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1.
Christos H. Halios Costas G. Helmis Helena A. Flocas Stephan Nyeki Dimosthenis N. Assimakopoulos 《Meteorology and Atmospheric Physics》2012,118(3-4):107-115
Synoptic climatology relates the atmospheric circulation with the surface environment. The aim of this study is to examine the variability of the surface meteorological patterns, which are developing under different synoptic scale categories over a suburban area with complex topography. Multivariate Data Analysis techniques were performed to a data set with surface meteorological elements. Three principal components related to the thermodynamic status of the surface environment and the two components of the wind speed were found. The variability of the surface flows was related with atmospheric circulation categories by applying Correspondence Analysis. Similar surface thermodynamic fields develop under cyclonic categories, which are contrasted with the anti-cyclonic category. A strong, steady wind flow characterized by high shear values develops under the cyclonic Closed Low and the anticyclonic H–L categories, in contrast to the variable weak flow under the anticyclonic Open Anticyclone category. 相似文献
2.
Mesoscale surface turbulent fluxes over a complex terrain surrounded by oceans have been investigated using a 3-D numerical mesoscale model, under conditions with and without synoptic flows. The study indicated that under synoptically calm condition, the allocation and intensity of mesoscale surface turbulent fluxes (MSTFs) were greatly impacted by the thermally forced mesoscale circulation (TFMC) over mesoscale heterogeneous landscape. The max-imum values of sensible (Hs) and latent (LE) heat fluxes were located over the convergent zones and considerably im-pacted by the soil wetness (M), but did not depend strongly on the atmospheric background thermal stability (β0). The simulated results suggested that the sensible heat flux was closely proportional to the square of wind speed in the surface layer. By the action of synoptic flow, the allocation of LE was shifted to downwind, its intensity increased. 相似文献
3.
Summary This paper describes an attempt to define mesoscale daily precipitation and temperature regimes over Sardinia and their relation
to different synoptic patterns. In order to address this task an extensive Cluster Analysis was performed on the whole data
set using a number of methods, each including several distance measures. Thirty years of daily data, for the period ranging
from 1951 to 1980 for the 114 stations with precipitation and 20 with temperature, were used in the study.
In order to retrieve homogeneous clusters, non-hierarchical methods were found to be more effective and the use of a correlation-like
distance was more effective for precipitation. To discriminate between the different clusters, the corresponding mean mass
fields for the 500 hPa height and sea level pressure were used and an analysis of synoptic situations linked to mesoscale
regimes was performed. The results show that at least two mean surface patterns exist corresponding to clearly different synoptic
situations. Nevertheless, physical considerations led us to consider three distinct clusters, two of which correspond to specific
synoptic circulations with slight, but meteorologically significant, differences.
Received November 28, 1997 Revised October 1, 1998 相似文献
4.
Summary The impact of pronounced positive and negative sea surface temperature (STT) anomalies in the tropical Pacific associated with the El Niño/Southern Oscillation (ENSO) phenomenon on the atmospheric circulation in the Northern Hemisphere extratropics during the boreal winter season is investigated. This includes both the impact on the seasonal mean flow and on the intraseasonal variability on synoptic time scales. Moreover, the interaction between the transient fluctuations on these times scales and the mean circulation is examined. Both data from an ensemble of five simulations with the ECHAM3 atmospheric general circulation model at a horizontal resolution of T42 each covering the period from 1979 through 1992 and operational analyses from ECMWF for the corresponding period are examined. In each of the simulations observed SSTs for the period of investigation are given as lower boundary forcing, but different atmospheric initial conditions are prescribed.The simulations with ECHAM3 reveal a distinct impact of the pronounced SST-anomalies in the tropical Pacific on the atmospheric circulation in the Northern Hemisphere extratropics during El Niño as well as during La Niña events. These changes in the atmospheric circulation, which are found to be highly significant in the Pacific/North American as well as in the Atlantic/European region, are consistent with the essential results obtained from the analyses. The pronounced SST-anomalies in the tropical Pacific lead to changes in the mean circulation, which are characterized by typical circulation patterns. These changes in the mean circulation are accompanied by marked variations of the activity of the transient fluctuations on synoptic time scales, that are changes in both the kinetic energy on these time scales and the atmospheric transports of momentum and heat accomplished by the short baroclinic waves. The synoptic disturbances, on the other hand, play also an important role in controlling the changes in the mean circulation associated with the ENSO phenomenon. They maintain these typical circulation patterns via barotropic, but counteract them via baroclinic processes.The hypothesis of an impact of the ENSO phenomenon in the Atlantic/European region can be supported. As the determining factor the intensification (reduction) of the Aleutian low and the simultaneous reduction (intensification) of the Icelandic low during El Niño and during La Niña events respectively, is identified. The changes in the intensity of the Aleutian low during the ENSO-events are accompanied by an alteration of the transport of momentum caused by the short baroclinic waves over the North American continent in such a way that the changes in the intensity of the Icelandic low during El Niño as well as during La Niña events are maintained.With 16 Figures 相似文献
5.
6.
The surface wind field is an important factor controlling the surface mass balance of Antarctica. This paper focuses on the observed atmospheric circulation during summer of an Antarctic blue ice area in Queen Maud Land. Blue ice areas are characterised by a negative surface mass balance and henceforth provide an interesting location to study the influence of meteorological processes on large local mass balance gradients. During lapse conditions, synoptic forcing determines the surface-layer flow. No significant horizontal temperature gradient with coastal stations could be detected along isobaric surfaces, indicating weak or absent thermal wind. Observations performed at the coastal stations Halley and Georg von Neumayer show the pronounced effects of synoptic forcing. The surface winds in the valley of the blue ice area could be divided into two distinct flow patterns, occurring with about equal frequency during the experiment. Flow type I is associated with cyclonic activity at the coast, resulting in strong easterly winds, precipitation and drifting snow. Flow characteristics inside and outside of the valley are similar during these conditions. Flow type II occurs when a high pressure system develops in the Weddell Sea, weakening the free atmosphere geostrophic winds. A local circulation is able to develop inside the valley of the blue ice area during these tranquil conditions. The transition from flow type II to flow type I is associated with front-like phenomena inside the valley. Some simple theoretical considerations show that surface-layer stability and the upper air geostrophic wind determine the surface flow direction in the valley. Finally, the influence of the observed circulation on the energy and mass balance of the blue ice area is discussed. 相似文献
7.
Summary A methodology developed for automatic classification of Objective Synoptic Processes (OSP) and its application to the study
of the mesoscale atmospheric circulatory patterns associated with them is described. The classification was based on the analysis
of the evolution of surface pressure and geopotencial height at 500 hPa during three days. An iterative procedure results
in an objective grouping of the main configurations describing different large-scale situations. This routine has been applied
over an appropriate domain covering the Iberian Peninsula to obtain OSPs in the region for the two month period July–August,
using daily synoptic maps for years 1990 to 1999 (a total of 7304 surface and 500 hPa synoptic maps have been used in the
analysis). Finally, for a characteristic day for two of the OSPs obtained, a mesoscale meteorological model (TAPM) has been
run at high resolution for the region of Catalonia, Northeastern Spain, in order to describe the local atmospheric circulatory
patterns associated with a given large-scale situation. Results show that the complex orography modifies the large-scale forcings
resulting in wind fields with a very important horizontal variability, significant daily cycle, and specific local features
related to orographic elements, which the model was able to incorporate due to the highly-resolved orography used. 相似文献
8.
Using a one-level numerical diagnostic model, the features of surface wind fields in Hainan Island and Leizhou Peninsula and maritime area around it are studied. In the experiments with prevailing synoptic situation for varying seasons there are obvious deflection flows, terrain slope drafts, convergence lines, sea/land breeze and mountain/valley breeze, and difference in season accounts for the features found in the mesoscale distribution.The complex terrain and seatland distribution in the area is shown to be the important cause for the formation of varying mesoscale circulation, and close relationships between local climatic distribution feature and mesoscale circulation are then revealed. 相似文献
9.
Synoptic-scale atmospheric circulation patterns drive wind forcing of dynamic and thermodynamic processes in Arctic sea ice. Synoptic typing and compositing are common techniques used to identify a limited number of prevailing weather classifications that govern a region's climate. This work investigates atmospheric circulation patterns (surface to 250?hPa) for the southern Beaufort Sea and corresponding surface wind regimes within each synoptic type. Significant changes (p?<?0.05) in relative frequencies of a number of synoptic types were attributed to declining summer sea ice. Corresponding upper-level circulation anomalies show increasingly meridional atmospheric circulation. Synoptic Types 9 and 11 were identified as key October-November-December circulation features that represent deepening of the Aleutian low with concomitant strengthening of pressure gradients over the southern Beaufort Sea. Classification of coastal-based wind observations shows a shift towards increased easterly wind forcing. A case study of surface wind data from the CCGS Amundsen (2009–2011) provided a direct example of the surface wind regime within the marginal ice zone within each synoptic type during a period of reduced Arctic sea-ice cover. 相似文献
10.
The synoptic and mesoscale conditions associated with waterspout occurrence in the Adriatic, Ionian and Aegean Sea are examined in an attempt to quantitatively assess the meteorological environment favourable to the development of waterspouts. For this study, synoptic circulation patterns have been examined for 28 waterspout events in the central-eastern Mediterranean. The waterspouts were reported within the summer and fall of 2002, from July to November, a period of unusually high whirlwind activity. The Adriatic was most active during July, August and September and the Ionian and Aegean during September, October and November. Of the examined waterspout cases, 13 out of the total of 28 were found to be fair-weather waterspouts, while 15 represent tornadic events. For waterspout days, the frequency and distribution of four basic synoptic types, namely, south-west flow (SW), long-wave trough (LW), closed low (CLOSED) and short-wave trough (SWT), were investigated. The particular synoptic features that contributed to the development of waterspout activity were examined, based on five selected waterspout case studies. The mesoscale environment was explored using thermodynamic indices, moisture and wind parameters as derived by operational soundings from the nearest sites (preferably upwind) and closest in time to the waterspout occurrences. The results present an analysis of waterspout types in conjunction to thermodynamic and wind parameters for the purpose of determining synoptic patterns and mesoscale conditions most relevant to waterspout occurrences in these sea areas of the Mediterranean. 相似文献
11.
G. A. Efstathiou C. J. Lolis N. M. Zoumakis P. Kassomenos D. Melas 《Theoretical and Applied Climatology》2014,115(1-2):259-279
Raingauge data from four meteorological stations in Chalkidiki peninsula (Greece) were used to identify the characteristics of the synoptic circulation patterns associated with cold-season heavy rainfall events and corresponding flooding over the area. Precipitation climatology over the complex topography of Chalkidiki is characterized by limited annual rainfall, but in the occurrence of heavy rainfall episodes daily accumulations are exceptionally high with increased precipitation rates, leading often to severe flooding. Fifty-five cases of high daily accumulations for the period of 1997 to 2010, mostly observed during December and October, were classified into eight clusters by applying S-Mode Factor Analysis and Cluster Analysis to the ERA-Interim grid point reanalysis data. The results revealed that, in most cases, intense rainfall and flooding is produced by synoptic scale disturbances that generate and sustain cyclonic activity over south Italy, the Ionian, and less frequently over the Aegean Sea. In particular, the atmospheric circulation patterns associated with heavy rainfall are characterized by the presence of a southeasterly–easterly low-level humid flow over Chalkidiki in conjunction with the potentially unstable lower troposphere influenced by mid-level cyclonic vorticity advection and enhanced low-level convergence over the complex terrain. 相似文献
12.
海陆风环流在天津2009年9月26日局地暴雨过程中的作用 总被引：8，自引：4，他引：4
利用常规天气资料、地面加密自动站资料、天津中尺度模式产品资料以及卫星云图和多普勒雷达等资料,对2009年9月26日出现在天津地区的局地暴雨过程进行天气学、动力学诊断分析和中尺度分析.结果表明,本次暴雨的天气尺度主要的影响系统是500 hPa高空槽,中尺度系统是由海陆风环流形成的地面中尺度辐合线.降水前天津市具有较好的热力不稳定条件,较好的能量储备,有利的动力条件,一定量级的水汽辐合,边界层的东风将渤海的水汽输送至天津市,是本次过程的主要水汽来源.天气尺度的积云对流与海风锋的碰撞触发不稳定能量的释放,引发第一阶段的强降水,边界层东风急流再度加强所产生的抬升效应引发第二阶段的降水.中尺度切变线通过提供带状辐合上升运动起着胚胎和组织积云对流的作用,使得降水回波和对流云团沿中尺度切变线发展、加强和移动,产生了明显的列车效应,导致了这场历史罕见的秋季局部暴雨过程,也充分凸显出海陆风环流对本次暴雨的重要作用. 相似文献
13.
C. Serra G. Fernández Mills M. C. Periago X. Lana 《Theoretical and Applied Climatology》1998,59(1-2):29-49
Summary Catalonian daily precipitation patterns were obtained by means of S-mode Principal Component Analysis (PCA) applied to subsets
built up according to synoptic surface airflow. Daily data from November to April 1990–1994 from 45 raingauge sites in Catalonia
without missing data were used. Eight circulation classes for days in this period were considered. A Precipitation Activity
Index (PAI) was calculated for each station and class, leading to the determination of the highest activity regions for each
subset. In addition, we determined which circulation type produced most precipitation at each station of the network. Separate
PCAs were performed for each of the eight classes considered and the first four Varimax rotated solutions were interpreted
for each circulation type. The physical meaning of the rest of the factors were omitted as they were associated with local
behaviour. Finally, some concluding remarks on the cyclogenic properties of the Western Mediterranean Basin and the diversity
of the extracted patterns are presented and supported by the authors experience in forecasting in Catalonia.
Received February, 11, 1997 Revised May 23, 1997 相似文献
14.
Using land-use types derived from satellite remote sensing data collected by the EOS Moderate Resolution Imaging Spectroradiometer (EOS/MODIS), the mesoscale and turbulent fluxes generated by inhomogeneities of the underlying surface over the Jinta Oasis, northwestern China, were simulated using the Regional Atmospheric Modeling System (RAMS4.4). The results indicate that mesoscale circulation generated by land-surface inhomogeneities over the Jinta Oasis is more important than turbulence. Vertical heat fluxes and water vapor are transported to higher levels by mesoscale circulation. Mesoscale circulation also produces mesoscale synoptic systems and prevents water vapor over the oasis from running off. Mesoscale circulation transports moisture to higher atmospheric levels as the land-surface moisture over the oasis increases, favoring the formation of clouds, which sometimes leads to rainfall. Large-scale wind speed has a significant impact on mesoscale heat fluxes. During the active phase of mesoscale circulation, the stronger large-scale winds are associated with small mesoscale fluxes; however, background wind seems to intensify the turbulent sensible heat flux and turbulent latent heat flux. If the area of oasis is enlarged properly, mesoscale circulation will be able to transport moisture to higher levels, favoring the formation of rainfall in the oasis and protecting its "cold island" effect. The impact of irrigation on rainfall is important, and increasing irrigation across the oasis is necessary to protect the oasis. 相似文献
15.
中尺度非均一边界层气候的数值研究: (Ⅱ) 夏季的数值试验 总被引：2，自引：1，他引：2
用修改的Nickerson等提出的中尺度模式，对我国北方夏季非均一下垫面上的边界层气候特征进行了研究。结果表明，在晴朗、静风和无扰动系统的条件下，下垫面的非均一性对边界层气候起着决定性的影响。边界层气候特征和低空急流强度与局地环流关系密切。干燥裸地上边界层内出现的逆湿现象，是由下垫面非均一的湿度场和中尺度平流共同引起的。 相似文献
16.
The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: a synoptic type approach 总被引：2，自引：1，他引：1
Andrew Lorrey Nicolas Fauchereau Craig Stanton Petra Chappell Steven Phipps Andrew Mackintosh James Renwick Ian Goodwin Anthony Fowler 《Climate Dynamics》2014,42(11-12):3039-3060
Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of ?0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the ‘HSE’-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the ‘T’- and ‘SW’-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity. 相似文献
17.
Dhanya Pushpadas P. Vethamony K. Sudheesh Smitha George M. T. Babu T. M. Balakrishnan Nair 《Meteorology and Atmospheric Physics》2010,109(3-4):91-106
A high-resolution mesoscale numerical model (MM5) has been used to study the coastal atmospheric circulation of the central west coast of India, and Goa in particular. The model is employed with three nested domains. The innermost domain of 3 km mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons—northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system. The simulated wind speed and direction match well with the observations. The model winds show the presence of a sea breeze during the NE monsoon season and transition period, and its absence during the SW monsoon season. In the winter period, the synoptic flow is northeasterly (offshore) and it weakens the sea breeze (onshore flow) resulting in less diurnal variation, while during the transition period, the synoptic flow is onshore and it intensifies the sea breeze. During the northeast monsoon at an altitude of above 750 m, the wind direction reverses, and this is the upper return current, indicating the vertical extent of the sea breeze. A well-developed land sea breeze circulation occurs during the transition period, with vertical extension of 300 and 1,100 m, respectively. 相似文献
18.
The spatial and temporal distributions of marine cold air outbreaks (MCAOs) over the northern North Atlantic have been investigated using re-analysis data for the period from 1958 to 2007. MCAOs are large-scale outbreaks of cold air over a relatively warm ocean surface. Such conditions are known to increase the severity of particular types of hazardous mesoscale weather phenomena. We used a simple index for identifying MCAOs: the vertical potential temperature gradient between the sea surface and 700 hPa. It was found that atmospheric temperature variability is considerably more important than the sea surface temperature variability in governing both the seasonal and the inter-annual variability of MCAOs. Furthermore, a composite analysis revealed that a few well-defined and robust synoptic patterns are evident during MCAOs in winter. Over the Labrador and Irminger Seas the MCAO index was found to have a correlation of 0.70 with the North Atlantic Oscillation index, while over the Barents Sea a negative correlation of 0.42 was found. 相似文献
19.
利用常规观测资料、FY-2E卫星观测的TBB资料,对2015年8月19日发生在林芝地区的一次暴雨过程进行天气分析,并利用中尺度数值模式WRF的模拟结果分析此次暴雨过程中尺度系统的结构特征。结果表明,此次暴雨过程发生在高原低涡切变的环流形势下,伴随辐合线发展的线状对流系统是此次暴雨发生的主要原因。WRF模式可较好地模拟出暴雨过程的环流形势和降水的落区、量级。西南风引导的暖湿气流为暴雨的发生、发展提供充沛的水汽条件;对中尺度结构的分析表明,低层辐合、高层辐散的结构以及在降水区存在的正涡度伴随强烈的上升运动为此次暴雨过程提供了有利的动力条件,假相当位温的分布能够为暴雨提供有利的热力条件,垂直螺旋度低层正中心的配置反映出大气的不稳定分布,有利于中尺度对流系统的发展与维持。 相似文献
20.
Synoptic and local scale atmospheric circulation associated with air pollution episodes in an urban Mediterranean area 总被引：4，自引：0，他引：4
H. Flocas A. Kelessis C. Helmis M. Petrakakis M. Zoumakis K. Pappas 《Theoretical and Applied Climatology》2009,95(3-4):265-277
Air pollution episodes in urban coastal areas follow certain pre-determined patterns, being associated with certain local meteorological conditions and emission of primary pollutants. In this study, the synoptic and local scale atmospheric circulation that prevails during air pollution episodes in a coastal major city in Greece, Thessaloniki, is examined for a period of 15 years (1989–2004). The study signifies the importance of studying air pollution meteorological patterns between coastal areas with different terrain characteristics. For Thessaloniki, it was found that the episodes occur mainly during the cold period of the year, while four types of synoptic scale circulation were recognized (I, II, III, IV) and five patterns of the local scale circulation (A1, A2, B1, B2 and B3). The highest percentage of episodes is associated with the presence of an anticyclone over the northern Greece (types I and IV), being characterized by weak or very weak surface pressure gradient intensity, according to the position and extension of the anticyclone. Moreover, a temperature increase of at least 1°C during the previous 3 days is required in the lower troposphere. Consistent with the synoptic conditions, the development of the sea breeze plays a crucial role in the occurrence of the episodes, even in the cold period of the year, when the sea breeze can still develop with smaller frequency and intensity. Finally, it was found that a small number of episodes is related with the advection of polluted air masses from the industrial area in the northwest of the city and from the Eordaia area in the west, which is the largest lignite producing area of Balkans. 相似文献