Large-scale high-latitude dayside auroral emissions

1990 ◽  
Vol 95 (A3) ◽  
pp. 2345 ◽  
Author(s):  
J. S. Murphree ◽  
R. D. Elphinstone ◽  
D. Hearn ◽  
L. L. Cogger
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Auroral Emissions

DMSP/SSUSI observations of the high-latitude dayside aurora (HiLDA

2020 ◽  
Author(s):  
Lei Cai ◽  
Anita Kullen ◽  
Yongliang Zhang ◽  
Tomas Karlsson ◽  
Andris Vaivads
Keyword(s):  
Southern Hemisphere ◽  
High Latitude ◽  
Large Scale ◽  
Current System ◽  
Potential Drop ◽  
Particle Spectrum ◽  
Northern Summer ◽  
Open Field Line ◽  
Polar Rain ◽  
Auroral Emissions

<p>High-latitude dayside aurora (HiLDA) are large-scale discrete arcs or spot-like aurora poleward of the cusp, observed previously in the northern hemisphere by the Viking UV imager [Murphree et al., 1990] and by the IMAGE FUV [Frey et al., 2003]. The particular interest on HiLDA is to understand its formation related to the dayside reconnection and the resulted field-aligned currents (FACs) configuration in the polar cap (open field line region). In addition, the occurrence of HiLDA in the southern hemisphere is not well known.</p><p>In this study, we investigate the properties of HiLDA using DMSP/SSUSI images from the satellites F16, F17, F18, and F19. The combined data with auroral images from DMSP/SSUSI, ion drift velocity from SSIES, magnetic field perturbations from SSM, and energetic particle spectrum from SSJ make it possible to study the electrodynamics in the vicinity of the HiLDA and its connection the dayside cusp. HiLDA is formed due to monoenergetic electron precipitation (inverted-V structures) with the absence of ion precipitation. The field-aligned potential drop can be up to tens of keV. Applying the current-voltage relation, we suggest accelerated polar rain as the source of HiLDA, indirectly controlled by the solar wind/magnetosheath plasma population. The upward field-aligned current associated with the potential drop is a part of the cusp current system, produced by the dayside reconnection. Both lobe reconnection and reconnection on the duskside flanks play a role in the formation of HiLDA.</p><p>The occurrence of HiLDA is highly associated with the sunlit hemisphere and IMF By dominated conditions. Our results agree with previous observations, which show that HiLDA occurs during positive By dominated conditions in the northern summer hemisphere. We also confirmed that HiLDA occurs during negative By dominated conditions in the southern hemisphere. In addition, the fine structures of HiLDA are studied.</p><p>References</p><p><span>Murphree, J. S.</span>, <span>Elphinstone, R. D.</span>, <span>Hearn, D.</span>, and <span>Cogger, L. L.</span> ( <span>1990</span>), <span>Large‐scale high‐latitude dayside auroral emissions</span>, <em>J. Geophys. Res.</em>, <span>95</span>( <span>A3</span>), <span>2345</span>– <span>2354</span>, doi:.</p><p><span>Frey, H. U.</span>, <span>Immel, T. J.</span>, <span>Lu, G.</span>, <span>Bonnell, J.</span>, <span>Fuselier, S. A.</span>, <span>Mende, S. B.</span>, <span>Hubert, B.</span>, <span>Østgaard, N.</span>, and <span>Le, G.</span> ( <span>2003</span>), <span>Properties of localized, high latitude, dayside aurora</span>, <em>J. Geophys. Res.</em>, <span>108</span>, 8008, doi:, <span>A4</span>.</p>

scholarly journals Small-scale characteristics of extremely high latitude aurora

2009 ◽  
Vol 27 (9) ◽  
pp. 3335-3347 ◽  
Author(s):  
J. A. Cumnock ◽  
L. G. Blomberg ◽  
A. Kullen ◽  
T. Karlsson ◽  
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Small Scale ◽  
Strong Correlations ◽  
Polar Cap ◽  
Plasma Flows ◽  
Ionospheric Convection ◽  
Local Closure ◽  
Scale Characteristics

Abstract. We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF By. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

scholarly journals An Interpretation of the Distribution of Metre Wavelength Radio Emission

1968 ◽  
Vol 21 (2) ◽  
pp. 167 ◽  
Author(s):  
KW Yates
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Absolute Calibration ◽  
Fundamental Difficulty ◽  
The Galaxy ◽  
Calibration Accuracy ◽  
Limit Estimate ◽  
Spiral Arm

A recent 85 MHz survey of the southern sky had an absolute calibration accuracy and resolution comparable with a number of surveys made for the northern skies. By combining the results of these surveys in both hemispheres a complete sky map has been produced, and in this paper an analysis is made of the distribution of the medium and high latitude emission. A fundamental difficulty encountered is the identification and isolation of the spurs of emission projecting from the galactic plane. Two hypotheses are proposed. The first attributes the spurs to a large-scale feature associated with the galactic core and the remaining emission to a galactic halo. The second postulates the origin of the spurs within the local spiral arm, which is itself considered to contribute significantly to the high latitude background. An upper-limit estimate of the emissivity of the local arm is made from currently available independent data. Using this result a model local arm is proposed, which, together with an isotropic component from beyond the Galaxy and a small additional galactic component, explains the observed distribution.

scholarly journals Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

2015 ◽  
Vol 11 (4) ◽  
pp. 2977-3018 ◽  
Author(s):  
K. M. Pascher ◽  
C. J. Hollis ◽  
S. M. Bohaty ◽  
G. Cortese ◽  
R. M. McKay
Keyword(s):  
Oxygen Isotope ◽  
High Latitude ◽  
Large Scale ◽  
Middle Eocene ◽  
Late Eocene ◽  
Climate History ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Radiolarian Assemblages

Abstract. The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene–Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40–33 Ma) to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM) event – a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma) there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are absent. These data indicate that, once the Tasman Gateway was fully open in the early Oligocene, a frontal system similar to the present day was established, with nutrient-depleted subantarctic waters bathing the area around DSDP Site 277, resulting in a more oligotrophic siliceous plankton assemblage.

scholarly journals Finding the VOICE: organic carbon isotope chemostratigraphy of Late Jurassic – Early Cretaceous Arctic Canada

2019 ◽  
Vol 157 (10) ◽  
pp. 1643-1657 ◽  
Author(s):  
Jennifer M. Galloway ◽  
Madeleine L. Vickers ◽  
Gregory D. Price ◽  
Terence Poulton ◽  
Stephen E. Grasby ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Isotope ◽  
High Latitude ◽  
Large Scale ◽  
The Arctic ◽  
Sudden Increase ◽  
Arctic Canada ◽  
Contributing Factors ◽  
Compositional Evolution ◽  
Sverdrup Basin

AbstractA new carbon isotope record for two high-latitude sedimentary successions that span the Jurassic–Cretaceous boundary interval in the Sverdrup Basin of Arctic Canada is presented. This study, combined with other published Arctic data, shows a large negative isotopic excursion of organic carbon (δ13Corg) of 4‰ (V-PDB) and to a minimum of −30.7‰ in the probable middle Volgian Stage. This is followed by a return to less negative values of c. −27‰. A smaller positive excursion in the Valanginian Stage of c. 2‰, reaching maximum values of −24.6‰, is related to the Weissert Event. The Volgian isotopic trends are consistent with other high-latitude records but do not appear in δ13Ccarb records of Tethyan Tithonian strata. In the absence of any obvious definitive cause for the depleted δ13Corg anomaly, we suggest several possible contributing factors. The Sverdrup Basin and other Arctic areas may have experienced compositional evolution away from open-marine δ13C values during the Volgian Age due to low global or large-scale regional sea levels, and later become effectively coupled to global oceans by Valanginian time when sea level rose. A geologically sudden increase in volcanism may have caused the large negative δ13Corg values seen in the Arctic Volgian records but the lack of precise geochronological age control for the Jurassic–Cretaceous boundary precludes direct comparison with potentially coincident events, such as the Shatsky Rise. This study offers improved correlation constraints and a refined C-isotope curve for the Boreal region throughout latest Jurassic and earliest Cretaceous time.

scholarly journals Statistical study of high-latitude plasma flow during magnetospheric substorms

2004 ◽  
Vol 22 (10) ◽  
pp. 3607-3624 ◽  
Author(s):  
G. Provan ◽  
M. Lester ◽  
S. B. Mende ◽  
S. E. Milan
Keyword(s):  
Plasma Flow ◽  
Growth Phase ◽  
High Latitude ◽  
Large Scale ◽  
Flow Region ◽  
Substorm Onset ◽  
Return Flow ◽  
Polar Cap ◽  
Magnetospheric Substorms ◽  
Superposed Epoch Analysis

Abstract. We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF Bz component was increasing (becoming less negative) during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.

scholarly journals Channelling of high-latitude boundary-layer flow

2008 ◽  
Vol 15 (1) ◽  
pp. 33-52 ◽  
Author(s):  
N. Nawri ◽  
R. E. Stewart
Keyword(s):  
Boundary Layer ◽  
High Latitude ◽  
Large Scale ◽  
Dynamical Downscaling ◽  
Geostrophic Wind ◽  
Horizontal Wind ◽  
Stationary States ◽  
Prevailing Wind ◽  
Surface Winds ◽  
Variable Surface

Abstract. Due to the stability of the boundary-layer stratification, high-latitude winds over complex terrain are strongly affected by blocking and channelling effects. Consequently, at many low-lying communities in the Canadian Archipelago, including Cape Dorset and Iqaluit considered in this study, surface winds for the most part are from two diametrically opposed directions, following the orientation of the elevated terrain. Shifts between the two prevailing wind directions can be sudden and are associated with geostrophic wind directions within a well defined narrow range. To quantitatively investigate the role of large-scale pressure gradients and the quasi-geostrophic overlying flow, an idealised dynamical system for the evolution of channelled surface winds is derived from the basic equations of motion, in which stability of stationary along-channel wind directions is described as a function of the geostrophic wind. In comparison with long-term horizontal wind statistics at the two locations it is shown that the climatologically prevailing wind directions can be identified as stationary states of the idealised wind model, and that shifts between prevailing wind directions can be represented as stability transitions between these stationary states. In that sense, the prevailing local wind conditions can be interpreted as attracting states of the actual flow, with observed surface winds adjusting to a new stable direction as determined by the idealised system within 3–9 h. Over these time-scales and longer it is therefore advantageous to determine the relatively slow evolution of the observationally well-resolved large-scale pressure distribution, instead of modelling highly variable surface winds directly. The simplified model also offers a tool for dynamical downscaling of global climate simulations, and for determining future scenarios for local prevailing wind conditions. In particular, it allows an estimation of the sensitivity of local low-level winds to changes in the large-scale atmospheric circulation.

scholarly journals Magnetic topology of coronal mass ejection events out of the ecliptic: Ulysses/HI-SCALE energetic particle observations

2003 ◽  
Vol 21 (6) ◽  
pp. 1249-1256 ◽  
Author(s):  
O. E. Malandraki ◽  
E. T. Sarris ◽  
G. Tsiropoula
Keyword(s):  
Magnetic Field ◽  
High Latitude ◽  
Energetic Particle ◽  
Large Scale ◽  
Energetic Electron ◽  
Solar Energetic Particle ◽  
Interplanetary Coronal Mass Ejections ◽  
Interplanetary Magnetic Fields ◽  
Interplanetary Physics ◽  
Field Lines

Abstract. Solar energetic particle fluxes (Ee > 38 keV) observed by the ULYSSES/HI-SCALE experiment are utilized as diagnostic tracers of the large-scale structure and topology of the Interplanetary Magnetic Field (IMF) embedded within two well-identified Interplanetary Coronal Mass Ejections (ICMEs) detected at 56° and 62° south heliolatitudes by ULYSSES during the solar maximum southern high-latitude pass. On the basis of the energetic solar particle observations it is concluded that: (A) the high-latitude ICME magnetic structure observed in May 2000 causes a depression in the solar energetic electron intensities which can be accounted for by either a detached or an attached magnetic field topology for the ICME; (B) during the traversal of the out-of-ecliptic ICME event observed in July 2000 energetic electrons injected at the Sun are channeled by the ICME and propagate freely along the ICME magnetic field lines to 62° S heliolatitude.Key words. Interplanetary physics (energetic particles; interplanetary magnetic fields)

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