积雪在El Niño影响东亚夏季气候异常中的作用          下载免费PDF全文

王妍凤  孙旭光  杨修群 《地球物理学报》2017,60(9):3325-3337

本文利用1948-2010年Global Land Data Assimilation System（GLDAS）NOAH陆面模式资料、GPCC月平均降水资料和NCAR/NCEP全球月平均再分析资料，采用滤波、距平合成和线性相关等方法，分析了El Niño成熟位相冬季欧亚大陆积雪异常的分布特征，研究了关键区积雪融化对后期春、夏季土壤湿度、土壤温度以及大气环流与降水的影响，揭示了El Niño事件通过关键区积雪储存其强迫信号并影响东亚夏季气候异常的机制和过程.主要结论如下：El Niño成熟阶段冬季伊朗高原、巴尔喀什湖东北部和青藏高原南麓区域是雪深异常的三个关键区，这些区域的雪深、雪融和土壤湿度有明显的正相关；这三个关键区雪深异常通过春季融雪将冬季El Niño信号传递给春、夏季局地土壤湿度，通过减少感热通量和增加潜热通量对大气环流产生影响；春末夏初伊朗高原土壤湿度异常对东亚夏季气候异常的影响最大，其引起的降水异常与El Niño次年夏季降水异常分布基本一致，春夏季青藏高原南麓和巴尔喀什湖附近土壤湿度也都明显增加，均会对中国华北降水增加有显著正贡献.总之，在利用El Niño事件研究和预测东亚夏季气候异常时，还应考虑关键区雪深异常对El Niño信号的存储和调制作用.  相似文献   

One‐dimensional consolidation with a threshold gradient: a Stefan problem with rate‐dependent latent heat     

Yang Zhou  Wan‐kui Bu  Meng‐meng Lu 《国际地质力学数值与分析法杂志》2013,37(16):2825-2832

During the process of one‐dimensional consolidation with a threshold gradient, the seepage front moves downward gradually, and the problem is indicated as a Stefan problem. The novel feature in this Stefan problem is a latent heat that varies inversely with the rate of the moving boundary. An exact solution for the external load that increases in proportion to the square root of time is constructed using the similarity transformation technique. Computational examples concerning the effect of different parameters on the motion of the seepage front are presented. The exact solution provides a worthwhile benchmark for verifying the accuracy of numerical and approximate methods. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Potential Influence of a Developing La Niña on the Sea-Ice Reduction in the Barents–Kara Seas     

Rui Luo  Peng Zhang  Juan Dou 《大气与海洋》2013,51(3):182-194

Abstract

The potential influence of a developing La Niña on Arctic sea-ice annual variability is investigated using both observational data and an atmospheric general circulation model. It is found that during the developing phase of an eastern Pacific (EP) La Niña event in June, July, and August (JJA) and September, October, and November (SON), the sea-ice concentration (SIC) over the Barents–Kara Seas declines more than 15%. The local atmospheric circulation pattern associated with the EP La Niña is characterized as a weak decrease in geopotential height over the Barents–Kara Seas, combined with an anticyclone in the North Atlantic. The corresponding southerly winds push warm waters northward into the key sea-ice reduction region and directly accelerate sea-ice melt. Meanwhile, the abundant moisture contained in the lower troposphere is transported into the Arctic region by winds resulting from the local barotropic structure. The humid atmosphere contributes to both net shortwave and longwave radiation and thus indirectly accelerates the decline in sea ice. Simulations by the European Centre Hamburg Model, version 5.4, are forced by observed sea surface temperature anomalies associated with EP La Niña events. The results of the simulations capture the North Atlantic anticyclone and reproduce the moisture transport, which supports the premise that an EP La Niña plays a crucial role in sea-ice reduction over the Barents–Kara sector from the perspective of atmospheric circulation and net surface heat flux.  相似文献   

Long-Term Variability of Volume and Heat Transport in the Nordic Seas: A Model Study     

Sarah Lundrigan 《大气与海洋》2013,51(2):156-168

This article presents results from a model study of interannual and decadal variability in the Nordic Seas. Fifty years of simulations were conducted in an initial condition ensemble mode forced with the National Centers for Environmental Prediction (NCEP) reanalysis. We studied two major events in the interannual and interdecadal variability of the Nordic Seas during the past fifty years: the Great Salinity Anomaly in the 1960s and early 1970s and the warming of the Arctic and subarctic oceans in the late 1990s.

Previous studies demonstrated that the Great Salinity Anomaly observed in the subarctic ocean in 1960 was originally generated by intensified sea-ice and freshwater inflow from the Arctic Ocean. Our model results demonstrate that the increase in the transport of fresh and cold waters through Fram Strait in the 1960s was concurrent with a reduction in the meridional water exchange over the Greenland–Scotland Ridge. The resulting imbalance in salinity and heat fluxes through the strait and over the ridge also contributed to the freshening of the water masses of the Nordic Seas and intensified the Great Salinity Anomaly in the Nordic Seas.

The warming of the Atlantic Waters in the Nordic Seas and Arctic Ocean during the past two decades had an important impact on the variability of these two ocean basins. Some previous observational and model studies demonstrated that the warming of the subpolar Atlantic Ocean in the late 1990s and the meridional transport of the Atlantic Water mass (AW) into the Nordic Seas and Arctic Ocean contributed to this process. At the same time, observations show that the warming of the AW in the Nordic Seas started in the 1980s (i.e., earlier than the warming of the subpolar North Atlantic Ocean). Our model results suggest that this process was triggered by an imbalance in the lateral heat fluxes through Fram Strait and over the Greenland–Scotland Ridge. In the late 1980s the AW transport over the Greenland–Scotland Ridge was stronger than normal while the exchange through Fram Strait was close to normal. The related imbalance in the lateral heat fluxes through the strait and over the ridge warmed the Nordic Seas and caused an increase in the temperature of the AW inflow to the Arctic Ocean in the late 1980s (i.e., about a decade earlier than the warming of the source of the AW in the subpolar North Atlantic Ocean). Thus the model results suggest that the imbalance in lateral heat and salinity fluxes through the strait and over the ridge connecting the Nordic Seas to the North Atlantic and Arctic oceans could amplify the interannual variability in the subarctic ocean.

[Traduit par la rédaction] Cet article présente les résultats d'une étude par modèle de la variabilité interannuelle et décennale dans les mers nordiques. Nous avons effectué des simulations sur une période de cinquante ans en mode d'ensemble de conditions initiales forcé avec les réanalyses des NCEP (National Centers for Environmental Prediction). Nous avons étudié deux événements majeurs survenus dans la variabilité interannuelle et décennale des mers nordiques au cours des cinquante dernières années : la grande anomalie de salinité des années 1960 et du début des années 1970 et le réchauffement des océans Arctique et subarctique vers la fin des années 1990.

Des études précédentes ont démontrées que la grande anomalie de salinité observée dans l'océan subarctique en 1960 a été causée par une intensification de l'apport de glace de mer et d'eau douce depuis l'océan Arctique. Les résultats que nous avons obtenus du modèle montrent que l'accroissement du transport d'eau douce et froide à travers le détroit de Fram dans les années 1960 s'est produit en même temps qu'une réduction dans l’échange méridien d'eau au-dessus de la crête Groenland–Écosse. Le déséquilibre résultant dans les flux de salinité et de chaleur à travers le détroit et au-dessus de la crête a aussi contribué à l'adoucissement des masses d'eau des mers nordiques et a intensifié la grande anomalie de salinité dans les mers nordiques.

Le réchauffement des eaux atlantiques dans les mers nordiques et dans l'océan Arctique au cours des deux dernières décennies a eu un impact important sur la variabilité de ces deux bassins océaniques. Des études observationnelles et par modèle précédentes ont établi que le réchauffement de l'océan Atlantique subpolaire dans les années 1990 et le transport méridien de la masse d'eau atlantique dans les mers nordiques et dans l'océan Arctique ont contribué à ce processus. En même temps, les observations montrent que le réchauffement des eaux atlantiques dans les mers nordiques a commencé dans les années 1980 (c.–à–d. plus tôt que le réchauffement de l'océan Nord-Atlantique subpolaire). Les résultats du modèle suggèrent que ce processus a été déclenché par un déséquilibre dans les flux de chaleur latéraux à travers le détroit de Fram et au-dessus de la crête Groenland–Écosse. À la fin des années 1980, le transport des eaux atlantiques au-dessus de la crête Groenland–Écosse était plus fort que la normale alors que l’échange à travers le détroit de Fram était près de la normale. Le déséquilibre résultant dans les flux de chaleur latéraux à travers le détroit et au-dessus de la crête a réchauffé les mers nordiques et causé une augmentation de la température des eaux atlantiques parvenant à l'océan Arctique à la fin des années 1980 (c.-à-d. environ une décennie avant le réchauffement de la source d'eaux atlantiques dans l'océan Nord-Atlantique subpolaire). Donc, les résultats du modèle suggèrent que le déséquilibre dans les flux de chaleur et de salinité latéraux à travers le détroit et au-dessus de la crête reliant les mers nordiques à l'Atlantique Nord et à l'Arctique pourrait amplifier la variabilité interannuelle dans l'océan subarctique.  相似文献   

Structural geometry and controls on basement‐involved deformation in the northern Flinders Ranges,Adelaide Fold Belt,South Australia     

E. Paul  T. Flöttmann  M. Sandiford 《Australian Journal of Earth Sciences》2013,60(3):343-354

In the northern Flinders Ranges, Neoproterozoic and Cambrian sedimentary rocks were deformed and variably metamorphosed during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across the northern Flinders Ranges show shortening of about 10–20%. Despite the presence of suitable evaporitic detachment horizons at the basement‐cover interface, the structural style is best interpreted to be thick‐skinned involving basement with only a minor proportion of the overall shortening accommodated along stratigraphically controlled detachments. Much of the contractional deformation was localised by the inversion of former extensional faults such as the Norwest and Paralana Faults, which both controlled the deposition of Neoproterozoic cover successions. As such, both faults represent major, long‐lived structures which effectively define the present boundaries of the northern Flinders Ranges with the Gawler Craton to the west and the Curnamona Craton to the east. The most intense deformation, which resulted in exhumation of the basement along the Paralana Fault to form the Mt Painter and Babbage Inliers, coincides with extremely high heat flows related to extraordinarily high heat‐production rates in the basement rocks. High heat flow in the northern Flinders Ranges suggests that the structural style not only reflects the pre‐Delamerian basin architecture but is also a consequence of the reactivation of thermally perturbed, weakened basement.  相似文献   

源区黑潮热输送低频变异及其与中国近海SST异常变化的关系   总被引：6，自引：0，他引：6  

齐庆华  蔡榕硕  张启龙 《台湾海峡》2010,29(1):106-113

基于长时间序列的水温和盐度资料，通过动力计算方法估算了源区黑潮（18°N断面）热输送量，分析了源区黑潮热输送变异和中国近海SST异常的年际、年代际时空变化特征及两者之间的相互关系．结果显示，源区黑潮热输送异常呈现出显著的以2—7、10～20a和约30a为主周期的年际、年代际变化，且具有线性增强的长期变化趋势．并约于1976年前后发生了一次显著气候跃变．中国近海SST年际、年代际异常变化的最显著区域位于渤海、黄海、东海海域和台湾海峡．源区黑潮热输送变异在年际、年代际尺度上与中国近海SST异常变化密切相关，源区黑潮热输送变异可能是影响中国近海SST异常变化的重要因素之一．  相似文献   

Energy balance and evaporation loss of an agricultural reservoir in a semi‐arid climate (south‐eastern Spain)     

B. Gallego‐Elvira  A. Baille  B. Martín‐Górriz  V. Martínez‐Álvarez 《水文研究》2010,24(6):758-766

A typical agricultural water reservoir (AWR) of 2400 m² area and 5 m depth, located in a semi‐arid area (southern Spain), was surveyed on a daily basis for 1 year. The annual evaporation flux was 102·7 W m^?2, equivalent to an evaporated water depth of 1310 mm year^?1. The heat storage rate G exhibited a clear annual cycle with a peak gain in April (G ～ 45 W m^?2) and a peak loss in November (G ～ 40 W m^?2), leading to a marked annual hysteretic trend when evaporation (λE) was related to net radiation (R_n). λE was strongly correlated with the available energy A, representing 91% of the annual AWR energy loss. The sensible heat flux H accounted for the remaining 9%, leading to an annual Bowen ratio in the order of 0·10. The equilibrium and advective evaporation terms of the Penman formula represented 76 and 24%, respectively, of the total evaporation, corresponding to a annual value of the Priestley–Taylor (P–T) coefficient (α) of 1·32. The P–T coefficient presented a clear seasonal pattern, with a minimum of 1·23 (July) and a maximum of 1·65 (December), indicating that, during periods of limited available energy, AWR evaporation increased above the potential evaporation as a result of the advection process. Overall, the results stressed that accurate prediction of monthly evaporation by means of the P–T formula requires accounting for both the annual cycle of storage and the advective component. Some alternative approaches to estimating R_n, G and α are proposed and discussed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Above‐stream microclimate and stream surface energy exchanges in a wildfire‐disturbed riparian zone     

J. A. Leach  R. D. Moore 《水文研究》2010,24(17):2369-2381

Stream temperature and riparian microclimate were characterized for a 1·5 km wildfire‐disturbed reach of Fishtrap Creek, located north of Kamloops, British Columbia. A deterministic net radiation model was developed using hemispherical canopy images coupled with on‐site microclimate measurements. Modelled net radiation agreed reasonably with measured net radiation. Air temperature and humidity measured at two locations above the stream, separated by 900 m, were generally similar, whereas wind speed was poorly correlated between the two sites. Modelled net radiation varied considerably along the reach, and measurements at a single location did not provide a reliable estimate of the modelled reach average. During summer, net radiation dominated the surface heat exchanges, particularly because the sensible and latent heat fluxes were normally of opposite sign and thus tended to cancel each other. All surface heat fluxes shifted to negative values in autumn and were of similar magnitude through winter. In March, net radiation became positive, but heat gains were cancelled by sensible and latent heat fluxes, which remained negative. A modelling exercise using three canopy cover scenarios (current, simulated pre‐wildfire and simulated complete vegetation removal) showed that net radiation under the standing dead trees was double that modelled for the pre‐fire canopy cover. However, post‐disturbance standing dead trees reduce daytime net radiation reaching the stream surface by one‐third compared with complete vegetation removal. The results of this study have highlighted the need to account for reach‐scale spatial variability of energy exchange processes, especially net radiation, when modelling stream energy budgets. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A comparison of fibre‐optic distributed temperature sensing to traditional methods of evaluating groundwater inflow to streams     

Martin A. Briggs  Laura K. Lautz  Jeffrey M. McKenzie 《水文研究》2012,26(9):1277-1290

There are several methods for determining the spatial distribution and magnitude of groundwater inputs to streams. We compared the results of conventional methods [dye dilution gauging, acoustic Doppler velocimeter (ADV) differential gauging, and geochemical end‐member mixing] to distributed temperature sensing (DTS) using a fibre‐optic cable installed along 900 m of Ninemile Creek in Syracuse, New York, USA, during low‐flow conditions (discharge of 1·4 m³ s^?1). With the exception of differential gauging, all methods identified a focused, contaminated groundwater inflow and produced similar groundwater discharge estimates for that point, with a mean of 66·8 l s^?1 between all methods although the precision of these estimates varied. ADV discharge measurement accuracy was reduced by non‐ideal conditions and failed to identify, much less quantify, the modest groundwater input, which was only 5% of total stream flow. These results indicate ambient tracers, such as heat and geochemical mixing, can yield spatially and quantitatively refined estimates of relatively modest groundwater inflow even in large rivers. DTS heat tracing, in particular, provided the finest spatial characterization of groundwater inflow, and may be more universally applicable than geochemical methods, for which a distinct and consistent groundwater end member may be more difficult to identify. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

MODIS数据北京城区热岛监测分析   总被引：1，自引：0，他引：1  

李新芝  王萍  陈庆运 《测绘科学》2010,35(4):100-102

随着城市化进程的深入,热岛效应问题越来越严重,从而影响城市及周边地区的生态环境与气候,因此备受人们的重视。本文从2000年—2007年724幅1km分辨率的MODIS地表温度产品中选取64幅质量较好,可以代表春、夏、秋、冬四个季节的昼夜影像,制作地表温度图和选取感兴趣区域分析北京城区热岛效应。结果表明,北京市城区温度明显高于周围地区,夏季夜间最高达到3.7℃,秋季白天相对热岛强度较大,夏季、冬季夜间热岛强度要大于白天,尤其冬季较为明显。  相似文献