Climate‐modulated sequence development in a tropical rift basin during the Late Palaeocene to Early Eocene super greenhouse Earth          下载免费PDF全文

Arpita Samanta  Melinda K. Bera  Anindya Sarkar 《Sedimentology》2016,63(4):917-939

Sequence developments in rift basins are considered to be influenced largely by tectonics and to a lesser extent by eustatic sea‐level and climate. Studies indicate that in passive margin basins, climate can mask the effects of tectonics and eustasy by modulating the sediment supply. It is, however, less understood how the sedimentary sequence in rift basins might respond to strong climatic fluctuations where tectonic pulses generate rapid accommodation space. Here a case study has been provided to assess the effect of climate vis à vis sea‐level and tectonics on sequence development in the Cambay rift basin, western India, during the Early Palaeogene (Late Palaeocene to Early Eocene) super greenhouse globe. Facies analysis of this shale–lignite sequence suggests deposition in a lagoon/bay, developed over the Deccan Trap basement. Detailed sequence stratigraphic analysis using basin‐wide representative composite sections, marker lignite seam, event bed and high‐resolution carbon isotope (δ¹³C) chemostratigraphy suggest an overall transgressive motif. Among the three prominent Early Eocene eustatic highstands, only the one at ca 53·7 Ma is expressed by the thickest coal accumulation throughout the basin. Expression of the other sequence stratigraphic surfaces is subdued and can be due to the overall finer grain size of the sediment or local variation in the subsidence rate at different fault‐controlled mini‐basins. Enigmatic presence of a maximum flooding surface coinciding with the 53·7 Ma climate event (Eocene Thermal Maximum 2), manifested by negative carbon isotope excursion, indicates possible influence of climate over and above tectonics in developing the rift sequence. Qualitative rainfall variation assessed using the magnitude of the carbon isotope excursion and pollen abundance show that a relatively dry/low precipitation climatic phase during the Eocene Thermal Maximum 2 hindered the siliclastic supply to the basin. Thus, it has been inferred that climate‐induced high siliciclastic supply possibly enhanced the autocyclic reorganization and hindered the development of the key sequence stratigraphic surfaces across the basin during climate extremes.  相似文献   

Research on Cultural Dimension of Natural Disaster:A Literature Review     

Sun Lei  Su Guiwu 《地球科学进展》2016,31(9):907-918

Culture provides an important perspective to understand society. It is one of the key factors that impact how people behave themselves, interact with one another, view the world; what they believe and value. Therefore, a good understanding of public disaster awareness and disaster coping is impossible without taking their culture context into consideration. Since the 1960s, cultural dimension in disaster issues and/or disaster reduction practices has been attracting increasingly attention; many empirical or theoretical explorations have been reported. This review aims to give an overview of research progresses on how culture impacts public awareness and coping of disasters, and analyze the corresponding implications for disaster research and disaster reduction practice. This review summarizes that: ①There is unanimous consensus on public awareness and coping of disaster, which are affected by their culture context. While the knowledge about the ways and degree of impact is still limited, further research is warranted. In addition, more systematic and in-depth studies conducted from cross-cultural perspectives are needed to design to further explore the origins of variance in public disaster awareness and coping, and to what extent from cultural differences. ②Research on public awareness of disaster, emergency response and recovery indicated that culture might have double-side impacts on disaster management—sometimes cultural factors such as value, norm, custom and belief might lead to people more vulnerable than the others, even could be the root causes, but they could also be the source of people’s resilience to disaster in some cases. How to identify those positive and negative impacts, then develop cultural-oriented disaster management policy is a challenge issue, which need special attention. ③There is an increasing acknowledgement that local knowledge and disaster subculture could play an important role in public disaster coping, while the lacking of the awareness of the value of local knowledge, the change of lifestyle, and the impact from external culture pose a threat to the inheritance of some local, traditional disaster coping strategies. So exploring how to conserve, protect, identify, document them, then combine them with modern science and technology should and will be the focus of relevant studies. On the bases of these summarizations, in terms of cultural dimension of natural disaster research in China, systematic and in-depth studies are needed to explore how Chinese culture affects public disaster awareness and coping, what cultural resources can be used in disaster (risk) reduction and for building and enhancing disaster resilience, and how to use them.  相似文献   

Prediction of extreme wave heights using neuro wavelet technique     

《Applied Ocean Research》2016

Precise prediction of extreme wave heights is still an evading problem whether it is done using physics based modeling or by extensively used data driven technique of Artificial Neural Network (ANN). In the present paper, Neuro Wavelet Technique (NWT) is used specifically to explore the possibility of prediction of extreme events for five major hurricanes Katrina 2005, Dean 2007, Gustav 2008, Ike 2008, Irene 2011 at four locations (NDBC wave buoys stations)¹ namely; 42040, 42039, 41004, 41041 in the Gulf of Mexico. Neuro Wavelet Technique is employed by combining Discrete Wavelet Transform and Artificial Neural Networks. Discrete wavelet transform analyzes frequency of signal with respect to time at different scales. It decomposes time series into low (approximate) and high (detail) frequency components. The decomposition of approximate components (extreme events in the ocean wave series) can be carried out up to the desired multiple levels in order to provide relatively smooth varying amplitude series. This feature of wavelet transforms make it plausible for predicting extreme events with a better accuracy. In the present study third, fifth and seventh level of decompositions are used which facilitates 3 to 7 times filtering of low frequency events and seems to pay the dividend in the form of better prediction accuracy at extreme events. To develop these Neuro wavelet models to forecast the waves with lead times of 12 hr to 36 hr in advance, previously measured significant wave heights at same locations were used. The results were judged by wave plots, scatter plots and other error measures. From the results it can be concluded that the Neuro Wavelet Technique can be employed to solve the ever eluding problem of accurate forecasting of the extreme events.  相似文献   

Stable isotope analysis of consumer food webs indicates ecosystem recovery following prolonged drought in a subtropical estuarine lake     

MS Bird  R Perissinotto  NAF Miranda  N Peer  JL Raw 《African Journal of Marine Science》2016,38(3):411-422

Assessing changes in food-web structure provides a useful monitoring tool for gauging the resilience of ecosystems in the face of climatic impacts. We consider the ecological resilience of a large estuarine lake (St Lucia Estuary, South Africa) in the wake of an extreme climatic event (prolonged drought). Using carbon and nitrogen stable isotopes, food-web structure was assessed at five sites across the estuary during the winter and spring of 2013. Sampling occurred approximately three years after heavy rains flooded the system and returned it to a relatively diluted state following an almost decade-long drought that decimated food webs in the upper parts of the estuary due to hypersalinity effects. Comparisons of niche width and variance of consumer food webs among sites revealed a general homogenisation of food webs across the entire system, contrasting with the spatial differentiation of food webs documented during the drought phase. Our results indicate that the estuary is able to maintain ecological resilience at the whole-system level in the face of an extreme drought. This is likely facilitated by source pools of species residing in the relatively stable lower estuary, which are able to rapidly recolonise areas denuded by drought in the upper estuary.  相似文献   

Characterizing the Seasonal and Directional Varying Properties in A Marine Environment     

张熠  程涛 《海洋工程》2016,(4):549-564

With noticing an increasing number of failure events for offshore structures in the present days, it is now realized that modeling the marine environment especially for exceptional environmental conditions is quite important. It is recognized that a possible improvement in the traditional modeling of environmental characteristics, which are the basis for the load models for structural analysis and design, may be needed. In this paper, the seasonal and directional varying properties in modeling the ocean parameter, the wave height, are studied. The peak over threshold (POT) method is selected to model the extreme wave height by utilizing a non-stationary discrete statistical extreme model. The varying parameters are taken into account with a changing pattern to reflect the seasonal and directional dependent behavior. Both the magnitude and the occurrence rate of the extreme values are investigated. Detailed discussion on the continuity of the established model is also given. The importance of the proposed model is demonstrated in reliability analysis for a jacket structure. The sensitivity to the changing marine environment in reliability analyses is investigated.  相似文献   

Evaluation of WRF-based convection-permitting multi-physics ensemble forecasts over China for an extreme rainfall event on 21 July 2012 in Beijing     

Kefeng Zhu  Ming Xue 《大气科学进展》2016,33(11):1240-1258

On 21 July 2012, an extreme rainfall event that recorded a maximum rainfall amount over 24 hours of 460 mm, occurred in Beijing, China. Most operational models failed to predict such an extreme amount. In this study, a convective-permitting ensemble forecast system (CEFS), at 4-km grid spacing, covering the entire mainland of China, is applied to this extreme rainfall case. CEFS consists of 22 members and uses multiple physics parameterizations. For the event, the predicted maximum is 415 mm d^-1 in the probability-matched ensemble mean. The predicted high-probability heavy rain region is located in southwest Beijing, as was observed. Ensemble-based verification scores are then investigated. For a small verification domain covering Beijing and its surrounding areas, the precipitation rank histogram of CEFS is much flatter than that of a reference global ensemble. CEFS has a lower (higher) Brier score and a higher resolution than the global ensemble for precipitation, indicating more reliable probabilistic forecasting by CEFS. Additionally, forecasts of different ensemble members are compared and discussed. Most of the extreme rainfall comes from convection in the warm sector east of an approaching cold front. A few members of CEFS successfully reproduce such precipitation, and orographic lift of highly moist low-level flows with a significantly southeasterly component is suggested to have played important roles in producing the initial convection. Comparisons between good and bad forecast members indicate a strong sensitivity of the extreme rainfall to the mesoscale environmental conditions, and, to less of an extent, the model physics.  相似文献   

Radiative effects on torrential rainfall during the landfall of Typhoon Fitow (2013)     

Lingyun Lou  Xiaofan Li 《大气科学进展》2016,33(1):101-109

Cloud microphysical and rainfall responses to radiative processes are examined through analysis of cloud-resolving model sensitivity experiments of Typhoon Fitow(2013) during landfall.The budget analysis shows that the increase in the mean rainfall caused by the exclusion of radiative effects of water clouds corresponds to the decrease in accretion of raindrops by cloud ice in the presence of radiative effects of ice clouds,but the rainfall is insensitive to radiative effects of water clouds in the absence of radiative effects of ice clouds.The increases in the mean rainfall resulting from the removal of radiative effects of ice clouds correspond to the enhanced net condensation.The increases(decreases) in maximum rainfall caused by the exclusion of radiative effects of water clouds in the presence(absence) of radiative effects of ice clouds,or the removal of radiative effects of ice clouds in the presence(absence) of radiative effects of water clouds,correspond mainly to the enhancements(reductions) in net condensation.The mean rain rate is a product of rain intensity and fractional rainfall coverage.The radiation-induced difference in the mean rain rate is related to the difference in rain intensity.The radiation-induced difference in the maximum rain rate is associated with the difference in the fractional coverage of maximum rainfall.  相似文献   

估算雨滴谱Γ分布三参数的阶矩法研究     

熊飞麟  周毓荃 《气象》2016,42(7):777-789

利用2014年8月4—23日山西忻州OTT-Parsivel二代激光雨滴谱仪获得的雨滴谱资料,研究了估算雨滴谱T分布三参数的阶矩法。把降水云分为层状云、积状云、积层混合云三种,采用最小二乘法和阶矩法估算雨滴谱,并在现有阶矩法的研究上,提出一种新矩量组合M036与其他矩量一起分1 min、5 min平均和5 mm滑动平均估算雨滴谱样本的均方根误差和误差谱分布,并进行比较,同时研究了不同降水云雨滴谱三参数随雨强R的变化关系。结果表明:阶矩法估算T分布雨滴谱,M036矩量组合代表雨滴数浓度、液态水含量和雷达反射率因子,三个物理量计算方便,物理意义清晰,实际应用中如能通过探测手段获得三个矩量,就能反演得到云中雨滴谱。阶矩法中M036估算最好;估算三种不同时间雨滴谱样本的均方根误差平均值,M036误差最小;分析三种不同时间雨滴谱样本的均方根误差谱分布,M036谱宽最窄,误差集中;估算三种降水云雨滴谱三参数随雨强R的增大而减少;拟合雨滴谱T分布三参数N_0、μ、λ满足二项式分布且相关系数较好。  相似文献   

ECMWF集合预报和确定性预报对淮河流域暴雨预报的对比分析   总被引：7，自引：6，他引：1  

董全  金荣花  代刊  康志明 《气象》2016,42(9):1146-1153

本文运用2012年5—9月欧洲中期天气预报中心(ECMWF)的集合预报系统(Ensemble Prediction System,EPS)和确定性模式(High-resolution Deterministic forecast,HDet)资料对比分析了淮河流域暴雨的预报效果。对于集合预报,主要对比了基于EPS的日降水量极端天气预报指数(Extreme Forecast Index,EFI),和改进的贝叶斯模型平均(Modified Bayesian Model Averaging,MBMA)法对降水的订正后概率。由于ROC(Relative Operating Characteristic)检验是与模式的系统性偏差无关的,所以选用ROC检验,对比了不同空报率下的TS评分,以及不同方法的相对经济价值。对比检验的结果显示,各时效预报MBMA预报效果最好,其次是HDet,EFI的预报效果最差,其中2 d内的预报HDet接近MBMA,随着预报时效的延长,MBMA相对于HDet和EFI的优势不断增强。在不同标准下确定三种方法对淮河流域暴雨预报的阈值,结果显示MBMA同样优于HDet,EFI预报效果最差。但MBMA的优势是通过增加预报偏差得到,如果将预报偏差限定为主观预报的1.37,此时MBMA的效果和HDet的效果接近。  相似文献   

黑龙江省非典型环境条件强迫下短时强对流天气特征研究     

吴迎旭  张慧君  周一  孟莹莹  周奕含 《沙漠与绿洲气象(新疆气象)》2016,10(6):59-67

本文利用常规气象观测资料、区域自动站加密观测资料、FY-2卫星云图、新一代天气雷达及NECP的1°×1°再分析资料对黑龙江省的2006-2014年冰雹和2008-2014年的强降水在非典型环境条件下表现出的局地要素特征以及卫星和雷达特征进行分析。分析结果显示：较大的对流有效位能、低层强暖空气为对流发生提供了热力不稳定;700hPa湿区配合冰雹500hPa干区和强降水低层弱水汽辐合使得对流具备了有利的水汽垂直分布条件;最终在地面局地辐合的触发下产生了对流;冰雹有较高的0℃层高度和较低的气压;冰雹和强降水有利的海拔高度分别在200-500m和100-200m。卫星云图和雷达上的表现往往比较孤立,移动较快,产生的时间和位置与两个小云块或小云块与大云团合并的时间及位置一致,低层水汽辐合明显时可能会伴有大的云团。雷达回波上冰雹云但很难探测到钩状回波等特征回波,强降水多为原地生消火或列车效应产生。  相似文献