Use of a synoptic classification scheme to define seasons

Summary This paper presents a synoptic surface weather map classification scheme, and uses the categorization technique to meteorologically define seasons. Winter is defined as that period of the year in which a location is most frequently poleward of the polar front, while summer occurs when the site is most commonly equatoward. Fall and Spring are the transition periods when, respectively, increasingly more frequent and less frequent periods of time poleward of the polar front occur.Using 10 years of data, the application of this definition of seasons to the Gulf and Atlantic coasts of the United States is presented. While the frequency of the specific types of major synoptic weather features varied with latitude, the meteorological definitions of season are comparatively invariant with latitude (differing by no more than a month) for this geographic area. Using the meteorological definitions of season, the average winter for this region occurs from late October or early November to late March or early April. Summer is from late May to early June until late August or late September.

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Zusammenfassung Diese Arbeit stellt ein synoptisches Klassifikationsschema nach Bodenwetterkarten vor, das eine Kategorisierungstechnik verwendet, um die Jahreszeiten meteorologisch zu definieren. Der Winter ist als die Periode des Jahres festgelegt, in der ein Ort meist polwärts der Polarfront, während der Sommer jene Periode ist, in der er äquatorwärts der Polarfront liegt. Herbst und Frühjahr sind die Übergangsperioden, in denen zunehmend häufigere bzw. weniger häufige Abschnitte polwärts der Polarfront vorkommen.Die Anwendung dieser Jahreszeitendefinition wird mit Hilfe der Daten aus 10 Jahren für die Atlantik- und Golfküste der Vereinigten Staaten vorgestellt. Während die Häufigkeiten bestimmter Wetterlagen mit der geographischen Breite schwanken, erwies sich diese meteorologische Jahreszeitendefinition demgegenüber als vergleichbar invariant (mit einem maximalen Unterschied von einem Monat) innerhalb des ausgewählten Gebiets. Der so definierte Winter dieser Region beginnt zwischen Ende Oktober und Anfang November und dauert bis Ende März bzw. Anfang April. Sommer ist zwischen Ende Mai/Anfang Juni und Ende August/Ende September.

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With 21 Figures     

An assessment of European synoptic variability in Hadley Centre Global Environmental models based on an objective classification of weather regimes

The frequency of occurrence of persistent synoptic-scale weather patterns over the European and North-East Atlantic regions is examined in a hierarchy of climate model simulations and compared to observational re-analysed data. A new objective method, employing pattern correlation techniques, has been constructed for classifying daily-mean mean-sea-level pressure and 500 hPa geopotential height fields with respect to a set of 29 European weather regime types, based on the widely known subjective Grosswetterlagen (GWL) system of the German Weather Service. The objective method is described and applied initially to ERA40 and NCEP re-analysis data. While the resulting daily Objective-GWL catalogue shows some systematic differences with respect to the subjectively-derived original GWL series, the method is shown to be sufficiently robust for application to climate model output. Ensemble runs from the most recent development of the Hadley Centre’s Global Environmental model, HadGEM1, in atmosphere-only, coupled and climate change scenario modes are analysed with regards to European synoptic variability. All simulations successfully exhibit a wide spread of GWL occurrences across all regime types, but some systematic differences in mean GWL frequencies are seen in spite of significant levels of interdecadal variability. These differences provide a basis for estimating local anomalies of surface temperature and precipitation over Europe, which would result from circulation changes alone, in each climate simulation. Comparison to observational re-analyses shows a clear and significant improvement in the simulation of realistic European synoptic variability with the development and resolution of the atmosphere-only models.     

An assessment of climatological synoptic typing by principal component analysis and kmeans clustering

A common method of automated synoptic typing for climatological investigations involves data reduction by principal component analysis followed by the application of a clustering method. The number of eigenvectors kept in the principal component analysis is usually determined by a threshold value of relative variance retained, typically 85% to 95%, under the implicit assumption that varying this relative variance will not affect the resultant synoptic catalogue. This assumption is tested using daily 500-mb geopotential heights over northwest Canada during the winter period (December to February) from 1948 to 2006. Results show that the synoptic catalogue and associated surface climatological characteristics undergo changes for values of relative variance retained over 99%, indicating the typical thresholds are too low and calling into question the validity of performing principal component analysis prior to objective clustering.     

Effects of air masses and synoptic weather on aerosol formation in the continental boundary layer

Nucleation of near nm sized aerosol particles and subsequent growth to ∼100 nm in 1–2 days has in recent years been frequently observed in the continental boundary layer at several European locations. In 1998–99, this was the focus of the BIOFOR experiment in Hyytiälä in the boreal Finnish forest. Nucleation occurred in arctic and to some extent in polar air masses, with a preference for maritime air in transition to continental air masses, and never in sub‐tropical air. The air masses originated north of the BIOFOR experiment by paths from the southwest to northeast sector. The nucleation was also associated with cold air advection behind cold fronts, never warm air advection. This may relate to low pre‐existing aerosol concentration, low cloudiness and large diurnal amplitudes in the continental boundary layer associated with cold air advection and clear skies. Arctic and polar air together with cold air advection did not always lead to nucleation. The most important limiting meteorological factors were cold front passages and high cloudiness, probably through reduced photochemistry and wet scavenging of precursor gases and new aerosol particles. The preference for nucleation to occur in arctic air masses, which seldom form in the summer, suggests a meteorological explanation for the annual cycle of nucleation, which has a minimum in summer. The connection to cold‐air outbreaks suggests that the maximum in nucleation events during spring and autumn may be explained by the larger latitudinal temperature gradients and higher cyclone activity at that time of the year. Nucleation was observed on the same days over large parts (1000‐km distance) of the same air mass. This suggests that the aerosol nucleation spans from the microphysical scale to the synoptic scale, perhaps connected through boundary layer and mesoscale processes.     

An overview of the Madden-Julian oscillation and its relation to monsoon and mid-latitude circulation

In the past decade there has been extensive research into tropical intraseasonal variability, one of the major com-ponents of the low frequency variability of the general atmospheric circulation. This paper briefly reviews the state-of-the-art in this research area: the nature of the Madden-Julian Oscillation, its relation to monsoonal and extratropical circulations, and the current theoretical understandings.     

一次典型转折性天气过程分析

利用常规观测资料对2007—07—10云南省大理州久旱转大雨天气进行分析,结果表明：此次久旱转大雨天气出现在中纬度环流经向度加大,副高东退的形势下;500hPa云南以西反气旋环流的减弱,高空冷平流的入侵对降雨的启动和加大至关重要,700hPa切变线为降雨提供了动力机制;水汽通量散度、垂直上升运动与大雨的发生有较好的对应关系。     

贵州省中部一次暴雨天气过程分析

利用常规气象资料、卫星云图、物理量场等对2007-07-09-10日出现在贵州省中部的暴雨天气过程的影响系统、物理量场分析等进行了分析,结果表明：副热带高压的快速东退使南支槽与北面高空浅槽在贵州西北部合并加深南移,引导位于四川南部的中低层切变快速南下到贵州中部,促使贵州中部地面辐合区锋生增强进而引发暴雨天气过程;水汽辐合中心为此次强降水提供了有利的水汽条件,加之强烈的上升运动,使辐合区得到加强发展,导致了暴雨天气的产生。     

Statistical comparison of European circulation patterns and development of a continental scale classification

Summary In this paper several circulation pattern classifications developed for different European regions are compared with respect to their mutual dependence. Circulation pattern (CP) classifications – both subjective and objective – for the British Isles, Germany and Greece were considered. Statistical tests were applied in order to investigate the relationships between each pair of CP classifications. It was found that each pair of classifications cannot be considered to be independent. Time dependence in the relationship between CP classifications shows anomalous behavior only when one of the classifications is subjective. This is due to a gradual change in the methodology, and therefore these classifications should be used for climate evolution studies with care. The dependence between each pair of CP classifications was motivation for developing a new CP classification for the whole European continent which is presented. It is shown that for the local precipitation variability almost no information is lost when comparing this new classification with local classifications.     

济南市区短时强降水特征分析与天气分型

利用2007—2015年济南市区及历城区自动气象观测站的逐小时降水量资料,以及常规高空、地面观测资料,统计了198次短时强降水过程的范围和强度特征,年际、月际变化特征,按照短时强降水发生时的天气形势和影响系统,分为切变线型、低槽冷锋型、西风槽型、冷涡型、台风外围型及无系统型6类,并分析了不同类型和不同范围短时强降水的关键环境参量。研究表明：短时强降水的强度与范围有较好的相关性,7月中旬—8月中旬出现强降水的次数最多;切变线型短时强降水发生范围与强度分布最广,7、8月的低槽冷锋型过程极易造成大范围高强度降水;地面露点（Td）、850 hPa假相当位温（θse）、对流有效位能（CAPE）以及暖云层厚度能较好地区分不同范围的短时强降水过程。在天气分型的基础上,结合不同降水范围和不同降水类型环境参量箱线图与阈值表,可为济南市区短时强降水的预报提供有价值的参考。      

2004年初冬时节一次强对流天气过程分析

通过对2004年初冬时节一次强对流天气过程的天气形势、物理量、卫星云图、雷达回波等实况资料和数值预报资料的分析，以及通过自动站临近数据的调用和上下信息通报反馈的临近实况资料分析，总结出初冬时节强对流天气出现的主要原因以及作好其预报和服务的手段、方法和措施建议。     

台风移动的分型统计预报方法

一、前言 近年来,用逐步回归的统计预报方法作台风路径的短期预报,已成为许多气象台预报业务中常用的工具之一,这个方法结合了预报员们的实践经验,经两年的使用结果证明是有一定参考价值的。目前的改进主要采取以下几个途径:(1)提高预报因子的质量,着重在各个因子的天气意义方面和台风移动之间相关性的提高。(2)对统计样本先作天气     

青岛市短时强降水的气候特征和天气系统分型

利用1981—2012年4—10月青岛市7个观测站逐时降水量资料和同期NCEP再分析资料,统计分析青岛市短时强降水的时空分布特征,建立青岛市短时强降水天气概念模型。结果表明：青岛市年短时强降水日数无明显变化趋势;4—10月均有短时强降水出现,7—8月是多发月份;短时强降水的日变化有2个多发时段,主峰在下午到傍晚时段,次峰在凌晨时段;即墨、平度、黄岛为青岛市短时强降水的多发区域,其中黄岛为连续性短时强降水出现最多的区域;青岛市产生短时强降水的天气系统可分为六种类型,西风槽型、横槽型、冷涡型、热带低值系统型、西北气流型、切变线型,其中西风槽型出现次数最多。     

天气预报现代化的途径

当前华主席、党中央为我们指明了科学技术现代化的目标,要求我们能尽快地实现科学技术现代化。大气科学的中心任务是提高天气予报的准确度,天气予报的进展是整个大气科学发展的基础。因此怎样使我国的天气予报科学实现现代化,是我们气象工作者应该考虑的重要问题。本文想从近代天气予报科学的进展情况讨论一下这个问题。     

Diurnal and seasonal variations of radioactivity and electrical conductivity near the surface for a continental location Mysore, India

Simultaneous measurements of the activity concentrations of radon and its progeny, and conductivity of both polarities i.e., positive and negative conductivities, were made at a height of 1 m above the ground at Mysore (12°N, 76°E, 767 m above mean sea level), India. Diurnal and seasonal variations of activities of radon and its progeny show their peak values in the early morning hours throughout the year. Observations show an increase in the concentration of radon and its progeny during nighttime compared to the daytime values, and are higher in winter than in other seasons. The electrical conductivity of the atmosphere that depends on the ionization rate also exhibits similar trends. These results are discussed in terms of ionization rate due to radioactivity and the influence of meteorological parameters on radioactivity. The results also show that the concentrations of radon, its progeny, and the electrical conductivity of both polarities exhibit a positive correlation with the relative humidity and are negatively correlated with the temperature of the atmosphere.     

An assessment of the climate change impacts on groundwater recharge at a continental scale using a probabilistic approach with an ensemble of GCMs

This study used 16 Global Climate Models and three global warming scenarios to make projections of recharge under a 2050 climate for the entire Australian continent at a 0.05° grid resolution. The results from these 48 future climate variants have been fitted to a probability distribution to enable the results to be summarised and uncertainty quantified. The median results project a reduction in recharge across the west, centre and south of Australia and an increase in recharge across the north and a small area in the east of the continent. The range of results is quite large and for large parts of the continent encompasses both increases and decreases in recharge. This makes it difficult to utilise for water resources management so the results have been analysed with a risk analysis framework; this enables the future projections for groundwater recharge to be communicated to water managers in terms of likelihood and consequence of a reduction in recharge. This highlights an important message for water resource managers that in most areas of Australia they will be making decisions on water allocations under considerable uncertainty as to the direction and magnitude of recharge change under a future climate and that this uncertainty may be irreducible.     

北极臭氧垂直分布和天气尺度变化的观测研究

北极地区臭氧对北极气候和环境系统起着重要作用。研究其分布和变化有助于了解北极的气候和环境及其对全球气候系统的影响,有助于气候和环境变化的数值预报。中国北极科学探测1999在北冰洋楚可奇海域成功的进行了大气臭氧观测。通过在中国“雪龙”号破冰船甲板上（于1999年8月18-24日在75°N,160°W附近处）释放大气臭氧探空仪获得了高分辨率的大气垂直结构和臭氧分布资料,可以进行大气尺度的大气臭氧变化研究。分析大气监测资料、TOMS臭氧总量资料和NCEP大气环流资料表明,大气臭氧总量随着对流层顶的低一高一低变化呈高一低一高的变化过程。研究还表明,大气柱的臭氧总量与13公里以下的大气臭氧含量关系密切,而在约20公里处的大气臭氧浓度最大值的变化与整个气柱臭氧的关系不大。500 hPa天气形势图上一个弱一强一弱的西南天气型造成的弱臭氧平流可能是这次臭氧变化的主要原因。     

Sensitivity to domain size of mid-latitude summer simulations with a regional climate model

The issue of Regional Climate Model (RCM) domain size is studied here by using a perfect-model approach, also known as the Big-Brother experiment. It is known that the control exerted by the lateral boundary conditions (LBC) on nested simulations increases when reducing the domain size. The large-scale component of the simulation that is forced by the LBC influences the small-scale features that develop along the large-scale flow. Small-scale transient eddies need space and time to develop sufficiently however, and small domains can impede their development. Our tests performed over eastern North America in summer reveal that the small-scale features are systematically underestimated over the entire domain, even for domain as large as 140 by 140 grid points. This result differs from that obtained in winter where the small scales were mainly underestimated on the west (inflow) side of the domain. This difference is due to the circulation regime over Eastern Canada, which is characterized by weak and variable flow in summer, but strong and westerly flow in winter. For both seasons, the small-scale transient-eddy amplitudes are systematically underestimated at higher levels, but this problem is less severe in summer. Overall the model is more skilful in regenerating the small scales in summer than in winter for comparable domain sizes, which can be related to the weaker summer flow and stronger physical processes occurring in this season.     

陕南一次突发性暴雨天气过程分析

根据突发性暴雨的定义，选择了陕西1980-06-15的一次突发性暴雨过程，通过对涡度、散度、位势稳定度、水汽通量等物理量分析，试图揭示突发性暴雨发生的内在机理、机制，以便对突发性暴雨有进一步认识。     

天气系统预报效果的量化检验方法及应用

对中国天气过程进行了分类,并介绍了一种针对模式对于降水及各种天气系统预报效果的天气学检验方法,将此方法应用于AREM模式对2007年降水个例预报及2005—2007年汛期天气过程的批量预报检验,得出结论如下:(1)此天气学检验方法能够对各类天气系统及降水进行有效的检验,(2)对于中国典型高空槽类降水,AREM模式总体上对高空槽预报较为稳定、强度接近实况,对降水预报稳定性相对较差、强度偏弱,槽预报的较好(差)与降水预报的较好(差)不完全对应,(3)对于梅雨锋类降水,AREM模式对副高预报总体偏西、偏北、偏强,对高空槽、降水预报均总体偏弱,副高预报的较好(差)对应降水预报的较好(差)。