Electrodynamics of Auroral and Polar Cap Arcs at Very High Latitudes

Author(s):  
R. R. Vondrak ◽  
R. M. Robinson
Keyword(s):  
2016 ◽  
Vol 36 (2) ◽  
pp. 141-160 ◽  
Author(s):  
Sofwan Noerwidi

In 2014 there was found two "enigmatic" specimens of mandible, which named as Semedo 3417 and 3418. Both mandibles are morphologically similar but twice bigger than common primate’s jaw. In this research, we use morphology and morphometric analysis to determine the species identity and taxonomic position of those specimens. For comparison study we use some samples from Homo erectus (Java and China), Gigantopithecus (blacki and bilaspurensis), Australopithecines (robust and gracile). Based on morphology and morphometric characters on the mandible and teeth, it is concluded that Semedo specimen tends to be close to Gigantopithecus blacki. The discoveries of Gigantopithecus fossil in Java has implication on some research problem, especially regarding the adaptation pattern of this species which known only found at high latitudes environment. Furthermore this discovery has reinforced the perspective that tropical environment has a very high biodiversity, particularly on primate fossils.


1998 ◽  
pp. 327-342 ◽  
Author(s):  
C. G. Maclennan ◽  
L. J. Lanzerotti ◽  
D. J. Thomson
Keyword(s):  

1986 ◽  
Vol 91 (A1) ◽  
pp. 375 ◽  
Author(s):  
L. J. Lanzerotti ◽  
C. G. Maclennan ◽  
L. V. Medford ◽  
D. L. Carpenter
Keyword(s):  

2009 ◽  
Vol 27 (3) ◽  
pp. 1139-1152 ◽  
Author(s):  
S. E. Pryse ◽  
E. L. Whittick ◽  
A. D. Aylward ◽  
H. R. Middleton ◽  
D. S. Brown ◽  
...  

Abstract. Electric potential patterns obtained by the SuperDARN radar network are used as input to the Coupled Thermosphere-Ionosphere-Plasmasphere model, in an attempt to improve the modelling of the spatial distribution of the ionospheric plasma at high latitudes. Two case studies are considered, one under conditions of stable IMF Bz negative and the other under stable IMF Bz positive. The modelled plasma distributions are compared with sets of well-established tomographic reconstructions, which have been interpreted previously in multi-instrument studies. For IMF Bz negative both the model and observations show a tongue-of-ionisation on the nightside, with good agreement between the electron density and location of the tongue. Under Bz positive, the SuperDARN input allows the model to reproduce a spatial plasma distribution akin to that observed. In this case plasma, unable to penetrate the polar cap boundary into the polar cap, is drawn by the convective flow in a tongue-of-ionisation around the periphery of the polar cap.


1973 ◽  
Vol 21 (2) ◽  
pp. 201 ◽  
Author(s):  
W Hartley

Maps are presented showing the world distributions of the subfamily Festucoideae and the tribe Festuceae, based on data on relative specific frequency derived from about 500 widely-distributed floras and floristic lists. The maps show many points of similarity and, especially in N. America, there is a very high correlation between the numbers of species of the subfamily and tribe in regional floras. Both the Festucoideae and the Festuceae attain their highest relative specific frequency in high latitudes or at high altitudes. There is a strong negative correlation between high specific frequency and midsummer temperature in the flora of the United States, and evidence of a similar, though less marked, relationship in other regions. The effect of rainfall is not apparent in the distribution maps. Regions of high relative specific frequency of the tribes Agrostideae, Aveneae, Stipeae, and Triticeae are mapped, and discussed in relation to climate. In their geographical relationships, the tribes studied fall into two groups, viz. (1) Agrostideae, Aveneae, and Festuceae; (2) Stipeae and Triticeae. The significance of the distribution patterns is discussed in relation to the evolutionary development of the subfamily Festucoideae and its constituent tribes. The phytogeographical evidence supports the view that each tribe is monophyletic, with the exception of the Aveneae (sensu str.), which is well developed in regions of diverse climate. A strongly developed enclave of high relative specific frequency of Festuceae in part of south-eastern Europe, which shows no obvious relationship to climate, is interpreted as evidence for the occurrence of a cycle of secondary evolution of the tribe in this region.


2009 ◽  
Vol 27 (7) ◽  
pp. 2623-2631 ◽  
Author(s):  
D. M. Wright ◽  
R. S. Dhillon ◽  
T. K. Yeoman ◽  
T. R. Robinson ◽  
E. C. Thomas ◽  
...  

Abstract. On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs). The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt) and collapse (Pc) of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR) failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.


Author(s):  
M. J. Engebretson ◽  
J. L. Posch ◽  
V. A. Pilipenko ◽  
O. M. Chugunova
Keyword(s):  

Polar Record ◽  
1992 ◽  
Vol 28 (166) ◽  
pp. 191-204 ◽  
Author(s):  
D.A.R. Simmons ◽  
K. Henriksen

ABSTRACTDiscrete auroral arcs frequently bridge the polar cap connecting the morning and evening sectors of the auroral oval along the line of the transpolar (electron) current. Very high-latitude stations that lie wholly within the oval during the earth's diurnal rotation pass under this bridge twice a day, giving morning and evening maxima. Stations at slightly lower latitudes on Spitsbergen lie within the oval in the evening but under, or even south of, the oval in the morning. From such stations the evening, but not the morning, maximum is readily observed. This study is primarily concerned with the orientation of discrete polar cap arcs in the evening skies over Spitsbergen. It shows that the geomagnetic alignment of these arcs is latitude-dependent between geomagnetic colatitudes 6 to 20°N. At the highest latitudes within this range, the arcs are in transpolar alignment, whereas at the lowest latitudes within the polar cap, they are oval-aligned. At intermediate latitudes, the arcs are observed in transitional phases between transpolar and ovalalignment. The solar alignment of discrete polar cap arcs is a function of corrected geomagnetic local time. In the early afternoon, solar alignment is poor but this gradually improves throughout the late afternoon until there is excellent alignment at the time of the evening maximum. Recent satellite studies of plasma convection in the polar ionosphere have helped to explain some of the visual characteristics of discrete polar cap aurora observed from Spitsbergen, particularly the irregular alignment of arcs in the region of the Harang discontinuity.


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