亚洲中低纬环流特征与浙北丰枯梅雨的关系

本文着重讨论了6月500hPa亚洲中低纬环流特征与浙北丰枯梅雨的关系以及以3月环流特征量为主体建立丰枯梅雨的长期预报的问题。分析发现:6月500hPa环流变高场出现“X”型和“V”型是丰梅特征,出现“M”型是枯梅特征,梅雨丰枯环流特征对比鲜明。用3月环流特征量为主体作梅雨丰枯的长期预报效果良好。     

长江中下游丰枯梅雨环流配置及其前期演变特征

本文着重讨论了长江中下游地面(3月)气温与长江中下游丰枯梅雨环流系统的关系,以及丰枯梅雨的前期环流演变特征问题.分析发现:3月份是长江中下游地区季节转换的关键时期,长江中下游3月近地面气温(T_3)的变化,对6月环流特征、季节转换、梅雨丰枯等反映最敏感,是个较好的预报特征量.在前期环流演变中发现极涡、东亚槽、副高等对梅雨的丰枯亦有较好的预兆反映.     

南召县近50年降水变化特征分析

利用南召县19582007年降水资料,对降水量的季节分配、年际变化、丰枯变化趋势以及频率特征进行了分析,结果表明:68.52%的降水量集中在69月;年降水量呈递增趋势,趋向率为8.15 mm/10a;夏季是影响年降水量变化的主要因素;丰、枯年变化均匀.     

陕西省径流丰枯变化及其资料系列代表性分析

选用陕西15处水文站长系列径流资料,应用差积曲线分析径流的周期性丰枯变化;采用径流连丰连枯统计及其丰枯水年所占比例,分析径流的丰枯变化规律;通过对径流长短系列相对误差对比及不同频率年径流分析,评价径流资料系列的代表性。结果表明:1956—2000年系列丰水期、枯水期长度基本相同,也基本包括了完整的丰枯周期,是最具有代表性的水文短系列。     

青南高原大气降水变化规律及其对黄河上游地区水资源的影响

利用1959～1997年黄河上游地区降水、流量资料,用EOF、REOF等数理统计方法,分析了黄河上游地区降水与流量之间的关系,并对黄河上游地区的水资源进行了估算。分析得出：龙羊峡年入库流量的丰枯主要与黄河上游地区的年降水量有关,春季流量的丰枯主要与上一年秋季的流量、春季的降水量有关,夏、秋季流量的丰枯主要与同期的降水量有关。     

环流系统低频变化与黄河上游流量的关系

一、引言西北电网覆盖了陕、甘、宁、青四省,对四省的工农业生产和人民生活有很大影响。在西北电网中一半依靠黄河水力发电,而黄河上游的流量年际变化较大,因此,其流量丰、枯的预报对电力部门的决策起着重要的参考作用。目前,对黄河上游流量丰、枯的预报方法有多种。如纯统计方法、利用地温预报、利用平流层特征预报等等,但预     

唐乃亥流量年变程分型与地温场的相关分析

１９５６－１９９４年唐乃亥流量年变程可分为丰、平、枯等前枯后丰（平）、前丰（平）后枯两种类型，黄河上游主产流区春，夏季平均３．２ｍ地温距平场可分为暖涡，暖涡偏东，暖涡偏西，暖涡减弱消失，均温场和冷涡六种类型。分析发现，地温场型与流量年变程分之间有较好的相关性，以此可以对唐乃亥水库年流量进行初步的定性预报。     

水文模型参数选取对模拟径流的年际年内分布影响评估

使用水文模型进行气候变化对水文水资源的影响评估时,通常假定水文模型参数在历史和未来时期是固定不变的,并未区分水文模型参数受环境变化的影响差异。针对该问题,采用集对分析法以年降水量和年径流量为依据进行丰、平、枯水年的划分,利用SWAT分布式水文模型分别率定不同水平年的模型参数,探究月尺度模型参数的非稳定性对年际年内径流的影响。研究结果表明,分别以年降水量和年径流量划分丰、平、枯水年时,1961—2010年这50年中有70%的年份为同枯或同丰。如果仅选择某一水平年（丰、平、枯）背景下的资料进行建模,将导致模拟精度较丰、平、枯整体考虑时降低,且是以偏大为主。用同样的水文资料与代表不同环境条件下模型参数推求径流过程时,从年际变化角度看,使用某一水平年（丰、平、枯）背景下的参数,总体上模拟径流偏湿润,使得丰水年比重增加、枯水年比重降低;从年内分布看,受不同水平年参数影响,径流的集中度减小,年内分配更加均匀,径流集中期延迟。本研究可为提高未来变化环境下水文模拟可靠性提供参考,对于应对变化环境下的水资源适应性管理具有重要意义。     

乐山水稻赤枯病的气候分析及服务对策初探

采用乐山市气象台站资料,参考相关研究成果,对比分析了乐山市2005、2010年水稻发生赤枯病的气候特征,提出了相应的为农服务对策:(1)根据乐山中、长期天气趋势预报、对春季和初夏可能发生寡照、低温、连阴雨天气的年份,建议农业生产上提高水稻移栽基本苗,以减少因分蘖不足造成减产。(2)二是防,在培育壮秧的基础上,应针对易发生水稻赤枯病的田块着重改善秧苗的生长环境。(3)三是治,水稻栽后10~15天,如秧苗难返青,出现发生赤枯病特征时,应用科学施肥和相应病药物进行防治。      

气候变化对南水北调中线工程水源区与受水区降水丰枯遭遇的影响

运用Copula方法构建南水北调中线工程水源区与各受水区汛期、非汛期及全年降水量的联合分布,并基于IPCC第四次评估报告中大气环流模式的降水结果,用所建模型探讨了气候变化情景下,南水北调中线工程水源区与受水区丰枯遭遇的变化。结果表明,从汛期来看,汉唐（汉江水源区-唐白河受水区）和汉海（汉江水源区-海河受水区）遭遇的丰枯同步频率呈增加趋势,不同排放情景下分别增加3.34%~16.48%和2.56%~8.21%,而汉黄（汉江水源区-黄河受水区）遭遇的丰枯同步频率呈减小趋势,不同排放情景下减小-1.97%~9.57%;从非汛期来看,汉唐和汉海遭遇的丰枯同步频率呈减小趋势,不同排放情景下分别减小-0.21%~9.42%和0.99%~5.54%,而汉黄遭遇的丰枯同步频率呈增加趋势,不同排放情景下增加1.79%~13.28%;从全年尺度来看,汉唐、汉黄和汉海遭遇的丰枯同步频率基本均呈减小趋势,不同排放情境下分别减小-2.88%~10.97%、-1.28%~5.05%和-2.33%~7.01%。     

The Structure of a Typical Mei-yu Front Identified by the Equivalent Temperature

In mainland China, the summer monsoon rainy band is referred to as the mei-yu precipitation front, which extends northward from South China to the Yangtze River, Huaihe River, and Yellow River, depending on the season. This paper describes the structure of the mei-yu front associated with a persistent heavy rainfall event that occurred in the summer of 2007. The mei-yu front occurs when the subtropical oceanic warm, moist air mass and the extra tropical continental dry, cold air mass converge on the lee side of the Tibetan Plateau. The authors defined the equivalent temperature using two terms of dry-air temperature and the specific humidity and calculated its horizontal gradient to indicate the mei-yu front. The vertical structure of the mei-yu front and the moist thermal winds surrounding it were examined based on the equivalent temperature.     

Diagnostic study on the structural characteristics of a typical mei-yu front system and its maintenance mechanism

In this paper, a typical mei-yu front process with heavy rainfall from June 12 to 15 in 1998 is analyzed. The results show that the mei-yu front is a front system which consists of an iso-θe dense area with strong horizontal gradient, a deep-convective cloud tower band, a passageway transporting warm and moist air flow from the summer monsoon surge in the mid and low levels to the south of the mei-yu front,and a migrating synoptic scale trough to the north of the mei-yu front, which transports cold and dry air southward in the mid and upper levels. The maintenance of the mei-yu front is realized by: (1) is a positive feedback between the moist physical process enhancing frontogenesis and the development of the strong convective system in front of the mei-yu front; (2) the sustaining system to the north of the mei-yu front which is a migrating synoptic scale trough transporting cold and dry air to the mei-yu front and positive vorticity to the mesoscale system in front of the mei-yu front.     

The Thermodynamic and Dynamical Features of Double Front Structures During 21-31 July 1998 in China

1. IntroductionDuring June and July, from the mid-lower reachesof the Yangtze River basin in China to southern Japan,a precipitation zone with intensive torrential rain ap-pears and lasts for two to three weeks. This phe-nomenon is called the "mei-yu" in …     

2000年江淮梅雨的分析和中期预报着眼点

20 0 0年江淮梅雨期的环流特征 ,在其入梅时表现为 :西太平洋副热带高压 1 2 0°E脊线的季节性北移具有明显的两周振荡周期 ;南亚高压脊线北移至 2 5°N和印度季风的爆发——加尔各答稳定西风的结束均能很好地预示江淮梅雨的开始。在出梅时 :亚洲地区地转风急流轴入梅后持续北移到 47.5°N,5 0°N稳定的超长波脊先于西太平洋副高调整 ,梅雨期后期在菲律宾东部洋面生成的 3号台风的北上 ,均对出梅的环流调整起到了显著的作用。     

The Forced Secondary Circulation of the Mei-yu Front

Using National Centers for Environmental Prediction reanalysis data for the period 28 June to 12 July during 2001 to2013, the secondary circulation(SC) associated with the mei-yu front was quantitatively diagnosed by numerically solving a primitive version of the Sawyer-Eliassen equation. Results demonstrate that a direct SC exists near the mei-yu front zone during mid-summer and the synoptic-scale geostrophic deformations are the main factors determining SC structures. About94% of the sinking strength and 61% of the ascending strength in the SC are induced by the geostrophic deformations.Other terms, such as diabatic heating, ageostrophic dynamical forcing, and frictional forcing, mainly influence the fine flow pattern of the SC. The forced SC produces a frontogenesis area tilting to the north with altitude. Further diagnosis clarifies the positive feedback involving the geostrophic shear forcing and vorticity frontogenesis in the upper-level mei-yu front zone. Furthermore, statistical results indicate that all 34 deep convection cases that occurred in the warm region of the meiyu front over the period 2004-2013 experienced high-level frontogenesis associated with along-jet cold advection. The cyclonic shear forcing "moved" the monsoon SC's subsidence branch to the warm side of the mei-yu front and caused the subsidence branch to extend downwards to the lower troposphere, conducive to the initiation of deep convection in the warm region of the mei-yu front.     

Interdecadal Modulation of the Influence of La Nina Events on Mei-yu Rainfall over the Yangtze River Valley

The aim of this study was to investigate changes in the relationship between mei-yu rainfall over East China and La Nin a events in the late 1970s,a period concurrent with the Pacific climate shift,using meiyu rainfall data and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis.This relationship was modulated by the climate shift:Before the 1977/1978 climate shift and after the 1992/1993 climate shift,mei-yu rainfall levels were above normal in most La Nin a years,whereas during the period 1979-1991,mei-yu rainfall was usually below normal levels in La Nin a years.Both composite analyses and results from an atmospheric general circulation model show remarkable detail in terms of La Nin a’s impacts on mei-yu rainfall in the late 1970s due to the change in the mean climatic state over the tropical Pacific.After the late 1970s,the tropical Pacific SSTs were warmer,and the mean state of low-level anticyclone circulation over the western North Pacific (WNP) weakened.Superimposed on La Nin a-related cyclonic anomaly over the WNP,anticyclonic circulation weakened.Prior to the late 1970s,the mean state of low-level anticyclone circulation over the WNP was stronger and was less affected by La Nin a-related anomalous cyclones.Anticyclone circulation may have brought moisture to the Yangtze River valley,leading to above-normal rainfall.     

梅雨期长江流域两类气旋性扰动和暴雨

文章通过分析长江中游大暴雨和特大暴雨个例，研究了两类梅雨涡的产生、演变及与之联系的暴雨发展过程。一类是移到长江中游的典型西南涡，其斜压结构出现在副热带暖环境中，是在这个系统本身发生、发展的动力-热力过程中产生的；另一类是串行于梅雨切变线上的小型正涡度扰动，其演变过程更复杂一些。文章结合这两次个例对作者过去的一些结果作了验证、充实和归纳。并论及复杂暴雨发展过程的一些预报难点。     

Mesoscale predictability of mei-yu heavy rainfall

Recently reported results indicate that small amplitude and small scale initial errors grow rapidly and subsequently contaminate short-term deterministic mesoscale forecasts. This rapid error growth is dependent on not only moist convection but also the flow regime. In this study, the mesoscale predictability and error growth of mei-yu heavy rainfall is investigated by simulating a particular precipitation event along the mei-yu front on 4-6 July 2003 in eastern China. Due to the multi-scale character of th...     

Atmospheric Rivers and Mei-yu Rainfall in China:A Case Study of Summer 2020※

Atmospheric rivers (ARs) are long, narrow, and transient filaments of strong horizontal water vapor transport that can lead to extreme precipitation. To investigate the relationship between ARs and mei-yu rainfall in China, the mei-yu season of 2020 in the Yangtze-Huaihe River basin is taken as an example. An adjusted AR-detection algorithm is applied on integrated water vapor transport (IVT) of the ERA5 reanalysis. The JRA-55 reanalysis and the data from Integrated Multi-satellite Retrievals for GPM (IMERG) are also utilized to study the impacts of ARs on mei-yu rainfall in 2020. The results reveal that ARs in East Asia have an average length of 5400 km, a width of 600 km, a length/width ratio of 9.3, and a northeastward orientation of 30°. ARs are modulated by the western North Pacific subtropical high. The IVT core is located at the south side of low pressure systems, moving eastward with a speed of 10° d^?1. For the cross sections of ARs in the Yangtze-Huaihe River basin, 75% of the total flux is concentrated below 4 km with low-level jets near AR cores. Moreover, ARs occur mainly in the mei-yu period with a frequency of 20%–60%. The intensity of AR-related precipitation is 6–12 times that of AR-unrelated precipitation, and AR-related precipitation contributes about 50%–80% to total mei-yu precipitation. As shown in this case study of summer 2020, ARs are an essential part of the mei-yu system and have great impacts on mei-yu rainfall. Thus, ARs should receive more attention in research and weather forecast practices.     

Rain-based factors of high agricultural impacts over Senegal. Part I: integration of local to sub-regional trends and variability

The evolution of seasonal cycle and interannual rainfall, the number of rainy days and daily rainfall types, dry spells frequency of occurrence, onset/cessation/length of rainy season, sowing dates, and the duration of the cropping period, are investigated at local (individual sites) and sub-regional scales (four different rainfall zones) using daily records of station data (83 sites) over Senegal. In the limits of a case study, these analyses complement and update previous studies conducted in the extreme Western Sahel (11?C16° N and 20° W?C10° E). The results unveil noticeable evolution of some of these rain-based factors in the recent periods as compared to the previous dry years. In the regions recording less than 800?mm/year (Sudan and Sahel sub-regions), the positive and statistically significant trends of rainfall amount are associated with new features of increasing frequency of short dry spell category, increasing number of some classes of extreme daily rainfall amounts and shifts in the peak number of rainy days. At sub-regional scales, the starting years (or change points) the magnitude and the signs of the new trends are unevenly distributed in the period post-1990. Earlier and higher amplitude changes are found at local scales and not less than one third of the sites in each sub-regional network are significantly affected. The extreme Southern sub-region exhibits no significant changes. Statistically significant trends are not observed on daily rain records ??10?mm, onset/cessation dates, successful sowing dates, rainy season length, cropping period, medium and extreme dry spell categories. Rather, some of these factors such as the successful sowing date and the cropping season length exhibit significant variability. The onset (cessation) dates of the rainy season are followed (preceded) by extreme dry spell episodes. In the perspectives of climate impact assessments on the local agriculture a sub-regional periodic synopsis of the major rain-based factors of interest to agricultural applications are provided at the end the paper. They document some important internal variability patterns to reckon with in a multi-decadal work over the 1950?C2008 period for this region.