夏季江淮暴雨过程对大尺度湿度场的敏感性试验

用全球谱模式T42L11对1991年6月底至7月初江淮暴雨的中期过程作敏感性试验。结果表明，在初始场中，当印度洋～孟加拉湾高湿中心附近(100°E以西)的水汽减弱后，江淮雨量减少45%，且东亚夏季风环流减弱。若南海～西太平洋高湿中心附近(100°E以东)的水汽减弱时，则东亚夏季风环流反而加强，雨带移向华北。     

攀西裂谷的多期活动性及其深部地质意义

攀西裂谷具有明显的长期、继承和多期活动性特点,为一“上叠裂谷”,其基底在晋宁期就已存在裂谷系。是海西—印支期时,随着攀西由板内—低纬度被动陆缘—中纬度活动陆缘—板内的变化,裂谷活动和地幔涌流特点也有所不同。攀西裂谷的演化提供了一个深断裂诱发地幔涌流,并随板块飘移而移动的典型例证。这种壳、幔关系可能正是地槽多旋回活动的主因。自第三纪以来,攀西浅、深部地壳应力场明显不一致,这种现象有可能是不同构造学说结合的纽带。     

中国东南部的晚元古界和裂陷活动带

本文从阐述中国东南部晚元古多旋回火山作用,特殊的火山—沉积建造及有规律的构造组合形式入手,论证了该地区晚元古界地层发育特征和空间上一条重要相区界线,并提出了中国东南部存在一条古裂谷带的观点。通过对古裂谷带特征的详细论述,阐明了古裂谷带的研究对揭示中国东南部多种金属成矿作用和开展第二轮找矿的理论意义和巨大经济价值。     

Spectral study of the Bouguer anomaly map of a rift valley and adjacent areas in Central India

The spectral study of the Bouguer anomally map of Central India suggests an uplifted crust-mantle interface under the Mahandi graben. This study has delineated three subsurface levels of anomalous masses at the respective depths of 23 km, 8 km, and 2 km apparently representing the Moho, an intermediate discontinuity in the sialic part of the crust and the basement, respectively. Model study of the Bouguer anomaly along a profile suggests a typical continental graben type subsurface structure with a low density depression in the sialic part of the crust between 8 and 18 km supported by an elevated upper mantle of intermediate density (3.4 g/cm³) varying in depth from 25 km to 55 km. The depths of the inferred interfaces in case of Bundelkhand granite are 32 km, 11 km, and 1.5 km, which might represent the Moho, the base of intruded granite massif, and some shallow compositional variation. Similar studies in case of Vindhyan basin have brought out three discontinuities at the respective depths of 16 km, 6–4.5 km, and 2.4 km. The first horizon at the depth of 16 km probably represents the interface between the granitic and the basaltic part of the crust. The 6–4.5 km is the depth of the basement, with the 2.4 km interface separating Bijawar rocks from Vindhyans wherever they are present. A generalized inversion of a profile across a positive belt of Bouguer anomaly representing the subsurface Bijawar rocks support the above result.     

100—200km热层大气光电离率及电子密度剖面对太阳活动的响应

本文利用新的太阳EUV辐射资料、中性大气结构模式及大气成分的吸收及电离特性,计算了100—200km大气的光电离率随高度、太阳天顶角及太阳活动的变化,求得了E-F_1谷的变化特征;利用完整的光化模式求得了电子密度随太阳天顶角的变化及对太阳活动的响应,并与IRI模式作了比较.结果表明,1.太阳活动指数与光电离率间的相关关系一般为正,但在一定的高度范围内,或在天顶角大于临界值X_(cr)=60°时,两者之间可出现负相关;2.太阳活动明显地影响E-F_1谷高与谷厚,当天顶角不变时,谷高与谷厚均与太阳活动成正相关;3.本模式与IRI间的偏差因子明显随高度及太阳天顶角而变化.     

长江河口南支水下地质灾害的初步研究

本文根据笔者在1984—1988年期间,从事长江河口南支水域浅地层剖面调查,所得大量实际资料的介释、分析、研究。指出该地区存在的多种水下地质灾害现象,探讨了它们形成的原因以及对水下工程和航运事业的危害。提供了水下地质灾害现象的实际位置和有关正确数据。     

Sedimentology and depositional architecture of tidal compound dunes on a carbonate ramp: The lower Miocene deposits of the central Apennine (Latium,Italy)

The sedimentology and sequence stratigraphy of the central Apennine lower Miocene carbonate deposits (Guadagnolo Formation) are the goal of this paper. The Guadagnolo carbonate ramp deposits consist of a thick succession of three main lithofacies: marls, marly limestones and cross-bedded limestones. The lateral and vertical facies distribution, as well as the biota assemblages, suggests a deposition of these sediments along the middle-outer ramp sector of the Latium-Abruzzi carbonate platform. All the data suggest sedimentation under the influence of tidal currents that were responsible of bedforms generation as simple and compound dunes. These bodies are developed on metric and decametric scale, and are stacked one to other to form complex sedimentary bodies extending both in strike and dip section for several tens to hundred meters. The dune system developed in a semiclosed basin (the Paleoadriatic sea), open in the southern and closed in the northern sector respectively. Within this basin a probably amphidromic system developed. The flow sediment transport was dominantly westward, and was conditioned by the ramp paleotopography. From a sequence stratigraphic point of view several high and low rank depositional sequences that were differentiated basing on their relative physical scale (thickness of each unit) and on the lateral extension of the unconformities and the correlative conformities bounding them were recognized. The hierarchy of recognized sequence-stratigraphic units include, from the smallest to the largest: simple depositional sequences, low-rank composite depositional sequences and high-rank composite depositional sequences. In the Guadagnolo succession four high-rank composite depositional sequences having a duration variable from 0.9 to 1.6 Ma, and named Guadagnolo 1, 2, 3, and 4, were recognized. These high-rank composite sequences are internally constituted by a stacking of simple and low-rank composite depositional sequences, having a duration ranging from 40 ka to 200 ka. All these units constitute part of a higher-rank composite sequence developing between 21 and 14.80 Ma that we name “The Guadagnolo Depositional Sequence”. The wedge-shaped geometry, the thickness variation and the stacking pattern of the Guadagnolo succession are the response to eustasy and tectonic subsidence. The glacial eustasy mostly controlled the formation of the high-frequency depositional sequences, tectonic subsidence, related to the roll-back of the hinge west-directed subduction in turn connected to the advancement of the Apennine thrust modulated the accommodation space.     

Evaluating the Ozone Valley over the Tibetan Plateau in CMIP6 Models

Total column ozone (TCO) over the Tibetan Plateau (TP) is lower than that over other regions at the same latitude, particularly in summer. This feature is known as the “TP ozone valley”. This study evaluates long-term changes in TCO and the ozone valley over the TP from 1984 to 2100 using Coupled Model Intercomparison Project Phase 6 (CMIP6). The TP ozone valley consists of two low centers, one is located in the upper troposphere and lower stratosphere (UTLS), and the other is in the middle and upper stratosphere. Overall, the CMIP6 models simulate the low ozone center in the UTLS well and capture the spatial characteristics and seasonal cycle of the TP ozone valley, with spatial correlation coefficients between the modeled TCO and the Multi Sensor Reanalysis version 2 (MSR2) TCO observations greater than 0.8 for all CMIP6 models. Further analysis reveals that models which use fully coupled and online stratospheric chemistry schemes simulate the anticorrelation between the 150 hPa geopotential height and zonal anomaly of TCO over the TP better than models without interactive chemistry schemes. This suggests that coupled chemical-radiative-dynamical processes play a key role in the simulation of the TP ozone valley. Most CMIP6 models underestimate the low center in the middle and upper stratosphere when compared with the Microwave Limb Sounder (MLS) observations. However, the bias in the middle and upper stratospheric ozone simulations has a marginal effect on the simulation of the TP ozone valley. Most CMIP6 models predict the TP ozone valley in summer will deepen in the future.     

Ramp sedimentation across a middle Albian,Arctic embayment: Influence of subsidence,eustasy and sediment supply on stratal architecture and facies distribution,Lower Cretaceous,Western Canada Foreland Basin

Regional mapping of Middle Albian, shallow‐marine clastic strata over ca 100 000 km² of the Western Canada Foreland Basin was undertaken to investigate the relationship between large‐scale stratal architecture and lithology. Results suggest that, over ca 5 Myr, stratal geometry and facies were dynamically linked to tectonic activity in the adjacent Cordillera. Higher frequency modulation of accommodation is most reasonably ascribed to eustasy. The Harmon and Cadotte alloformations were deposited at the southern end of an embayment of the Arctic Ocean. The Harmon alloformation, forming the lower part of the succession, constitutes a wedge of marine mudstone that thickens westward over 400 km from <5 m near the forebulge to >150 m in the foredeep. Constituent allomembers are also wedge‐shaped but lack distinct clinothems, a rollover point or downlapping geometry. Ubiquitous wave ripples indicate that the sea floor lay above storm wave base. Deposition took place on an extremely low‐gradient ramp, where accommodation was limited by effective wave base. Lobate, river‐dominated deltas fringed the southern margin of the basin. The largest deltas are stacked in the same area, suggesting protracted stability of the feeder river. A buried palaeo‐valley on the underlying sub‐Cretaceous unconformity may have influenced compaction and controlled river location for ca 3 Myr. Adjacent to the western Cordillera, a predominantly mudstone succession is interbedded with abundant storm beds of very fine‐grained sandstone and siltstone that reflect supply from the adjacent orogen. Bioturbation indices in the Harmon alloformation range from zero to six which reflects the influence of stressors related to river‐mouth proximity. Harmon alloformation mudstone grades abruptly upward into marine sandstone and conglomerate of the overlying Cadotte alloformation. The Cadotte is composed of three allomembers ‘CA’ to ‘CC’, that represent the deposits of prograding strandplains 200 × 300 km in extent. Allomembers ‘CA’ and ‘CB’ are strongly sandstone‐dominated, whereas allomember ‘CC’ contains abundant conglomerate in the west. The dominantly aggradational wedge of Harmon alloformation mudstone records flexural subsidence driven by active thickening in the adjacent orogen: the high accommodation rate trapped coarser clastic detritus close to the basin margin. In contrast, the tabular, highly progradational sandstone and conglomerate bodies of the Cadotte alloformation record a low subsidence rate, implying tectonic quiescence in the adjacent orogen. Erosional unloading of the orogen through Cadotte time steepened rivers to the extent that they delivered gravel to the shore. These observations support an ‘anti‐tectonic’ model of gravel supply proposed previously for the United States portion of the Cretaceous foreland basin. Because Cadotte allomembers do not thicken appreciably into the foredeep, accommodation changes that controlled these transgressive–regressive successions were probably of eustatic origin.     

Evaluating the Impact of Drought Using Remote Sensing in a Mediterranean,Semi-arid Region

This paper analyses monthly differences in drought impact on vegetation activity in a semi-arid region in the north-east of the Iberian Peninsula between 1987 and 2000. The study determines spatial differences in the effects of drought on the natural vegetation and agricultural crops by means of the joint use of vegetation indexes derived from AVHRR images, a drought index (standardized precipitation index), and Geographic Information Systems. The results show that the effect of drought on vegetation varies noticeably between areas, a pattern that is determined mainly by the location of land-cover types. The influence also varies each month and, in general, is higher during the spring and summer. Aridity and vegetation characteristics similarly account, in part, for spatial differences in the impact of drought on vegetation. In general, the most arid areas, where vegetation cover and activity are low, are those in which the interannual variability of vegetation activity is more determined by the drought occurrence. In assessing drought impact, this analysis takes into account the effects of drought on the vegetation and also considers spatial and seasonal differences. The results should be useful for the management of natural vegetation and crops and for the development of better drought mitigation strategies.