bluuebunny/crossref_metadata_2025_split huggingface dataset:
Global distributions of diurnal and semi-diurnal tides: observations from HRDI-UARS of the MLT region
Authors: Manson A. H. , Luo Y. , Meek C. 
Published: June 2010

Abstract. HRDI (High Resolution Doppler Interferometer-UARS) winds data have been analyzed in 4° latitude by 10° longitude cells at 96 km to obtain global contour maps of solar-tidal amplitudes and phases, and also mean winds. The solstices June–July (1993), December–January (1993–1994), and one equinox September–October (1994) are shown. The 24-h diurnal tide that maximizes near the 20–25° latitude has significant seasonal changes with equinoctial maxima, and very clear longitudinal variability. Maxima are very clear over the oceans. In contrast, the 12-h semi-diurnal tides that maximize near the 40–55° latitude have very strong seasonal changes with winter maxima, and more modest longitudinal changes. The similarities with MLT (mesosphere-lower thermosphere) radar observations (90 km) and the GSWM (Global Scale Wave Model) are very satisfactory. The mean winds are consistent with expectations and show clear poleward flow from summer to winter hemispheres in the solstices.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides) Radio science (remote sensing)
Coordinated ground-based and Cluster observations of large amplitude global magnetospheric oscillations during a fast solar wind speed interval
Authors: Mann I. R. , Voronkov I. , Dunlop M. , Donovan E. , Yeoman T. K. , Milling D. K. , Wild J. , Kauristie K. , Amm O. , Bale S. D. , Balogh A. , Viljanen A. , Opgenoorth H. J. 
Published: June 2010

Abstract. We present magnetospheric observations of very large amplitude global scale ULF waves, from 9 and 10 December 2000 when the upstream solar wind speed exceeded 600 km/s. We characterise these ULF waves using ground-based magnetometer, radar and optical instrumentation on both the dawn and dusk flanks; we find evidence to support the hypothesis that discrete frequency field line resonances (FLRs) were being driven by magnetospheric waveguide modes. During the early part of this interval, Cluster was on an outbound pass from the northern dusk side magnetospheric lobe into the magnetosheath, local-time conjugate to the Canadian sector. In situ magnetic fluctuations, observed by Cluster FGM, show evidence of quasi-periodic motion of the magnetosheath boundary layer with the same period as the ULF waves seen on the ground. Our observations represent the first simultaneous magnetometer, radar and optical observations of the characteristics of FLRs, and confirm the potential importance of ULF waves for magnetosphere-ionosphere coupling, particularly via the generation and modulation of electron precipitation into the ionosphere. The in situ Cluster measurements support the hypothesis that, during intervals of fast solar wind speed, the Kelvin-Helmholtz instability (KHI) can excite magnetospheric waveguide modes which bathe the flank magnetosphere with discrete frequency ULF wave power and drive large amplitude FLRs. Paper submitted to the special issue devoted to "Cluster: First scientific results", Ann. Geophysicae, 19, 10/11/12, 2001.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; MHD waves and instabilities; solar wind-magnetosphere interactions)
Long-term variations of the UV-B radiation over Central Europe as derived from the reconstructed UV time series
Authors: Krzyscin J. W. , Eerme K. , Janouch M. 
Published: June 2010

Abstract. The daily doses of the erythemally weighted UV radiation are reconstructed for three sites in Central Europe: Belsk-Poland (1966–2001), Hradec Kralove-Czech Republic (1964–2001), and Tõravere-Estonia (1967–2001) to discuss the UV climatology and the long-term changes of the UV-B radiation since the mid 1960s. Various reconstruction models are examined: a purely statistical model based on the Multivariate Adaptive Regression Splines (MARS) methodology, and a hybrid model combining radiative transfer model calculations with empirical estimates of the cloud effects on the UV radiation. Modeled long-term variations of the surface UV doses appear to be in a reasonable agreement with the observed ones. A simple quality control procedure is proposed to check the homogeneity of the biometer and pyranometer data. The models are verified using the results of UV observations carried out at Belsk since 1976. MARS provides the best estimates of the UV doses, giving a mean difference between the modeled and observed monthly means equal to 0.6±2.5%. The basic findings are: similar climatological forcing by clouds for all considered stations (~30% reduction in the surface UV), long-term variations in UV monthly doses having the same temporal pattern for all stations with extreme low monthly values (~5% below overall mean level) at the end of the 1970s and extreme high monthly values (~5% above overall mean level) in the mid 1990s, regional peculiarities in the cloud long-term forcing sometimes leading to extended periods with elevated UV doses, recent stabilization of the ozone induced UV long-term changes being a response to a trendless tendency of total ozone since the mid 1990s. In the case of the slowdown of the total ozone trend over Northern Hemisphere mid-latitudes it seems that clouds will appear as the most important modulator of the UV radiation both in long- and short-time scales over next decades. Key words. Atmospheric composition and structure (biospheric-atmosphere interaction) – Meteorology and atmospheric dynamics (climatology; radiative processes)
High-latitude poynting flux from combined Iridium and SuperDARN data
Authors: Waters C. L. , Anderson B. J. , Greenwald R. A. , Barnes R. J. , Ruohoniemi J. M. 
Published: June 2010

Abstract. Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S||, by combining electric field estimates from the Super Dual Auroral Radar Network (SuperDARN) with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S|| for any magnetic local time (MLT) from the pole to 60° magnetic latitude (MLAT). The effective spatial resolutions are 2° MLAT, 2h MLT, and the time resolution is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S|| and its spatial distribution on one hour time scales with two key advantages: (1) it yields the net S|| including the contribution of neutral winds; and (2) the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S|| that it gives. Comparisons with in-situ S|| estimates from DMSP satellites show agreement to a few mW/m2 and in the locations of S|| enhancements to within the technique's resolution. The total electromagnetic energy flux was 50GW for these events. At auroral latitudes, S|| tends to maximize in the morning and afternoon in regions less than 5° in MLAT by two hours in MLT having S||=10 to 20mW/m2 and total power up to 10GW. The power poleward of the Region 1 currents is about one-third of the total power, indicating significant energy flux over the polar cap.
Effects of the solar wind termination shock and heliosheath on theheliospheric modulation of galactic and anomalous Helium
Authors: Langner U. W. , Potgieter M. S. 
Published: June 2010

Abstract. The interest in the role of the solar wind termination shock and heliosheath in cosmic ray modulation studies has increased significantly as the Voyager 1 and 2 spacecraft approach the estimated position of the solar wind termination shock. The effect of the solar wind termination shock on charge-sign dependent modulation, as is experienced by galactic cosmic ray Helium (He++) and anomalous Helium (He+), is the main topic of this work, and is complementary to the previous work on protons, anti-protons, electrons, and positrons. The modulation of galactic and anomalous Helium is studied with a numerical model including a more fundamental and comprehensive set of diffusion coefficients, a solar wind termination shock with diffusive shock acceleration, a heliosheath and particle drifts. The model allows a comparison of modulation with and without a solar wind termination shock and is applicable to a number of cosmic ray species during both magnetic polarity cycles of the Sun. The modulation of Helium, including an anomalous component, is also done to establish charge-sign dependence at low energies. We found that the heliosheath is important for cosmic ray modulation and that its effect on modulation is very similar for protons and Helium. The local Helium interstellar spectrum may not be known at energies
Plasma bubble zonal velocity variations with solar activity in the Brazilian region
Authors: Terra P. M. , Sobral J. H. A. , Abdu M. A. , Souza J. R. , Takahashi H. 
Published: June 2010

Abstract. A statistical study of the zonal drift velocities of the ionospheric plasma bubbles using experimental airglow data acquired at the low-latitude station Cachoeira Paulista (Geogr. 22.5° S, 45° W, dip angle 28° S) during the period of October to March, between 1980 and 1994, is presented here. This study is based on 109 nights of zonal plasma bubble velocity estimations as determined from bubbles signatures on the OI 630nm scanning photometer airglow data. The zonal velocity magnitudes of the plasma bubbles are investigated with respect to solar activity and local time. It is verified that these velocities tend to increase with the solar EUV flux, using the solar 10.7-cm radio flux as a proxy (F10.7). These velocities are seen to be larger during the solar maximum activity period than in the solar minimum period. As to the local time variation, they are seen to peak before midnight, in the 20:30-22:30 LT time frame, depending on the season. The all-data plot based on the 109 nights of airglow experiments shows that the plasma bubble mean zonal drift velocities tend to decrease with local time, but they peak at 22:25 LT, where the velocity magnitude reaches 127.4ms-1. The zonal drift variations with local time and solar flux are shown in Figs. 1 and 2, respectively.
Improving and testing the empirical equatorial electrojet model with CHAMP satellite data
Authors: Doumouya V. , Cohen Y. 
Published: June 2010

Abstract. The longitudinal variation of the Equatorial Electrojet (EEJ) intensity has been revised including data from the equatorial station of Baclieu (Vietnam), where an unexpected enhancement of the EEJ magnetic effects is observed. The features of this longitudinal variation were also obtained with the CHAMP satellite, except in the Pacific and Atlantic Oceans, where no ground level data points were available.The EEJ magnetic signatures recorded on board the CHAMP satellite have been isolated for 325 passes in different longitude sectors around local noon. The results have been compared with the EEJ magnetic effects computed using the Empirical Equatorial Electrojet Model (3EM) proposed by Doumouya et al. (2003). The modeled EEJ magnetic effects are generally in good agreement with CHAMP observed EEJ magnetic signatures.
The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere
Authors: Wild J. A. , Milan S. E. , Owen C. J. , Bosqued J. M. , Lester M. , Wright D. M. , Frey H. , Carlson C. W. , Fazakerley A. N. , Rème H. 
Published: June 2010

Abstract. As a measure of the degree of coupling between the solar wind-magnetosphere-ionosphere systems, the rate at which the size of the polar cap (the region corresponding to ionospheric termini of open magnetic flux tubes) varies is of prime importance. However, a reliable technique by which the extent of the polar cap might be routinely monitored has yet to be developed. Current techniques provide particularly ambiguous indications of the polar cap boundary in the dawn sector. We present a case study of space- and ground-based observations of the dawn-sector auroral zone and attempt to determine the location of the polar cap boundary using multi-wavelength observations of the ultraviolet aurora (made by the IMAGE FUV imager), precipitating particle measurements (recorded by the FAST, DMSP, and Cluster 1 and 3 satellites), and SuperDARN HF radar observations of the ionospheric Doppler spectral width boundary. We conclude that in the dawn sector, during the interval presented, neither the poleward edge of the wideband auroral UV emission (140-180nm) nor the Doppler spectral width boundary were trustworthy indicators of the polar cap boundary location, while narrow band UV emissions in the range 130-140nm appear to be much more reliable.
Evolutionary signatures in complex ejecta and their driven shocks
Authors: Farrugia C. J. , Berdichevsky D. B. 
Published: June 2010

Abstract. We examine interplanetary signatures of ejecta-ejecta interactions. To this end, two time intervals of inner-heliospheric (≤1AU) observations separated by 2 solar cycles are chosen where ejecta/magnetic clouds are in the process of interacting to form complex ejecta. At the Sun, both intervals are characterized by many coronal mass ejections (CMEs) and flares. In each case, a complement of observations from various instruments on two spacecraft are examined in order to bring out the in-situ signatures of ejecta-ejecta interactions and their relation to solar observations. In the first interval (April 1979), data are shown from Helios-2 and ISEE-3, separated by ~0.33AU in radial distance and 28° in heliographic longitude. In the second interval (March-April 2001), data from the SOHO and Wind probes are combined, relating effects at the Sun and their manifestations at 1AU on one of Wind's distant prograde orbits. At ~0.67AU, Helios-2 observes two individual ejecta which have merged by the time they are observed at 1AU by ISEE-3. In March 2001, two distinct Halo CMEs (H-CMEs) are observed on SOHO on 28-29 March approaching each other with a relative speed of 500kms-1 within 30 solar radii. In order to isolate signatures of ejecta-ejecta interactions, the two event intervals are compared with expectations for pristine (isolated) ejecta near the last solar minimum, extensive observations on which were given by Berdichevsky et al. (2002). The observations from these two event sequences are then intercompared. In both event sequences, coalescence/merging was accompanied by the following signatures: heating of the plasma, acceleration of the leading ejecta and deceleration of the trailing ejecta, compressed field and plasma in the leading ejecta, disappearance of shocks and the strengthening of shocks driven by the accelerated ejecta. A search for reconnection signatures at the interface between the two ejecta in the March 2001 event was inconclusive because the measured changes in the plasma velocity tangential to the interface (Δνt) were not correlated with Δ(Bt /ρ). This was possibly due to lack of sufficient magnetic shear across the interface. The ejecta mergers altered interplanetary parameters considerably, leading to contrasting geoeffects despite broadly similar solar activity. The complex ejecta on 31 March 2001 caused a double-dip ring current enhancement, resulting in two great storms (Dst, corrected for the effect of magnetopause currents, <-450nT), while the merger on 5 April 1979 produced only a corrected Dst of ~-100nT, mainly due to effects of magnetopause currents.
Interplanetary magnetic field control of dayside transient event occurrence and motion in the ionosphere and magnetosphere
Authors: Korotova G. I. , Sibeck D. G. , Singer H. J. , Rosenberg T. J. , Engebretson M. J. 
Published: June 2010

Abstract. The pressure pulse model for dayside transient ionospheric events predicts dawnward moving events at and prior to local noon during periods of spiral interplanetary magnetic field (IMF) orientation, but duskward moving events at and after local noon during rarer periods of orthospiral IMF orientation. We use this model to interpret ground and geosynchronous magnetometer observations of a duskward-moving transient event that occurred on 10 August 1995 during a period of orthospiral IMF orientation. We then survey geosynchronous GOES-8, 9, and 10 magnetometer observations to determine the directions of motion for 67 isolated magnetic impulse events seen in South Pole magnetograms from 1995-1999. The occurrence patterns and directions of motion inferred from both case and statistical studies are consistent with pressure pulse model predictions. Key words. Interplanetary physics (Interplanetary magnetic fields; discontinuities) – Magnetospheric physics (Magnetosphere-ionosphere interactions)
Identification of broad-band waves above the auroral acceleration region: Cluster observations
Authors: Backrud M. , André M. , Balogh A. , Buchert S. , Cornilleau-Wehrlin N. , Vaivads A. 
Published: June 2010

Abstract. We investigate broad-band emissions at frequencies above the ion gyrofrequency on auroral field lines at geocentric distances of about 4.5 Earth radii. Observations by the Cluster satellites are used to study the wave characteristics and to determine the wave modes involved. All events include some bursts of broad-band emissions with a substantial component of the electric field parallel to the geomagnetic field. Studying the polarization of the emissions we find that linear waves in a homogeneous plasma can be used to theoretically describe the observations. The broad-band emissions include short bursts of ion acoustic waves, and longer periods of ion Bernstein and Electrostatic Ion Cyclotron (EIC) waves. All waves occur during the same event within a few seconds, with EIC waves as the most common. Theoretically, there is no sharp limit between these wave modes and they can be described by the same dispersion surface. These emissions are closely associated with low-frequency Alfvén waves, indicating a possible generation mechanism. Key words. Magnetospheric physics (auroral phenomena; electric fields; plasma waves and instabilities)
Plasma depletion layer: the role of the slow mode waves
Authors: Wang Y. L. , Raeder J. , Russell C. T. 
Published: June 2010

Abstract. The plasma depletion layer (PDL) is a layer on the sunward side of the magnetopause with lower plasma density and higher magnetic field compared to their corresponding values in the upstream magnetosheath. The depletion layer usually occurs during northward (IMF) conditions with low magnetic shear across the magnetopause. We have previously validated the Raeder global model by comparing the computed formation of a magnetosheath density depletion with in-situ observations. We also have performed a detailed force analysis and found the varying roles that different MHD forces play along the path of a plasma parcel flowing around the magnetopause. That study resulted in a new description of the behavior of magnetosheath magnetic flux tubes which better explains the plasma depletion along a flux tube. The slow mode waves have been observed in the magnetosheath and have been used to explain the formation of the PDL in some of the important PDL models. In this study, we extend our former work by investigating the possible role of the slow mode waves for the formation of the PDL, using global MHD model simulations. We propose a new technique to test where a possible slow mode front may occur in the magnetosheath by comparing the slow mode group velocity with the local flow velocity. We find that the slow mode fronts can exist in certain regions in the magnetosheath under certain solar wind conditions. The existence and location of such fronts clearly depend on the IMF. We do not see from our global simulation results either the sharpening of the slow mode front into a slow mode shock or noticeable changes of the flow and field in the magnetosheath across the slow mode front, which implies that the slow mode front is not likely responsible for the formation of the PDL, at least for the stable solar wind conditions used in these simulations. Also, we do not see the two-layered slow mode structures shown in some observations and proposed in certain PDL models. Instead, we see only a one-layered spatial PDL structure under the stable solar wind conditions used in this study.
Anomalous nighttime electron temperatures over Millstone Hill: a statistical study
Authors: Lobzin V. V. , Pavlov A. V. 
Published: June 2010

Abstract. A statistical study of anomalous nighttime electron temperature enhancements, NETEs, observed on 336 nights during Millstone Hill radar measurements on 730 nights from 1976 to 2001 is carried out. NETEs are most frequent in winter and in autumn. The NETE occurrence has a maximum probability in February and a minimum probability in July. The asymmetry between spring and autumn NETE occurrences is found for NETEs, which are observed during geomagnetially quiet time periods. The calculated value of the NETE occurrence probability is decreased with the solar activity index F10.7 increase. The increase in a 3-h geomagnetic index Kp or the decrease in a 1-h geomagnetic index Dst leads to the increase in the NETE occurrence probability. This tendency is more pronounced for current values of Kp or Dst rather than for delayed ones and becomes more weak with the delay increase. The NETEs are most likely to begin between 19:00 and 20:00 UT. The studied NETEs are characterized by the most typical duration from 1 to 3h with the percentage peak between 1 and 2h. The electron temperature increases are predominately between 100K and 300K. We did not find any relationship between the amplitude and duration of the NETEs studied. It is shown that there is a tendency for the NETE amplitude to increase if the value of Kp or ∣Dst∣ increases. To determine whether there exists a difference between NETEs observed during different solar cycles, we chose the data subsets corresponding to 21 and 22solar cycles and performed the statistical studies for each subset. It was found that, within the errors, the corresponding dependencies are the same for the cycles considered and for the entire data set. Key words. Ionosphere (plasma temperature and density; ionospheric disturbances; modeling and forecasting)
Variations of thermospheric composition according to AE-C data and CTIP modelling
Authors: Rishbeth H. , Heelis R. A. , Müller-Wodarg I. C. F. 
Published: June 2010

Abstract. Data from the Atmospheric Explorer C satellite, taken at middle and low latitudes in 1975-1978, are used to study latitudinal and month-by-month variations of thermospheric composition. The parameter used is the "compositional Ρ-parameter", related to the neutral atomic oxygen/molecular nitrogen concentration ratio. The midlatitude data show strong winter maxima of the atomic/molecular ratio, which account for the "seasonal anomaly" of the ionospheric F2-layer. When the AE-C data are compared with the empirical MSIS model and the computational CTIP ionosphere-thermosphere model, broadly similar features are found, but the AE-C data give a more molecular thermosphere than do the models, especially CTIP. In particular, CTIP badly overestimates the winter/summer change of composition, more so in the south than in the north. The semiannual variations at the equator and in southern latitudes, shown by CTIP and MSIS, appear more weakly in the AE-C data. Magnetic activity produces a more molecular thermosphere at high latitudes, and at mid-latitudes in summer. Key words. Atmospheric composition and structure (thermosphere – composition and chemistry)