bluuebunny/crossref_metadata_2025 huggingface dataset:
High-energy charged particle bursts in the near-Earth space as earthquake precursors
Authors: Aleksandrin S. Yu. , Galper A. M. , Grishantzeva L. A. , Koldashov S. V. , Maslennikov L. V. , Murashov A. M. , Picozza P. , Sgrigna V. , Voronov S. A.
Published: June 2010

Abstract. The experimental data on high-energy charged particle fluxes, obtained in various near-Earth space experiments (MIR orbital station, METEOR-3, GAMMA and SAMPEX satellites) were processed and analyzed with the goal to search for particle bursts. Particle bursts have been selected in every experiment considered. It was shown that the significant part of high-energy charged particle bursts correlates with seismic activity. Moreover, the particle bursts are observed several hours before strong earthquakes; L-shells of particle bursts and corresponding earthquakes are practically the same. Some features of a seismo-magnetosphere connection model, based on the interaction of electromagnetic emission of seismic origin and radiation belt particles, were considered. Key words. Ionospheric physics (energetic particles, trapped; energetic particles, precipitating; magnetosphere-ionosphere interactions)
The estimation of D-region electron densities from riometer data
Authors: Hargreaves J. K. , Friedrich M.
Published: June 2010

Abstract. At high latitude the hard electron precipitation associated with auroral activity is a major source of ionization for the D-region, one consequence being the absorption of radio waves. Direct measurements of the D-region electron density are not readily available, however. This paper investigates the relationship between the electron density at altitudes between 100 and 70 km and the total radio absorption observed with a riometer, with a view to using the latter to predict the former. Tables are given of the median electron density corresponding to 1 dB absorption at 27.6 MHz for each hour of the day, and it is shown that at certain heights the estimates will be accurate to within a factor of 1.6 on 50% of the occasions. A systematic variation with time of day is probably associated with a progressive hardening of the typical electron spectrum during the morning hours. There is also evidence for a seasonal effect possibly due to seasonal variations of the mesosphere.Key words. Ionosphere (auroral ionosphere) – Radio science (ionospheric propagation; instruments and techniques)
On ALADIN precipitation modeling and validation in an Alpine watershed
Authors: Ahrens B. , Jasper K. , Gurtz J.
Published: June 2010

Abstract. Highly resolved precipitation forecasts are necessary in many applications, especially in mountain meteorology and flash flood forecasts for small- to medium-sized alpine watersheds. Here we present precipitation forecasts simulated by the limited area model ALADIN applying different grid resolutions (Dx = 10 km and 4 km). Target area of the investigations is the Alpine Ticino-Verzasca-Maggia watershed (total area: 2627 km2). We discuss problems of validation of high-resolution precipitation forecasts by comparison with observed precipitation fields and apply an indirect validation approach by using ALADIN forecasts as input to hydrologic simulations. These simulations are carried out with the distributed hydrologic model WaSiM-ETH (Dx = 500 m, Dt = 1 h). The time step of meteorological input to WaSiM-ETH is fixed at 1 h but spatial resolution varies. The main result of the validation experiments for three heavy precipitation events is, that coarser-scale ALADIN forecasts (in model version 11.2) provide better precipitation predictors for hydrologic modeling than higher-resolution forecasts. The experiments demonstrate that hydrologic modeling is a promising tool for the evaluation of high-resolution precipitation fields.Key words. Hydrology (floods) – Meteorology and atmospheric dynamics (mesoscale meteorology; precipitation)
A new regularized inversion method for the retrieval of stratospheric aerosol size distributions applied to 16 years of SAGE II data (1984–2000): method, results and validation
Authors: Bingen C. , Vanhellemont F. , Fussen D.
Published: June 2010

Abstract. We apply a regularization method for the optical inversion of SAGE II aerosol extinction profiles and derive the particle number density N, the mode radius r and width s of an effective lognormal aerosol size distribution. The constraint applied to the inversion scheme allows us to appreciably enhance the stability of the solution. Therefore, because of the disposal of a more stable inversion scheme and of the wide extend of SAGE II data in time and space, we were able to improve the estimation of the aerosol parameter profiles with respect to previous published retrievals and, hence, our knowledge of the aerosol distribution characteristics in space and time. After presenting the inversion method and retrieved profiles concerning the particle number density profile over the time period 1984–2000, we validate our results by means of data derived from both in situ and remote spectral measurements. We also discuss the limits of the comparison between the various types of measurements due to their respective particularities. The validation gives a satisfying agreement with other data sources for N and r as long as the mode radius is not too small compared to the shortest SAGE II wavelength, whereas s appears to be less easily retrieved with a good accuracy.Key words. Atmospheric composition and structure (aerosols and particles; middle atmosphere – composition and chemistry; volcanic effects)
On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm
Authors: Parkinson M. L. , Pinnock M. , Ye H. , Hairston M. R. , Devlin J. C. , Dyson P. L. , Morris R. J. , Ponomarenko P.
Published: June 2010

Abstract. A -190-nT negative bay in the geomagnetic X component measured at Macquarie Island ( -65° L) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a pre-cursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beam-swinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ~ 800 ms-1 (47 mVm-1) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum west-ward drifts of >1.3 km s-1 (>77 mVm-1) occurred during a ~ 5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ~ 300 ms-1 (18 mVm-1) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near -65° L in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal ex-tent >20° (>1.3 h magnetic local time), and latitudinal width ~2° L. Using a half-width of ~ 100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s-1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggest the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ~ 2-h interval following the flow channel, an ~ 3° L wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ~ 50 ms-1 (3 mVm -1). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)
Spacecraft potential during an active experiment: a comparison of experimental results with a simple model
Authors: Žilavý P. , Přech L. , Nĕmeček Z. , Šafránková J.
Published: June 2010

Abstract. The Active Plasma Experiment (APEX) used intensive electron beam and/or a release of the low-energy Xenon plasma to study dynamic processes in the magnetosphere and upper ionosphere. It was shown by Prech et al. (1999) that the release of the Xe plasma increases the spacecraft potential when the ambient plasma density is low, but decreases it when the density is high enough. In the present paper, a simple computer model of the dust particle charging has been adapted for a calculation of the potential difference between a planar probe and a spherical satellite moving in the ionospheric plasma. The influence of a quasineutral plasma emission on the measured spacecraft potential difference is discussed and the calculated results are compared with experimental data from the APEX project.Key words. Ionosphere (active experiments)
A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements
Authors: Chisham G. , Freeman M. P.
Published: June 2010

Abstract. Accurately measuring the location and motion of the polar cap boundary (PCB) in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB) between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1–2 range gates (~ 1° latitude). It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering), before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of the enhanced boundary determination algorithm in the cusp region. Away from the cusp, the resulting SWB locations are often dependent on the choice of threshold. This suggests that there is not a sharp latitudinal SWB in regions of the dayside ionosphere away from the cusp, but that there is a shallower latitudinal gradient in spectral width near the boundary location.Key words. Ionosphere (instruments and techniques) – Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions)
The 22-year cycle in the geomagnetic 27-day recurrences reflecting on the F2-layer ionization
Authors: Apostolov E. M. , Altadill D. , Todorova M.
Published: June 2010

Abstract. Solar cycle variations of the amplitudes of the 27-day solar rotation period reflected in the geomagnetic activity index Ap, solar radio flux F10.7cm and critical frequency foF2 for mid-latitude ionosonde station Moscow from the maximum of sunspot cycle 18 to the maximum of cycle 23 are examined. The analysis shows that there are distinct enhancements of the 27-day amplitudes for foF2 and Ap in the late declining phase of each solar cycle while the amplitudes for F10.7cm decrease gradually, and the foF2 and Ap amplitude peaks are much larger for even-numbered solar cycles than for the odd ones. Additionally, we found the same even-high and odd-low pattern of foF2 for other mid-latitude ionosonde stations in Northern and Southern Hemispheres. This property suggests that there exists a 22-year cycle in the F2-layer variability coupled with the 22-year cycle in the 27-day recurrence of geomagnetic activity. Key words. Ionosphere (mid-latitude ionosphere; ionosphere- magnetosphere interactions) – Magnetospheric physics (solar wind-magnetosphere interactions)
An investigation of latitudinal transitions in the SuperDARN Doppler spectral width parameter at different magnetic local times
Authors: Chisham G. , Freeman M. P.
Published: June 2010

Abstract. Latitudinal transitions from low to high Doppler spectral width in backscatter measured by the Super Dual Auroral Radar Network (SuperDARN) are now routinely used as proxies for the polar cap boundary (PCB) in the cusp-region ionosphere. In this paper we perform a statistical study of the nature of similar spectral width transitions at other magnetic local times (MLTs). This analysis illustrates that these latitudinal spectral width transitions exist at all magnetic local times, and that the latitude, gradient, and amplitude of the transitions vary systematically with MLT. In particular, the probability of a transition occurring at any latitude, identified independently in each MLT sector, is continuous with MLT from the cusp, through the morning sector, to the nightside. This suggests that the transition represents the PCB, as this is known to be what it represents in the cusp region. However, the picture in the afternoon sector (12:00-18:00 MLT) is more complex with no clearly preferred transition latitudes. Key words. Ionosphere (ionosphere-magnetosphere interactions; instruments and techniques). Magnetospheric physics (magnetopause, cusp, and boundary layers.)
Four-spacecraft determination of magnetopause orientation, motion and thickness: comparison with results from single-spacecraft methods
Authors: Haaland S. E. , Sonnerup B. U. Ö. , Dunlop M. W. , Balogh A. , Georgescu E. , Hasegawa H. , Klecker B. , Paschmann G. , Puhl-Quinn P. , Rème H. , Vaith H. , Vaivads A.
Published: June 2010

Abstract. In this paper, we use Cluster data from one magnetopause event on 5 July 2001 to compare predictions from various methods for determination of the velocity, orientation, and thickness of the magnetopause current layer. We employ established as well as new multi-spacecraft techniques, in which time differences between the crossings by the four spacecraft, along with the duration of each crossing, are used to calculate magnetopause speed, normal vector, and width. The timing is based on data from either the Cluster Magnetic Field Experiment (FGM) or the Electric Field Experiment (EFW) instruments. The multi-spacecraft results are compared with those derived from various single-spacecraft techniques, including minimum-variance analysis of the magnetic field and deHoffmann-Teller, as well as Minimum-Faraday-Residue analysis of plasma velocities and magnetic fields measured during the crossings. In order to improve the overall consistency between multi- and single-spacecraft results, we have also explored the use of hybrid techniques, in which timing information from the four spacecraft is combined with certain limited results from single-spacecraft methods, the remaining results being left for consistency checks. The results show good agreement between magnetopause orientations derived from appropriately chosen single-spacecraft techniques and those obtained from multi-spacecraft timing. The agreement between magnetopause speeds derived from single- and multi-spacecraft methods is quantitatively somewhat less good but it is evident that the speed can change substantially from one crossing to the next within an event. The magnetopause thickness varied substantially from one crossing to the next, within an event. It ranged from 5 to 10 ion gyroradii. The density profile was sharper than the magnetic profile: most of the density change occured in the earthward half of the magnetopause. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; instruments and techniques) – Space plasma physics (discontinuities)
Impact of absorbing aerosols on the simulation of climate over the Indian region in an atmospheric general circulation model
Authors: Chakraborty A. , Satheesh S. K. , Nanjundiah R. S. , Srinivasan J.
Published: June 2010

Abstract. The impact of anthropogenic absorbing aerosols (such as soot) on the climate over the Indian region has been studied using the NCMRWF general circulation model. The absorbing aerosols increase shortwave radiative heating of the lower troposphere and reduce the heating at the surface. These effects have been incorporated as heating of the lower troposphere (up to 700hPa) and cooling over the continental surface based on INDOEX measurements. The heating effect is constant in the pre-monsoon season and reduces to zero during the monsoon season. It is shown that even in the monsoon season when the aerosol forcing is zero, there is an overall increase in rainfall and a reduction in surface temperature over the Indian region. The rainfall averaged over the Tropics shows a small reduction in most of the months during the January to September period. The impact of aerosol forcing, the model's sensitivity to this forcing and its interaction with model-physics has been studied by changing the cumulus parameterization from the Simplified Arakawa-Schubert (SAS) scheme to the Kuo scheme. During the pre-monsoon season the major changes in precipitation occur in the oceanic Inter Tropical Convergence Zone (ITCZ), where both the schemes show an increase in precipitation. This result is similar to that reported in Chung2002. On the other hand, during the monsoon season the changes in precipitation in the continental region are different in the SAS and Kuo schemes. It is shown that the heating due to absorbing aerosols changes the vertical moist-static stability of the atmosphere. The difference in the precipitation changes in the two cumulus schemes is on account of the different responses in the two parameterization schemes to changes in vertical stability. Key words. Atmospheric composition and structure (aerosols and particles) – Meteorology and atmospheric dynamics (tropical meteorology; precipitation)
Origin of the SuperDARN broad Doppler spectra:simultaneous observation with Oersted satellite magnetometer
Authors: Hosokawa K. , Yamashita S. , Stauning P. , Sato N. , Yukimatu A. S. , Iyemori T.
Published: June 2010

Abstract. We perform a case study of a favorable conjunction of an overpass of the Oersted satellite with the field-of-view of the SuperDARN Syowa East radar during an interval of the southward IMF Bz. At the time, the radar observed an L-shell aligned boundary in the spectral width around the dayside ionosphere. Simultaneously, high-frequency (0.2–5Hz) magnetic field fluctuations were observed by the Oersted satellite's high-time resolution magnetometer. These magnetic field fluctuations are considered to be Alfvén waves possibly associated with the particle which precipitates into the dayside high-latitude ionosphere when magnetic reconnection occurs. It has been theoretically predicted that the time-varying electric field is the dominant physical process to expand the broad HF radar Doppler spectra. Our observation clearly demonstrates that the boundary between narrow and broad spectral widths is corresponding well to the boundary in the level of the fluctuations, which supports the previous theoretical prediction. A close relationship between electric and magnetic field fluctuations and particle precipitations during southward IMF conditions has been confirmed by many authors. The present observation allows us to suggest that the boundary between narrow and broad Doppler spectral widths observed in the dayside ionosphere is connected with the signature of the open/closed field line boundary, such as the cusp particle precipitations via electric and magnetic field fluctuations for the case of the negative IMF Bz conditions. Key words. Ionosphere (ionosphere-magnetosphere interactions; plasma convection). Magnetospheric physics (magnetopause, cusp, and boundary layers)
Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements
Authors: Mori H. , Ishii M. , Murayama Y. , Kubota M. , Sakanoi K. , Yamamoto M.-Y. , Monzen Y. , Lummerzheim D. , Watkins B. J.
Published: June 2010

Abstract. This study is a statistical analysis on energy distribution of precipitating electrons, based on CNA (cosmic noise absorption) data obtained from the 256-element imaging riometer in Poker Flat, Alaska (65.11° N, 147.42° W), and optical data measured with an MSP (Meridian Scanning Photometer) over 79 days during the winter periods from 1996 to 1998. On the assumption that energy distributions of precipitating electrons represent Maxwellian distributions, CNA is estimated based on the observation data of auroral 427.8-nm and 630.0-nm emissions, as well as the average atmospheric model, and compared with the actual observation data. Although the observation data have a broad distribution, they show systematically larger CNA than the model estimate. CNA determination using kappa or double Maxwellian distributions, instead of Maxwellian distributions, better explains the distribution of observed CNA data. Kappa distributions represent a typical energy distribution of electrons in the plasma sheet of the magnetosphere, the source region of precipitating electrons. Pure kappas are more likely during quiet times – and quiet times are more likely than active times. This result suggests that the energy distribution of precipitating electrons reflects the energy distribution of electrons in the plasma sheet. Key words. Ionosphere (auroral ionosphere; particle precipitation; polar ionosphere)
Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase
Authors: Jussila J. R. T. , Aikio A. T. , Shalimov S. , Marple S. R.
Published: June 2010

Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (Te) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced Te play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation. Key words. Ionosphere (auroral ionosphere; particle precipitation; electric fields and currents)
High-latitude propagation studies using a meridional chain of LF/MF/HF receivers
Authors: LaBelle J.
Published: June 2010

Abstract. For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz) show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.Key words. Magnetospheric physics (annual phenomena) – Radio science (ionosphere propagation; radio-wave propagation)6
Evidence for storm-time ionospheric ion precipitation in the cusp with magnetosheath energy
Authors: Stenuit H. , Sauvaud J.-A.
Published: June 2010

Abstract. We present evidence for a sporadic precipitation into the north polar cusp of ionospheric O+ and He+ ions accelerated up to the magnetosheath flow speed during a magnetic storm. This is deduced from data obtained on board the Interball-Auroral satellite showing that the energy/charge ratios of the H+, He++, He+ and O+ populations are similar to those of ion masses. These measurements pertain to a very disturbed magnetic period. A storm was in progress with a Dst reaching -149nT during the cusp measurements, while the AE index reached values higher than 1000nT. This result is discussed in terms of ion circulation from the magnetosphere to the magnetosheath and back to the magnetosphere. We suggest that the acceleration of O+ and He+ ions up to a magnetosheath-like velocity is directly linked to the large By component of the IMF.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosheath; storms and substorms)
Model results for the ionospheric lower transition height over mid-latitude
Authors: Lei J. , Liu L. , Wan W. , Zhang S.-R.
Published: June 2010

Abstract. Theoretical calculations of the ionospheric lower transition height (LTH), a level of equal O+ and molecular ion densities, were performed and compared with empirical models by Zhang et al. (1996). This paper represents a substantial extension of the prior work by including the AE-C data of ion composition analysis and by detailed quantitative studies of the LTH simulation, and by creating a new LTH empirical model based on our simulations. Results show that: (1) the calculated LTH, in general, is lowest near 11-13LT and reaches the diurnal maximum after midnight (about 01~02LT). The local time asymmetry becomes more evident in summer, when the time of minimum shifts to 16LT. (2) The simulated LTH presents a dominant, semiannual variation during nighttime, and a pronounced annual variation during daytime. (3) The simulated LTH increases with solar activity at night and decreases by day, while the standard IRI option has an opposite tendency at night in summer and equinox. Therefore, the day-night difference of simulated LTH significantly increases with solar activity. (4) Both daytime and nighttime LTHs, tend to increase with the increasing geomagnetic activity Ap index, with a mean slope about 0.1455km per Ap unit. (5) The diurnal variation of LTH is found to be more than 20 km, which is much larger than the seasonal variation under F107=100 and Ap=10. Thus, the diurnal and solar activity variations of LTH are more pronounced than its seasonal and magnetic activity variations.
A numerical study of two interacting coronal mass ejections
Authors: Schmidt J. M. , Cargill P. J.
Published: June 2010

Abstract. The interaction in the solar wind between two coronal mass ejections (CMEs) is investigated using numerical simulations. We show that the nature of the interaction depends on whether the CME magnetic structures interact, but in all cases the result is an equilisation of the speed of the two CMEs. In the absence of magnetic interaction, the forward shock of the faster trailing CME interacts with the slow leading CME, and accelerates it. When the two CMEs have magnetic fields with the same sense of rotation, magnetic reconnection occurs between the two CMEs, leading to the formation of a single magnetic structure: in the most extreme cases, one CME "eats" the other. When the senses of rotation are opposite, reconnection does not occur, but the CMEs collide in a highly non-elastic manner, again forming a single structure. The possibility of enhanced particle acceleration in such processes is assessed. The presence of strong magnetic reconnection provides excellent opportunities for the acceleration of thermal particles, which then form a seed population for further acceleration at the CME shocks. The presence of a large population of seed particles will thus lead to an overall increase in energetic particle fluxes, as suggested by some observations.
Nonstationarity of quasi-perpendicular shocks: a comparison of full particle simulations with different ion to electron mass ratio
Authors: Scholer M. , Matsukiyo S.
Published: June 2010

Abstract. We have performed 3 one-dimensional full particle electromagnetic simulations of a quasi-perpendicular shock with the same Alfvén Mach number MA=4.5, shock normal - magnetic field angle ΘBn=87°, and ion and electron beta (particle to magnetic field pressure) of 0.05, but with different ion to electron mass ratios (mi/me=80, 400, 1840). At high ion beta it has been shown previously that the shock is steady. At low ion beta, as in the present simulations, the shock periodically reforms itself. However, whereas at unrealistically low mass ratios the reformation is due to accumulation of specularly reflected particles at the upstream edge of the foot, at the realistic mass ratio the modified two-stream instability between the incoming solar wind ions and solar wind electrons leads to ion phase mixing and thermalization. The reformation process is thereby considerably modified. At the lowest mass ratio the Buneman instability between the solar wind electrons and the reflected ions is excited, which is stabilized at higher mass ratios.
Multifractal structure of turbulence in the magnetospheric cusp
Authors: Yordanova E. , Grzesiak M. , Wernik A. W. , Popielawska B. , Stasiewicz K.
Published: June 2010

Abstract. Magnetospheric cusps are regions which are characterized by highly turbulent plasma. We have used Polar magnetic field data to study the structure of turbulence in the cusp region. The wavelet transform modulus maxima method (WTMM) has been applied to estimate the scaling exponent of the partition function and singularity spectra. Their features are similar to those found in the nonlinear multifractal systems. We have found that the scaling exponent does not allow one to conclude which intermittency model fits the experiment better. However, the singularity spectra reveal that different models can be ascribed to turbulence observed under various IMF conditions. For northward IMF conditions the turbulence is consistent with the multifractal p-model of fully developed fluid turbulence. For southward IMF experimental data agree with the model of non-fully developed Kolmogorov-like fluid turbulence.
Cluster observations of mid-latitude hiss near the plasmapause
Authors: Masson A. , Inan U. S. , Laakso H. , Santolík O. , Décréau P.
Published: June 2010

Abstract. In the vicinity of the plasmapause, around the geomagnetic equator, the four Cluster satellites often observe banded hiss-like electromagnetic emissions (BHE); below the electron gyrofrequency but above the lower hybrid resonance, from 2kHz to 10kHz. We show that below 4kHz, these waves propagate in the whistler mode. Using the first year of scientific operations of WHISPER, STAFF and WBD wave experiments on Cluster, we have identified the following properties of the BHE waves: (i) their location is strongly correlated with the position of the plasmapause, (ii) no MLT dependence has been found, (iii) their spectral width is generally 1 to 2kHz, and (iv) the central frequency of their emission band varies from 2kHz to 10kHz. All these features suggest that BHE are in fact mid-latitude hiss emissions (MLH). Moreover, the central frequency was found to be correlated with the Kp index. This suggests either that these banded emissions are generated in a given f/fce range, or that there is a Kp dependent Doppler shift between the satellites and a possible moving source of the MLH.
Characteristics of magnetospherically reflected chorus waves observed by CLUSTER
Authors: Parrot M. , Santolík O. , Gurnett D. A. , Pickett J. S. , Cornilleau-Wehrlin N.
Published: June 2010

Abstract. Chorus emissions are often observed by the STAFF spectrum analyser on board the 4 satellites of CLUSTER. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the propagation characteristic of these chorus waves. Measurements of the parallel component of the Poynting vector around the magnetic equator indicate that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it has also been observed that lower intensity waves propagate toward the equator at the same frequency. Using the wave normal directions of these waves, a ray tracing study has shown that the waves have suffered a Lower Hybrid Resonance (LHR) reflection at low altitudes and now return to the equator at a different location with a lower intensity. The paper presents other similar events when WBD data are simultaneously recorded. The WBD experiment provides a much better time resolution and allows one to check the structure of the returning waves. It is observed that these waves have still a high degree of polarization, even if they started to lose the coherent structure of the chorus elements. They reach the equator with a small wave normal angle which is more efficient for a further amplification. It is explained that these emissions could be a source of hiss.
Spatial and temporal properties of AKR burst emission derived from Cluster WBD VLBI studies
Authors: Mutel R. L. , Gurnett D. A. , Christopher I. W.
Published: June 2010

Abstract. We have determined the locations of over 6000 individual auroral kilometric radiation (AKR) bursts between July 2002 and May 2003 using a very long baseline interferometer (VLBI) array. Burst locations were determined by triangulation using differential delays from cross-correlated Cluster WBD waveforms. Typical position uncertainties are 200-400km in the plane normal to the source-spacecraft line, but much larger along this line. The AKR bursts are generally located above the auroral zone with a strong preference for the evening sector (22:00 MLT±2h). However, a few epochs imaged during the austral summer have loci in the daytime sector, especially near 15:00 MLT. There is marginal evidence for a small N-S hemispheric asymmetry in mean MLT and invariant latitude.
Instantaneous local wave vector estimation from multi-spacecraft measurements using few spatial points
Authors: Carozzi T. D. , Buckley A. M. , Gough M. P.
Published: June 2010

Abstract. We introduce a technique to determine instantaneous local properties of waves based on discrete-time sampled, real-valued measurements from 4 or more spatial points. The technique is a generalisation to the spatial domain of the notion of instantaneous frequency used in signal processing. The quantities derived by our technique are closely related to those used in geometrical optics, namely the local wave vector and instantaneous phase velocity. Thus, this experimental technique complements ray-tracing. We provide example applications of the technique to electric field and potential data from the EFW instrument on Cluster. Cluster is the first space mission for which direct determination of the full 3-dimensional local wave vector is possible, as described here.
Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns
Authors: Ramana M. V. , Krishnan P. , Muraleedharan Nair S. , Kunhikrishnan P. K.
Published: June 2010

Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.
Geomagnetic field variations at the equatorial electrojet station in Sri Lanka, Peredinia
Authors: Rastogi R. G. , Kitamura T. , Kitamura K.
Published: June 2010

Abstract. The paper discusses the variations of the horizontal (H), vertical (Z) and eastward (Y) components of the geomagnetic field at Peredinia (PRD), an electrojet station in Sri Lanka, with the time of the day, season, sudden commencement (SSC) and during geomagnetic storms. The daily variation of H showed a large peak around midday. The daily variation of Z appeared to be almost a time gradient curve of the daily variation of H, showing a maximum around 09:00 LT (75° EMT) when the H field was increasing fastest and not at noon when Δ H was the maximum. Storm time variation of H resembled the variation of the Dst index but that of Z showed a large minimum about 2-3h before the time of minimum Dst or at the time of maximum time gradient of Dst variation. These features are compared with corresponding variations at the equatorial stations Trivandrum (TRD) in India, and remarkable similarity in all observations is noticed at PRD and TRD. It is suggested that the observed abnormal features of Z variations at electrojet stations in India-Sri Lanka are due to (i) direct effect of the ionospheric electrojet current (ii) the induction effect of the image current by the average spatially extended conductivity region and (iii) the induction current in the local subsurface conductor. It is suggested that the conductor responsible for the observed features in Z in India and Sri Lanka has to have extended spatial domain to latitudes well south of India, rather than confined to narrow Palk Strait.
Ionospheric conductivity dependence of dayside region-0, 1, and 2 field-aligned current systems: statistical study with DMSP-F7
Authors: Haraguchi K. , Kawano H. , Yumoto K. , Ohtani S. , Higuchi T. , Ueno G.
Published: June 2010

Abstract. The present study statistically examines the dependence of the intensities of dayside (MLT=8-12h) large-scale field-aligned currents (FACs) on the ionospheric conductance using the summary data of DMSP-F7 constructed by the procedure of Higuchi and Ohtani (2000). We have found that, in the dayside region, R1 and R0 have a higher correlation between ionospheric conductivity and FAC intensity than R2, suggesting that R0 and R1 are driven by a more voltage-like source than R2. This result is consistent with the idea that R1 and R0 are driven by the interaction between the solar wind and the open magnetospheric magnetic field. We have also found that dayside FAC intensities are latitudinally well balanced when they have a three sheet structure (R0, R1 and R2); on the other hand, for a two sheet structure (R1 and R2), the intensity of R1 is larger than that of R2, so that the net current has the polarity of R1.
Observations of lower hybrid cavities in the inner magnetosphere by the Cluster and Viking satellites
Authors: Tjulin A. , André M. , Eriksson A. I. , Maksimovic M.
Published: June 2010

Abstract. Observations by the Viking and Cluster satellites at altitudes up to 35000km show that Lower Hybrid Cavities (LHCs) are common in the inner magnetosphere. LHCs are density depletions filled with waves in the lower hybrid frequency range. The LHCs have, until recently, only been found at altitudes up to 2000km. Statistics of the locations and general shape of the LHCs is performed to obtain an overview of some of their properties. In total, we have observed 166 LHCs on Viking during 27h of data, and 535 LHCs on Cluster during 87h of data. These LHCs are found at invariant latitudes from the auroral region to the plasmapause. A comparison with lower altitude observations shows that the LHC occurrence frequency does not scale with the flux tube radius, so that the LHCs are moderately rarer at high altitudes. This indicates that the individual LHCs do not reach from the ionosphere to 35000km altitude, which gives an upper bound for their length. The width of the LHCs perpendicular to the geomagnetic field at high altitudes is a few times the ion gyroradius, consistent with observations at low altitudes. The estimated depth of the density depletions vary with altitude, being larger at altitudes of 20000-35000km (Cluster, 10-20%), smaller around 1500-13000km (Viking and previous Freja results, a few percent) and again larger around 1000km (previous sounding rocket observations, 10-20%). The LHCs in the inner magnetosphere are situated in regions with background electrostatic hiss in the lower hybrid frequency range, consistent with investigations at low altitudes. Individual LHCs observed at high altitudes are stable at least on time scales of 0.2s (about the ion gyro period), which is consistent with previous results at lower altitudes, and observations by the four Cluster satellites show that the occurrence of LHCs in a region in space is a stable phenomenon, at least on time scales of an hour.
A possible origin of dayside Pc1 magnetic pulsations observed at high latitudes
Authors: Safargaleev V. , Serebryanskaya A. , Koustov A. , Lester M. , Pchelkina E. , Vasilyev A.
Published: June 2010

Abstract. Induction magnetometer observations of dayside Pc1 activity at Barentsburg (BAB, Spitsbergen archipelago, 78.05°N, 14.12°E) are combined with data from two magnetometers located in Scandinavia and the Kola peninsula. Seven events with very large negative IMF Bz components were considered. For all of the events, the cusp location was expected to be significantly shifted equatorward from the statistical position such that the BAB magnetometer was located well inside the polar cap. The DMSP particle data indicated that the BAB magnetometer was indeed inside the polar cap, whereas other magnetometers were collocated with the ionospheric projections of the cusp, the low-latitude boundary layer or the boundary plasma sheet. Pc1 magnetic pulsations were observed only at BAB. In three cases, for which SuperDARN convection data were available, the Pc1 activity correlated with intervals of large-scale convection reconfiguration, such that the plasma flow crossing the BAB location was associated with newly-reconnected magnetic flux tubes drifting tailward. The convection reconfigurations were in response to a decrease in the IMF By component. We argue that the source of the observed Pc1 pulsations is anisotropic plasma of the depletion layer within the magnetosheath. The plasma anisotropy supports the excitation of electromagnetic ion cyclotron waves that are detectable with a ground-based magnetometer when the flux tubes containing the unstable plasma become connected to the Earth's ionosphere in the course of the dayside reconnection processes.
Multistation digisonde observations of equatorial spread F in South America
Authors: Reinisch B. W. , Abdu M. , Batista I. , Sales G. S. , Khmyrov G. , Bullett T. A. , Chau J. , Rios V.
Published: June 2010

Abstract. Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.
Magnetic storm-induced enhancement in neutral composition at low latitudes as inferred by O(1D) dayglow measurements from Chile
Authors: Pallamraju D. , Chakrabarti S. , Valladares C. E.
Published: June 2010

Abstract. We describe the effect of the 6 November 2001 magnetic storm on the low latitude thermospheric composition. Daytime red line (OI 630.0nm) emissions from Carmen Alto, Chile showed anomalous 2-3 times larger emissions in the morning (05:30-08:30 Local Time; LT) on the disturbed day compared to the quiet days. We interpret these emission enhancements to be caused due to the increase in neutral densities over low latitudes, as a direct effect of the geomagnetic storm. As an aftereffect of the geomagnetic storm, the dayglow emissions on the following day show gravity wave features that gradually increase in periodicities from around 30min in the morning to around 100min by the evening. The integrated dayglow emissions on quiet days show day-to-day variabilities in spatial structures in terms of their movement away from the magnetic equator in response to the Equatorial Ionization Anomaly (EIA) development in the daytime. The EIA signatures in the daytime OI 630.0nm column-integrated dayglow emission brightness show different behavior on days with and without the post-sunset Equatorial Spread F (ESF) occurrence.