bluuebunny/crossref_metadata_2025 huggingface dataset:
IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements
Authors: Förster M. , Rentz S. , Köhler W. , Liu H. , Haaland S. E.
Published: June 2010

Abstract. Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern obtained from the Cluster EDI plasma drift measurements under the same sorting conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for ByIMF+ (ByIMF−) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for ByIMF+ than for ByIMF− and is systematically larger (~5°) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for BzIMF−/ByIMF− conditions at the Northern Hemisphere, but for BzIMF−/ByIMF+ conditions at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.
Rotation of sea/land breezes along the northeastern Adriatic coast
Authors: Prtenjak M. T. , Pasarić Z. , Orlić M. , Grisogono B.
Published: June 2010

Abstract. The diurnal evolution of the sea/land breeze hodographs over the northeastern Adriatic coast has been examined for several episodes, each lasting a few days. A limited set of observations, as well as the results of a three-dimensional nonhydrostatic mesoscale model are studied by applying a rotary-component method. This revealed a spatial distribution of the clockwise versus anti-clockwise rotation of the wind vectors for the sea/land breeze events. An application of the rotary-component method to the results of additional numerical sensitivity tests showed that the coastal topography height considerably influences both the shape of the wind hodographs and the sense of wind rotation. The method also displayed which areas are under a strong influence of the 24-h topographic forcing and which areas show a large wind consistency. A further analysis of the 24-h modeled wind hodographs at several selected stations has been performed, thus revealing the hodograph shapes and the reasons for them.
VHF scintillations, orientation of the anisotropy of F-region irregularities and direction of plasma convection in the polar cap
Authors: Tereshchenko E. D. , Romanova N. Yu. , Koustov A. V.
Published: June 2010

Abstract. Scintillation data recorded at the polar cap station Barentsburg are shown to occasionally exhibit two or more peaks in the latitudinal profiles of the amplitude dispersion. Comparison with concurrent SuperDARN radar convection maps indicates that multiple peaks occur when Barentsburg is located within the area of strong changes in the plasma flow direction. When parameters of the ionospheric irregularities are inferred from the scintillation data, the orientation of the irregularity anisotropy in a plane perpendicular to the magnetic field is found to coincide well with the E×B flow direction, individually for each peak of the scintillation data. The differences were found to be mostly less than 20° for a data set comprised of 104 events. The conclusion is made that analysis of scintillation data allows one to infer the direction of plasma flow with a certain degree of detail.
The shape of the Sq current system
Authors: Stening R. J.
Published: June 2010

Abstract. Many years ago Mayaud (1965) suggested that a tilted, rather than symmetric, current system may be responsible for the form of daily magnetic variations near the focus of the current system. With arrays of magnetometer stations, both in Australia and in Europe, it is now demonstrated that such tilted systems do exist at certain times. At other times the magnetic variation near the focus is deformed by a previously reported extra morning current system which is apparently unconnected to the regular Sq system.
Spatio-temporal structure of a poloidal Alfvén wave detected by Cluster adjacent to the dayside plasmapause
Authors: Schäfer S. , Glassmeier K. H. , Eriksson P. T. I. , Mager P. N. , Pierrard V. , Fornaçon K. H. , Blomberg L. G.
Published: June 2010

Abstract. A case study of a poloidal ULF pulsation near the dayside plasmapause is presented based on Cluster observations of magnetic and electric fields. The pulsation is detected close to the magnetic equatorial plane at L shells L=[4.4, 4.6] and oscillates with a frequency of f=23 mHz. Investigating the wave energy flux reveals the standing wave nature of the observed pulsation. An estimation of the azimuthal wave number exposes a narrow azimuthal structure of the wave field with m≈160. Spatial and temporal characteristics of the pulsation are analyzed in detail by representing data in a field line related coordinate system and a range-time-intensity representation. This allows an estimation of both the spatial extension of the wave field in the radial direction and its temporal decay rate. The analysis furthermore indicates that the same field lines are excited to a standing wave oscillation twice. Furthermore an accurate identification of a phase jump of the wave field across L shells is possible. Comparing the radial localization of the detected wave with theoretically expected field line eigenfrequencies reveals that the wave field is confined in the Alfvén resonator at the outer edge of the plasmapause.
A survey of Galileo plasma wave instrument observations of Jovian whistler-mode chorus
Authors: Menietti J. D. , Horne R. B. , Gurnett D. A. , Hospodarsky G. B. , Piker C. W. , Groene J. B.
Published: June 2010

Abstract. A survey of plasma wave observations at Jupiter obtained by the plasma wave instrument on board the Galileo spacecraft is presented. The observations indicate that chorus emissions are observed commonly in the Jovian magnetosphere near the magnetic equator in the approximate radial range 6<r<10 RJ. The survey includes almost all local times but not equally sampled in radial distance due to the spacecraft trajectory. The data suggest that chorus emissions are somewhat more intense on the dayside, but this may be a result of insufficient nightside observations. The orbit of Galileo is also restricted to ±3° of the Jovigraphic equator, but the tilt of the magnetic field permits coverage of a range of magnetic latitudes of −13°<λmag<+13°. The similarities of chorus emissions to terrestrial observations are a good reason to speculate that Jovian chorus emission may play a significant role in the stochastic acceleration of electrons in the radial range 6–10 RJ as recent studies indicate. These electrons may then be transported inward by radial diffusion where they are additionally accelerated to form the synchrotron radiation belt source.
Impact of convective downdrafts on model simulations: results from aqua-planet integrations
Authors: Sahany S. , Nanjundiah R. S.
Published: June 2010

Abstract. The role of convective scale downdrafts has been examined, using the NCAR-CAM3.0 aqua-planet configuration. We find that, convective downdrafts make the atmosphere more unstable thus increasing the convective available potential energy (CAPE) of the atmosphere. It is noticed that, although the rate of CAPE consumption increases with the incorporation of downdrafts, the generation of CAPE increases with a higher rate. Also, it is noted that there is a reduction in the deep convective rainfall, with the inclusion of downdrafts, which is primarily due to the re-evaporation of precipitation within the downdrafts. There is a large increase in the low cloud fraction and the shortwave cloud forcing with the inclusion of convective scale downdrafts in the cumulus scheme, which along with the evaporation within the downdraft causes cooling in the troposphere. This is in contrast to previous studies on the impact of downdrafts using single column models. In Zhang and McFarlane (1995), using a single column model, it was shown that with the increase in the strength of the downdrafts, there was a reduction in CAPE. In the present study, using an aqua-planet framework, it is shown that CAPE is actually found to increase when the downdrafts are incorporated into the cumulus scheme, as compared to the case when there are no downdrafts. The rate of CAPE consumption which, is the same as the rate of stabilization of the atmosphere, is found to increase, but the mean CAPE as such is higher compared to the case when there are no downdrafts.
D region HF radar echoes associated with energetic particle precipitation and pulsating aurora
Authors: Milan S. E. , Hosokawa K. , Lester M. , Sato N. , Yamagishi H. , Honary F.
Published: June 2010

Abstract. Milan et al. (2001) identified a class of narrow, slow-moving HF radar backscatter echoes which originate between altitudes of 80 and 100 km, the ionospheric D- and lower E-regions. These echoes appeared to be associated with the occurrence of pulsating aurora, which are known to be created by energetic electrons capable of penetrating to D region altitudes. In this study we show that these echoes are observed in tandem with enhancements in cosmic noise absorption (auroral absorption), additional evidence that energetic (>30 keV) particle precipitation is responsible for generating the irregularities from which a radar can scatter. In addition, we show that the D region backscatter echoes occur predominantly in the post-midnight sector during substorm recovery phase, in common with auroral absorption events and pulsating aurora.
Estimates of magnetic cloud expansion at 1 AU
Authors: Lepping R. P. , Wu C.-C. , Berdichevsky D. B. , Ferguson T.
Published: June 2010

Abstract. In this study we analyze 53 magnetic clouds (MCs) of standard profiles observed in WIND magnetic field and plasma data, in order to estimate the speed of MC expansion (VE) at 1 AU, where the expansion is investigated only for the component perpendicular to the MCs' axes. A high percentage, 83%, of the good and acceptable quality cases of MCs (N(good)=64) were actually expanding, where "good quality" as used here refers to those MCs that had relatively well determined axial attitudes. Two different estimation methods are employed. The "scalar" method (where the estimation is denoted VE,S) depends on the average speed of the MC from Sun-to-Earth (), the local MC's radius (RO), the duration of spacecraft passage through the MC (at average local speed ), and the assumption that =. The second method, the "vector determination" (denoted VE,V), depends on the decreasing value of the absolute value of the Z-component (in MC coordinates) of plasma velocity (|VZ|) across the MC, the closest approach distance (YO), and estimated RO; the Z-component is related to spacecraft motion through the MC. Another estimate considered here, VE,V', is similar to VE,V in its formulation but depends on the decreasing |VZ| across part of the MC, that part between the maximum and minimum points of |VZ| which are usually close to (but not the same as) the boundaries points. The scalar means of estimating VE is almost independent of any MC parameter fitting model results, but the vector means slightly depends on quantities that are model dependent (e.g. |CA|≡|YO|/RO). The most probable values of VE from all three means, based on the full set of N=53 cases, are shown to be around 30 km/s, but VE has larger average values of =49 km/s, =36 km/s, and =44 km/s, with standard deviations of 27 km/s, 38 km/s, and 38 km/s, respectively. The linear correlation coefficient for VE,S vs. VE,V' is 0.85 but is lower (0.76) for VE,S vs. VE,V, as expected. The individual values of VE from all three means are usually well below the local Alfvén velocities, which are on average (for the cases considered here) equal to 116 km/s around the inbound boundary, 137 km/s at closest approach, and 94 km/s around the outbound boundary. Hence, a shock upstream of a MC is not expected to be due to MC expansion. Estimates reveal that the errors on the "vector" method of estimating VE (typically about ±7 km/s, but can get as large as ±25 km/s) are expected to be markedly smaller than those for the scalar method (which is usually in the range ±(15⇔20) km/s, depending on MC speed). This is true, despite the fact that |CA| (on which the vector method depends) is not always well determined by our MC parameter fitting model (Lepping et al., 1990), but the vector method only weakly depends on knowledge of |CA|.
Eastward sub-auroral ion drifts or ASAID
Authors: Voiculescu M. , Roth M.
Published: June 2010

Abstract. From satellite data sampling the top ionosphere in the Northern Hemisphere we have identified strong eastward ion drifts, with speeds larger than 1 km/s, widths of 1°–2°, occurring at similar temporal and spatial locations as rapid westward ion drifts known as sub-auroral ion drifts (SAID). We have called these events "abnormal sub-auroral ion drifts" (ASAID). Two events observed in the 20:00–22:00 MLT interval are discussed: the first occurring on 21 September 2003 and the other on 12 October 2003. Tomographic reconstructions of the electron density in the F-region, based on satellite data, provided by the Scandinavian tomography chain, were also available. We have observed that ASAID are accompanied by upward flows with a speed of the same order as that of the zonal ion drift. They coincide with deep, narrow troughs in the total ion density, both at the altitude of the F15 DMSP satellite (850 km) and in the F-region of the ionosphere, but do not seem to be a feature of the convective transport. During the entire duration of ASAID the electron temperature is very high while, contrary to SAID, the ion temperature has no clear variation. Both events described in this paper end up turning into classical SAID. Satellite data indicate that the generator of ASAID could be located inside the plasmasphere close to the plasmapause and we suggest a possible mechanism for their formation.
Pc5 waves generated by substorm injection: a case study
Authors: Zolotukhina N. A. , Mager P. N. , Klimushkin D. Yu.
Published: June 2010

Abstract. We analyzed the spectral-polarized characteristics of Pc5 ULF waves observed on 17 September 2000 after the 03:20:25 UT substorm onset with the satellites GOES 8 and 10 located east and west of the onset location. In the course of the event, the wave polarization changed from mixed (between toroidal and poloidal) to poloidal, and then to mixed again. The hodogram of magnetic field oscillations rotated counterclockwise at GOES 8, and clockwise at GOES 10. It is suggested that the satellites detected the waves generated by the substorm injected clouds of the charged particles drifting in the magnetosphere in the opposite azimuthal directions: GOES 8 (located east of the substorm onset) detected the wave generated by an electron cloud, and GOES 10 (west of the onset) detected the wave generated by a positive ion cloud. This interpretation is confirmed by the energetic particles data recorded by LANL satellites.
Different long-term trends of the oxygen red 630.0 nm line nightglow intensity as the result of lowering the ionosphere F2 layer
Authors: Gudadze N. B. , Didebulidze G. G. , Lomidze L. N. , Javakhishvili G. Sh. , Marsagishvili M. A. , Todua M.
Published: June 2010

Abstract. Long-term observations of total nightglow intensity of the atomic oxygen red 630.0 nm line at Abastumani (41.75° N, 42.82° E) in 1957–1993 and measurements of the ionosphere F2 layer parameters from the Tbilisi ionosphere station (41.65° N, 44.75° E) in 1963–1986 have been analyzed. It is shown that a decrease in the long-term trend of the mean annual red 630.0 nm line intensity from the pre-midnight value (+0.770±1.045 R/year) to its minimum negative value (−1.080±0.670 R/year) at the midnight/after midnight is a possible result of the observed lowering of the peak height of the ionosphere F2 layer electron density hmF2 (−0.455±0.343 km/year). A theoretical simulation is carried out using a simple Chapman-type layer (damping in time) for the height distribution of the F2 layer electron density. The estimated values of the lowering in the hmF2, the increase in the red line intensity at pre-midnight and its decrease at midnight/after midnight are close to their observational ones, when a negative trend in the total neutral density of the upper atmosphere and an increase in the mean northward wind (or its possible consequence – a decrease in the southward one) are assumed.
Statistics of fine dispersion structures events in energetic particle spectra: their origin and role in the outer magnetosphere
Authors: Lutsenko V. N. , Gavrilova E. A. , Grechko T. V.
Published: June 2010

Abstract. Fine Dispersion Structures (FDS) in energetic particle spectra in outer magnetosphere were discovered in DOK-2 experiments onboard of Interball-1 and -2 spacecrafts (1995–2000). First results of these studies were published in 2000–2005. It was shown that FDS can be a result of a gradient-curvature drift of ions and electrons around the Earth after their pulse injection from the geotail plasma sheet to some point in the night side of the outer magnetosphere. Since that time hundreds of such events have been examined additionally. They proved to be a rather common phenomenon in the outer Earth's magnetosphere. We present here statistics of FDS observations and properties which confirms our interpretation and clarifies the role of magnetotail plasma sheet and FDS particles in dynamics and replenishment of the outer radiation belt population.
Modification of conductivity due to acceleration of the ionospheric medium
Authors: Denisenko V. V. , Biernat H. K. , Mezentsev A. V. , Shaidurov V. A. , Zamay S. S.
Published: June 2010

Abstract. A quantitative division of the ionosphere into dynamo and motor regions is performed on the base of empirical models of space distributions of ionospheric parameters. Pedersen and Hall conductivities are modified to represent an impact of acceleration of the medium because of Ampére's force. It is shown that the currents in the F2 layer are greatly reduced for processes of a few hours duration. This reduction is in particular important for the night-side low-latitude ionosphere. The International Reference Ionosphere model is used to analyze the effect quantitatively. This model gives a second high conducting layer in the night-side low-latitude ionosphere that reduces the electric field and equatorial electrojets, but intensifies night-side currents during the short-term events. These currents occupy regions which are much wider than those of equatorial electrojets. It is demonstrated that the parameter σd=σP+σHΣH/ΣP that involves the integral Pedersen and Hall conductances ΣP, ΣH ought to be used instead of the local Cowling conductivity σC in calculations of the electric current density in the equatorial ionosphere. We may note that Gurevich et al. (1976) derived a parameter similar to σd for more general conditions as those which we discuss in this paper; a more detailed description of this point is given in Sect. 6. Both, σd and σC, appear when a magnetic field line is near a nonconducting domain which means zero current through the boundary of this domain. The main difference between σd and σC is that σd definition includes the possibility for the electric current to flow along a magnetic field line in order to close all currents which go to this line from neighboring ones. The local Cowling conductivity σC corresponds to the current closure at each point of a magnetic field line. It is adequate only for a magnetic field line with constant local conductivity at the whole line when field-aligned currents do not exist because of symmetry, but σC=σd in this case. So, there is no reason to use the local Cowling conductivity while the Cowling conductance ΣC=ΣP+ΣH2/ΣP is a useful and well defined parameter.
Diurnal behaviour of the ionospheric Alfvén resonator signatures as observed at high latitude observatory Barentsburg (L=15)
Authors: Semenova N. V. , Yahnin A. G.
Published: June 2010

Abstract. The signature of the ionospheric Alfvén resonator (IAR), so called spectral resonant structures (SRS) in the spectra of the electromagnetic noise in the range of 0.1–10 Hz is rather frequently observed with the search coil magnetometer at observatory Barentsburg on Svalbard (L=15). In this report we discuss some peculiarities of diurnal occurrence of SRS at this high latitude station. We show that the pronounced minimum of the SRS occurrence around noon can not be explained by the diurnal variations of the solar zenith angle (illumination of ionosphere). We conclude that the SRS occurrence minimum is the result of the enhanced variability of ionospheric parameters when the observing point enters (during the Earth's rotation) the region of the ionospheric projection of the dayside cusp and its vicinity.
Nonlinear solar cycle forecasting: theory and perspectives
Authors: Baranovski A. L. , Clette F. , Nollau V.
Published: June 2010

Abstract. In this paper we develop a modern approach to solar cycle forecasting, based on the mathematical theory of nonlinear dynamics. We start from the design of a static curve fitting model for the experimental yearly sunspot number series, over a time scale of 306 years, starting from year 1700 and we establish a least-squares optimal pulse shape of a solar cycle. The cycle-to-cycle evolution of the parameters of the cycle shape displays different patterns, such as a Gleissberg cycle and a strong anomaly in the cycle evolution during the Dalton minimum. In a second step, we extract a chaotic mapping for the successive values of one of the key model parameters – the rate of the exponential growth-decrease of the solar activity during the n-th cycle. We examine piece-wise linear techniques for the approximation of the derived mapping and we provide its probabilistic analysis: calculation of the invariant distribution and autocorrelation function. We find analytical relationships for the sunspot maxima and minima, as well as their occurrence times, as functions of chaotic values of the above parameter. Based on a Lyapunov spectrum analysis of the embedded mapping, we finally establish a horizon of predictability for the method, which allows us to give the most probable forecasting of the upcoming solar cycle 24, with an expected peak height of 93±21 occurring in 2011/2012.
First results from the CAWSES-India Tidal Campaign
Authors: Gurubaran S. , Narayana Rao D. , Ramkumar G. , Ramkumar T. K. , Dutta G. , Krishna Murthy B. V.
Published: June 2010

Abstract. The first CAWSES-India Tidal Campaign was conducted by the Indian scientific community during March–April 2006. The objectives of this campaign were: (1) To determine the characteristics of tides in the troposphere and lower stratosphere (0–20 km) and mesosphere and lower thermosphere (MLT) region (80–100 km), (2) to explore and identify what lower atmospheric processes drive middle atmospheric tides in the Indian continental region and (3) to provide information on those short-term variabilities of MLT tides that are likely to have an impact on the ionospheric variabilities and contribute to the upper atmospheric weather. Data sets from experiments conducted at the three low latitude radar sites, namely, Trivandrum (8.5° N, 76.9° E), Tirunelveli (8.7° N, 77.8° E) and Gadanki (13.5° N, 79.2° E) and fortnightly rocket launches from Thumba were made use of in this study. An important observational finding reported in this work is that the radar observations at Tirunelveli/Trivandrum indicate the presence of 15–20 day modulation of diurnal tide activity at MLT heights during the February–March period. A similar variation in the OLR fields in the western Pacific (120–160° longitude region) suggests a possible link between the observed tidal variabilities and the variations in the deep tropical convection through the nonmigrating tides it generates.
Phase calibration approaches for radar interferometry and imaging configurations: equatorial spread F results
Authors: Chau J. L. , Hysell D. L. , Kuyeng K. M. , Galindo F. R.
Published: June 2010

Abstract. In recent years, more and more radar systems with multiple-receiver antennas are being used to study the atmospheric and ionospheric irregularities with either interferometric and/or imaging configurations. In such systems, one of the major challenges is to know the phase offsets between the different receiver channels. Such phases are intrinsic to the system and are due to different cable lengths, filters, attenuators, amplifiers, antenna impedance, etc. Moreover, such phases change as function of time, on different time scales, depending on the specific installation. In this work, we present three approaches using natural targets (radio stars, meteor-head and meteor trail echoes) that allow either an absolute or relative phase calibration. In addition, we present the results of using an artificial source (radio beacon) for a continuous calibration that complements the previous approaches. These approaches are robust and good alternatives to other approaches, e.g. self-calibration techniques using known data features, or for multiple-receiver configurations constantly changing their receiving elements. In order to show the good performance of the proposed phase calibration techniques, we present new radar imaging results of equatorial spread F (ESF) irregularities. Finally we introduce a new way to represent range-time intensity (RTI) maps color coded with the Doppler information. Such modified map allows the identification and interpretation of geophysical phenomena, previously hidden in conventional RTI maps, e.g. the time and altitude of occurrence of ESF irregularities pinching off from the bottomside and their respective Doppler velocity.
What is the best method to calculate the solar wind propagation delay?
Authors: Mailyan B. , Munteanu C. , Haaland S.
Published: June 2010

Abstract. We present a statistical study of propagation times of solar wind discontinuities between Advanced Composition Explorer (ACE) spacecraft orbiting the L1 libration point and the Cluster quartet of spacecraft near the Earth's magnetopause. The propagation times for almost 200 events are compared with the predicted times from four different models. The simplest model assumes a constant convective motion of solar wind disturbances along the Sun-Earth line, whereas more sophisticated models take the orientation of the discontinuity as well as the real positions of the solar wind monitor and target into account. The results show that taking orientation and real position of the solar wind monitor and target into account gives a more precise time delay estimation in most cases. In particular, we show that recent modifications to the minimum variance technique can improve the estimation of propagation times of solar wind discontinuities.
On the diurnal variability in F2-region plasma density above the EISCAT Svalbard radar
Authors: Moen J. , Qiu X. C. , Carlson H. C. , Fujii R. , McCrea I. W.
Published: June 2010

Abstract. Two long runs of EISCAT Svalbard Radar (ESR), in February 2001 and October 2002, have been analysed with respect to variability in the F2 region peak density and altitude. The diurnal variation in the F2 peak density exhibits one maximum around 12:00 MLT and another around 23:00 MLT, consistent with solar wind controlled transport of EUV ionized plasma across the polar cap from day to night. High density plasma patch material is drawn in through the cusp inflow region independent of IMF BY. There is no apparent IMF BY asymmetry on the intake of high density plasma, but the trajectory of its motion is strongly BY dependent. Comparison with the international reference ionosphere model (IRI2001) clearly demonstrates that the model does not take account of the cross-polar transport of F2-region plasma, and hence has limited applicability in polar cap regions.
Automatic detection and tracking of filaments for a solar feature database
Authors: Aboudarham J. , Scholl I. , Fuller N. , Fouesneau M. , Galametz M. , Gonon F. , Maire A. , Leroy Y.
Published: June 2010

Abstract. A new method for the automatic detection and tracking of solar filaments is presented. The method addresses the problems facing existing catalogs, such as the one developed recently in the frame of the European Grid of Solar Observations (EGSO) project. In particular, it takes into account the structural and temporal evolution of filaments, differences in intensity as seen from one observation to the next, and the possibility of sudden disappearance followed by reappearance. In this study, the problem of tracking is solved by plotting all detected filaments during each solar rotation on a Carrington map and then by applying region growing techniques on those plots. Using this approach, the "fixed" positions of the envelopes in the Carrington system can be deduced. This is followed by a backward tracking of each filament by considering one full solar rotation. The resulting shifted Carrington map then enables one to follow any filament from one rotation to the next. Such maps should prove valuable for studies of the role of filaments in solar activity, notably coronal mass ejections (CMEs).
Momentum transfer at the high-latitude magnetopause and boundary layers
Authors: Lund E. J. , Farrugia C. J. , Sandholt P. E.
Published: June 2010

Abstract. How and where momentum is transferred from the solar wind to the magnetosphere and ionosphere is one of the key problems of space physics. Much of this transfer occurs through direct reconnection on the dayside, particularly when the IMF is southward. However, momentum transfer also occurs at higher latitudes via Alfvén waves on old open field lines, even for southward IMF. This momentum is transferred to the ionosphere via field-aligned currents (FACs), and the flow channel associated with these FACs produces a Hall current which causes magnetic variations at high latitude (the Svalgaard-Mansurov effect). We show examples where such momentum transfer is observed with multiple spacecraft and ground-based instruments.
Lower E-region echoes over the magnetic equator as observed by the MF radar at Tirunelveli (8.7° N, 77.8° E) and their relationship to Esq and Esb
Authors: Dhanya R. , Gurubaran S. , Emperumal K.
Published: June 2010

Abstract. The spaced antenna medium frequency (MF) radar at Tirunelveli (8.7° N, 77.8° E, geographic; 1.7° N, magnetic dip), the only one of its kind currently operating close to the magnetic equator, has provided an opportunity to investigate the electrodynamical processes related to the equatorial electrojet (EEJ) and their influence on the radar scatterers at medium frequencies in the lower E-region heights (90–98 km). Making use of the full correlation analysis that enables determination of useful geometrical parameters from the ground diffraction pattern, the present work delineates for the first time the characteristics of the radar scatterers during the occurrences of equatorial sporadic E (Esq) and blanketing sporadic E (Esb) noticed in simultaneous ionospheric sounding records at Tirunelveli. The ground magnetometer data provide indirect information on the strength of the EEJ and afternoon reverse EEJ or counterelectrojet (CEJ). The results presented in this work also reveal the height dependence of the radar echo intensity and some of the geometrical parameters at certain times, thus clearly bringing out the complex interplay of various physical processes in the probing region.
Identification of the sources of inertia-gravity waves in the Andes Cordillera region
Authors: Spiga A. , Teitelbaum H. , Zeitlin V.
Published: June 2010

Abstract. Four major sources of inertia-gravity waves are known in the Earth atmosphere: upper-tropospheric jet-streams, lower-tropospheric fronts, convection and topography. The Andes Cordillera region is an area where all of these major sources are potentially present. By combining ECMWF and NCEP-NCAR reanalysis, satellite and radiosoundings data and mesoscale WRF simulations in the Andes Cordillera region, we were able to identify the cases where, respectively, the jet-stream source, the convective source and the topography source are predominantly in action. We retrieve emitted wave parameters for each case, compare them, and analyse possible emission mechanisms. The WRF mesoscale model shows very good performance in reproducing the inertia-gravity waves identified in the data analysis, and assessing their likely sources.
Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006
Authors: Janicot S. , Thorncroft C. D. , Ali A. , Asencio N. , Berry G. , Bock O. , Bourles B. , Caniaux G. , Chauvin F. , Deme A. , Kergoat L. , Lafore J.-P. , Lavaysse C. , Lebel T. , Marticorena B. , Mounier F. , Nedelec P. , Redelsperger J.-L. , Ravegnani F. , Reeves C. E. , Roca R. , de Rosnay P. , Schlager H. , Sultan B. , Tomasini M. , Ulanovsky A. ,   ACMAD forecasters team
Published: June 2010

Abstract. The AMMA (African Monsoon Multidisciplinary Analysis) program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circulation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15° N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas.
Predicting cycle 24 using various dynamo-based tools
Authors: Dikpati M.
Published: June 2010

Abstract. Various dynamo-based techniques have been used to predict the mean solar cycle features, namely the amplitude and the timings of onset and peak. All methods use information from previous cycles, including particularly polar fields, drift-speed of the sunspot zone to the equator, and remnant magnetic flux from the decay of active regions. Polar fields predict a low cycle 24, while spot zone migration and remnant flux both lead to predictions of a high cycle 24. These methods both predict delayed onset for cycle 24. We will describe how each of these methods relates to dynamo processes. We will present the latest results from our flux-transport dynamo, including some sensitivity tests and how our model relates to polar fields and spot zone drift methods.
High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements
Authors: Förster M. , Haaland S. E. , Paschmann G. , Quinn J. M. , Torbert R. B. , Vaith H. , Kletzing C. A.
Published: June 2010

Abstract. In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007), and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward) convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum) potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South) Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the other intensifies and merges with the opposite main cell of the same polarity to form the large "round-shaped" convection cell when approaching a well-known IMFBy-dominated configuration. Opposite scenarios with interchanged roles of the respective cells occur for the opposite turning of the clock angle and at the Southern Hemisphere. The high-latitude dayside cells become more pronounced with increasing magnitude of the IMF vector.
On the use of IMAGE FUV for estimating the latitude of the open/closed magnetic field line boundary in the ionosphere
Authors: Boakes P. D. , Milan S. E. , Abel G. A. , Freeman M. P. , Chisham G. , Hubert B. , Sotirelis T.
Published: June 2010

Abstract. A statistical comparison of the latitude of the open/closed magnetic field line boundary (OCB) as estimated from the three far ultraviolet (FUV) detectors onboard the IMAGE spacecraft (the Wideband Imaging camera, WIC, and the Spectrographic Imagers, SI-12 and SI-13) has been carried out over all magnetic local times. A total of over 400 000 OCB estimations were compared from December 2000 and January and December of 2001–2002. The modal latitude difference between the FUV OCB proxies from the three detectors is small, <1°, except in the predawn and evening sectors, where the SI-12 OCB proxy is found to be displaced from both the SI-13 and WIC OCB proxies by up to 2° poleward in the predawn sector and by up to 2° equatorward in the evening sector. Comparing the IMAGE FUV OCB proxies with that determined from particle precipitation measurements by the Defense Meteorological Satellites Program (DMSP) also shows systematic differences. The SI-12 OCB proxy is found to be at higher latitude in the predawn sector, in better agreement with the DMSP OCB proxy. The WIC and SI-13 OCB proxies are found to be in better agreement with the DMSP OCB proxy at most other magnetic local times. These systematic offsets may be used to correct FUV OCB proxies to give a more accurate estimate of the OCB latitude.
Conjugate observation of sharp dynamical boundary in the inner magnetosphere by Cluster and DMSP spacecraft and ground network
Authors: Apatenkov S. V. , Sergeev V. A. , Amm O. , Baumjohann W. , Nakamura R. , Runov A. , Rich F. , Daly P. , Fazakerley A. , Alexeev I. , Sauvaud J. A. , Chotyaintsev Yu.
Published: June 2010

Abstract. We investigate an unusual sharp boundary separating two plasma populations (inner magnetospheric plasma with high fluxes of energetic particles and plasma sheet) observed by the Cluster quartet near its perigee on 16 December 2003. Cluster was in a pearl-on-string configuration at 05:00 MLT and mapped along magnetic field lines to ~8–9 RE in the equatorial plane. It was conjugate to the MIRACLE network and the DMSP F16 spacecraft passed close to Cluster footpoint. The properties of the sharp boundary, repeatedly crossed 7 times by five spacecraft during ~10 min, are: (1) upward FAC sheet at the boundary with ~30 nA/m2 current density at Cluster and ~2000 nA/m2 at DMSP; (2) the boundary had an embedded layered structure with different thickness scales, the electron population transition was at ~20 km scale at Cluster (<7 km at DMSP), proton population had a scale ~100 km, while the FAC sheet thickness was estimated to be ~500 km at Cluster (~100 km at DMSP); (3) the boundary propagated in the earthward-eastward direction at ~8 km/s in situ (equatorward-eastward ~0.8 km/s in ionosphere), and then decelerated and/or stopped. We discuss the boundary formation by the collision of two different plasmas which may include dynamical three-dimensional field-aligned current loops.
Near-Earth magnetic signature of magnetospheric substorms and an improved substorm current model
Authors: Ritter P. , Lühr H.
Published: June 2010

Abstract. Based on a comprehensive catalogue with more than 4000 magnetospheric substorm entries from the years 2000–2005, the spatial distribution of the substorm-related magnetic signatures at mid and low latitudes around local midnight was investigated. Superposed epoch analysis of a larger number of recent observatory data from mid and low latitudes revealed a field strength increase that is consistent with the results of earlier studies. For the first time, the magnetic signature of the substorm current wedge formation is studied also in near-Earth satellite data from CHAMP. The average maximal deflection measured on board the satellite is smaller by a factor of 2 than that determined from ground observations. The recurrence frequency of substorms as well as the amplitude of their magnetic signature depends strongly on the prevailing magnetic activity. The observed average substorm-related magnetic field signatures cannot be described adequately by a simple current wedge model. A satisfactory agreement between model results and observations at satellite height and on ground can be achieved only if the current reconfiguration scenario combines four elements: (1) the gradual decrease of the tail lobe field, (2) the re-routing of a part of the cross-tail current through the ionosphere, (3) eastward ionospheric currents at low and mid latitudes driven by Region-2 field-aligned currents, and (4) a partial ring current connected to these Region-2 FACs.
Comparison of simulated and observed large-scale, field-aligned current structures
Authors: Nenovski P.
Published: June 2010

Abstract. Recently, a model of large-scale, field-aligned current (FAC) structures, based on zero-frequency MHD surface wave (SW) modes that can emerge from the solar wind-Earth's magnetosphere interaction, has been proposed. The FAC polarity and intensity distribution are quantified as a function of the solar wind parameters and the interplanetary magnetic field (IMF) magnitude that enter as input parameters. Besides, there are input parameters intrinsic to the Earth's magnetosphere – the size of the polar cap and the boundary regions and their plasma density variations. Influence of the IMF By component on the FAC structure is examined here. Depending on the IMF By magnitude, the predicted six-cell FAC structure tends to evolve in a spiral-like fashion. This large-scale FAC model is compared with experimental evidences and empirical FAC models based on DE-2 satellite data and high-precision Oersted and Magsat satellite magnetometer data. Among the various achievements of these long-term satellite measurements, an observation/discovery of a ground-based state of FACs which includes a pair of large-scale FACs in the polar cap under both positive and negative IMF Bz has been pointed out. The FAC pattern is qualitatively and quantitatively consistent with experimental data for both polar cap FAC and Region 1 and Region 2 FAC systems.
Modeling of the Farley-Buneman instability in the E-region ionosphere: a new hybrid approach
Authors: Kovalev D. V. , Smirnov A. P. , Dimant Y. S.
Published: June 2010

Abstract. A novel approach to nonlinear simulations of the Farley-Buneman (FB) instability in the E-region ionosphere is developed. The mathematical model includes a fluid description of electrons and a simplified kinetic description of ions based on a kinetic equation with the Bhatnagar-Gross-Crook (BGK) collision term. This hybrid model takes into account all major factors crucial for development and nonlinear stabilization of the instability (collisional drag forces, ion inertia and Landau damping, dominant electron nonlinearity, etc.). At the same time, these simulations are free of noises caused by the finite number of particles and may require less computer resources than particle-in-cell (PIC) or hybrid – semi-fluid semi-PIC – simulations. First results of 2-D simulations are presented which agree reasonably well with those of previous 2-D PIC simulations. One of the potentially useful applications of the novel computational approach is modeling of the FB instability not far from its threshold.
Derivation of inner magnetospheric electric field (UNH-IMEF) model using Cluster data set
Authors: Matsui H. , Puhl-Quinn P. A. , Jordanova V. K. , Khotyaintsev Y. , Lindqvist P.-A. , Torbert R. B.
Published: June 2010

Abstract. We derive an inner magnetospheric electric field (UNH-IMEF) model at L=2–10 using primarily Cluster electric field data for more than 5 years between February 2001 and October 2006. This electric field data set is divided into several ranges of the interplanetary electric field (IEF) values measured by ACE. As ring current simulations which require electric field as an input parameter are often performed at L=2–6.6, we have included statistical results from ground radars and low altitude satellites inside the perigee of Cluster in our data set (L~4). Electric potential patterns are derived from the average electric fields by solving an inverse problem. The electric potential pattern for small IEF values is probably affected by the ionospheric dynamo. The magnitudes of the electric field increase around the evening local time as IEF increases, presumably due to the sub-auroral polarization stream (SAPS). Another region with enhanced electric fields during large IEF periods is located around 9 MLT at L>8, which is possibly related to solar wind-magnetosphere coupling. Our potential patterns are consistent with those derived from self-consistent simulations. As the potential patterns can be interpolated/extrapolated to any discrete IEF value within measured ranges, we thus derive an empirical electric potential model. The performance of the model is evaluated by comparing the electric field derived from the model with original one measured by Cluster and mapped to the equator. The model is open to the public through our website.