Interrelation of total precipitation over Eurasia with atmospheric centers of action of the northern hemisphere and with major modes of the North Atlantic surface temperature variability

Conventional average values of Wallace-Gutzler indices for the regional circulations and average values of major variability components of the fields of the North Atlantic surface temperature anomalies are plotted on the geographical map used to analyze the total daily precipitation fields. The computation conditions of average values are defined by the dates classified according to three equiprobable gradations of total precipitation. A projection of conditional average values to the precipitation field points enables to estimate the atmospheric and oceanic “tracks” within the marked out gradations of total precipitation. The stratification and computation of characteristics are carried out for the summer and winter seasons. Large regions are revealed of statistically significant interrelation of the atmospheric circulation and major components of variability of the sea surface temperature anomalies with the extreme gradations of total precipitation for summer and winter seasons. The recommendations are formulated for the use of obtained results in the practice of the seasonal forecasting of meteorological conditions.     

Inter-annual temperature and precipitation variations over the Litani Basin in response to atmospheric circulation patterns

This study examines the sensitivity of a mid-size basin’s temperature and precipitation response to different global and regional climate circulation patterns. The implication of the North Atlantic Oscillation (NAO), El Ni?o Southern Oscillation (ENSO), Indian Monsoon and ten other teleconnection patterns of the Northern Hemisphere are investigated. A methodology to generate a basin-scale, long-term monthly surface temperature and precipitation time series has been established using different statistical tests. The Litani River Basin is the focus of this study. It is located in Lebanon, east of the Mediterranean Basin, which is known to have diverse geophysical and environmental characteristics. It was selected to explore the influence of the diverse physical and topographical features on its hydroclimatological response to global and regional climate patterns. We also examine the opportunity of conducting related studies in areas with limited long-term measured climate and/or hydrological data. Litani's monthly precipitation and temperature data have been collected and statistically extrapolated using remotely sensed data products from satellites and as well as in situ gauges. Correlations between 13 different teleconnection indices and the basin’s precipitation and temperature series are investigated. The study shows that some of the annual and seasonal temperature and precipitation variance can be partially associated with many atmospheric circulation patterns. This would give the opportunity to relate the natural climate variability with the watershed’s hydroclimatology performance and thus differentiate it from other anthropogenic induced climate change outcomes.     

Trends and periodicity of daily temperature and precipitation extremes during 1960–2013 in Hunan Province,central south China

In this study, the trends and periodicity in climate extremes are examined in Hunan Province over the period 1960–2013 on the basis of 27 extreme climate indices calculated from daily temperature and precipitation records at 89 meteorological stations. The results show that in the whole province, temperature extremes exhibit a warming trend with more than 50% stations being statistically significant for 7 out of 16 temperature indices, and the nighttime temperature increases faster than the daytime temperature at the annual scale. The changes in most extreme temperature indices show strongly coherent spatial patterns. Moreover, the change rates of almost all temperature indices in north Hunan are greater than those of other regions. However, the statistically significant changes in indices of extreme precipitation are observed at fewer stations than in extreme temperature indices, forming less spatially coherent patterns. Positive trends in indices of extreme precipitation show that the amount and intensity of extreme precipitation events are generally increasing in both annual and seasonal scales, whereas the significant downward trend in consecutive wet days indicates that the precipitation becomes more even over the study period. Analysis of changes in probability distributions of extreme indices for 1960–1986 and 1987–2013 also demonstrates a remarkable shift toward warmer condition and increasing tendency in the amount and intensity of extreme precipitation during the past decades. The variations in extreme climate indices exhibit inconstant frequencies in the wavelet power spectrum. Among the 16 temperature indices, 2 of them show significant 1-year periodic oscillation and 7 of them exhibit significant 4-year cycle during some certain periods. However, significant periodic oscillations can be found in all of the precipitation indices. Wet-day precipitation and three absolute precipitation indices show significant 1-year cycle and other seven provide significant power at the 4-year period, which are mainly found during 1970–1980 and after 1992.     

Regional climate model projections for the State of Washington

Global climate models do not have sufficient spatial resolution to represent the atmospheric and land surface processes that determine the unique regional climate of the State of Washington. Regional climate models explicitly simulate the interactions between the large-scale weather patterns simulated by a global model and the local terrain. We have performed two 100-year regional climate simulations using the Weather Research and Forecasting (WRF) model developed at the National Center for Atmospheric Research (NCAR). One simulation is forced by the NCAR Community Climate System Model version 3 (CCSM3) and the second is forced by a simulation of the Max Plank Institute, Hamburg, global model (ECHAM5). The mesoscale simulations produce regional changes in snow cover, cloudiness, and circulation patterns associated with interactions between the large-scale climate change and the regional topography and land-water contrasts. These changes substantially alter the temperature and precipitation trends over the region relative to the global model result or statistical downscaling. To illustrate this effect, we analyze the changes from the current climate (1970–1999) to the mid twenty-first century (2030–2059). Changes in seasonal-mean temperature, precipitation, and snowpack are presented. Several climatological indices of extreme daily weather are also presented: precipitation intensity, fraction of precipitation occurring in extreme daily events, heat wave frequency, growing season length, and frequency of warm nights. Despite somewhat different changes in seasonal precipitation and temperature from the two regional simulations, consistent results for changes in snowpack and extreme precipitation are found in both simulations.     

Comparison of Wintertime North American Climate Impacts Associated with Multiple ENSO Indices

This analysis compares the climate impacts over North America during winter associated with various El Niño–Southern Oscillation (ENSO) indices, including the Niño 3.4 index, the leading tropical Pacific outgoing longwave radiation and sea surface temperature (OLR-SST) covariability, and the eastern Pacific (EP) and central Pacific (CP) types of ENSO identified from both partial-regression–empirical orthogonal function (EOF) and regression–EOF approaches. The traditional Niño 3.4 SST index is found to be optimal for monitoring the tropical Pacific OLR-SST covariability and for the tropical SST impact on North America. The circulation anomalies associated with the Niño 3.4 index project on both the Pacific/North American (PNA) and Tropical/Northern Hemisphere (TNH) patterns. The ENSO associated with the PNA tends to come from both the EP and CP ENSOs, whereas that associated with the TNH comes more from the EP ENSO. The variability of ENSO significantly affects North American temperature and precipitation, as well as temperature and precipitation extremes. For either the EP or CP types of ENSO, qualitatively similar patterns of climate and climate extreme anomalies are apparent associated with the indices identified by the two EOF approaches, with differences mainly in the anomalous amplitude. The anomalous patterns are generally field significant over North America for the EP ENSO but not field significant for the CP ENSO.

The circulation anomalies associated with ENSO are reinforced and maintained by synoptic vorticity fluxes in the upper troposphere. The anomalous surface temperature is mainly determined by the anomalies in surface radiative heating in the face of upward surface longwave radiative damping. The precipitation anomalies are supported by the vertically integrated moisture transport. The differences in atmospheric circulation, surface temperature, and precipitation among the various ENSO indices, including the intensity and spatial structure of the fields, can be attributed to the corresponding differences in synoptic eddy vorticity forcing, surface radiative heating, and vertically integrated moisture transport.     

我国四季极端雨日数时空变化及其与海表温度异常的关系

利用1960—2004年我国586个气象站的逐日降水观测资料,对每个季节和每个站点,以雨日降水量升序排列的第90个百分位值定义极端日降水阈值,分析揭示了我国四季极端雨日数的时空变化特征、与海表温度异常的关系以及相联系的大气环流异常型。结果表明,我国长江流域极端雨日数在冬季和夏季呈显著增加趋势,华北地区极端雨日数在冬季显著增加、而在夏季显著减少,华南地区极端雨日数在春季显著增加,东北地区极端雨日数在冬季和春季显著增加,而西北地区极端雨日数在四季均显著增加。各季极端雨日数在线性趋势变化之上表现年际和年代际变化特征,并且其典型异常型明显不同,春、秋季表现为长江以南与以北地区反位相的"偶极型"变化,夏季表现为长江流域与华南、华北地区反位相的"三极型"变化,冬季表现为全国大部分地区同位相的"单极型"变化。我国季节极端雨日数与印度洋-太平洋海表温度异常的关系主要表现为与ENSO的关系,而ENSO影响我国极端降水异常是通过相应的大气环流异常型来实现的。     

中国东部夏季雨带类型与前期北半球500 hPa环流异常的关系

根据1951～1986年的资料,在文献[1]对中国东部夏季（6～8月）雨带分布类型的基础上,分析了各雨型与前期北半球500 hPa环流异常的关系。重点研究了各雨型的长期天气过程。发现不同雨型前期环流有不同的长期演变过程。指出中高纬和低纬环流不同季节变异及其相互作用,可能是导致中国东部各种雨带分布类型的一个重要因素。并提出了一些预报线索,可供夏季我国大范围旱涝趋势的长期预报参考。     

Modulation of monthly precipitation patterns over East China by the Pacific Decadal Oscillation

Previous studies suggest that the Pacific Decadal Oscillation (PDO) modulates annual and summer precipitation patterns over East China. In this study, the effect of the PDO on monthly precipitation anomalies over this region is investigated. The new results show that the effect is month-dependent. The well-known North–South dipole patterns of annual precipitation are dominated by the July–August precipitation. In other months, the corresponding patterns vary in strength, position, and even shape. For example, the May and June precipitation patterns show opposite signs to the July–August or annual mean patterns, whereas the September–December monthly precipitation anomalies show a triple pattern. Monthly precipitation patterns over East China are largely determined by large-scale moisture transport controlled by atmospheric circulation. The PDO affects East China precipitation patterns by modulating the large-scale circulation pattern.     

A Regression-based Assessment of the Predictability of New Zealand Climate Anomalies

Summary Estimates of the predictability of New Zealand monthly and seasonal temperature and rainfall anomalies are calculated using a cross-validated linear regression procedure. Predictors are indices of the large scale circulation, sea-surface temperatures, the Southern Oscillation Index and persistence. Statistical significance is estimated through a series of Monte Carlo trials. No significant forecast relationships are found for rainfall anomalies at either the monthly or seasonal time scale. Temperature forecasts are however considered to exhibit significant skill, with variance reductions of the order of 10–20% in independent trials. Temperature anomalies are most skilfully predicted over the North Island, and skill is greatest in Spring and Summer in most areas. At the monthly time scale, predictors local to the New Zealand region account for most of the forecast skill, while at the seasonal time scale, skill depends strongly upon “remote” predictors defined over regions of the southern hemisphere distant from New Zealand. Indices of meridional flow over the Tasman Sea/New Zealand region are found to be useful predictors, especially for monthly forecasts, perhaps as a proxy for atmospherically-forced sea surface temperature anomalies. Sea surface temperature anomalies to the west of New Zealand and in the tropical Indian Ocean are also useful, especially for seasonal predictions. Forecast skill is more reliably estimated at the monthly time scale than at the seasonal time scale, as a result of the larger sample size of monthly mean data. While long-term mean levels of skill may be estimated reliably over the whole data set, statistically significant decadal-scale variations are found in the predictability of temperature anomalies. Therefore, even if long-term forecast skill levels are reliably estimated, it may be impossible to predict the short-term skill of operational seasonal climate forecasts. Implications for operational climate predictions in mid-latitudes are discussed. Received July 18, 1997 Revised April 2, 1998     

冬季各月北太平洋涛动的年际变化及其与我国降水异常的联系

利用ERA-Interim的海平面气压(Sea Level Pressure,SLP)再分析资料和中国160站的降水观测资料,分析了冬季各月(当年12月、次年1月和2月)北太平洋涛动(North Pacific Oscillation,NPO)的年际变化特征,及其与我国同期降水异常之间的联系。结果表明:1)冬季各月NPO指数的年际变化较为显著,但各月NPO指数年际变化之间的相关性较差,1979—2012年冬季12月与1月NPO指数年际变化之间的相关系数为0.09,而1月与2月NPO指数的相关系数仅为-0.003,均没有通过信度检验。2)1月和12月NPO指数年际变化与同期我国黄淮流域降水异常之间存在明显的正相关,而2月NPO指数年际变化与同期我国华北降水异常之间为明显的负相关。3)当1月(12月)NPO指数增加1个标准差时,我国黄淮流域降水量比多年平均值增加约50%(40%);而当2月NPO指数增加1个标准差时,我国华北降水量比多年平均值减少约30%。     

Circulation statistics and climate change in Central Europe: PRUDENCE simulations and observations

PRUDENCE simulations of the climate in Central Europe are analysed with respect to mean temperature, mean precipitation and three monthly mean geostrophic circulation indices. The three global models show important circulation biases in the control climate, in particular in the strength of the west-circulations in winter and summer. The nine regional models inherit much of the circulation biases from their host model, especially in winter. In summer, the regional models show a larger spread in circulation statistics, depending on nesting procedures and other model characteristics. Simulated circulation biases appear to have a significant inluence on simulated temperature and precipitation. The PRUDENCE ensemble appears to be biased towards warmer and wetter than observed circulations in winter, and towards warmer and dryer circulations in summer. A2-scenario simulations show important circulation changes, which have a significant impact on changes in the distributions of monthly mean temperature and precipitation. It is likely that interactions between land–surface processes and atmospheric circulation play an important role in the simulated changes in the summer climate in Central Europe.     

东亚地区夏季大气环流季节循环进程及其在区域持续性降水异常形成中的作用

利用32年(1968～1999年)月平均NCAR/NCEP再分析资料,分析了东亚地区夏季大气环流的季节循环进程, 并以1991/1994年为例,探讨了东亚地区夏季7～8月对流层上层环流的季节循环提前和延迟与气候平均的季节循环的差异,以及在江淮流域持续性降水异常过程中的作用,证实东亚地区季节循环的变异对形成我国东部地区持续性降水异常,特别是7月旱涝起着重要作用,江淮流域旱涝一般是和东亚地区大气环流季节循环的提早或推迟一个月左右相对应.通过波作用量的动力学诊断分析,研究了欧亚大陆沿副热带西风急流传播的异常准静止波的传播特征,并从以副热带西风急流为波导的准静止波(或者遥相关)角度对东亚地区夏季7～8月环流季节循环进程提前和延迟的可能机制作了分析.     

Impacts of large-scale teleconnections on climate variability over Southwest Asia

The atmospheric low frequency variability at a regional or global scale is represented by teleconnection. Using monthly dataset of the Climatic Research Unit (CRU) for the period 1971–2016, the impacts of four large-scale teleconnection patterns on the climate variability over Southwest Asia are investigated. The large-scale features include the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and the East Atlantic (EA) teleconnection patterns, as well as western tropical Indian Ocean (WTIO) sea surface temperature anomaly index. Results indicate that ENSO and EA are the first leading modes that explain variation of Southwest Asian precipitation, with positive (negative) anomalies during El Niño (La Niña) and the negative (positive) phase of EA. Variation of Southwest Asian near-surface temperature is most strongly related to WTIO index, with above-average (below-average) temperature during the positive (negative) phase of WTIO index, although the negative (positive) phase of NAO also favours the above-average (below-average) temperature. On the other hand, temperature (precipitation) over Southwest Asia shows the least response to ENSO (WTIO). ENSO and EA individually explain 13 percent annual variance of precipitation, while WTIO index explains 36 percent annual variance of near-surface temperature over Southwest Asia. Analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim) data indicated establishments of negative (positive) geopotential height anomalies in the middle troposphere over Southwest Asia during El Niño (La Niña) or the negative (positive) phase of NAO, EA and WTIO. The response of precipitation variability over Southwest Asia to NAO is opposite to that expected from the geopotential height anomalies, but the correlation between precipitation and NAO is not statistically significant. Due to predictability of large-scale teleconnections, results of this study are encouraging for improvement of the state-of-the-art seasonal prediction of the climate over Southwest Asia.     

BCC二代气候系统模式的季节预测评估和可预报性分析

本文利用国家气候中心（BCC）第二代季节预测模式系统历史回报数据,从确定性预报和概率预报两个方面系统地评估了该模式对气温、降水和大气环流的季节预报性能,并与BCC一代气候预测模式的结果进行了对比,重点分析了二代模式的季节可预报性问题。结果显示,BCC二代模式对全球气温、降水和环流的预报性能整体上优于一代模式,特别在热带中东太平洋、印度洋和海洋大陆地区的温度和降水的预报效果改进尤为明显。这些热带地区降水预报的改进,可以通过激发太平洋—北美型（PNA）、东亚—太平洋型（EAP）等遥相关波列提升该模式在中高纬地区的季节预报技巧。分析表明,厄尔尼诺和南方涛动（ENSO）信号在热带和热带外地区均是模式季节可预报性的重要来源,BCC二代模式能够较好把握全球大气环流对ENSO信号的响应特征,从而通过对ENSO预报技巧的改进有效地提升了模式整体的预报性能。从概率预报来看,BCC二代模式对我国冬季气温和夏季降水具备一定的预报能力,特别是对我国东部大部分地区冬季气温正异常和负异常事件预报的可靠性和辨析度相对较高。因此,进一步提高模式对热带大尺度异常信号和大气主要模态的预报能力、加强概率预报产品释用对提高季节气候预测水平具有重要意义。     

Detection of trends in precipitation during 1960–2008 in Jiangxi province, southeast China

Changes in precipitation exert an enormous impact on human life, and it is of vital importance to study regular patterns of meteorological and hydrological events. In order to explore the changing spatial and temporal patterns of precipitation amounts, precipitation extremes and precipitation concentration in Jiangxi province in southeast China between 1960 and 2008, several precipitation indices series were analysed using the Mann–Kendall test in this study. Our results indicate remarkable differences among the stations with negative and positive precipitation trends at the annual, seasonal and monthly scales, significant increasing trends are mainly found during January, August, winter and summer, while significant decreasing trends mostly are observed during October and autumn. For precipitation extremes, most precipitation indices suggest that both the intensity and the days of extreme precipitation are increasing; the mean precipitation amount, especially, on a wet day shows a significant positive trend. When it comes to precipitation concentration, the monthly rainfall heterogeneity shows an insignificant downward trend, while the contribution of the days with greatest rainfall displays an insignificant upward trend. Furthermore, the long-range persistence is detected for changing process of precipitation amount, extreme precipitation and precipitation concentration using the Rescaled Range Analysis.     

La Niña diversity and Northwest Indian Ocean Rim teleconnections

The differences in tropical Pacific sea surface temperature (SST) expressions of El Niño-Southern Oscillation (ENSO) events of the same phase have been linked with different global atmospheric circulation patterns. This study examines the dynamical forcing of precipitation during October–December (OND) and March–May (MAM) over East Africa and during December–March (DJFM) over Central-Southwest Asia for 1950–2010 associated with four tropical Pacific SST patterns characteristic of La Niña events, the cold phase of ENSO. The self-organizing map method along with a statistical distinguishability test was used to isolate La Niña events, and seasonal precipitation forcing was investigated in terms of the tropical overturning circulation and thermodynamic and moisture budgets. Recent La Niña events with strong opposing SST anomalies between the central and western Pacific Ocean (phases 3 and 4), force the strongest global circulation modifications and drought over the Northwest Indian Ocean Rim. Over East Africa during MAM and OND, subsidence is forced by an enhanced tropical overturning circulation and precipitation reductions are exacerbated by increases in moisture flux divergence. Over Central-Southwest Asia during DJFM, the thermodynamic forcing of subsidence is primarily responsible for precipitation reductions, with moisture flux divergence acting as a secondary mechanism to reduce precipitation. Eastern Pacific La Niña events in the absence of west Pacific SST anomalies (phases 1 and 2), are associated with weaker global teleconnections, particularly over the Indian Ocean Rim. The weak regional teleconnections result in statistically insignificant precipitation modifications over East Africa and Central-Southwest Asia.     

Variability and trends in daily precipitation extremes on the northern and southern slopes of the central Himalaya

This study focuses on the precipitation extremes recorded on the northern and southern slopes of the central Himalaya, especially those documented at higher altitudes. Daily precipitation data recorded over a 35-year period at nine meteorological stations in the region were studied. We used the precipitation extreme indices delineated by the Expert Team on Climate Change Detection and Indices (ETCCDI). The spatial and temporal variations in these precipitation extremes were calculated. When regional patterns were investigated to detect any anomalies, only 1 of the 10 precipitation extreme indices from the southern slopes of the central Himalaya showed a statistically significant trend; none from the northern slopes of the central Himalaya highlighted a statistically significant trend. On the southern slopes, all indices increased, apart from the maximum 1-day precipitation (RX1) and simple daily precipitation intensity (SDII) indices. Indices such as the consecutive dry days (CDDs) and RX1 indices exhibited similar increases on both the northern and southern slopes of the central Himalaya. These results suggest that increases in precipitation have been accompanied by an increasing frequency of extremes over the southern central Himalaya. Nonetheless, no relation could be established between the precipitation extreme indices and circulation indices for higher altitudes.

     

海河流域夏季降水与北半球环流异常的相关

使用1981—2013年6—8月的月平均海河流域站点降水资料以及NCEP/NCAR再分析资料,采用SVD方法分析了北半球高度场环流异常与海河流域夏季降水的关系。结果表明夏季海河流域的一致型降水异常主要受热带地区高度场异常的影响,而北半球中高纬的高度异常分布对海河流域东南部降水异常有重要作用。热带及中高纬地区的高度场异常与副热带西风急流和流域上空的水汽输送有一定的对应关系,急流强度和位置的变化以及水汽辐合异常造成海河流域降水异常,尤其中高纬高度异常的这种对应关系更加明显,并且两个地区的高度异常分布对应的海河流域异常水汽输送有不同来源。     

夏季长白山天池站降水量年际变化特征及其对应的环流异常

长白山地处吉林省东南部,作为国家级重点生态功能区,其降水变化特征对该地森林生态系统和水资源结构变化有重要影响.本文基于1979～2016年吉林省47个台站逐月降水资料,探究了长白山天池站夏季降水的气候特征及其相关的环流异常,并与吉林省降水进行对比.分析结果表明天池夏季降水量以及年际变率高出吉林省其它站点一倍左右.此外,...