长期天气预报的一种客观方案

本文叙述了用天气-统计学方法制作中长期亚洲范围内大气环流型预报的一种客观方案。本方案是以统计学方法划分自然天气季节和对每个自然天气季节内的候平均环流型进行分类为基础的,着重点在于强调以认识大气中的物理过程为基础来选择预报因子。本文的结果指出,用经验方法制作长期天气预报是可行的。     

北半球大气遥相关型的统计诊断及数值试验

此项研究旨在通过对北半球大气遥相关型的统计诊断及数值试验,探讨旬平均尺度遥相关型的存在和时空规律及其成因,以及各遥相关型之间的相互关系。结果表明:5种遥相关型在旬时间尺度上表现得十分清楚,且具有冬强夏弱的特点;各种遥相关型特征指数时间序列具有随时间演变的一般规律;某些海区的海温异常能激发出一定的遥相关型,5种遥相关型之间存在非线性相互作用;各种遥相关型特征指数能反映一定的大气环流和天气异常的特征,因而可以作为研究长期天气过程和预报方法的依据。     

应用自然正交函数逐年划分东亚自然天气季节的尝试

本文利用自然正交函数法研究了1964—1978年每年亚洲500毫巴候平均环流的季节变化特征,给出一种比较客观地划分东亚自然天气季节的方法。按照这个方法,东亚每年均可划分六个自然天气季节,即春、初夏、盛夏、秋、前冬和后冬,与文献[19]中用多年平均资料展开所得的结论一致。对这六个自然天气季节的平均环流状况和天气特征做了分析研究。     

平均经圈环流型的转变与长期天气过程

本文揭露,热带太平洋地区的平均经圈环流存在着两种最基本的类型:经典哈得来环流圈和哈得来反环流圈。它们的出现,不仅具有明显的季节特点,而且还存在着一类值得重视的非季节性的长期变化。平均经圈环流强度,具有周期大约48个月的长期振荡。这一振荡与赤道纬圈平面上垂直环流的变化有密切关系,并能对该地区大气的水平环流产生重要的影响。     

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。     

Identifying extreme hottest days from large scale upper air data: a pilot scheme to find California Central Valley summertime maximum surface temperatures

A pilot scheme uses upper air data from a few extreme hottest days to identify those and other extreme hottest days measured by 3 stations sampling the California Central Valley (CV). Prior work showed that CV extreme heat wave onsets have characteristic large scale patterns in many upper-air variables; those patterns also occur for the hottest days. A pilot scheme uses areas of two upper-air variables with high significance and consistency to forecast extreme surface temperatures. The scheme projects key parts of composite patterns for one or more variables onto daily weather maps of the corresponding variables resulting in a ??circulation index?? for each day. The circulation index measures how similar the pattern on that day is to the composite patterns in areas dynamically relevant to a CV extremely hot day, with a larger value for a stronger match and larger amplitude. The scheme is tested on the development period (1979?C1988) and on the subsequent 18?year ??independent?? period (1989?C2006). The pilot scheme captures about half of the rare events in the development period, with similar skill for the independent period. Based only on 16?days of extreme heat in the first 10?years, the scheme is not intended to represent the general distribution; however the circulation index has similar kurtosis, variance, and skewness as the observed maximum temperatures. Properties of the high end tail of the distribution are notably improved by adding the second predictor. The scheme outperforms simply using 850?hPa temperature above the CV.     

Winter atmospheric circulation patterns and their relationship with the meteorological conditions in Greece

This study presents an analysis of the relationship between winter large-scale circulation and surface meteorological conditions over Greece for the period 1979–2009. The adopted methodology involves the application of an automated atmospheric circulation classification scheme based on the self-organizing map approach. The impact of each of the identified relevant 19 winter atmospheric circulation patterns on local meteorological condition is examined at seven sites by calculating the corresponding differences from the mean meteorological conditions. The conditional transition probabilities of circulation patterns indicate the existence of increased 1-day persistence, especially for the anticyclonic and the pattern related to Genoa depressions. Positive temperature anomalies are observed for the cyclonic patterns, while negative anomalies are attributed to the effect of anticyclonic circulation.     

台风环流对远距离暴雨水汽输送影响研究

利用NCEP再分析资料,结合WRF模式对2008年7月17—19日发生在山东省的台风远距离暴雨水汽输送过程进行分析。结果表明：台风环流不仅有利于低纬度西太平洋水汽输送到山东内陆地区,而且迫使来自孟加拉湾的气流强度和方向发生变化,进而对远距离降水强度和持续时间产生重大影响;台风环流对鲁东南地区的水汽贡献远大于鲁西南地区,移除台风环流能间接地增强鲁西南地区的水汽供应;台风环流使远距离降水区水汽辐合范围集中,辐合强度增强,从而增强降水强度。     

Interannual horizontal heat advection in the surface mixed layer over the equatorial Pacific Ocean: assimilation versus TAO analysis

This study is motivated by an interest in obtaining a new automated classification scheme of daily circulation types suitable for use throughout Europe. The classification scheme is performed on 500 hPa geopotential height anomalies (NCEP Reanalysis data, 2.5°×2.5°). Nine grid points represent the study area. Five anticyclonic types (Anw, Ane, A, Asw and Ase) and seven cyclonic types (C, Cnnw, Cwnw, Cwsw, Cssw, Cse, Cne) are defined. Each of the circulation types has a distinct underlying synoptic pattern that produces the expected type and direction of flow over the study area. The classification scheme is applied to three different case studies in the Mediterranean Basin: Greece, Cyprus and central Italy. The precipitation percentage of the cyclonic type and the mean seasonal correlation coefficients for all circulation types are the two criteria used to evaluate the performance of the classification scheme. The ability of the HadAM3P general circulation model to reproduce the mean pattern and frequency of circulation types at the 500 hPa level in comparison to the NCEP dataset for the period 1960–1990 is also evaluated. The percentage of rainfall that corresponds to the cyclonic circulation types is greater than 85% for the three study regions. Furthermore, the correlation coefficients for the three classifications are very encouraging, for nearly all days of the study period. Compared to observations, the GCM is able to capture the mean patterns but not able to replicate exactly the observed variability of the circulation types over the three study regions.     

Global response to tropical diabatic heating variability in boreal winter

Global teleconnections associated with tropical convective activities were investigated, based on monthly data of 29 Northern Hemisphere winters: December, January, February, and March (DJFM). First, EOF analyses were performed on the outgoing long-wave radiation (OLR) data to characterize the convective ac- tivity variability in the tropical Indian Ocean and the western Pacific. The first EOF mode of the convective activity was highly correlated with the ENSO. The second EOF mode had an east-west dipole structure, and the third EOF mode had three convective activity centers. Two distinct teleconnection patterns were identified that were associated, respectively, with the second and third EOF modes. A global primitive equation model was used to investigate the physical mechanism that causes the global circulation anoma- lies. The model responses to anomalous tropical thermal forcings that mimic the EOF patterns matched the general features of the observed circulation anomalies well, and they were mainly controlled by linear processes. The importance of convective activities in the tropical Indian Ocean and western Pacific to the extended- and long-range forecasting capability in the extratropics is discussed.     

基于迁移CNN的江淮持续性强降水环流分型

利用新建的1981-2018年区域持续性强降水个例集、1981-2018年中国逐日降水量及NCEP/NCAR全球再分析资料,运用江淮地区持续性强降水典型模态个例样本及残差神经网络(CNN),通过迁移学习分步训练建立针对江淮强降水的环流客观分型模型;并运用该模型对1981-2015年全国持续性强降水个例的环流进行客观分型...     

利用多时次资料的EOF迭代温度长期预报

考虑多时次历史资料，基于ＥＯＦ迭代方案，将观测事实与统计方法结合，建立预报因子与预报对象的联系，开展长期预报试验。对四川盆地夏季温度的预报表明：这种容纳多时次资料、基于ＥＯＦ迭代的物理－统计预报方法是一种有效的长期预报途径。     

Role of intra-seasonal oscillations in modulating Indian summer monsoon rainfall

The day-to-day behavior of Indian summer monsoon rainfall (IMR) is associated with a hierarchy of quasi-periods, namely 3?C7, 10?C20 and the 30?C60?days. These two periods, the 10?C20?days and the 30?C60?days have been related with the active and break cycles of the monsoon rainfall over the Indian sub-continent. The seasonal strength of Indian summer monsoon rainfall may depend on the frequency and duration of spells of break and active periods associated with the fluctuations of the above intra-seasonal oscillations (ISOs). Thus the predictability of the seasonal (June through September) mean Indian monsoon depends on the extent to which the intra-seasonal oscillations could be predicted. The primary objective of this study is to bring out the dynamic circulation features during the pre-monsoon/monsoon season associated with the extreme phases of these oscillations The intense (weak) phase of the 10?C20 (30?C60) days oscillation is associated with anti-cyclonic circulation over the Indian Ocean, easterly flow over the equatorial Pacific Ocean resembling the normal or cold phase (La Nina) of El Nino Southern Oscillation (ENSO) phenomenon, and weakening of the north Pacific Sub-tropical High. On the other hand the weak phase of 10?C20?days mode and the intense phase of 30?C60?days mode shows remarkable opposite flow patterns. The circulation features during pre-monsoon months show that there is a tendency for the flow patterns observed in pre-monsoon months to persist during the monsoon months. Hence some indications of the behavior of these modes during the monsoon season could be foreshadowed from the spring season patterns. The relationship between the intensity of these modes and some of the long-range forecasting parameters used operationally by the India Meteorological Department has also been examined.     

A seasonal study of the atmospheric dynamics over the Iberian Peninsula based on circulation types

A seasonal analysis of the atmospheric circulation over the Iberian Peninsula (IP) based on circulation types (CTs) obtained from sea level pressure and 500-hPa geopotential height is presented. The study covers the period of 1958–2008, when a high variability and important changes in winter and spring precipitation and temperature have been reported. Frequency, persistence, and the most probable transitions of the circulation types are analyzed. Among the clustering methods available in the literature, two of the most reliable classification methods have been tested, K-means and simulated annealing and diversified randomization. A comparison of both methods over the IP is presented for winter (DJF). The quality of the circulation types obtained through both methods as well as the better stability achieved by K-means suggest this method as more appropriated for our target area. Twelve CTs were obtained for each season and were analyzed. The patterns obtained were regrouped in five general situations: anticyclonic, cyclonic, zonal, summertime, and hybrid-mixed. The analysis of frequencies of these situations offers a similar characterization of the atmospheric circulation that others previously obtained by subjective methods. The analysis of the trends in frequency and persistence for each CT shows few significant trends, mainly in winter and spring with a general decrease of the cyclonic patterns and an increase of the anticyclonic situations. This can be related to the negative precipitation trends reported by other authors. Regarding the persistence, an interesting result is that there is a high interannual variability of the persistence in autumn and spring, when patterns can persist longer than in other seasons. An analysis of the most probable transitions between the CTs has been performed, revealing the existence of cyclic sequences in all seasons. These sequences are related to the high frequency of certain patterns such as the anticyclonic situations in winter. Finally, a clear seasonal dependence of the transitions between cyclonic situations associated with extratropical disturbances was found. This dependence suggests that the transitions of low-pressure systems towards the south of the IP are more likely in spring and autumn than in winter.     

The influence of regional circulation patterns on wet and dry mineral dust and sea salt deposition over Greenland

Annually resolved ice core records from different regions over the Greenland ice sheet (GrIS) are used to investigate the spatial and temporal variability of calcium (Ca²⁺, mainly from mineral dust) and sodium (Na⁺, mainly from sea salt) deposition. Cores of high common inter-annual variability are grouped with an EOF analysis, resulting in regionally representative Ca²⁺ and Na⁺ records for northeastern and central Greenland. Utilizing a regression and validation method with ERA-40 reanalysis data, these common records are associated with distinct regional atmospheric circulation patterns over the North American Arctic, Greenland, and Central to Northern Europe. These patterns are interpreted in terms of transport and deposition of the impurities. In the northeastern part of the GrIS sea salt records reflect the intrusion of marine air masses from southeasterly flow. A large fraction of the Ca²⁺ variability in this region is connected to a circulation pattern suggesting transport from the west and dry deposition. This pattern is consistent with the current understanding of a predominantly Asian source of the dust deposited over the GrIS. However, our results also indicate that a significant fraction of the inter-annual dust variability in NE and Central Greenland is determined by the frequency and intensity of wet deposition during the season of high atmospheric dust loading, rather than representing the variability of the Asian dust source and/or long-range transport to Greenland. The variances in the regional proxy records explained by the streamfunction patterns are high enough to permit reconstructions of the corresponding regional deposition regimes and the associated circulation patterns.     

热带季节内振荡模拟研究的若干进展

大气季节内振荡（ISO）在长期天气和气候变化中有重要作用,它是20世纪70～80年代以来大气科学领域的重要研究课题。本文简要介绍近年来季节内振荡的数值模拟研究的成果和进展,包括数值模式模拟季节内振荡能力的进展; 模式模拟ISO能力对模式中对流参数化方案的敏感性;ISO模拟结果与基本态的关系;外强迫对模拟结果的影响; ENSO与ISO关系的模拟研究,以及全球变暖对ISO影响的模拟研究等。最后,对今后的研究工作提出了一些建议。     

大气环流变化对云南5月雨量的影响及其预报

本文分析了云南５月份降水与前期１－３月北半球１００，５００ｈＰａ高度场的关系，研究了影响云南５月份旱涝的大气环流系统及主要大气活动中心，探讨了遥相关场的波列结构，建立了基于环流演变物理概念的分析预报模式。     

全球热带海表温度异常的POP预报模型

在对全球热带海表温度异常（ＳＳＴＡ）进行主振荡型（ＰＯＰ）分析的基础上上综合考虑大尺度海洋运动状况和长期预报的特征引入了相位划分预报方案,将典型ＰＯＰ模态进行相位划分并综合考虑它们的相关位承替规律预报ＳＳＴＡ未来发展趋势,独立样本事后预报结核下实相位划分预报方案能提供较好的预报信息。     

Multivariate and multiscale dependence in the global climate system revealed through complex networks

A systematic characterization of multivariate dependence at multiple spatio-temporal scales is critical to understanding climate system dynamics and improving predictive ability from models and data. However, dependence structures in climate are complex due to nonlinear dynamical generating processes, long-range spatial and long-memory temporal relationships, as well as low-frequency variability. Here we utilize complex networks to explore dependence in climate data. Specifically, networks constructed from reanalysis-based atmospheric variables over oceans and partitioned with community detection methods demonstrate the potential to capture regional and global dependence structures within and among climate variables. Proximity-based dependence as well as long-range spatial relationships are examined along with their evolution over time, yielding new insights on ocean meteorology. The tools are implicitly validated by confirming conceptual understanding about aggregate correlations and teleconnections. Our results also suggest a close similarity of observed dependence patterns in relative humidity and horizontal wind speed over oceans. In addition, updraft velocity, which relates to convective activity over the oceans, exhibits short spatiotemporal decorrelation scales but long-range dependence over time. The multivariate and multi-scale dependence patterns broadly persist over multiple time windows. Our findings motivate further investigations of dependence structures among observations, reanalysis and model-simulated data to enhance process understanding, assess model reliability and improve regional climate predictions.     

中国东部夏季降水与东亚垂直环流结构及其预测试验

本文在分析中国东部夏季降水的时空分布特征基础上, 从东亚高、中、低层大尺度环流异常着手, 选取对中国东部夏季降水异常有显著影响的大气环流预报因子, 分别应用逐步回归和最优子集回归法两种统计降尺度方法, 以动力气候模式CAM3.1预报输出的大气环流预报因子为基础, 以中国东部夏季降水的典型空间分布型为预报对象, 建立动力与统计相结合的中国东部夏季降水预测模型, 并对1981～2000年的中国东部夏季降水进行回报试验。结果表明: 中国东部夏季降水具有4类典型的空间分布型式, 且具有显著的准2年和年代际尺度振荡周期; 东亚高、中、低层大气环流异常的特定配置, 对东部夏季降水的空间分布型有显著影响; 使用两种降尺度方案建立的动力与统计相结合的预测模型对中国东部夏季降水异常具有一定的预报技巧, 可以在一定程度上提高动力模式对中国东部夏季降水的预报效果。