驻马店夏季短时暴雨预报业务系统   总被引：1，自引：0，他引：1  

崔焕东李顺利  王裕亭李晨 张红卫 《河南气象》2003,(3):12-13

利用驻马店市1985～2001年6～8月高空、地面、雷达回波、卫星云图等资料，分析了短时暴雨的气候特征，确定了产生短时暴雨的天气形势及消空指标，并通过温度平流、湿度条件、稳定度、动力条件的诊断，挑选出对短时暴雨反映敏感的气象要素作为预报因子，最后通过逻辑判定，由微机自动输出预报结论。通过2002年的业务应用，该系统预报成功率为85．7％。  相似文献   

塔克拉玛干沙漠南缘水资源开发与绿洲生态环境负效应   总被引：2，自引：10，他引：2  

高前兆 《干旱区地理》2003,26(3):193-201

主要讨论塔克拉玛干沙漠南缘的自然环境特点、水资源及其开发利用，揭示在百年来气候变化和人类活动影响下，特别是近50年来，对沙漠南缘的生态脆弱带的绿洲产生明显的生态环境负效应，引起的生态环境退化极不利于区域可持续发展。为此需要从区域生态环境战略考虑，调整水资源配置和优化利用，实施天然绿洲与人工绿洲相应的保护和并重发展，逐步恢复天然绿洲的水分生态平衡。这样，才能遏制住强劲的区域土地退化态势，抵御沙漠化灾害，并走向良性循环。  相似文献   

A general mathematical model for balanced global isostasy     

James A. Dockal  Richard A. Laws  Thomas R. Worsley 《Mathematical Geology》1989,21(2):147-170

A general mathematical model of balanced global isostasy is presented that describes the geometrical relationships among atmospheric, oceanic, lithospheric, and asthenospheric components relative to a fixed, external frame of reference in terms of 19 parameters of mass, density, area, and thickness in five basic equations and various corollaries. The model is applicable and necessary for evaluating lithospheric processes that operate on a global scale or that affect globally oriented parameters such as sea level, freeboard, and ocean basin depth. It also provides a means of testing the internal consistency of a given set of mass, density, volume, and area parameters relative to present crustal geometry by showing how well they combine to predict present continental free-board. With modification, the basic model can be used to examine more complex questions involving glacially induced sea level fluctuations and long-term crustal evolution resulting from differential energy flux to Earth, short-term modulation of heat flux from the asthenosphere, and long-term monotonic cooling.  相似文献   

俯冲带的负浮力及其影响因素   总被引：9，自引：5，他引：9       下载免费PDF全文

臧绍先  宋杰远 《地球物理学报》1994,37(2):174-183

基于Ｍｕｒｎａｇｈａｎ－Ｂｉｒｃｈ状态方程，计算了密度Ｐ、热膨胀系数ａｖ、定压比热ｃｐ等物性参数在上地幔温压条件下的分布，给出了热传导系数ｋ在上地幔温压条件下的分布．采用准动力学计算方案，用有限元方法计算了板块不同俯冲速度、角度、不同厚度及不同俯冲深度情况下俯冲带的温度分布和密度分布．计算了不同俯冲模型下俯冲带的负浮力及其对岩石层板块形成的等效应力，发现负浮力在俯冲过程中是变化的，俯冲速度和板块厚度对其有明显的影响，在稳定俯冲状态，负浮力约为（１．５－２．３）×１０^１３Ｎｍ^－１，等效张应力约为０．２５－０．２９Ｇｐａ．  相似文献   

利用CryoSat-2测高数据研究南极威德尔海海冰出水高度时空变化     

高翔  庞小平  季青 《武汉大学学报(信息科学版)》2021,(1)

为了提高南极海冰出水高度的估算精度,以威德尔海为例,基于CryoSat-2卫星测高数据,联合冰桥计划(IceBridge)机载测高数据和科考船走航观测数据,获取应用最低点高程法反演海冰出水高度的最佳估计参数,进而估算并分析了2011—2017年,每年5月—10月威德尔海海冰出水高度的时空变化。结果表明,最佳的出水高度估算方案为采用0.8倍标准差剔除高度计观测值粗差后,选择沿轨10 km数据段并取最小5%的样本点平均值作为局地海面高估算海冰出水高度;近7年来南极威德尔海月均海冰出水高度总体呈现略微变薄的趋势,变化范围在17.9~27.4 cm之间;威德尔海海冰出水高度的分布呈现东薄西厚的特征,较大值主要分布在西威德尔海以及南极半岛东部海域。上述结论可为进一步研究南极海冰厚度变化对气候变化的响应提供参考。  相似文献   

玉溪空气负氧离子预测模型的建立     

王宝  解福燕  张自祥  刘春学 《高原气象》2015,34(1)

利用玉溪市九县区14台空气负氧离子自动测报系统实时观测数据和同步气象要素观测资料,使用相关分析、回归分析等方法,分析了影响空气中负氧离子浓度的主要气象因子,以及影响因子与空气负氧离子浓度的关系,并建立预测模型。结果表明,玉溪市空气负氧离子浓度年变化、季节变化与各气象因子之间无显著的相关关系。影响玉溪空气负氧离子浓度日变化的主要气象因子为空气相对湿度和空气温度。当空气温度20.4℃时,空气负氧离子浓度日变化与空气温度呈负相关关系。当空气湿度45.6%时,空气负氧离子浓度与空气湿度呈正相关关系。通过建立负氧离子浓度预测模型,实现了负氧离子预报的定量化。经检验,预报方程效果显著,在预报业务中具有参考价值。  相似文献   

一次多回击负地闪放电过程的甚高频辐射和传输特征分析   总被引：1，自引：0，他引：1  

孙竹玲  郄秀书  刘明远 《大气科学》2015,39(4):667-676

利用短基线时间差甚高频(VHF)辐射源定位系统对一次多回击负地闪放电过程进行详细研究发现, 负地闪的预击穿、梯级先导、直窜先导及回击后云内放电过程伴随有较强烈的VHF辐射。结合同步观测的闪电快、慢电场变化资料, 分析VHF辐射源时空发展特征发现, 预击穿阶段辐射源在云中的放电通道为双向发展, 平均速度均在104 m s-1量级, 预击穿下行分支直接转化为梯级先导, 并产生多个分支通道同时向地面发展, 先导平均速度在105 m s-1量级。继后回击之前先导过程均产生多个分支通道, 直窜先导平均速度在105～106 m s-1量级, 新开辟的梯级先导速度在105 m s-1量级。闪击间及地闪后期云内放电活动较为复杂, 主要表现为辐射源从闪电起始区域发展, 进一步延伸云内闪电通道。地闪后期多次负极性K变化过程(Kitagawa and Kobayashi, 1958)主要表现为负极性流光沿之前的正极性电离通道快速发展, 平均速度在106 m s-1量级。  相似文献   

Estimation of Sea Ice Freeboard from SARAL/AltiKa Data     

Megha Maheshwari  C. Mahesh  Kamaljit Singh Rajkumar  J. Pallipad  Sandip R. Oza 《Marine Geodesy》2015,38(3):487-496

An attempt has been made to derive sea ice freeboard from Ka-band Altimeter (SARAL/AltiKa) over Arctic region for 15 March–15 April 2013 (spring) and 15 September–15 October 2013 (autumn). A waveform template matching technique is employed for classification of leads and floe pixels. The estimated sea ice freeboards were found in close agreement with “Operation IceBridge quick look” freeboards (RMSD = 0.30 m). The differences between the two freeboards were largely due to snow layer over sea ice (R = 0.8). The estimated freeboards were of the order of 0.08–0.15 m during the two seasons.  相似文献   

Climate variability in the Aral Sea basin (Central Asia) during the late Holocene based on vegetation changes   总被引：1，自引：1，他引：0  

Philippe Sorrel  Speranta-Maria Popescu  Stefan Klotz  Jean-Pierre Suc  Hedi Oberhnsli 《Quaternary Research》2007,67(3):357-370

High-resolution pollen analyses ( 50 yr) from sediment cores retrieved at Chernyshov Bay in the NW Large Aral Sea record shifts in vegetational development from subdesertic to steppe vegetation in the Aral Sea basin during the late Holocene. Using pollen data to quantify climatic parameters, we reconstruct and date for the first time significant changes in moisture conditions in Central Asia during the past 2000 yr. Cold and arid conditions prevailed between ca. AD 0 and 400, AD 900 and 1150, and AD 1500 and 1650 with the extension of xeric vegetation dominated by steppe elements. These intervals are characterized by low winter and summer mean temperatures and low mean annual precipitation (P_mm < 250 mm/yr). Conversely, the most suitable climate conditions occurred between ca. AD 400 and 900, and AD 1150 and 1450, when steppe vegetation was enriched by plants requiring moister conditions (P_mm  250–500 mm/yr) and some trees developed. Our results are fairly consistent with other late Holocene records from the eastern Mediterranean region and the Middle East, showing that regional rainfall in Central Asia is predominantly controlled by the eastern Mediterranean cyclonic system when the North Atlantic Oscillation (NAO) is in a negative phase.  相似文献   

Axis Translation and Negative Water Column Techniques for Suction Control   总被引：1，自引：0，他引：1  

Sai K. Vanapalli  M. V. Nicotera  Radhey S. Sharma 《Geotechnical and Geological Engineering》2008,26(6):645-660

Negative water column and axis translation techniques are conventionally used experimental techniques for obtaining data to interpret the engineering behavior of unsaturated soils. The negative or the hanging water column technique is used as a suction control method in the low suction range (i.e., 0–30 kPa). The axis translation technique is used in the suction range 0 to 500 kPa or higher. This technique is particularly useful for testing specimens with suction values greater than 100 kPa avoiding problems associated with cavitation. While the axis-translation technique has been commonly used, the limitations associated with this technique related to air diffusion, water volume change and evaporation are not discussed in greater detail in the literature. This paper highlights some of the key aspects related to the negative water column and axis translation technique that are of interest both to the researchers and practicing engineers.  相似文献