scholarly journals Pinnacles on the surface of the comet 67P/Churyumov-Gerasimenko: regional distribution and morphology

2019 ◽  
Author(s):  
S S Krasilnikov ◽  
Y V Skorov ◽  
A T Basilevsky ◽  
S F Hviid ◽  
U Mall ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Regional Distribution ◽  
Surface Erosion ◽  
Maximum Height ◽  
Minimum Thickness ◽  
Mean Values ◽  
The North ◽  
Evolutionary Changes ◽  
Nucleus Surface ◽  
North And South

Abstract Pinnacles are local topographic promontories of different shapes considered to be formed due to uneven surface erosion. In the case of comets, areal changes in the degree of erosion could be related to inhomogeneities of the nucleus. However, the amount of solar radiation and the thermal gradient is different across the orbit for geomorphological regions, which can result in different erosion and shape for a similar composition among two differently illuminated areas. Therefore, a study of the areal distribution of pinnacles on the nucleus surface and their morphology may help to understand the structure and properties of the nucleus material. We mapped 166 pinnacles on the comet nucleus surface of 67P/Churyumov-Gerasimenko. About a third of them have planimetrically rounded shape (rounded pinnacles) and the rest are planimetrically elongated (local ridges). In the southern hemisphere, number of both round pinnacles and local ridges is larger than in the northern hemisphere. This difference possibly indicates the higher effectiveness of the pinnacles’ formation in the southern hemisphere. At the same time the mean values of the measured parameters, including the height, show no statistically reliable difference between the north and south. We found that the maximum height of the pinnacles is about a hundred meters. Suggesting that they have been formed by sublimational erosion, this value allows estimating the minimum thickness of the eroded material and thus the degree of the evolutionary changes of the nucleus. In our future study, we will model pinnacles formation based on the here presented analysis of observations.

The Excavation of Winklebury Camp, Basingstoke, Hampshire

1977 ◽  
Vol 43 ◽  
pp. 31-129 ◽  
Author(s):  
Ken Smith
Keyword(s):  
Iron Age ◽  
Maximum Height ◽  
The South ◽  
North West ◽  
North East ◽  
The North ◽  
River Valleys ◽  
The Hill ◽  
Housing Estates ◽  
North And South

Winklebury Camp (SU61355290), an Iron Age 'plateau fort’, now of some 7.6 hectares (19 acres), is situated in the parish of Basingstoke, approximately 1 mile north-west of the town centre of Basingstoke, (fig. 1), though it is now surrounded by housing estates. It occupies a hill of Upper Chalk which has been isolated from the main mass of the North Hampshire Downs by two dry river valleys, one trending south-east, the other north-east. Both are tributary to the R. Loddon. The hill rises to a maximum height of 126 m a.s.l., near the projected line of the western rampart and slopes off gradually to north and south, and more steeply to the south-east. About half a mile to the south of the fort, a tributary of the R. Loddon, now culverted, would have provided the nearest source of water.Winklebury Camp has suffered from gradual encroachment by the surrounding housing estates, losing the ditch and rampart face to the north and east, and ditch, rampart and a small part of the interior, to the west. Only to the south does any of the bank and ditch survive. In the south-west corner of the fort, in an area protected by the remains of a small copse, a 90 m length of eroded rampart remains to an approximate height of 2 m. There is no ditch fronting this rampart now, but immediately east of the end of the stretch of rampart is the only remaining length of ditch. This extends for some 200 m along the remainder of the south side of the fort, averaging 2 m deep and 5 m wide. It rises in the south-east corner at a causeway, beyond which is another short stretch of ditch which is rapidly lost in house gardens. This causeway is faced by rampart, but there are indications, for example a slight change in the direction of the rampart at this point, that this is in fact a blocked entrance.

Hemispheric Asymmetry in the Mars Summer Ionosphere at Various Solar Forcing Conditions

2020 ◽  
Author(s):  
Marcin Pilinski ◽  
Laila Andersson ◽  
Ed Thiemann
Keyword(s):  
Magnetic Fields ◽  
Electron Temperature ◽  
Southern Hemisphere ◽  
Polar Regions ◽  
The North ◽  
Northern Summer ◽  
Solar Wind Magnetic Field ◽  
The Difference ◽  
North And South ◽  
Ionospheric Dynamics

<p>The MAVEN satellite has now made two Martian-years of ionosphere-thermosphere (I-T) observations enabling limited studies of seasonal changes in the upper atmosphere. Before examining the ionospheric dynamics associated with space weather, we wish to understand the climatological conditions of the system.  For example, previous studies have revealed the morning electron temperature overshoot as well as a close dependence between electron temperatures and neutral densities in the equatorial regions. In this presentation, we will examine differences in the northern and southern dayside ionosphere during the summer season of each hemisphere. The differences between these two cases will be contrasted with the seasonal dependence at the equator. Differences between the equatorial and polar regions are expected due to (A) differences in neutral scale heights, (B) differences in the solar zenith angle, and (C) the equilibration of I-T coupling due to differences in solar illumination.</p><p>In this work, we present a statistical analysis of MAVEN measurements comparing the north and south summer I-T. We find that when controlling for neutral pressure and latitude, the north and south plasma densities and temperatures are nearly identical below the demagnetization altitude (higher neutral pressures). Above the demagnetization altitude (lower neutral pressures), the southern hemisphere electron densities are higher than those in the northern hemisphere by ~100%. A significantly lower electron temperature is also observed in the south at these lower pressures. Given that the difference in solar EUV (and corresponding neutral heating) is ~20% between the two summer seasons, we postulate that the significantly lower plasma densities (above the demagnetization altitude) in the northern summer are due in part to an increase in ionospheric loss. This loss may be associated with the acceleration of ionospheric particles by the draped magnetic fields at an altitude where ions are not demagnetized. Furthermore, the loss may be diminished in the southern hemisphere where crustal magnetic fields increase the standoff distance to the solar wind magnetic field.</p>

Wawea Fruticulosa, a New Genus and Species from the Southern Hemisphere

1985 ◽  
Vol 17 (1) ◽  
pp. 85-97 ◽  
Author(s):  
Aino Henssen ◽  
G. Kantvilas
Keyword(s):  
New Zealand ◽  
Southern Hemisphere ◽  
New Genus ◽  
Single Species ◽  
Monotypic Genus ◽  
New Genus And Species ◽  
The North ◽  
Initial Stage ◽  
The Family ◽  
North And South

AbstractThe monotypic genus Wawea gen. nov. is described as a second genus in the family Arctomiaceae. The single species, Wawea fruticulosa sp. nov., is characterized by its fruticose habit, rugose and corticate lobes, secondarily multidivided and coalescing apothecia, two-celled spores, and by the unique initial stage of ascocarp ontogeny which includes simultaneous development of ascogonia as well as short-celled, branched conldiophores producing conidia. W. fruticulosa is widespread in Tasmania and is known also from New Zealand with single collections from the North and South Island. A new pyrenomyceteRhynchomeliola lichenicola sp. nov., parasymbiotic on Wawea fruticulosa, is also described.

Taxonomic And Distributional Notes on The Genus Sphaerophorus (Caliciales) In the Southern Hemisphere

1992 ◽  
Vol 24 (2) ◽  
pp. 119-131
Author(s):  
Mats Wedinal
Keyword(s):  
New Zealand ◽  
South America ◽  
Southern Hemisphere ◽  
Spore Wall ◽  
Spore Ornamentation ◽  
The North ◽  
First Time ◽  
North And South

Abstract Sphaerophorus diplotypus Vainio is reported as new to mainland Africa (Tanzania). Sphaerophorus digitaius Wang-Yang & Lai is reduced to a synonym of S. diplotypus. The name Sphaerophorus dodgei Ohlsson is validated and a description of the species is given. Sphaerophorus dodgei is recorded as being widespread and common in the Valdivian rainforest of Chile and Argentina. Sphaerophorus imshaugii Ohlsson is reported as new to the North and South Islands of New Zealand. Sphaerophorus macrocarpus Ohlsson is reported as new to South America (Chile). In S. dodgei and S. macrocarpus the spore ornamentation consists of mazaedial material added to the spore wall after the spores have been released from the asci. Concentric bodies occur in young ascospores of S. macrocarpus. A protocetraric-acid-deficient strain of S. microsporus Ohlsson is reported for the first time. Sphaerophorus tibellii Wedin, from northern New Zealand, is described as new.

Preliminary results of the study on the reasons of the Hai Hau erosion phenomenon

2007 ◽  
Vol 29 (3) ◽  
pp. 415-426
Author(s):  
Pham Van Ninh ◽  
Phan Ngoc Vinh ◽  
Nguyen Manh Hung ◽  
Dinh Van Manh
Keyword(s):  
Mathematical Modeling ◽  
Historical Data ◽  
Middle Part ◽  
Red River ◽  
Erosion Process ◽  
Red River Delta ◽  
The North ◽  
Severe Erosion ◽  
North And South ◽  
Very High

Overall the evolution process of the Red River Delta based on the maps and historical data resulted in a fact that before the 20th century all the Nam Dinh coastline was attributed to accumulation. Then started the erosion process at Xuan Thuydistrict and from the period of 1935 - 1965 the most severe erosion was contributed in the stretch from Ha Lan to Hai Trieu, 1965 - 1990 in Hai Chinh - Hai Hoa, 1990 - 2005 in the middle part of Hai Chinh - Hai Thinh (Hai Hau district). The adjoining stretches were suffered from not severe erosion. At the same time, the Ba Lat mouth is advanced to the sea and to the North and South direction by the time with a very high rate.The first task of the mathematical modeling of coastal line evolution of Hai Hau is to evaluate this important historical marked periods e. g. to model the coastal line at the periods before 1900, 1935 - 1965; 1965 - 1990; 1990 - 2005. The tasks is very complicated and time and working labors consuming.In the paper, the primarily results of the above mentioned simulations (as waves, currents, sediments transports and bottom - coastal lines evolution) has been shown. Based on the obtained results, there is a strong correlation between the protrusion magnitude and the southward moving of the erosion areas.

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