Projected evolution of circulation types and their temperatures over Central Europe in climate models

The study deals with changes in large-scale atmospheric circulation (represented by circulation types) and associated surface air temperatures as projected in an ensemble of regional climate models (RCMs) from the ENSEMBLES project. We examine changes of circulation type frequencies and means of daily maximum and minimum temperatures within circulation types in individual seasons for two time slices of transient runs under the SRES A1B scenario (2021–2050 and 2071–2100) with respect to the control period (1961–1990). To study the influence of driving data, simulations of the driving general circulation models (GCMs) also are evaluated. We find that all models project changes of atmospheric circulation that are statistically significant for both future time slices. The models tend to project strengthening of the westerly circulation in winter and its weakening in summer. We show that increases of daily maximum and minimum temperatures in all seasons differ for individual circulation types. There are, however, only few features of the projected changes in the future circulation–temperature links that are common among the models, in particular relatively smaller warming for westerly types. Only in winter, projected changes in circulation types tend to contribute to the projected overall warming. This effect is negligible and mostly opposite in the other seasons. We also detect a strong influence of driving data on RCMs’ simulation of atmospheric circulation and temperature changes.     

A shift of the NAO and increasing storm track activity over Europe due to anthropogenic greenhouse gas forcing

 In accordance with a number of other general circulation model experiments, the coupled atmosphere-ocean-GCM ECHAM4+OPYC3 simulates increasing upper air storm track activity over the east Atlantic and Western Europe with rising greenhouse gas forcing. This paper addresses the question to what extent this change is attributable to the variable north Atlantic Oscillation (NAO), which is closely related to the intensity of the Atlantic storm track’s extension into Europe. The NAO index, which is based on sea level pressure fluctuations over the north Atlantic in the 300-y control run of this model, only shows a moderate increase within the 240-y scenario run, so that its long-term trend does not exceed the variability of the control climate before the end of the simulation. In contrast, the steadily growing storm track activity over northwestern Europe already surpasses the standard deviation defined from the control run after about 160 y. This effect is associated with a change of the NAO pattern. A determination of the centres of action for subsequent 10-y periods based on empirical orthogonal functions shows a systematic northeastward shift of the NAO’s northern variability centre from a position close to the east coast of Greenland, where it is also located in the control run, to the Norwegian Sea. Received: 10 September / Accepted: 15 January 1999     

Biogenic and anthropogenic organic matter in aerosol over continental Europe: source characterization in the east Baltic region

An Aerodyne quadruple aerosol mass spectrometer (Q-AMS) has been used to provide on-line measurements of size dependent chemical composition of fine aerosol particles (PM₁) at the Air Pollution Research Station in Preila, Lithuania, representing the east Baltic region. The size dependent chemical composition measurements by AMS have revealed that in marine air masses 118?nm mode organics-containing particles were fresher compared to sulfate-containing particles (295?nm), likely originated as secondary aerosol from forest emissions or produced by primary sea spray over the Baltic Sea. In polluted continental air masses sulfate and organics were highly internally mixed and aged. The mass spectral results indicated that the major components of organic compounds were oxygenated organic species with strong signals at m/z 18, 43, 44 with several specific features. Positive matrix factorization (PMF) of AMS organic mass spectral data has identified three factors: aged oxygenated low-volatility organic aerosol (LV-OOA), less oxygenated semi-volatile organic aerosol (SV-OOA), and biogenic organic aerosol (BGOA) of either terrestrial or marine origin. The measurements were compared with a real-time particulate matter Beta Absorption Monitor (Thermo ESM Andersen) and Micro Orifice Uniform Deposit Impactor (MOUDI) data. The intercomparison showed a good correlation and a stable ratio between PM₁ and PM_2.5 concentrations. A comparison of the on-line Q-AMS data and the off-line MOUDI fine particle (<1???m) data yielded a reasonable agreement in size distributions but not the absolute mass concentrations due to sampling conditions, evaporation of acidic species from sampling substrates and bounce of the particles in the MOUDI.     

The anthropogenic influence on carbonaceous aerosol in the European background

To constrain the relatively uncertain anthropogenic impact on the organic aerosol load, radiocarbon analyses were performed on aerosol samples, collected year-round, at six non-urban sites including a maritime background and three remote mountain stations, lying on a west-east transect over Western Europe. From a crude three component model supported by TOC and levoglucosan filter data, the fossil fuel, biomass burning and biogenic TOC fraction are estimated, showing at all stations year-round, a relatively constant fossil fuel fraction of around  (26 ± 6)%  , a dominant biogenic contribution of on average  (73 ± 7)%  in summer and the continental as well as the maritime background TOC to be only about 50% biogenic. Assuming biomass burning as completely anthropogenic, the carbonaceous aerosol concentration at the mountain sites was found to have increased by a factor of up to  (1.4 ± 0.2)  in summer and up to  (2.5 ± 1.0)  in winter. This figure is significantly lower, however, than the respective TOC change since pre-industrial times seen in an Alpine ice core. Reconciling both observations would require an increase, since pre-industrial times, of the background biogenic aerosol load, which is estimated at a factor of 1.3–1.7.     

The natural aerosol over Northern Europe and its relation to anthropogenic emissions—implications of important climate feedbacks

We use a recently developed parametrization to estimate the regional particle field in the summer time troposphere over Scandinavia that would result if the forest were the only source of particles. The calculated field is compared with available observational data. It is concluded that the needle leaf forest above 58°N alone is capable of producing aerosol mass concentrations corresponding to 12–50% of today's values in the boundary layer over Scandinavia. We also demonstrate that the forest itself could produce up to 200 CCN per cubic centimetre on average over Scandinavia and further show that an increase in temperature by 5.8 °C compared to today's average temperature could increase this CCN population by 40%. The study shows that we are able to approximate the natural aerosol field resulting from biogenic emissions over the boreal forest in the northern hemispheric region. This information provide an important contribution in the evaluation of the climate effect caused by anthropogenic emissions of particles over the forest and also opens the possibility to better address the climate feedbacks believed to be associated with the boreal region.     

ENSO influence on Europe during the last centuries

El Niño/Southern Oscillation (ENSO) affects climate not only in the Pacific region and the tropics, but also in the North Atlantic-European area. Studies based on twentieth-century data have found that El Niño events tend to be accompanied in late winter by a negative North Atlantic Oscillation index, low temperatures in northeastern Europe and a change in precipitation patterns. However, many questions are open, for example, concerning the stationarity of this relation. Here we study the relation between ENSO and European climate during the past 500 years based on statistically reconstructed ENSO indices, early instrumental station series, and reconstructed fields of surface air temperature, sea-level pressure, precipitation, and 500 hPa geopotential height. After removing years following tropical volcanic eruptions (which systematically mask the ENSO signal), we find a consistent and statistically significant ENSO signal in late winter and spring. The responses to El Niño and La Niña are close to symmetric. In agreement with studies using twentieth-century data only, the ENSO signal in precipitation is different in fall than in late winter. Moving correlation analyses confirm a stationary relationship between ENSO and late winter climate in Europe during the past 300 years. However, the ENSO signal is modulated significantly by the North Pacific climate. A multi-field cluster analysis for strong ENSO events during the past 300 years yields a dominant pair of clusters that is symmetric and represents the ‘classical’ ENSO effects on Europe.     

亚洲地区人为气溶胶对东亚冬季风影响的研究

利用耦合化学过程的区域气候模式RegCM4.0,研究亚洲地区硫酸盐、黑碳和有机碳3种人为气溶胶的直接气候效应对东亚冬季风的影响;并运用相关分析与合成分析方法,研究了东亚人为气溶胶主要分布区中人为气溶胶浓度变化对东亚冬季风的影响。结果表明:人为气溶胶对东亚热带和副热带冬季风均起增强作用;人为气溶胶使得中国南方东部地区的冬季降水减少。2000—2007年,秋、冬季东亚人为气溶胶主要分布区中,人为气溶胶总体呈现减少的趋势,分别导致了东亚冬季风建立的推迟和东亚冬季风的减弱。相关分析和合成分析也表明:在东亚人为气溶胶主要分布区中的人为气溶胶柱浓度含量增加,东亚冬季风的建立提前并且东亚冬季风加强,反之亦然。人为气溶胶引起陆地地表降温,而对海洋温度几乎没有影响,使低层海陆温差加大,从而导致低层海陆气压差加大,东亚冬季风的增强可能与此有关。     

基于BCC＿CSM模式的破纪录高温事件研究

利用国家气候中心发展的海气耦合模式BCC_CSM 1.1模拟的北半球逐日最高气温数据探讨了近年来破纪录高温事件频数变化特征,并预估了其在未来不同情景排放下的可能变化。基于单点逐日最高气温模拟资料呈正态分布及破纪录高温事件符合随机理论,对北半球近50 a破纪录高温事件频数进行了模拟与理论的对比分析。结果表明:破纪录高温事件频数模拟理论比呈现显著的上升趋势,且这种上升趋势海洋大于陆地,低纬大于高纬;通过与气温相关分析得知破纪录高温事件频数模拟理论比的上升趋势主要是由北半球气温上升导致。在此基础上,比较了RCP4.5与RCP8.5两种不同排放情景下破纪录高温事件频数模拟理论比的变化特征,结果表明在后期(2060—2098)二者差异显著,前者变化较为平稳,而后者具有显著上升趋势,这种差异是对气温不同变化的响应,且低纬海洋的响应比陆地更为敏感。     

The influence of the Arctic Oscillation on winter temperatures in Iran

Summary The impact of the Arctic Oscillation (AO) on the winter surface air temperature (SAT) over Iran is demonstrated. Winter SAT data for 50 years (1951–2000) are analyzed for the negative and the positive AO phases. Using the Median Sequential Correlation Analysis (MSCA) technique it is shown that the winter SAT is negatively correlated to the winter AO index for most parts of Iran. The winter AO index accounts for about 14% to 46% of the winter SAT variance. The positive (negative) SAT anomaly is found to be associated with the onset of the negative (positive) phase. The overall probability of below long-term mean temperature during the positive and the negative phases are estimated to be around 70% and 25%, respectively. For the negative phase, westerly winds that originate from the warm Atlantic regions increase over Iran and consequently positive temperature anomalies are found across the country. The positive AO phase is accompanied by northerly winds that allow continental polar and arctic air masses to move into Iran, producing below normal temperatures. The summer AO is found to explain about 25–32% of the winter SAT variance in Iran. The reason for this is explained by the significant correlation (+0.38) between the summer and the following winter AO indices. These results indicate that the summer climate is linked to changes in atmospheric circulation which persist through to the following autumn and winter.     

Occurrence and features of ducted modes of internal gravity waves over western Europe and their influence on microwave propagation

Several years of intense investigation of internal gravity waves propagating in low-level ducts in the atmosphere over a rather flat region not influenced by land-sea circulation or mountains are reported. This study gives a rather complete picture of the occurrence, features, and of some of the excitation conditions of these waves. Simultaneous direct measurements made on a meteorological tower, 250 m high, using temperature, vector wind, and sonic anemometer sensors at different altitudes are reported along with indirect measurements using an array of microbarographs with separations over a range of more than 100 km. The study also included microwave propagation links crossing over the meteorological site. Individual wave crests some tens of kilometers long could be followed over a path of more than 100 km. Because of the variability and non-stationary conditions of the lower atmosphere, a direct correlation between a propagating internal wave group and the fading pattern of EM propagation could be found in only a few cases.It is interesting to note Goldie's references to Kelvin and Helmholtz in this regard.     

Detection of anthropogenic climate change using an atmospheric GCM

 Atmosphere-only general circulation models are shown to be a useful tool for detecting an anthropogenic effect on climate and understanding recent climate change. Ensembles of atmospheric runs are all forced with the same observed changes in sea surface temperatures and sea-ice extents but differ in terms of the combinations of anthropogenic effects included. Therefore, our approach aims to detect the `immediate' anthropogenic impact on the atmosphere as opposed to that which has arisen via oceanic feedbacks. We have adapted two well-used detection techniques, pattern correlations and fingerprints, and both show that near-decadal changes in the patterns of zonal mean upper air temperature are well simulated, and that it is highly unlikely that the observed changes could be accounted for by sea surface temperature variations and internal variability alone. Furthermore, we show that for zonally averaged upper air temperature, internal `noise' in the atmospheric model is small enough that a signal emerges from the data even on interannual time scales; this would not be possible in a coupled ocean-atmosphere general circulation model. Finally, although anthropogenic forcings have had a significant impact on global mean land surface temperature, we find that their influence on the pattern of local deviations about this mean is so far undetectable. In order to achieve this in the future, as the signal grows, it will also be important that the response of the Northern Hemisphere mid-latitude westerly flow to changing sea surface temperatures is well simulated in climate model detection studies. Received: 3 December 1999 / Accepted: 30 October 2000     

Simulation of the anthropogenic aerosols over South Asia and their effects on Indian summer monsoon

A regional climate model coupled with a chemistry-aerosol model is employed to simulate the anthropogenic aerosols including sulfate, black carbon and organic carbon and their direct effect on climate over South Asia. The model is driven by the NCAR/NCEP re-analysis data. Multi-year simulations with half, normal and double emission fluxes are conducted. Results show that the model performs well in reproducing present climate over the region. Simulations of the aerosol optical depth and surface concentration of aerosols are also reasonable although to a less extent. The negative radiative forcing is found at the top of atmosphere and largely depended on emission concentration. Surface air temperature decreases by 0.1?C0.5°C both in pre-monsoon and monsoon seasons. The range and intensity of cooling areas enlarge while aerosol emission increases. Changes in precipitation are between ?25 and 25%. Different diversifications of rainfall are showed with three emission scenarios. The changes of precipitation are consistent with varieties of monsoon onset dates in pre-monsoon season. In the regions of increasing precipitation, monsoon onset is advanced and vice versa. In northeast India and Myanmar, aerosols lead the India summer monsoon onset advancing 1?C2 pentads, and delaying by 1?C2 pentads in central and southeast India. These changes are mainly caused by the anomaly of local Hadley circulations and enhancive precipitation. Tibetan Plateau played a crucial role in the circulation changes.     

Mathematical modeling used for assessing the influence of anthropogenic factors on the Tom River water regime

The results of mathematical modeling of the unsteady water motion in the Tom River over the section between the town of Tomsk and the river mouth, when it is under pressure head of the Ob River flood waves, are presented. The research is performed based on the analysis of field materials, numerical computation results of field and hypothetical hydrological regimes simulating the process of interaction of long waves of the Ob and Tom rivers in the region of their confluence. Mathematical modeling is performed with the help of mathematical models of the river channel “Tom” and “Confluence” in order to reveal a possible formation on the Tom River of a counterflow under extreme conditions connected with the joint impact of anthropogenic and natural factors.     

Competing impact of anthropogenic emissions and meteorology on the distribution of trace gases over Indian region

The spatial distribution of trace gases exhibit large spatial heterogeneity over the Indian region with an elevated pollution loading over densely populated Gangetic Plains (IGP). The contending role and importance of anthropogenic emissions and meteorology in deciding the trace gases level and distribution over Indian region, however, is poorly investigated. In this paper, we use an online regional chemistry transport model (WRF/Chem) to simulate the spatial distribution of trace gases over Indian region during one representative month of only three meteorological seasons namely winter, spring/summer and monsoon. The base simulation, using anthropogenic emissions from SEAC⁴RS inventory, is used to simulate the general meteorological conditions and the realistic spatial distribution of trace gases. A sensitivity simulation is conducted after removing the spatial heterogeneity in the anthropogenic emissions, i.e., with spatially uniform emissions to decouple the role of anthropogenic emissions and meteorology and their role in controlling the distribution of trace gases over India. The concentration levels of Ozone, CO, SO₂ and NO₂ were found to be lower over IGP when the emissions are uniform over India. A comparison of the base run with the sensitivity run highlights that meteorology plays a dominant role in controlling the spatial distribution of relatively longer-lived species like CO and secondary species like Ozone while short-lived species like NO_X and SO₂ are predominantly controlled by the spatial variability in anthropogenic emissions over the Indian region.     

Mean and variance evolutions of the hot and cold temperatures in Europe

In this paper, we examine the trends of temperature series in Europe, for the mean as well as for the variance in hot and cold seasons. To do so, we use as long and homogenous series as possible, provided by the European Climate Assessment and Dataset project for different locations in Europe, as well as the European ENSEMBLES project gridded dataset and the ERA40 reanalysis. We provide a definition of trends that we keep as intrinsic as possible and apply non-parametric statistical methods to analyse them. Obtained results show a clear link between trends in mean and variance of the whole series of hot or cold temperatures: in general, variance increases when the absolute value of temperature increases, i.e. with increasing summer temperature and decreasing winter temperature. This link is reinforced in locations where winter and summer climate has more variability. In very cold or very warm climates, the variability is lower and the link between the trends is weaker. We performed the same analysis on outputs of six climate models proposed by European teams for the 1961–2000 period (1950–2000 for one model), available through the PCMDI portal for the IPCC fourth assessment climate model simulations. The models generally perform poorly and have difficulties in capturing the relation between the two trends, especially in summer.     

Statistics of anomalous events in the ozonosphere over Europe

Statistics of anomalous ozone over Europe is determined for the period of instrumental observations. The increased number of the Atlantic-type negative total ozone (TO) anomalies in the annual cycles over the last decades is confirmed. The frequency of the Arctic-type negative and positive TO anomalies has not virtually changed. The seasonal distribution of the relative frequency of anomalies of all types has not significantly changed. The seasonal distribution of the relative frequency of most intense Atlantic-type negative anomalies is “narrower” compared with the distribution of anomalies of average intensity. There are significant differences in the seasonal frequency distribution of mean and intense negative TO anomalies of the Arctic type.     

Spatial gridding of daily maximum and minimum temperatures in Europe

We developed an operationally applicable land-only daily high-resolution (5?km?×?5?km) gridding method for station observations of minimum and maximum 2?m temperature (T _min/T _max) for Europe (WMO region VI). The method involves two major steps: (1) the generation of climatological T _min/T _max maps for each month of the year using block regression kriging, which considers the spatial variation explained by applied predictors; and (2) interpolation of transformed daily anomalies using block kriging, and combination of the resulting anomaly maps with climatological maps. To account for heterogeneous climatic conditions in the estimation of the statistical parameters, these steps were applied independently in overlapping climatic subregions, followed by an additional spatial merging step. Uncertainties in the gridded maps and the derived error maps were quantified: (a) by cross-validation; and (b) comparison with the T _min/T _max maps estimated in two regions having very dense temperature observation networks. The main advantages of the method are the high quality of the daily maps of T _min/T _max, the calculation of daily error maps and computational efficiency.