1948—2001年全球陆地春季降水长期变化的时空特征

利用全球陆地月降水资料(PREC/L)中3个月的资料,研究了1948—2001年全球陆地3—5月降水长期变化的时空特征。结果表明,1948—2001年,全球3—5月的降水量以负趋势为主要变化特征,明显减少的区域是:热带非洲、亚洲中西部、中国中东部、俄罗斯东部、南极的恩德比地和威尔克斯地等9个地区;降水量增加的区域是:俄罗斯西北部、美国西北部、加拿大西南部、南美洲南部、加拿大北部等7个地区。还研究了35个纬圈3—5月平均降水量的趋势系数。在分析全球季节降水量与ENSO的关系中,指出春季是春夏秋三季中最不显著的。     

1948～2001年全球陆地9～11月降水的长期变化

本文用Chen等(2001)最新创建的全球陆地月降水资料(PREC／L)，计算了1948～2001年全球9～11月陆地降水量趋势变化。结果表明，在1948～2001年，全球9～11月的降水量场有明显的趋势变化，全球大约2／3左右的陆地9～11月降水量是负趋势，明显减少的区域是：热带非洲，俄罗斯西北部，中国东部，南亚及东南亚，南极的威尔克斯地，格陵兰北部，等六个地区。全球仅1／3左右的陆地9～11月降水量是正趋势，降水量增加的地区是：加拿大北部，墨西哥北部及美国西南部，南美的阿根廷，非洲南部的南非、博茨瓦纳南部，等四个地区。正负趋势面积的差异在统计上是显著的。本文还研究了36个纬度带9～11月平均降水量的趋势系数，指出全球共有8个纬圈的9～11月降水量的趋势变化达到0．05信度的显著性，初步讨论了全球9～11月降水量趋势变化的原因。     

1948-2001年全球陆地6-8月降水长期变化的时空特征

采用PREC/L的全球陆地月降水资料,研究了1948-2001年全球陆地6-8月降水长期变化的时空特征.结果表明,在该时段内,6-8月降水量较大的区域是全球几个主要的季风区,而且季风区的降水均方差较大;全球陆地6-8月降水量以负趋势为主要特征,降水量明显减少的区域是热带非洲,中国的淮河以北,俄罗斯的东部,中、西西伯利亚,朝鲜,南亚等8个区域;降水量增加的区域是加拿大北部、格陵兰中部等4个区域;全球36个纬度带中共有12个纬度带6-8月降水量趋势变化达到了0.05显著性水平的Monte Carlo检验,但是只有1个纬度带(65～60°S)是正趋势.全球陆地6-8月降水量正趋势的范围是很小的.初步探讨了ENSO与全球陆地6-8月降水量趋势变化的关系.     

1948～2000年全球陆地年降水量场趋势变化的时、空特征

用全球陆地月降水资料(PREC/L),计算了1948～2000年全球陆地年降水量场的趋势变化.结果表明,在1948～2000年期间,全球陆地年降水量场有明显的趋势变化,全球大约2/3左右的陆地年降水量是负趋势(降水量减少),1/3左右的年降水量是正趋势,正负趋势面积及强度的差异在统计上是显著的.年降水量明显减少的地区是:热带非洲,加拿大的东南部及美国的东北部,中国的淮河以北,蒙古、俄罗斯的中、西西伯利亚及朝鲜、韩国和日本等9个地区.陆地年降水量增加地区是:加拿大的北部、南美的阿根廷及智利、格陵兰等6个区域.分别研究了36个纬圈的年平均降水量的趋势系数,指出有13个纬圈的年平均降水量的趋势变化达到0.05的信度的显著性,其中有1个纬度带(75～80°N)是正趋势.全球年降水量正趋势的范围是很小的,仅在70°N以北.初步研究了全球年降水量场趋势变化的原因.     

1948-2003年热带地区降水气候特征与变化

使用1948—2003年全球陆地和海洋的月降水资料,研究了热带地区年降水量场的趋势变化,同时还研究了ENSO事件与热带地区年降水量的关系。结果表明,在1948—2003年,热带地区年降水量场以负趋势为主要变化特征。给出了降水趋势明显的13个区域,指出热带海洋降水趋势明显的地区比陆地的范围广而且强度大,正趋势区基本都在南半球的海洋上,且北半球降水趋势明显的海洋区域都呈负趋势。研究结果还表明,ENSO事件可能是热带地区年降水量减少的一个重要原因;同时给出了ENSO事件发生时热带地区的明显旱涝区,并与以往的研究进行了比较。     

1948—2003年热带地区降水气候特征与变化

使用1948—2003年全球陆地和海洋的月降水资料,研究了热带地区年降水量场的趋势变化,同时还研究了ENSO事件与热带地区年降水量的关系。结果表明,在1948—2003年,热带地区年降水量场以负趋势为主要变化特征。给出了降水趋势明显的13个区域,指出热带海洋降水趋势明显的地区比陆地的范围广而且强度大,正趋势区基本都在南半球的海洋上,且北半球降水趋势明显的海洋区域都呈负趋势。研究结果还表明,ENSO事件可能是热带地区年降水量减少的一个重要原因;同时给出了ENSO事件发生时热带地区的明显旱涝区,并与以往的研究进行了比较。     

1948～2001年全球陆地12～2月降水旱涝长期变化

本文利用1948～2001全球陆地月降水资料(PREC／L)，研究了全球、北、南半球及欧亚、非洲、澳洲、北美、南美和南极大陆6个大尺度区域12～2月的降水趋势变化及早涝气候变化。结果表明：全球、南、北半球的12～2月的陆面降水有明显的年代际变化，全球12～2月降水量从1975年开始有明显的下降趋势，回归系数约为-0．017mm／a。北半球有明显的降水减少，约为-0．028mm／a，南半球12～2月降水表现为极微弱的下降趋势，且在统计上是不显著的。划分出了全球、南北半球、全球6个大尺度区域12～2月旱涝年，指出全球及北、南半球12～2月的旱涝有明显的年代际变化。70年代中期以前是全球洪涝多发期，80年代到90年代为全球干旱多发期。北半球旱涝特征与全球特征相近，南、北半球12～2月的旱涝没有明显的联系。12～2月大尺度区域中：欧亚大陆、北美洲、南极大陆旱涝年的分布有明显的年代际特征，并指出全球大部分地区的旱涝年降水量有显著的差异。6个大尺度区域12～2月的降水相关关系中，欧亚大陆和非洲大陆的相关系数最高，为-0．35，北美大陆与欧亚大陆，南美洲和澳洲的12～2月降水也有较高的相关关系。     

内蒙古地区与北半球云水资源分布

利用ISCCP D2云资料、内蒙古116个气象站地面降水资料、NCEP同化资料，分析研究了全球云水时空分布特征及内蒙古地区云水时空分布特征、降水分布特征。研究表明：20年年均变化来看，可降水量在波动过程中有增多的趋势；降水量从1984年到1998年有增多的趋势，1998年到2001年有明显的减少趋势；从24年实际降水量空间变化趋势来看，内蒙古东部地区有明显的减少趋势，中西部地区有增多趋势，尤其中部地区乌兰察布市、呼和浩特市、包头市等地区有明显的增多趋势。     

川北绵阳地区降水量的时空分布特征及变化趋势

选用四川省绵阳地区8个台站1959~2005年日降水资料,采用经验正交函数分解法和连续功率谱分析等方法分析了绵阳地区年降水量的时空分布特征及变化趋势,结果表明,绵阳地区年降水量的空间分布不均匀,局地差异大,主要表现为3种分布型:①区域一致型;②东南—西北型;③中部型。绵阳地区的年降水量呈整体下降趋势,但降水剧烈程度加大,同时东南—西北分布型在加剧;功率谱分析发现,绵阳年降水量的变化具有2.9年和6.7年的显著变化周期;绵阳地区各站的年降水和不同等级降水的降水量和降水日数大致呈不同程度的下降趋势和减少趋势,但不同站点暴雨以上量级的降水量和降水日数变化特征又有所不同;绵阳地区区域平均年降水量呈减少趋势主要是由于雨季降水量和降水日数均出现减少趋势造成的。      

内蒙古地区近43年来极端降水事件演变特征

利用全区52个站点1961—2004年的降水资料，通过气候统计诊断分析方法，探讨在全球变暖背景下，内蒙古地区各降水要素的区域分布格局及演变特征，结果表明：中西部地区降水量总趋势为增加态势，东部区为缓慢减少趋势，但从20世纪90年代之后，东部和中郜降水呈减少趋势，西部地区呈明显的增加态势。而极端降水要素如暴雨日数、积雪日数则呈现相反的变化趋势，说明越是年降水量减少的地区，极端气候要素出现的几率越高，该地区极端降水事件发生频率越高。     

Terrestrial vegetation dynamics and global climate controls

Monthly data from the moderate resolution imaging spectroradiometer (MODIS) and its predecessor satellite sensors was used to reconstruct vegetation dynamics in response to climate patterns over the period 1983–2005. Results suggest that plant growth over extensive land areas of southern Africa and Central Asia were the most closely coupled of any major land area to El Niño–southern oscillation (ENSO) effects on regional climate. Others land areas strongly tied to recent ENSO climate effects were in northern Canada, Alaska, western US, northern Mexico, northern Argentina, and Australia. Localized variations in precipitation were the most common controllers of monthly values for the fraction absorbed of photosynthetically active radiation (FPAR) over these regions. In addition to the areas cited above, seasonal FPAR values from MODIS were closely coupled to rainfall patterns in grassland and cropland areas of the northern and central US. Historical associations between global vegetation FPAR and atmospheric carbon dioxide (CO₂) anomalies suggest that the terrestrial biosphere can contribute major fluxes of CO₂ during major drought events, such as those triggered by 1997–1998 El Niño event.     

与西澳州西南部冬季降水相联系的大气环流特征分析

西澳大利亚州西南部(SWWA)是西澳大利亚州首府Perth的所在地,也是西澳州政治、经济、文化、教育和旅游的中心.自20世纪中期以来,SWWA地区雨季降水持续减少.本文利用近60年的观测及再分析数据,分析了已知的影响澳大利亚降水的热带海洋模态:厄尔尼诺—南方涛动(ENSO)、印度洋偶极子(IOD)和ENSOModoki...     

Seasonal variability of Indonesian rainfall in ECHAM4 simulations and in the reanalyses: The role of ENSO

Summary A study of the skill of the ECHAM version 4 atmospheric general circulation model and two reanalyses in simulating Indonesian rainfall is presented with comparisons to 30 years of rain gauge data. The reanalyses are those performed by the European Centre for Medium-Range Weather Forecasts and of the National Centers for Environmental Prediction jointly with National Center for Atmospheric Research. This study investigates the skill of the reanalyses and ECHAM4 with regard to three climate regions of Indonesia, the annual and interannual variability of rainfall and its responses to El Ni?o-Southern Oscillation (ENSO) events. The study is conducted at two spectral resolutions, T42 and T106. The skill of rainfall simulations in Indonesia depends on the region, month and season, and the distribution of land and sea. Higher simulation skills are confined to years with ENSO events. With the exception of the northwest region of Indonesia, the rainfall from June (Molucca) and July (south Indonesia) to November is influenced by ENSO, and is more sensitive to El Ni?o than La Ni?a events. Observations show that the Moluccan region is more sensitive to ENSO, receives a longer ENSO impact and receives the earliest ENSO impact in June, which continues through to December. It is found that the reanalyses and the climate model simulate seasonal variability better than monthly variability. The seasonal skill is highest in June/July/August, followed by September/October/November, December/January/February and March/April/May. The correlations usually break down in April (for monthly analysis) or in the boreal spring (for seasonal analysis). This period seems to act as a persistent barrier to Indonesian rainfall predictability and skill. In general, the performance of ECHAM4 is poor, but in ENSO sensitive regions and during ENSO events, it is comparable to the reanalyses.     

The influence of stochasticism on Indian summer monsoon rainfall and its impact on prediction

Output from a multi-millennial control simulation of the CSIRO Mark 2 coupled model has been used to investigate quantitatively the relation between the Indian summer monsoon rain and El Nino/Southern Oscillation events. A moving window correlation between these two features revealed marked interannual and multi-decadal variability with the correlation coefficient varying between ?0.8 and +0.2. This suggests that current observations showing a decline in this correlation are due to natural climatic variability. A scatter diagram of the anomalies of the Indian summer monsoon rainfall and NINO 3.4 surface temperature showed that in almost 40 % of the cases ENSO events were associated with rainfall anomalies opposite to those implied by the climatological correlation coefficient. Case studies and composites of global distributions of surface temperature and rainfall anomalies for El Nino (or La Nina) events highlight the opposite rainfall anomalies over India that can result from very similar ENSO surface temperature anomalies. Composite differences are used to demonstrate the unique sensitivity of Indian summer monsoon rainfall anomalies to ENSO events. The problem of predicting such anomalies is discussed in relation to the fact that time series of the monsoon rainfall, both observed and simulated, consist of white noise. Based on the scatter diagram it is concluded that in about 60 % of the cases seasonal or annual prediction of monsoon rainfall based on individual ENSO events will result in the correct outcome. Unfortunately, there is no way, a priori, of determining for a given ENSO event whether the correct or a rogue prediction will result. Analysis of the present model’s results suggest that this is an almost world-wide problem for seasonal predictions of rainfall.     

我国夏季降水与全球气温场的关系

用蒙特卡罗的相关方法研究我国夏季大尺度降水与全球气温场关系，发现我国夏季大尺度降水与全球气温场有密切相关，以同期相关为最密切；除与热带西太平洋、东太平洋等海域有密切相关外，还与欧洲东部、北美洲东北部以及东亚等内陆地区的不同季节气温场有关系。研究还表明，印度洋地区春季气温和北美洲北部及北太平洋西南部夏季气温偏高时，长江中下游夏季易涝。且它们与长江中下游夏季降水的相关均有阶段性，相关密切程度随时间有所增强。     

西南地区春季及其各月降水的气候特征分析

利用1951～2017年我国西南地区26个台站的降水观测资料,本文研究了该地区春季及其各月降水的基本气候特征。结果表明:5月是春季我国西南地区降水最多的月份,其占春季总降水的55.3%,此外,5月降水年际变化强度最大;西南地区春季及其各月降水均具有显著的年代际变化特征,5月降水在春季降水的年代际变化特征中占据主导地位;在年代际突变特征方面,西南地区春季降水存在显著的年代际突变特征,其在1970年代后期发生了减少突变,而在1990年代中后期发生了增加突变;在变化趋势方面,春季西南区域平均降水的变化趋势不明显,但从空间上看,西南地区东部表现出显著增多的趋势,而西部则表现出显著减少的趋势;在周期方面,西南地区春季及其4～5月降水均具有显著的年际和年代际变化周期,需要说明的是,3月降水没有明显的年代际变化周期,总体上看,5月降水在春季降水周期变化中占据主导地位。     

Relationships Between QBO in the Lower Equatorial Stratospheric Zonal Winds and East African Seasonal Rainfall

Summary Teleconnections between the seasonal rainfall anomalies of March through May (“long-rains”) over eastern Africa (Uganda, Kenya and Tanzania) and the lower equatorial stratospheric (30-mb) zonal winds for the 32-year period 1964–1995 are examined using statistical methods. The analysis is based on the application of the simple correlation method and QBO/rainfall composite analysis. A statistical study of spatial correlation patterns is made in an effort to understand the climatic associations between the equatorial stratospheric zonal wind and regional rainfall at the interannual scale. The aim of this analysis is to establish whether this global signal can be employed as predictor variable in the long-range forecasts. The study is part of an ongoing investigation, which aims at designing a comprehensive and objective, multi-variate-forecast system of seasonal rainfall over eastern Africa. The correlation parameters include simultaneous (zero lag), and the non-zero lag correlations. The statistical significance of the correlation coefficient [r] is tested based on the Monte Carlo t-statistical method, and the standard correlation tables. Our results indicate significant positive simultaneous and non-zero lag correlations between rainfall over parts of East Africa and lower equatorial stratospheric zonal wind during the months of March–May and June–August. Significantly high correlations are concentrated over the western regions of eastern Africa with peak values of (+ 0.8) observed over these areas. These associations have been observed to be more prominent during lag than in the simultaneous correlations. Strong month to month lag coherence is observed after June prior to the onset of the March to May seasonal rainfall and persists for more than 4 months. Correlation indices for the eight homogeneous rainfall regions over eastern Africa which are derived from our Empirical Orthogonal Function/Cluster analysis shows a clear annual cycle with significant relationships between QBO and seasonal rainfall occurring during boreal summer (June–August). The season with the weakest relationship is December–February. It is however, noted that although the coherence between QBO-Index and rainfall during the long-rains is significantly high, there are some wet/dry years for which the relationship between the long rains and the lower equatorial zonal wind are not significant (for example in 1966, 1973 and 1983). These years have been associated with strong and prolonged ENSO events. Preliminary comparison of the QBO-Index and the newly found Indian Ocean dipole mode index (DMI) indicates that the two climate variables may be significantly related. Of the six high dipole mode events in the Indian Ocean that were observed in 1961, 1967, 1972, 1982, 1994 and 1997, all except 1967 coincided with the easterly phase of the QBO-Index and below normal rainfall over western highlands of eastern Africa. Contingency analyses indicate 60 percent likelihood for the occurrence of above normal rainfall during the westerly phase of the QBO and 63 percent likelihood of below normal rainfall during the east phase of the QBO. Our correlation analysis results indicate that about 36 percent of the variability of the long-rains season over eastern Africa are associated with the QBO-Index. Our results further show that the tendency of the lower equatorial stratosphe ric zonal wind prior to the season is a good indicator of the performance of the long rains of eastern Africa. A positive OND minus JJA QBO trend is a good indicator for the non-occurrence of drought over eastern Africa. Similarly, a negative trend is a good indicator for the non-occurrence of high rainfall over the region. The identified characteristics and domain of influence of the QBO signal in different regions of East Africa suggests that this global oscillator may offer useful input to objective multi-variate rainfall prediction models for eastern Africa. Received June 4, 1999 Revised November 25, 1999     

Tropical influence on Euro-Asian autumn rainfall variability

The connection between autumn rainfall variability in the Euro-Asian domain and tropical climate is documented using state-of-the-art global observational datasets and re-analyses. Results suggest a robust statistical relationship between the El Niño Southern Oscillation (ENSO) and autumn rainfall in parts of southwest Europe, northern Africa and southwest Asia. The correlation between area-mean anomalies over this region (P_ea) and the NIÑO3.4 index is 0.68, stationary over the last 50 years. Global ENSO-like tropical climate anomalies are observed in conjunction with P_ea anomalies confirming the relationship found with the NIÑO3.4 index. Overall, the connection with Indo-Pacific variability is stronger than that with the eastern Pacific.While rainfall anomalies in southwest Europe and southwest Asia appear to largely co-vary as one pattern under the influence of ENSO, our results suggest that different mechanisms may be contributing to the observed anomalies. In the North Atlantic/European region, it is speculated that while a PNA-like mode maybe the prevailing teleconnection mechanism for high P_ea, for low P_ea tropical Atlantic ENSO related SST anomalies may be playing a more relevant role forcing northeastward propagating Rossby waves. Over southwest Asia, a more direct connection to the Indo-Pacific region is suggested by the upper air anomaly observed over southern Asia, possibly the Rossby wave response to enhanced heating in the Indian Ocean.     

On the recent strengthening of the relationship between ENSO and northeast monsoon rainfall over South Asia

The southeastern parts of India and Sri Lanka receive substantial rainfall from the northeast monsoon (NEM) during October through December. The interannual variability in NEM rainfall is known to be significantly influenced by the El-Niño/Southern Oscillation (ENSO). Unlike the southwest monsoon (SWM), the NEM rainfall is enhanced during the warm ENSO events, and vice versa. In the context of the recent weakening of the inverse relationship between Southwest Monsoon (SWM) and ENSO, we examine the secular variations in the positive relationship between ENSO and NEM rainfall over South Asia, showing that their relationship has strengthened over the recent years. Based on the analysis of GISST, IMD/CRU precipitation and NCEP/NCAR reanalysis data, we suggest that this secular variation of the relationship is due to epochal changes in the tropospheric circulation associated with ENSO over the region.