bluuebunny/crossref_metadata_2025 huggingface dataset:
Airborne lidar study of the vertical distribution of aerosols over Hyderabad, an urban site in central India, and its implication for radiative forcing calculations
Authors: Gadhavi H. , Jayaraman A.
Published: June 2010

Abstract. Use of a compact, low power commercial lidar onboard a small aircraft for aerosol studies is demonstrated. A Micro Pulse Lidar fitted upside down in a Beech Superking aircraft is used to measure the vertical distribution of aerosols in and around Hyderabad, an urban location in the central India. Two sorties were made, one on 17 February 2004 evening hours and the other on 18 February 2004 morning hours for a total flight duration of four hours. Three different algorithms, proposed by Klett (1985), Stephens et al. (2001) and Palm et al. (2002) for deriving the aerosol extinction coefficient profile from lidar data are studied and is shown that the results obtained from the three methods compare within 2%. The result obtained from the airborne lidar is shown more useful to study the aerosol distribution in the free troposphere than that obtained by using the same lidar from ground. Using standard radiative transfer model the aerosol radiative forcing is calculated and is shown that knowledge on the vertical distribution of aerosols is very important to get more realistic values than using model vertical profiles of aerosols. We show that for the same aerosol optical depth, single scattering albedo and asymmetry parameter but for different vertical profiles of aerosol extinction the computed forcing values differ with increasing altitude and improper selection of the vertical profile can even flip the sign of the forcing at tropopause level.
Local structure of the magnetotail current sheet: 2001 Cluster observations
Authors: Runov A. , Sergeev V. A. , Nakamura R. , Baumjohann W. , Apatenkov S. , Asano Y. , Takada T. , Volwerk M. , Vörös Z. , Zhang T. L. , Sauvaud J.-A. , Rème H. , Balogh A.
Published: June 2010

Abstract. Thirty rapid crossings of the magnetotail current sheet by the Cluster spacecraft during July-October 2001 at a geocentric distance of 19 RE are examined in detail to address the structure of the current sheet. We use four-point magnetic field measurements to estimate electric current density; the current sheet spatial scale is estimated by integration of the translation velocity calculated from the magnetic field temporal and spatial derivatives. The local normal-related coordinate system for each case is defined by the combining Minimum Variance Analysis (MVA) and the curlometer technique. Numerical parameters characterizing the plasma sheet conditions for these crossings are provided to facilitate future comparisons with theoretical models. Three types of current sheet distributions are distinguished: center-peaked (type I), bifurcated (type II) and asymmetric (type III) sheets. Comparison to plasma parameter distributions show that practically all cases display non-Harris-type behavior, i.e. interior current peaks are embedded into a thicker plasma sheet. The asymmetric sheets with an off-equatorial current density peak most likely have a transient nature. The ion contribution to the electric current rarely agrees with the current computed using the curlometer technique, indicating that either the electron contribution to the current is strong and variable, or the current density is spatially or temporally structured.
Gravity waves observed from the Equatorial Wave Studies (EWS) campaign during 1999 and 2000 and their role in the generation of stratospheric semiannual oscillations
Authors: Deepa V. , Ramkumar G. , Krishna Murthy B. V.
Published: June 2010

Abstract. The altitude profiles of temperature fluctuations in the stratosphere and mesosphere observed with the Rayleigh Lidar at Gadanki (13.5° N, 79.2° E) on 30 nights during January to March 1999 and 21 nights during February to April 2000 were analysed to bring out the temporal and vertical propagation characteristics of gravity wave perturbations. The gravity wave perturbations showed periodicities in the 0.5–3-h range and attained large amplitudes (4–5 K) in the mesosphere. The phase propagation characteristics of gravity waves with different periods showed upward wave propagation with a vertical wavelength of 5–7 km. The mean flow acceleration computed from the divergence of momentum flux of gravity waves is compared with that calculated from monthly values of zonal wind obtained from RH-200 rockets flights. Thus, the contribution of gravity waves towards the generation of Stratospheric Semi Annual Oscillation (SSAO) is estimated.
A numerical study of cell merger over Cuba – Part I: implementation of the ARPS/MM5 models
Authors: Pozo D. , Borrajero I. , Marín J. C. , Raga G. B.
Published: June 2010

Abstract. On 21 July 2001 a number of severe storms developed over the region of Camaguey, Cuba, which were observed by radar. A numerical simulation was performed in order to realistically reproduce the development of the storms observed that day. The mesoscale model MM5 was used to determine the initial, boundary and update conditions for the storm-scale simulation with the model ARPS. Changes to the source code of ARPS were made in order to assimilate the output from the MM5 as input data and a new land-use file with a 1-km horizontal resolution for the Cuban territory was created. A case representing the merger between cells at different stages of development was correctly reproduced by the simulation and is in good agreement with radar observations. The state of development of each cell, the time when the merger occurred, starting from the formation of clouds, the propagation motion of the cells and the increase in precipitation, due to the growth of the area after the merger, were correctly reproduced. Simulated clouds matched the main characteristics of the observed radar echoes, though in some cases, reflectivity tops and horizontal areas were overestimated. Maximum reflectivity values and the heights where these maximum values were located were in good agreement with radar data, particularly when the model reflectivity was calculated without including the snow. The MM5/ARPS configuration introduced in this study, improved sensibly the ability to simulate convective systems, thereby enhancing the local forecasting of convection in the region.
Model of daytime emissions of electronically-vibrationally excited products of O3 and O2 photolysis: application to ozone retrieval
Authors: Yankovsky V. A. , Manuilova R. O.
Published: June 2010

Abstract. The traditional kinetics of electronically excited products of O3 and O2 photolysis is supplemented with the processes of the energy transfer between electronically-vibrationally excited levels O2(a1Δg, v) and O2(b1Σ+g, v), excited atomic oxygen O(1D), and the O2 molecules in the ground electronic state O2(X3Σg−, v). In contrast to the previous models of kinetics of O2(a1Δg) and O2 (b1Σ+g), our model takes into consideration the following basic facts: first, photolysis of O3 and O2 and the processes of energy exchange between the metastable products of photolysis involve generation of oxygen molecules on highly excited vibrational levels in all considered electronic states – b1Σ+g, a1Δg and X3Σg−; second, the absorption of solar radiation not only leads to populating the electronic states on vibrational levels with vibrational quantum number v equal to 0 – O2(b1Σ+g, v=0) (at 762 nm) and O2(a1Δg, v=0) (at 1.27 µm), but also leads to populating the excited electronic–vibrational states O2(b1Σ+g, v=1) and O2(b1Σ+g, v=2) (at 689 nm and 629 nm). The proposed model allows one to calculate not only the vertical profiles of the O2(a1Δg, v=0) and O2(b1Σ
Comparison of long-term Moscow and Danish NLC observations: statistical results
Authors: Dalin P. , Kirkwood S. , Andersen H. , Hansen O. , Pertsev N. , Romejko V.
Published: June 2010

Abstract. Noctilucent clouds (NLC) are the highest clouds in the Earth's atmosphere, observed close to the mesopause at 80–90 km altitudes. Systematic NLC observations conducted in Moscow for the period of 1962–2005 and in Denmark for 1983–2005 are compared and statistical results both for seasonally summarized NLC parameters and for individual NLC appearances are described. Careful attention is paid to the weather conditions during each season of observations. This turns out to be a very important factor both for the NLC case study and for long-term data set analysis. Time series of seasonal values show moderate similarity (taking into account the weather conditions) but, at the same time, the comparison of individual cases of NLC occurrence reveals substantial differences. There are positive trends in the Moscow and Danish normalized NLC brightness as well as nearly zero trend in the Moscow normalized NLC occurrence frequency but these long-term changes are not statistically significant. The quasi-ten-year cycle in NLC parameters is about 1 year shorter than the solar cycle during the same period. The characteristic scale of NLC fields is estimated for the first time and it is found to be less than 800 km.
Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign – Part I: Observations with collocated radars
Authors: Hoffmann P. , Serafimovich A. , Peters D. , Dalin P. , Goldberg R. , Latteck R.
Published: June 2010

Abstract. During the {MaCWAVE} campaign, combined rocket, radiosonde and ground-based measurements have been performed at the Norwegian Andøya Rocket Range (ARR) near Andenes and the Swedish Rocket Range (ESRANGE) near Kiruna in January 2003 to study gravity waves in the vicinity of the Scandinavian mountain ridge. The investigations presented here are mainly based on the evaluation of continuous radar measurements with the ALWIN VHF radar in the upper troposphere/ lower stratosphere at Andenes (69.3° N, 16.0° E) and the ESRAD VHF radar near Kiruna (67.9° N, 21.9° E). Both radars are separated by about 260 km. Based on wavelet transformations of both data sets, the strongest activity of inertia gravity waves in the upper troposphere has been detected during the first period from 24–26 January 2003 with dominant vertical wavelengths of about 4–5 km as well as with dominant observed periods of about 13–14 h for the altitude range between 5 and 8 km under the additional influence of mountain waves. The results show the appearance of dominating inertia gravity waves with characteristic horizontal wavelengths of ~200 km moving in the opposite direction than the mean background wind. The results show the appearance of dominating inertia gravity waves with intrinsic periods in the order of ~5 h and with horizontal wavelengths of 200 km, moving in the opposite direction than the mean background wind. From the derived downward energy propagation it is supposed, that these waves are likely generated by a jet streak in the upper troposphere. The parameters of the jet-induced gravity waves have been estimated at both sites separately. The identified gravity waves are coherent at both locations and show higher amplitudes on the east-side of the Scandinavian mountain ridge, as expected by the influence of mountains.
First observations of SPEAR-induced artificial backscatter from CUTLASS and the EISCAT Svalbard radars
Authors: Robinson T. R. , Yeoman T. K. , Dhillon R. S. , Lester M. , Thomas E. C. , Thornhill J. D. , Wright D. M. , van Eyken A. P. , McCrea I. W.
Published: June 2010

Abstract. Results are presented from the first two active experimental campaigns undertaken by the new SPEAR (Space Plasma Exploration by Active Radar) high-power system that has recently become operational on Spitzbergen, in the Svalbard archipelago. SPEAR's high-power beam was used to excite artificial enhancements in the backscatter detected by the ESR (EISCAT Svalbard Radar) parallel to the geomagnetic field, as well as coherent backscatter detected by both of the CUTLASS (Co-operative UK Twin Located Auroral Sounding System) coherent radars, in directions orthogonal to the geomagnetic field. The ESR detected both enhanced ion-lines as well as enhanced plasma-lines, that were sustained for the whole period when SPEAR was transmitting ordinary mode radio waves, at frequencies below the maximum F-region plasma frequency. On a number of occasions, coherent backscatter was also observed in one or in both of the CUTLASS radars, in beams that intersected the heated volume. Although the levels of enhanced backscatter varied considerably in time, it appeared that ion-line, plasma-line and coherent backscatter were all excited simultaneously, in contrast to what has typically been reported at Tromsø, during EISCAT heater operations. A description of the technical and operational aspects of the new SPEAR system is also included.
Ionospheric height variations observed by ionosondes along magnetic meridian and plasma bubble onsets
Authors: Saito S. , Maruyama T.
Published: June 2010

Abstract. Since October 2004, a Frequency Modulated–Continuous Wave (FM–CW) ionosonde chain along the magnetic meridian has been operating in Southeast Asia, in Kototabang (0.2° S, 100.3° E), Indonesia, Chumphon (10.7° N, 99.4° E), Thailand, and Chiang Mai (18.8° N, 98.9° E), Thailand. Variations in the virtual height of the bottomside of the F-region (h'F) at 2.5 MHz were analyzed, in order to study the day-to-day variability of plasma bubble occurrence for the periods of October 2004 and March–April 2005. When plasma bubbles were generated, h'F was enhanced at the three stations. However, even when h'F at the equatorial station, Chumphon, was largely enhanced, plasma bubbles were not generated when a noticeable north-south asymmetry of h'F existed. This asymmetry could be attributed to the transequatorial thermospheric wind. Our results show that the strong transequatorial thermospheric wind can suppress the plasma bubble generation and is one of the important factors which controls the day-to-day variability of plasma bubble occurrences.
Implications of unusual pitch-angle distributions observed by ISEE-1 and 2
Authors: Zuluaga C. A. , Beiser E. S. , Chen J. , Fritz T. A.
Published: June 2010

Abstract. Unusual energetic particle pitch angle distributions (PADs) were observed by the ISEE-1 and 2 satellites at 3 h MLT and a radial distance of about 10–15 RE during the time period of 07:00-14:00 UT on 3 March 1979. The ISEE-1 satellite obtained complete 3-D distributions of energetic proton and electron fluxes as a function of energy, while ISEE-2 was configured to provide higher time resolution but less angular resolution than ISEE-1. The ISEE-1 observed a butterfly PAD (a minimum in the 90° PA particle flux) for a period of about 2 h (10:00–12:00 UT) for the electrons, and 3 h (09:00–12:00 UT) for the protons over an energy range of 22.5–189 keV (E1–E4) for the electrons and 24–142 keV (P1–P4) for the protons. The small pitch angle (15°, 30°) charged particles (electrons and protons) are seen to behave collectively in all four energy ranges. The relative differences in electron fluxes between 15° PA and 90° PA are more significant for higher energy channels during the butterfly PAD period. Three different types of electron PADs (butterfly, isotropic, and peaked-at-90°) were observed at the same location and time as a function of energy for a short period of time before 10:00 UT. Electron butterfly distributions were also observed by the ISEE-2 for about 1.5 h over 28–62 keV (E2–E4), although less well resolved than ISEE-1. Unlike the ISEE-1, no butterfly distributions were resolved in the ISEE-2 proton PADs due to less angular resolution. The measured drift effects by ISEE-1 suggest that the detected protons were much closer to the particle source than the electrons along their trajectories, and thus ruled out a nightside source within 18:00 MLT to 03:00 MLT. Compared to 07:30 UT, the charged particle fluxes measured by ISEE-1 were enhanced by up to three orders of magnitude during the period 08:30–12:00 UT. From 09:10:00 UT to 11:50 UT, the geomagnetic conditions were quiet (AE<100 nT), the LANL geosynchronous satellites observed no substorms, and the local magnetic field measured by ISEE-1 was almost constant, while the small PA charged particle (both electron and proton) fluxes measured by ISEE-1 increased gradually, which implies a particle source other than the substorm source. Based on detailed particle trajectory tracings in a realistic geomagnetic field model, the 50–200 keV protons with small PA at 10:00 UT ISEE-1 location on 3 March 1979 were passing through the northern high-altitude and high-latitude morningside region where the cusp should be located under a dawnward IMF component condition, while those protons with large PA may connect to the high-latitude morningside magnetopause. It is possible that the cusp source is responsible for the all particles observed during the event.
The cusp: a window for particle exchange between the radiation belt and the solar wind
Authors: Zhou X.-Z. , Fritz T. A. , Zong Q.-G. , Pu Z. Y. , Hao Y.-Q. , Cao J.-B.
Published: June 2010

Abstract. The study focuses on a single particle dynamics in the cusp region. The topology of the cusp region in terms of magnetic field iso-B contours has been studied using the Tsyganenko 96 model (T96) as an example, to show the importance of an off-equatorial minimum on particle trapping. We carry out test particle simulations to demonstrate the bounce and drift motion. The "cusp trapping limit" concept is introduced to reflect the particle motion in the high latitude magnetospheric region. The spatial distribution of the "cusp trapping limit" shows that only those particles with near 90° pitch-angles can be trapped and drift around the cusp. Those with smaller pitch angles may be partly trapped in the iso-B contours, however, they will eventually escape along one of the magnetic field lines. There exist both open field lines and closed ones within the same drift orbit, indicating two possible destinations of these particles: those particles being lost along open field lines will be connected to the surface of the magnetopause and the solar wind, while those along closed ones will enter the equatorial radiation belt. Thus, it is believed that the cusp region can provide a window for particle exchange between these two regions. Some of the factors, such as dipole tilt angle, magnetospheric convection, IMF and the Birkeland current system, may influence the cusp's trapping capability and therefore affect the particle exchanging mechanism. Their roles are examined by both the analysis of cusp magnetic topology and test particle simulations.
On the excitation of ULF waves by solar wind pressure enhancements
Authors: Eriksson P. T. I. , Blomberg L. G. , Schaefer S. , Glassmeier K.-H.
Published: June 2010

Abstract. We study the onset and development of an ultra low frequency (ULF) pulsation excited by a storm sudden commencement. On 30 August 2001, 14:10 UT, the Cluster spacecraft are located in the dayside magnetosphere and observe the excitation of a ULF pulsation by a threefold enhancement in the solar wind dynamic pressure. Two different harmonics are observed by Cluster, one at 6.8 mHz and another at 27 mHz. We observe a compressional wave and the development of a toroidal and poloidal standing wave mode. The toroidal mode is observed over a narrow range of L-shells whereas the poloidal mode is observed to have a much larger radial extent. By looking at the phase difference between the electric and magnetic fields we see that for the first two wave periods both the poloidal and toroidal mode are travelling waves and then suddenly change into standing waves. We estimate the azimuthal wave number for the 6.8 mHz to be m=10±3. For the 27 mHz wave, m seems to be several times larger and we discuss the implications of this. We conclude that the enhancement in solar wind pressure excites eigenmodes of the geomagnetic cavity/waveguide that propagate tailward and that these eigenmodes in turn couple to toroidal and poloidal mode waves. Thus our observations give firm support to the magnetospheric waveguide theory.
On the distribution of energy versus Alfvénic correlation for polar wind fluctuations
Authors: Bavassano B. , Bruno R.
Published: June 2010

Abstract. Previous analyses have shown that polar wind fluctuations at MHD scales appear as a mixture of Alfvénic fluctuations and variations with an energy imbalance in favour of the magnetic term. In the present study, by separately examining the behaviour of kinetic and magnetic energies versus the Alfvénic correlation level, we unambiguously confirm that the second population is essentially related to a large increase of the magnetic energy with respect to that of the Alfvénic population. The relevant new result is that this magnetic population, though of secondary importance in terms of occurrence frequency, corresponds to a primary peak in the distribution of total energy. The fact that this holds in the case of polar wind, which is the least structured type of interplanetary plasma flow and with the slowest evolving Alfvénic turbulence, strongly suggests the general conclusion that magnetic structures cannot be neglected when modeling fluctuations for all kinds of wind regime.
Parameter estimation using the genetic algorithm and its impact on quantitative precipitation forecast
Authors: Lee Y. H. , Park S. K. , Chang D.-E.
Published: June 2010

Abstract. In this study, optimal parameter estimations are performed for both physical and computational parameters in a mesoscale meteorological model, and their impacts on the quantitative precipitation forecasting (QPF) are assessed for a heavy rainfall case occurred at the Korean Peninsula in June 2005. Experiments are carried out using the PSU/NCAR MM5 model and the genetic algorithm (GA) for two parameters: the reduction rate of the convective available potential energy in the Kain-Fritsch (KF) scheme for cumulus parameterization, and the Asselin filter parameter for numerical stability. The fitness function is defined based on a QPF skill score. It turns out that each optimized parameter significantly improves the QPF skill. Such improvement is maximized when the two optimized parameters are used simultaneously. Our results indicate that optimizations of computational parameters as well as physical parameters and their adequate applications are essential in improving model performance.
Temporal and spatial variations in TEC using simultaneous measurements from the Indian GPS network of receivers during the low solar activity period of 2004–2005
Authors: Rama Rao P. V. S. , Gopi Krishna S. , Niranjan K. , Prasad D. S. V. V. D.
Published: June 2010

Abstract. With the recent increase in the satellite-based navigation applications, the ionospheric total electron content (TEC) and the L-band scintillation measurements have gained significant importance. In this paper we present the temporal and spatial variations in TEC derived from the simultaneous and continuous measurements made, for the first time, using the Indian GPS network of 18 receivers located from the equator to the northern crest of the equatorial ionization anomaly (EIA) region and beyond, covering a geomagnetic latitude range of 1° S to 24° N, using a 16-month period of data for the low sunspot activity (LSSA) years of March 2004 to June 2005. The diurnal variation in TEC at the EIA region shows its steep increase and reaches its maximum value between 13:00 and 16:00 LT, while at the equator the peak is broad and occurs around 16:00 LT. A short-lived day minimum occurs between 05:00 to 06:00 LT at all the stations from the equator to the EIA crest region. Beyond the crest region the day maximum values decrease with the increase in latitude, while the day minimum in TEC is flat during most of the nighttime hours, i.e. from 22:00 to 06:00 LT, a feature similar to that observed in the mid-latitudes. Further, the diurnal variation in TEC show a minimum to maximum variation of about 5 to 50 TEC units, respectively, at the equator and about 5 to 90 TEC units at the EIA crest region, which correspond to range delay variations of about 1 to 8 m at the equator to about 1 to 15 m at the crest region, at the GPS L1 frequency of 1.575 GHz. The day-to-day variability is also significant at all the stations, particularly during the daytime hours, with maximum variations at the EIA crest regions. Further, similar variations are also noticed in the corresponding equatorial electrojet (EEJ) strength, which is known to be one of the major contributors for the observed day-to-day variability in TEC. The seasonal variation in TEC maximizes during the equinox months followed by winter and is minimum during the summer months, a feature similar to that observed in the integrated equatorial electrojet (IEEJ) strength for the corresponding seasons. In the Indian sector, the EIA crest is found to occur in the latitude zone of 15° to 25° N geographic latitudes (5° to 15° N geomagnetic latitudes). The EIA also maximizes during equinoxes followed by winter and is not significant in the summer months in the LSSA period, 2004–2005. These studies also reveal that both the location of the EIA crest and its peak value in TEC are linearly related to the IEEJ strength and increase with the increase in IEEJ.
Latitudinal and temporal variation of equatorial ionospheric irregularities determined from GPS scintillation observations
Authors: Cervera M. A. , Thomas R. M.
Published: June 2010

Abstract. In this paper we investigate the spatial and temporal distribution of ionospheric irregularities in the South-East Asian longitude sector by analysing the scintillation of GPS signals received at ground based stations. The data used for this work were collected during 1998 to 2002 with our regional network of GPS based scintillation monitors (Thomas et al., 2001). The aim of this analysis is to better understand the morphology and climatology of ionospheric irregularities in our region. Interesting differences between the north and south anomalies are noted when we examine the latitudinal–temporal variation of irregularity activity. We investigate the possible causes of these differences and note that variations in the irregularity seeding mechanism and in the background ionosphere at the two anomalies could be important. Phase screen diffraction theory is used to analyse our scintillation data and we note problems with this theory for ray-paths with large off-zenith angles. The height of the phase screen is another important issue. We discuss the implications for models which rely on phase screen diffraction theory.
On the structure of field-aligned currents in the mid-altitude cusp
Authors: Marchaudon A. , Cerisier J.-C. , Bosqued J.-M. , Owen C. J. , Fazakerley A. N. , Lahiff A. D.
Published: June 2010

Abstract. We analyse two crossings of the polar cusp at mid-altitudes (≈4 RE) by Cluster in order to study the structure of field-aligned currents associated with the injection of magnetosheath plasma. The current density is deduced independently from magnetic field and from particle flux measurements. In both cases the data are carefully tested. Magnetic fluctuations are analysed by discriminating between those compatible with the plane current sheet hypothesis under which the current density can be calculated safely, and those resulting from filamentary current structures. At medium transverse scales (80 km), the structure of the currents is more often tube-like than sheet-like, and current sheets are not systematically elongated in the east-west direction. The total particle current is calculated from the electron and ion measurements. For electrons, the full energy range is taken into account, from above the photoelectron threshold up to 32 keV. Magnetosheath plasma injections are well correlated with pairs of field-aligned currents. In both cases, the parallel current is mainly carried by electrons while ions contribute for about 20%. In the plane current sheets, the ratio between magnetic and particle currents shows large variations between 0.4 and 1.1. These fluctuations can be explained by the convective motion of the current sheets.
Dayside aurorae and polar arcs under south-east IMF orientation
Authors: Sandholt P. E. , Dyrland M. , Farrugia C. J.
Published: June 2010

Abstract. We document a characteristic spatial and temporal structure of the aurora in the postnoon sector present during a 10-h-long interval of very steady southeast IMF orientation (clock angle=135°) ending in a sharp south-to-north transition. Focus is placed on the detailed morphology of auroral forms/activities corresponding to merging and lobe convection cells obtained from SuperDARN convection data and Greenland magnetograms. The ground optical instruments at Ny Ålesund, Svalbard (76° MLAT) recorded different auroral forms/activities as the station moved to higher magnetic local times (MLTs) in the 13:00–17:00 MLT sector. Whereas the 13:00–15:00 MLT sector is characterized by classical poleward moving auroral forms (PMAFs) associated with merging cell transients, the aurora in the 15:00–17:00 MLT sector shows instead a characteristic latitudinal bifurcation consisting of standard oval forms and polar arcs, and a corresponding composite pattern of merging and lobe convection cells. The merging and lobe cells respond to the southward and northward IMF transitions by activation/fading and fading/activation, respectively. A sequence of brightening events is characterized by successive activations progressing in latitude from the merging cell regime to the lobe cell regime. Emphasis is placed on the association between polar arc brightenings and the activation of the channel of enhanced sunward flow in the lobe cell. The observations are discussed in relation to recent work on solar wind-magnetosphere-ionosphere interconnection topology.
A statistical study of magnetic dipolarization for sawtooth events and isolated substorms at geosynchronous orbit with GOES data
Authors: Cai X. , Henderson M. G. , Clauer C. R.
Published: June 2010

Abstract. We investigate whether the dipolarization process during sawtooth events is global or not through an examination of the local time distribution of the magnetic tilt angle (i.e. the angle between the B vector and the equatorial plane in dipole VDH coordinates) at geostationary orbit. From the statistical analysis of 207 individual teeth and 212 isolated substorms, we find that individual teeth follow a dipolarization pattern similar to that observed for isolated substorms. The dipolarization for individual teeth initiates in the sector between 22:00 magnetic local time (MLT) and 00:00 MLT. Then the dipolarization expands both eastward and westward. However, relative to isolated substorms, we find that the nightside magnetosphere is much more stretched prior to the onset, and the change of the tilt angle during the dipolarization process is much larger during individual teeth. The magnetic dipolarization is seen over a wider local time sector during individual teeth than during isolated substorms. However, the magnetic dipolarization is rarely observed near local noon during individual teeth. This suggests that the magnetic dipolarization process during individual teeth is still confined primarily to the nightside.
Global manifestations of a substorm onset observed by a multi-satellite and ground station network
Authors: Wang H. , Ma S. Y. , Lühr H. , Liu Z. X. , Pu Z. Y. , Escoubet C. P. , Frey H. U. , Réme H. , Ritter P.
Published: June 2010

Abstract. With a favorable constellation of spacecraft and ground stations, a study is made on the global manifestations of a substorm onset. The onset occurred simultaneously and conjugately in both hemispheres, confirmed by observations of the auroral breakup from IMAGE FUV-WIC and a sudden intensification of a westward electrojet from ground-based magnetometers. Concurrently with the onset, field-aligned and Hall currents in the auroral ionosphere are observed by CHAMP, which are consistent with the signature of a Harang discontinuity. Immediately after the onset a magnetic field dipolarization is clearly observed by Double Star TC-1, located near the central magnetotail and subsequently, by the Cluster quartet. The observations can be explained by a dawnward propagation of the substorm current wedge at a speed of about 300 km/s.
Remote sensing of a near-Earth neutral line during the 5 October 2000 substorm
Authors: Nagata D. , Machida S. , Ohtani S. , Mende S. B. , Saito Y. , Mukai T.
Published: June 2010

Abstract. In this paper we examined the continuous motions of a near-Earth neutral line during the recovery phase of the 5 October 2000 substorm. Estimation was based on the PSBL ion beam model proposed by Onsager (1991) and the Geotail observations. Estimated distances from the Earth ranged from 20 to 60 RE and retreated tailward at velocities of 250 and 300 km/s. This event initiated with the arrival of solar wind discontinuity. Simultaneous observations of electromagnetic field and electrons indicate the existence of earthward propagating waves associated with field-aligned currents. Based on these observations, we suggest that the source of the PSBL ion beams was the retreating near-Earth neutral line formed by the compression of the magnetosphere. Two scenarios of near-Earth neutral line motion in the tail dynamics are also proposed. One is the formation of plural neutral lines to create a long plasmoid. The other is the oscillation of one neutral line between the near-Earth region and the mid-tail stagnant plasmoid.
Energetic ion injection and formation of the storm-time symmetric ring current
Authors: Xie L. , Pu Z. Y. , Zhou X. Z. , Fu S. Y. , Zong Q.-G. , Hong M. H.
Published: June 2010

Abstract. An extensive study of ring current injection and intensification of the storm-time ring current is conducted with three-dimensional (3-D) test particle trajectory calculations (TPTCs). The TPTCs reveal more accurately the process of ring current injection, with the main results being the following: (1) an intense convection electric field can effectively energize and inject plasma sheet particles into the ring current region within 1–3 h. (2) Injected ions often follow chaotic trajectories in non-adiabatic regions, which may have implications in storm and ring current physics. (3) The shielding electric field, which arises as a consequence of enhanced convection and co-exists with the injection and convection electric field, may cause the original open trajectories of injected ions with higher energy to change into closed ones, thus playing a role in the formation of the symmetric ring current.
Low-latitude geomagnetic signatures during major solar energetic particle events of solar cycle-23
Authors: Rawat R. , Alex S. , Lakhina G. S.
Published: June 2010

Abstract. The frequency of occurrence of disruptive transient processes in the Sun is enhanced during the high solar activity periods. Solar cycle-23 evidenced major geomagnetic storm events and intense solar energetic particle (SEP) events. The SEP events are the energetic outbursts as a result of acceleration of heliospheric particles by solar flares and coronal mass ejections (CMEs). The present work focuses on the geomagnetic variations at equatorial and low-latitude stations during the four major SEP events of 14 July 2000, 8 November 2000, 24 September 2001 and 4 November 2001. These events have been reported to be of discernible magnitude following intense X-ray flares and halo coronal mass ejections. Low-latitude geomagnetic records evidenced an intense main phase development subsequent to the shock impact on the Earth's magnetosphere. Satellite observations show proton-flux enhancements associated with solar flares for all events. Correlation analysis is also carried out to bring out the correspondence between the polar cap magnetic field perturbations, AE index and the variations of low-latitude magnetic field. The results presented in the current study elucidate the varying storm development processes, and the geomagnetic field response to the plasma and interplanetary magnetic field conditions for the energetic events. An important inference drawn from the current study is the close correspondence between the persistence of a high level of proton flux after the shock in some events and the ensuing intense magnetic storm. Another interesting result is the role of the pre-shock southward IMF Bz duration in generating a strong main phase.
Dust aerosols over India and adjacent continents retrieved using METEOSAT infrared radiance Part I: sources and regional distribution
Authors: Deepshikha S. , Satheesh S. K. , Srinivasan J.
Published: June 2010

Abstract. Mineral dust constitutes the single largest contributor to continental aerosols. To accurately assess the impact of dust aerosols on climate, the spatial and temporal distribution of dust radiative properties is essential. Regional characteristics of dust radiative properties, however, are poorly understood. The magnitude and even sign of dust radiative forcing is uncertain, as it depends on a number of parameters, such as vertical distribution of dust, cloud cover and albedo of the underlying surface. In this paper, infrared radiance (10.5-12.5 µm), acquired from the METEOSAT-5 satellite ( resolution), was used to retrieve regional characteristics of dust aerosols for all of 1999. The infrared radiance depression, due to the presence of dust in the atmosphere, has been used as an index of dust load, known as the Infrared Difference Dust Index (IDDI). There have been several studies in the past carried out over the Sahara using IDDI as a measure of dust load. Over the Indian region, however, studies on dust aerosols are sparse. Spatial and temporal variability in dust loading and its regional distribution over various arid and semiarid regions of India and adjacent continents (0-35° N; 30° E-100° E) (excluding Sahara) have been studied and the results are examined along with surface soil conditions (such as vegetation cover and soil moisture). The advantage of the IDDI method is that information on aerosol properties, such as chemical composition or microphysical properties, is not needed. A large day-to-day variation in IDDI was observed over the entire study region, with values ranging from 4 to 22 K. It was observed that dust activity starts by March over the Indian deserts, as well as over deserts of the Africa and Arabian regions. The IDDI reaches maximum during the period of May to August. Regional maps of IDDI, in conjunction with biomass burning episodes (using TERRA satellite fire pixel counts), suggest that large IDDI values observed during the winter months over Northern India could be due to a possible deposition of black carbon on larger dust aerosols. The IDDI values have been compared with another year (i.e. 2003), with a large number of dust storms reported by meteorological departments based on visibility data. During the dry season, the magnitude of the monthly average IDDI during 2003 was slightly higher than that of 1999. The monthly mean IDDI was in the range from 4 to 9 K over the Indian deserts, as well as over the deserts of Africa and Arabia. The maximum IDDI during a month was in the range from 6 to 18 K. Large IDDI values were observed even over vegetated regions (such as the vegetated part of Africa and central India), attributed to the presence of transported dust from nearby deserts.
Flux Transfer Events: 1. generation mechanism for strong southward IMF
Authors: Raeder J.
Published: June 2010

Abstract. We use a global numerical model of the interaction of the solar wind and the interplanetary magnetic field with Earth's magnetosphere to study the formation process of Flux Transfer Events (FTEs) during strong southward IMF. We find that: (i) The model produces essentially all observational features expected for FTEs, in particular the bipolar signature of the magnetic field BN component, the correct polarity, duration, and intermittency of that bipolar signature, strong core fields and enhanced core pressure, and flow enhancements; (ii) FTEs only develop for large dipole tilt whereas in the case of no dipole tilt steady magnetic reconnection occurs at the dayside magnetopause; (iii) the basic process by which FTEs are produced is the sequential generation of new X-lines which makes dayside reconnection inherently time dependent and leads to a modified form of dual or multiple X-line reconnection; (iv) the FTE generation process in this model is not dependent on specific assumptions about microscopic processes; (v) the average period of FTEs can be explained by simple geometric arguments involving magnetosheath convection; (vi) FTEs do not develop in the model if the numerical resolution is too coarse leading to too much numerical diffusion; and (vii) FTEs for nearly southward IMF and large dipole tilt, i.e., near solstice, should only develop in the winter hemisphere, which provides a testable prediction of seasonal modulation. The semiannual modulation of intermittent FTE reconnection versus steady reconnection is also expected to modulate magnetospheric and ionospheric convection and may thus contribute to the semiannual variation of geomagnetic activity.
Plasma environment of magnetized asteroids: a 3-D hybrid simulation study
Authors: Simon S. , Bagdonat T. , Motschmann U. , Glassmeier K.-H.
Published: June 2010

Abstract. The interaction of a magnetized asteroid with the solar wind is studied by using a three-dimensional hybrid simulation code (fluid electrons, kinetic ions). When the obstacle's intrinsic magnetic moment is sufficiently strong, the interaction region develops signs of magnetospheric structures. On the one hand, an area from which the solar wind is excluded forms downstream of the obstacle. On the other hand, the interaction region is surrounded by a boundary layer which indicates the presence of a bow shock. By analyzing the trajectories of individual ions, it is demonstrated that kinetic effects have global consequences for the structure of the interaction region.
Analysis of wind data in the low atmosphere from a RASS sodar
Authors: Pérez I. A. , García M. A. , Sánchez M. L. , de Torre B.
Published: June 2010

Abstract. This paper focuses on the ability of a sodar to describe some characteristics of the atmospheric vertical structure and presents some techniques for meteorological data evaluation. The measuring campaign took place in April 2001 and consisted of 10-min averages covering the lower atmosphere from 40 to 500 m at 20-m levels. Three methods were considered, the first of which was a scalar analysis performed using a combination of wind and temperature median profiles. A noticeable contrast between day and night was obtained. Flat wind profiles during the day were a consequence of prevailing convective conditions that determined thermal turbulence. A stable layer above 260 m capped the unstable layer situated below and guaranteed the stability of the boundary layer. During the night, the presence of a low level jet was the most significant feature. The height of the core was 340 m and the higher vertical winds defined it clearly. The second method focused on the wind vector. In this analysis, the anti-cyclonic rotation of hourly averages was considered in the lower levels where it was observed. After a translation of the origin, an empirical, robust model with two parts was then proposed for the resulting vector. The angle was described linearly and the module by a second order model for cylindrical data. Finally, as a third method, three regression analyses were investigated: vectorial, taking every wind component separately and scalar. The two first seemed to be more complete due to their description of anti-cyclonic wind rotation when height increased. Correlation coefficients also proved to be more satisfactory. As a consequence, these techniques, although less frequently used, are more suitable to study wind in the low atmosphere.
Daily and annual variations of erythemal ultraviolet radiation in Southwestern Spain
Authors: Serrano A. , Antón M. , Cancillo M. L. , Mateos V. L.
Published: June 2010

Abstract. The potential danger of ultraviolet (UV) radiation and its increasing levels at the Earth's surface due to ozone depletion have demanded worldwide representative measurements of UV radiation. This study presents four and one-half years of original records of high temporal resolution ultraviolet erythemal radiation (UVER) measured in Badajoz, Spain. Its principal aim is to statistically characterize the UVER magnitude and temporal variations, but also to address the interesting special cases of cloud-free and cloudy skies. In particular, the study reports reliable values of fundamental statistical indices, which can serve as relevant values for comparison with other studies and model results. Moreover, the daily and annual evolution of the main central moments of the distribution function are analyzed and interpreted in terms of the forcing and attenuation sources. The analysis focuses on two different temporal scales: hourly and daily values. Integrated hourly and daily data allow for the study of daily and annual variations of the fundamental statistical indices. All of them exhibit high symmetry with respect to solar noon and to certain dates near summer and winter solstices. The analysis shows the great influence of cloudiness in the distribution of UVER values. Thus, both daily and hourly UVER data present a slightly asymmetrical, left tailed, mesokurtic distribution for all months, except for summer, when the lack of clouds produces a leptokurtic distribution which is skewed to the left.
Dust grain dynamics due to nonuniform and nonstationary high-frequency radiations in cold magnetoplasmas
Authors: Nekrasov A. K. , Feygin F. Z.
Published: June 2010

Abstract. A general nonlinear theory for low-frequency electromagnetic field generation due to high-frequency nonuniform and nonstationary electromagnetic radiations in cold, uniform, multicomponent, dusty magnetoplasmas is developed. This theory permits us to consider the nonlinear action of all waves that can exist in such plasmas. The equations are derived for the dust grain velocities in the low-frequency nonlinear electric fields arising due to the presence of electromagnetic cyclotron waves travelling along the background magnetic field. The dust grains are considered to be magnetized as well as unmagnetized. Different regimes for the dust particle dynamics, depending on the spatio-temporal change of the wave amplitudes and plasma parameters, are discussed. It is shown that induced nonlinear electric fields can have both an electrostatic and electromagnetic nature. Conditions for maximum dust acceleration are found. The results obtained may be useful for understanding the possible mechanisms of dust grain dynamics in astrophysical, cosmic and laboratory plasmas under the action of nonuniform and nonstationary electromagnetic waves.
Infrasound - the cause of strong Polar Mesosphere Winter Echoes?
Authors: Kirkwood S. , Chilson P. , Belova E. , Dalin P. , Häggström I. , Rietveld M. , Singer W.
Published: June 2010

Abstract. The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE) during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here.