Fatigue Safety Assessment of Concrete Continuous Rigid Frame Bridge Based on Rain Flow Counting Method and Health Monitoring Data

The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.

Climatic Analysis of Continuous Rain in Southwest of Shandong

The continuous rain data from 1961 to 2007 in Heze city was analyzed in this paper.The results showed that continuous rain increased from north to south.Continuous rain processes took place most frequently in summer,next in autumn,and the least in winter.Using wavelet to analyze the sequence of seasonal and annual continuous rain,it had a 5 years cycle oscillation at 2Y(year) level and a 20 years cycle oscillation at 10Y level.An abrupt climate change of continuous rain took place in 1986.Continuous rain was in a more period from 2001 to 2010 and would decrease gradually within the period.

Comparative Analysis on the Rainfall and Snowfall Weather with Close Interval Time and the Key Point of Forecast

From the circulation situation,the influence system,the temperature stratification characteristics in middle and low levels,the application of numerical forecast products and so on,the rainfall and snowfall weather processes with shorter interval time in February of 2009 were contrasted and analyzed.The results showed that it not only needed analyze in detail the vertical distribution situation of temperature,but also needed exactly forecast the invasion time of cold air and the decline speed of temperature to judge the precipitation form in winter was the rain or the snow.Particularly,the temperature threshold in high-low level which coordinated with the boundary of rain and snow was the key point of rain and snow forecast.Before the precipitation,different temperatures in high-altitude and on the ground were main causes of different precipitation natures.

POSSIBLE IMPACTS OF MADDEN–JULIAN OSCILLATION ON THE SEVERE RAIN-SNOW WEATHER IN CHINA DURING NOVEMBER 2009

Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors.MJO is very active over the Indian Ocean in November 2009.Especially,it maintains 9 days in MJO phase 3,just corresponding to the two strongest rain-snow processes.Composites of MJO events show that when the MJO convective center is located over the Indian Ocean,the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China,which is consistent with the situation in November of 2009.Atmospheric circulation anomalies of mid-and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection.When the MJO is over the Indian Ocean,it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid-and higher-latitudes.Meanwhile,the western Pacific subtropical high is stronger and more westward than normal,and a significant convective belt appears over eastern East Asia.All these circulation anomalies shown in the composite result also appeared in the observations in November 2009,which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics.Besides the zonal circulation anomalies,the MJO convection can also lead to meridional circulation anomalies.When the MJO convection is located over the Indian Ocean,the western Pacific is dominated by anomalous descending motion,and the eastern East Asia is controlled by strong convergence and ascending motion.Therefore,an anomalous meridional circulation is formed between the tropics and middle latitudes,enhancing the northward transportation of low-level moisture.It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.

Simulation of a Freezing Rain and Snow Storm Event over Southern China in January 2008 Using RIEMS 2.0

The Regional Integrated Environmental Model System （RIEMS 2.0） with NCEP Reanalysis II is utilized to simulate the severe freezing rain and snow storm event over southern China in January 2008, which caused severe damage in the region. The relationships between the freezing rain process and the large-scale cir- culation, in terms of the westerly and low-level jets, water vapor transportation, and northerly wind area/intensity indices, were analyzed to tmderstand the mechanisms of the freezing rain occurrence. The results indicate the fol- lowing： （1） RIEMS 2.0 reproduced the pattern of precipi- tation in January 2008 well, especially for the temporal evolution of daily precipitation averaged over the Yangtze River valley and southern China; （2） RIEMS 2.0 repro- duced the persistent trough in the South Branch of the westerlies, of which the southwesterly currents trans- ported abundant moisture into southern China; （3） RIEMS 2.0 reasonably reproduced the pattern of frequencies of light and moderate rain, although it overestimated the frequency of rain in southern China. This study shows that RIEMS 2.0 can be feasibly applied to study extreme weather and climate events in East Asia.

THE FEATURES OF EAST ASIAN JET STREAM IN PERSISTENT SNOWSTORM AND FREEZING RAIN PROCESSES OVER SOUTHERN CHINA IN EARLY 2008

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research(NCEP/NCAR) daily reanalysis data and the upper-level objective analysis data provided by the Meteorological Information Comprehensive Analysis and Process System(MICAPS),the feature of the spatio-temporal variation of the East Asian jet stream(EAJS) in persistent snowstorm and freezing rain processes over southern China in January 2008 have been investigated.Each of the storm events was closely linked with the extraordinarily abnormal variations of East Asian subtropical jet(EASJ) and East Asian polar front jet(EAPJ) at that time.The stronger EASJ with abnormally northward position of the jet axis corresponded to the more intense storm event with broader ranges and longer duration time.The heavy freezing-rain-and-snow event occurred over the region where a strong southerly wind of EASJ prevailed.Meanwhile,the westerly and northerly winds of the EAPJ were significantly intensified,which were also closely related to the beginning,enhancement,and ending of the heavy snowfall.The meridional component of the EAPJ was dominated by the northerly wind during the snowstorm.Thus,the intensification of the snowstorm was attributed to both the strengthening of the meridional wind of EAPJ and the southerly wind of EASJ.Further analysis indicated that wind speed and the zonal wind of the two jets exhibited precursory signals about half a month prior to this extreme event,and the precursory signals were found in the meridional components of the two jets about 20 days preceding the event.The sudden weakening of the meridional component of EASJ and the zonal component of EAPJ signified the ending of this persistent snowstorm.

Test of newly developed conceptual hydrological model for simulation of rain-on-snow events in forested watershed

A conceptual hydrological model that links the Xin＇anjiang hydrological model and a physically based snow energy and mass balance model, described as the XINSNOBAL model, was developed in this study for simulating rain-on-snow events that commonly occur in the Pacific Northwest of the United States. The resultant model was applied to the Lookout Creek Watershed in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon, and its ability to simulate streamflow was evaluated. The simulation was conducted at 24-hour and one-hour time scales for the period of 1996 to 2005. The results indicated that runoffand peak discharge could be underestimated if snowpack accumulation and snowmelt under rain-on-snow conditions were not taken into account. The average deterministic coefficient of the hourly model in streamflow simulation in the calibration stage was 0.837, which was significantly improved over the value of 0.762 when the Xin＇anjiang model was used alone. Good simulation performance of the XINSNOBAL model in the WS 10 catchment, using the calibrated parameter of the Lookout Creek Watershed for proxy-basin testing, demonstrates that transplanting model parameters between similar watersheds can orovide a useful tool for discharge forecastin~, in un^au^ed basins.

The Effects of Power Control on Free-Space Optical Communications during Snowfall and Rainfall

Free-space optical (FSO) communication requires a line-of-sight connection between a transmitter and a receiver in which the information signal is modulated by an optical carrier that propagates in free space. The FSO channel is greatly affected by weather conditions such as fog, rain, and snow. In the literature, several adaptive techniques, such as power control (PC), have been suggested to mitigate channel link degradations. In this paper, we investigate the effects of snow and rain attenuation on the bit error rate (BER) of the FSO system using two types of modulations, the on-off keying (OOK) modulation and the pulse-position modulation (16-PPM). The effect of PC on the performance of FSO communications is also examined in this study. We evaluated the system’s performance with two types of snow, wet snow and dry snow, as well as with different rain regions. Results show that PC improves the BER of the FSO system;a high rate of improvement is found for wet snow and rain. PC has almost no effect with dry snow because of the high attenuation and the limitations on transmitted power. The BER for 16-PPM is better than that for OOK modulation.

The Utility of 1000 - 500 mb Thickness and Weather Type as a Rain-Snow Divide: A 30-Year Study at Albany, NY

Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce rain or mixed precipitation. It is beneficial for meteorologists to better understand the commonly used 5400 and 1300 GPM line to better forecast rain versus snow events. Other studies have looked into the use of the 5400 GPM (540 dm) line but none have assessed the validity of this boundary with respect to weather type characterization at Albany. This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events. The mean daily 500, 850, 925 and 1000 mb heights and weather type frequency of the Spatial Synoptic Classification between November and March of 1980 - 2012 are analyzed. Results indicate that the standard vertical boundaries are inaccurate indicators of a rain versus snow event in Albany. More reasonable rain-snow cut offs for the 1000 - 500 and 1000 - 850 mb thicknesses are 5222 and 1262 GPM. For the 1000 - 925 mb level, 606 GPM is a helpful aid of identifying the rain-snow boundary. Further scrutinizing by weather type indicates that the rain-snow boundary also varies depending on what air mass/weather type is present on a given day. For instance, when the most prominent weather type is observed over Albany (Dry Polar), at the 1000 - 850 mb and 1000 - 500 mb layers, a boundary of 1242 GPM and 5152 GPM is found to be most representative. Results indicate only for the rarest of winter weather types observed over Albany, Moist Tropical, are the standard cut offs useful. Determining the reliability of this precipitation indicator at a specific station, like Albany, could enable meteorologists in other regions of the country to draw parallels between weather type, precipitation, and thickness in their forecast zones.

湖北省持续低温雨雪过程评估与分析

气候变化背景下,极端持续低温雨雪过程时有发生,给社会生活带来诸多不利影响,为了进一步评估持续低温雨雪天气,对湖北省单站持续低温雨雪过程的评估指标进行了修订,同时建立区域性持续低温雨雪过程评估模型,并将修订后的评估指标应用于湖北省单站及区域性持续低温雨雪过程的梳理及分析。结果表明:(1)湖北省最严重的5次区域性持续低温雨雪过程分别出现在1954、1969、1977、1984和2008年,最严重的是1954年12月24日-1955年1月18日的过程,其次是2008年1月12日-2008年2月5日的过程。(2)湖北省区域性持续低温雨雪过程的易发区主要集中在鄂西的高山或半高山地区、江汉平原荆州一带、汉江河谷一带、鄂东南南部低山平原地区以及鄂东北山脉的缺口处。(3)气候变暖的背景下,湖北省单站和区域性持续低温雨雪过程均是在20世纪80年代前发生次数多,90年代后属于减少的阶段,但其强度更趋极端。

2024年2月17—23日中国大范围强寒潮雨雪冰冻强对流过程涉及的若干问题

2024年2月中下旬我国出现一次多灾种高影响天气过程。这是一次几十年一遇的过程,出现了大范围强寒潮雨雪冰冻天气并伴随强对流发生,涉及到强寒潮、沙尘、降雨、降雪、冻雨,以及强对流和伴随的大冰雹和雷暴大风,多种高影响天气在一次过程中都有所呈现,其过程之复杂异常罕见。本文针对此次过程中值得深入探讨的问题、高影响天气发生发展可能机理、相应的预报挑战等进行简要梳理,为后续对此次过程的细致和深入分析研究做一个引子。

基于CAMM和CLDAS的黄淮海冬小麦成熟期连阴雨时空特征

利用黄淮海地区2008—2023年的CLDAS数据和同期65个农业气象观测站的冬小麦花期、成熟期观测数据,订正机理性中国农业气象模式(CAMM)中发育模块(RAM)的参数,评估模式对冬小麦成熟期的模拟精度,而后重构格点化的历年成熟期日期,统计成熟期前6天后9天共16天的降水量和雨日数,随后基于连阴雨指标,研究连阴雨的时空分布特征。结果表明:(1)RAM模式对冬小麦成熟期具有较好的模拟能力,各站RMSE平均值为2.28±0.46 d,模拟值与实测值的R2为0.915。(2)黄淮海地区冬小麦成熟期降水量和雨日数均呈南北两端高中间低的空间分布格局,区域平均降水量为8.8~84.6 mm,平均值为31.9 mm,雨日数为1.0~9.1天,平均值为5.4天。(3)2008—2023年连阴雨灾害波动较大,其中2009、2013、2018和2023年较为严重,大致呈4~5年发生一次的周期性规律,且灾情呈加重的趋势。(4)连阴雨灾害在黄淮海地区北部很少发生,河北和山东交界处偶发,灾害高发重发区主要集中在河南省,尤其是郑州以南的驻马店和信阳一带最为严重,发生频率约为5年一遇,持续天数多在9天以上。

我国南方西南和中东部区域两次持续性低温雨雪过程与关键环流系统的关系研究

利用NCEP再分析资料和国家气象信息中心提供的753站逐日气温和降水资料,对比分析了我国南方西南和中东部区域两次持续10 d以上的低温雨雪过程,结果表明:(1)两次过程中欧亚大陆中高纬东亚大槽均加深,但环流形势有差异。西南过程呈现"北高南低"形势,关键脊区在贝加尔湖,而中东部区域过程"北高南低"和"西高东低"形势共存,关键脊区从乌拉尔山延伸至贝加尔湖。两次过程异常的环流与北大西洋向东传播的波列有关。(2)西南过程关键脊区提前过程3 d发展并东移至贝加尔湖,形成稳定形势;而中东部区域过程关键脊区提前过程一周发展,在开始日达最强。两次过程均伴随蒙古高压东移南压使地面降温,500 hPa关键脊区超前蒙古高压2 d变化。西南过程降温主要受到冷平流和绝热冷却影响,而中东部区域过程主要受到冷平流的影响。(3)西南过程水汽来自孟加拉湾,只受南支槽支配。中东部区域过程水汽来自孟加拉湾、南海和西太平洋,由南支槽和西太平副热带高压的共同影响。两次过程水汽正收支主要来自南边界。

后冬奥时代大学生冰雪运动持续参与行为的促进模型研究

北京冬奥会为我国冰雪运动的开展奠定了良好的社会基础,深入探索冰雪运动持续参与行为的促进机制有助于推动冰雪运动长期发展。以社会生态理论模型为框架,以大学生对持续参与冰雪运动的态度评价为研究对象,运用建模法、问卷调查法和数理统计法,构建大学生冰雪运动持续参与行为促进机制的AMOS结构方程模型,探讨自我效能对于大学生冰雪运动持续参与行为的中介效应。得出结论:行为动机对大学生冰雪运动持续参与行为影响不显著,且自我效能在其路径中中介效应不显著;知识技能、社会环境对大学生冰雪运动持续参与行为具有显著影响,且自我效能在其路径中存在显著中介效应,效应值分别为0.151及0.258。建议在后冬奥时代持续强化政策引领,营造良好社会氛围,开展冰雪运动科普宣传以及公益指导,以期完善冰雪运动参与生态。

西南地区一次典型冰冻雨雪复合极端灾害天气事件的环流特征及降水相态差异分析

在全球变暖气候背景下,复合型极端灾害天气事件频发。2008年以来我国南方冬季频发的雨雪冰冻,就是一种典型的复合型致灾极端天气事件。因此,本研究分析了西南地区一次典型大雪冻雨复合天气事件的大雪与冻雨期环流特征及降水相态差异,揭示了二者的关联特征。冻雨发生在贵州境内的云贵准静止锋锋面强斜压环境中,降雪主要发生在四川北部,位于静止锋以北的冷区。降雪区和冻雨区的垂直环流存在显著差异:降雪区以上升运动为主,温度基本随高度递减;冻雨区大气中低层存在逆温层,导致温度层结出现冷—暖—冷的分布,垂直运动呈两层环流模态,低层的上升运动受到中层下沉运动抑制,强上升运动不易发展。借助可综合表征环流特征和水汽相变的广义湿位涡理论,分别诊断大雪和冻雨发生发展时期的广义湿位涡分布特点,发现其斜压项的异常能更好体现准静止锋附近的大气斜压性,也可指示出大雪冻雨降水的落区及变化,可作为大雪冻雨区的动力识别特征量之一。通过气压扰动方程的计算分析,表明向下的扰动气压梯度力与浮力的平衡差异,是降雪与冻雨垂直环流特征差异的主要原因。本研究从环流特征入手开展雨雪冰冻复合极端灾害天气分析,可为复合降水相态预报和发电企业电力运行保障提供参考。

我国南方两次低温雨雪天气成因对比分析

2018年末和2021年末我国南方分别发生了一次大范围的低温雨雪天气,通过对比分析两次低温雨雪天气成因,结果表明:两次过程期间,对流层中层中高纬阻塞流场显著,阻高位于贝加尔湖西侧,脊前偏北气流在下游横槽后部堆积,使得西伯利亚高压强度增强。东传的Rossby波在阻高区域发生能量频散,利于阻高减弱、崩溃,横槽转竖引导槽后冷空气南下,导致地面强烈降温,同时在西伯利亚高压东侧和南侧,低频风温度平流是造成强降温的主要原因。低纬南支槽活跃,向北的暖湿空气与中高纬南下的冷空气汇合,造成我国南方大范围的低温雨雪、冻雨天气。与2018年过程相比,2021年过程持续时间较短,降水范围小,关键区域降温幅度更大,是因为2021年过程期间Rossby波能量频散更快,阻高维持时间较短,冷空气从中高纬地区直接南下侵袭我国,而2018年冷空气在贝加尔湖附近发生堆积、西折,向南渗透时势力减弱。

Analysis of A Heavy Snow Process in Liaoning Province in 2009

Based on the conventional meteorological data and 4 times daily NCEP reanalysis data,the causes of rain changing snowstorm in Liaoning during February 12-13 of 2009 were discussed.The low-level jet conditions,temperature conditions and coupling mechanism of water vapor and dynamics of heavy snow were diagnosed and analyzed.The low-level jet provided abundant water vapor for this process.The convergence at low level,divergence in the upper troposphere and strong ascend movement provided dynamic conditions for the snowstorm.The wedging of cold air was the chief cause of rain changing snow.The strongprecipitation area corresponded to the moist potential vorticity well.

2023年河南冬小麦成熟期连阴雨强度综合评估

为构建适合河南小麦成熟期连阴雨灾害强度指数,并明确河南小麦受连阴雨影响的敏感时段,利用河南省111个测站1961—2023年气象资料及有关农业气象观测站数据,分析了2023年河南小麦连阴雨受灾及相关发育期情况,以及主要气象因子和连阴雨灾害调查数据的相关性,并根据前人研究成果,结合河南实际,构建了3种小麦成熟期连阴雨灾害强度指数。结果表明:(1)小麦开花后35天以上,是小麦籽粒品质受连阴雨天气影响最敏感的时段。(2)成熟期连阴雨灾害强度指数L2和L3均能够很好地吻合2023年河南小麦因连阴雨灾害的受灾情况,特别是L3兼具实用性和准确性,能够满足业务服务需要。(3)2023年河南省小麦成熟期连阴雨灾害强度指数L2、L3空间分布都表现为南高北低,全省平均L2为0.81,L3为0.32,均为1961年以来的最高值。

2024年2月我国两次雨雪冰冻过程中闪电活动特征对比分析

2024年1月31日-2月5日和2月18-25日(以下分别简称为"0131"和0218"过程)我国南方遭遇两次雨雪冰冻天气,并伴随密集的闪电发生。利用三维闪电定位数据、CLDAS-V2.0降水产品和Himawari-9号卫星红外云图资料,对比分析两次雨雪冰冻天气背景下的地闪时空分布、地闪回击数和雷电流累计概率分布特征,并研究了地闪与降水量及卫星黑体辐射亮温(TBB)间的关系。结果表明:(1)两次过程中共监测到地闪数13万余次,正、负地闪分别为2万和11万余次;两次过程的地闪均具有夜发性,正地闪较总地闪和负地闪峰值滞后约1~2h。两次过程中正地闪产生大电流的概率大于负地闪。(2)"0131"过程中地闪密度大值区出现在贵州南部及贵州、重庆、湖北三省交界处;"0218"过程中地闪密度大值区出现在湖北东部、江西北部、安徽、江苏和浙江大部。(3)"0131"过程中降水量和地闪的时空分布不一致,降水量峰值集中在白天,降水集中在湖南东南部、江西、安徽和江苏南部、浙江和福建大部;而"0218"过程中降水量和地闪的时空分布较一致,地闪出现的峰值较降水量峰值延迟2h。(4)两次过程中地闪的分布均很好地指示了对流区。地闪主要分布在对流云团发展方向的尾部且偏南处TBB变化梯度大的区域;对流合并会导致合并处地闪频数的跃增;对流发展最旺盛的冷云核心区几乎没有地闪发生。两次过程地闪密度随着TBB的增大呈现先增大后减小的变化特征。

江西双季早稻播种育秧期低温连阴雨灾害分析

基于江西省82个国家气象站点1961—2023年的逐日气象资料,研究了江西省双季早稻播种育秧期低温连阴雨气象灾害风险,结果表明:1961—2023年江西省早稻播种育秧期平均气温以0.379℃/10 a的速度升高,日照时数呈先减后增趋势;不同等级低温连阴雨灾害发生天数均呈先增后减趋势,高频区发生在1980s、1990s,2000年以后则发生较少;2001—2023年的整体发生频率比1961—2000年的低,但高频区向赣西北转移,赣东北和赣中有所减弱;综合风险等级显示,高风险区主要分布在抚州市、吉安市、萍乡市、宜春市、南昌市和九江市,中风险区主要包括赣南北部和赣东北地区,低风险区以赣南南部地区为主。