bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatic interaction between Interball-2 and the ambient plasma. 1. Determination of the spacecraft potential from current calculations
Authors: Bouhram M. , Dubouloz N. , Hamelin M. , Grigoriev S. A. , Malingre M. , Torkar K. , Veselov M. V. , Galperin Y. , Hanasz J. , Perraut S. , Schreiber R. , Zinin L. V.
Published: June 2010

Abstract. The Interball-2 spacecraft travels at altitudes extending up to 20 000 km, and becomes positively charged due to the low-plasma densities encountered and the photoemission on its sunlit surface. Therefore, a knowledge of the spacecraft potential Fs is required for correcting accurately thermal ion measurements on Interball-2. The determination of Fs  is based on the balance of currents between escaping photoelectrons and incoming plasma electrons. A three-dimensional model of the potential structure surrounding Interball-2, including a realistic geometry and neglecting the space-charge densities, is used to find, through particle simulations, current-voltage relations of impacting plasma electrons Ie (Fs ) and escaping photoelectrons Iph (Fs ). The inferred relations are compared to analytic relationships in order to quantify the effects of the spacecraft geometry, the ambient magnetic field B0 and the electron temperature Te . We found that the complex geometry has a weak effect on the inferred currents, while the presence of B0 tends to decrease their values. Providing that the photoemission saturation current density Jph0 is known, a relation between Fs and the plasma density Ne can be derived by using the current balance. Since Jph0 is critical to this process, simultaneous measurements of Ne from Z-mode observations in the plasmapause, and data on the potential difference Fs  - Fp  between the spacecraft and an electric probe (p) are used in order to reverse the process. A value Jph0 ~ = 32 µAm-2 is estimated, close to laboratory tests, but less than typical measurements in space. Using this value, Ne and Fs  can be derived systematically from electric field measurements without any additional calculation. These values are needed for correcting the distributions of low-energy ions measured by the Hyperboloid experiment on Interball-2. The effects of the potential structure on ion trajectories reaching Hyperboloid are discussed quantitatively in a companion paper.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)
Electrostatic interaction between Interball-2 and the ambient plasma. 2. Influence on the low energy ion measurements with Hyperboloid
Authors: Hamelin M. , Bouhram M. , Dubouloz N. , Malingre M. , Grigoriev S. A. , Zinin L. V.
Published: June 2010

Abstract. The measurement of the thermal ion distributions in space is always strongly influenced by the ion motion through the complex 3D electrostatic potential structure built around a charged spacecraft. In this work, we study the related aberrations of the ion distribution detected on board, with special application to the case of the Hyperboloid instrument borne by the Interball-2 auroral satellite. Most of the time, the Interball-2 high altitude auroral satellite is charged at some non-negligible positive potential with respect to the ambient plasma, as shown in part 1; in consequence, the measurement of magnetospheric low energy ions (< 80 eV) with the Hyperboloid instrument can be disturbed by the complex electric potential environment of the satellite. In the case of positive charging, as in previous experiments, a negative bias is applied to the Hyperboloid structure in order to reduce this effect and to keep as much as possible the opportunity to detect very low energy ions. Then, the ions reaching the Hyperboloid entrance windows would have travelled across a continuous huge electrostatic lens involving various spatial scales from ~ 10 cm (detector radius) to ~ 10 m (satellite antennas). Neglecting space charge effects, we have computed the ion trajectories that are able to reach the Hyperboloid windows within their acceptance angles. There are three main results: (i) for given values of the satellite potential, and for each direction of arrival (each window), we deduced the related energy cutoff; (ii) we found that all ions in the energy channel, including the cutoff, can come from a large range of directions in the unperturbed plasma, especially when the solar panels or antennas act as electrostatic mirrors; (iii) for higher energy channels, the disturbances are reduced to small angular shifts. Biasing of the aperture is not very effective with the Hyperboloid instrument (as on previous missions with instruments installed close to the spacecraft body) because the potential environment is driven by effects from the spacecraft. Our results are used to explain some unexpected features of the low energy ion measurements, especially during polar wind events recorded by Hyperboloid. In conclusion, knowing the satellite potential from IESP measurements, we were able to reject any low energy doubtful data and to perform angular corrections for all higher energy ion data. Then the selected and corrected data are a reliable basis for interpretation and estimation of the thermal ion distributions.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)
HF radar polar patch formation revisited: summer and winter variations in dayside plasma structuring
Authors: Milan S. E. , Lester M. , Yeoman T. K.
Published: June 2010

Abstract. Three intervals of polar patch formation, as observed by the CUTLASS Finland HF coherent radar, are presented. Simultaneous observations from a vertical ionosonde located at Longyearbyen on Svalbard, situated in the dayside convection throat region, allow for F-region plasma structuring, leading to polar cap patch formation to be determined. Solar wind and interplanetary magnetic field (IMF) precursors of polar patch formation are investigated with MFI and SWE measurements from the Wind spacecraft. We find that in the cases studied polar cap patches are formed in response to changes in the orientation of the IMF, especially in the By component. The resultant changes in the dayside convection pattern alter the source of plasma drifting through the convection throat region into the polar cap. When the convection flow is directed predominantly polewards, high density sub-auroral or mid-latitude plasma enters the polar cap; when flow is directed zonally, low density plasma entrained in the convection return flow replaces it. This mechanism can act to significantly structure the plasma density at sub-auroral or mid-latitudes as well as in the polar cap. In winter months, polar patches appear to be produced by depletions in an otherwise high plasma density tongue of ionisation. In summer months, patches are enhancements of an otherwise low density tongue of ionisation.Key words. Ionosphere (ionospheric irregularities; plasma convection; polar ionosphere)
Ozone generation over the Indian Ocean during the South African biomass-burning period: case study of October 1992.
Authors: Taupin F. G. , Beekmann M. , Brémaud P. J. , Randriambelo T.
Published: June 2010

Abstract. In this study, we present an estimation of photochemical ozone production during free tropospheric transport between the African biomass burning area and Reunion Island (Indian Ocean) by means of trajectory-chemistry model calculations. Indeed, enhanced ozone concentrations (80–100 ppbv) between 5 and 8 km height over Reunion Island are encountered during September–October when African biomass burning is active. The measurements performed during flight 10 of the TRACE-A campaign (October 6, 1992) have been used to initialise the lagrangian trajectory-chemistry model and several chemical forward trajectories, which reach the area of Reunion Island some days later, are calculated. We show that the ozone burden already present in the middle and upper troposphere over Southern Africa, formed from biomass burning emissions, is further enhanced by photochemical production over the Indian Ocean at the rate of 2.5 - 3 ppbv/day. The paper presents sensitivity studies of how these photochemical ozone production rates depend on initial conditions. The rates are also compared to those obtained by other studies over the Atlantic Ocean. The importance of our results for the regional ozone budget over the Indian Ocean is briefly discussed.Key words. Atmospheric composition and structure (evolution of the atmosphere; troposphere – composition and chemistry); meterorology and atmospheric dynamics (tropical meteorology)
Measurements and estimation of the columnar optical depth of tropospheric aerosols in the UV spectral region
Authors: Cachorro V. E. , Vergaz R. , Martin M. J. , de Frutos A. M. , Vilaplana J. M. , de la Morena B.
Published: June 2010

Abstract. We report values of the columnar tropospheric aerosol optical depth at UV wavelengths based on experimental measurements of the direct spectral irradiances carried out by a commercial spectroradiometer (Li1800 of Licor company) covering the range from 300–1100 nm at two stations with different climate characteristics in Spain. The first station is located in a rural site in north central Spain with continental climate. The data extend from March to the end of October of 1995. The other station is a coastal site in the Gulf of Cádiz (southwest Spain) of maritime climate type. This study is mainly focused on the capability of estimating aerosol optical depth values in the UV region based on the extracted information in the visible and near infrared ranges. A first method has been used based on the Ångström turbidity parameters. However, since this method requires detailed spectral information, a second method has also been used, based on the correlation between wavelengths. A correlation has been established between the experimental aerosol optical depth values at 350 nm and 500 nm wavelengths. Although the type of aerosol seems to be the key factor that determines the quality of these estimations, the evaluation of the associated error is necessary to know the behaviour of these estimations in each area of study.Key words. Atmospheric composition and structure (aerosols and particles; transmission and scattering of radiation; troposphere – composition and chemistry)
The relationship between the Sahelian and previous 2nd Guinean rainy seasons: a monsoon regulation by soil wetness?
Authors: Philippon N. , Fontaine B.
Published: June 2010

Abstract. The correlation of 0.61 found between observed July–September Sahelian rainfall in year 0 and September–November Guinean rainfall in year - 1, led us to explore the statistical relationships between precipitation, soil moisture and near surface Moist Static Energy (MSE) gradients in West Africa. These analyses were performed over successive 30-year periods and specifically, the most recent period between 1968–1998. It is shown from observations, National Centers for Environmental Predictions and National Center for Atmospheric Research (NCEP/NCAR) reanalyses and from the Global Soil Wetness Project (GSWP) database, that wet Sahelian rainy seasons are preceded by abnormally wet soils over the Sudan-Guinean belt during northern winter. Such moisture anomalies tend to hold during the dry season, then generate increasing MSE gradients just above the continent by March–April. These gradients have been shown to be of prime importance for monsoon dynamics and associated rainfall.Key words. Hydrology (soil moisture) – Meteorology and atmospheric dynamics (climatology)
Aeronomy, a 20th Century emergent science: the role of solar Lyman series
Authors: Kockarts G.
Published: June 2010

Abstract. Aeronomy is, by definition, a multidisciplinary science which can be used to study the terrestrial atmosphere, as well as any planetary atmosphere and even the interplanetary space. It was officially recognized in 1954 by the International Union of Geodesy and Geophysics. The major objective of the present paper is to show how aeronomy developed since its infancy. The subject is so large that a guide-line has been chosen to see how aeronomy affects our atmospheric knowledge. This guideline is the solar Lyman alpha radiation which has different effects in the solar system. After a short description of the origins of aeronomy the first observations of this line are summarized since the beginning of the space age. Then the consequences of these observations are analyzed for the physics and chemistry of the neutral terrestrial atmosphere. New chemical processes had to be introduced, as well as new transport phenomena. Solar Lyman alpha also influences the structure of the Earth’s ionosphere, particularly the D-region. In the terrestrial exosphere, solar Lyman alpha scattered resonantly by atomic hydrogen is at present the only way to estimate this constituent in an almost collisionless medium. Since planetary atmospheres also contain atomic hydrogen, the Lyman alpha line has been used to deduce the abundance of this constituent. The same is true for the interplanetary space where Lyman alpha observations can be a good tool to determine the concentration. The last section of the paper presents a question which is intended to stimulate further research in aeronomy.Key words. Atmospheric composition and structure (middle atmosphere – composition and chemistry; thermosphere – composition and chemistry) – history of geophysics (atmospheric sciences)
Seasonal variations of the semi-diurnal and diurnal tides in the MLT: multi-year MF radar observations from 2–70° N, modelled tides (GSWM, CMAM)
Authors: Manson A. H. , Meek C. , Hagan M. , Koshyk J. , Franke S. , Fritts D. , Hall C. , Hocking W. , Igarashi K. , MacDougall J. , Riggin D. , Vincent R.
Published: June 2010

Abstract. In an earlier paper (Manson et al., 1999a) tidal data (1990–1997) from six Medium Frequency Radars (MFR) were compared with the Global Scale Wave Model (GSWM, original 1995 version). The radars are located between the equator and high northern latitudes: Christmas Island (2° N), Hawaii (22° N), Urbana (40° N), London (43° N), Saskatoon (52° N) and Tromsø (70° N). Common harmonic analysis was applied, to ensure consistency of amplitudes and phases in the 75–95 km height range. For the diurnal tide, seasonal agreements between observations and model were excellent while for the semi-diurnal tide the seasonal transitions between clear solstitial states were less well captured by the model. Here the data set is increased by the addition of two locations in the Pacific-North American sector: Yamagawa 31° N, and Wakkanai 45° N. The GSWM model has undergone two additional developments (1998, 2000) to include an improved gravity wave (GW) stress parameterization, background winds from UARS systems and monthly tidal forcing for better characterization of seasonal change. The other model, the Canadian Middle Atmosphere Model (CMAM) which is a General Circulation Model, provides internally generated forcing (due to ozone and water vapour) for the tides. The two GSWM versions show distinct differences, with the 2000 version being either closer to, or further away from, the observations than the original 1995 version. CMAM provides results dependent upon the GW parameterization scheme inserted, but one of the schemes provides very useful tides, especially for the semi-diurnal component.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
The 16-day planetary waves: multi-MF radar observations from the arctic to equator and comparisons with the HRDI measurements and the GSWM modelling results
Authors: Luo Y. , Manson A. H. , Meek C. E. , Meyer C. K. , Burrage M. D. , Fritts D. C. , Hall C. M. , Hocking W. K. , MacDougall J. , Riggin D. M. , Vincent R. A.
Published: June 2010

Abstract. The mesospheric and lower thermospheric (MLT) winds (60–100 km) obtained by multiple MF radars, located from the arctic to equator at Tromsø (70° N, 19° E), Saskatoon (52° N, 107° W), London (43° N, 81° W), Hawaii (21° N, 157° W) and Christmas Island (2° N, 157° W), respectively, are used to study the planetary-scale 16-day waves. Based on the simultaneous observations (1993/1994), the variabilities of the wave amplitudes, periods and phases are derived. At mid- and high-latitude locations the 16-day waves are usually pervasive in the winter-centred seasons (October through March), with the amplitude gradually decreasing with height. From the subtropical location to the equator, the summer wave activities become strong at some particular altitude where the inter-hemisphere wave ducts possibly allow for the leakage of the wave from the other hemispheric winter. The observational results are in good agreement with the theoretical conclusion that, for slowly westward-traveling waves, such as the 16-day wave, vertical propagation is permitted only in an eastward background flow of moderate speed which is present in the winter hemisphere. The wave period also varies with height and time in a range of about 12–24 days. The wave latitudinal differences and the vertical structures are compared with the Global Scale Wave Model (GSWM) for the winter situation. Although their amplitude variations and profiles have a similar tendency, the discrepancies are considerable. For example, the maximum zonal amplitude occurs around 40° N for radar but 30° N for the model. The phase differences between sites due to the latitudinal effect are basically consistent with the model prediction of equatorward phase-propagation. The global 16-day waves at 95 km from the HRDI wind measurements during 1992 through 1995 are also displayed. Again, the wave is a winter dominant phenomenon with strong amplitude around the 40–60° latitude-band on both hemispheres.Key words. Meteorology and atmospheric dynamics – waves and tides – middle atmosphere dynamics – thermospheric dynamics
Instabilities of continuously stratified zonal equatorial jets in a periodic channel model
Authors: Masina S.
Published: June 2010

Abstract. Several numerical experiments are performed in a nonlinear, multi-level periodic channel model centered on the equator with different zonally uniform background flows which resemble the South Equatorial Current (SEC). Analysis of the simulations focuses on identifying stability criteria for a continuously stratified fluid near the equator. A 90 m deep frontal layer is required to destabilize a zonally uniform, 10° wide, westward surface jet that is symmetric about the equator and has a maximum velocity of 100 cm/s. In this case, the phase velocity of the excited unstable waves is very similar to the phase speed of the Tropical Instability Waves (TIWs) observed in the eastern Pacific Ocean. The vertical scale of the baroclinic waves corresponds to the frontal layer depth and their phase speed increases as the vertical shear of the jet is doubled. When the westward surface parabolic jet is made asymmetric about the equator, in order to simulate more realistically the structure of the SEC in the eastern Pacific, two kinds of instability are generated. The oscillations that grow north of the equator have a baroclinic nature, while those generated on and very close to the equator have a barotropic nature.  This study shows that the potential for baroclinic instability in the equatorial region can be as large as at mid-latitudes, if the tendency of isotherms to have a smaller slope for a given zonal velocity, when the Coriolis parameter vanishes, is compensated for by the wind effect.Key words. Oceanography: general (equatorial oceanography; numerical modeling) – Oceanography: physics (fronts and jets)
Evolutions of various solar indices around sunspot maximum and sunspot minimum years
Authors: Kane R. P.
Published: June 2010

Abstract. The smoothed monthly sunspot numbers showed that in many solar cycles, (a) during years around sunspot maxima, there was only one prominent maximum, but in some cycles there was a broad plateau. If the beginning and end of these are termed as first and second maxima (separated by several months), the first maximum was generally the higher one, and the valley in between was very shallow. Solar indices at or near the photosphere generally showed similar structures with maxima matching with sunspot maxima within a month or two. Indices originating in the chromosphere and above showed two peaks in roughly the same months as sunspots (with some exceptions, notably the Coronal green line, and the Total Solar Irradiance). Yet often, the second maximum was larger than the first maximum, and the valley between the two maxima was deeper, as compared to sunspot maxima, and (b) during years around sunspot minima, the smoothed sunspot minimum could be sharp and distinct, lasting for a month or two, or could spread over several months. Among the indices originating at or near the photosphere, the Ca K line intensity showed good matching with sunspots, but the Ca Plage area, the Sunspot Group Area, and the solar magnetic fields seemed to show minima earlier than the sunspots, indicating that these activities died out first. These also showed recoveries from the minima later than sunspots. Most of the other indices originating in the chromosphere and corona attained minima coincident with sunspot minima, but in some cases, minima earlier than sunspots were seen, while in some other cases minima occurred after the sunspot minima. Thus, the energy dissipation in the upper part of the solar atmosphere sometimes lagged or led the evolution of sunspots near sunspot minimum. In a few cases, after the minimum, the indices recovered faster than the sunspots. In general, the chromospheric indices seemed to evolve similar to sunspots, but the evolution of coronal indices was not always similar to sunspots, and may differ considerably between themselves.Key words. Solar physics, astrophysics and astronomy (Corona and transition region; Magnetic fields; Photosphere and chromosphere)
On the incidence of Kelvin-Helmholtz instability for mass exchange process at the Earth’s magnetopause
Authors: Smets R. , Delcourt D. , Chanteur G. , Moore T. E.
Published: June 2010

Abstract. Due to the velocity shear imposed by the solar wind flowing around the magnetosphere, the magnetopause flanks are preferred regions for the development of a Kelvin-Helmholtz instability. Since its efficiency for momentum transfer across the magnetopause has already been established, we investigate its efficiency for mass transfer. Using nonresistive magnetohydrodynamic simulations to describe the magnetic field shape in the instability region, we use test-particle calculations to analyse particle dynamics. We show that the magnetopause thickness and the instability wave-length are too large to lead to nonadiabatic motion of thermal electrons from the magnetosphere. On the other hand, the large mass of H+, He+ and O+ ions leads to such nonadiabatic motion and we thus propose the Kelvin-Helmholtz instability as a mechanism for either magnetospheric ion leakage into the magnetosheath or solar wind ion entry in the magnetosphere. Test-particle calculations are performed in a dimensionless way to discuss the case of each type of ion. The crossing rate is of the order of 10%. This rate is anti-correlated with shear velocity and instability wavelength. It increases with the magnetic shear. The crossing regions at the magnetopause are narrow and localized in the vicinity of the instability wave front. As a Kelvin-Helmholtz instability allows for mass transfer through the magnetopause without any resistivity, we propose it as an alternate process to reconnection for mass transfer through magnetic boundaries. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; MHD waves and instabilities) – Space plasma physics (numerical simulation studies)
Strong sunward propagating flow bursts in the night sector during quiet solar wind conditions: SuperDARN and satellite observations
Authors: Senior C. , Cerisier J.-C. , Rich F. , Lester M. , Parks G. K.
Published: June 2010

Abstract. High-time resolution data from the two Iceland SuperDARN HF radars show very strong nightside convection activity during a prolonged period of low geomagnetic activity and northward interplanetary magnetic field (IMF). Flows bursts with velocities ranging from 0.8 to 1.7 km/s are observed to propagate in the sunward direction with phase velocities up to 1.5 km/s. These bursts occur over several hours of MLT in the 20:00–01:00 MLT sector, in the evening-side sunward convection. Data from a simultaneous DMSP pass and POLAR UVI images show a very contracted polar cap and extended regions of auroral particle precipitation from the magnetospheric boundaries. A DMSP pass over the Iceland-West field-of-view while one of these sporadic bursts of enhanced flow is observed, indicates that the flow bursts appear within the plasma sheet and at its outward edge, which excludes Kelvin-Helmholtz instabilities at the magnetopause boundary as the generation mechanism. In the nightside region, the precipitation is more spot-like and the convection organizes itself as clockwise U-shaped structures. We interpret these flow bursts as the convective transport following plasma injection events from the tail into the night-side ionosphere. We show that during this period, where the IMF clock angle is around 70°, the dayside magnetosphere is not completely closed.Key words. Ionosphere (Auroral ionosphere; Ionospheremagnetosphere interactions; Particle precipitation)
Mean winds of the mesosphere and lower thermosphere at 52° N in the period 1988–2000
Authors: Middleton H. R. , Mitchell N. J. , Muller H. G.
Published: June 2010

Abstract. A meteor radar in the UK (near 52° N) has been used to measure the mean winds of the mesosphere/lower-thermosphere (MLT) region over the period 1988–2000. The seasonal course and interannual variability is characterised and comparisons are made with a number of models. Annual mean wind trends were found to be + 0.37 ms-1 yr-1 for the zonal component and + 0.157 ms-1 yr-1 for the meridional component. Seasonal means revealed significant trends in the case of meridional winds in spring ( + 0.38 ms-1 yr-1) and autumn ( + 0.29 ms-1 yr-1), and zonal winds in summer ( + 0.48 ms-1 yr-1) and autumn ( + 0.38 ms-1 yr-1). Significant correlation coefficients, R, between the sunspot number and seasonal mean wind are found in four instances. In the case of the summer zonal winds, R = + 0.732; for the winter meridional winds, R = - 0.677; for the winter zonal winds, R = - 0.472; and for the autumn zonal winds R = + 0.508.Key words. Meteorology and atmospheric dynamics (climatology; general circulation; middle atmospheric dynamics)
Statistical study of seismic and ground pressure oscillations with steady frequencies in the 0.7–5 h period range
Authors: Karpova N. V. , Petrova L. N. , Shved G. M.
Published: June 2010

Abstract. Product spectra of ground pressure variation and seismic oscillations have been calculated in the period sub-ranges of 42–90 min and 2.5–5 h, based on synchronous, co-located microbarograph and seismograph measurements at St. Petersburg (60° N, 30° E). The 200 records of 2–3.5 days in length and a combined duration of 525 days have been used. The product spectra have been computed for winter, spring, summer, and autumn, both individually and in combination. The spectra of different seasons are distinct from each other for both microbarograph and seismograph measurements; this can be caused by a seasonal variation in both frequency and amplitude of free oscillations of the atmosphere. There are pressure and seismic oscillations with close frequencies in the spectra for both, for each season and when all seasons are combined. At present, suggestions may only be made regarding the origin of most of these common oscillations. Once again, the penetration of the Earth’s free oscillation 0S2 with a period of about 54 min into the atmosphere has been confirmed. A common pressure and seismic oscillation with the 206 min period has been detected and has attracted considerable interest. The 159-min periodicity revealed in pressure variations may be associated with the well-known solar oscillation of the 160.01 min period.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
STRATAQ: A three-dimensional Chemical Transport Model of the stratosphere
Authors: Grassi B. , Redaelli G. , Visconti G.
Published: June 2010

Abstract. A three-dimensional (3-D) Chemical Transport Model (CTM) of the stratosphere has been developed and used for a test study of the evolution of chemical species in the arctic lower stratosphere during winter 1996/97. This particular winter has been chosen for testing the model’s capabilities for its remarkable dynamical situation (very cold and strong polar vortex) along with the availability of sparse chlorine, HNO3 and O3 data, showing also very low O3 values in late March/April. Due to those unusual features, the winter 1996/97 can be considered an excellent example of the impact of both dynamics and heterogeneous reactions on the chemistry of the stratosphere. Model integration has been performed from January to March 1997 and the resulting long-lived and short-lived tracer fields compared with available measurements. The model includes a detailed gas phase chemical scheme and a parameterization of the heterogeneous reactions occurring on liquid aerosol and polar stratospheric cloud (PSC) surfaces. The transport is calculated using a semi-lagrangian flux scheme, forced by meteorological analyses. In such form, the STRATAQ CTM model is suitable for short-term integrations to study transport and chemical evolution related to "real" meteorological situations. Model simulation during the chosen winter shows intense PSC formation, with noticeable local HNO3 capture by PSCs, and the activation of vortex air leading to chlorine production and subsequent O3 destruction. The resulting model fields show generally good agreement with satellite data (MLS and TOMS), although the available observations, due to their limited number and time/space sparse nature, are not enough to effectively constraint the model. In particular, the model seems to perform well in reproducing the rapid processing of air inside the polar vortex on PSC converting reservoir species in active chlorine. In addition, it satisfactorily reproduces the morphology of the continuous O3 decline as shown by the satellite during the investigated period, with a tendency, however, to underestimate the total column values inside the polar vortex during late winter. As possible causes of this model/observation difference we suggest an incorrect estimation of the vertical transport and of the tropospheric contribution.Key words. Atmospheric composition and structure (Middle atmosphere-composition and chemistry) Meterology and atmospheric dynamics (middle atmosphere dynamics)
Some features of stepped and dart-stepped leaders near the ground in natural negative cloud-to-ground lightning discharges
Authors: Qie X. , Yu Y. , Guo C. , Laroche P. , Zhang G. , Zhang Q.
Published: June 2010

Abstract. Characteristics of the electric fields produced by stepped and dart-stepped leaders 200 µs just prior to the return strokes during natural negative cloud-to-ground (CG) lightning discharges have been analyzed by using data from a broad-band slow antenna system with 0.08 µs time resolution in southeastern China. It has been found that the electric field changes between the last stepped leader and the first return stroke could be classified in three categories. The first type is characterized by a small pulse superimposed on the abrupt beginning of the return stroke, and accounts for 42% of all the cases. The second type accounts for 33.3% and is characterized by relatively smooth electric field changes between the last leader pulse and the following return stroke. The third type accounts for 24.7%, and is characterized by small pulses between the last recognizable leader pulse and the following return stroke. On the average, the time interval between the successive leader pulses prior to the first return strokes and subsequent return strokes was 15.8 µs and 9.4 µs, respectively. The distribution of time intervals between successive stepped leader pulses is quite similar to Gaussian distribution while that for dart-stepped leader pulses is more similar to a log-normal distribution. Other discharge features, such as the average time interval between the last leader step and the first return stroke peak, the ratio of the last leader pulse peak to that of the return stroke amplitude are also discussed in the paper.Key words. Meteology and atmospheric dynamics (atmospheric electricity; lightning) – Radio science (electromagnetic noise and interference)
Letter to the Editor Seasonal variations and vertical movement of the tropopause in the UTLS region
Authors: Wang K.-Y. , Shallcross D. E. , Pyle J. A.
Published: June 2010

Abstract. Based on the tracking of the movement of the tropopause over the whole year, the extent/depth of stratosphere-troposphere exchange (STE) events and their seasonal variations is investigated. It is found that a stratospheric signature can be observed at pressures as high as 400 hPa in a hemisphere during its winter to spring period, while a tropospheric signature can be observed at pressures as low as 190 hPa during the hemispheric summer to autumn months. The major implication for such a pronounced vertical movement is that the downward penetration of air from the stratosphere is likely to deposit elevated levels of O3 into the upper troposphere. Though the analysis at 250 hPa reveals that the values of the stratosphere-troposphere index are similar all year round, a result which is consistent with other studies, it is found that an intrusion from the stratosphere to the troposphere is more likely to occur during the hemispheric winter to spring period than other seasons.Key words. Atmospheric composition and structure (pressure, density, and temperature; troposphere–composition and chemistry)
Neural network prediction of relativistic electrons at geosynchronous orbit during the storm recovery phase: effects of recurring substorms
Authors: Fukata M. , Taguchi S. , Okuzawa T. , Obara T.
Published: June 2010

Abstract. During the recovery phase of geomagnetic storms, the flux of relativistic (>2 MeV) electrons at geosynchronous orbits is enhanced. This enhancement reaches a level that can cause devastating damage to instruments on satellites. To predict these temporal variations, we have developed neural network models that predict the flux for the period 1–12 h ahead. The electron-flux data obtained during storms, from the Space Environment Monitor on board a Geostationary Meteorological Satellite, were used to construct the model. Various combinations of the input parameters AL, SAL, Dst and SDst were tested (where S denotes the summation from the time of the minimum Dst). It was found that the model, including SAL as one of the input parameters, can provide some measure of relativistic electron-flux prediction at geosynchronous orbit during the recovery phase. We suggest from this result that the relativistic electron-flux enhancement during the recovery phase is associated with recurring substorms after Dst minimum and their accumulation effect.Key words. Magnetospheric physics (energetic particles, trapped; magnetospheric configuration and dynamics; storms and substorms)
The relativistic electron response in the outer radiation belt during magnetic storms
Authors: Iles R. H. A. , Fazakerley A. N. , Johnstone A. D. , Meredith N. P. , Bühler P.
Published: June 2010

Abstract. The relativistic electron response in the outer radiation belt during magnetic storms has been studied in relation to solar wind and geomagnetic parameters during the first six months of 1995, a period in which there were a number of recurrent fast solar wind streams. The relativistic electron population was measured by instruments on board the two microsatellites, STRV-1a and STRV-1b, which traversed the radiation belt four times per day from L ~ 1 out to L ~ 7 on highly elliptical, near-equatorial orbits. Variations in the E > 750 keV and E > 1 MeV electrons during the main phase and recovery phase of 17 magnetic storms have been compared with the solar wind speed, interplanetary magnetic field z-component, Bz , the solar wind dynamic pressure and Dst *. Three different types of electron responses are identified, with outcomes that strongly depend on the solar wind speed and interplanetary magnetic field orientation during the magnetic storm recovery phase. Observations also confirm that the L-shell, at which the peak enhancement in the electron count rate occurs has a dependence on Dst *.Key words. Magnetospheric physics (energetic particles, trapped; storms and substorms) – Space plasma physics (charged particle motion and accelerations)
Model interpretation of the ionospheric F-region electron density structures observed by ground-based satellite tomography at sub-auroral and auroral latitudes in Russia in January–May 1999
Authors: Namgaladze A. N. , Evstafiev O. V. , Khudukon B. Z. , Namgaladze A. A.
Published: June 2010

Abstract. A satellite tomographic campaign was carried out in Russia during January–May 1999. The receiver chain consisted of four sites extending from the north of Karelia to the north of the Kola Peninsula. The F-region electron density measurements were performed during the main seasons (the winter, equinox and summer), and the data contained typical levels of solar activity (F10.7 varied from 100 to 200). The magnetic activity was quite low (Kp = 2 - 3). The Upper Atmosphere Model (UAM), the theoretical model of the Earth’s atmosphere, as well as two known empirical ionospheric models, IRI-95 and RIM-88, have been applied to compare with experimental data. The tomographic images were interpreted by using simulation results obtained by the models which were also compared to one another. The analysis shows the following: (a) all three models show the best agreement with the tomography data at the height 300 km (near hmF2) in comparison with the heights below and above hmF2 (200 and 400 km); (b) all three models systematically underestimate the electron density values in comparison with the tomography data at the height 200 km and overestimate them at the height 400 km; (c) for all investigated events the Ne (UAM) values are closest to Ne (tomo) in 399 of 1125 examined data points (36%), Ne(RIM-88) values are closest to Ne(tomo) in 510 cases (45%) and Ne (IRI-95) values are closest to Ne (tomo) in 216 cases (19%). For the only day-time events, the Ne (UAM) values are closest to Ne (tomo) in 274 of 624 data points (44%), whereas Ne (RIM-88) day-time values are closest to Ne (tomo) in 221 cases (36%) and closest to Ne (IRI-95) values in 129 cases (20%). It means that for all events RIM-88 has the best agreement with the tomography measured electron densities, whereas UAM has the best agreement with the daytime tomography measured electron densities, and IRI-95 has the worst agreement for both daytime and all events; (d) simulated UAM daytime values of electron density near the F2-layer maximum agree with corresponding tomography images for all seasons for the first half of 1999, covering almost the total range of the solar activity, so that no correction of the solar EUV flux (used as an input parameter in the UAM) is required; (e) a necessary correction of simulated precipitating soft electron flux intensities has to be made, in order to improve the consistency between measured night-time values of the electron density and those estimated by the theoretical model; (f) the simulated electron density behaviour caused by spatial, diurnal, seasonal variations, as well as due to a solar activity is consistent with the experimental tomographic images. This indicates a good reliability of both experimental and simulated data (at least in the central part of the examined latitudinal interval).Key words. Ionosphere (auroral ionosphere; modeling and forecasting)
Verification of the backward wave oscillator model of VLF chorus generation using data from MAGION 5 satellite
Authors: Titova E. E. , Kozelov B. V. , Jiriček F. , Smilauer J. , Demekhov A. G. , Trakhtengerts V. Yu.
Published: June 2010

Abstract. We present a detailed study of chorus emissions in the magnetosphere detected on board Magion 5, when the satellite was not far from the magnetic equator. We determine the frequency sweep rate of more than 8500 electromagnetic VLF chorus elements. These results are compared with the backward wave oscillator (BWO) regime of chorus generation. Comparison of the frequency sweep rate with the BWO model shows: (i) There is a correlation between the frequency sweep rates and the chorus amplitudes. The frequency sweep rate increases with chorus amplitude, in accordance with expectations from the BWO model; (ii) The chorus growth rate, estimated from the frequency sweep rate, is in accord with that inferred from the BWO generation mechanism; (iii) The BWO regime of chorus generation ensures the observed decrease in the frequency sweep rate of the chorus elements with increasing L-shell.Key words. Magnetospheric physics (VLF emissions, energetic particles) – Space plasma physics (wave-particle interactions)
Predictability of geomagnetic series
Authors: Bellanger E. , Kossobokov V. G. , Le Mouël J.-L.
Published: June 2010

Abstract. The aim of this paper is to lead a practical, rational and rigorous approach concerning what can be done, based on the knowledge of magnetic series, in the field of prediction of the extreme geomagnetic events. We compare the magnetic vector differential at different locations computed with different resolutions, from an entire day to minutes. We study the classical correlations and the simplest possible prediction scheme to conclude a high level of predictability of the magnetic vector variation. The results obtained are far from a random guessing: the error diagrams are either comparable with earthquake prediction studies or out-perform them when the minute sampling is used in accounting for hourly magnetic vector variation. We demonstrate how the magnetic extreme events can be predicted from the hourly value of the magnetic variation with a lead time of several hours. We compute the 2-D empirical distribution of consecutive values of the magnetic vector variation for the estimation of conditional probabilities of different types. The achieved results encourage further development of the approach to prediction of the extreme geomagnetic events.Key words. Ionosphere (modeling and forecasting) – Magnetospheric physics (storms and substorms)
Variations in the polar cap area during two substorm cycles
Authors: Milan S. E. , Lester M. , Cowley S. W. H. , Oksavik K. , Brittnacher M. , Greenwald R. A. , Sofko G. , Villain J.-P.
Published: June 2010

Abstract. This study employs observations from several sources to determine the location of the polar cap boundary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral images from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the magnetosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, allowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and decreases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to decrease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap boundary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times supports this finding.Key words. Ionosphere (plasma convection; polar ionosphere) – Magnetospheric physics (magnetospheric configuration and dynamics)
Collisional Rayleigh-Taylor instability and shear-flow in equatorial Spread-F plasma
Authors: Chakrabarti N. , Lakhina G. S.
Published: June 2010

Abstract. Collisional Rayleigh-Taylor (RT) instability is considered in the bottom side of the equatorial F-region. By a novel nonmodal calculation it is shown that for an applied shear flow in equilibrium, the growth of the instability is considerably reduced. Finite but small amounts of diffusion enhances the stabilization process. The results may be relevant to the observations of long-lived irregularities at the bottom-side of the F-layer.Key words. Ionosphere (ionospheric irregularities, equatorial ionosphere, plasma waves and instabilities)
Ulysses COSPIN observations of cosmic rays and solar energetic particles from the South Pole to the North Pole of the Sun during solar maximum
Authors: McKibben R. B. , Connell J. J. , Lopate C. , Zhang M. , Anglin J. D. , Balogh A. , Dalla S. , Sanderson T. R. , Marsden R. G. , Hofer M. Y. , Kunow H. , Posner A. , Heber B.
Published: June 2010

Abstract. In 2000–2001 Ulysses passed from the south to the north polar regions of the Sun in the inner heliosphere, providing a snapshot of the latitudinal structure of cosmic ray modulation and solar energetic particle populations during a period near solar maximum.  Observations from the COSPIN suite of energetic charged particle telescopes show that latitude variations in the cosmic ray intensity in the inner heliosphere are nearly non-existent near solar maximum, whereas small but clear latitude gradients were observed during the similar phase of Ulysses’ orbit near the 1994–95 solar minimum. At proton energies above ~10 MeV and extending up to >70 MeV, the intensities are often dominated by Solar Energetic Particles (SEPs) accelerated near the Sun in association with intense solar flares and large Coronal Mass Ejections (CMEs). At lower energies the particle intensities are almost constantly enhanced above background, most likely as a result of a mix of SEPs and particles accelerated by interplanetary shocks. Simultaneous high-latitude Ulysses and near-Earth observations show that most events that produce large flux increases near Earth also produce flux increases at Ulysses, even at the highest latitudes attained. Particle anisotropies during particle onsets at Ulysses are typically directed outwards from the Sun, suggesting either acceleration extending to high latitudes or efficient cross-field propagation somewhere inside the orbit of Ulysses. Both cosmic ray and SEP observations are consistent with highly efficient transport of energetic charged particles between the equatorial and polar regions and across the mean interplanetary magnetic fields in the inner heliosphere.Key words. Interplanetary physics (cosmic rays) – Solar physics, astrophysics and astronomy (energetic particles; flares and mass ejections)