灰色系统理论在降水量、气温超长期预测中的应用

本文应用灰色系统理论,根据乌鲁木齐地区46年(1941—86年)降水量、气温资料,建立了一套灰色动态模型,并对未来降水量(6年)、气温(6年)趋势进行了研究,还用1981—86年的资料进行验证,得到了较为理想的结果,可为小麦、水稻及其他粮食作物、棉花、瓜类产量预测及制定农业规划提供科学依据。

INSTABILITY OF THE TELECONNECTION OF SUMMER RAINFALLS BETWEEN NORTH CHINA AND INDIA

Summer rainfall variations in North China closely relate to that in India. It seems that an alternation of signs of“＋, -, ＋” exists in the geographical pattern of the correlation in summer rainfall from North China to India through the Tibetan Plateau. However, it appears that the teleconnection of summer rainfall variations between North China and India is unstable. Over 1945 - 1974, the correlation coefficient （hereafter as CC） is as large as 0.7. In contrast, the CC is about -0.3 over 1827-1856. Further studies, based on observations starting from 1813, showed that the correlation is strong when summer rainfalls in both North China and India are large, and vice versa. In order to find what induce the change of the teleconnection, variations of summer rainfall in both North China and India, mean sea surface temperature （SST） in the eastern equatorial Pacific and the frequency of ENSO events were examined in relation to the change of the teleconnection. The result showed that the teleconnection appears weak when the mean SST is high and the frequency ofLa Nifia events is low; the teleconnection is strong when the mean SST is low and the frequency ofLa Nina events is high. At last, it is notable that La Nifia happens in only 3 years during the recent 30 years from 1976 to 2005 and the teleconnection becomes weak too.

AN ANALYSIS OF THE ASYMMETRICAL STRUCTURE OF TYPHOON AERE'S PRECIPITATION

The structural characteristics of 2004 typhoon Aere's precipitation are analyzed using the high-resolution data from the Tropical Rainfall Measuring Mission(TRMM) of the National Aeronautics Space Administration(NASA).It is found that the typhoon's characteristics vary at different stages of its development.To analyze the asymmetric causation of precipitation distribution,data from the National Center for Environmental Prediction(NCEP) reanalysis are used to calculate the vertical integral of the water vapor flux vector.The results show that because of this process,along with the unique phenomenon of twin-typhoon circulation,the easterly air current of the typhoon's northern side and the southwesterly air current of its southern side play a joint role in transporting water vapor.Furthermore,its transport effects vary greatly at the different stages of development,showing the peculiarity of the water source for this typhoon process.The distributions of the typhoon convection area—characterized by heavy precipitation and a maximum-value area of the water vapor flux,as well as a strong ascending-motion area—differ at different stages of the typhoon's development.The non-uniform distribution of water vapor flux and the vertical motion bring about asymmetrical distribution of the typhoon precipitation.

IMPACT OF URBANIZATION IN DIFFERENT REGIONS OF EASTERN CHINA ON PRECIPITATION AND ITS UNCERTAINTY

Climate effect caused by urbanization has been an indispensable anthropogenic factor in the research on regional climate change.Based on daily precipitation data,possible effects of precipitation on the development of three city groups in eastern China are discussed.With three classification methods(TP,PD and MODIS land cover),urban and rural stations are identified.The main findings are as follows.Climate effects caused by urbanization are different from place to place.In 1960 to 2009,the urbanization brought more precipitation to the Yangtze River Delta and Pearl River Delta city groups but had no obvious effect on the precipitation of the Beijing-Tianjin-Tangshan city group.The difference of precipitation is slight between urban and suburban areas during slow period of the urbanization from 1960 to 1979.It is more evident in the rapid period(1980 to 2009) that urbanization has positive effects on precipitation in every city group.The difference of precipitation between urban and rural stations is sensitive to the ways of distinguishing rural from urban area,which may cause uncertainties in 1960 to 1979,while it is very different in 1980 to 2009 in which urbanization favors more precipitation in all city groups and their differences in precipitation are not sensitive to the division methods.

Change in Extreme Climate Events over China Based on CMIP5

The changes in a selection of extreme climate indices(maximum of daily maximum temperature(TXx),minimum of daily minimum temperature(TNn),annual total precipitation when the daily precipitation exceeds the 95th percentile of wet-day precipitation(very wet days,R95p),and the maximum number of consecutive days with less than 1 mm of precipitation(consecutive dry days,CDD))were projected using multi-model results from phase 5 of the Coupled Model Intercomparison Project in the early,middle,and latter parts of the 21st century under different Representative Concentration Pathway(RCP)emissions scenarios.The results suggest that TXx and TNn will increase in the future and,moreover,the increases of TNn under all RCPs are larger than those of TXx.R95p is projected to increase and CDD to decrease significantly.The changes in TXx,TNn,R95p,and CDD in eight sub-regions of China are different in the three periods of the 21st century,and the ranges of change for the four indices under the higher emissions scenario are projected to be larger than those under the lower emissions scenario.The multi-model simulations show remarkable consistency in their projection of the extreme temperature indices,but poor consistency with respect to the extreme precipitation indices.More substantial inconsistency is found in those regions where high and low temperatures are likely to happen for TXx and TNn,respectively.For extreme precipitation events(R95p),greater uncertainty appears in most of the southern regions,while for drought events(CDD)it appears in the basins of Xinjiang.The uncertainty in the future changes of the extreme climate indices increases with the increasing severity of the emissions scenario.

Biophysical Regulation of Carbon Flux in Different Rainfall Regime in a Northern Tibetan Alpine Meadow

Inter-annual variability in total precipitation can lead to significant changes in carbon flux.In this study,we used the eddy covariance（EC） technique to measure the net CO_2 ecosystem exchange（NEE） of an alpine meadow in the northern Tibetan Plateau.In 2005 the meadow had precipitation of 489.9 mm and in 2006 precipitation of 241.1 mm,which,respectively,represent normal and dry years as compared to the mean annual precipitation of 476 mm.The EC measured NEE was 87.70 g C m^（-2） yr^（-1） in 2006 and-2.35 g C m^（-2） yr^（-1） in 2005.Therefore,the grassland was carbon neutral to the atmosphere in the normal year,while it was a carbon source in the dry year,indicating this ecosystem will become a CO_2 source if climate warming results in more drought conditions.The drought conditions in the dry year limited gross ecosystem CO_2 exchange（GEE）,leaf area index（LAI） and the duration of ecosystem carbon uptake.During the peak of growing season the maximum daily rate of NEE and Pmax and a were approximately 30%-50% of those of the normal year.GEE and NEE were strongly related to photosynthetically active radiation（PAR） on half-hourly scale,but this relationship was confounded by air temperature（Ta）,soil water content（SWC） and vapor pressure deficit（VPD）.The absolute values of NEE declined with higher Ta,higher VPD and lower SWC conditions.Beyond the appropriate range of PAR,high solar radiation exacerbated soil water conditions and thus reduced daytime NEE.Optimal T_a and VPD for maximum daytime NEE were 12.7℃ and 0.42 KPa respectively,and the absolute values of NEE increased with SWC.Variation in LAI explained around 77% of the change in GEE and NEE.Variations in R_e were mainly controlled by soil temperature（T_s）,whereas soil water content regulated the responses of R_e to T_s.

Parametric sensitivity analysis of precipitation and temperature based on multi-uncertainty quantification methods in the Weather Research and Forecasting model

Sensitivity analysis(SA) has been widely used to screen out a small number of sensitive parameters for model outputs from all adjustable parameters in weather and climate models, helping to improve model predictions by tuning the parameters. However, most parametric SA studies have focused on a single SA method and a single model output evaluation function, which makes the screened sensitive parameters less comprehensive. In addition, qualitative SA methods are often used because simulations using complex weather and climate models are time-consuming. Unlike previous SA studies, this research has systematically evaluated the sensitivity of parameters that affect precipitation and temperature simulations in the Weather Research and Forecasting(WRF) model using both qualitative and quantitative global SA methods. In the SA studies, multiple model output evaluation functions were used to conduct various SA experiments for precipitation and temperature. The results showed that five parameters(P3, P5, P7, P10, and P16) had the greatest effect on precipitation simulation results and that two parameters(P7 and P10) had the greatest effect for temperature. Using quantitative SA, the two-way interactive effect between P7 and P10 was also found to be important, especially for precipitation. The microphysics scheme had more sensitive parameters for precipitation, and P10(the multiplier for saturated soil water content) was the most sensitive parameter for both precipitation and temperature. From the ensemble simulations, preliminary results indicated that the precipitation and temperature simulation accuracies could be improved by tuning the respective sensitive parameter values, especially for simulations of moderate and heavy rain.