New evidence of orographic precipitation suppression by aerosols in central China   总被引：1，自引：0，他引：1  

Xin Yang  Marion Ferrat  Zhanqing Li 《Meteorology and Atmospheric Physics》2013,119(1-2):17-29

The correlation between light precipitation events and visibility at Mt. Hua, (Shannxi Province, China) and at the surrounding plains stations was analyzed. Trends and changes in visibility, precipitation, the precipitation difference between Mt. Hua and the plains stations (De) and wind speed over the study area during the years 1980–2009 were also investigated. The significant positive correlation between visibility and light precipitation throughout the study period indicates that light precipitation events, notably orographic precipitation, are suppressed by aerosol pollution in this region. The trend of increasing air pollution aerosols since 1980, represented by visibility at Mt. Hua, ended in 2002 with a decreasing trend observed in more recent years. These changes were mirrored by corresponding changes in De. However, the total precipitation trends at Mt. Hua and the plains stations are consistent in both frequency and amount during the two periods, suggesting that the suppressive effect of pollution aerosols on light and moderate precipitation is the most likely cause for the changes in orographic precipitation at Mt. Hua during this time. The analysis of wind strength suggests that the increase in winds at Mt. Hua is highly related to the aerosol radiative effects; this increase of mountain winds is therefore a potential cause for the reduction in precipitation at Mt. Hua. This research provides further support for the hypothesis that aerosol microphysical effects can reduce orographic precipitation and suggests that aerosol radiative effects might act to suppress orographic precipitation through changes in wind speed.  相似文献   

Cloud-Aerosol-Radiation (CAR) ensemble modeling system: Overall accuracy and efficiency     

曾庆存 《大气科学进展》2013,30(4):955-973

The Cloud-Aerosol-Radiation (CAR) ensemble modeling system has recently been built to better understand cloud/aerosol/radiation processes and determine the uncertainties caused by different treatments of cloud/aerosol/radiation in climate models. The CAR system comprises a large scheme collection of cloud, aerosol, and radiation processes available in the literature, including those commonly used by the world's leading GCMs. In this study, detailed analyses of the overall accuracy and efficiency of the CAR system were performed. Despite the different observations used, the overall accuracies of the CAR ensemble means were found to be very good for both shortwave (SW) and longwave (LW) radiation calculations. Taking the percentage errors for July 2004 compared to ISCCP (International Satellite Cloud Climatology Project) data over (60°N, 60°S) as an example, even among the 448 CAR members selected here, those errors of the CAR ensemble means were only about-0.67% (-0.6 W m-2 ) and-0.82% (-2.0 W m-2 ) for SW and LW upward fluxes at the top of atmosphere, and 0.06% (0.1 W m-2 ) and -2.12% (-7.8 W m-2 ) for SW and LW downward fluxes at the surface, respectively. Furthermore, model SW frequency distributions in July 2004 covered the observational ranges entirely, with ensemble means located in the middle of the ranges. Moreover, it was found that the accuracy of radiative transfer calculations can be significantly enhanced by using certain combinations of cloud schemes for the cloud cover fraction, particle effective size, water path, and optical properties, along with better explicit treatments for unresolved cloud structures.  相似文献   

The impact of the MJO on clusters of wintertime circulation anomalies over the North American region   总被引：3，自引：2，他引：1  

Emily E. Riddle  Marshall B. Stoner  Nathaniel C. Johnson  Michelle L. L’Heureux  Dan C. Collins  Steven B. Feldstein 《Climate Dynamics》2013,40(7-8):1749-1766

Recent studies have shown that the Madden–Julian Oscillation (MJO) impacts the leading modes of intraseasonal variability in the northern hemisphere extratropics, providing a possible source of predictive skill over North America at intraseasonal timescales. We find that a k-means cluster analysis of mid-level geopotential height anomalies over the North American region identifies several wintertime cluster patterns whose probabilities are strongly modulated during and after MJO events, particularly during certain phases of the El Niño-Southern Oscillation (ENSO). We use a simple new optimization method for determining the number of clusters, k, and show that it results in a set of clusters which are robust to changes in the domain or time period examined. Several of the resulting cluster patterns resemble linear combinations of the Arctic Oscillation (AO) and the Pacific/North American (PNA) teleconnection pattern, but show even stronger responses to the MJO and ENSO than clusters based on the AO and PNA alone. A cluster resembling the positive (negative) PNA has elevated probabilities approximately 8–14 days following phase 6 (phase 3) of the MJO, while a negative AO-like cluster has elevated probabilities 10–20 days following phase 7 of the MJO. The observed relationships are relatively well reproduced in the 11-year daily reforecast dataset from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). This study statistically links MJO activity in the tropics to common intraseasonal circulation anomalies over the North American sector, establishing a framework that may be useful for improving extended range forecasts over this region.  相似文献   

EU 20-20-20 energy policy as a model for global climate mitigation     

Katherine Calvin  Bjorn Bakken  Marshall Wise  Sonny Kim  Patrick Luckow 《Climate Policy》2013,13(5):581-598

The EU has established an aggressive portfolio with explicit near-term targets for 2020 – to reduce GHG emissions by 20%, rising to 30% if the conditions are right, to increase the share of renewable energy to 20%, and to make a 20% improvement in energy efficiency – intended to be the first step in a long-term strategy to limit climate forcing. The effectiveness and cost of extending these measures in time are considered along with the ambition and propagation to the rest of the world. Numerical results are reported and analysed for the contribution of the portfolio's various elements through a set of sensitivity experiments. It is found that the hypothetical programme leads to very substantial reductions in GHG emissions, dramatic increases in use of electricity, and substantial changes in land-use including reduced deforestation, but at the expense of higher food prices. The GHG emissions reductions are driven primarily by the direct limits. Although the carbon price is lower under the hypothetical protocol than it would be under the emissions cap alone, the economic cost of the portfolio is higher, between 13% and 22%.  相似文献   

2015—2017年夏季南京雨滴谱特征          下载免费PDF全文

梅海霞  梁信忠  曾明剑  李力  祖繁  李玉涛 《应用气象学报》2020,31(1):117-128

利用2015—2017年夏季南京地区的雨滴谱数据,对南京在梅雨开始前、梅雨期及梅雨结束后3个不同时段降水的宏微观特征进行分析发现:梅雨开始前对流活动强度偏弱,但对流降水的雨滴平均质量加权直径、分钟级强降水频率和逐小时累积短时强降水的频率为3个时段中最高;天气尺度强迫提供的有利于降水的持续性条件、弱对流强度下充分的凝结过程及微物理相关过程对云粒子的损耗偏弱,是有利于该时段大雨滴形成和降水效率提高的重要因素。梅雨结束后,高温高湿环境易产生剧烈对流活动,导致对流降水的大尺度雨滴样本比例及分钟级极端降水发生频率位于3个时段的首位。层云降水时,梅雨期降水频率、降水率及雨滴尺度平均值均位于首位,小尺度雨滴样本比例最低;有利天气尺度强迫条件下的充分碰并作用是主要原因之一。不同时段雨滴谱谱形参数（μ）与斜率（Λ）之间的二项式关系式的差异与μ的取值有关。  相似文献   

Satellite altimeter observations of nonlinear Rossby eddy–Kuroshio interaction at the Luzon Strait     

Quanan Zheng  Chang-Kuo Tai  Jianyu Hu  Hongyang Lin  Rong-Hua Zhang  Feng-Chun Su  Xiaofeng Yang 《Journal of Oceanography》2011,67(4):365-376

Satellite altimeter sea level data from 1993 to 2008 are used to analyze the interaction of nonlinear Rossby eddies with the Kuroshio at the Luzon Strait (LS). The sea level anomaly data show that the west Pacific (WP) is a source of nonlinear Rossby eddies, and the South China Sea (SCS) is a sink. The LS serves as a gateway between the two. The scale analysis indicates that eddies with a radius larger than 150 km are strong enough to significantly alter the Kuroshio and are able to modify the local circulation pattern. Statistical analysis indicates that the probability for eddies to penetrate through the Kuroshio may reach at least 60%. A case study of an anticyclonic mesoscale eddy passing through the LS in June–July 2004 indicates that the Kuroshio behaves as an unsteady flow with its stream path frequently modified, in a way of cutting off, meandering and branching during its interaction with the eddy. We therefore suggest that nonlinear Rossby eddies may play a significant role in modification of the local circulation system near the LS and in exchanges of the mass, momentum and energy between the WP and the SCS.  相似文献   

Binary near-Earth asteroid formation: Rubble pile model of tidal disruptions     

Kevin J. Walsh  Derek C. Richardson 《Icarus》2006,180(1):201-216

We present numerical simulations of near-Earth asteroid (NEA) tidal disruption resulting in bound, mutually orbiting systems. Using a rubble pile model we have constrained the relative likelihoods for possible physical and dynamical properties of the binaries created. Overall 110,500 simulations were run, with each body consisting of ∼1000 particles. The encounter parameters of close approach distance and velocity were varied, as were the bodies' spin, elongation and spin axis direction. The binary production rate increases for closer encounters, at lower speeds, for more elongated bodies, and for bodies with greater spin. The semimajor axes for resultant binaries are peaked between 5 to 20 primary radii, and there is an overall trend for high eccentricity, with 97% of binaries having e > 0.1. The secondary-to-primary size ratios of the simulated binaries are peaked between 0.1 and 0.2, similar to trends among observed asteroid binaries. The spin rates of the primary bodies are narrowly distributed between 3.5- and 6-h periods, whereas the secondaries' periods are more evenly distributed and can exceed 15-h periods. The spin axes of the primary bodies are very closely aligned with the angular momenta of the binary orbits, whereas the secondary spin axes are nearly random. The shapes of the primaries show a large distribution of axis ratios, where those with low elongation (ratio of long and short axis) are both oblate and prolate, and nearly all with large elongation are prolate. This work presents results that suggest tidal disruption of gravitational aggregates can make binaries physically similar to those currently observed in the NEA population. As well, tidal disruption may create an equal number of binaries with qualities different from those observed, mostly binaries with large separation and with elongated primaries.  相似文献   

A fast method for finding bound systems in numerical simulations: Results from the formation of asteroid binaries     

Zoë M. Leinhardt  Derek C. Richardson 《Icarus》2005,176(2):432-439

We present a new code (companion) that identifies bound systems of particles in O(NlogN) time. Simple binaries consisting of pairs of mutually bound particles and complex hierarchies consisting of collections of mutually bound particles are identifiable with this code. In comparison, brute force binary search methods scale as O(N²) while full hierarchy searches can be as expensive as O(N³), making analysis highly inefficient for multiple data sets with N?¹⁰³. A simple test case is provided to illustrate the method. Timing tests demonstrating O(NlogN) scaling with the new code on real data are presented. We apply our method to data from asteroid satellite simulations [Durda et al., 2004. Icarus 167, 382-396; Erratum: Icarus 170, 242; reprinted article: Icarus 170, 243-257] and note interesting multi-particle configurations. The code is available at http://www.astro.umd.edu/zoe/companion/ and is distributed under the terms and conditions of the GNU Public License.  相似文献   

An integrated assessment of global and regional water demands for electricity generation to 2095     

《Advances in water resources》2013

Electric power plants account for approximately half the global industrial water withdrawal. Although continued electric-sector expansion is probable, significant variations in water intensity by electricity technology and cooling system type make its effects on water demands uncertain. Using GCAM, an integrated assessment model of energy, agriculture, and climate change, we establish lower-, median-, and upper-bound estimates for current electric-sector water withdrawals and consumption in 14 geopolitical regions, and compare them with available estimates. We then explore water use for electricity to 2095, focusing on uncertainties in water withdrawal and consumption intensities, power plant cooling system changes, and adoption rates of water-saving technologies. Results reveal a probable decrease in the water withdrawal intensity with capital stock turnover, but a corresponding increase in consumptive use, for which technologies under development may compensate. At a regional scale, water use varies significantly based on the existing capital stock and its evolution over the century.  相似文献   

Economically consistent long-term scenarios for air pollutant emissions   总被引：1，自引：0，他引：1  

Steven J. Smith  J. Jason West  Page Kyle 《Climatic change》2011,108(3):619-627

Pollutant emissions such as aerosols and tropospheric ozone precursors substantially influence climate. While future century-scale scenarios for these emissions have become more realistic through the inclusion of emission controls, they still potentially lack consistency between surface pollutant concentrations and regional levels of affluence. We find that the default method of scenario construction, whereby emissions factors converge to similar values in different regions, does not yield pollution concentrations consistent with historical experience. We demonstrate a methodology combining use of an integrated assessment model and a three-dimensional atmospheric chemical transport model, whereby a reference scenario is constructed by requiring consistent surface pollutant concentrations as a function of regional income over the 21st century. By adjusting air pollutant emission control parameters, we improve consistency between projected PM_2.5 and economic income among world regions through time; consistency for ozone is also improved but is more difficult to achieve because of the strong influence of upwind world regions. Reference case pollutant emissions described here were used to construct the RCP4.5 Representative Concentration Pathway climate policy scenario.  相似文献