deeper L-shells in the presence of the westward component of the electric field. The injection near the tip of the HD is assumed here. The initial development stage of the PJ band, considered only qualitatively, is supposed to lead to its inclination inward toward evening with respect to the lines B = const. Within the model proposed, the PJ band, once formed, will be sustained by the continuous charging at its equatorial side, at first, mainly by the newly injected ring current ions, and later by the plasma sheet ions convected inward through the HD. In addition, an important charging of the PJ band occurs at its polar side by energetic electrons drifting eastward. These electrons were either previously on the trapped orbits or convected inward from the plasma sheet, and encounter the PJ polar border. The model semi-quantitatively describes the main features of the PJ events: the typical cross-PJ voltage drop ( ~ 10 kV), the resulting double-sheet current loop feeding the PJ, the recently observed short PJ formation time near midnight ( ~ 10 min or less) accompanied by a fast westward HD displacement, the nearly steady-state PJ location in the evening to midnight MLT sector and width in the ionospheric frame, the bell-shape of the electric field latitude profile, and the long PJ lifetime (up to several hours) - all are in rough accord with observations. Further developments of the model now in progress are briefly described.Key words. Magnetospheric physics (electric fields; magnetosphere-ionosphere interactions; storms and sub-storms)
Particle transport in 3He-rich events: wave-particle interactions and particle anisotropy measurements
Authors: Tsurutani B. T. , Zhang L. D. , Mason G. L. , Lakhina G. S. , Hada T. , Arballo J. K. , Zwickl R. D.
Published: June 2010

Abstract. Energetic particles and MHD waves are studied using simultaneous ISEE-3 data to investigate particle propagation and scattering between the source near the Sun and 1 AU. 3 He-rich events are of particular interest because they are typically low intensity "scatter-free" events. The largest solar proton events are of interest because they have been postulated to generate their own waves through beam instabilities. For 3 He-rich events, simultaneous interplanetary magnetic spectra are measured. The intensity of the interplanetary "fossil" turbulence through which the particles have traversed is found to be at the "quiet" to "intermediate" level of IMF activity. Pitch angle scattering rates and the corresponding particle mean free paths lW - P are calculated using the measured wave intensities, polarizations, and k directions. The values of lW - P are found to be ~ 5 times less than the value of lHe , the latter derived from He intensity and anisotropy time profiles. It is demonstrated by computer simulation that scattering rates through a 90° pitch angle are lower than that of other pitch angles, and that this is a possible explanation for the discrepancy between the lW - P and lHe values. At this time the scattering mechanism(s) is unknown. We suggest a means where a direct comparison between the two l values could be made. Computer simulations indicate that although scattering through 90° is lower, it still occurs. Possibilities are either large pitch angle scattering through resonant interactions, or particle mirroring off of field compression regions. The largest solar proton events are analyzed to investigate the possibilities of local wave generation at 1 AU. In accordance with the results of a previous calculation (Gary et al., 1985) of beam stability, proton beams at 1 AU are found to be marginally stable. No evidence for substantial wave amplitude was found. Locally generated waves, if present, were less than 10-3 nT 2 Hz-1 at the leading proton event edge, where dispersion effects (beaming) are the greatest, and at the point of peak proton flux, where the particle energy flux is the greatest.Key words. Interplanetary physics (energetic particles; MHD waves and turbulence) – Space plasma physics (charged particle motion and acceleration; wave-particle interactions)
Energetic particle observations at the subsolar magnetopause
Authors: Eccles A. A. , Fritz T. A.
Published: June 2010

Abstract. The pitch-angle distributions (PAD) of energetic particles are examined as the ISEE-1 satellite crosses the Earth’s magnetopause near the subsolar point. The investigation focuses on the possible existence of a particular type of distribution that would be associated with a source of energetic particles in the high-latitude magnetosphere. PADs, demonstrating broad, persistent field-aligned fluxes filling a single hemisphere (upper/northern or lower/southern), were observed just sunward of the magnetopause current layer for an extended period of many minutes. These distributions are a direct prediction of a possible source of energetic particles located in the high altitude dayside cusp and we present five examples in detail of the three-dimensional particle distributions to demonstrate their existence. From these results, other possible causes of such PADs are examined.Key words. Magnetospheric physics (energetic particles, precipitating; magnetopause, cusp and boundary layers; magnetospheric configuration and dynamics)
He+ dominance in the plasmasphere during geomagnetically disturbed periods: 1. Observational results
Authors: Denton M. H. , Bailey G. J. , Wilford C. R. , Rodger A. S. , Venkatraman S.
Published: June 2010

Abstract. Observations made by the DMSP F10 satellite during the recovery phase from geomagnetic disturbances in June 1991 show regions of He+ dominance around 830 km altitude at 09:00 MLT. These regions are co-located with a trough in ionisation observed around 55° in the winter hemisphere. Plasma temperature and concentration observations made during the severe geomagnetic storm of 24 March 1991 are used as a case study to determine the effects of geomagnetic disturbances along the orbit of the F10 satellite. Previous explanations for He+ dominance in this trough region relate to the part of the respective flux tubes that is in darkness. Such conditions are not relevant for this study, since the whole of the respective flux tubes are sunlit. A new mechanism is proposed to explain the He+ dominance in the trough region. This mechanism is based on plasma transport and chemical reaction effects in the F-region and topside ionosphere, and on the time scales for such chemical reactions. Flux tubes previously depleted by geomagnetic storm effects refill during the recovery phase from the ionosphere as a result of pressure differences along the flux tubes. Following a geomagnetic disturbance, the He+ ion recovers quickly via the rapid photoionisation of neutral helium, in the F-region and the topside. The recovery of the O+ and H+ ions is less rapid. This is proposed as a result of the respective charge exchange reactions with neutral atomic hydrogen and oxygen. Preliminary model calculations support the proposed mechanism.Key words. Magnetospheric physics (storms and sub-storms, plasmasphere)
Relationship of upflowing ion beams and conics around the dayside cusp/cleft region to the interplanetary conditions
Authors: Miyake W. , Mukai T. , Kaya N.
Published: June 2010

Abstract. The dayside cusp/cleft region is known as a major source of upflowing ionospheric ions to the magnetosphere. Since the ions are supposed to be energized by an input of energy from the dayside magnetospheric boundary region, we examined the possible influence of the interplanetary conditions on dayside ion beams and conics observed by the polar-orbiting Exos-D (Akebono) satellite. We found that both the solar wind velocity and density, as well as IMF By and Bz , affect the occurrence frequency of ion conics. The energy of ion conics also depends on the solar wind velocity, IMF By and Bz . The ion beams around the local noon are not significantly controlled by the interplanetary conditions. The results reveal that ion convection, as well as the energy source, is important to understand the production of dayside ion conics while that of ion beams basically reflects the intensity of local field-aligned currents.Key words. Ionosphere (particle acceleration) – magnetospheric physics (magnetopause, cusp, and boundary layers; magnetosphere ionosphere interaction)
EISCAT Svalbard radar observations of ionospheric signatures of magnetopause reconnection during a changing IMF Bz polarity
Authors: Pryse S. E. , Smith A. M. , Kersley L. , McCrea I. W.
Published: June 2010

Abstract. Observations by the EISCAT Svalbard radar are presented that show the response of the spatial structure of the ionosphere in the dayside cusp region to a rotational trend in the IMF clock angle. Over a period of one hour, the clock angle increased from about 45° to some 150°, moving the likely location of the magnetopause reconnection site from the high-latitude lobe to near the equatorial plane. Increased topside electron temperatures measured by the ESR identified footprints of the reconnection process. Temporal changes in the spatial distribution of the temperature reflected the change from lobe to equatorial reconnection. Discrete spatial enhancements in ion temperature were found resulting from ion-neutral frictional heating in the fast flows where it was likely that field lines were being convected from the reconnection locations. The corresponding electron density structuring is interpreted in terms of the particle precipitation, field-aligned currents and convection flows driven by the IMF.Key words. Ionosphere (ionosphere – magnetosphere interactions; plasma temperature and density; polar ionosphere)
The method of determination of the long-term trends in the F2 region independent of geomagnetic activity
Authors: Danilov A. D.
Published: June 2010

Abstract. A detailed analysis of the f oF2 data at the Sverdlovsk station is performed to answer the question: whether the long-term trends of the F2-layer parameter detected recently are mainly due to the long-term changes in geomagnetic activity during the recent decades. Two methods to derive trends independent of geomagnetic activity are developed. It is found that both methods agree well and give a relative nongeomagnetic trend of about - 0.0015 per year (or an absolute nongeomagnetic trend of about - 0.015 MHz per year). The close relation of foF2 to Ap found by several authors is mainly due to a high correlation between the foF2 deviations from the regression line and year-to-year changes in the Ap index rather than to systematic long-term changes of Ap as has been suggested earlier.Key words. Ionosphere (ionospheric distances; modeling and forecasting)
G condition in the F2 region peak electron density: a statistical study
Authors: Lobzin V. V. , Pavlov A. V.
Published: June 2010

Abstract. We present a study of statistical relationships between the G condition, F1-layer and NmF2 negative disturbance occurrence probabilities and geomagnetic and solar activity indices Kp and F10.7, season, and geomagnetic latitude, busing experimental data acquired by the Ionospheric Digital Database of the National Geophysical Data Center, Boulder, Colorado from 1957 to 1990. It is shown that the dependence of the G condition occurrence probability, yG, on Kp is mainly determined by processes that control the behaviour of the F2 layer with Kp changes. We found that the relationship for log yG versus Kp is very close to the linear one. The G condition occurrence probability decreases from 0.55% to 0.17% as the value of  F10.7 increases from low to middle values, reaches its minimum at the middle solar activity level of F10.7 = 144 – 170, increasing from the minimum value of 0.17% to 0.49% when the F10.7 index increases from the middle solar activity level to F10.7 = 248 – 274. Interhemispheric asymmetry is found for the G condition occurrence probability in the ionosphere, with a stronger enhancement seen in the magnetic latitude range close to the northern magnetic pole and a deep minimum of the G condition occurrence probability in the low magnetic latitude range from – 30° to 30°. The measured magnetic latitude variation of the F1-layer occurrence probability is also asymmetrical relative to the geomagnetic equator. Our results provide additional evidence the F1-layer is more likely to be formed in summer than in winter. The Northern Hemisphere peak F1-layer occurrence probability is found to exceed that in the Southern Hemisphere. The G condition occurrence probability has maximum values of 0.91 and 0.75% in summer, and minimum values of 0.01 and 0.05% in winter for the Northern and Southern Hemisphere, respectively.Key words. Ionosphere; ion chemistry and composition; ionosphere-atmosphere interactions; ionospheric disturbances
Are variations in PMSE intensity affected by energetic particle precipitation?
Authors: Barabash V. , Kirkwood S. , Chilson P. B.
Published: June 2010

Abstract. The correlation between variations in Polar Mesosphere Summer Echoes (PMSE) and variations in energetic particle precipitation is examined. PMSE were observed by the Esrange VHF MST Radar (ESRAD) at 67°53' N, 21°06' E. The 30 MHz riometer in Abisko (68°24' N, 18°54' E) registered radio wave absorption caused by ionization changes in response to energetic particle precipitation. The relationship between the linear PMSE intensity and the square of absorption has been estimated using the Pearson linear correlation and the Spearman rank correlation. The mean diurnal variation of the square of absorption and the linear PMSE intensity are highly correlated. However, their day-to-day variations show significant correlation only during the late evening hours. The correlation in late evening does not exceed 0.6. This indicates that varying ionization cannot be considered as a primary source of varying PMSE, and the high correlation found when mean diurnal variations are compared is likely a by-product of daily variations caused by other factors.Key words. Ionosphere (particle precipitation) Magnetospheric physics (energetic particles, precipitating) Meteorology and atmospheric dynamics (precipitation)