Onset of southwesterly wind over eastern China and associated atmospheric circulation and rainfall

Using the 5-day averaged data from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, and precipitation from rain gauge stations in China for the period 1981–2000, we investigated seasonal variations and associated atmospheric circulation and precipitation of the southwesterly wind over eastern China. The southwesterly wind over eastern China begins earliest over southeastern China and strengthens gradually from spring to the early summer, as it extends northward. The strengthening of the spring southwesterly wind, the tropospheric upward motion, and the convergence of low-level water vapor over southeastern China results in the beginning of the local rainy season. The beginning of the Mei-yu (Plum rainfall) is connected with the northward march of the southwesterly wind. The southwesterly wind reaches the valley of the Yangtze River in the early summer and northern China in the middle summer. This signifies an onset of the large-scale southwesterly wind over eastern China. Accordingly, the rain belt over southeastern China moves to the valley of the Yangtze River in the early summer and to northern China in the middle summer. Moreover, the southerly wind extends southward to the South China Sea from the spring to summer, though it does not stretch from the South China Sea to southeastern China at those times. The strengthening of the southerly wind over southeastern China is associated with a weakening/strengthening of the eastward/westward subtropical tropospheric temperature gradient between southwestern China and the western North Pacific. The developments of a low-pressure system over southwestern China and the subtropical high-pressure system over the western North Pacific may contribute to the strengthening of the southwesterly wind. A northward advance of the high-pressure system favors the southwesterly wind stretching from southeastern China to northern China. The onset of the Indian summer monsoon also strengthens the summer southwesterly wind over eastern China.     

Relationship between wind power production and North Atlantic atmospheric circulation over the northeastern Iberian Peninsula

The wind power generated during winter months 1999–2003 at several wind farms in the northeastern Iberian Peninsula is investigated through the application of a statistical downscaling. This allows for an improved understanding of the wind power variability and its relationship to the large scale atmospheric circulation. It is found that 97 % of the variability of this non-climatic variable is connected to changes in the atmospheric circulation. The methodological uncertainty associated with multiple configurations of the statistical downscaling method replicates well the observed variability of the wind power, an indication of the robustness of the methodology to changes in the model set up. In addition, the use of the statistical model is extended out of the observational period providing an estimation of the long-term variability of wind power throughout the twentieth century. The extended wind power reconstruction shows large inter-annual and multidecadal variability. Alternative approaches to calibrate the empirical downscaling model using actual wind power observations have also been investigated. They involve the estimation of wind power changes from downscaled wind values and make use of several transfer functions based on the linearity between wind and wind energy. The performance of the latter approaches is similar to the direct downscaling of wind power and may allow wind power production estimations even in the absence of historical wind turbine records. These results can be of great interest for deriving medium/long term impact-oriented energy assessments, especially when wind power observations are missing as well as in the context of climate change scenarios.     

Evidence of the terdiurnal,S 3, atmospheric tide in the surface wind field over the ocean

Surface winds were measured from anchored buoys at the corners of a 100-km triangle in the Atlantic ocean for three weeks in September 1972. The measurements were part of the British Royal Society Joint Air-Sea Interaction Project, JASIN-72. Peaks were found at a frequency of 0.125 cph (8-h period) in various wind statistics, indicating the presence of the terdiurnal, S ₃, component of the atmospheric tides that had previously been extensively studied because it is a prominent component in surface air-pressure records.     

非均匀地面近地层风速廓线的实验研究

本文以Monin-Obukhov(1954)相似理论为基础,分析研究了北京西郊八角村地区80米高的铁塔上观测的风速和温度资料。 指出在均匀粗糙地面条件下,中性平均风速廓线在77米高度内很好地满足对数规律;稳定层结下,对数一线性规律在(0.03 ≤R_i≤0.69)一个很宽的稳定范围内都是适用的,但是必须十分注意其线性项常数β是随稳定度R_i而变的。本文给出了β-R_i之间的经验关系为β=0.35R(-0.9)对于不稳定层结描写风速切变函数φ_m,我们得到:弱不稳定范围使用|z/L| ~((-1)/4)规律     

Influence of atmospheric circulation patterns on local cloud and solar variability in Bergen,Norway

In a previous paper, we have shown that long-term cloud and solar observations (1965–2013) in Bergen, Norway (60.39°N, 5.33°E) are compatible with a largely cloud dominated radiative climate. Here, we explicitly address the relationship between the large scale circulation over Europe and local conditions in Bergen, identifying specific circulation shifts that have contributed to the observed cloud and solar variations. As a measure of synoptic weather patterns, we use the Grosswetterlagen (GWL), a daily classification of European weather for 1881–2013. Empirical models of cloud cover, cloud base, relative sunshine duration, and normalised global irradiance are constructed based on the GWL frequencies, extending the observational time series by more than 70 years. The GWL models successfully reproduce the observed increase in cloud cover and decrease in solar irradiance during the 1970s and 1980s. This cloud-induced dimming is traced to an increasing frequency of cyclonic and decreasing frequency of anticyclonic weather patterns over northern Europe. The changing circulation patterns in winter can be understood as a shift from the negative to the positive phase of the North Atlantic and Arctic Oscillation. A recent period of increasing solar irradiance is observed but not reproduce by the GWL models, suggesting this brightening is associated with factors other than large scale atmospheric circulation, possibly decreasing aerosol loads and local cloud shifts.     

Dominant patterns of winter surface air temperature over Central Asia and their connection with atmospheric circulation

The dominant patterns of the winter (December–February) surface air temperature anomalies (SATAs) over Central Asia (CA) are investigated in this study. The first two leading modes revealed by empirical orthogonal function (EOF) analysis represent the patterns by explaining 74% of the total variance. The positive phase of EOF1 is characterized by a monopole pattern, corresponding to cold SATAs over CA, while the positive phase of EOF2 shows a meridional dipole pattern with warm and cold SATAs over northern and southern CA. EOF1 is mainly modulated by the negative phase of the Arctic Oscillation (AO) in the troposphere, and the negative AO phase may be caused by the downward propagation of the precursory anomalies of the stratospheric polar vortex. EOF2 is mainly influenced by the Ural blocking pattern and the winter North Atlantic Oscillation (NAO). The SATAs associated with EOF2 can be attributed to a dipole-like pattern of geopotential height anomalies over CA. The dipole-like pattern is mainly caused by the Ural blocking pattern, and the NAO can also contribute to the northern part of the dipole.摘要本文利用经验正交函数分解方法 (Empirical orthogonal function, EOF) , 针对1979–2019年冬季 (12月–2月) 中亚地区地面气温异常进行了研究. 结果表明, 中亚地区冬季地面气温异常的前两个EOF模态解释方差总占比可达74%. 其中, 第一模态 (EOF1) 正位相为一致型变化, 对应中亚地区气温冷异常; 第二模态 (EOF2) 正位相则为南北偶极型变化, 对应于中亚地区南冷北暖型气温异常. EOF1可能受到冬季北极涛动 (Arctic Oscillation, AO) 负位相的调制, 而AO的负位相则可能来自于前期平流层极涡正位势高度异常下传. EOF2则可能受到乌拉尔山阻塞及冬季北大西洋涛动 (North Atlantic Oscillation, NAO) 的共同调制. 乌拉尔山阻塞可引起中亚区域南北偶极型气温异常, 而冬季NAO可对该偶极型气温异常的北侧产生贡献.     

North Atlantic atmospheric circulation and surface wind in the Northeast of the Iberian Peninsula: uncertainty and long term downscaled variability

The variability and predictability of the surface wind field at the regional scale is explored over a complex terrain region in the northeastern Iberian Peninsula by means of a downscaling technique based on Canonical Correlation Analysis. More than a decade of observations (1992–2005) allows for calibrating and validating a statistical method that elicits the main associations between the large scale atmospheric circulation over the North Atlantic and Mediterranean areas and the regional wind field. In an initial step the downscaling model is designed by selecting parameter values from practise. To a large extent, the variability of the wind at monthly timescales is found to be governed by the large scale circulation modulated by the particular orographic features of the area. The sensitivity of the downscaling methodology to the selection of the model parameter values is explored, in a second step, by performing a systematic sampling of the parameters space, avoiding a heuristic selection. This provides a metric for the uncertainty associated with the various possible model configurations. The uncertainties associated with the model configuration are considerably dependent on the spatial variability of the wind. While the sampling of the parameters space in the model set up moderately impact estimations during the calibration period, the regional wind variability is very sensitive to the parameters selection at longer timescales. This fact illustrates that downscaling exercises based on a single configuration of parameters should be interpreted with extreme caution. The downscaling model is used to extend the estimations several centuries to the past using long datasets of sea level pressure, thereby illustrating the large temporal variability of the regional wind field from interannual to multicentennial timescales. The analysis does not evidence long term trends throughout the twentieth century, however anomalous episodes of high/low wind speeds are identified.     

Variability of cold season surface air temperature over northeastern China and its linkage with large-scale atmospheric circulations

Theoretical and Applied Climatology - In recent times, Ibadan has been experiencing an increase in mean temperature which appears to be linked to anthropogenic global warming. Previous studies have...     

我国中部地区夏季干旱的多时间尺度特征及其环流、海温异常

基于CRU逐月降水和NCEP/NCAR再分析等资料,利用集合经验模态分解(Ensemble Empirical Mode Decomposition,EEMD)方法,分析1948—2016年中国中部地区夏季降水变化的多时间尺度特征及其对应的环流、海温异常,进而解释不同时期影响干旱发生的背景场有何不同。结果表明,中部地区夏季降水以年际变化为主,周期长度为3.8 a和6.9 a,年代际和多年代际变化的方差贡献不足20%。然而,各时间尺度降水变化对不同时期干旱事件的贡献存在较大差异,1960s、1970s,降水年际变化偏弱,相反地,多年代际变化正处于负位相的极小值期;1980s、1990s,多年代际变化位相转正;2000s初,年际变化明显增强。此外,通过分析不同时间尺度降水变化对应的环流、海温背景场,发现热带印度洋海温异常及其引起的西北太平洋副热带高压的变化、大西洋北部海温异常激发的纬向波列以及贝加尔湖地区的阻塞活动、1970s末PDO位相转变伴随的东亚夏季风突变是分别解释降水年际、年代际和多年代际变化的主要原因,进而揭示影响中部地区夏季干旱发生的关键因子及其相对重要性。     

Variability of UTCI index in South Warsaw depending on atmospheric circulation

Theoretical and Applied Climatology - The aim of the study is the assessment and analysis of the variability of human-bioclimatic conditions in southern part of Warsaw, depending on the atmospheric...     

南海北部冷涌及其环流特征

利用中国南部沿海风向、地面气温及南海北部风速的变化确定南海北部冷涌的判别标准,构建了一个冷涌发生频率指数,对南海北部冷涌的年际变化特征及其环流异常进行讨论。结果表明,南海北部冷涌频率指数能够更加全面地描述冷涌系统的特征,与全国范围的冷空气爆发关系密切。南海北部冷涌与中高纬、中低纬环流具有密切的联系,是二者共同作用的结果。当贝加尔湖以西高压脊偏强,中高纬环流经向度加大,西太平洋副热带高压强度偏弱、位置偏东时,有利于大陆上冷空气南下入海,在南海北部形成冷涌。冷涌发生时,经向Hadley环流加强,调整中纬与低纬地区的大气质量,高层向北输送的大气在科氏力作用下导致东亚副热带西风急流加强,有利于冷涌的维持和加强。     

Sensitivity of Arctic warming to sea surface temperature distribution over melted sea-ice region in atmospheric general circulation model experiments

Substantial reduction in Arctic sea ice in recent decades has intensified air-sea interaction over the Arctic Ocean and has altered atmospheric states in the Arctic and surrounding high-latitude regions. This study has found that the atmospheric responses related to Arctic sea-ice melt in the cold season (October–March) depend on sea-ice fraction and are very sensitive to in situ sea surface temperature (SST) from a series of atmospheric general circulation model (AGCM) simulations in which multiple combinations of SSTs and sea-ice concentrations are prescribed in the Arctic Ocean. It has been found that the amplitude of surface warming over the melted sea-ice region is controlled by concurrent in situ SST even if these simulations are forced by the same sea-ice concentration. Much of the sensitivity of surface warming to in situ SST are related with large changes in surface heat fluxes such as the outgoing long-wave flux in early winter (October–December) and the sensible and latent heat fluxes for the entire cold season. Vertical extension of surface warming and moistening is sensitive to these changes as well; the associated condensational heating modulates a static stability in the lower troposphere. This study also indicates that changes in SST fields in AGCM simulations must be implemented with extra care, especially in the melted sea-ice region in the Arctic. The statistical method introduced in this study for adjusting SSTs in conjunction with a given sea-ice change can help to model the atmospheric response to sea-ice loss more accurately.     

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.     

冬季北太平洋大气低频环流的年际和年代际变化特征及其与大气环流和海温异常的联系

利用1979—2015年ECMWF逐日再分析资料,通过EOF分解和回归分析研究了冬季北太平洋大气低频环流的年际和年代际变化特征及其与海表面温度异常(SSTA)和大气环流异常之间的联系。研究结果表明:冬季中纬度北太平洋地区850 h Pa低频尺度环流存在3个明显的变化模态:第一模态为海盆尺度的单极型异常气旋(反气旋)式环流,同期太平洋SSTA呈现El Ni1o(La Ni1a)以及PDO暖位相(冷位相)空间分布,阿留申低压强度增强(减弱),对流层中高层是正位相(负位相)的PNA型遥相关,北太平洋天气尺度风暴轴中东部南压(北抬);第二模态为在白令海峡和副热带地区呈气旋式与反气旋式环流南北向偶极型变化,同时中纬度北太平洋SSTA呈现NPGO(North Pacific Gyre Oscillation)正位相(负位相)的空间分布,黑潮区域SSTA偏暖(偏冷),北太平洋SSTA经向梯度加大(减小),对流层中高层为负位相(正位相)的WP型遥相关,北太平洋天气尺度风暴轴整体偏北(偏南),强度增强(减弱);第三模态为北太平洋中西部和北美西岸呈气旋式与反气旋式环流东西向偶极型异常,黑潮区域SSTA偏冷(偏暖)而北太平洋东部SSTA偏暖(偏冷),SSTA纬向梯度加大(减弱),同时赤道东太平洋出现类似La Ni1a(El Ni1o)的SSTA分布,北太平洋天气尺度风暴轴中东部明显减弱(加强)而西部略有加强(减弱)。     

High-frequency patterns of the atmospheric circulation over the southern hemisphere and South America

Summary Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed data obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to March) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990–1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in selected areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the western hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15° N and 70° S are discussed. The high-frequency winter and summer patterns for both variables feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the southeastern Pacific. Analysis of the western hemisphere data reveal that the wavetrain in the South American sector extends northeastward over the continent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequential instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.     

热带太平洋低层环流主模态与东亚大气环流的可能联系

利用1958—2001年NCEP/NCAR再分析资料,探讨了热带太平洋(100°E~60°W,10°S~10°N)10 m风场的时空变化特征及其与东亚大气环流的可能联系。结果表明:1)热带太平洋风场异常存在两种主模态,第一模态对应中西太平洋一致的西(东)风异常,关于赤道呈准对称分布,与ENSO(El Nio-Southern Oscillation)暖(冷)位相时风场的分布对应;第二模态则关于赤道呈反对称分布,西北太平洋存在显著的反气旋(气旋)式环流,中太平洋异常西风不再位于赤道上,而是南移到了10°S左右,对应ENSO暖(冷)位相向相反位相转换时的风场分布特征。2)两模态时间系数的主振荡周期不同,与ENSO循环的位相关系也不同。研究发现,当两模态呈正(负)位相分布时,贝加尔湖南侧(South to Lake Baikal,SLB)容易发生持续的高压(低压)异常环流。3)两模态与SLB异常环流的联系途径不同。第一模态正位相对应热带中东太平洋大范围暖海温引起的二极型Walker环流异常,SLB异常高压不仅能通过东亚沿岸北风和南海低槽的作用促进第一模态的前期发展,还对其后期维持起重要作用。负位相时,情况相反。该环流系统既与热带中东太平洋大范围垂直运动有关,还与邻近的中国东南沿海低层异常辐合有关;第二模态则对应热带西太平洋及东印度洋为主、大西洋为辅的暖海温引起的热带四极型Walker环流异常。此时热带西太平洋到东印度洋局地偏强的经圈Hadley环流可能是SLB异常环流维持的主要原因。     

Dangerous wind waves in the North Atlantic at different regimes of atmospheric circulation

Studied are the formation processes of dangerous wind waves in the water area of the North Atlantic during three cold periods (October–March) from 2007 to 2010. Obtained are the estimates of variability of cyclone trajectories, wind fields, and wave height in the North Atlantic at the intensification of zonal or meridional atmospheric circulation.     

The relationship between the wind and waves in the North Atlantic and atmospheric circulation oscillations

Characteristics of wind and waves are computed using the data of instrumental observations on the moored buoys in the northeastern part of the North Atlantic during the cold periods (November–March) of 2009–2013. Their comparison is carried out for different phases of the North Atlantic and East Atlantic oscillations and for the combinations of these phases.