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>

Interannual Variability in the Southern Hemisphere Circulation Organized by Stratospheric Final Warming Events

2007 ◽  
Vol 64 (8) ◽  
pp. 2968-2974 ◽  
Author(s):  
Robert X. Black ◽  
Brent A. McDaniel
Keyword(s):  
Southern Hemisphere ◽  
High Latitude ◽  
Large Scale ◽  
Lower Troposphere ◽  
Southern Annular Mode ◽  
Atmospheric Variability ◽  
Middle Latitudes ◽  
Stratospheric Final Warming ◽  
Circulation Change ◽  
Large Scale Atmospheric Circulation

A composite observational analysis is presented demonstrating that austral stratospheric final warming (SFW) events provide a substantial organizing influence upon the large-scale atmospheric circulation in the Southern Hemisphere. In particular, the annual weakening of high-latitude westerlies in the upper troposphere and stratosphere is accelerated during SFW onset. This behavior is associated with a coherent annular circulation change with zonal wind decelerations (accelerations) at high (low) latitudes. The high-latitude stratospheric decelerations are induced by the anomalous wave driving of upward-propagating tropospheric waves. Longitudinally asymmetric circulation changes occur in the lower troposphere during SFW onset with regionally localized height increases (decreases) at subpolar (middle) latitudes. Importantly, the tropospheric and stratospheric circulation change patterns identified here are structurally distinct from the Southern Annular Mode. It is concluded that SFW events are linked to interannual atmospheric variability with potential bearing upon weather and climate prediction.

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

scholarly journals Rapid radiation of Southern Ocean shags in response to receding sea ice

2021 ◽  
Author(s):  
Nicolas J. Rawlence ◽  
Alexander T. Salis ◽  
Hamish G. Spencer ◽  
Jonathan M. Waters ◽  
Lachie Scarsbrook ◽  
...  
Keyword(s):  
Southern Ocean ◽  
High Latitude ◽  
Large Scale ◽  
Sequence Data ◽  
Current System ◽  
Ecosystem Change ◽  
Biological Research ◽  
Dispersal Capacity ◽  
Island Endemic ◽  
Circumpolar Distribution

ABSTRACTAimUnderstanding how wild populations respond to climatic shifts is a fundamental goal of biological research in a fast-changing world. The Southern Ocean represents a fascinating system for assessing large-scale climate-driven biological change, as it contains extremely isolated island groups within a predominantly westerly, circumpolar wind and current system. The blue-eyed shags (Leucocarbo spp.) represent a paradoxical Southern Ocean seabird radiation; a circumpolar distribution implies strong dispersal capacity yet their speciose nature suggests local adaptation and isolation. Here we use genetic tools in an attempt to resolve this paradox.LocationSouthern Ocean.Taxa17 species and subspecies of blue-eyed shags (Leucocarbo spp.) across the geographical distribution of the genus.MethodsHere we use mitochondrial and nuclear sequence data to conduct the first global genetic analysis of this group using a temporal phylogenetic framework to test for rapid speciation.ResultsOur analysis reveals remarkably shallow evolutionary histories among island-endemic lineages, consistent with a recent high-latitude circumpolar radiation. This rapid sub-Antarctic expansion contrasts with significantly deeper lineages detected in more temperate regions such as South America and New Zealand that may have acted as glacial refugia. The dynamic history of high-latitude expansions is further supported by ancestral demographic and biogeographic reconstructions.Main conclusionsThe circumpolar distribution of blue-eyed shags, and their highly dynamic evolutionary history, potentially make Leucocarbo a strong sentinel of past and ongoing Southern Ocean ecosystem change given their sensitivity to climatic impacts.

Dayside ionospheric electrodynamics in association with high-latitude dayside aurora (HiLDA)

2021 ◽  
Author(s):  
Lei Cai ◽  
Anita Kullen ◽  
Tomas Karlson ◽  
Andris Vaivads ◽  
Yongliang Zhang
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Potential Drop ◽  
Polar Cap ◽  
Ionospheric Electrodynamics ◽  
Defense Meteorological Satellite Program ◽  
Current Region ◽  
Fine Structures ◽  
Field Aligned Current ◽  
Set Up

<p>The Defense Meteorological Satellite Program (DMSP) Special Sensor Ultraviolet Spectrographic Imager (SSUSI) has observed the large-scale high-latitude dayside aurora (HiLDA) during its long lifetime of hours. HiLDA has dynamical changes in form, size, location, and development of fine structures. However, the associated electrodynamics is not fully understood. In general, HiLDA occurs in the dayside polar cap during IMF By+ (By-) prevailing conditions in the sunlit northern (southern) hemisphere.  The prevailing conditions drive strong upward field-aligned current in the polar cap. Within the upward field-aligned current region, the field-aligned potential drop can be set up and accelerate the electrons, forming the monoenergetic electron precipitation (up to 10s keV) and producing HiLDA.</p><p> </p><p>This study investigates the ionospheric flows, currents, and auroral precipitation in association with HiLDA, benified from the simultaneous measurements from the DMSP satellites, the AMPERE project, and ground-based magnetometers and SuperDARN coherent radars. We will show HiLDA interacts with duskside oval-aligned arcs or transpolar arcs. The interactions are associated with the cusp and the dayside reconnection at the duskside flank/high latitudes. The reconnection produces strong dusk-dawn convection with flow shears in the polar cap, which generates the upward Region 0 current. We find that HiLDA is formed in the high-latitude part of the upward Region 0 current. We apply the Knight relation and identify the lobe electrons (< 0.3 cm<sup>-3</sup>) as the source of HiLDA. The fine structures revealed in the emission intensity of HiLDA may suggest the uneven distribution of the electron density in the high-latitude lobe.</p>

scholarly journals Southern Hemisphere Synoptic Behavior in Extreme Phases of SAM, ENSO, Sea Ice Extent, and Southern Australia Rainfall

2008 ◽  
Vol 21 (21) ◽  
pp. 5566-5584 ◽  
Author(s):  
Alexandre Bernardes Pezza ◽  
Tom Durrant ◽  
Ian Simmonds ◽  
Ian Smith
Keyword(s):  
Sea Ice ◽  
Southern Hemisphere ◽  
High Latitude ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Rainfall Anomalies ◽  
Western Side

Abstract The association between Southern Hemisphere cyclones and anticyclones and the El Niño–Southern Oscillation (ENSO), southern annular mode (SAM), Antarctic sea ice extent (SIE), and rainfall in Perth and Melbourne is explored. Those cities are, respectively, located in the southwestern and southeastern corners of Australia, where substantial decreasing rainfall trends have been observed over the last decades. The need for a more unified understanding of large-scale anomalies in storm indicators associated with the climate features itemized above has motivated this study. The main aim is to identify cyclone-anomalous areas that are potentially important in characterizing continental rainfall anomalies from a hemispheric perspective, focusing on midlatitude Australia. The study covers the “satellite era” from 1979 to 2003 and was conducted for the southern winter when midlatitude rainfall is predominantly baroclinic. The results indicate a well-organized hemispheric cyclone pattern associated with ENSO, SAM, SIE, and rainfall anomalies. There is a moderate large-scale, high-latitude resemblance between La Niña, negative SAM, and reduced SIE in some sectors. In particular, there is a suggestion that SIE anomalies over the Indian Ocean and Western Australia sectors are associated with a large-scale pattern of cyclone/anticyclone anomalies that is more pronounced over the longitudes of Australia and New Zealand. Spatial correlation analysis suggests a robust link between cyclone density over the sectors mentioned above and rainfall in Perth and Melbourne. Statistical analyses of rainfall and SIE show modest correlations for Perth and weak correlations for Melbourne, generally corroborating the above. It is proposed that SAM and SIE are part of a complex physical system that is best understood as a coupled mechanism, and that their impacts on the circulation can be seen as partially independent of ENSO. While SAM and SIE have greater influence on the circulation affecting rainfall in the western side of Australia, ENSO is the dominant influence on the eastern half of the country. A contraction of the sea ice seems to be accompanied by a southward shift of high-latitude cyclones, which is also hypothesized to increase downstream cyclone density at midlatitudes via conservation of mass, similarly to what is observed during the extreme positive phase of the SAM. These associations build on previous developments in the literature. They bring a more unified view on high-latitude climate features, and may also help to explain the declining trends in Australian rainfall.

scholarly journals P/Halley: The Disconnection Event of 1986 April 11

1988 ◽  
Vol 98 ◽  
pp. 155-157 ◽  
Author(s):  
P.M. Bergé ◽  
G. Mahoux ◽  
A.C. Levasseur-Regourd
Keyword(s):  
Southern Hemisphere ◽  
Large Scale ◽  
Focal Length ◽  
La Réunion ◽  
Structure Dynamics ◽  
Plasma Tail

This work was carried out by an expedition organized by the S.A.F. in 1986 April to La Réunion. The aim was to observe and photograph P/Halley, within the framework of IHW, as part of the Island Network in the southern hemisphere. To be more precise, our work consisted of studying large-scale phenomena: the structure, dynamics and possible disconnection events in the plasma tail. We were lucky enough to observe one of the latter on the night of April 11/12, and describe it here.For the Island Network, IHW had a number of Schmidt telescopes (Celestron 8). One was lent to the S.A.F. and this is what we used. This telescope has a focal ratio of 1.5, with a 200-mm (8-inch) objective and 300-mm focal length. We used only Kodak TP2415 film, hypersensitized in forming gas (24h at 60°C).

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