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Northwest flow severe weather outbreaks (NWF outbreaks) describe a type of summer convective storm that occurs in areas of mid-level NWF in the central United States. Convective storms associated with NWF outbreaks often travel a long distance systematically along a northwest-southeast oriented track across the northern plains. Previous studies have observed that these migrating convective storms are frequently coupled with subsynoptic-scale midtropospheric perturbations (MPs) initiated over the Rocky Mountains. This study traces MPs for the decade of 1997–2006 using the North American Regional Reanalysis to examine their climatology and possible influence on NWF outbreaks. MPs are characterized by a well organized divergent circulation with persistent ascending motion at the leading edge promoting convection. The divergent circulation is further enhanced by low-level convergence along the northern terminus of the Great Plains low-level jet. The downstream propagation of MPs assists in forming the progressive feature of the associated convective storms. MPs have a maximum frequency in July, consistent with NWF outbreaks. In July and August, the fully developed North American anticyclone produces prevailing NWF over the northern plains, where up to 60% of rainfall and storm reports are linked to MPs. The movement, timing and rainfall distribution of MPs remarkably resemble those of NWF outbreaks. When encountering strong low-level jets, ascending motion and convergence of water vapor flux associated with MPs intensify considerably and precipitation is greatly enhanced. It is likely that NWF outbreaks are generated whenever MPs occur in association with strong low-level jets.  相似文献
2.
Propagating convective storms across the US northern plains are often coupled with preexisting midtropospheric perturbations (MPs) initiated over the Rocky Mountains. A companion study (Part I) notes that such MPs occur most commonly at 12 UTC (early morning) and 00 UTC (late afternoon). Using a regional reanalysis and a general circulation model (GCM), this study investigates how such a bimodal distribution of the MP frequency is formed. The results point to two possible mechanisms working together while each has a different timing in terms of maximum effect. The diurnal evolutions between the midtropospheric flows over the Rockies and over the Great Plains are nearly out-of-phase due to inertial oscillation. During the nighttime, the westerly flows at 700?C500?mb over the Rockies intensify while flows at the same level over the Great Plains turn easterly. These two flows converge over the eastern Rockies and induce cyclonic vorticity through vortex stretching. After sunrise, the convergence dissipates and the cyclonic vorticity is redistributed by horizontal vorticity advection, moving it downstream. This process creates a climatological zonally propagating vorticity signal which, in turn, facilitates the early-morning MP genesis at 12 UTC. The analysis also reveals marked dynamic instability conducive to subsynoptic-scale disturbances in the midtroposphere over the Rockies. Strong meridional temperature gradients appear over the north-facing slopes of the Rockies due to terrain heating to the south and the presence of cooler air to the north. This feature, along with persistent vertical shear, creates a Charney?CStern type of instability (i.e. sign changes of the meridional potential vorticity gradient). Meanwhile, the development of terrain boundary layer reduces the Rossby deformation radius which, subsequently, enhances the likelihood for baroclinic short waves. Such effects are most pronounced in the late afternoon and therefore are supportive to the MP genesis around 00 UTC. Examination of GCM experiments with and without orography further supports the critical role of the Rocky Mountains and its associated boundary layer impacts on the formation of MPs.  相似文献
3.
张曼  范雪波  李林  常晨 《干旱气象》2013,(4):831-834
为提高自动气象站蓄电池的维护效率,本文将预测性维护引入气象保障领域,通过对蓄电池预测性维护的技术要点、测试方案及流程等的介绍,选取3种不同劣化程度的蓄电池依次进行离线状态测试、浮充状态测试以及放电测试,通过数据对比分析初步给出了蓄电池预测性维护监测系统的综合评定。结果表明,在浮充状态下,监测系统电压和内阻的测试精度良好,能够很好地测试出蓄电池在不同健康状况下的电压与内阻值,即对报废电池、具有一定劣化程度电池和新电池的测试数据存在显著差别,在自动气象站蓄电池预测性维护中可利用浮充状态下测得的内阻数据对蓄电池劣化程度进行有效判别。  相似文献
4.
Mean radiant temperature (T mrt) based on two measurement methods and outputs from three models are compared in this study. They are the six direction radiation method, globe thermometer method, RayMan model, ENVI-met model and SOLWEIG model. The comparison shows that globe thermometer method may overestimate the T mrt since wind velocity is a key variable in the estimation based on this method. For better estimation, T mrt measured by the globe-thermometer method be corrected by the imported wind speed (stable, low and assuming wind speed) and validated by the six-direction radiation method. The comparison of models shows that the RayMan model’s evaluation of T mrt involving global radiation with fine time resolution was better than the corresponding evaluations under the other two models (ENVI-met and SOLWEIG) in this case. However, the RayMan model can only assess T mrt for a one-point one-time context, whereas the other two models can evaluate two-dimensional T mrt. For two-dimensional evaluations of T mrt, SOLWEIG have a better prediction of T mrt than ENVI-met, and ENVI-met can simulate several different variables, which are wind field, particle distribution, CO2 distribution and the other thermal parameters (T a, surface temperature and radiation fluxes), that SOLWEIG cannot.  相似文献
5.
Summary The global-scale intraseasonal and annual variations of divergent water-vapor transport and water vapor itself were examined by using outgoing longwave radiation (OLR) and data for 1979–1986 produced by the Global Data Assimilation System of the National Meteorological Center. An effort was also made to contrast results of this study with previous analyses of OLR and upper-level divergent circulation.As for intraseasonal oscillation, positive (negative) precipitable-water (W) anomalies and negative (positive) OLR couple with the convergent (divergent) center of the potential function of water vapor transport () anomalies and the divergent (convergent) center of upper-level divergent-circulation anomalies. It is inferred that the eastward-propagating divergent circulation of intraseasonal oscillation converges water vapor to maintain cumulus convection, which releases latent heat, possibly to support this low-frequency oscillation. Fluctuations of W and cumulus convection associated with this oscillation are large over the equatorial Indian Ocean and the equatorial western Pacific, but small over the tropical Americas and equatorial Africa. Moreover, during northern summer, W anomaly bands migrate regularly northward, following the low-level transient 30–50 day monsoon troughs and ridges over the northern Indian Ocean. To the south of the equator, a regular southward propagation of W anomaly bands is identified in both northern summer and winter. In contrast; over the northwestern Pacific, a signature depicting the north-south intraseasonal oscillation of the north Pacific Convergence Zone can be inferred by W anomalies.The annual cycle components of W and cumulus convection inferred from OLR anomalies exhibit three pairs of maximum-minimum centers over tropical continents. These centers correspond to those of and upper-level divergent circulation anomalies. It is shown that landmass cooling in the winter hemisphere and landmass warming in the summer hemisphere establish a pair of upper-level convergent-divergent centers over each tropical continent. Water vapor is converged (diverged) by divergent circulation, in order to maintain maximum (minimum) centers of W and cumulusconvection anomalies over each tropical continent.With 7 Figures  相似文献
6.
孟青  吕伟涛  姚雯  何平  张义军  刘强  李林  张曼  常晨 《气象》2005,31(9):30-33
论述利用地面电场仪的探测资料对雷电预警预报的技术方法,以大气电场测量为基础,利用地面电场仪的组网,实现自动、连续、实时监测雷雨云中强雷电活动中心在地面产生的电场强度、极性以及闪电数等,提供监测范围内雷暴强电荷活动中心的发生发展演变特征和整个雷暴过程中雷电活动位置和发展信息。同时结合闪电定位系统的观测,为雷电的监测和预报提供更充分的信息。  相似文献
7.
范雪波  张鹏  常晨  刘金城  张曼  李林 《气象科技》2017,45(4):641-646
为不断提高气象探测装备保障业务的科技含量与信息化水平,亟待建立高效及时的相关管理平台。本文结合北京市气象装备管理的实际情况和业务需求,设计了一种基于射频识别(Radio Frequency Identification,RFID)的气象探测装备动态信息管理平台,对平台结构设计进行相关阐述,重点分析了平台基于RFID技术的信息传输以及详细功能,并针对平台建设提出一些思考与展望。  相似文献
8.
常晨  李林  范雪波  张曼  崔炜 《气象科技》2017,45(6):1141-1145
称重式降水传感器已经在全国地面观测站中广泛应用,承担着冬季降水量的观测任务,为冬季降水量预报和服务提供观测资料。北京市气象局目前使用的126套称重降水传感器中,DSC2型称重式降水传感器占90%。本文根据对DSC2型称重式降水传感器的研究,重点介绍了其基本原理和数据质控算法,并针对其在实际运行中出现的两类常见故障进行分析,介绍对应的判断方法与解决思路,最后提出DSC2称重式降水传感器日常维护注意事项,以减少相关设备发生故障。  相似文献
9.
李林  常晨  范雪波  崔炜 《气象科技》2013,41(6):1008-1012
为掌握称重式降水传感器的液态降水观测性能,推进降水自动化观测进程,按照降水过程强弱,依照北京市观象台2011年春夏季降水观测数据的统计结果,对DSH1型称重式降水传感器与业务用SL3 1型双翻斗雨量传感器进行比较分析。结果表明:以SL3 1型双翻斗雨量传感器为参照,DSH1型称重式降水传感器的观测数据基本可靠,在小雨过程中,两种型号传感器的观测数据有较好一致性;在中雨及大雨过程中,DSH1型称重式传感器与SL3 1型双翻斗雨量传感器还有一定的差异,有待于进一步试验与研究。试验过程中,DSH1型称重式传感器曾有故障出现,仪器可靠性有待提高。  相似文献
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