Abstract:Wind is an available main form of renewable energy. Following the development of installed capacity growth in China, an improvement is needed in wind resource assessment and wind power forecasting techniques. Numerous studies on the numerical simulation of complex terrain flow fields have been conducted worldwide. With the increasing capacity of numerical calculation, Computational Fluid Dynamics (CFD) models have been used in the meteorological field and are coupled with mesosacle models to simulate the flow fields on complex terrains. In this paper, a coupled model system for wind resource assessment was studied. In this study, a mesoscale meteorological model, the Weather Research and Forecasting (WRF) model, was used to downscale data from the global scale to the inner nested grid scale of a few kilometers and was then coupled with the Fluent method. High-resolution results of wind speed distribution data and refined wind farm information were obtained. The refined WRF/Fluent system was then applied to the complex terrain flow field of the Poyang Lake region and Yangmeishan in Yunnan. The results showed that this approach is viable for the assessment and forecasting of wind energy.

Abstract:Aerosol Index (AI) data was used to study the spatio-temporal distribution of ultraviolet (UV)-absorbing aerosols over East Asia. The main conclusions are as follows. In addition to continuity from the Earth Probe (EP)/Total Ozone Mapping Spectrometer (TOMS) AI to the Ozone Monitoring Instrument (OMI) AI, which differs from the Nimbus 7 (N7)/TOMS AI to EP/TOMS AI, good consistency was shown among N7/TOMS, EP/TOMS, and OMI AI. UV-absorbing aerosols are mostly located in the Taklimakan Desert, Kumutage Desert, Qaidam Basin Desert, Gurbantünggüt Desert, Midwestern Inner Mongolian Autonomous Region, Southern Mongolia, Northeastern China, and North China. Moreover, UV-absorbing aerosols have obvious characteristics of inter-monthly variation. Rotated Empirical Orthogonal Function (REOF) analysis can isolate source domains of UV-absorbing aerosols and provide quantitative information on the relative strengths of these sources.

Abstract:The phenomenon known as the Antarctic Circumpolar Wave (ACW) was determined to have occurred during the last two decades of the 21th century. In this study, a new reanalysis dataset of 20th century reanalysis Version 2 (20CRV2) spanning 1871-2008 and several long-term observation series were used to investigate the interdecadal fluctuation and transmission of the ACW since 1871. The results indicate an obvious interdecadal variation of the ACW signal, which occurred in 1940-1960 and in 1980-2000 and disappeared during the other periods. The greatest amplitude of the ACW was detected near the southeast Pacific, implying the essential influence of ocean-atmosphere interaction at this region to the emergence of the ACW. Moreover, it was determined that a noticeable ACW phenomenon appeared during the period in which the Antarctic Oscillation (AO) was relatively stronger, which indicates that the enhanced AO may intensify the circumpolar westerly and benefit the emergence of the ACW.

Abstract:There has been relatively less research on the physical properties of mid-level clouds. In this study, the CloudSat and CALIPSO satellite cloud data from Jan 2007 to Dec 2010 for the North China (area A1), Sea of Japan (area A2), and the Pacific (area A3) was used to analyze the physical characteristics of mid-level clouds (As and Ac). The occurrences of middle level clouds are around 1/3 over all the three areas. The As occurs higher (4-8 km) than the Ac (3.5-5.5 km). The average size of mid-level clouds increases from land to sea. Temperature in the middle troposphere supports the condition for mid-level clouds to contain both ice and supercooled liquid particles. Our statistical results indicate that ice particles dominate in As, while the proportions of liquid and ice particles are similar in Ac. The IER (Ice Effective Radius) of As and Ac varied from 35 to 80 μm and the height and IER of As and Ac ice particles were negatively correlated. The LER (Liquid Effective Radius) of As is highly positively correlated with height, but this correlation is weakened in Ac. The LER values in Ac and As mainly range between 5-15 μm. The IWC and LWC of As and Ac show no obvious correlation with height.

Abstract:Based on a combination of historical runs, one of the core experiments of the 5th Coupled Model Inter-comparison Project (CMIP5), and remote sensing data, simulations of the snow cover fraction over Eurasia from 13 coupled climate models were evaluated, using correlation analysis, root-mean-square error (RMSE), standard deviation, and other statistical metrics. The ensemble mean of the 13 models was used to project changes in snow cover fraction (SCF) over Eurasia under the conditions of three different representative concentration pathways (rcp2.6, rcp4.5, and rcp8.5). The results show that, although large differences are seen among simulations and between simulation and observation on the Tibetan Plateau, on the whole, the models were able to adequately simulate the spatial patterns, seasonal changes, and annual variation in SCF. The projection scenarios indicated a clearly decreasing trend from 2006 to 2040 under the different emission scenarios, with little difference between them. However, after 2040, the decreasing trend tends to be smoother under rcp2.6 and rcp4.5, whereas under rcp8.5 the trend is less pronounced. In this, the areas experiencing the most significant decrease are located to the west of Europe and on the Tibetan Plateau, and the greatest decrease is seen in winter, spring, and autumn. The results suggest that to maintain Eurasian snow cover, it is important to control greenhouse gas emissions in the future.

Abstract:The applicability of surface meteorological elements such as surface air temperature, relative humidity, and wind speed from the European Centre for Medium-Range Weather Forecasts (ECMWF), Japan Meteorological Agency (JMA), and Global Forecast System (GFS) is evaluated in China by comparison with automatic observations from 2421 stations reported by the Chinese Meteorological Administration from 1 July 2010 to 30 June 2013. The results indicate that the three numerical models can essentially display spatiotemporal consistence with observation and that their performance in East China is more reliable than that in the western area. The various surface meteorological variables of the numerical models are key to these differences. For example, the surface air temperature and relative humidity of ECMWF are closer to the observations than the JMA and GFS. Moreover, the qualities of surface air temperature and relative humidity from both ECMWF and JMA are better in the analysis field than those in prediction field. In addition, for surface air temperature, the largest differences with observation are noted with ECMWF and JMA in winter and GFS in summer. For surface relative humidity, the discrepancy of the three numerical models is the most significant in autumn and in winter. For the surface wind speed from these numerical models, JMA is the closest to the observation in eastern China, whereas ECMWF is the best in northern and western China. However, from the perspective of time, the differences among JMA, GFS, and the observations are the most obvious in winter.

Abstract:Using the Community Atmospheric Model Version 3.1 (CAM3.1) of NCAR, the influence of greenhouse gas, global sea surface temperature (SST), solar constant, and volcanic activity on surface temperature is studied. The results show that increase of greenhouse gas and global SST contributes to the warming trend. Over recent 100 years, annual surface temperature in China undergoes two decadal oscillations and increases. China experienced two warm-periods during 1940s and 1990s respectively and two relative cold periods during 1910s and the period of 1950s-1960s. The variations of surface temperate over China, solar constant and SST have an oscillation period of 60 years, two decadal oscillations of surface temperature over China are induced by two decadal oscillations of solar constant and SST, the variation of surface temperature lagged behind of solar constant and SST. The volcanic activities before 1920s and after 1960s are one of the reasons of cooling trend during 1910s and 1960s-1980s.

Abstract:Base on three-year eddy covariance system measurements, environmental controls on rainfed maize cropland have been analyzed. The results show that energy factors (radiation and temperature) and water conditions (rain, soil moisture, and vapor pressure deficit) are crucial to water and heat exchanges in different ways. The effects of energy factors on water and heat exchanges are gradually weakening with increasing time scales. While, change in the impacts of water conditions on water and heat exchanges in inverse way. In different hydrological years, there are significant distinctions in environmental controls on water and heat exchanges. In humid year, available energy is primary controls on water and heat exchanges without water stress; and in arid year, available energy and soil moisture all strongly affect on water and heat exchanges.

Abstract:The daily rainfall data from May to September of 71 stations in the Jianghuai region from 1961 to 2011 with no missing data were used to introduce the GPD (Generalized Pareto Distribution) based on the POT (Peaks- Over-Threshold) method in a study of the spatial distribution of extreme rainfall characteristics and trends. The results indicate that the maximum thresholds are at the border of Anhui and Jiangxi, whereas smaller thresholds are in northwest and southeast. The trends of the thresholds are positive in most places. At the stations in eastern Hubei and northern Jiangxi, the trends are more than 0.8 mm (10 a)^-1 and pass the 0.01 significance level of the Mann-Kendall test. In the mid-east region, extreme rainfall is nearly continuous; therefore, an automatic declustering scheme is used to select the independent extreme events exceeding the threshold. The largest values of scale parameter are in the south, whereas in areas northwest, southwest, and north of the Huaihe River, the values are smaller. In most parts of the Jianghuai region, the trends of scale parameter are positive, which indicates a greater occurrence probability of maximum rainfall. The border region of Anhui, Jiangxi, and Hubei has the highest probability of extreme rainfall, whereas the probabilities are lower in the northwest, southeast, and middle parts of Anhui. The trends of extreme rainfall are positive in most places, particularly in the Dabie mountains nearby and in eastern Henan, where the trends of 2-a and 20-a return levels are more than 6 mm (10 a)^-1 and 20 mm (10 a)^-1, respectively.

Abstract:The outputs of PRECIS (Providing Regional Climates for Impacts Studies) were used to analyze the changes in the maximum (Tmax) and minimum temperature (Tmin) and diurnal temperature range (DTR) during 2011-2040, 2041-2070, and 2071-2100 relative to the baseline period (1961-1990) under the SRES A1B scenario for China. The results show a consistent increase in the Tmax and Tmin, annually and for the four seasons, during 2011-2040, 2041-2070, and 2071-2100; however, the DTR shows a consistent decrease. The annual warming amplitude (WA) of the Tmax and Tmin are 1.7, 3.2, and 3.9 and 1.9, 3.6, and 4.7 ℃, during 2011-2040, 2041-2070, and 2071-2100, respectively, and the increase in the amplitude of the Tmin is more than 1.1 times that of the Tmax. The WA of the Tmax and Tmin are projected to be largest in winter and smallest in spring, and the decreasing amplitude of the DTR is projected to be largest in winter and smallest in summer. The spatial distribution of the change of the Tmax, Tmin, and DTR over China shows that the Tmax will have its largest WA in Northeast China, a large WA in Northwest China, the Loess Plateau, and the Sichuan Basin, but a small WA in the northern Qinghai-Tibet Plateau and South China. On the contrary, the Tmin will have its largest WA in Northwest China, a large WA in Northeast China and the Northern Qinghai-Tibet Plateau, and a small WA in the Sichuan Basin and the eastern Yunnan-Guizhou Plateau. The DTR shows a decreased trend for northern China, especially in the northern Qinghai-Tibet Plateau, but an increase in the Sichuan Basin and the eastern Yunnan-Guizhou Plateau.

Abstract:Gross Primary Productivity (GPP) determines the initial substance and energy in the terrestrial ecosystem, which is an important link between the terrestrial carbon cycle and the atmospheric carbon pool. This study simulates the GPP in China from 1982 to 2004 by using the CLM4-CN (Community Land Model version 4 with Carbon-Nitrogen interactions) and evaluates its capability by comparing it with the MTE (Model Tree Ensemble)_GPP derived from upscaling of FLUXNET eddy covariance observations. We use the results to investigate the effects of different land cover datasets on GPP modeling. CLM4-CN is shown to effectively capture the spatial patterns of the GPP in China, which declines from southeast to northwest. However, the model overestimates the magnitude in most areas, particularly those south of 30°N. The annual GPP in China given by CLM4-CN (CLM4_GPP) is 13.7 PgC a^-1 on average; and that given by MTE_GPP is only 6.9 PgC a^-1. Although the CLM4_GPP and MTE_GPP show similar intra-annual cycles (R>0.9) for different dominant PFTs (Plant Functional Types) in China, the magnitude differs for most PFTs. Inter-annual variability in CLM4_GPP is higher than that in MTE_GPP for all PFTs. In addition, both the products show the same trends for tropical evergreen needleleaf trees, boreal deciduous broadleaf trees, and C3 grass; Differences are shown for the other PFTs. Precipitation is determined to be the main climate factor controlling temporal variation of the GPP in China during the experiment period. By modeling GPP using two different land cover datasets, we determine that different land cover datasets can cause obvious changes in the GPP for most regions in China. Thus, accuracy in the land cover dataset is important for the GPP simulation.

Abstract:A scheme for regionalization of temperature zones was established on the basis of daily surface air temperature observations from 512 stations in China during 1961-2010. Days with daily surface air temperature ≥10 ℃ were used as indicators for zoning the temperature distribution. After REOF (Rotated Empirical Orthogonal Function) analysis, areas with similar temperature changes in the time evolution were classified as one zone. The temperature zones were classified by three types of clustering analysis methods. The national area was divided into ten temperature zones by using the K-means method, nine temperature zones by using the Ward method, and 13 temperature zones by using the CAST (Cluster Analysis with Statistical Test) method. The boundaries of the various regions show a good consistency with the Chinese topography. Calculation by using the K-means method is considered to be simple and quick because, the results are revised until the best results are achieved. Moreover, the clustering process of the Ward method is clear; any number of categories may be selected. Finally, the results of the CAST method pass the significance test; therefore, this method is meaningful for zoning.

Abstract:On the basis of daily precipitation observations at 743 stations in China and monthly surface sensible heat flux data from the European Centre for Medium-Range Weather Forecasts reanalysis data (ERA40 and ERA-interim) as well as that of NCEP/NCAR reanalysis data, the physical mechanism and possible linkage between spring surface sensible heat flux anomalies in the mid-high latitudes of the Eurasian Continent and summer precipitation over the middle-lower reaches of the Yangtze River is analyzed in this study. The results show a significant positive correlation between them. Further analysis indicates that strong spring surface sensible heating in the mid-high latitudes of the Eurasian Continent always exists concurrently with the eastward shifted and strengthened East Asia subtropical westerly jet. In such a situation, evidently anomalous ascension and divergence of the water vapor transport result in increased summer precipitation over the middle-lower reaches of the Yangtze River. On the contrary, weak surface sensible heating tends to cause less precipitation in this area. Therefore, the spring surface sensible heat flux anomalies over the Eurasian Continent in the mid-high latitudes can be a potential predictor for the summer precipitation prediction in the middle-lower reaches of the Yangtze River.