bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of an interplanetary shock on the high-latitude ionospheric convection during an IMF By-dominated period
Authors: Coco I. , Amata E. , Marcucci M. F. , Ambrosino D. , Villain J.-P. , Hanuise C.
Published: June 2010

Abstract. On 6 January 1998 an interplanetary shock hit the magnetosphere around 14:15 UT and caused a reconfiguration of the northern high-latitude ionospheric convection. We use SuperDARN, spacecraft and ground magnetometer data to study such reconfiguration. We find that the shock front was tilted towards the morning flank of the magnetosphere, while the Interplanetary Magnetic Field (IMF) was By-dominated, with By<0, IMF Bz>0 and |By|>>Bz. As expected, the magnetospheric compression started at the first impact point of the shock on the magnetopause causing an increase of the Chapman-Ferraro current from dawn to dusk and yielding an increase of the geomagnetic field at the geostationary orbit and on the ground. Moreover, the high-latitude magnetometer data show vortical structures clearly related to the interaction of the shock with the magnetosphere-ionosphere system. In this context, the SuperDARN convection maps show that at very high latitudes above the northern Cusp and in the morning sector, intense sunward convection fluxes appear, well correlated in time with the SI arrival, having a signature typical for Bz>0 dominated lobe reconnection. We suggest that in this case the dynamic pressure increase associated to the shock plays a role in favouring the setting up of a new lobe merging line albeit |By|>>Bz≥0.
Off-limb EUV observations of the solar corona and transients with the CORONAS-F/SPIRIT telescope-coronagraph
Authors: Slemzin V. , Bougaenko O. , Ignatiev A. , Kuzin S. , Mitrofanov A. , Pertsov A. , Zhitnik I.
Published: June 2010

Abstract. The SPIRIT telescope aboard the CORONAS-F satellite (in orbit from 26 July 2001 to 5 December 2005), observed the off-limb solar corona in the 175 Å (Fe IX, X and XI lines) and 304 Å (He II and Si XI lines) bands. In the coronagraphic mode the mirror was tilted to image the corona at the distance of 1.1...5 Rsun from the solar center, the outer occulter blocked the disk radiation and the detector sensitivity was enhanced. This intermediate region between the fields of view of ordinary extreme-ultraviolet (EUV) telescopes and most of the white-light (WL) coronagraphs is responsible for forming the streamer belt, acceleration of ejected matter and emergence of slow and fast solar wind. We present here the results of continuous coronagraphic EUV observations of the solar corona carried out during two weeks in June and December 2002. The images showed a "diffuse" (unresolved) component of the corona seen in both bands, and non-radial, ray-like structures seen only in the 175 Å band, which can be associated with a streamer base. The correlations between latitudinal distributions of the EUV brightness in the corona and at the limb were found to be high in 304 Å at all distances and in 175 Å only below 1.5 Rsun. The temporal correlation of the coronal brightness along the west radial line, with the brightness at the underlying limb region was significant in both bands, independent of the distance. On 2 February 2003 SPIRIT observed an expansion of a transient associated with a prominence eruption seen only in the 304 Å band. The SPIRIT data have been compared with the corresponding data of the SOHO LASCO, EIT and UVCS instruments.
Magnetic reconnection processes induced by a CME expansion
Authors: Bemporad A. , Poletto G. , Landini F. , Romoli M.
Published: June 2010

Abstract. On 10–11 December 2005 a slow CME occurred in the Western Hemisphere in between two coronal streamers. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere: a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the CME expansion affects both of them and induces the release of plasma within or close to the nearby streamers. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion and occurring inside the streamer current sheet or between the CME flanks and the streamer. These events have been observed by the SOHO/UVCS with the spectrometer slit centered at 1.8 R⊙ over about a full day. In this work we focus on the interaction between the CME and the streamer: the UVCS spectral interval included UV lines from ions at different temperatures of maximum formation such as O VI, Si XIII and Al Xi. These data gave us the opportunity to infer the evolution of plasma temperature and density at the reconnection site and adjacent regions. These are relevant to characterize secondary reconnection processes occurring during a CME development.
A review of the quantitative links between CMEs and magnetic clouds
Authors: Démoulin P.
Published: June 2010

Abstract. Magnetic clouds (MCs), and more generally, interplanetary coronal mass ejections (ICMEs), are believed to be the interplanetary counterparts of CMEs. The link has usually been shown by taking into account the CME launch position on the Sun, the expected time delay and by comparing the orientation of the coronal and interplanetary magnetic field. Making such a link more quantitative is challenging since it requires a relation between very different kinds of magnetic field measurements: (i) photospheric magnetic maps, which are observed from a distant vantage point (remote sensing) and (ii) in-situ measurements of MCs, which provide precise, directly measured, magnetic field data merely from one-dimensional linear samples. The association between events in these different domains can be made using adequate coronal and MC models. Then, global quantities like magnetic fluxes and helicity can be derived and compared. This review paper describes all the general trends found in the above association criteria. A special focus is given for the cases which do not follow the earlier derived mean laws since interesting physics is usually involved.
Ionospheric weather: cloning missed foF2 observations for derivation of variability index
Authors: Gulyaeva T. L. , Stanislwska I. , Tomasik M.
Published: June 2010

Abstract. A techique for filling the gaps of the missing F2-layer critical frequency is proposed and applied for the derivation of the ionospheric weather index, characterizing the degree of disturbance at each particular station. A daily-hourly analysis of ionosonde observations of foF2 for 16 stations at latitude range 37° to 70° N, longitudes of 10° W to 150° E, is performed during the solar minimum, 2006. Missed ionosonde observations are reconstructed by cloning data of another station. The process of gap filling considers hourly values of the F peak density NmF2 (deduced from foF2), normalized to the respective median, and assumes that this ratio remains the same for the parent and cloned data. It is shown that the correlation coefficient between cloned fcF2 and observed foF2 is greater than 0.75 for the positive and negative ionospheric disturbed days during a year at solar minimum, independent of the distance between the stations in high and middle latitudes. The quiet reference is determined as a running daily-hourly median for 27 days, preceding the day of observation calibrated for a seasonal trend with ITU-R foF2 predictions. The hourly deviation DNmF2 is defined as the logarithm of ratio of NmF2/NmF2med. A segmented logarithmic scale of the ionospheric weather index, W, is introduced, so that W=±1 refers to the quiet state, W=±2 to a moderate disturbance, W=±3 to the ionospheric storm, and W=±4 to the extreme or anomalous conditions. The catalog of the ionospheric disturbances for W exceeding ±2 at least during 3 consecutive hours is produced and presented online at the SRC and IZMIRAN web pages. It is found that the moderate disturbance is a prevailing state of the ionospheric weather for all stations. The stormy conditions comprise 1 to 20% of the times which occur more frequently at high latitudes, by night, during equinox and winter.
Quantifying and containing the curse of high resolution coronal imaging
Authors: Delouille V. , Chainais P. , Hochedez J.-F.
Published: June 2010

Abstract. Future missions such as Solar Orbiter (SO), InterHelioprobe, or Solar Probe aim at approaching the Sun closer than ever before, with on board some high resolution imagers (HRI) having a subsecond cadence and a pixel area of about (80 km)2 at the Sun during perihelion. In order to guarantee their scientific success, it is necessary to evaluate if the photon counts available at these resolution and cadence will provide a sufficient signal-to-noise ratio (SNR). For example, if the inhomogeneities in the Quiet Sun emission prevail at higher resolution, one may hope to locally have more photon counts than in the case of a uniform source. It is relevant to quantify how inhomogeneous the quiet corona will be for a pixel pitch that is about 20 times smaller than in the case of SoHO/EIT, and 5 times smaller than TRACE. We perform a first step in this direction by analyzing and characterizing the spatial intermittency of Quiet Sun images thanks to a multifractal analysis. We identify the parameters that specify the scale-invariance behavior. This identification allows next to select a family of multifractal processes, namely the Compound Poisson Cascades, that can synthesize artificial images having some of the scale-invariance properties observed on the recorded images. The prevalence of self-similarity in Quiet Sun coronal images makes it relevant to study the ratio between the SNR present at SoHO/EIT images and in coarsened images. SoHO/EIT images thus play the role of "high resolution" images, whereas the "low-resolution" coarsened images are rebinned so as to simulate a smaller angular resolution and/or a larger distance to the Sun. For a fixed difference in angular resolution and in Spacecraft-Sun distance, we determine the proportion of pixels having a SNR preserved at high resolution given a particular increase in effective area. If scale-invariance continues to prevail at smaller scales, the conclusion reached with SoHO/EIT images can be transposed to the situation where the resolution is increased from SoHO/EIT to SO/HRI resolution at perihelion.
Subauroral polarization streams: observations with the Hokkaido and King Salmon SuperDARN radars and modeling
Authors: Koustov A. , Nishitani N. , Ebihara Y. , Kikuchi T. , Hairston M. R. , Andre D.
Published: June 2010

Abstract. The newly installed SuperDARN Hokkaido HF radar monitors ionospheric plasma flow between magnetic latitudes of 45° and 65° and thus has a great potential for studies of subauroral polarization streams (SAPS) in combination with another SuperDARN radar located at King Salmon, Alaska as well as the DMSP satellites and ground-based instruments in the Alaskan sector of the Arctic. Preliminary survey shows that although SAPS are often detected with the Hokkaido radar, their velocities are rather low, to the order of 150 m/s in its most suitable central beams. In this study, observations of unusually fast Hokkaido flows of up to 800 m/s are presented. The event of 1 April 2007 is investigated in detail. It is shown that high-velocity echoes appear after substorm onsets over North America with a delay of ~30 min. In terms of latitude, the velocity peaks just outside the auroral oval; signatures of a detached polarization jet are occasional and not pronounced. The King Salmon radar operating concurrently detects SAPS signatures as well but at different times and locations. Simulation with the Comprehensive Ring Current Model for the 1 April event reasonably identifies the period of fast flow occurrence but the velocity is underestimated. The event studied suggests that substorm-injected particle populations may intensify the pre-existing SAPS flow and lead to a mismatch of the predictions and observations.
Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread F
Authors: Rodrigues F. S. , Hysell D. L. , de Paula E. R.
Published: June 2010

Abstract. The 30 MHz coherent backscatter radar located at the equatorial observatory in São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip lat) has been upgraded to perform coherent backscatter radar imaging. The wide field-of-view of this radar makes it well suited for radar imaging studies of ionospheric irregularities. Radar imaging observations were made in support to the spread F Experiment (SpreadFEx) campaign. This paper describes the system and imaging technique and presents results from a bottom-type layer that preceded fully-developed radar plumes on 25 October 2005. The radar imaging technique was able to resolve decakilometric structures within the bottom-type layer. These structures indicate the presence of large-scale waves (~35 km) in the bottomside F-region with phases that are alternately stable and unstable to wind-driven gradient drift instabilities. The observations suggest that these waves can also cause the initial perturbation necessary to initiate the Generalized Rayleigh-Taylor instability leading to spread F. The electrodynamic conditions and the scale length of the bottom-type layer structures suggest that the waves were generated by the collisional shear instability. These results indicate that monitoring bottom-type layers may provide helpful diagnostics for spread F forecasting.
The electron drift velocity, ion acoustic speed and irregularity drifts in high-latitude E-region
Authors: Uspensky M. V. , Pellinen R. J. , Janhunen P.
Published: June 2010

Abstract. The purpose of this study is to examine the STARE irregularity drift velocity dependence on the EISCAT line-of-sight (los or l-o-s) electron drift velocity magnitude, VE×Blos, and the flow angle ΘN,F (superscript N and/or F refer to the STARE Norway and Finland radar). In the noon-evening sector the flow angle dependence of Doppler velocities, VirrN,F, inside and outside the Farley-Buneman (FB) instability cone (|VE×Blos|>Cs and |VE×Blos|<Cs, respectively, where Cs is the ion acoustic speed), is found to be similar and much weaker than suggested earlier. In a band of flow angles 45°<ΘN,F<85° it can be reasonably described by |VirrN,F|∝AN,FCscosnΘN,F, where AN,F≈1.2–1.3 are monotonically increasing functions of VE×B and the index n is ~0.2 or even smaller. This study (a) does not support the conclusion by Nielsen and Schlegel (1985), Nielsen et al. (2002, their #[18]) that at flow angles larger than ~60° (or |VirrN,F|≤300 m/s) the STARE Doppler velocities are equal to the component of the electron drift velocity. We found (b) that if the data points are averages over 100 m/s intervals (bins) of l-o-s electron velocities and 10 deg intervals (bins) of flow angles, then the largest STARE Doppler velocities always reside inside the bin with the largest flow angle. In the flow angle bin 80° the STARE Doppler velocity is larger than its driver term, i.e. the EISCAT l-o-s electron drift velocity component, |VirrN,F|>|VE×Blos|. Both features (a and b) as well as the weak flow angle velocity dependence indicate that the l-o-s electron drift velocity cannot be the sole factor which controls the motion of the backscatter ~1-m irregularities at large flow angles. Importantly, the backscatter was collected at aspect angle ~1° and flow angle Θ>60°, where linear fluid and kinetic theories invariably predict negative growth rates. At least qualitatively, all the facts can be reasonably explained by nonlinear wave-wave coupling found and described by Kudeki and Farley (1989), Lu et al. (2008) for the equatorial electrojet and studied in numerical simulation by Otani and Oppenheim (1998, 2006).
The Hall current system revealed as a statistical significant pattern during fast flows
Authors: Snekvik K. , Nakamura R. , Østgaard N. , Haaland S. , Retinò A.
Published: June 2010

Abstract. We have examined the dawn-dusk component of the magnetic field, BY, in the night side current sheet during fast flows in the neutral sheet. 237 h of Cluster data from the plasma sheet between 2 August 2002 and 2 October 2002 have been analysed. The spatial pattern of BY as a function of the distance from the centre of the current sheet has been estimated by using a Harris current sheet model. We have used the average slopes of these patterns to estimate earthward and tailward currents. For earthward fast flows there is a tailward current in the inner central plasma sheet and an earthward current in the outer central plasma sheet on average. For tailward fast flows the currents are oppositely directed. These observations are interpreted as signatures of Hall currents in the reconnection region or as field aligned currents which are connected with these currents. Although fast flows often are associated with a dawn-dusk current wedge, we believe that we have managed to filter out such currents from our statistical patterns.
Rapid energization of radiation belt electrons by nonlinear wave trapping
Authors: Katoh Y. , Omura Y. , Summers D.
Published: June 2010

Abstract. We show that nonlinear wave trapping plays a significant role in both the generation of whistler-mode chorus emissions and the acceleration of radiation belt electrons to relativistic energies. We have performed particle simulations that successfully reproduce the generation of chorus emissions with rising tones. During this generation process we find that a fraction of resonant electrons are energized very efficiently by special forms of nonlinear wave trapping called relativistic turning acceleration (RTA) and ultra-relativistic acceleration (URA). Particle energization by nonlinear wave trapping is a universal acceleration mechanism that can be effective in space and cosmic plasmas that contain a magnetic mirror geometry.
Properties of a cusp diamagnetic cavity boundary
Authors: Walsh B. M. , Fritz T. A. , Chen J.
Published: June 2010

Abstract. While crossing through the high-altitude dayside cusp on 29 September 1978 and again on 30 October 1978, the ISEE-1 spacecraft observed enhanced energetic particle flux and a depressed and turbulent magnetic field, the signature characteristics of a cusp diamagnetic cavity. As ISEE-1 approached the cavity during each event, a boundary sounding technique was used to measure properties of an emitting boundary. Sounding over multiple energy channels reveals an energy dependent boundary with lower energy particles filling a larger cavity than higher energy particles. Relative motion of the boundary as well as boundary orientation are also measured. The two cusp events were measured at different locations and during different geomagnetic and solar wind conditions; however, they show similar results.
First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM)
Authors: Angling M. J.
Published: June 2010

Abstract. Ground based measurements of slant total electron content (TEC) can be assimilated into ionospheric models to produce 3-D representations of ionospheric electron density. The Electron Density Assimilative Model (EDAM) has been developed for this purpose. Previous tests using EDAM and ground based data have demonstrated that the information on the vertical structure of the ionosphere is limited in this type of data. The launch of the COSMIC satellite constellation provides the opportunity to use radio occultation data which has more vertical information. EDAM assimilations have been run for three time periods representing quiet, moderate and disturbed geomagnetic conditions. For each run, three data sets have been ingested – only ground based data, only COSMIC data and both ground based and COSMIC data. The results from this preliminary study show that both ground and space based data are capable of improving the representation of the vertical structure of the ionosphere. However, the analysis is limited by the incomplete deployment of the COSMIC constellation and the use of auto-scaled ionosonde data. The first of these can be addressed by repeating this type of study once full deployment has been achieved. The latter requires the manual scaling of ionosonde data; ideally an agreed data set would be scaled and made available to the community to facilitate comparative testing of assimilative models.
Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations
Authors: Alexandrova O. , Lacombe C. , Mangeney A.
Published: June 2010

Abstract. We investigate the spectral shape, the anisotropy of the wave vector distributions and the anisotropy of the amplitudes of the magnetic fluctuations in the Earth's magnetosheath within a broad range of frequencies [10−3, 10] Hz which corresponds to spatial scales from ~10 to 105 km. We present the first observations of a Kolmogorov-like inertial range of Alfvénic fluctuations δB2⊥}~f−5/3 in the magnetosheath flanks, below the ion cyclotron frequency fci. In the vicinity of fci, a spectral break is observed, like in solar wind turbulence. Above the break, the energy of compressive and Alfvénic fluctuations generally follows a power law with a spectral index between −3 and −2. Concerning the anisotropy of the wave vector distribution, we observe a clear change in its nature in the vicinity of ion characteristic scales: if at MHD scales there is no evidence for a dominance of a slab (kł>>k⊥) or 2-D (k⊥>>kł) turbulence, above the spectral break, (f>fci, kc/ωpi>1) the 2-D turbulence dominates. This 2-D turbulence is observed in six selected one-hour intervals among which the average ion β varies from 0.8 to 10. It is observed for both the transverse and compressive magnetic fluctuations, independently on the presence of linearly unstable modes at low frequencies or Alfvén vortices at the spectral break. We then analyse the anisotropy of the magnetic fluctuations in a time dependent reference frame based on the field B and the flow velocity V directions. Within the range of the 2-D turbulence, at scales [1,30]kc/ωpi, and for any β we find that the magnetic fluctuations at a given frequency in the plane perpendicular to B have more energy along the B×V direction. This non-gyrotropy of the fluctuations at a fixed frequency is consistent with gyrotropic fluctuations at a given wave vector, with k⊥>>kł, which suffer a different Doppler shift along and perpendicular to V in the plane perpendicular to B.
PFISR nightside observations of naturally enhanced ion acoustic lines, and their relation to boundary auroral features
Authors: Michell R. G. , Lynch K. A. , Heinselman C. J. , Stenbaek-Nielsen H. C.
Published: June 2010

Abstract. We present results from a coordinated camera and radar study of the auroral ionosphere conducted during March of 2006 from Poker Flat, Alaska. The campaign was conducted to coincide with engineering tests of the first quarter installation of the Poker Flat Incoherent Scatter Radar (PFISR). On 31 March 2006, a moderately intense auroral arc, (~10 kR at 557.7 nm), was located in the local magnetic zenith at Poker Flat. During this event the radar observed 7 distinct periods of abnormally large backscattered power from the F-region. These were only observed in the field-aligned radar beam, and radar spectra from these seven times show naturally enhanced ion-acoustic lines (NEIALs), the first observed with PFISR. These times corresponded to (a) when the polar cap boundary of the auroral oval passed through the magnetic zenith, and (b) when small-scale filamentary dark structures were visible in the magnetic zenith. The presence of both (a) and (b) was necessary for their occurrence. Soft electron precipitation occurs near the magnetic zenith during these same times. The electron density in the vicinity where NEIALs have been observed by previous studies is roughly between 5 and 30×1010 m−3. Broad-band extremely low frequency (BBELF) wave activity is observed in situ by satellites and sounding rockets to occur with similar morphology, during active auroral conditions, associated with the poleward edge of the aurora and soft electron precipitation. The observations presented here suggest further investigation of the idea that NEIALs and BBELF wave activity are differently-observed aspects of the same wave phenomenon. If a connection between NEIALs and BBELF can be established with more data, this could provide a link between in situ measurements of downward current regions (DCRs) and dynamic aurora, and ground-based observations of dark auroral structures and NEIALs. Identification of in situ processes, namely wave activity, in ground-based signatures could have many implications. One specific example of interest is identifying and following the temporal and spatial evolution of regions of potential ion outflow over large spatial and temporal scales using ground-based optical observations.
Relationship between solar wind corotating interaction regions and the phasing and intensity of Saturn kilometric radiation bursts
Authors: Badman S. V. , Cowley S. W. H. , Lamy L. , Cecconi B. , Zarka P.
Published: June 2010

Abstract. Voyager spacecraft measurements of Saturn kilometric radiation (SKR) identified two features of these radio emissions: that they pulse at a period close to the planetary rotation period, and that the emitted intensity is correlated with the solar wind dynamic pressure (Desch and Kaiser, 1981; Desch, 1982; Desch and Rucker, 1983). In this study the inter-relation between the intensity and the pulsing of the SKR is analysed using Cassini spacecraft measurements of the interplanetary medium and SKR over the interval encompassing Cassini's approach to Saturn, and the first extended orbit. Cassini Plasma Spectrometer ion data were only available for a subset of the dates of interest, so the interplanetary conditions were studied primarily using the near-continuously available magnetic field data, augmented by the ion moment data when available. Intense SKR bursts were identified when solar wind compressions arrived at Saturn. The intensity of subsequent emissions detected by Cassini during the compression intervals was variable, sometimes remaining intense for several planetary rotations, sometimes dimming and rarely disappearing. The timings of the initial intense SKR peaks were sometimes independent of the long-term pulsing behaviour identified in the SKR data. Overall, however, the pulsing of the SKR peaks during the disturbed intervals was not significantly altered relative to that during non-compression intervals.
Formation of current density profile in tilted current sheets
Authors: Petrukovich A. A. , Baumjohann W. , Nakamura R. , Runov A.
Published: June 2010

Abstract. We investigate Cluster observations of strongly tilted sheets (flapping events) in the magnetotail. In accordance with the simple model of slip deformation (vertical differential displacement of neighboring flux tubes), the Jy current density component in the tilted sheet remains constant and equal to that in the horizontal undisturbed sheet. However, a substantial Jz component appears proportional to the local sheet tilt. Slip-type variations, having smaller scale than the full crossing, locally change the tilt and Jz and may thus create a variety of non-classical (bifurcated, asymmetric etc) current density profiles.
Seasonal, annual and inter-annual features of turbulence parameters over the tropical station Pune (18°32' N, 73°51' E) observed with UHF wind profiler
Authors: Singh Narendra , Joshi R. R. , Chun H.-Y. , Pant G. B. , Damle S. H. , Vashishtha R. D.
Published: June 2010

Abstract. The present study is specifically focused on the seasonal, annual and inter-annual variations of the refractive index structure parameter (Cn2) using three years of radar observations. Energy dissipation rates (ε) during different seasons for a particular year are also computed over a tropical station, Pune. Doppler spectral width measurements made by the Wind Profiler, under various atmospheric conditions, are utilized to estimate the turbulence parameters. The refractive index structure parameter varies from 10−17.5 to 10−13 m−2/3 under clear air to precipitation conditions in the height region of 1.05 to 10.35 km. During the monsoon months, observed Cn2 values are up to 1–2 orders of magnitude higher than those during pre-monsoon and post-monsoon seasons. Spectral width correction for various non-turbulent spectral broadenings such as beam broadening and shear broadening are made in the observed spectral width for reliable estimation of ε under non-precipitating conditions. It is found that in the lower tropospheric height region, values of ε are in the range of 10−6 to 10−3 m2 s−3. In summer and monsoon seasons the observed values of ε are larger than those in post-monsoon and winter seasons in the lower troposphere. A comparison of Cn2 observed with the wind profiler and that estimated using Radio Sonde/Radio Wind (RS/RW) data of nearby Met station Chikalthana has been made for the month of July 2003.
Comparison of wind measurements in the troposphere and mesosphere by VHF/MF radars and in-situ techniques
Authors: Engler N. , Singer W. , Latteck R. , Strelnikov B.
Published: June 2010

Abstract. Radar wind observations at frequencies between 1.98 and 53.5 MHz obtained at polar latitudes were compared to in-situ wind measurements by radiosondes at tropospheric altitudes and to winds from falling spheres at mesospheric altitudes. Comparisons are shown for several campaigns of radiosonde and falling sphere observations. The radar wind directions agree well to the radiosonde and falling sphere observations and are highly correlated. The winds estimated from radar measurements are less than the radiosonde data by about 15% for spaced antenna observations and by about 10% for the Doppler beam swinging experiment. At mesospheric altitudes the spaced antenna winds obtained from the wide-beam Andenes MF radar are underestimated in the order of 35% and winds from the narrow-beam Saura MF radar are underestimated by about 20% compared to falling sphere winds at altitudes between 70 and 80 km. Furthermore, the relation between wind measurements using narrow-beam and wide-beam antenna arrangements for the MF radars is discussed and VHF radar observations are compared to the wide-beam MF radar.
Time series autoregression technique implemented on-line in DIAS system for ionospheric forecast over Europe
Authors: Koutroumbas K. , Tsagouri I. , Belehaki A.
Published: June 2010

Abstract. A new method for ionospheric predictions based on time series autoregressive models (AR) that was recently developed to serve the needs of the European Digital Upper Atmosphere Server (DIAS) for short term forecast of the foF2 parameter over Europe (up to the next 24 h) is described. Its performance for various steps ahead is compared with the outcome of neural network predictors for both storm and quiet periods in two DIAS locations, Athens and Pruhonice. The results indicate that the proposed method provides robust short term forecasts of the foF2 for the middle latitude ionosphere.
Spatiotemporal variation of the ozone QBO in MLS data by wavelet analysis
Authors: Fadnavis S. , Beig G.
Published: June 2010

Abstract. Spatiotemporal characteristics of the ozone quasi-biennial oscillation (QBO) over the tropical-subtropical stratosphere (40° S–40° N) have been examined by analyzing data from the Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) for the period 1992–1999. A combination of regression analysis and wavelet analysis combines to act as an accurate QBO filter. Wavelet analysis provides inter-annual variability of amplitude and phase of the ozone QBO in the vertical structure of tropical-subtropical stratosphere. It gives minute details of phase propagation and descend rates, which can be used as input to models. Latitude-height structure shows evidence of a secondary meridional circulation induced by the QBO as double peak structure at the equator with maximum amplitude at two pressure levels 30 hPa and 9 hPa and a node at 14 hPa. The equatorial maxima are out of phase with each other. The maximum amplitude (~1.4 ppmv) of the ozone QBO was observed near the equator at 10 hPa. Descent rate of the easterly phase is greater than westerly. The lag correlation of the ozone QBO with circulation and variation of descent rates in the vertical structure of the stratosphere are examined in detail. In the equatorial upper stratosphere ozone anomalies descent with the rate ~1.5 km/month but in tropics and subtropics (above 2 hPa) they propagate upward.
Influence of gravity waves and tides on mesospheric temperature inversion layers: simultaneous Rayleigh lidar and MF radar observations
Authors: Sridharan S. , Sathishkumar S. , Gurubaran S.
Published: June 2010

Abstract. Three nights of simultaneous Rayleigh lidar temperature measurements over Gadanki (13.5° N, 79.2° E) and medium frequency (MF) radar wind measurements over Tirunelveli (8.7° N, 77.8° E) have been analyzed to illustrate the possible effects due to tidal-gravity wave interactions on upper mesospheric inversion layers. The occurrence of tidal gravity wave interaction is investigated using MF radar wind measurements in the altitude region 86–90 km. Of the three nights, it is found that tidal gravity wave interaction occurred in two nights. In the third night, diurnal tidal amplitude is found to be significantly larger. As suggested in Sica et al. (2007), mesospheric temperature inversion seems to be a signature of wave saturation in the mesosphere, since the temperature inversion occurs at heights, when the lapse rate is less than half the dry adiabatic lapse rate.
Temperature retrieval with VHF radar using combined techniques
Authors: Klaus V.
Published: June 2010

Abstract. The purpose of this study is to evaluate the practical contribution of a VHF radar to high time resolution automatic temperature profiling both for research and operational applications in the frame of an integrated system of ground-based remote-sensing instruments. Based on the most prominent results already mentioned about this instrumentation, different techniques, related to the temperature data retrieval, are experimentally tested and documented using the INSU/Meteo 45 MHz wind profiler operating at CNRM/Toulouse or during cooperative campaigns. In parallel to the self-sufficient Radio Acoustic Sounding System (RASS), other approaches, using the Brunt-Vaisala frequency measurements, allow an extension of height coverage up to the higher troposphere and the tropopause. As only temperature gradients can be measured by this way, complementary data from other instruments are desirable. This makes it particularly fitted to an integrated remote-sensing system operating from the ground combining wind profilers with GPS, radiometers, lidar ceilometers and sodars.
Significance tests for the wavelet cross spectrum and wavelet linear coherence
Authors: Ge Z.
Published: June 2010

Abstract. This work attempts to develop significance tests for the wavelet cross spectrum and the wavelet linear coherence as a follow-up study on Ge (2007). Conventional approaches that are used by Torrence and Compo (1998) based on stationary background noise time series were used here in estimating the sampling distributions of the wavelet cross spectrum and the wavelet linear coherence. The sampling distributions are then used for establishing significance levels for these two wavelet-based quantities. In addition to these two wavelet quantities, properties of the phase angle of the wavelet cross spectrum of, or the phase difference between, two Gaussian white noise series are discussed. It is found that the tangent of the principal part of the phase angle approximately has a standard Cauchy distribution and the phase angle is uniformly distributed, which makes it impossible to establish significance levels for the phase angle. The simulated signals clearly show that, when there is no linear relation between the two analysed signals, the phase angle disperses into the entire range of [−π,π] with fairly high probabilities for values close to ±π to occur. Conversely, when linear relations are present, the phase angle of the wavelet cross spectrum settles around an associated value with considerably reduced fluctuations. When two signals are linearly coupled, their wavelet linear coherence will attain values close to one. The significance test of the wavelet linear coherence can therefore be used to complement the inspection of the phase angle of the wavelet cross spectrum. The developed significance tests are also applied to actual data sets, simultaneously recorded wind speed and wave elevation series measured from a NOAA buoy on Lake Michigan. Significance levels of the wavelet cross spectrum and the wavelet linear coherence between the winds and the waves reasonably separated meaningful peaks from those generated by randomness in the data set. As with simulated signals, nearly constant phase angles of the wavelet cross spectrum are found to coincide with large values in the wavelet linear coherence between the winds and the waves. Not limited to geophysics, the significance tests developed in the present work can also be applied to many other quantitative studies using the continuous wavelet transform.
Solar wind dependence of ion parameters in the Earth's magnetospheric region calculated from CLUSTER observations
Authors: Denton M. H. , Taylor M. G. G. T.
Published: June 2010

Abstract. Moments calculated from the ion distributions (~0–40 keV) measured by the Cluster Ion Spectrometry (CIS) instrument are combined with data from the Cluster Flux Gate Magnetometer (FGM) instrument and used to characterise the bulk properties of the plasma in the near-Earth magnetosphere over five years (2001–2005). Results are presented in the form of 2-D xy, xz and yz GSM cuts through the magnetosphere using data obtained from the Cluster Science Data System (CSDS) and the Cluster Active Archive (CAA). Analysis reveals the distribution of ~0–40 keV ions in the inner magnetosphere is highly ordered and highly responsive to changes in solar wind velocity. Specifically, elevations in temperature are found to occur across the entire nightside plasma sheet region during times of fast solar wind. We demonstrate that the nightside plasma sheet ion temperature at a downtail distance of ~12 to 19 Earth radii increases by a factor of ~2 during periods of fast solar wind (500–1000 km s−1) compared to periods of slow solar wind (100–400 km s−1). The spatial extent of these increases are shown in the xy, xz and yz GSM planes. The results from the study have implications for modelling studies and simulations of solar-wind/magnetosphere coupling, which ultimately rely on in situ observations of the plasma sheet properties for input/boundary conditions.
Towards understanding the electrodynamics of the 3-dimensional high-latitude ionosphere: present and future
Authors: Amm O. , Aruliah A. , Buchert S. C. , Fujii R. , Gjerloev J. W. , Ieda A. , Matsuo T. , Stolle C. , Vanhamäki H. , Yoshikawa A.
Published: June 2010

Abstract. Traditionally, due to observational constraints, ionospheric modelling and data analysis techniques have been devised either in one dimension (e.g. along a single radar beam), or in two dimensions (e.g. over a network of magnetometers). With new upcoming missions like the Swarm ionospheric multi-satellite project, or the EISCAT 3-D project, the time has come to take into account variations in all three dimensions simultaneously, as they occur in the real ionosphere. The link between ionospheric electrodynamics and the neutral atmosphere circulation which has gained increasing interest in the recent years also intrinsically requires a truly 3-dimensional (3-D) description. In this paper, we identify five major science questions that need to be addressed by 3-D ionospheric modelling and data analysis. We briefly review what proceedings in the young field of 3-D ionospheric electrodynamics have been made in the past to address these selected question, and we outline how these issues can be addressed in the future with additional observations and/or improved data analysis and simulation techniques. Throughout the paper, we limit the discussion to high-latitude and mesoscale ionospheric electrodynamics, and to directly data-driven (not statistical) data analysis.
Wavelength dependence of the Es layer instability, and of coupling to the F layer, in the nonlinear regime
Authors: Cosgrove R. B.
Published: June 2010

Abstract. The Es layer instability has been suggested as a participant in the creation of frontal structures observed in both the Es and F layers of the nighttime midlatitude ionosphere, in spite of the fact that the spatial scales of the frontal structures are very different in the two layers. The linear growth rate of the instability has a maxima in the vicinity of the wavelength observed for the Es layer structures (short wavelengths). However, the maxima is non-distinct, and simulations have shown that the instability is extremely nonlinear. Therefore, to understand the wavelength dependence of the Es layer instability it is necessary to factor in nonlinear behavior. Simulations have shown that the instability is active at the wavelengths observed in the F layer, and revealed that the Es layer behavior at these long wavelengths is so nonlinear that the common, highly localized Es layer observation techniques would likely miss the signature, which is highly visible in the F layer. However, there is currently no explanation for why long wavelengths so clearly dominate short (or intermediate) wavelengths in the F layer observations, and this is a weakness in arguments that the Es layer instability participates in the creation of F-region frontal structures. Herein we remove this weakness by showing that longer wavelengths grow to larger amplitudes before eventual nonlinear saturation, and couple more effectively to the F-region.
Surface buoyancy flux in Bay of Bengal and Arabian Sea
Authors: Anitha G. , Ravichandran M. , Sayanna R.
Published: June 2010

Abstract. The seasonal variation of thermal, haline, net surface buoyancy flux, the Monin-Obukhov length (M-O length, L) and stability parameter, i.e. the ratio of M-O length to mixed layer depth (h) were studied in the Bay of Bengal (BoB) and the Arabian Sea (AS) for the years 2003 and 2004 using Argo temperature and salinity profiles. The relative quantitative influence of winds to surface buoyancy and the applicability of scaling mixed layer using M-O length in BoB and AS was brought out. Rotation and light penetration modify the mixed layer depth from M-O length during shoaling in spring giving L/h<1.
Relation between the occurrence rate of ESF and the equatorial vertical plasma drift velocity at sunset derived from global observations
Authors: Stolle C. , Lühr H. , Fejer B. G.
Published: June 2010

Abstract. In this study, we investigate two global climatological data sets; the occurrence rate of Equatorial Spread-F (ESF), associated with equatorial plasma irregularities, at ~400 km altitude obtained from CHAMP observations, and the evening equatorial vertical plasma drift, vz, from ROCSAT-1 measurements. First, as retrieved for a solar flux level of F10.7=150, the longitudinal variation of the two independently derived quantities correlates between 84% and 93% in the seasons December solstice, equinox and June solstice. The highest correlation is found for the solstice seasons when vz is integrated over local time around the prereversal enhancement (PRE) and displaced 6° towards east. The integrated vz is a suitable estimate of the ionospheric height at the time just after the PRE and the 6° displacement is consistent with ESF eastward drift during 2 h which is assumed between creation and detection at satellite altitudes. Second, our analyses reveal a global threshold vz which is required to observe ESF at satellite altitudes. This threshold depends linearly on solar flux with correlations of 97%. Both results bring global evidence on the linear relations between ESF and the vertical plasma drift which have been proven only by local observations so far. This paper includes the first global map of the seasonal/longitudinal variation of the ESF occurrence rate over local time being valid for high solar flux years 2001–2004. The map reveals, e.g. a longitudinal dependence of the persistence of the plasma irregularities indicating that longitude dependent mechanisms other than the PRE determine the ESF lifetime.
Forecasting intense geomagnetic activity using interplanetary magnetic field data
Authors: Saiz E. , Cid C. , Cerrato Y.
Published: June 2010

Abstract. Southward interplanetary magnetic fields are considered traces of geoeffectiveness since they are a main agent of magnetic reconnection of solar wind and magnetosphere. The first part of this work revises the ability to forecast intense geomagnetic activity using different procedures available in the literature. The study shows that current methods do not succeed in making confident predictions. This fact led us to develop a new forecasting procedure, which provides trustworthy results in predicting large variations of Dst index over a sample of 10 years of observations and is based on the value Bz only. The proposed forecasting method appears as a worthy tool for space weather purposes because it is not affected by the lack of solar wind plasma data, which usually occurs during severe geomagnetic activity. Moreover, the results obtained guide us to provide a new interpretation of the physical mechanisms involved in the interaction between the solar wind and the magnetosphere using Faraday's law.
Influence of tides and gravity waves on layering processes in the polar summer mesopause region
Authors: Hoffmann P. , Rapp M. , Fiedler J. , Latteck R.
Published: June 2010

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.