Changes in daily and monthly rainfall in the Middle Yellow River,China

Highly concentrated precipitation, where a large percentage of annual precipitation occurs over a few days, may include a high risk of flooding and severe soil erosion. Thus, areas with severe erosion such as the Loess Plateau in China are particularly vulnerable to highly concentrated precipitation events due to climate change. In this study, we investigated spatial and temporal patterns in the concentration of rainfall in the Middle Yellow River (MYR) from the last 56 years (1958–2013). We used daily and monthly precipitation data from 26 meteorological stations in the study area to calculate the precipitation concentration index (PCI) and the concentration index (CI). The southern and northern parts of the MYR were characterized by a lower CI with a decreasing trend, while the middle parts had a higher CI with an increasing trend. High PCI values occurred in the southern MYR, while lower PCIs with a more homogenous rainfall distribution were found mainly in the northern parts of the MYR. The annual PCI and CI exhibited positive trends at most stations, although only a minority of stations had significant trends (P < 0.05). At seasonal scales, CI exhibited significantly increasing trends in winter at most stations, while a few stations had significant trends in the other three seasons. These findings provide important reference information to facilitate ecological restoration and farming operations in the study region.     

中国东部降水特征及其与印度、北美降水的关系

本文应用了10年平均的旬、候和日平均降水资料,研究了中国东部4—9月降水分布特点。结果指出,华南、华中4—9月候降水量高值中心区存在准一个月的振荡现象,东北、华北4—9月的日平均降水量低值中心区具有准一周的振荡现象。而在长江流域,4—9月的旬降水量高值中心区以不连续跳跃方式在东西方向上传播,高值中心区“重现”的准周期约为一个月左右。 同时,本文也应用了1957—1985年月平均降水资料,计算了中国东部和印度中部、北美西部同期降水相关系数。结果指出,华南、华中5—7月降水相关场的分布作反时针旋转。在6月梅雨季节,长江中下游地区是降水正相关区,而华南是负相关区。在6—8月,中国东部和北美西部的月平均降水量之间存在稳定的负相关关系。     

有关暴雨分析预报的一些问题

近二十年来,大气科学发展很快。为了使我国广大气象工作者对大气科学各个领域的现状和近期内的发展趋势有所了介,本刊从今年第一期起开辟专栏,就大气科学中某一领域或菜一重要专题的任务、目前水平、存在问题、动向等方面作比较全面的介绍和评述,并开展讨论。希望读者踊跃撰写稿件,提出意见和要求,以不断改进工作,把专栏办得更加生动活泼。     

Surface and upper air temperatures over India in relation to monsoon rainfall

Summary The relationship between the all-India summer monsoon rainfall and surface/upper air (850, 700, 500 and 200 mb levels) temperatures over the Indian region and its spatial and temporal characteristics have been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India and subdivisional summer monsoon rainfall and various seasonal air temperatures at 73 surface observatories and 9 radiosonde stations (1951–1980) have been used in the analysis. The Correlation Coefficients (CCs) between all-India monsoon rainfall and seasonal surface air temperatures with different lags relative to the monsoon season indicate a systematic relationship.The CCs between the monsoon rainfall and surface-air temperature of the preceding MAM (pre-monsoon spring) season are positive over many parts of India and highly significant over central and northwestern regions. The average surface air temperature of six stations i.e., Jodhpur, Ahmedabad, Bombay, Indore, Sagar and Akola in this region (Western Central India, WCI) showed a highly significant CC of 0.60 during the period 1951–1980. This relationship is also found to be consistently significant for the period from 1950 to present, though decreasing in magnitude after 1975. WCI MAM surface air temperature has shown significant CCs with the monsoon rainfall over eleven sub-divisions mainly in northwestern India, i.e., north of 15 °N and west of 80 °E.Upper air temperatures of the MAM season at almost all the stations and all levels considered show positive CCs with the subsequent monsoon rainfall. These correlations are significant at some central and north Indian stations for the lower and middle tropospheric temperatures.The simple regression equation developed for the period 1951–1980 isy = – 183.20 + 8.83x, wherey is the all-India monsoon rainfall in cm andx is the WCI average surface air temperature of MAM season in °C. This equation is significant at 0.1% level. The suitability of this parameter for inclusion in a predictive regression model along with five other global and regional parameters has been discussed. Multiple regression analysis for the long-range prediction of monsoon rainfall, using several combinations of these parameters indicates that the improvement of predictive skill considerably depends upon the selection of the predictors.With 9 Figures     

中东急流的季节变化特征及其与热力影响的关系

采用多年平均的NCEP/NCAR再分析资料,研究了中东急流强度和位置的季节变化特征及其与南北温差的关系。结果表明：1）中东地区上空西风带的强度和位置的垂直结构均具有明显的季节变化特征,冬、春季西风中心强度较大,夏、秋季西风中心强度较小;600hPa以上,冬、春季西风中心位置偏南,夏、秋季西风中心位置偏北。各季节的所有高度上,200hPa的西风中心风速最大。2）中东急流的强度和位置具有明显的季节变化特征。冬半年（11月—次年4月）中东急流较强,南北位置基本维持在27.5°N附近;夏半年（5—10月）中东急流较弱,5月后急流中心位置偏北,6—9月位于40°N附近,10月南撤至32.5°N。3）中东急流的强度和南北位置变化与500～200hPa整层平均的南北温差的对应关系很好,根据热成风原理,认为南北温差的季节性变化对中东急流的强度和南北位置变化具有重要影响。     

A note on the intercornparison between monthly mean radiance equivalent and rocketsonde temperatures

Summary Rocketsonde monthly mean temperature structure of the stratosphere is compared with that derived from Nimbus-5 SCR radiance measurements for the solsticial months in 1973 and for the equinoctial months in 1974. The comparison shows good agreement only at pressure levels between about 5 mb and 15 mb (upper-middle stratosphere). The satellite minus rocket bias is highest at the stratopause region possibly due to the constraints applied in retrieving the radiance equivalent temperatures.

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Über einen Vergleich zwischen Monatsmittelwerten von strahlungsäquivalenten Temperaturen und Temperaturen von Raketensonden

Zusammenfassung Die mit Raketensonden gewonnene mittlere monatliche Temperaturstruktur der Stratosphäre wird mit der aus Strahlungsmessungen von Nimbus-5 SCR abgeleiteten für die Monate Juni und Dezember 1973 und für März und September 1974 verglichen. Der Vergleich zeigt eine gute Übereinstimmung nur in den Druckniveaus zwischen 5 mb und 15 mb, das ist in der oberen mittleren Stratosphäre. Die Differenz zwischen den mit Satelliten und den mit Raketensonden gewonnenen Temperaturen ist am größten in der Stratopausenregion, möglicherweise zufolge der zur Ableitung der strahlungsäquivalenten Temperaturen angewendeten Methode.

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With 2 Figures     

主汛期相当暴雨日数与降水量的关系对暴雨预报的指导意义

通过研究黔东南州及其6个代表站近40年6－8月主汛期降水量及各月降雨量与相当暴雨日数的关系，结果表明二者之间有很好的线性相关性，并建立了回归方程。在此基础上，依据长期降水趋势预报，初步探讨了相当暴雨日数在短期预报中的强降水预报的指导意义。     

Northern East Asian low and its impact on the interannual variation of East Asian summer rainfall

The strength of the East Asian summer monsoon and associated rainfall has been linked to the western North Pacific subtropical high (WNPSH) and the lower-tropospheric low pressure system over continental East Asia (EA). In contrast to the large number of studies devoted to the WNPSH, little is known about the variability of the East Asian continental low. The present study delineates the East Asian continental low using 850-hPa geopotential height. Since the low is centered over northern EA (NEA), we refer to it as the NEA low (NEAL). We show that the intensity of the NEAL has large interannual variation, with a dominant period of 2–4 years. An enhanced NEAL exhibits a barotropic structure throughout the whole troposphere, which accelerates the summer-mean upper-tropospheric westerly jet and lower-tropospheric monsoon westerly to its south. We carefully identify the anomalous NEAL-induced rainfall anomalies by removal of the tropical heating effects. An enhanced NEAL not only increases rainfall locally in northern Northeast China, but also shifts the East Asian subtropical front northward, causing above-normal rainfall extending eastward from the Huai River valley across central-northern Japan and below-normal rainfall in South China. The northward shift of the East Asian subtropical front is attributed to the following processes without change in the WNPSH: an enhanced NEAL increases meridional pressure gradients and the monsoon westerly along the East Asian subtropical front, which in turn induces a cyclonic shear vorticity anomaly to its northern side. The associated Ekman pumping induces moisture flux convergence that shifts the East Asian subtropical front northward. In addition, the frequent occurrence of synoptic cut-off lows is found to be associated with an enhanced NEAL. Wave activity analysis indicates that the interannual intensity change of the NEAL is significantly associated with the extratropical Polar Eurasian teleconnection, in addition to the forcing of the tropical WNP heating.     

Long memory, seasonality and time trends in the average monthly temperatures in Alaska

This paper deals with the analysis of monthly temperatures in 19 meteorological stations in Alaska during the last 50?years. For this purpose, we employ a procedure that permits us to examine in a single framework several features observed in climatological time series such as time trends, long-range persistence and seasonality. The results indicate that the highest degrees of persistence are observed in stations located in the southern regions and seasonality appears as a major issue in all cases. Removing the seasonal structure and focussing on the anomalies with respect to the monthly means, the time trend coefficients appear significantly positive in the majority of the cases, implying that temperatures have increased during the last 50?years.     

Investigating the correlation between monthly average temperatures and tithe proxy data from the Low Countries

The likely intensification of extreme droughts from climate change in many regions across the United States has increased interest amongst researchers and water managers to understand not only the magnitude of drought impacts and their consequences on water resources, but also what they can do to prevent, respond to, and adapt to these impacts. Building and mobilizing ‘adaptive capacity’ can help in this pursuit. Researchers anticipate that drought preparedness measures will increase adaptive capacity, but there has been minimal testing of this and other assumptions about the governance and institutional determinants of adaptive capacity. This paper draws from recent extreme droughts in Arizona and Georgia to empirically assess adaptive capacity across spatial and temporal scales. It combines quantitative and qualitative methodologies to identify a handful of heuristics for increasing adaptive capacity of water management to extreme droughts and climate change, and also highlights potential tradeoffs in building and mobilizing adaptive capacity across space and time.     

中国东部月降水量分布的统计特征

本文利用中国东部(105°E以东)110个站的30年(1953—1982用降水量资料,分析了月降水量分布的统计特征,经计算,月降水量的变差系数大多在0.5—1.0之间。大部分站点月降水量的频数分布呈较明显的正偏形式,但偏斜程度因时间、地点的不同而异。假设检验的结果表明:在统计意义下(α=0.05),各地都有一些站点的月降水记录遵从正态分布。这些站点的时空分布反映了我国东部干湿季明显的季风气候特点。各地遵从正态分布站点数较高的月份大体上与该地变差系数较小的月份相对应,而这些月份均位于各地的多雨时段。对于其它一些无法用正态分布拟合的月降水的频数分布,绝大部分可用三种偏斜分布模式较好地拟合。     

Spatial interpolation of monthly and annual rainfall in northeast of Iran

Precipitation maps are the key input to many hydrological models. In this paper different univariate (inverse distance weighing and ordinary kriging) and multivariate (linear regression, ordinary cokriging, simple kriging with varying local mean and kriging with an external drift) interpolation methods are used to map monthly and annual rainfall from sparse data measurements. The study area is Golestan Province, located in northeast of Iran. A digital elevation model is used as complementary information for multivariate approaches. The prediction performance of each method is evaluated through cross-validation and visual examination of the precipitation maps produced. Results indicate that geostatistical algorithms clearly outperform inverse distance weighting and linear regression. Among multivariate techniques, ordinary cokriging or kriging with an external drift yields the smallest error of prediction for months April to October (autumn and winter) for which the correlation between rainfall and elevation is greater than 0.54. For all other months and annual rainfall, ordinary kriging provides the most accurate estimates.     

On the mean monthly equivalent potential temperature and rainfall in West Africa

Summary Rainfall in West Africa is examined in relation to monthly mean equivalent potential temperature ( _e )at the earth's surface. The study revealed that monthly mean equivalent potential temperature ( _e ) and monthly rainfall (R) generally decreased northwards from the equator.A good relationship existed betweenR and _e in the northern zone of West Africa (i.e., north of 7.5° N). No definite relationship existed in the southern zone. In the northern zone, the departure of _e from its annual mean ( ) first became positive about a month before the onset of the rains. Positive departures from ) generally resulted in more than normal (or average) rainfall in this zone. In general, little or no rainfall occurred in West Africa whenever _e was less than 320 K.

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Zusammenfassung Der Niederschlag (MonatssummeR) in Westafrika wird in Zusammenhang mit der mittleren monatlichen Äquivalent-temperatur ( _e ) an der Erdoberfläche untersucht. Es zeigte sich, daß die Monatswerte beider Elemente im allgemeinen vom Äquator nach Norden abnehmen.ZwischenR und _e ergab sich für das nördliche Westafrika (nördlich von 7.5° N) eine gute, für die südliche Zone jedoch keine beweisbare Übereinstimmung. In der nördlichen Zone übertraf _e das Jahresmittel erstmals etwa einen Monat vor Beginn der Regenzeit. Positive Abweichungen vom mittleren _e hatten immer übernormalen Niederschlag in dieser Zone zur Folge. Dagegen gab es wenig oder keinen Niederschlag in Westafrika, wenn _e unter 320 K lag.

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With 7 Figures     

Reversal of monthly East Asian winter air temperature in 2020/21 and its predictability

在全球变暖的背景下,近年来东亚冬季气温存在复杂的季节内变化.本文研究了2020/21年东亚冬季气温的月际转折及可预测性.结果 表明,2020/21年东亚冬季气温前冬(2020年12月-2021年1月中旬)偏冷,后冬(2021年1月中旬-2月)偏暖.西伯利亚高压强度在前冬和后冬也出现转折变化.在前冬,由于2020年9月巴...     

冬季中东急流中心位置的年际变化及其与大气环流的联系

利用NCEP/DOE再分析资料,通过EOF分解、合成分析和线性回归等多种统计学方法,对年际时间尺度上冬季中东副热带西风急流(Middle East subtropical westerly Jet stream,MEJ)中心位置的变化进行研究,分析了MEJ中心位置的年际变化与大气环流的联系,找到了与MEJ中心位置相联系...     

Long-term changes and variability of monthly extreme temperatures in India

Extreme temperatures are changing worldwide together with changes in the mean temperatures. This study investigates the long-term trends and variations of the monthly maximum and minimum temperatures and their effects on seasonal fluctuations in various climatological regions in India. The magnitude of the trends and their statistical significance were determined by parametric ordinary least square regression techniques and the variations were determined by the respective coefficient of variations. The results showed that the monthly maximum temperature increased, though unevenly, over the last century. Minimum temperature changes were more variable than maximum temperature changes, both temporally and spatially, with results of lesser significance. The results of this study are good indicators of Indian climate variability and its changes over the last century.     

Teleconnection between rainfall over South China and the East European Plain in July and August

In the present reported work, we identified that there is a significant negative relationship between rainfall over South China (SC) and the East European Plain (EEP) in the months of July and August, and investigated the possible reason for this negative relationship. The correlation coefficients between SC and the EEP rainfall were calculated to be ?0.42 for July and ?0.35 for August, both significant at the 95 % confidence level. We report that a wave-like train of circulation anomalies and a pathway of wave-activity flux stretching from Europe to East China connect the anticyclonic anomaly over Europe and the cyclonic anomaly over central and southern China, which are responsible for less EEP rainfall and more SC rainfall. We suggest that the teleconnection between SC and EEP rainfall results from the extension of stationary Rossby waves in the mid-latitudes in the upper troposphere for both July and August. This stationary Rossby wave is contributed to by summer North Atlantic Oscillation (NAO) and its extension features are determined by the location and intensity of the climatological upper-tropospheric westerly jet. Furthermore, we found that there was an interdecadal change around the mid-1970s in the negative SC–EEP rainfall relationship for both July and August. The negative correlation was significant and strong in the period 1976–2005, but much weaker in the period 1955–1975. The extension of stationary Rossby waves from Europe to East China was responsible for the significant negative relationship during the period 1976–2005.     

An investigation of the relationship between sub‐Saharan rainfall and global sea surface temperatures

Abstract

The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa.

An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively.

The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented.     

Perspectives on the non-stationarity of the relationship between Indian and East Asian summer rainfall variations

观测和气候模式中印度和东亚夏季降水变化的关系是不稳定的。本文讨论外部强迫和大气内部过程在上述关系变化中的作用。虽然厄尔尼诺-南方涛动在印度和东亚夏季降水变化中有重要作用,但它并不能解释印度-东亚降水关系的长期变化。蒙特卡罗试验说明随机过程的作用不能完全排除。气候模式结果分析表明印度-东亚夏季降水的关系在不同模式之间和同一模式不同模拟之间都有明显变化。这指出了大气内部过程对印度-东亚夏季降水关系变化的影响。此观点为100年气候平均海温强迫的大气环流模式试验结果所支持。     

东亚副热带急流与东北夏季降水异常的关系

利用东北地区88个气象站点观测的7、8月(夏季)降水量和NCEP/NCAR再分析资料,分析了东北地区夏季降水与同期东亚副热带西风急流之间的关系,发现东北地区夏季降水异常偏多年,位于青藏高原上空200 hPa西风急流中心强度偏强,东北地区上空急流轴向东北方向倾斜;东北地区夏季降水异常偏少年,青藏高原上空200 hPa西风...