广西强降水强对流天气专业预报服务系统     

李勇  钟利华 《广西气象》2007,28(4):49-51

分析了当前专业预报服务的现状,根据需要建立了一套完善的强降水、强对流天气动态监测、分析和预报服务系统。该系统具有对气象信息采集、加工、分发、传输等自动化的功能,实现了对强降水、强对流天气、台风的实时监测和及时发布。  相似文献   

14时探空在改进北京地区对流天气潜势预报中的作用   总被引：4，自引：0，他引：4  

廖晓农  俞小鼎  谭一洲 《气象》2007,33(3):28-32

为了探讨增加14时探空对于对流天气短时临近潜势预报的作用。用1995—2005年北京地区22个人工观测站资料统计了夏季常见的对流天气日变化特征。结果表明，41．6％的雷阵雨、61．3％的冰雹以及58．5％的雷暴大风发生在15—-20时之间。利用探空资料计算并对比了出现在2006年7—9月14时探空释放后到20时期问11个雷暴个例的08时和14时BCAPE、DCAPE、CIN等对流参数。结果表明，对于多数个例，在判断对流是否发生时14时探空优于08时。因此，增加14时探空对于提高对流天气有无预报准确率有帮助。  相似文献   

利用双多普勒雷达分析对流云垂直运动结构试验   总被引：1，自引：0，他引：1       下载免费PDF全文

袁野 杨光胡雯  曾光平 《应用气象学报》2007,18(3):306-313

对流云是我国南方地区主要的降水云系, 含有丰富的云水资源, 是南方人工增雨作业的主要对象。为了研究江淮地区对流云发生发展规律, 利用双多普勒雷达反演技术分析了发生在2004年7月31日的一块对流云不同发展阶段的垂直运动结构。对流云在发展阶段以上升气流为主, 底层辐合明显, 结构紧密; 成熟阶段的上升与下沉气流势力相当, 且比发展阶段强盛, 强回波位置下移, 结构较发展阶段松散; 减弱阶段上升和下沉速度均减小, 水平辐散增强。结果表明:反演的不同阶段对流云垂直运动结构合理, 可以利用双多普勒雷达反演技术进行对流云三维运动结构研究。  相似文献   

海河流域一次大到暴雨天气过程的预报分析   总被引：3，自引：0，他引：3  

吕江津  王庆元  杨晓君 《气象》2007,33(10):52-60

利用数值预报、常规天气图、各种物理量场、卫星云图、雷达资料等,对2005年7月22—24日影响海河流域的典型暴雨天气过程进行了综合分析。该过程是由高空槽、副热带高压边缘的暖湿气流和5号台风海棠减弱后的低气压云系的共同作用下产生的;其触发机制是冷空气从近地层楔入暖空气中,在高温高湿、层结不稳定等诸多有利条件下,冷空气前沿的上升气流在暖区激发出几个较旺盛的中小尺度的强对流云团造成此次的降水过程;数值预报在对流层中部冷平流入侵海河流域的时间和地点,对于强降水出现的时间和落区预报有一定的指示意义,日本模式和T213在此次海河流域强降水的落区预报上存在优势,德国模式在强降水量级的预报上最接近实况,但三家数值模式预报西太平洋副高西伸的位置不够准确,导致海河流域的降水预报的时空分布有一定误差。  相似文献   

华南6月持续性致洪暴雨与孟加拉湾对流异常活跃的关系   总被引：7，自引：1，他引：7  

许晓林  徐海明  司东 《南京气象学院学报》2007,30(4):463-471

利用NCEP/NCAR再分析逐日及逐月资料、NOAA卫星观测的向外长波辐射（Outgoing Long-wave Radiation,OLR）资料、我国160站月降水资料及华南45站逐日降水资料,分析了2005年6月华南持续性致洪暴雨的发生与孟加拉湾对流异常活跃及西太平洋副热带高压演变的关系,并对华南6月有无持续性大范围暴雨年进行合成分析,结果表明华南持续性大范围暴雨发生的年份,孟加拉湾对流相对活跃,西太平洋副高强度偏强、位置偏西;反之亦然。华南6月持续性大范围暴雨发生前,孟加拉湾对流经历了一次活跃过程,同时西太平洋副高也明显经历了一次增强西伸过程。孟加拉湾对流活跃可能通过东西向垂直环流诱使西太平洋副高增强西伸,从而对华南暴雨的形成产生影响。  相似文献   

Transfer processes in a simulated urban street canyon     

E. Solazzo  R. E. Britter 《Boundary-Layer Meteorology》2007,124(1):43-60

The transfer processes within and above a simulated urban street canyon were investigated in a generic manner. Computational fluid dynamics (CFD) was used to aid understanding and to produce some simple operational parameterisations. In this study we addressed specifically the commonly met situation where buoyancy effects arising from elevated surface temperatures are not important, i.e. when mechanical forces outweigh buoyancy forces. In a geophysical context this requires that some suitably defined Richardson number is small. From an engineering perspective this is interpreted as the important case when heat transfer within and above urban street canyons is by forced convection. Surprisingly, this particular scenario (for which the heat transfer coefficient between buildings and the flow is largest), has been less well studied than the situation where buoyancy effects are important. The CFD technique was compared against wind-tunnel experiments to provide model evaluation. The height-to-width ratio of the canyon was varied through the range 0.5–5 and the flow was normal to the canyon axis. By setting the canyon’s facets to have the same or different temperatures or to have a partial temperature distribution, simulations were carried out to investigate: (a) the influence of geometry on the flow and mixing within the canyon and (b) the exchange processes within the canyon and across the canyon top interface. Results showed that the vortex-type circulation and turbulence developed within the canyon produced a temperature distribution that was, essentially, spatially uniform (apart from a relatively thin near-wall thermal boundary layer) This allowed the temperatures within the street canyon to be specified by just one value T _can , the canyon temperature. The variation of T _can with wind speed, surface temperatures and geometry was extensively studied. Finally, the exchange velocity u _E across the interface between the canyon and the flow above was calculated based on a heat flux balance within the canyon and between the canyon and the flow above. Results showed that u _E was approximately 1% of a characteristic wind velocity above the street canyon. The problem of radiative exchange is not addressed but it can, of course, be introduced analytically, or computationally, when necessary.  相似文献   

Intra-plate volcanism in North Queensland and eastern new Guinea: A cryptic mantle plume?     

《Gondwana Research》2020

  相似文献   

The kinematic dynamo action of spiralling convective flows     

G.R.Sarson  F.HBusse 《Geophysical Journal International》1998,133(1):140-158

We consider the kinematic production of magnetic fields in a sphere by velocity fields dominated by differential rotation and spiralling convective cells. The high magnetic Reynolds number limit of Braginsky (1964) is considered and formulae are derived allowing an α-effect parametrization of such flows to be easily calculated. This permits an axisymmetric system to be investigated in parallel with the direct 3-D numerical computations. Good agreement between the asymptotic and 3-D calculations is found. The 'spiralling' property typical of convective motion in rotating spheres is important in terms of dynamo action; the differential rotation coexisting with this feature is also vital. Indeed, it is the presence of both features which allows the analysis of Braginsky to be employed. With flows approximating the columnar form anticipated for rapidly rotating convection, dynamo action is relatively easily achieved for all azimuthal wavenumbers; modes of differing wavenumbers interact almost by a simple superposition. With flows of more complex latitudinal form, the mutual interactions between modes become more complicated. For columnar-type flows, dipole magnetic fields are favoured when the sense of outward spiralling is prograde and the zonal flow is eastwards, as is physically preferred.  相似文献   

Substorm associated radar auroral surges: a statistical study and possible generation model     

B. A. Shand  M. Lester  T. K. Yeoman 《Annales Geophysicae》1998,16(4):441-449

Substorm-associated radar auroral surges (SARAS) are a short lived (15–90 minutes) and spatially localised (5° of latitude) perturbation of the plasma convection pattern observed within the auroral E-region. The understanding of such phenomena has important ramifications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and ionosphere system. A statistical investigation is undertaken of SARAS, observed by the Sweden And Britain Radar Experiment (SABRE), in order to provide a more extensive examination of the local time occurrence and propagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT and 2200 MLT with a maximum occurrence centred around 1700 MLT. The propagation velocity of the SARAS feature through the SABRE field of view was found to be predominately L-shell aligned with a velocity centred around 1750 ms^–1 and within the range 500 m s^–1 and 3500 m s^–1. This comprehensive examination of the SARAS provides the opportunity to discuss, qualitatively, a possible generation mechanism for SARAS based on a proposed model for the production of a similar phenomenon referred to as sub-auroral ion drifts (SAIDs). The results of the comparison suggests that SARAS may result from a similar geophysical mechanism to that which produces SAID events, but probably occurs at a different time in the evolution of the event.  相似文献   

Modelling the dynamics and thermodynamics of volcanic degassing     

David S. Stevenson  Stephen Blake 《Bulletin of Volcanology》1998,60(4):307-317

 The rates of passive degassing from volcanoes are investigated by modelling the convective overturn of dense degassed and less dense gas-rich magmas in a vertical conduit linking a shallow degassing zone with a deep magma chamber. Laboratory experiments are used to constrain our theoretical model of the overturn rate and to elaborate on the model of this process presented by Kazahaya et al. (1994). We also introduce the effects of a CO₂–saturated deep chamber and adiabatic cooling of ascending magma. We find that overturn occurs by concentric flow of the magmas along the conduit, although the details of the flow depend on the magmas' viscosity ratio. Where convective overturn limits the supply of gas-rich magma, then the gas emission rate is proportional to the flow rate of the overturning magmas (proportional to the density difference driving convection, the conduit radius to the fourth power, and inversely proportional to the degassed magma viscosity) and the mass fraction of water that is degassed. Efficient degassing enhances the density difference but increases the magma viscosity, and this dampens convection. Two degassing volcanoes were modelled. At Stromboli, assuming a 2 km deep, 30% crystalline basaltic chamber, containing 0.5 wt.% dissolved water, the ∼700 kg s^–1 magmatic water flux can be modelled with a 4–10 m radius conduit, degassing 20–100% of the available water and all of the 1 to 4 vol.% CO₂ chamber gas. At Mount St. Helens in June 1980, assuming a 7 km deep, 39% crystalline dacitic chamber, containing 4.6 wt.% dissolved water, the ∼500 kg s^–1 magmatic water flux can be modelled with a 22–60 m radius conduit, degassing ∼2–90% of the available water and all of the 0.1 to 3 vol.% CO₂ chamber gas. The range of these results is consistent with previous models and observations. Convection driven by degassing provides a plausible mechanism for transferring volatiles from deep magma chambers to the atmosphere, and it can explain the gas fluxes measured at many persistently active volcanoes. Received: 26 September 1997 / Accepted: 11 July 1998  相似文献