bluuebunny/crossref_metadata_2025 huggingface dataset:
Unusual strong quasi-monochromatic ground Pc5 geomagnetic pulsations in the recovery phase of November 2003 superstorm
Authors: Kleimenova N. G. , Kozyreva O. V. , Manninen J. , Ranta A.
Published: June 2010

Abstract. Unusually large-amplitude morning Pc5 magnetic pulsations during the recovery phase of the huge magnetic storm in November 2003 have been studied by using ground-based multi-point observations. Two main spectral Pc5 enhancements were observed: at f≈2 mHz, which featured slowly increasing frequency with decreasing latitude, and at f≈3 mHz, which was latitude independent. The Pc5 pulsations were observed at wide range of latitudes (more than 10°) with the same very strong amplitude (up to 500nT) and with the same polarization. Only the 3-mHz peak was clearly seen in the spectra of pulsating auroral radio absorption, as observed by the Finnish riometer chain. Short and localized bursts of PiB (f~50–100 mHz) magnetic pulsations and simultaneous short bursts of energetic electron precipitation were observed in the morning sector, as well. The beginning of the large-amplitude morning Pc5 activity occurred simultaneously with a substorm onset in the evening and midnight sectors. However, the spectra of pulsations in the morning and evening sectors were different. They were compared with spectra of IMF and solar wind parameters, measured by ACE spacecraft. The similarity between the spectra of morning Pc5 and IMF By was found, but the spectra of evening Pi3 pulsations were similar to the spectra of solar wind density variations. The Pc5 and PiB pulsations, as well as bursts of the auroral radio absorption, suddenly disappeared, when the solar wind density abruptly dropped. We suppose that the ~2-mHz Pc5 geomagnetic pulsations could be attributed to field line resonance (FLR), however, the 3-mHz oscillations were apparently non-resonance origin. Keywords. Magnetospheric physics (MHD waves and instabilities; Solar wind-magnetosphere interaction; Storms and substorms)
Comparisons between EUV/IMAGE observations and numerical simulations of the plasmapause formation
Authors: Pierrard V. , Cabrera J.
Published: June 2010

Abstract. Simulations of plasmapause formation described in Pierrard and Lemaire (2004) predict the shape and equatorial distance of the plasmapause as a function of the geomagnetic activity index Kp. The equatorial positions predicted by this model are compared with the observations of EUV/IMAGE during the geomagnetic storm of 24 May 2000, substorm events of 10 June 2001 and 25 June 2000, and also during a prolonged quiet period (2 May 2001) when the plasmasphere was very extended. The formation of structures, like plumes and shoulders observed during periods of high geomagnetic activity, is quite well reproduced by the simulations. These structures are directly related to specific time sequences of Kp variations. The radial distances of the plasmapause are also reproduced, on average, by the model. Keywords. Magnetospheric physics (Plasmasphere; Storms and substorms; Solar wind magnetosphere interactions)
The new Athens center on data processing from the neutron monitor network in real time
Authors:   Mavromichalaki,   Souvatzoglou,   Sarlanis,   Mariatos,   Gerontidou,   Papaioannou,   Plainaki,   Tatsis,   Belov,   Eroshenko,   Yanke
Published: June 2010

Abstract. The ground-based neutron monitors (NMs) record galactic and solar relativistic cosmic rays which can play a useful key role in space weather forecasting, as a result of their interaction with interplanetary disturbances. The Earth's-based neutron monitor network has been used in order to produce a real-time prediction of space weather phenomena. Therefore, the Athens Neutron Monitor Data Processing Center (ANMODAP) takes advantage of this unique multi-directional device to solve problems concerning the diagnosis and forecasting of space weather. At this moment there has been a multi-sided use of neutron monitors. On the one hand, a preliminary alert for ground level enhancements (GLEs) may be provided due to relativistic solar particles and can be registered around 20 to 30 min before the arrival of the main part of lower energy particles responsible for radiation hazard. To make a more reliable prognosis of these events, real time data from channels of lower energy particles and X-ray intensity from the GOES satellite are involved in the analysis. The other possibility is to search in real time for predictors of geomagnetic storms when they occur simultaneously with Forbush effects, using hourly, on-line accessible neutron monitor data from the worldwide network and applying a special method of processing. This chance of prognosis is only being elaborated and considered here as one of the possible uses of the Neutron Monitor Network for forecasting the arrival of interplanetary disturbance to the Earth. The achievements, the processes and the future results, are discussed in this work.
A comparison of satellite scintillation measurements with HF radar backscatter characteristics
Authors: Milan S. E. , Basu S. , Yeoman T. K. , Sheehan R. E.
Published: June 2010

Abstract. We examine the correspondence between high latitude ionospheric scintillation measurements made at 250MHz with the occurrence of 10MHz HF coherent radar backscatter, on 13 and 14 December 2002. We demonstrate that when the ionospheric intersection point of the scintillation measurements is co-located with significant HF radar backscatter, the observed scintillation, quantified by the S4 index, is elevated. Conversely, when the radar indicates that backscatter is observed away from the intersection point due to movements of the auroral zone, the observed scintillation is low. This suggests that scintillation is highly location-dependent, being enhanced in the auroral zone and being lower at sub-auroral latitudes. The coexistence of scintillation and HF radar backscatter, produced by ionospheric density perturbations with scale sizes of 100s of metres and ~15 m, respectively, suggests that a broad spectrum of density fluctuations is found in the auroral zone.
Numerical study of the Middle Adriatic coastal waters' sensitivity to the various air pressure travelling disturbances
Authors: Vilibić I.
Published: June 2010

Abstract. The paper documents resonant coupling between an air pressure travelling disturbance and the Middle Adriatic coastal waters, examined theoretically by using a barotropic numerical model and then comparing the model to the observed events. The model is forced first with a cosine and box air pressure disturbance travelling with a constant speed and direction but varying its eulerian period/duration, whereas the sensitivity to the disturbance speed is examined by varying it, keeping all the other parameters constant. Larger resonant transfer of energy is documented for shorter disturbances and for the box versus cosine variation, especially in the high-frequency domain. Bands of enlarged sea level amplification are found in front of Stari Grad Bay (6.7 and 11.0 min) close to its natural modes (6.1 and 10.6 min), which may be a reason for the very large amplification and sporadic severe floods observed at the inner bay area. The lack of coincidence in the Stari Grad and Vela Luka observed floods may be partially a result of different disturbance speeds and energy transfer rates due to various depths off the bays, yet some additional factors (basin shape, real disturbance energy, disturbance direction) should be examined in the future.
Spatial localization and azimuthal wave numbers of Alfvén waves generated by drift-bounce resonance in the magnetosphere
Authors: Mager P. N. , Klimushkin D. Yu.
Published: June 2010

Abstract. Spatial localization and azimuthal wave numbers m of poloidal Alfvén waves generated by energetic particles in the magnetosphere are studied in the paper. There are two factors that cause the wave localization across magnetic shells. First, the instability growth rate is proportional to the distribution function of the energetic particles, hence waves must be predominantly generated on magnetic shells where the particles are located. Second, the frequency of the generated poloidal wave must coincide with the poloidal eigenfrequency, which is a function of the radial coordinate. The combined impact of these two factors also determines the azimuthal wave number of the generated oscillations. The beams with energies about 10 keV and 150 keV are considered. As a result, the waves are shown to be strongly localized across magnetic shells; for the most often observed second longitudinal harmonic of poloidal Alfvén wave (N=2), the localization region is about one Earth radius across the magnetic shells. It is shown that the drift-bounce resonance condition does not select the m value for this harmonic. For 10 keV particles (most often involved in the explanation of poloidal pulsations), the azimuthal wave number was shown to be determined with a rather low accuracy, -100<m<0. The 150 keV particles provide a little better but still a poor determination of this value, -90<m<-70. For the fundamental harmonic (N=1), the azimuthal wave number is determined with a better accuracy, but both of these numbers are too small (if the waves are generated by 150 keV particles), or the waves are generated on magnetic shells (in 10 keV case) which are too far away. The calculated values of γ/ω are not large enough to overcome the damping on the ionosphere. All these have cast some suspicion on the possibility of the drift-bounce instability to generate poloidal pulsations in the magnetosphere.
Cluster multispacecraft observations at the high-latitude duskside magnetopause: implications for continuous and component magnetic reconnection
Authors: Retinò A. , Bavassano Cattaneo M. B. , Marcucci M. F. , Vaivads A. , André M. , Khotyaintsev Y. , Phan T. , Pallocchia G. , Rème H. , Möbius E. , Klecker B. , Carlson C. W. , McCarthy M. , Korth A. , Lundin R. , Balogh A.
Published: June 2010

Abstract. We report multispacecraft Cluster observations of magnetic reconnection at the high-latitude magnetopause/magnetospheric boundary layer (MP/BL) under mainly northward interplanetary magnetic field (IMF) conditions. The event we study is on 3 December 2001 when the Cluster spacecraft were skimming the high-latitude duskside MP/BL during a period of about four hours. The orbit and configuration of the spacecraft were such that at least one satellite was present in the MP/BL during most of that period. We present the evidence of reconnection in the form of tangential stress balance between the magnetosheath and the MP/BL (Walén test) and in several cases in the form of transmitted magnetosheath ions in the MP/BL and incident/reflected magnetosheath ions in the magnetosheath boundary layer (MSBL) . The observations are consistent with magnetic reconnection occurring tailward of the cusp and going on continuously for a period of about four hours. The observed directions of the reconnection flows are consistent with the IMF orientation, thus indicating that reconnection is globally controlled by the IMF. Observations of a few flow reversals suggest passages of the spacecraft close to the X-line. The observation of low magnetic shear across the magnetopause during a flow reversal is consistent with component merging at least in one case. The observation of reconnection flows on the duskside magnetopause irrespective of the change in the sign of the IMF BY also suggests a better agreement with the component merging model, though antiparallel merging cannot be excluded because the distance from the X-line is not known.
A statistical comparison of SuperDARN spectral width boundaries and DMSP particle precipitation boundaries in the morning sector ionosphere
Authors: Chisham G. , Freeman M. P. , Sotirelis T. , Greenwald R. A. , Lester M. , Villain J.-P.
Published: June 2010

Abstract. Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial for making accurate ionospheric measurements of many magnetospheric processes (e.g. magnetic reconnection). This study compares the latitudes of Spectral Width Boundaries (SWBs), identified in the morning sector ionosphere using the Super Dual Auroral Radar Network (SuperDARN), with Particle Precipitation Boundaries (PPBs) determined using the low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the SWB represents a good proxy for the ionospheric projection of the OCB. The latitudes of SWBs and PPBs were identified using automated algorithms applied to 5 years (1997-2001) of data measured in the 00:00-12:00 Magnetic Local Time (MLT) range. A latitudinal difference was measured between each PPB and the nearest SWB within a ±10min Universal Time (UT) window and within a ±1h MLT window. The results show that the SWB represents a good proxy for the OCB close to midnight (~00:00-02:00 MLT) and noon (~08:00-12:00 MLT), but is located some distance (~2°-4°) equatorward of the OCB across much of the morning sector ionosphere (~02:00-08:00 MLT). On the basis of this and other studies we deduce that the SWB is correlated with the poleward boundary of auroral emissions in the Lyman-Birge-Hopfield ``Long" (LBHL) UV emission range and hence, that spectral width is inversely correlated with the energy flux of precipitating electrons. We further conclude that the combination of two factors may explain the spatial distribution of spectral width values in the polar ionospheres. The small-scale structure of the convection electric field leads to an enhancement in spectral width in regions close to the OCB, whereas increases in ionospheric conductivity (relating to the level of incident electron energy flux) lead to a reduction in spectral width in regions just equatorward of the OCB.
Phenomena in the ionosphere-magnetosphere system induced by injection of powerful HF radio waves into nightside auroral ionosphere
Authors: Blagoveshchenskaya N. F. , Borisova T. D. , Kornienko V. A. , Thidé B. , Rietveld M. T. , Kosch M. J. , Bösinger T.
Published: June 2010

Abstract. Experimental results from three ionospheric HF pumping experiments in overdense E or F regions are summarized. The experiments were conducted by the use of the EISCAT HF Heating facility located near Tromsø, Norway, allowing HF pumping the ionosphere in a near geomagnetic field-aligned direction. Distinctive features related to auroral activations in the course of the experiments are identified. Typical features observed in all experiments are the following: generation of scattered components in dynamic HF radio scatter Doppler spectra; strong increase of ion temperatures Ti and local ionospheric electric field E0; modification of the auroral arc and local spiral-like formation. However, some effects were observed only when the HF pump wave was reflected from the F2 layer. Among them are the generation of intense field-aligned ion outflows, and a strong increase in the electron temperature Te with altitude. A possible scenario for the substorm triggering due to HF pumping into an auroral ionosphere is discussed. The authors present their interpretation of the data as follows. It is suggested that two populations of charged particles are at play. One of them is the runaway population of electrons and ions from the ionosphere caused by the effects of the powerful HF radio wave. The other is the population of electrons that precipitate from the magnetosphere. It is shown that the hydrodynamical equilibrium was disrupted due to the effects of the HF pumping. We estimate that the parallel electric field can reach values of the order of 30mV/m during substorm triggering.
First E- and D-region incoherent scatter spectra observed over Jicamarca
Authors: Chau J. L. , Kudeki E.
Published: June 2010

Abstract. We present here the first Jicamarca observations of incoherent scatter radar (ISR) spectra detected from E- and D-region altitudes. In the past such observations have not been possible at Jicamarca due a combined effect of strong equatorial electrojet (EEJ) clutter and hardware limitations in the receiving system. The observations presented here were made during weak EEJ conditions (i.e., almost zero zonal electric field) using an improved digital receiving system with a wide dynamic range and a high data throughput. The observed ISR spectra from E- and D-region altitudes are, as expected, narrow and get even narrower with decreasing altitude due to increasing ion-neutral collision frequencies. Therefore, it was possible to obtain accurate spectral measurements using a pulse-to-pulse data analysis. At lower altitudes in the D-region where signal correlation times are relatively long we used coherent integration to improve the signal-to-noise ratio of the collected data samples. The spectral estimates were fitted using a standard incoherent scatter (IS) spectral model between 87 and 120 km, and a Lorentzian function below 110 km. Our preliminary estimates of temperature and ion-neutral collisions frequencies above 87 km are in good agreement with the MSISE-90 model. Below 87 km, the measured spectral widths are larger than expected, causing an overestimation of the temperatures, most likely due to spectral distortions caused by atmospheric turbulence.
The atmospheric implications of radiation belt remediation
Authors: Rodger C. J. , Clilverd M. A. , Ulich Th. , Verronen P. T. , Turunen E. , Thomson N. R.
Published: June 2010

Abstract. High altitude nuclear explosions (HANEs) and geomagnetic storms can produce large scale injections of relativistic particles into the inner radiation belts. It is recognised that these large increases in >1 MeV trapped electron fluxes can shorten the operational lifetime of low Earth orbiting satellites, threatening a large, valuable population. Therefore, studies are being undertaken to bring about practical human control of the radiation belts, termed "Radiation Belt Remediation" (RBR). Here we consider the upper atmospheric consequences of an RBR system operating over either 1 or 10 days. The RBR-forced neutral chemistry changes, leading to NOx enhancements and Ox depletions, are significant during the timescale of the precipitation but are generally not long-lasting. The magnitudes, time-scales, and altitudes of these changes are no more significant than those observed during large solar proton events. In contrast, RBR-operation will lead to unusually intense HF blackouts for about the first half of the operation time, producing large scale disruptions to radio communication and navigation systems. While the neutral atmosphere changes are not particularly important, HF disruptions could be an important area for policy makers to consider, particularly for the remediation of natural injections.
Limits on the core temperature anisotropy of solar wind protons
Authors: Marsch E. , Zhao L. , Tu C.-Y.
Published: June 2010

Abstract. We analyse the temperature anisotropy of the protons in the solar wind and thereby concentrate on plasma data obtained in the year 1976 of the Helios 1 and Helios 2 missions. We derive the core proton temperatures and , in the directions perpendicular and parallel to the magnetic field, as well as the core parallel plasma beta, . The data are separately analysed for two distance ranges, AU and AU, and divided into 24 bins for the plasma beta, in the range from to , and into 72 bins for the total temperature anisotropy, , which is here considered in the range from −0.9 to 0.9. The number of spectra in each bin is determined to obtain distributions. The statistical results are presented in two-dimensional histograms. For each column we define a critical upper and lower limit of the anisotropy. The resulting empirical points are compared with the known theoretical instability thresholds. The protons are found to come with increasing radial distance closer to the fire-hose instability threshold.
Ionospheric signatures of the low-latitude boundary layer under conditions of northward IMF and small clock angle
Authors: Pryse S. E. , Sims R. W. , Moen J. , Oksavik K.
Published: June 2010

Abstract. A case study is presented that concerns the footprints of the low-latitude boundary layer in the high-latitude ionosphere. The measurements were made near local magnetic noon in summertime under conditions of Bz>0 and small clock angle. Of particular interest are particle fluxes measured in the region by the NOAA-12 satellite that revealed energetic (>30 keV) electrons, characteristic of trapped particles, together with a population of softer precipitating magnetosheath particles. The particle energy-distribution was distinct from those identifying the central plasma sheet at lower latitudes. On its poleward side the layer extended to at least the latitude of the polar cap boundary as identified in ion flows and electron densities measured by the EISCAT Svalbard radar. It is proposed that the particles of the low-latitude boundary layer occurred on newly-closed magnetic field lines, which were formed by the closure of open polar cap field by lobe reconnection in both Northern and Southern Hemispheres.
IRI-2001 model predictions compared with ionospheric data observed at Brazilian low latitude stations
Authors: Bertoni F. , Sahai Y. , Lima W. L. C. , Fagundes P. R. , Pillat V. G. , Becker-Guedes F. , Abalde J. R.
Published: June 2010

Abstract. In this work, the F-region critical frequency (foF2) and peak height (hmF2) measured by digital ionosondes at two Brazilian low-latitude stations, namely Palmas (10.17° S, 48.20° W, dip –10.80°) and São José dos Campos (23.20° S, 45.86° W, dip –38.41°), are compared with the IRI-2001 model predictions. The comparison at the latter station shows quite a reasonable agreement for both parameters. The former station exhibits a better agreement for hmF2 than for foF2. In general, the model generates good results, although some improvements are still necessary to implement in order to obtain better simulations for equatorial ionospheric regions.
Magnetosonic resonance in a dipole-like magnetosphere
Authors: Leonovich A. S. , Kozlov D. A. , Pilipenko V. A.
Published: June 2010

Abstract. A theory of resonant conversion of fast magnetosonic (FMS) waves into slow magnetosonic (SMS) oscillations in a magnetosphere with dipole-like magnetic field has been constructed. Monochromatic FMS waves are shown to drive standing (along magnetic field lines) SMS oscillations, narrowly localized across magnetic shells. The longitudinal and transverse structures, as well as spectrum of resonant SMS waves are determined. Frequencies of fundamental harmonics of standing SMS waves lie in the range of 0.1–1 mHz, and are about two orders of magnitude lower than frequencies of similar Alfvén field line resonance harmonics. This difference makes an effective interaction between these MHD modes impossible. The amplitude of SMS oscillations rapidly decreases along the field lines from the magnetospheric equator towards the ionosphere. In this context, magnetospheric SMS oscillations cannot be observed on the ground, and the ionosphere does not play any role either in their generation or dissipation. The theory developed can be used to interpret the occurrence of compressional Pc5 waves in a quiet magnetosphere with a weak ring current.
Spatial structure and dispersion of drift mirror waves coupled with Alfvén waves in a 1-D inhomogeneous plasma
Authors: Klimushkin D. Yu.
Published: June 2010

Abstract. The paper employs the frame of a 1-D inhomogeneous model of space plasma,to examine the spatial structure and growth rate of drift mirror modes, often suggested for interpreting some oscillation types in space plasma. Owing to its coupling with the Alfvén mode, the drift mirror mode attains dispersion across magnetic shells (dependence of the frequency on the wave-vector's radial component, kr). The spatial structure of a mode confined across magnetic shells is studied. The scale of spatial localization of the wave is shown to be determined by the plasma inhomogeneity scale and by the azimuthal component of the wave vector. The wave propagates across magnetic shells, its amplitude modulated along the radial coordinate by the Gauss function. Coupling with the Alfvén mode strongly influences the growth rate of the drift mirror instability. The mirror mode can only exist in a narrow range of parameters. In the general case, the mode represents an Alfvén wave modified by plasma inhomogeneity.
Antiparallel magnetic merging signatures during IMF BY>>0: longitudinal and latitudinal cusp aurora bifurcations
Authors: Massetti S.
Published: June 2010

Abstract. A prominent dayside auroral event, occurred during an IMF BY-dominated time interval, and characterized by the contemporaneous longitudinal and latitudinal cusp bifurcations, is reported. The event was recorded the 19 December 2002, between about 09:30–10:45 UT, by the ITACA2 twin auroral monitors system, in the Greenland-Svalbard zone. The splitting of the ionospheric footprint of the geomagnetic cusp, traced by the dayside auroral activity, was recently identified with the signatures of antiparallel reconnection episodes ongoing at different magnetopause locations, during large IMF BY periods. The first part of the event showed a broad longitudinal bifurcation of the red-dominated cusp aurora, displaced in the prenoon and postnoon, with a separation up to ~1800 km, during northeast directed IMF (clock-angle rotating from 45° to 90°). This observation widens the range of IMF regimes that are known to drive a longitudinal bifurcation of the cusp, since previous case-studies reported these events to occur during southeast/southwest oriented IMF (clock-angle ≈135°). The second part of the event, developed when the IMF turned to a nearly horizontal orientation (BY>>0, BZ~0, clock-angle ~90°), and exhibited the simultaneous activation of the cusp auroras in three distinct areas: i) two of them associated to the above-mentioned longitudinally bifurcated cusp (~73°–75° CGM latitude, type 1 cusp aurora), and linked to (near)antiparallel magnetic reconnection patches equatorward the northern and the southern cusp, ii) the other one characterized by isolated high-latitude (~76°–77° CGM latitude, type 2 cusp aurora) rayed arc(s) with intense green emission, and triggered by (near)antiparallel merging at the northern lobe (usually observed during positive IMF BZ), poleward the local cusp. During this phase, the longitudinal separation of the low-latitude type~1 cusp aurora was about 1000 km wide, with a 500 km gap, while the latitudinal separation between low- (type 1) and high-latitude (type 2) cusp auroras, in the postnoon, was about 270–280 km at its maximum. The longitudinal gap, corresponding to a zone with weak auroral emission, was found to likely map to the component reconnection region at the subsolar magnetopause. The magnetic merging topology that can be drawn on the basis of the reported cusp auroras support the idea of a "mixed" merging scheme, with (near)antiparallel reconnection at high-latitudes, and component reconnection in the subsolar region, as recently proposed by other authors.
The solar eruption of 13 May 2005: EISCAT and MERLIN observations of a coronal radio burst
Authors: Jones R. A. , Breen A. R. , Fallows R. A. , Bisi M. M. , Thomasson P. , Wannberg G. , Jordan C. A.
Published: June 2010

Abstract. We report results from EISCAT and MERLIN observations of radio scintillation during a solar eruptive event in May 2005. Anomalous increases in signal strength detected at sites more than 2000 km apart are shown to arise from the detection of a strong coronal radio burst in the distant off-axis response of the MERLIN and EISCAT antennas. These observations show that EISCAT is capable of detecting the signatures of explosive events in the solar atmosphere with a high degree of time resolution. We further suggest that the highly time-structured variation in signal strength caused by distant off-axis detection of a powerful coronal radio signal could provide an explanation for previously unexplained anomalies in EISCAT IPS observations, as well as being a potential source of errors in active observations using radar codes with a completion time longer than the time-variation of the coronal signal.
Impact of missing sounding reports on mandatory levels and tropopause statistics: a case study
Authors: Antuña J. C. , Añel J. A. , Gimeno L.
Published: June 2010

Abstract. This paper describes the effect of missing sounding reports on temperature and pressure mean values for mandatory levels using the aerological information from the Camagüey Meteorological Centre. Also it is described the effect of missing data on mean temperature and pressure values at the multiple tropopause levels. The case study belongs to one station for a time lag of eight years. Up to the present these types of studies have been conducted using simulated datasets. The present one uses a real inhomogeneous radiosonde dataset. The main reason for missing reports were transmission problems and possible encoding-decoding difficulties. It has been found that profiles of the mean temperature and altitude show little differences between the complete and incomplete datasets. Moreover, no statistical significant differences were found for the mean values of the variables for the complete and incomplete datasets. The most probable reason for those results is that the cause of the missing reports has a random behaviour. Finally we have found that the only two effects noticed on the statistics were slightly higher values of the mean temperatures in the complete dataset and the decrease in the percent of multiple tropopause reports for the incomplete dataset.
Evidence of standing waves during a Pi2 pulsation event observed on Cluster
Authors: Collier A. B. , Hughes A. R. W. , Blomberg L. G. , Sutcliffe P. R.
Published: June 2010

Abstract. Observations of Pi2 pulsations at middle and low latitudes have been explained in terms of cavity mode resonances, whereas transients associated with field-aligned currents appear to be responsible for the high latitude Pi2 signature. Data from Cluster are used to study a Pi2 event observed at 18:09 UTC on 21 January 2003, when three of the satellites were within the plasmasphere (L=4.7, 4.5 and 4.6) while the fourth was on the plasmapause or in the plasmatrough (L=6.6). Simultaneous pulsations at ground observatories and the injection of particles at geosynchronous orbit corroborate the occurrence of a substorm. Evidence of a cavity mode resonance is established by considering the phase relationship between the orthogonal electric and magnetic field components associated with radial and field-aligned standing waves. The relative phase between satellites located on either side of the geomagnetic equator indicates that the field-aligned oscillation is an odd harmonic. Finite azimuthal Poynting flux suggests that the cavity is effectively open ended and the azimuthal wave number is estimated as m~13.5.
Diurnal internal tides detected in the Adriatic
Authors: Mihanović H. , Orlić M. , Pasarić Z.
Published: June 2010

Abstract. Strong diurnal oscillations, documented by temperature data that were collected along a submarine cliff on the Lastovo Island (southern Adriatic), are studied and compared with sea level and wind measurements at Dubrovnik and Komiža (island of Vis). Three thermistors were deployed at the depths of 15, 22 and 36 m between March 2001 and March 2002. Pronounced diurnal temperature oscillations were detected at 15 and 22 m during the stratified season. The correlation between the sea surface and thermocline displacements was highest in June 2001, when diurnal wind changes were not significant, while diurnal sea level oscillations achieved annual maxima. Thermocline oscillations were in phase with sea level changes. The range of diurnal sea surface variability was close to 19 cm, while the range of corresponding thermocline variability was about 5.4 m. The findings summarize the outcome of the first dedicated study of internal tides in the Adriatic.
Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign – Part II: Radar investigations and modelling studies
Authors: Serafimovich A. , Zülicke Ch. , Hoffmann P. , Peters D. , Dalin P. , Singer W.
Published: June 2010

Abstract. We present an experimental and modelling study of a strong gravity wave event in the upper troposphere/lower stratosphere near the Scandinavian mountain ridge. Continuous VHF radar measurements during the MaCWAVE rocket and ground-based measurement campaign were performed at the Norwegian Andoya Rocket Range (ARR) near Andenes (69.3° N, 16° E) in January 2003. Detailed gravity wave investigations based on PSU/NCAR Fifth-Generation Mesoscale Model (MM5) data have been used for comparison with experimentally obtained results. The model data show the presence of a mountain wave and of an inertia gravity wave generated by a jet streak near the tropopause region. Temporal and spatial dependencies of jet induced inertia gravity waves with dominant observed periods of about 13 h and vertical wavelengths of ~4.5–5 km are investigated with wavelet transform applied on radar measurements and model data. The jet induced wave packet is observed to move upstream and downward in the upper troposphere. The model data agree with the experimentally obtained results fairly well. Possible reasons for the observed differences, e.g. in the time of maximum of the wave activity, are discussed. Finally, the vertical fluxes of horizontal momentum are estimated with different methods and provide similar amplitudes. We found indications that the derived positive vertical flux of the horizontal momentum corresponds to the obtained parameters of the jet-induced inertia gravity wave, but only at the periods and heights of the strongest wave activity.
A Statistical investigation of the invariant latitude dependence of unstable magnetospheric ion populations in relation to high m ULF wave generation
Authors: Wilson M. E. , Yeoman T. K. , Baddeley L. J. , Kellet B. J.
Published: June 2010

Abstract. A statistical study is presented of the unstable proton populations, which contain the free energy required to drive small-scale poloidal mode ULF waves in the magnetosphere, observed at invariant latitudes of 60° to 80°. The data are all in the form of Ion Distribution Functions (IDFs) amassed over ~6 years using the CAMMICE (MICS) instrument on the Polar spacecraft, and cover proton energies of 1 keV to 328 keV. The free energy contained in the unstable, positive gradient regions of the IDFs is available to drive resonant wave growth. The results show that positive gradient regions in IDFs on magnetic field lines corresponding to the lower invariant latitudes in the range under study occur predominantly in the afternoon sector at proton energies of 5 keV to 20 keV. In the morning and dawn sectors positive gradient regions are seen with a typical proton energy range of 5 keV to 45 keV. While the proton energy peaks in the afternoon sector at around ~7 keV the morning sector has two peaks occurring at ~10 keV and ~20–30 keV. The technique of Baddeley et al. (2004), employed to quantify the free energy in each IDF, found that as invariant latitude increased the free energy contained in the positive gradient regions fell. Positive gradient regions in the afternoon sector decrease in number with invariant latitude at a faster rate than those in the morning sector. The majority of positive gradient regions had free energy values of >1010 J with many at the lowest invariant latitudes having free energies of in excess of 1011 J. Positive gradient regions at proton energies of >100 keV are rarely observed, and have free energies of typically <10
Signatures of 3–6 day planetary waves in the equatorial mesosphere and ionosphere
Authors: Takahashi H. , Wrasse C. M. , Pancheva D. , Abdu M. A. , Batista I. S. , Lima L. M. , Batista P. P. , Clemesha B. R. , Shiokawa K.
Published: June 2010

Abstract. Common periodic oscillations have been observed in meteor radar measurements of the MLT winds at Cariri (7.4° S, 36.5° W) and Ascension Island (7.9° S, 14.4° W) and in the minimum ionospheric virtual height, h'F, measured at Fortaleza (3.9° S, 38.4° W) in 2004, all located in the near equatorial region. Wavelet analysis of these time series reveals that there are 3–4-day, 6–8-day and 12–16-day oscillations in the zonal winds and h'F. The 3–4 day oscillation appeared as a form of a wave packet from 7–17 August 2004. From the wave characteristics analyzed this might be a 3.5-day Ultra Fast Kelvin wave. The 6-day oscillation in the mesosphere was prominent during the period of August to November. In the ionosphere, however, it was apparent only in November. Spectral analysis suggests that this might be a 6.5-day wave previously identified. The 3.5-day and 6.5-day waves in the ionosphere could have important roles in the initiation of equatorial spread F (plasma bubble). These waves might modulate the post-sunset E×B uplifting of the base of the F-layer via the induced lower thermosphere zonal wind and/or the E-region conductivity.
Comparative investigations of equatorial electrodynamics and low-to-mid latitude coupling of the thermosphere-ionosphere system
Authors: Colerico M. J. , Mendillo M. , Fesen C. G. , Meriwether J.
Published: June 2010

Abstract. The thermospheric midnight temperature maximum (MTM) is a highly variable, but persistent, large scale neutral temperature enhancement which occurs at low latitudes. Its occurrence can impact many fundamental upper atmospheric parameters such as pressure, density, neutral winds, neutral density, and F-region plasma. Although the MTM has been the focus of several investigations employing various instrumentation including photometers, satellites, and Fabry-Perot interferometers, limited knowledge exists regarding the latitude extent of its influence on the upper atmosphere. This is largely due to observational limitations which confined the collective geographic range to latitudes within ±23°. This paper investigates the MTM's latitudinal extent through all-sky imaging observations of its 6300Å airglow signature referred to by Colerico et al. (1996) as the midnight brightness wave (MBW). The combined field of view of three Southern Hemisphere imaging systems located at Arequipa, Peru, and Tucuman and El Leoncito, Argentina, for the first time extends the contiguous latitudinal range of imager observations to 8° S-39° S in the American sector. Our results highlight the propagation of MBW events through the combined fields of view past 39° S latitude, providing the first evidence that the MTM's effect on the upper atmosphere extends into mid-latitudes. The observations presented here are compared with modeled 6300Å emissions calculated using the NCAR thermosphere-ionosphere-electrodynamic general circulation model (TIEGCM) in conjunction with an airglow code. We report that at this time TIEGCM is unable to simulate an MBW event due to the model's inability to reproduce an MTM of the same magnitude and occurrence time as those observed via FPI measurements made from Arequipa. This work also investigates the origins of an additional low latitude airglow feature referred to by Colerico et al. (1996) as the pre-midnight brightness wave (PMBW) and described as an enhancement in 6300Å emission which occurs typically between 20:00-22:00 LT and exhibits equatorward propagation. We present the first successful simulation of a PMBW event using the TIEGCM and the airglow code. We find that the PMBW's origin is electro-dynamical in nature, resulting from the expected evening decay of the inter-tropical arcs.
Saturation and hysteresis effects in ionospheric modification experiments observed by the CUTLASS and EISCAT radars
Authors: Wright D. M. , Davies J. A. , Yeoman T. K. , Robinson T. R. , Shergill H.
Published: June 2010

Abstract. The results of high latitude ionospheric modification experiments utilising the EISCAT heating facility at Tromsø are presented. As a result of the interaction between the high power pump waves and upper hybrid waves in the ionosphere, field-aligned electron density irregularities are artificially excited. Observations of these structures with the CUTLASS coherent HF radars and the EISCAT incoherent UHF radar exhibit hysteresis effects as the heater output power is varied. These are explained in terms of the two-stage mechanism which leads to the growth of the irregularities. Experiments which involve preconditioning of the ionosphere also indicate that hysteresis could be exploited to maximise the intensity of the field-aligned irregularities, especially where the available heater power is limited. In addition, the saturation of the irregularity amplitude is considered. Although, the rate of irregularity growth becomes less rapid at high heater powers it does not seem to fully saturate, indicating that the amplification would continue beyond the capabilities of the Tromsø heater - currently the most powerful of its kind. It is shown that the CUTLASS radars are sensitive to irregularities produced by very low heater powers (effective radiated powers <4 MW). This fact is discussed from the perspective of a new heating facility, SPEAR, located on Spitzbergen and capable of transmitting high frequency radio waves with an effective radiated power ~10% of that of the Tromsø heater (28MW).
Dispersion equations for field-aligned cyclotron waves in axisymmetric magnetospheric plasmas
Authors: Grishanov N. I. , Raupp M. A. , Loula A. F. D. , Pereira Neto J.
Published: June 2010

Abstract. In this paper, we derive the dispersion equations for field-aligned cyclotron waves in two-dimensional (2-D) magnetospheric plasmas with anisotropic temperature. Two magnetic field configurations are considered with dipole and circular magnetic field lines. The main contribution of the trapped particles to the transverse dielectric permittivity is estimated by solving the linearized Vlasov equation for their perturbed distribution functions, accounting for the cyclotron and bounce resonances, neglecting the drift effects, and assuming the weak connection of the left-hand and right-hand polarized waves. Both the bi-Maxwellian and bi-Lorentzian distribution functions are considered to model the ring current ions and electrons in the dipole magnetosphere. A numerical code has been developed to analyze the dispersion characteristics of electromagnetic ion-cyclotron waves in an electron-proton magnetospheric plasma with circular magnetic field lines, assuming that the steady-state distribution function of the energetic protons is bi-Maxwellian. As in the uniform magnetic field case, the growth rate of the proton-cyclotron instability (PCI) in the 2-D magnetospheric plasmas is defined by the contribution of the energetic ions/protons to the imaginary part of the transverse permittivity elements. We demonstrate that the PCI growth rate in the 2-D axisymmetric plasmasphere can be significantly smaller than that for the straight magnetic field case with the same macroscopic bulk parameters.
Alfvénic turbulence in solar wind originating near coronal hole boundaries: heavy-ion effects?
Authors: Bavassano B. , Schwadron N. A. , Pietropaolo E. , Bruno R.
Published: June 2010

Abstract. The mid-latitude phases of the Ulysses mission offer an excellent opportunity to investigate the solar wind originating near the coronal hole boundaries. Here we report on Alfvénic turbulence features, revealing a relevant presence of in-situ generated fluctuations, observed during the wind rarefaction phase that charaterizes the transition from fast to slow wind. Heavy-ion composition and magnetic field measurements indicate a strict time correspondence of the locally generated fluctuations with 1) the crossing of the interface between fast and slow wind and 2) the presence of strongly underwound magnetic field lines (with respect to the Parker spiral). Recent studies suggest that such underwound magnetic configurations correspond to fast wind magnetic lines that, due to footpoint motions at the Sun, have their inner leg transferred to slow wind and are stretched out by the velocity gradient. If this is a valid scenario, the existence of a magnetic connection across the fast-slow wind interface is a condition that, given the different state of the two kinds of wind, may favour the development of processes acting as local sources of turbulence. We suggest that heavy-ion effects could be responsible of the observed turbulence features.
Solar cycle changes in the geo-effectiveness of small-scale solar wind turbulence measured by Wind and ACE at 1 AU
Authors: Parkinson M. L. , Healey R. C. , Dyson P. L.
Published: June 2010

Abstract. Multi-scale structure of the solar wind in the ecliptic at 1 AU undergoes significant evolution with the phase of the solar cycle. Wind spacecraft measurements during 1995 to 1998 and ACE spacecraft measurements during 1997 to 2005 were used to characterise the evolution of small-scale (~1 min to 2 h) fluctuations in the solar wind speed vsw, magnetic energy density B2, and solar wind ε parameter, in the context of large-scale (~1 day to years) variations. The large-scale variation in ε most resembled large-scale variations in B2. The probability density of large fluctuations in ε and B2 both had strong minima during 1995, a familiar signature of solar minimum. Generalized Structure Function (GSF) analysis was used to estimate inertial range scaling exponents aGSF and their evolution throughout 1995 to 2005. For the entire data set, the weighted average scaling exponent for small-scale fluctuations in vsw was aGSF=0.284±0.001, a value characteristic of intermittent MHD turbulence (>1/4), whereas the scaling exponents for corresponding fluctuations in B2 and ε were aGSF=0.395±0.001 and 0.334±0.001, respectively. These values are between the range expected for Gaussian fluctuations (1/2) and Kolmogorov turbulence (1/3). However, the scaling exponent for ε changed from a Gaussian-Kolmogorov value of 0.373±0.005 during 1997 (end of solar minimum) to an MHD turbulence value of 0.247±0.004 during 2003 (recurrent fast streams). Changes in the characteristics of solar wind turbulence may be reproducible from one solar cycle to the next.
High time resolution measurements of the thermosphere from Fabry-Perot Interferometer measurements of atomic oxygen
Authors: Ford E. A. K. , Aruliah A. L. , Griffin E. M. , McWhirter I.
Published: June 2010

Abstract. Recent advances in the performance of CCD detectors have enabled a high time resolution study of the high latitude upper thermosphere with Fabry-Perot Interferometers (FPIs) to be performed. 10-s integration times were used during a campaign in April 2004 on an FPI located in northern Sweden in the auroral oval. The FPI is used to study the thermosphere by measuring the oxygen red line emission at 630.0 nm, which emits at an altitude of approximately 240 km. Previous time resolutions have been 4 min at best, due to the cycle of look directions normally observed. By using 10 s rather than 40 s integration times, and by limiting the number of full cycles in a night, high resolution measurements down to 15 s were achievable. This has allowed the maximum variability of the thermospheric winds and temperatures, and 630.0 nm emission intensities, at approximately 240 km, to be determined as a few minutes. This is a significantly greater variability than the often assumed value of 1 h or more. A Lomb-Scargle analysis of this data has shown evidence of gravity wave activity with waves with short periods. Gravity waves are an important feature of mesosphere-lower thermosphere (MLT) dynamics, observed using many techniques and providing an important mechanism for energy transfer between atmospheric regions. At high latitudes gravity waves may be generated in-situ by localised auroral activity. Short period waves were detected in all four clear nights when this experiment was performed, in 630.0 nm intensities and thermospheric winds and temperatures. Waves with many periodicities were observed, from periods of several hours, down to 14 min. These waves were seen in all parameters over several nights, implying that this variability is a typical property of the thermosphere.