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191.
Assoc. Prof. Dr. M. A. Mohamed Salih 《GeoJournal》1991,25(1):51-57
During the past half century Moro society has undergone immense economic and social transformations. The Moro adopted rural-urban and rural-rural migration, among other things, to diversify their incomes and augment their sources of livelihood. Politically, the introduction of modern political parties since independence in 1956 and the emergence of regional movements have influenced Moro perception of their reality and relationship with their Hawazma and Jellaba neighbours.I argue in this paper that due to disappointments emanating from harsh living conditions in discordant Northern Sudanese towns, the Moro translate past experiences into a common identity. Migration, in this sense, is seen as a major factor in explaining the Moro crisis of identity and their oscillation between integration and aloofness or modernity and traditionalism. 相似文献
192.
A total of 269 tropical storms and hurricanes originated in the North Atlantic basin from 1960–1989. Of these, 76 made landfall on the continental United states. This study divides the 76 tropical storms into their month of formation. Seasonal shifts in the principal areas of tropical cyclone formation over the Atlantic basin have been recognized for many decades. The results of the study suggest that the early and late season tropical cyclones develop in areas which are first affected by the position of the sun, resulting in an increase in water temperatures. These cyclones normally make landfall along the Gulf Coast and usually are of low intensity. Formation areas shift eastward in mid-summer with a slight increase in intensity. By late August and early September, the formation areas have extended to the Cape Verde Islands. These storms tend to strike the east coast of the US and are normally more intense. By the end of the hurricane season, the primary formation area has shifted back to the Gulf of Mexico, with low intensity storms affecting the Gulf Coast. 相似文献
193.
Summary A fine-mesh regional model simulation of upper-level cyclogenesis is carried out to examine the structure and evolution of the accompanying tropopause fold and its relationship to the surface and upper-level cyclones. The initial state for the simulation, conducted using the 80-km, 16-level version of the National Meteorological Center Eta model, uses the Level III-b gridded dataset for 1200 UTC, 18 January 1986, during the First Intensive Observing Period (IOP-1) of the Genesis of Atlantic Lows Experiment (GALE) project.Results are presented from a 48 hour integration of the model. The emphasis is on the examination of the synoptic scale evolution and structure of the upper-level cyclone and tropopause fold, both of which were successfully simulated in the model. The potential vorticity structure associated with a propagating jet-streak displayed distinctive structure, with its tilt reversing as the jet-streak moved around the base of an amplifying upper-level trough. In addition, the model simulates the intrusion of dry, stratospheric air containing high potential vorticity anomalies into the lower troposphere as well as subsidence warming when the folding of the tropopause occurs. the model also predicts upper-level frontogenesis as a result of a thermally indirect secondary circulation in the exit region of the jet-streak. The success of the model simulation is most likely the result of comprehensive physics and the fine grid resolution employed and, more importantly, the excellent distribution of subsynoptic scale initial data during the GALE project.With 16 Figures 相似文献
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Summary At least in case of semidiurnal tides, theirmotions contain most of their relative angular momentum. There are other periodic currents in the ocean with cycles of months to years which may influence the Earth's rotation within such time scales. These currents are mainly due to seasonal or climatic variations of the wind stress and the water mass distribution in the oceans. The main question is: how much of the oceanic angular momentum is temporarily stored within the oceans and what is the time scale of the transfer to the solid Earth. As an example, we have estimated the phase and the amplitude of the angular momentum which is stored in the Antarctic Circumpolar Current. Its phase resembles the one of the whole observed semiannual discrepancy in the angular momentum budget of the solid Earth plus the atmosphere; the amplitudes are comparable.
Der Antarktische Ringstrom und sein Einfluß auf die Erdrotation
Zusammenfassung Zumindest im Fall der halbtägigen Gezeiten der Ozeane enthalten derenBewegungen den größten Teil ihres variablen Drehimpulses. Andere periodische Meeresströmungen mit Perioden von Monaten bis Jahren könnten die Erdrotation ebenfalls beeinflussen. Solche Strömungen werden vor allem durch jahreszeitliche oder klimatische Veränderungen der Schubspannung des Windes und der Wasserstände verursacht. Die Hauptfrage ist jedenfalls diese: Wieviel Drehimpuls ist in jeder Phase in den Ozeanen gespeichert, und in welcher Zeit wird er mit der festen Erde ausgetauscht. Als Beispiel haben wir Phase und Amplitude des Drehimpulses abgeschätzt, der im Antarktischen Ringstrom enthalten ist. Diese Werte wurden mit den entsprechenden der Diskrepanz verglichen, die in der Bilanz feste Erde plus Atmosphäre offen bleibt. Die Phasen stimmen gut überein, und die Amplituden sind vergleichbar.
Le courant circumpolaire antarctique et son influence sur la rotation de la terre
Résumé Au moins dans le cas des marées semi-diurnes lesmouvements des océans «contiennent» la plus grande partie de la variabilité de la quantité de moment angulaire de la terre. D'autres courants océaniques périodiques dont la période varie du mois à l'année peuvent aussi avoir une influence sur la rotation de la terre. De tels courants sont avant tout provoqués par des variations saisonnières ou climatiques de la tension superficielle due aux vents et des niveaux d'eau dans les océans. La question principale est en tout cas la suivante: quelle est à chaque phase la quantité de moment angulaire stockée dans les océans et en combien de temps est-elle échangée avec la masse solide de la terre. A titre d'exemple, nous avons évalué la phase et l'amplitude de la quantité de moment angulaire stockée dans le courant circumpolaire antarctique. Ces valeurs furent comparées aux valeurs correspondantes de l'anomalie qui subsiste dans le bilan terre solide plus atmosphère. Les phases sont concordantes et les amplitudes sont comparables.相似文献
199.
The concentrations of PCBs and DDT at the surface of sediments of rivers in the Canton of Geneva were examined. Concentration variations observed along the rivers are discussed. In the case of the Rhône River, recent pollution at the surface of sediments is compared with that of aged underlying layers. 相似文献
200.
Degradation and formation of refractory DOM by bacteria during simultaneous growth on labile substrates and persistent lake water constituents 总被引:3,自引:0,他引:3
Dr. Annette Geller 《Aquatic Sciences - Research Across Boundaries》1985,47(1):27-44
Changes in molecular size distribution associated with degradation of refractory DOM (macromolecules, apparent mol wt. ≥1500)
by 3 strains of bacteria were investigated by Sephadex G-15 gel permeation chromatography and DOC analysis of the eluates.
Macromolecules and bacteria were isolated from the same lake water sample, one taken in summer and one in winter. The decompositional
changes of the DOM fraction were compared with respect to substance- and bacterial species-specific differences, and with
respect to the action of photolysis and co-substrate supplementation. The metabolite patterns resulting from the simultaneous
growth of the bacteria on the persistent DOM fraction and the labile co-substrate, glutamic acid were analyzed. The macromolecules
differed in accessible components, and the bacteria degraded most effectively the DOM fraction of the parent lake water sample.
Photolysis was the prerequisite for the reduction of the inaccessible bulk of the macromolecules. Glutamic acid enhanced the
degradation of the macromolecules. The enhancement effect was impaired by the build up of waste products which balanced the
losses of the DOM fraction. Three formation modes of refractory metabolites could be distinguished: formation of intensely
UV absorbing small sized products which were poor in DOC during degredation of (1) the macromolecules of winter, and (2) of
glutamic acid, and formation of (3) apparent high molecular weight substances from glutamic acid in cultures containing the
macromolecules of summer which probably results from a stable linkage between the small sized metabolites of the amino acid
and the DOM fraction.
The research was supported by the Deutsche Forschungsgemeinschaft. 相似文献