scholarly journals Energy–latitude dispersion patterns near the isotropy boundaries of energetic protons

2015 ◽  
Vol 33 (8) ◽  
pp. 1059-1070 ◽  
Author(s):  
V. A. Sergeev ◽  
S. A. Chernyaeva ◽  
S. V. Apatenkov ◽  
N. Y. Ganushkina ◽  
S. V. Dubyagin
Keyword(s):  
Flux Ratio ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Frequent Pattern ◽  
Lower Latitude ◽  
Dispersion Pattern ◽  
Mesoscale Structures ◽  
Angle Scattering ◽  
Dispersion Patterns ◽  
Wave Induced

Abstract. Non-adiabatic motion of plasma sheet protons causes pitch-angle scattering and isotropic precipitation to the ionosphere, which forms the proton auroral oval. This mechanism related to current sheet scattering (CSS) provides a specific energy–latitude dispersion pattern near the equatorward boundary of proton isotropic precipitation (isotropy boundary, IB), with precipitation sharply decreasing at higher (lower) latitude for protons with lower (higher) energy. However, this boundary maps to the inner magnetosphere, where wave-induced scattering may provide different dispersion patterns as recently demonstrated by Liang et al. (2014). Motivated by the potential usage of the IBs for the magnetotail monitoring as well as by the need to better understand the mechanisms forming the proton IB, we investigate statistically the details of particle flux patterns near the proton IB using NOAA-POES polar spacecraft observations made during September 2009. By comparing precipitated-to-trapped flux ratio (J0/J90) at >30 and >80 keV proton energies, we found a relatively small number of simple CSS-type dispersion events (only 31 %). The clear reversed (wave-induced) dispersion patterns were very rare (5 %). The most frequent pattern had nearly coinciding IBs at two energies (63 %). The structured precipitation with multiple IBs was very frequent (60 %), that is, with two or more significant J0/J90 dropouts. The average latitudinal width of multiple IB structures was about 1°. Investigation of dozens of paired auroral zone crossings of POES satellites showed that the IB pattern is stable on a timescale of less than 2 min (a few proton bounce periods) but can evolve on a longer (several minutes) scale, suggesting temporal changes in some mesoscale structures in the equatorial magnetosphere. We discuss the possible role of CSS-related and wave-induced mechanisms and their possible coupling to interpret the emerging complicated patterns of proton isotropy boundaries.

scholarly journals On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere

2003 ◽  
Vol 21 (8) ◽  
pp. 1847-1868 ◽  
Author(s):  
M. L. Parkinson ◽  
J. C. Devlin ◽  
H. Ye ◽  
C. L. Waters ◽  
P. L. Dyson ◽  
...  
Keyword(s):  
Electric Fields ◽  
Spectral Width ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Ionospheric Irregularities ◽  
Lower Latitude ◽  
Doppler Velocity ◽  
Auroral Ionosphere ◽  
Polar Cap ◽  
Sunspot Maximum

Abstract. The statistical occurrence of decametre-scale ionospheric irregularities, average line-of-sight (LOS) Doppler velocity, and Doppler spectral width in the sub-auroral, auroral, and polar cap ionosphere ( - 57°L to - 88°L) has been investigated using echoes recorded with the Tasman International Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island, Tasmania (147.2° E, 43.4° S geographic; - 54.6 °L). Results are shown for routine soundings made on the magnetic meridian beam 4 and the near zonal beam 15 during the sunspot maximum interval December 1999 to November 2000. Most echoes were observed in the nightside ionosphere, typically via 1.5-hop propagation near dusk and then via 0.5-hop propagation during pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near magnetic midnight and ~ - 70 °L. They increased and shifted equatorward and toward pre-midnight with increasing Kp (i.e. Bz southward). The occurrence rates remained very high for Kp > 4, de-spite enhanced D-region absorption due to particle precipitation. Average occurrence rates on beam 4 exhibited a relatively weak seasonal variation, consistent with known longitudinal variations in auroral zone magnetic activity (Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two populations of echoes were identified on both beams, those with low spectral width and a mode value of ~ 9 ms-1 (bin size of 2 ms-1) concentrated in the auroral and sub-auroral ionosphere (population A), and those with high spectral width and a mode value of ~ 70 ms-1 concentrated in the polar cap ionosphere (population B). The occurrence of population A echoes maximised post-midnight because of TIGER’s lower latitude, but the subset of the population A echoes observed near dusk had characteristics reminiscent of "dusk scatter" (Ruohoniemi et al., 1988). There was a dusk "bite out" of large spectral widths between ~ 15 and 21 MLT and poleward of - 67 °L, and a pre-dawn enhancement of large spectral widths between ~  03 and 07 MLT, centred on ~ - 61 °L. The average LOS Doppler velocities revealed that frequent westward jets of plasma flow occurred equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight sector.Key words. Ionosphere (auroral ionosphere; electric fields and currents, ionospheric irregularities)

scholarly journals Magnetic local time, substorm, and particle precipitation-related variations in the behaviour of SuperDARN Doppler spectral widths

2004 ◽  
Vol 22 (12) ◽  
pp. 4103-4122 ◽  
Author(s):  
M. L. Parkinson ◽  
G. Chisham ◽  
M. Pinnock ◽  
P. L. Dyson ◽  
J. C. Devlin
Keyword(s):  
Spectral Width ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Lower Latitude ◽  
Velocity Spread ◽  
Doppler Velocity ◽  
High Time Resolution ◽  
Particle Precipitation ◽  
Study Interval ◽  
Present Case Study

Abstract. Super Dual Auroral Radar Network (DARN) radars often detect a distinct transition in line-of-sight Doppler velocity spread, or spectral width, from <50ms–1 at lower latitude to >200ms–1 at higher latitude. They also detect a similar boundary, namely the range at which ionospheric scatter with large spectral width suddenly commences (i.e. without preceding scatter with low spectral width). The location and behaviour of the spectral width boundary (SWB) (and scatter boundary) and the open-closed magnetic field line boundary (OCB) are thought to be closely related. The location of the nightside OCB can be inferred from the poleward edge of the auroral oval determined using energy spectra of precipitating particles measured on board Defence Meteorology Satellite Program (DMSP) satellites. Observations made with the Halley SuperDARN radar (75.5° S, 26.6° W, geographic; –62.0°Λ) and the Tasman International Geospace Environment Radar (TIGER) (43.4° S, 147.2° E; –54.5°Λ) are used to compare the location of the SWB with the DMSP-inferred OCB during 08:00 to 22:00 UT on 1 April 2000. This study interval was chosen because it includes several moderate substorms, whilst the Halley radar provided almost continuous high-time resolution measurements of the dayside SWB location and shape, and TIGER provided the same in the nightside ionosphere. The behaviour of the day- and nightside SWB can be understood in terms of the expanding/contracting polar cap model of high-latitude convection change, and the behaviour of the nightside SWB can also be organised according to substorm phase. Previous comparisons with DMSP OCBs have proven that the radar SWB is often a reasonable proxy for the OCB from dusk to just past midnight (Chisham et al., 2004). However, the present case study actually suggests that the nightside SWB is often a better proxy for the poleward edge of Pedersen conductance enhanced by hot particle precipitation in the auroral zone. Simple modeling implies that the large spectral widths must be caused by ~10-km scale velocity fluctuations. Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions) – Magnetospheric physics (storms and substorms)

scholarly journals Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

2004 ◽  
Vol 22 (1) ◽  
pp. 63-72 ◽  
Author(s):  
S. V. Apatenkov ◽  
V. A. Sergeev ◽  
R. Pirjola ◽  
A. Viljanen
Keyword(s):  
Dynamic Pressure ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Middle Part ◽  
Magnetic Storms ◽  
Geomagnetically Induced Currents ◽  
Geomagnetic Variations ◽  
Ionospheric Current ◽  
Solar Wind Parameters ◽  
Current Systems

Abstract. To learn about the geometry and sources of the ionospheric current systems which generate strong geomagnetically induced currents, we categorize differential equivalent current systems (DEC) for events with strong dB/dt by decomposing them into the contributions of electrojet-type and vortex-type elementary systems. By solving the inverse problem we obtain amplitudes and locations of these elementary current systems. One-minute differences of the geomagnetic field values at the IMAGE magnetometer network in 1996–2000 are analysed to study the spatial distributions of large dB/dt events. The relative contributions of the two components are evaluated. In particular, we found that the majority of the strongest dB/dt events (100–1000nT/min) appear to be produced by the vortex-type current structures and most of them occur in the morning LT hours, probably caused by the Ps6 pulsation events associated with auroral omega structures. For strong dB/dt events the solar wind parameters are shifted toward strong (tens nT) southward IMF, enhanced velocity and dynamic pressure, in order for the main phase of the magnetic storms to occur. Although these events appear mostly during magnetic storms when the auroral oval greatly expands, the area of large dB/dt stays in the middle part of the auroral zone; therefore, it is connected to the processes taking part in the middle of the magnetosphere rather than in its innermost region populated by the ring current. Key words. Geomagnetism and paleomagnetism (rapid time variations) – Ionosphere (auroral ionosphere; ionospheric disturbances)

scholarly journals Past and current sediment dispersion pattern estimates through numerical modeling of wave climate: an example of the Holocene delta of the Doce River, Espírito Santo, Brazil

2007 ◽  
Vol 79 (2) ◽  
pp. 333-341 ◽  
Author(s):  
Abílio C.S.P. Bittencourt ◽  
José M.L. Dominguez ◽  
Louis Martin ◽  
Iracema R. Silva ◽  
Karla O.P. de-Medeiros
Keyword(s):  
Numerical Modeling ◽  
Boundary Conditions ◽  
Late Holocene ◽  
Climate Model ◽  
Coastal Region ◽  
Wave Climate ◽  
Aerial Photographs ◽  
Dispersion Pattern ◽  
Dispersion Patterns ◽  
Doce River

This paper presents a numerical modeling estimation of the sediment dispersion patterns caused by waves inciding through four distinct coastline contours of the delta plain of the Doce River during the Late Holocene. For this, a wave climate model based on the construction of wave refraction diagrams, as a function of current boundary conditions, was defined and was assumed to be valid for the four coastlines. The numerical modeling was carried out on basis of the refraction diagrams, taking into account the angle of approximation and the wave height along the coastline. The results are shown to be comparable with existing data regarding the directions of net longshore drift of sediments estimated from the integration of sediment cores, interpretation of aerial photographs and C14 datings. This fact apparently suggests that, on average, current boundary conditions appear to have remained with the same general characteristics since 5600 cal yr BP to the present. The used approach may prove useful to evaluate the sediment dispersion patterns during the Late Holocene in the Brazilian east-northeast coastal region.

Does the Contrast Dispersion Pattern During Fluoroscopically Guided Cervical Transforaminal Epidural Steroid Injection Predict Short-Term Pain and Functional Outcomes? An Exploratory Analysis of Prospective Cohort Data

Pain Medicine ◽  
2020 ◽  
Vol 21 (12) ◽  
pp. 3350-3359
Author(s):  
Aaron Conger ◽  
Beau P Sperry ◽  
Cole W Cheney ◽  
Keith Kuo ◽  
Russel Petersen ◽  
...  
Keyword(s):  
Neck Pain ◽  
Epidural Space ◽  
Functional Outcomes ◽  
Steroid Injection ◽  
Epidural Steroid Injection ◽  
Dispersion Pattern ◽  
Arm Pain ◽  
Dispersion Patterns ◽  
Transforaminal Epidural Steroid Injection ◽  
Epidural Steroid

Abstract Summary of Background Data No study has evaluated the relationship between contrast dispersion patterns and outcomes after fluoroscopically guided cervical transforaminal epidural steroid injection (CTFESI). Objectives Determine whether contrast dispersion patterns predict pain and functional outcomes after CTFESI. Methods Secondary analysis of data collected during two prospective studies of CTFESI for the treatment of refractory radicular pain. Contrast dispersion patterns visualized by true anteroposterior (AP) projections during CTFESIs were categorized by flow: 1) completely external to the lateral border of the neuroforamen (zone 1); 2) within the neuroforamen but without entry into the lateral epidural space (zone 2); and 3) with extension into the lateral epidural space (zone 3). At baseline and at 1 month post-CTFESI, neck pain, arm pain, and “dominant index pain” (the greater of arm or neck pain) were evaluated using a numeric rating scale (NRS); physical function was assessed using the Five-Item Version of the Neck Disability Index (NDI-5). Results One-month post-CTFESI, neck pain, arm pain, and “dominant index pain” reductions of ≥50% were observed in 39.4% (95% confidence interval [CI], 28.2–51.8), 55.6% (95% CI, 43.0–67.5), and 44.1% (95% CI, 32.7–56.2) of participants, respectively. Regarding “dominant index pain,” 72.7% (95% CI, 40.8–91.2), 39.4% (95% CI, 24.2–57.0), and 37.5% (95% CI, 20.5–58.2) of participants reported ≥50% pain reduction when zone 1, zone 2, and zone 3 contrast flow patterns were observed. Contrast dispersion zone was not significantly associated with subgroup differences in neck pain, arm pain, or NDI-5 scores (P&gt;0.05). Conclusion Improvements in pain and function 1 month after treatment with CTFESI did not differ significantly based on the contrast dispersion pattern. Future study is needed to confirm or refute these findings in other procedural settings, in broader patient populations, and with longer-term outcome assessment.

On the apparent equatorward propagation of auroral substorm absorption events at low auroral latitudes

1978 ◽  
Vol 56 (11) ◽  
pp. 1412-1416 ◽  
Author(s):  
Syed Ziauddin ◽  
M. A. Abdu
Keyword(s):  
Time Dependence ◽  
Local Time ◽  
Electric Fields ◽  
Auroral Zone ◽  
Lower Latitude ◽  
Precipitation Region ◽  
Auroral Substorm ◽  
Strong Electric Fields ◽  
Local Time Dependence ◽  
Consistent Tendency

Auroral substorm absorption events observed at two stations. Val d'Or, P.Q. and Ottawa, Ont., located on the lower latitude side of the auroral zone (around L = 4) show a consistent tendency for an apparent equatorward propagation of the events. The observed velocities of propagation do not show any local time dependence or other trends expected from a pure gradient B drift of substorm electrons from the midnight precipitation region to the day side. Though a limited number of events are analysed the results indicate the possible influence of strong electric fields on the drift velocities of the substorm electrons.

scholarly journals Nano- and Mesoscale Structures of Amorphous Calcium Carbonate Indicate Nanoscale Assembly Processes

2021 ◽  
Author(s):  
Simon M. Clark ◽  
Bruno Colas ◽  
Dorrit E. Jacob ◽  
Jӧrg Neuefeind ◽  
Hsiu-Wen Wang ◽  
...  
Keyword(s):  
Self Assembly ◽  
Amorphous Materials ◽  
Scattering Data ◽  
Amorphous Calcium Carbonate ◽  
Detailed Model ◽  
Mesoscale Structures ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Process Computer ◽  
High Degree

<div>Here, we approach the issue of ACC ultrastructure by applying a method for determining atomically resolved structures of amorphous materials using Monte Carlo simulations constrained by both X-ray and neutron scattering data. This structural analysis approach allows us to develop a detailed model for ACC at the atomic level. Our findings reveal that synthetic ACC, rapidly precipitated at high pH, consists of two-nanometer sized units containing a high degree of near range order similar to partially disordered nano-crystals. Small-angle scattering analyses show a multi-scale hierarchical organisation of the structure, supportive of a multi-step colloid self-assembly process. Computer simulations and high-resolution transmission electron microscopy show that the mesostructure of ACC resembles that of a glassy gel with crystalline material in domains. Our findings support the formation of ACC by a nanoparticle aggregation process that likely starts from prenucleation clusters in solution.</div>

scholarly journals Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

2014 ◽  
Vol 5 (1) ◽  
pp. 81-134 ◽  
Author(s):  
Y. I. Feldstein ◽  
V. G. Vorobjev ◽  
V. L. Zverev ◽  
M. Förster
Keyword(s):  
Local Time ◽  
18Th Century ◽  
Spectral Composition ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Planetary Scale ◽  
Magnetospheric Convection ◽  
International Geophysical Year ◽  
Auroral Substorm ◽  
Auroral Luminosity

Abstract. Research results about planetary-scale auroral distributions are presented in a historical retrospective, beginning with the first "maps of isochasms" – lines of equal visibility of auroras in the firmament (Fig. 2) – up to "isoaurora maps" – lines of equal occurrence frequency of auroras in the zenith (Fig. 4). The exploration of auroras in Russia from Lomonosov in the 18th century (Fig. 1) until the start of the International Geophysical Year (IGY) in 1957 is shortly summed up. A generalised pattern of discrete auroral forms along the auroral oval during geomagnetically very quiet intervals is presented in Fig. 5. The changes of discrete auroral forms versus local time exhibit a fixed pattern with respect to the sun. The auroral forms comprise rays near noon, homogeneous arcs during the evening, and rayed arcs and bands during the night and in the morning. This fixed auroral pattern is unsettled during disturbances, which occur sometimes even during very quiet intervals. The azimuths of extended auroral forms vary with local time. Such variations in the orientation of extended forms above stations in the auroral zone have been used by various investigators to determine the position of the auroral oval (Fig. 9). Auroral luminosity of the daytime and nighttime sectors differ owing to different luminosity forms, directions of motion of the discrete forms, the height of the luminescent layers, and the spectral composition (predominant red emissions during daytime and green emissions during the night). Schemes that summarise principal peculiarities of daytime luminosity, its structure in MLT (magnetic local time) and MLat (magnetic latitude) coordinates, and the spectral composition of the luminosity are presented in Figs. 15 and 19. We discuss in detail the daytime sector dynamics of individual discrete forms for both quiet conditions and auroral substorms. The most important auroral changes during substorms occur in the nighttime sector. We present the evolution of conceptions about the succession of discrete auroral forms and their dynamics during disturbance intervals. This ranges from Birkeland's polar elementary storms, over the prospect of a fixed auroral pattern up to the auroral substorm model. The classic schemes of the spatial distribution and motion of discrete auroral forms during single substorms are shown in Fig. 20 (expansive and recovery phases) and Fig. 21 (creation, expansive and recovery phases). In this review we discuss various models of bulge formation, in particular as a result of new formation of arcs about 50–100 km poleward of previously existing auroral structures (Fig. 24). Discrete steps in the development of an expanding bulge are separated by 1–3 min from each other. The model of successive activations confines only to a ~40° longitudinal portion of the magnetotail (Fig. 28). We consider differences in the development of single substorms and substorms during magnetic storms. The structure and dynamics of auroras during steady magnetospheric convection (SMC) periods are dealt with in Sect. 8. A generalised scheme of the auroral distribution during SMC periods is shown in Fig. 34. Separate sections describe discrete auroras in the polar cap (Sect. 5), and the diffuse luminosity equatorward of the auroral oval (Sect. 9). Visual observations of diffuse auroral forms at midlatitudes suggest that the whole latitudinal interval between the auroral oval and the stable auroral red (SAR) arc is filled up with diffuse luminosity. SAR arcs with intensities of several tens of Rayleigh enclose systematically the region of diffuse luminosity; they are positioned at the border of the plasmasphere.

scholarly journals Spiral structures and regularities in magnetic field variations and auroras

2012 ◽  
Vol 3 (1) ◽  
pp. 1-31 ◽  
Author(s):  
Y. I. Feldstein ◽  
L. I. Gromova ◽  
M. Förster ◽  
A. E. Levitin
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Current System ◽  
Temporal Distribution ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Upper Atmosphere ◽  
Polar Coordinates ◽  
Magnetospheric Substorms ◽  
Field Lines

Abstract. The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern Hemispheres. The N- and M-spirals drawn in polar coordinates form an oval, along which one observes most often auroras in the zenith together with a westward electrojet. The nature of spiral distributions in geomagnetic field variations was unabmibuously interpreted after the discovery of the spiral's existence in the auroras had been established and this caused a change from the paradigm of the auroral zone to the paradigm of the auroral oval. Zenith forms of auroras are found within the boundaries of the auroral oval. The oval is therefore the region of most frequent precipitations of corpuscular fluxes with auroral energy, where anomalous geophysical phenomena occur most often and with maximum intensity. S. Chapman and L. Harang identified the existence of a discontinuity at auroral zone latitudes (Φ ∼ 67°) around midnight between the westward and eastward electrojets, that is now known as the Harang discontinuity. After the discovery of the auroral oval and the position of the westward electrojet along the oval, it turned out, that there is no discontinuity at a fixed latitude between the opposite electrojets, but rather a gap, the latitude of which varies smoothly between Φ ∼ 67° at midnight and Φ ∼ 73° at 20:00 MLT. In this respect the term ''Harang discontinuity'' represents no intrinsic phenomenon, because the westward electrojet does not experience any disruption in the midnight sector but continues without breaks from dawn to dusk hours.

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