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1.
Poor daytime and night-time micrometeorological conditions are issues that influence the quality of environmental conditions and can undermine a comfortable human lifestyle. The sky view factor (SVF) is one of the essential physical parameters used to assess the micrometeorological conditions and thermal comfort levels within city streets. The position of the visible sky relative to the path of the sun, in the cardinal and ordinal directions, has not been widely discerned as a parameter that could have an impact on the micrometeorological conditions of urban streets. To investigate this parameter, different urban streets that have a similar SVF value but diverse positions of visible sky were proposed in different street directions intersecting with the path of the sun, namely N–S, NE–SW and NW–SE. The effects of daytime and night-time micrometeorological variables and human thermal comfort variables on the street were investigated by applying ENVI-met V3.1 Beta software. The results show that the position of the visible sky has a greater influence on the street’s meteorological and human thermal comfort conditions than the SVF value. It has the ability to maximise or minimise the mean radiation temperature (Tmrt, °C) and the physiological equivalent temperature (PET, °C) at street level. However, the visible sky positioned to the zenith in a NE–SW or N–S street direction and to the SW of a NW–SE street direction achieves the best daytime micrometeorological and thermal comfort conditions. Alternatively, the visible sky positioned to the NE for a NW–SE street direction, to the NW and the zenith for a NE–SW street direction and to the zenith for a N–S street direction reduces the night-time air temperature (Ta, °C). Therefore, SVF and the position of the visible sky relative to the sun’s trajectory, in the cardinal and ordinal directions, must be considered during urban street planning to better understand the resultant micrometeorological and human thermal comfort conditions.  相似文献   

2.
华北区域环流型与河北气候的关系   总被引：2，自引：1，他引：1  
利用Lamb-Jenkinson方法和NCEP/NCAR再分析的1951—2006年月平均海平面气压场资料,对华北区域环流进行分型并分析了对河北气候的影响。结果表明,影响华北的主要环流型有8种（A、SW、NE、W、C、N、ANE、AN）,占全部环流型的64.43%。冬季主要盛行A、NE环流型,夏季主要盛行SW、C环流型,冬季最主要的环流型A和夏季最主要的环流型SW出现次数呈反相变化。河北夏季降水量与SW出现次数呈明显的同相变化,而与A型出现次数呈非常好的反相变化,即冬季A环流型出现多,夏季SW环流型出现就少,夏季降水量就少,反之亦然。冬季的主要环流型在20世纪60年代中期发生了明显改变,夏季环流型在60年代和70年代发生了两次明显改变,之后基本维持改变后的环流型。河北气候与区域环流型变化有很好的对应关系。  相似文献   

3.
The trends and fluctuations of observed and CMIP5-simulated yearly mean surface air temperature over China were analyzed.In general,the historical simulations replicate the observed increase of temperature,but the multi-model ensemble （MME） mean does not accurately reproduce the drastic interannual fluctuations.The correlation coefficient of the MME mean with the observations over all runs and all models was 0.77,which was larger than the largest value （0.65） from any single model ensemble.The results showed that winter temperatures are increasing at a higher rate than summer temperatures,and that winter temperatures exhibit stronger interannual variations.It was also found that the models underestimate the differences between winter and summer rates.The ensemble empirical mode decomposition technique was used to obtain six intrinsic mode functions （IMFs） for the modeled temperature and observations.The periods of the first two IMFs of the MME mean were 3.2 and 7.2,which represented the cycle of 2-7-yr oscillations.The periods of the third and fourth IMFs were 14.7 and 35.2,which reflected a multi-decadal oscillation of climate change.The corresponding periods of the first four IMFs were 2.69,7.24,16.15 and 52.5 in the observed data.The models overestimate the period of low frequency oscillation of temperature,but underestimate the period of high frequency variation.The warming rates from different representative concentration pathways （RCPs） were calculated,and the results showed that the temperature will increase by approximately 0.9℃,2.4℃,3.2℃ and 6.1℃ in the next century under the RCP2.6,RCP4.5,RCP6.0 and RCP8.5 scenarios,respectively.  相似文献   

4.
华西秋雨起止与秋冬季节大气环流转换   总被引：1，自引：0，他引：1  
袁旭  刘宣飞 《气象学报》2013,71(5):913-924
根据1961—2010年平均的逐候NCEP/NCAR再分析资料、1979—2008年平均的逐候CMAP降水资料以及1961—2010年逐候平均的中国553个台站降水资料,讨论了华西秋雨起止日期与秋冬季大气环流转换特征的关系。结果表明,华西地区降水年变化表现为明显的夏、秋双峰特征,8月4—8日(第44候)为双峰间的低谷,10月8—12日(第57候)以后降水降至年平均以下。由此,将华西秋雨建立和结束日期分别确定为8月9—13日(第45候)和10月8—12日(第57候)。华西秋雨的建立对应于东亚夏季风开始向冬季风转变,其标志性环流调整特征是江南地区的西南风转为东南风。东亚经向海平面气压梯度在8月9—13日(第45候)由南高北低转为南低北高,造成850 hPa江南地区的西南风转为东南风,该东南风与来自孟加拉湾的热带西南季风交汇于华西地区,形成风向和水汽的辐合,使得华西地区的降水在夏峰之后再次增强,华西秋雨由此建立。华西秋雨的结束则对应于孟加拉湾热带西南季风结束和东亚冬季风完全建立,其标志性环流调整特征是孟加拉湾地区的西南风转为东北风。随着东亚纬向海平面气压梯度由北向南依次发生东高西低向东低西高的转变,东亚冬季风也逐步向南推进,9月8—12日(第51候)东北冬季风到达江南地区,10月8—12日(第57候)进一步推进到南海地区,此时来自孟加拉湾的热带西南季风消失,造成华西地区完全受大陆冷高压控制,东亚季风经圈环流也转为冬季型哈得来环流,东亚冬季风完全建立,华西秋雨也随之结束。因此,华西秋雨起止可能与东亚夏季风、南亚夏季风向冬季风的转变时间不同步有关,东亚季风与南亚季风的共同作用使得华西秋雨成为亚洲夏季风在中国大陆上的最后一个雨季。  相似文献   

5.
In terms of the expansion by extended empirical orthogonal function(EEOF) with data of ECMWF/WMO and of outgoing longwave radiation(OLR) furnished by the NOAA polar-orbiting satellite,a study is made of November 1981 to March 1982 low-frequency(30-60 day) summer monsoon activity in the Indonesian-North Australian zone(INAZ) together with its relation to atmospheric circulations in the Northern and Southern Hemispheres. Results show that at 850 hPa the southward blowing low-frequency NE(SW) wind from the eastern Asian coast changes, after crossing the euqator, to summer NW(SE) monsoon in the INAZ, which, when converging with(diverging from) the western-Australian enforced low-frequency SW(NE) wind, brings about strengthened(weakened) convection in the summer monsoon area and its eastward advance, with corresponding low-frequency variation shown in 850 hPa geopotential height. These outcomes are similar to those from the study of non-filtered actual observations, leading to the conclusion that the component of low-frequency variation illustrates major features characteristic of the variation in the tropical circulation.  相似文献   

6.
In this study, regional patterns of precipitation in Marmara are described for the first time by means of Ward’s hierarchical cluster analysis. Daily values of winter precipitation data based on 19 meteorological stations were used for the period from 1960 to 2012. Five clusters of coherent zones were determined, namely Black Sea-Marmara, Black Sea, Marmara, Thrace, and Aegean sub-regions. To investigate the prevailing atmospheric circulation types (CTs) that cause precipitation occurrence and intensity in these five different rainfall sub-basins, objective Lamb weather type (LWT) methodology was applied to National Centers of Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis of daily mean sea level pressure (MSLP) data. Precipitation occurrence suggested that wet CTs (i.e. N, NE, NW, and C) offer a high chance of precipitation in all sub-regions. For the eastern (western) part of the region, the high probability of rainfall occurrence is shown under the influence of E (SE, S, SW) atmospheric CTs. In terms of precipitation intensity, N and C CTs had the highest positive gradients in all the sub-basins of the Marmara. In addition, although Marmara and Black Sea sub-regions have the highest daily rainfall potential during NE types, high daily rainfall totals are recorded in all sub-regions except the Black Sea during NW types.  相似文献   

7.
Variations of the North Atlantic subtropical high (NASH) western ridge and their implication to the Southeastern United States (SE US) summer precipitation were analyzed for the years 1948–2007. The results show that the movement of the NASH western ridge regulates both moisture transport and vertical motion over the SE US, especially in the last three decades, during which the ridge moved westward towards the American continent. When the NASH western ridge is located southwest (SW) of its mean climate position, excessive summer precipitation is observed due to an enhanced moisture transport. In contrast, when the western ridge is located in the northwest (NW), a precipitation deficit prevails as downward motion dominates the region. Composite analysis indicates that SW ridging results mainly from the NASH center’s intensification; whereas NW ridging is likely caused by stationary wave propagation from the eastern Pacific/US western coast. In recent decades, both the SW and NW ridge positions have been observed to increase in frequency. Our results suggest that the increase in the SW ridging consistently follows the NASH’s intensification associated with anthropogenic forcing as projected by coupled climate models. However, the increased frequency of NW ridging tends to follow the positive Pacific decadal oscillation (PDO) index. Thus, the enhanced variability in the SE US summer precipitation in recent decades might be a combined result of anthropogenic forcing and internal variability of the climate system. Results suggest that, as anthropogenic forcing continues to increase, the SE US will experience more frequent wet summers and an increase in the frequency of dry summers during positive PDO phases.  相似文献   

8.
The aim of this study was to analyse the effect of slope aspect on the response of snowpack to climate warming in the Pyrenees. For this purpose, data available from five automatic weather stations were used to simulate the energy and mass balance of snowpack, assuming different magnitudes of an idealized climate warming (upward shifting of 1, 2 and 3 °C the temperature series). Snow energy and mass balance were simulated using the Cold Regions Hydrological Modelling platform (CRHM). CRHM was used to create a model that enabled correction of the all-wave incoming radiation fluxes from the observation sites for various slope aspects (N, NE, E, SE, S, SW,W,NW and flat areas), which enabled assessment of the differential impact of climate warming on snow processes on mountain slopes. The results showed that slope aspect was responsible for substantial variability in snow accumulation and the duration of the snowpack. Simulated variability markedly increased with warmer temperature conditions. Annual maximum snow accumulation (MSA) and annual snowpack duration (ASD) showed marked sensitivity to a warming of 1 °C. Thus, the sensitivity of the MSA in flat areas ranged from 11 to 17 % per degree C amongst the weather stations, and the ASD ranged from 11 to 20 days per degree C. There was a clear increase in the sensitivity of the snowpack to climate warming on those slopes that received intense solar radiation (S, SE and SW slopes) compared with those slopes where the incident radiation was more limited (N, NE and NW slopes). The sensitivity of the MSA and the ASD increased as the temperature increased, particularly on the most irradiated slopes. Large interannual variability was also observed. Thus, with more snow accumulation and longer duration the sensitivity of the snowpack to temperature decreased, especially on south-facing slopes.  相似文献   

9.
This study presents projections of twenty-first century wintertime surface temperature changes over the high-latitude regions based on the third Coupled Model Inter-comparison Project (CMIP3) multi-model ensemble. The state-dependence of the climate change response on the present day mean state is captured using a simple yet robust ensemble linear regression model. The ensemble regression approach gives different and more precise estimated mean responses compared to the ensemble mean approach. Over the Arctic in January, ensemble regression gives less warming than the ensemble mean along the boundary between sea ice and open ocean (sea ice edge). Most notably, the results show 3?°C less warming over the Barents Sea (~7?°C compared to ~10?°C). In addition, the ensemble regression method gives projections that are 30?% more precise over the Sea of Okhostk, Bering Sea and Labrador Sea. For the Antarctic in winter (July) the ensemble regression method gives 2?°C more warming over the Southern Ocean close to the Greenwich Meridian (~7?°C compared to ~5?°C). Projection uncertainty was almost half that of the ensemble mean uncertainty over the Southern Ocean between 30° W to 90° E and 30?% less over the northern Antarctic Peninsula. The ensemble regression model avoids the need for explicit ad hoc weighting of models and exploits the whole ensemble to objectively identify overly influential outlier models. Bootstrap resampling shows that maximum precision over the Southern Ocean can be obtained with ensembles having as few as only six climate models.  相似文献   

10.
东北地区降水与大气环流关系   总被引：6，自引：2，他引：6       下载免费PDF全文
利用Lamb-Jenkinson大气环流分型方法, 将1951—2004年逐日的海平面气压场分型, 得到27种不同的环流型, 研究了大气环流型与我国东北地区降水的关系。给出了8种出现频率最高的主要环流型出现的规律及它们平均的环流形势, 分析了8种主要环流型下东北地区降水异常分布状况, 并选出东北地区资料齐全、有代表性的9个站点进行了深入细致地分析, 成功地建立了降水与环流型出现频率的统计关系, 并用此重建了9个代表站54年的降水序列。结果表明:Lamb-Jenkinson大气环流分型方法可以很好地应用于我国东北地区, 由此划分的环流型符合实际情况; 8种主要环流型与降水的空间分布特征有很好的对应关系; 所建立的9个代表站降水距平回归方程能够解释近54年各站的大部分降水变化, 进一步证明了东北地区降水与大气环流之间的密切关系。  相似文献   

11.
Predominantly in the context of Japan GMS-derived T_(BB) data,study is undertaken of therelationship between the winter thermal conditions of the Qinghai-Xizang Plateau(QXP)andanomaly in Asian-Australian monsoons during northern summer.Evidence suggests that anti-correlation of cold air activity of East Asia with that of Mid Asia is responsible for the counterpartof the ground thermal characteristics anomaly on an interannual basis between the SW and NEQXP;the winter thermal pattern bears a closer correlativity with the subsequent summertimeAsian-Australian monsoons anomaly;as the thermal distribution is reversed,so are the convectionfeatures over North and South China,maritime continent,the NW and SW Pacific at tropical andequatorial latitudes,resulting in vast difference between East-Asian summer and Indonesian-NorthAustralian winter monsoons;the subtropical monsoon-associated rainbelt over the mid-lowerChangjiang basins exhibits the discrepancy in vigor and northerly shift timing.Besides,part of theresults has been further borne out through analysis of temperature and precipitation records of theeastern portion of the country in monsoon climate.  相似文献   

12.
利用基于英国Lamb(1950年)发展的大气环流分型方法的Jenkinson(1977年)法对东北地区1951—2002年的月平均海平面气压场(MSLP)进行环流分型。由月平均海平面气压场算出6个环流指数,并由此划分出27种环流类型,分析了其中出现频率最高的5种主要环流类型(N,NW,C,CSW,SW)在不同时间尺度下的变化规律及它们与哈尔滨月平均温度的关系,利用逐步回归方法得到了温度距平的拟合曲线。给出了各种环流类型的月平均降水量和与哈尔滨降水密切相关的C,CSW和SW 3种环流类型对应的平均海平面气压合成图。结果表明:哈尔滨冬季以N,NW型为主,夏季以C,CSW和SW型为主。出现N和NW型时气温偏低,降水偏少;而出现C,CSW和SW型时气温较高,降水偏多。用6个环流指数中的地转风V和大尺度平均温度t可以建立其与温度距平之间的一个统计模式,利用此模式,能解释哈尔滨1951—2002年温度变化方差的77.3%。C,CSW和SW 3种环流类型为哈尔滨的主要降水类型,C型与哈尔滨总降水的相关关系很好,并且近20年来哈尔滨主要以C型降水为主。这种研究大尺度大气环流与区域气候变量—温度、降水之间关系的方法是一种统计降尺度(statistical downscaling)方法,可以用于区域气候预测。  相似文献   

13.
2℃全球变暖背景下中国未来气候变化预估   总被引：14，自引：4，他引：10  
姜大膀  富元海 《大气科学》2012,36(2):234-246
相对于工业化革命前期, 全球年平均地表气温上升2℃的时间和相应的气候变化受到了广泛关注, 特别是包括欧盟成员国在内的许多国家和国际组织已经将避免2℃全球变暖作为温室气体减排的首要目标。为此, 本文作者基于16个气候模式在20世纪气候模拟试验和SRES B1、A1B和A2温室气体和气溶胶排放情景下的数值模拟试验结果, 采用多模式集合方法预估研究了2℃全球变暖发生的时间、对应的大气中主要温室气体浓度以及中国气候变化情况。根据模式集合平均结果, 三种排放情景下2℃全球变暖分别发生在2064年、2046年和2049年, 大气二氧化碳当量浓度分别为625 ppm、645 ppm和669 ppm (1 ppm=10-6)。对应着2℃全球变暖, 中国气候变暖幅度明显更大。从空间分布形势上看, 变暖从南向北加强, 在青藏高原地区存在一个升温大值区; 就整体而言, 中国区域平均的年平均地表气温上升2.7～2.9℃, 冬季升温幅度 (3.1～3.2℃) 要较其他季节更大。年平均降水量在华南大部分地区减少0～5%, 而在其余地区增加0～20%, 中国区域年平均降水增加3.4%～4.4%, 各季节增加量在0.5%～6.6%之间。  相似文献   

14.
全球变暖形势下中国陆表水分的变化   总被引：1，自引：1，他引：0  
利用政府间气候变化委员会第四次评估报告（IPCCAR4）中的10个耦合模式CO：加倍试验和控制试验的模拟结果,分析了全球变暖背景下中国水分的变化。结果表明,随着全球变暖,东亚夏季风增强,冬季风减弱,使得冬夏季向中国区域输送的水汽都增强;中国区域降水,夏季除长江流域外基本都增加,冬季除华南外都增加。夏季降水蒸发差（P—E）除了在东北和南方增加外,从长江流域一直到西北有一带状减小带;冬季几乎所有模式的P—E表现为北方增加、南方减小。在全球变暖背景下,降水、蒸发和径流的综合结果以及积雪的作用使得土壤湿度在干旱区增加,且冬季干旱区土壤变湿的强度和范围大于夏季,然而在其他区域土壤湿度减少。上述结论是基于多模式集合平均结果,对未来气候的预估具有一定的参考价值,然而模式间存在较强差异性,仍具有较大不确定性。  相似文献   

15.
This study analyses the atmospheric boundary layer over the Bilbao metropolitan area during summer (13–18 Jul 2009) and winter (20–29 Jan 2010) episodes using the Environment–High Resolution Limited Area Model (Enviro-HIRLAM) coupled with the building effect parameterisation (BEP). The main objectives of this study are: to evaluate the performance of the model to simulate the land–sea breezes over this complex terrain; to assess the simulations with the integration of an urban parameterisation in Enviro-HIRLAM and finally; and to analyse the urban–atmosphere interactions. Even if the hydrostraticity of the model is a limitation to simulate atmospheric flows over complex terrain, sensibility tests demonstrate that 2.4 km is the optimal horizontal resolution over Bilbao that allows at the same time: to obtain satisfactory reproducibility of the large-scale processes and to explore the urban effects at local scale. During the summer episode, a typical regime of diurnal sea breeze from the NW-N-NE direction and nocturnal valley breezes from the SE direction are observed over Bilbao. The urban heat island (UHI) phenomenon is developed in the city centre expanding to the suburbs from 22 to 10 local time (LT), covering an area of 130 km2. The maximum UHI intensity, 1 °C, is reached at the end of the night (5 LT), and it is advected 12 km towards the sea by the land breezes. The urban boundary layer (UBL) height amplitude varies from 100 (night time) to 1,360 m (at 14 LT). During the winter episode, the land breeze dominates the atmospheric diffusion during the day and night time. The maximum UHI intensity, 1.7 °C, is observed at 01 LT. It is spread and remained over the city covering an area of 160 km2, with a vertical extension of 33 m. The UBL reaches 780 m height at 16 LT the following day.  相似文献   

16.
Based on hourly rainfall observational data from 442 stations during 1960–2014, a regional frequency analysis of the annual maxima(AM) sub-daily rainfall series(1-, 2-, 3-, 6-, 12-, and 24-h rainfall, using a moving window approach) for eastern China was conducted. Eastern China was divided into 13 homogeneous regions: Northeast(NE1, NE2), Central(C), Central North(CN1, CN2), Central East(CE1, CE2, CE3), Southeast(SE1, SE2, SE3, SE4), and Southwest(SW).The generalized extreme value performed best for the AM series in regions NE, C, CN2, CE1, CE2, SE2, and SW, and the generalized logistic distribution was appropriate in the other regions. Maximum return levels were in the SE4 region, with value ranges of 80–270 mm(1-h to 24-h rainfall) and 108–390 mm(1-h to 24-h rainfall) for 20- and 100 yr, respectively.Minimum return levels were in the CN1 and NE1 regions, with values of 37–104 mm and 53–140 mm for 20 and 100 yr,respectively. Comparing return levels using the optimal and commonly used Pearson-III distribution, the mean return-level differences in eastern China for 1–24-h rainfall varied from-3–4 mm to-23–11 mm(-10%–10%) for 20-yr events, reaching-6–26 mm(-10%–30%) and-10–133 mm(-10%–90%) for 100-yr events. In view of the large differences in estimated return levels, more attention should be given to frequency analysis of sub-daily rainfall over China, for improved water management and disaster reduction.  相似文献   

17.
In this paper, the concept of stationary-wave nonstationarity is presented and elucidated in the framework of the Lorenz circulation decomposition. This concept indicates the relative magnitude of the zonal nonuniform abnormity to the intensity of stationary waves on the monthly mean scale. Based on the Lorenz circulation decomposition, the nonstationarity degree Ius(Ilus) of the global (local) stationary waves is defined, and then used to analyze the stationary-wave nonstationarity at 30° 60°N, where the intensity of stationary waves at 500 hPa in the Northern Hemisphere, as is well known, is very high. The following findings are obtained: (1) There exist seasonal southward and northward movements in the position of the nonstationarity zones of the global stationary waves. The steady stationary waves occur in midlatitudes (35°-55°N) in winter and in the subtropical region (south of 35°N) in summer, associated with the major troughs over East Asia and North America and the weak European trough in winter, and with the relatively steady subtropical high system in summer. A high value center of Ius is at 35°N in spring and 50°N in summer, which might be caused by the seasonal variation of stationary-wave intensity, particularly in association with the interannual variability of trough ridge positions of stationary waves on the monthly mean maps. (2) There exists obvious asymmetry in Ilus, with the steady zones always located in the areas controlled by strong troughs/ridges and the unsteady ones in the areas where the stationary-wave intensity is low. The Ilus in the subtropics (south of 35°N) is larger in winter than in summer, and vice versa in the midlatitude region (north of 35°N). The summertime distribution of Ilus on the whole shows a rather complicated structure. However, North Europe is the most unsteady area for local stationary waves, as represented by high values of Ilus in both summer and winter, while over the North American continent (about 120°E-60°W), the °Ilus is slightly less than 1 in summer, indicating that the stationary waves in this region are more steady than those over other mid and high latitude regions. (3) From North China to Northwest Pacific, there is a high value zone of Ilus in summer, with its center (45°N, 130°E) located in the east of Heilongjiang Province. This influences the summer climate of northern China, including Northeast, North, and Northwest China. It is obvious that the nonstationarity is an intrinsic attribute of stationary waves, and can be regarded as being of the same importance as the intensity and energy-spectrum structure of stationary waves in the studies of the general circulation system.  相似文献   

18.
In this study,the classification scheme developed by Jenkinson and Collison (1977) based on a typing scheme of Lamb (1950) is applied to obtain circulation types from the mean sea-level pressure on a monthly basis.Monthly mean sea-level pressure data from 1951 to 2002 are used to derive six circulation indices and to provide a circulation catalogue with 27 circulation types.Five major types (N,NW,C,CSW,and SW) which occurred most frequently are analyzed to reveal their relationships with the temperature of Harbin on various time scales.Stepwise multiple regression is used to reconstruct temperature anomaly.The monthly mean rainfall of all types occurring and the composite maps of three major types (C,CSW,and SW) relevant to Harbin's precipitation are studied. The results show that the dominant types in winter are types N and NW.types C,CSW,and SW occur frequently in summer.Types N and NW favor a negative temperature anomaly and correspond to less rainfall,while types C,CSW,and SW often induce a positive temperature anomaly and correspond to more rainfall.Moreover,a successful statistical model can be established with only one of the six indices and large-scale mean temperature.Using the model,77.3% of the total variance in the temperature anomaly between 1951 and 2002 can be reconstructed.Type C has a close relationship with total rainfall and type C precipitation plays a major role in determining the total rainfall of Harbin in recent years.This classification scheme is a statistical downscaling model and its relationships with temperature and precipitation can be used to forecast regional climate.  相似文献   

19.
Using a regional climate model MM5 nested with an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate responses of the mid-Holocene climate to different factors over China. Model simulations of the mid-Holocene climate change, especially the precipitation change, are in good agreement with the geologic records. Model results show that relative to the present day (PD) climate, the temperature over China increased in the mid-Holocene, and the increase in summer is more than that in winter. The summer monsoon strengthened over the eastern China north of 30°N, and the winter monsoon weakened over the whole eastern China; the precipitation increased over the west part of China, North China, and Northeast China, and decreased over the south part of China.The sensitive experiments indicate that changes in the global climate (large-scale circulation background),vegetation, earth orbital parameter, and CO2 concentration led to the mid-Holocene climate change relative to the PD climate, and changes in precipitation, temperature and wind fields were mainly affected by change of the large-scale circulation background, especially with its effect on precipitation exceeding 50%. Changes in vegetation resulted in increasing of temperature in both winter and summer over China, especially over eastern China; furthermore, its effect on precipitation in North China accounts for 25% of the total change.Change in the orbital parameter produced the larger seasonal variation of solar radiation in the mid-Holocene than the PD, which resulted in declining of temperature in winter and increasing in summer; and also had an important effect on precipitation with an effect equivalent to vegetation in Northeast China and North China. During the mid-Holocene, CO2 content was only 280×10-6, which reduced temperature in a very small magnitude. Therefore, factors affecting the mid-Holocene climate change over China from strong to weak are large-scale circulation pattern, vegetation, earth orbital parameter, and CO2 concentration.  相似文献   

20.
This paper investigates monthly and seasonal precipitation–temperature relationships (PTRs) over Northeast China using a method proposed in this study. The PTRs are influenced by clouds, latent and sensible heat conversion, precipitation type, etc. In summer, the influences of these factors on temperature decrease are different for various altitudes, latitudes, longitudes, and climate types. Stronger negative PTRs ranging from ?0.049 to ?0.075 °C/mm mostly occur in the semi-arid region, where the cold frontal-type precipitation dominates. In contrast, weaker negative PTRs ranging from ?0.004 to ?0.014 °C/mm mainly distribute in Liaoning Province, where rain is mainly orographic rain controlled by the warm and humid air of East Asian summer monsoon. In winter, surface temperature increases owing to the release of latent heat and sensible heat when precipitation occurs. The stronger positive PTRs ranging from 0.963 to 3.786 °C/mm mostly occur at high altitudes and latitudes due to more release of sensible heat. The enhanced atmospheric counter radiation by clouds is the major factor affecting increases of surface temperature in winter and decreases of surface temperature in summer when precipitation occurs.  相似文献   

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