共查询到20条相似文献，搜索用时 15 毫秒
1.
HUBEX试验区近地面层的湍流输送 总被引：8，自引：1，他引：7
1998年淮河流域能量和水循环试验(HUBEX)期间曾进行了1个月的近地面层湍流观测.分析不稳定条件下湍流的统计特性和谱特征,并与Monin-Obukhov相似理论进行了比较.结果表明,不稳定的时候各湍流量的统计特征与相似理论的预期相符.虽然不稳定条件下温度和湿度涨落的相关系数很高,谱的式样也相近,但湿度谱的峰值频率高于温度谱.协谱曲线的形状显示感热通量的谱峰较宽,表现出w和T在较宽范围的强相关性,而水汽通量谱在高频段下降很快,说明水汽的输送更多地出现在低频部分.从谱相关系数可见,在近中性的时候,各尺度湍流涡的热量输送效率普遍较低,随着不稳定性增强而显著提高.分析还发现,不论不稳定性的程度如何,小尺度湍流的水汽输送效率都较低.水汽通量谱的相关系数随稳定度的变化不如热通量的谱相关系数大,表明近中性时除小尺度湍流外其他湍流涡的水汽输送效率高于热量输送. 相似文献
2.
河南省不同土壤类型墒情变化规律 总被引：4，自引：2，他引：2
分析河南省台站土壤墒情数据库1997年10月至2003年6月资料,找出不同土壤类型的墒情变化规律。土壤有效水分含量分析表明：壤土最大,粘土次之,沙土最小;土壤墒情受地下水影响较大,地下水位较浅的地区不容易出现干旱。根据土壤墒情资料确定了土壤墒情订正系数和不同土壤类型田间持水量在全省的分布,并将其应用到墒情预报模型中。 相似文献
3.
Changes in Extreme Rainfall Events in South Africa 总被引：7，自引：0，他引：7
Simon J. Mason Peter R. Waylen Gillian M. Mimmack Balakanapathy Rajaratnam J. Michael Harrison 《Climatic change》1999,41(2):249-257
Extreme rainfall events can have severe impacts on society, so possible long-term changes in the intensity of extreme events are of concern. Testing for long-term changes in the intensity of extreme events is complicated by data inhomogeneities resulting from site and instrumentation changes. Using rainfall data from stations in South Africa that have not involved site relocations, but which have not been tested for inhomogeneities resulting from changes in instrumentation, a method of testing for changes in the intensity of extreme events is adopted. Significant increases in the intensity of extreme rainfall events between 1931–1960 and 1961–1990 are identified over about 70% of the country. The intensity of the 10-year high rainfall events has increased by over 10% over large areas of the country, except in parts of the north-east, north-west and in the winter rainfall region of the south-west. Percentage increases in the intensity of high rainfall events are largest for the most extreme events. While some inhomogeneities remain in the data used, the observed changes in the intensity of extreme rainfall events over South Africa are thought to be at least partly real. 相似文献
4.
P. A. Iyer 《Boundary-Layer Meteorology》1973,5(1-2):53-66
An analysis is made of the stability of a buoyancy boundary layer existing on an inclined wall which is either heated or cooled relative to ambient, stably stratified fluid. A Boussinesq fluid, with various Prandtl numbers, is considered. Detailed calculations of the linear stability boundaries are made for both streamwise periodic, travelling disturbances and spanwise periodic, stationary disturbances. The former type is found to become unstable first for all angles of tilt, but calculations at a particular angle indicate that the latter can have a higher growth rate once the Reynolds number is sufficiently above the critical value. Energy integrals are evaluated at the critical Reynolds number for various angles of tilt in order to clarify the mechanisms for energy transfer to the disturbance. 相似文献
5.
6.
中国当代强对流天气研究与业务进展 总被引：1，自引：0，他引：1
对当代中国几十年来强对流天气研究和业务进展做了阐述，主要包括强对流系统产生的环境背景和主要组织形态，以及具体强对流天气的有利环境条件、触发机制、卫星云图特征、多普勒天气雷达回波特征以及预报、预警技术等诸方面。总体来看，中国学者对强对流以及不同类型强对流天气（强冰雹、龙卷、雷暴大风）发生、发展的环流背景以及通过雷达和卫星观测到的组织结构及其演变特征都已有了明确认识，研究了对流系统的多种触发机制，深入认识了超级单体、飑线等对流系统的环境条件、组织结构特征和维持机制，了解了中国中尺度对流系统的组织形态和气候分布特征，获得了强冰雹、龙卷、下击暴流和雷暴大风等的雷达、卫星和闪电等的多尺度观测特征、形成机制和现场灾害调查特征，发展了各类强对流天气识别、监测和分析方法以及基于“配料法”和深度学习方法等的预报、预警技术等。因此，强对流天气业务预报水平已得到显著提升。 相似文献
7.
Trends in graded precipitation in China from 1961 to 2000 总被引：3，自引：0，他引：3
Daily precipitation rates observed at 576 stations in China from 1961 to 2000 were classified into six grades of intensity, including trace （no amount）, slight （≤ 1 mm d^-1）, small, large, heavy, and very heavy. The last four grades together constitute the so called effective precipitation （〉 1 mm d^-1）. The spatial distribution and temporal trend of the graded precipitation days are examined. A decreasing trend in trace precipitation days is observed for the whole of China, except at several sites in the south of the middle section of the Yangtze River, while a decreasing trend in slight precipitation days only appears in eastern China. The decreasing trend and interannual variability of trace precipitation days is consistent with the warming trend and corresponding temperature variability in China for the same period, indicating a possible role played by increased surface air temperature in cloud formation processes. For the effective precipitation days, a decreasing trend is observed along the Yellow River valley and for the middle reaches of the Yangtze River and Southwest China, while an increasing trend is found for Xinjiang, the eastern Tibetan Plateau, Northeast China and Southeast China. The decreasing trend of effective precipitation days for the middle- lower Yellow River valley and the increasing trend for the lower Yangtze River valley are most likely linked to anomalous monsoon circulation in East China. The most important contributor to the trend in effective precipitation depends upon the region concerned. 相似文献
8.
Kristie L. Ebi 《Climatic change》2011,108(4):693-700
The Guidance Notes for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties describes a process for consistently evaluating and communicating levels of certainty in findings. The process begins with
an assessment of the scientific evidence and agreement supporting a finding, where evidence is defined as including mechanistic
understanding, theory, data, models, and expert judgment. The appropriateness of categorizing theory as one line of evidence
varies by scientific discipline; for the natural and social sciences, developing theory and collecting data are different
steps in the scientific method. Further, decision-makers often find it valuable for scientists to differentiate situations
where a theory is generally agreed but for which supporting data are limited, from situations where empirical data lack an
explanatory theory. The paper describes the approach used by the International Agency for Research on Cancer (IARC) for assessing
the relative robustness of a theory separately from the strength and quality of its supporting evidence, and then developing
consensus statements of whether an agent is a human carcinogenic. Although the IARC and IPCC processes are very similar, the
IARC process also differs by combining theory, evidence, and agreement as equal partners in a limited set of standardized
categories of confidence. Incorporating aspects of the IARC approach into the IPCC guidance could improve the evaluation and
communication of theory, evidence, and agreement in future versions of the uncertainty guidance. 相似文献
9.
WAFS产品中GRIB资料中国区产品评估 总被引：1，自引：0，他引：1
为了给使用WAFS产品的用户提供量化参考依据，选取WAFS产品中常用区域和层次的GRIB数据，利用由国家气象中心提供的风、温客观分析网格点资料，与WAFS中同时刻的预报场产品（风、温网格点资料），用均方根误差进行数字化形式分析比较。结果表明：WAFS提供的风、温预报，通常是短时效的风、温预报比长时效的风、温预报更接近客观分析场；低层的预报比高层的预报更接近客观分析场；风的预报以v矢量的预报优于u矢量的预报；风的误差主要来源于u矢量的误差。 相似文献
10.
近年来，我国政府和科技界十分关注气候王馥棠变暖对我国经济发展可能影响的评估, 开展了许多重大项目和课题的研究。该文仅就气候变暖对我国自然植被、农业、森林、水资源、能源利用和区域海平面上升等领域影响评估研究的若干有意义的初步结果简要归纳和评述如下:取自不同GCM模型的未来气候变化情景下的影响评估模拟表明，我国的特征性自然植被类型将会发生明显的变化。同当前气候（1951~1980年）下的模拟分布相比，到2050年我国几乎所有地方的农业种植制度均将发生较大变化；气候变暖将导致复种指数增加和种植方式多样化，但降水与蒸散之间可能出现的负平衡和土壤水分胁迫的增加以及生育期的可能缩短，最终将导致我国主要作物的产量下降。气候变暖对我国水资源最明显的影响将会发生在黄淮海流域，这个区域的水资源供需短缺将大大提高。同时，气候变暖将改变我国室内取暖和降温的能源需求关系:北方冬季取暖的能源消耗将减少, 而南方夏季降温的能源消耗将会增加。海平面的上升将使我国三个主要沿海低洼脆弱区，即珠江三角洲、长江三角洲和黄河三角洲，面临部分遭受海水淹没的威胁。 相似文献
11.
A preliminary investigation of monthly rainfall patterns analysed from 24‐hour computer forecasts of precipitation was performed. These patterns are compared with the observed precipitation and long‐term normal patterns. Recommendations are made to incorporate the method into a verification program for the computer product. 相似文献
12.
T. Mavromatis 《Climatic change》2012,110(1-2):249-267
The aim of the present study is, primarily, to compare the frequencies of exceptional hydrological and meteorological weekly events, employing the self-calibrated versions of Palmer’s drought indices (PDSI and PHDI, respectively), from 17 stations across Greece in the decade 1997–2006 with these of 1961–1990; on second level, to identify the trends and define the time lags between these two indices for the study period 1961–2006. The changes in the spatial distribution of exceptional weekly event frequencies between the most recent decade and the baseline period were similar for both drought indices. When 1997–2006 was compared with 1961–1990, the number of stations with a frequency of exceptionally dry weekly events >93rd percentile, increased by seven stations (41%) for PDSI and nine (53%) for PHDI, at the expense of exceptionally moist weekly spells. PDSI was found to lead PHDI by three to 20?weeks. If exceptional weekly events continue to be more frequent in the future, major implications for natural water resources are expected. 相似文献
13.
J.J. Moakler 《大气与海洋》2013,51(2):59-62
Abstract Weather observations made at Eureka, on Ellesmere Island in the Canadian High Arctic, have been archived since 1953. The time series, averages, and seasonal cycles of surface temperature, pressure, dew point, relative humidity, cloud cover, wind speed, and direction are presented for the period from 1954 to 2007. Also shown are the time series and averages for the 500 mb temperature, 900 to 500 mb thickness, 500 mb wind speed, and various boundary‐layer stability parameters. Some of the main trends found are 1) an annual average surface warming of 3.2°C since 1972, with summer exhibiting the least warming, 2) a reduction in the frequency of strong anticyclonic events in the winter, 3) a reduction in surface wind speeds except in the summer, 4) a 1.0°C warming in the 500 mb temperature since 1961, with the greatest warming occurring in the spring and summer, and 5) a 10% increase in precipitable water all year round since 1961 but dominated by the spring, summer, and autumn seasons. The importance of open water in the Arctic Ocean for summer temperatures and humidity, of the North Atlantic Oscillation for winter interannual pressure variability, and of precipitable water for winter temperatures are highlighted in this climatology. 相似文献
14.
The micromixing technique, widely used in engineering calculations of mixing and chemical reaction, is extended to atmospheric boundary-layer flows. In particular, a model based on the interaction-by-exchange-with-the-conditional-mean (IECM) micromixing approach is formulated to calculate concentration fluctuation statistics for a line source and a point source in inhomogeneous and non-Gaussian turbulence in the convective boundary layer. The mixing time scale is parameterised as a linear function of time with the intercept value determined by the source size at small times. Good agreement with laboratory data for the intensity of concentration fluctuations is obtained with a value of 0.9 for the coefficient of the linear term in the time-scale parameterisation for a line source, and a value of 0.6 for a point source. Calculation of higher-order moments of the concentration field for a line source shows that non-Gaussian effects persist into the vertically well-mixed region. The cumulative distribution function predicted by the model for a point source agrees reasonably well with laboratory data, especially in the far field. In the limit of zero mixing time scale, the model reduces to a meandering plume model, thus enabling the concentration variance to be partitioned into meandering and relative components. The meandering component is shown to be more persistent for a point source than for a line source. 相似文献
15.
Temporal and geographical variation in the onset of climatological spring in Northeast China 总被引：1，自引：0，他引：1
Haifeng Zheng Neil B. McLaughlin Xingyuan He Xingyang Yu Zhibin Ren Dan Zhang 《Theoretical and Applied Climatology》2013,114(3-4):605-613
Indications of earlier onset of spring have been observed in behavior of diverse animal and plant species in the Northern Hemisphere in response to recent climate warming. Knowledge of changes in the spring onset is a critical requirement for understanding ecosystem adaption to climate change, especially for agricultural regions. In this study, we present a climatological approach for detecting the temporal and spatial variability in onset of spring with particular emphasis on how they vary along geographical parameters. Yearly dates for spring onset were computed for 71 climate stations in Northeast China based on daily surface air temperature records. These analyses were conducted for the two study periods (1960–2004 and 1979–2004). We also examined the boundary shifts of spring onset for three selected dates between the periods of 1960–1978 and 1979–2004. The results showed that advancement of spring onset was more pronounced for the period of 1979–2004 than for the period of 1960–2004 (4.0 vs. 2.2 days/decade). For the 22 stations where the spring advancement was statistically significant in the two periods, the mean rate of advancement was ?0.6 days/decade during the period of 1960 to 1978. The trends of advancement of spring onset decreased with both increasing latitude and altitude up to 300 m above sea level, and these geographical effects were clearer during 1979–2004. Analysis of boundary shifts of three specific dates revealed that the spring onset has moved to higher latitudes for each date with an average shift of about 1° of latitude (about 110 km). Our results suggest that attempts to address how ecosystems will adapt to spring advancement associated with climate warming should consider the differences in response rates and geographical effects across the study area. 相似文献
16.
Miroslav Trnka Josef Eitzinger Daniela Semer��dov�� Petr Hlavinka Jan Balek Martin Dubrovsky Gerhard Kubu Petr ?t��p��nek Sabina Thaler Martin Mo?ny Zden��k ?alud 《Climatic change》2011,108(1-2):261-289
During the past few decades, the basic assumption of agroclimatic zoning, i.e., that agroclimatic conditions remain relatively stable, has been shattered by ongoing climate change. The first aim of this study was to develop a tool that would allow for effective analysis of various agroclimatic indicators and their dynamics under climate change conditions for a particular region. The results of this effort were summarized in the AgriClim software package, which provides users with a wide range of parameters essential for the evaluation of climate-related stress factors in agricultural crop production. The software was then tested over an area of 114,000 km2 in Central Europe. We have found that by 2020, the combination of increased air temperature and changes in the amount and distribution of precipitation will lead to a prolonged growing season and significant shifts in the agroclimatic zones in Central Europe; in particular, the areas that are currently most productive will be reduced and replaced by warmer but drier conditions in the same time the higher elevations will most likely experience improvement in their agroclimatic conditions. This positive effect might be short-lived, as by 2050, even these areas might experience much drier conditions than observed currently. Both the rate and the scale of the shift are amazing as by 2020 (assuming upper range of the climate change projections) only 20?C38% of agriculture land in the evaluated region will remain in the same agroclimatic and by 2050 it might be less than 2%. On the other hand farmers will be able to take advantage of an earlier start to the growing season, at least in the lowland areas, as the proportion of days suitable for sowing increases. As all of these changes might occur within less than four decades, these issues could pose serious adaptation challenges for farmers and governmental policies. The presented results also suggest that the rate of change might be so rapid that the concept of static agroclimatic zoning itself might lose relevance due to perpetual change. 相似文献
17.
It is widely acknowledged that private finance has a key role to play in achieving low-carbon development and resilience to climate change. However, while there have been several studies that have closely examined the data on public climate finance, there have been few such studies of the private climate-related finance data. There is a political dimension to accounting for ‘private finance’ given the commitment of industrialized countries – enshrined in the Copenhagen Accord and the Cancun Agreements – to mobilize US$100 billion of public and private finance for developing countries by 2020, on an annual basis. The availability and quality of data for different types of private climate finance flows with climate benefits (investments, carbon market payments, and voluntary funding) are analysed, and these flows are assessed according to various criteria for inclusion in the $100 billion figure. While existing data suggest that private climate finance invested in developing countries and mobilized by industrialized countries might currently be in the range of $27–123 billion per year, this number is a questionable point of reference. Existing data are limited and of very poor quality: definitions of ‘private climate finance’ are missing and data are hardly verified. Therefore, policy makers will first have to clearly define ‘private climate finance’ and develop systems for measuring, reporting, and verifying it, before using private finance numbers in international climate agreements. 相似文献
18.
Abstract The changes in normal precipitation amounts from 1931–60 to 1951–80 are examined for stations in Eastern Canada. The area covered comprises the Maritime Provinces and those parts of Ontario and Quebec south of a line approximately 200 km north of Lakes Erie and Ontario and the St Lawrence River. Changes are computed for each of the four seasons and for the entire year. On the whole, precipitation has increased, especially in winter and summer. However, there is considerable variation throughout the area, with precipitation decreasing in some regions. General circulation models that simulate the effect of doubling atmospheric CO2 also show an increase in precipitation. 相似文献
19.
Trends in Temperature Extremes in Association with Weather-Intraseasonal Fluctuations in Eastern China 总被引：3，自引：0，他引：3
Trends in the frequencies of four temperature extremes (the occurrence of warm days, cold days, warm nights and cold nights) with respect to a modulated annual cycle (MAC), and those associated exclusively with weather-intraseasonal fluctuations (WIF) in eastern China were investigated based on an updated homogenized daily maximum and minimum temperature dataset for 1960–2008. The Ensemble Empirical Mode Decomposition (EEMD) method was used to isolate the WIF, MAC, and longer-term components from the temperature series. The annual, winter and summer occurrences of warm (cold) nights were found to have increased (decreased) significantly almost everywhere, while those of warm (cold) days have increased (decreased) in northern China (north of 40°N). However, the four temperature extremes associated exclusively with WIF for winter have decreased almost everywhere, while those for summer have decreased in the north but increased in the south. These characteristics agree with changes in the amplitude of WIF. In particular, winter WIF of maximum temperature tended to weaken almost everywhere, especially in eastern coastal areas (by 10%–20%); summer WIF tended to intensify in southern China by 10%–20%. It is notable that in northern China, the occurrence of warm days has increased, even where that associated with WIF has decreased significantly. This suggests that the recent increasing frequency of warm extremes is due to a considerable rise in the mean temperature level, which surpasses the effect of the weakening weather fluctuations in northern China. 相似文献
20.
中国地区极端事件预估研究 总被引：11，自引：0，他引：11
高学杰 《气候变化研究进展》2007,3(3):162-166
简要介绍了极端气候事件预估的基本方法,概述了东亚和中国地区关于气候和极端气候事件预估研究的进展。针对极端事件变化预估研究中的重要问题,如高分辨率、长时间尺度的区域气候变化模拟和预估,高时空分辨率的网格化观测资料,除温室效应外的土地利用和气溶胶的作用,使用合理方法进行多模式结果的集合,以及统计降尺度方法的应用等,进行了讨论。 相似文献