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301.
Three satellite-tracked drifting buoys released in the south equatorial current in the Indian Ocean followed the path of the
current moving westward approximately zonally in the vicinity of 10 S latitude. On nearing the east coast of Africa two buoys
moved north and the third moved south. Over the open sea regime the buoys moved with a speed of approximately 30 cm/s at an
angle of about 35° to the left of the wind. The overall tendencies seen in the buoy drift are similar to those observed elsewhere
in the world oceans. 相似文献
302.
Monthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North
Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar
patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics
of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that
the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation
off the east coast of India: wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult
at present to assess the relative importance of these three processes. 相似文献
303.
由50余个测点的大地电磁测深资料,讨论了该区的地壳-上地幔电性横向变化特征。按照上地幔第一低阻层顶面埋深,将测区划分为四类地区:浅埋深(55-90公里)、中浅埋深(90-110公里)、中深埋深(110-160公里)和深埋深(160-250公里)。讨论了本区六次大震例的深部电性背景。指出了上地幔顶部的梯度带地区、地壳内电性横向变化剧烈的地区和地壳内存在局部特殊增厚的低阻层地区将可以作为潜在震源区的深部电性判据之一 相似文献
304.
Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships 总被引:1,自引:0,他引:1
Abstract Fossil pinnipeds in the extinct otariid subfamily Allodesminae are large, relatively highly evolved marine carnivores that became abundant and diverse in Middle Miocene time and were restricted to the North Pacific Ocean. Their record extends from early Middle Miocene through Late Miocene, with records from California, Oregon, Washington, Baja California and Japan. Allodesmines are characterized by extreme sexual dimorphism, a large orbit, retracted orbital margin of the zygomatic arch, a deeply mortised jugal-squamosal junction, wide palate, bulbous cheek tooth crowns, nearly flat tympanic bulla with wrinkled ventral surface, a large tympanohyal fossa, large ear ossicles and deep mandible. Eleven allodesmine species are known (eight of which are named), in at least four genera, and most belong to the typical genus Allodesmus Kellogg, 1922. The earliest and most generalized allodesmine known is from the early Middle Miocene (ca 16 Ma) Astoria Formation in coastal Oregon. The last known records are from Late Miocene rocks (ca 10 Ma) in California and Washington. New taxa proposed here are: the genus Brachyallodesmus Barnes and Hirota, to contain Allodesmus packardi Barnes, 1972; the genus Megagomphos Hirota and Barnes, to contain Allodesmus sinanoensis (Nagao, 1941); the species Allodesmus sadoensis Hirota, (Middle Miocene, Japan); the species Allodesmus megallos Hirota (Middle Miocene, Japan); and the species Allodesmus gracilis Barnes (Middle Miocene, California). Additionally, the genus Atopotarus Downs, 1956, and the species Allodesmus kelloggi Mitchell, 1966, are resurrected. Allodesmines were apparently a rapidly evolving group, and most appear to have been adapted to roles later filled by otariine, dusignathine and imagotariine otariids, and the Phocidae (true seals). They became extinct in Late Miocene time and left no living descendants. Although some of their characters evolved convergently with various living species of the pinniped family Phocidae, Allodesminae are an otariid group and not part of the evolutionary history of Phocidae. 相似文献
305.
本文是一个用大气环境模式研究中国西北地区陆面特征改变之后影响其降水的数值试验,模式中假定西北地区的植被完全被裸陆代替,对6、7、8月进行数值积分,以便检查夏季大气环流对陆面特征的响应,数值试验的结论是:陆面反照率升高后,与之相伴随的是降水率下降,并且大气的下沉运动控制了该地区。 相似文献
306.
307.
Monthly mean anomaly fields of various parameters like sea surface temperature, air temperature, wind stress, effective radiation
at the surface, heat gain over the ocean and the total heat loss between a good and bad monsoon composite and the evaporation
rates over the Arabian Sea and southern hemisphere have been studied over the tropical Indian Ocean. The mean rates of evaporation
on a seasonal scale over the Arabian Sea during a good and bad monsoon composites were equal (about 2·48 × 1010 tons/day). The evaporation rates over the southern hemisphere were greater during all the months. The mean evaporation rates
over the southern hemisphere on a seasonal scale for the good and bad monsoon composites were 4·4 × 1010 and 4·6 × 1010 tons/day respectively. The maximum evaporation rates over the southern hemisphere were observed in August. The anomalies
of wind stress, effective radiation at the surface and the heat gain over the ocean also exhibit large variations in August,
as compared to other monsoon months. 相似文献
308.
The warm pool in the Indian Ocean 总被引:2,自引:0,他引:2
The structure of the warm pool (region with temperature greater than 28°C) in the equatorial Indian Ocean is examined and
compared with its counterpart in the Pacific Ocean using the climatology of Levitus. Though the Pacific warm pool is larger
and warmer, a peculiarity of the pool in the Indian Ocean is its seasonal variation. The surface area of the pool changes
from 24 × 106 km2 in April to 8 × 106 km2 in September due to interaction with the southwest monsoon. The annual cycles of sea surface temperature at locations covered
by the pool during at least a part of the year show the following modes: (i) a cycle with no significant variation (observed
in the western equatorial Pacific and central and eastern equatorial Indian Ocean), (ii) a single maximum/minimum (northern
and southern part of the Pacific warm pool and the south Indian Ocean), (iii) two maxima/minima (Arabian Sea, western equatorial
Indian Ocean and southern Bay of Bengal), and (iv) a rapid rise, a steady phase and a rapid fall (northern Bay of Bengal). 相似文献
309.
The dynamics and thermodynamics of the surface layer of the Arabian Sea, north of about 10N, are dominated by the monsoon-related
annual cycle of air-sea fluxes of momentum and heat. The currents in open-sea regime of this layer can be largely accounted
for by Ekman drift and the thermal field is dominated by local heat fluxes. The geostrophic currents in open-sea subsurface
regime also show a seasonal cycle and there is some evidence that signatures of this cycle appear as deep as 1000 m. The forcing
due to Ekman suction is an important mechanism for the geostrophic currents in the central and western parts of the Sea. Recent
studies suggest that the eastern part is strongly influenced by the Rossby waves radiated by the Kelvin waves propagating
along the west coast of India.
The circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary
current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but
not during the northeast monsoon when a strong (approximately 7 × 106m3/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast
during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal.
The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward
and upwells into the layer of North Indian Deep Water (approximately 1500–3500m). It is further speculated that the flow in
this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if
there is an annual cycle associated with the deep and the bottom water circulation. 相似文献
310.
The Palaeozoic intracratonic basins in northwest Gondwana, i.e. the Amazonas, Parnaiba and Acera basins, probably opened during late Caradoc and Ashgill times. The fluviatile sedimentation later changed to littoral at the basinal margins. A transgression from the north-west region of Gondwana slowly overlapped the margins of the intracratonic basins. The transgression reached its maximum in the Rawtheyan (late Ashgill), as evidenced by fossiliferous shallow marine sediments in the Amazonas Basin. The Hirnantian glaciation in north Gondwana lowered the sea level, and in the Amazonas Basin a littoral sedimentation followed on shallow marine strata. From the opening of the basins onwards, a shallow sea probably existed close to the epicontinental basins in north-west Gondwana. The basins were connected via a narrow passage between the Guayana and Ivorian cratons. 相似文献