西沙北海槽第四纪的介形虫     

阮培华 《地球科学》1990,15(3):299-305,T001

西沙北海槽位于南海北部,是南海大陆坡上较大的海槽之一。本文所研究的介形虫化石系取自西沙北海槽东段的两个站位(KL37、KL41)柱样中。以上两站位中的介形虫化石组合以Krithe属居优势,其次是Wichmannella, Bradleya, Cytheropteron, Acantho-cythereis, Argilloecia, Abyssocythere, "Cythere", Parakrithe, Paijen-borchella等; KL37站、KL41站其沉积地层划分为中、上更新统及全新统。中、上更新统中介形虫化石数量比较丰富,化石面貌相似,均以Krithe sawanensis, Wichmannella dasy-derma, Acanthocythereis cf. araneosa等为主要成分。全新统中介形虫属种单调,化石少,含量较多的有"Cythere" sulcatoperfonata, Bradleya albatrossia, Kriteintrocurva, Abyssocythere regalis等。化石的破碎、溶蚀现象较普遍。  相似文献   

Orographic effects on the southwest monsoon: A review   总被引：1，自引：0，他引：1  

Sulochana Gadgil 《Pure and Applied Geophysics》1977,115(5-6):1413-1430

An overview of the problem of orographic effects on the southwest monsoon using the contributions of all the available analytical and numerical models is attempted. A quasi-geostrophic model is applied to deduce the effect of the topographic complex on the Indian peninsula. This model suggests that the southward bending of the low-level isobars on the peninsula can be ascribed to the topographically-induced southward velocity. This southward velocity triggers a Rossby wave to the east of the peninsula which is manifested as a trough on the southern Bay of Bengal.  相似文献   

Barotropic-Baroclinic instability of mean zonal wind during summer monsoon     

J. Shukla 《Pure and Applied Geophysics》1977,115(5-6):1449-1461

Barotropic-Baroclinic instability of horizontally and vertically shearing mean monsoon flow during July is investigated numerically by using a 10-layer quasi-geostrophic model. The most unstable mode has a wavelength of about 3000 km and westward phase speed of about 15 m sec^–1. The most dominant energy conversion is from zonal kinetic energy to eddy kinetic energy. The structure of the most unstable mode is such that the maximum amplitude is concentrated at about 150 mb and the amplitude at the lowest layers is negligibly small. Barotropic instability of the zonal flow at 150 mb seems to be the primary excitation mechanism for the most unstable mode which is also similar to the observed westward propagating waves in the upper troposphere during the monsoon season. The results further suggest that Barotropic-Baroclinic instability of the mean monsoon flow cannot explain the occurrence of monsoon depressions which have their maximum amplitude at the lower levels and are rarely detected at 200 mb.  相似文献   

Diagnosis of the satellite-observed radiative heating in relation to the summer monsoon     

Jay S. Winston  Arthur F. Krueger 《Pure and Applied Geophysics》1977,115(5-6):1131-1144

Seasonal and monthly global patterns of outgoing longwave radiation, albedo, absorbed solar radiation, and net radiation have been derived from scanning radiometer observations aboard the NOAA polar orbiting satellites since June 1974. These patterns, along with patterns of interannual differences in seasonal and monthly heating, are examined for the three summers of 1974–76 over the Eastern Hemisphere in relation to the variations in the summer monsoon and the major circulation features. During portions of the summer of 1975 the monsoon was more active than in 1974 and 1976, as evidenced by increased albedo and decreased longwave radiation over large sections of India, the Indian Ocean, Southeast Asia, and the Western Pacific. The roles of clouds, snow cover, and other surface characteristics in modulating the radiation balance and circulation are discussed. The pre-monsoon radiative heating in spring is examined with respect to monsoon onset and intensity in the three years.  相似文献   

澧阳平原晚冰期短尺度气候变化的风成沉积物稀土元素和粒度记录   总被引：3，自引：1，他引：2  

毛龙江  莫多闻  周昆叔  郭伟民  杨競红  邓辉  史辰羲  贾敬禹 《中国沙漠》2010,30(2):267-272

对澧阳平原SL剖面的系统采样和室内稀土元素分析、粒度分析和AMS14C年代测定,揭示了澧阳平原岗地黄土剖面成因特征,探讨了澧阳平原晚冰期短尺度的气候变化过程。结果表明,澧阳平原岗地黄土在稀土元素配分模式上与黄土高原黄土-古土壤、镇江下蜀黄土具有高度的一致性,而且岗地剖面沉积物无任何水流作用痕迹,因此表明,澧阳平原岗地黄土剖面为风成成因。粒度结果表明,SL剖面较好地记录了晚冰期短尺度的气候变化过程,SL遗址剖面自然沉积物记录了晚冰期千年尺度的气候事件,如BL事件、OlderYD事件、AL事件、YD事件。SL剖面全新世早期表现为升温阶段,9.0～8.00kaBP的彭头山文化在此区兴起,表明此时气候相当适宜,适合人类生存。  相似文献   

玉溪暴雨天气发生规律及成因分析   总被引：4，自引：1，他引：3  

解福燕  李文祥  白学文 《云南地理环境研究》2010,22(2):43-46,53

1951~2008年玉溪市暴雨发生次数最多的是澄江县,其次是华宁、元江、红塔区。进入21世纪后,随着全球气候变暖,暴雨次数比20世纪明显增多,主要集中在盛夏6~8月,占总次数的72%,其中单点暴雨和小范围暴雨占全部过程暴雨的95%,造成了玉溪市主汛期洪涝灾害频繁发生。形成玉溪暴雨时空分布差异大的天气环流系统主要有切变冷锋型、高原糟冷锋型、两高辐合型、热带天气系统北上型四大类,其次,特殊的地形地貌也是造成玉溪单点暴雨和小范围暴雨较多的原因。  相似文献   

Precise dating of abrupt shifts in the Asian Monsoon during the last deglaciation based on stalagmite data from Yamen Cave, Guizhou Province, China   总被引：1，自引：0，他引：1  

EDWARDS R. Lawrence 《中国科学:地球科学(英文版)》2010,(5)

Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 δ18O records are nominally dated at: 14750±50, 14100±60, 13870±80, 13370±80, and 12990±80 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) event is nominally at 12850±50 a BP and the end of the YD dates to 11500±40 a BP. The δ18O values shift by close to 3‰ during the transition into the Bφlling-Allerφd (BA, the onset of CIS A.1e) and at the end of the YD. Comparisons of Y1 to previously published early Holocene records show no significant phase differences. Thus, the East Asia Monsoon and the Indian Monsoon do not appear to have been out of phase during this interval. The Y1 record confirms earlier work that suggested that solar insolation and North Atlantic climate both affect the Asian Monsoon.  相似文献   

Modern changes of tidal troughs among the radial sand ridges in northern Jiangsu coastal zone   总被引：1，自引：0，他引：1  

黄海军  杜廷芹  郜昂 《中国海洋湖沼学报》2009,27(3):658-666

Using satellite images taken on different dates,GIS analysis of aerial photos,bathymetric maps and other field survey data,tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted.The results show that there have been three types of movement or migration of tidal trough in this area:(1) Periodic and restricted,this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the...  相似文献   

Time-dependence of salinity in monsoonal estuaries   总被引：1，自引：0，他引：1  

V. Vijith  D. SundarS.R. Shetye 《Estuarine, Coastal and Shelf Science》2009

The theories and classification schemes commonly used for understanding estuarine dynamics often refer to a steady state of the estuary in which the salinity field is time-independent. In this state salinity-ingress into the estuary due to different processes (diffusion, gravity current formation, impact of tidal asymmetries, etc.) is balanced by salinity-egress induced by runoff. Here we point out that the salinity field of the estuaries that are located on the coasts of the Indian subcontinent and come under the influence of the Indian Summer Monsoon (ISM) is never in a steady state. We refer to such estuaries as “monsoonal estuaries”, an example of which is the Mandovi estuary located on the west coast of India. We describe the annual cycle of the salinity field in this estuary and conclude that the essential unsteadiness of the salinity field arises from two features of the runoff into it. First, most of the runoff occurs as a series of episodes of highs and lulls spread over about 4 months of the wet summer monsoon. Second, the total runoff is large, well over an order of magnitude larger than the estuarine volume. We define two parameters to represent these two features, and show that they can be used to distinguish the monsoonal estuaries from others.  相似文献   

一次早台风暴雨的湿位涡分析     

罗艳艳  黄丽娜 《海洋预报》2008,25(1):102-110

0601号强台风"珍珠"是1949年以来5月份登陆我国最强的台风之一,与西风带系统在低纬度相互作用是早台风的预报要点.通过台风暴雨过程的湿位涡(MPV)分析,从湿位涡和湿位涡平流的的角度探讨西风带系统在早台风暴雨中的作用.结果表明:对流层中高层冷空气以漏斗状高MPV1柱的形式在江淮地区的维持及漏斗底部正MPV1向南入侵强台风环流,触发不稳定能量储存和释放,是此次早台风暴雨强度大的重要原因,同时也是台风登陆后迅速填塞,降水快速减弱的重要因素之一.正MPV2中心与暴雨中心有较好的对应.MPV2平流与MPV1平流量级相当,湿斜压作用与正压作用同样重要.  相似文献