吕梁市2005年9月20日暴雨过程分析     

武旭婷  冯志亮  高明 《山西气象》2006,(3):7-8

本文从天气形势、物理量场、卫星云图等方面对2005年9月20日出现在吕梁市的大到暴雨,局部大暴雨天气过程进行了综合分析,得到了一些有益的结论。  相似文献   

夏季澜沧江跨境径流量变化与夏季风的关系     

尤卫红  赵付竹  吴湘云 《高原气象》2007,26(5):1059-1066

以澜沧江跨境径流量观测数据、NCEP/NCAR的U场、V场和NOAA的OLR场资料为基础,应用统计分析方法,研究了纵向岭谷作用下的夏季澜沧江跨境径流量变化与夏季风的关系。结果表明:澜沧江夏季跨境径流量变化在20世纪60年代中期至80年代末期为显著减少时段,而从90年代初期以来则表现出了一种显著增多的演变趋势;夏季澜沧江跨境径流量变化与较低层东西风分量变化的相关性不显著,与较高层东西风分量变化的相关性显著;夏季澜沧江跨境径流量变化与中低层和较高层南北风分量变化的相关性都是显著的,与OLR场变化的负相关性也是显著的;根据这些相关性特征建立的影响澜沧江夏季跨境径流量变化的夏季风环流指数能够较好地反映出澜沧江夏季跨境径流量变化的基本特征和规律。  相似文献   

A high-resolution reconstruction of Storglaciären mass balance back to 1780/81 using tree-ring data and circulation indices     

Hans W. Linderholm  Peter Jansson 《Quaternary Research》2007,67(1):12-20

Storglaciären in northernmost Sweden has the world's longest ongoing continuous mass-balance record, starting in 1946. To extend this mass-balance record, we have reconstructed summer (b_S) and winter (b_W) mass balances separately back to the mass balance year 1780/81 with annual resolution. We used tree-ring data for b_S and a set of circulation indices, based on the sea-level pressure, for b_W. Both proxies have correlation coefficients with respective mass balance components of ca. 0.7. The reconstructed net balance (b_N) of Storglaciären was well correlated to the observations during 1946-1980 (r = 0.8, p < 0.05). Our reconstruction agrees well with previously obtained results of northern Sweden glacier variability, where the predominantly positive b_N years between 1890 and 1910 correspond to the well documented post-Little Ice Age advance of Storglaciären. Furthermore, the results suggest that b_S, as a function of summer temperatures, is more important than b_W in determining the b_N, which is contrary to glaciers in the maritime parts of western Scandinavia. In general, b_N has been negative over the last 220 yr, suggesting a predomination of continental conditions over northern Sweden. However, the influence of b_W increased in the late twentieth century, indicating a shift to a more oceanic climate regime.  相似文献   

The impact of freshwater discharges on the ocean circulation in the Skagerrak/northern North Sea area. Part II: energy analysis     

Jon Albretsen 《Ocean Dynamics》2007,57(4-5):287-304

We perform eddy-permitting to eddy-resolving simulations of the Skagerrak/northern North Sea with a terrain-following numerical ocean model. We demonstrate that realistic representations of freshwater input are not required when the focus is on modelling mesoscale structures such as meanders and eddies. To arrive at this conclusion, we analyze the results using a recently developed energy diagnostic scheme to study the sensitivity to realistic representations of the lateral freshwater flux provided to the area from the Baltic Sea and by the major rivers. The scheme is suitable for analysis of growth of instabilities, and it has four basic instability processes prominent. We recognize both horizontal and vertical shear instabilities. There are two processes where average potential energy is converted to eddy kinetic energy, and they are related to the mean gradient in surface elevation and the mean lateral density gradient, respectively. The latter process is known as frontal instability. We demonstrate that the change in the eddy kinetic energy field is small, despite the large variations in the hydrographic properties from experiment to experiment. Moreover, generation of eddy activity appears at the same locations and with approximately the same strength regardless of actual representations of freshwater input. Furthermore, we find that vertical shear instability dominates the energy conversion processes in the Norwegian Coastal Current. Finally, we find that the areas off the northwest coast of Denmark recognized with enhanced eddy kinetic energy level is not caused by instability processes but eddy–eddy interaction rooted in variations in the sea level.  相似文献   

对2005年盛夏十堰市一次连续强降水天气过程的分析     

朱明  姚道强  徐远波  谭永秀  董如根  王立华 《湖北气象》2007,26(3):236-240

使用2005年8月14～23日各层(850、700、500 hPa等)天气图资料,以及有关物理量场资料、雷达回波资料和卫星云图资料,采取天气诊断分析方法,对2005年盛夏十堰市一次连续强降水天气过程进行了分析。结果表明:此次过程是在西太平洋副热带高压、"珊瑚"台风、东南急流、南支低槽、中低层低涡切变线等系统共同影响下形成的;贝加尔湖低槽持续分裂冷空气与副热带高压边缘暖湿气流对峙是该过程能够维持的基本条件;短带状强回波与新生的强对流窄回波带相叠加并维持较长时间,中-β尺度云团在本地发展为中-α尺度云团且受地形作用维持近5 h,使得灾情更趋严重。  相似文献   

1999年6月长江中下游梅雨暴雨的环流特征分析   总被引：7，自引：12，他引：7  

隆霄  程麟生  王文 《高原气象》2007,26(3):563-571

利用客观分析资料和加强观测期资料,对1999年6月发生在我国长江流域的持续性梅雨期降水过程的大尺度环流特征进行了分析,结果表明:(1)1999年梅雨期,我国长江中下游强降水带状分布非常明显,强降水主要发生在长江中下游地区,强降水带呈东西向分布,并且雨带的南北边界非常清楚。(2)在对流层低层,从孟加拉湾来的西风气流和西太平洋副热带高压前缘的东南气流在长江流域维持,为此次强暴雨过程产生和发展提供了有利的大尺度条件。高空急流和低空急流的存在和维持为此次梅雨锋暴雨过程的发生提供了有利的抬升机制,而对流层中低层的中性对流不稳定特征则为持续性暴雨过程的发生提供了有利的不稳定机制。(3)梅雨锋区对流层低层的水汽辐合非常明显,水汽输送主要来自孟加拉湾和西太平洋,同时南海季风槽在向梅雨锋区输送水汽的过程中起到了非常重要的作用,它是热带海洋地区向我国内陆输送水汽的通道。(4)平均纬向风速u对流层高层出现了与高空西风急流与高空东风急流相对应的两个强风速核;径向平均风速v在400 hPa以下层次盛行南风,而在400 hPa以上的高层盛行北风;受两侧下沉气流的制约,梅雨锋降水带南北两侧存在位势不稳定层结中的不稳定能量无法释放,因此没有出现明显的降水。  相似文献   

影响辽东半岛两个台风Meari和Muifa暴雨环流特征的对比分析   总被引：4，自引：1，他引：3  

梁军  李英  张胜军  刘晓初 《大气科学》2015,39(6):1215-1224

Meari(1105)和Muifa(1109)是两个路径相似并在辽东半岛产生强降水的热带气旋。但Meari强降水持续时间长,而Muifa时间短。利用中国气象局热带气旋年鉴、FY_2D(0.1°×0.1°)云顶亮温资料、大连地区逐时自动气象站降雨量资料、常规观测资料和NCEP/NCAR再分析资料,对两个台风影响辽东半岛的降水过程进行了对比分析。结果表明:(1)Meari影响辽东半岛时强度较弱,但与低空东南急流相连获得丰富水汽供应,衰减缓慢;Muifa影响时强度较强但与低空急流水汽通道快速断开而衰减迅速。(2)两个台风均进入西风槽区而变性,但两者影响辽东半岛时处于不同的变性阶段。Meari为半冷半暖结构,其北侧中尺度对流活动发展旺盛,非对称结构明显;Muifa低层环流已变性为冷中心,云系结构孤立且无发展。(3)两次过程中辽东半岛位于台风不同的对流发展区域是其降水强度差异的原因之一。辽东半岛位于Meari北侧,低层的水平辐合较强,水平风垂直切变较大,深厚的上升运动维持;Muifa影响下辽东半岛位于其西侧,受偏北风下沉气流控制,不稳定度和动力抬升条件减弱。  相似文献   

On the recent warming of the southeastern Bering Sea shelf   总被引：1，自引：0，他引：1  

P.J. Stabeno  N.A. Bond  S.A. Salo 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2599

During the last decade, the southeastern Bering Sea shelf has undergone a warming of 3 °C that is closely associated with a marked decrease of sea ice over the area. This shift in the physical environment of the shelf can be attributed to a combination of mechanisms, including the presence over the eastern Bering Sea shelf of a relatively mild air mass during the winter, especially from 2000 to 2005; a shorter ice season caused by a later fall transition and/or an earlier spring transition; increased flow through Unimak Pass during winter, which introduces warm Gulf of Alaska water onto the southeastern shelf; and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter. While the relative importance of these four mechanisms is difficult to quantify, it is evident that for sea ice to form, cold arctic winds must cool the water column. Sea ice is then formed in the polynyas during periods of cold north winds, and this ice is advected southward over the eastern shelf. The other three mechanisms can modify ice formation and melt, and hence its extent. In combination, these four mechanisms have served to temporally and spatially limit ice during the 5-year period (2001–2005). Warming of the eastern Bering Sea shelf could have profound influences on the ecosystem of the Bering Sea—from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species.  相似文献   

Earthquakes as a potential contributing factor to climate change at multi-decadal scale     

KeYan Fang  Heikki Sepp? 《寒旱区科学》2014,6(2):0131-0138

Climate changes at the multi-decadal scale are often associated with multi-decadal phase shifts of the dominant sea surface temperature （SST） pattern, such as the Pacific Decadal Oscillation （PDO）. The PDO may be associated with the North Pacific branch of the Thermohaline Circulation （THC）. Great earthquakes （M 〉8）, particularly along the route of the THC, might modulate the vertical mixing and bring deep, cold water to surface, contributing to multi-decadal changes in surface currents and the PDO. This may eventually lead to multi-decadal climate changes. We tested this hypothesis for the Pacific Ocean where great earthquakes have been frequently recorded. We found associations between the PDO and recurrent earthquakes along the route of the deep currents of the THC in the modern period since 1900, and relationships between hydroclimate change in Monsoonal Asia and historical earthquakes since 1300. However, it should be noted that this hypothesis is very preliminary and has many gaps that needs further evidences from more observational records and modeling studies.  相似文献   

The East Greenland Spill Jet as an important component of the Atlantic Meridional Overturning Circulation     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean׳s role in climate.  相似文献