中—β尺度强对流风暴和暴雨数值模拟中的一些问题

本文利用数值模拟方法探讨各环境背景因子对强对流及暴雨系统发生发展所起的作用，分析了暴雨和强对流风暴的形成机制。结果表明：温度场和湿度场的垂直分布，决定着对流是否可以形成；其水平非均匀性只是改变风暴发展强度、生命期以及分裂特性。风场的动力影响对强风暴的移动、分裂及强度特征也十分重要。最后，对第三运动方程做了量纲分析，发现热浮力是对流风暴发展的决定性因素；而热浮力冲量能更细致地反映对流风暴的发展演变特征。     

乾安地区盐碱地显热通量的测量

文中给出了用大孔径闪烁仪在 2 0 0 0年生长季观测到的盐碱地区显热通量的主要结果 ,并初步计算了当地的水热平衡状况。结果表明 :乾安盐碱地区显热通量占净辐射量的百分比在干旱、非生长季达到 6 5 % ,在多雨、植被生长季仅为 11% ;显热通量因降水而明显降低 ,幅度与降水强度有关 ,反映了当地的气候和土壤特征。文中还把LAS的测量结果与传统的梯度法作了比较 ,结果基本一致。     

Assessing vegetation dynamics and their relationships with climatic variability in Heilongjiang province, northeast China

In this study, the vegetation dynamics in Heilongjiang province and their relationships with climate variability were assessed using normalized difference vegetation index (NDVI) and meteorological datasets from 1981 to 2003. The conclusions from our results are as follows: (1) After 1981, vegetation cover, as indicated by the NDVI, exhibited an insignificant increasing tendency. However, the inter-annual variations of the NDVI showed apparent spatial differentiations. (2) The inter-annual changes of the NDVI were different from season to season. The spring and autumn NDVI values increased, while the summer and winter NDVI decreased. (3) The annual NDVI was significantly correlated with precipitation. Thus, as compared to temperature, precipitation was the dominant climatic factor affecting the vegetation dynamics in Heilongjiang province. (4) The trend in the NDVI showed a marked homogeneity corresponding to regional and seasonal variations in climate. Additionally, land use changes also play an important role in influencing the NDVI trends over some regions. All of these findings will enrich our knowledge of the natural forces that impact the stability of boreal ecosystems and provide a scientific basis for the environmental management in Heilongjiang province in response to climate change and human activities.     

Evaluation of global climate model on performances of precipitation simulation and prediction in the Huaihe River basin

Using climate models with high performance to predict the future climate changes can increase the reliability of results. In this paper, six kinds of global climate models that selected from the Coupled Model Intercomparison Project Phase 5 (CMIP5) under Representative Concentration Path (RCP) 4.5 scenarios were compared to the measured data during baseline period (1960–2000) and evaluate the simulation performance on precipitation. Since the results of single climate models are often biased and highly uncertain, we examine the back propagation (BP) neural network and arithmetic mean method in assembling the precipitation of multi models. The delta method was used to calibrate the result of single model and multimodel ensembles by arithmetic mean method (MME-AM) during the validation period (2001–2010) and the predicting period (2011–2100). We then use the single models and multimodel ensembles to predict the future precipitation process and spatial distribution. The result shows that BNU-ESM model has the highest simulation effect among all the single models. The multimodel assembled by BP neural network (MME-BP) has a good simulation performance on the annual average precipitation process and the deterministic coefficient during the validation period is 0.814. The simulation capability on spatial distribution of precipitation is: calibrated MME-AM > MME-BP > calibrated BNU-ESM. The future precipitation predicted by all models tends to increase as the time period increases. The order of average increase amplitude of each season is: winter > spring > summer > autumn. These findings can provide useful information for decision makers to make climate-related disaster mitigation plans.     

Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore. Part II: Typhoon Intensity and Track

The impact of cloud microphysical processes on the simulated intensity and track of Typhoon Rananim is discussed and analyzed in the second part of this study. The results indicate that when the cooling effect due to evaporation of rain water is excluded, the simulated 36-h maximum surface wind speed of Typhoon Rananim is about 7 m s⁻¹ greater than that from all other experiments; however, the typhoon landfall location has the biggest bias of about 150 km against the control experiment. The simulated strong outer rainbands and the vertical shear of the environmental flow are unfavorable for the deepening and maintenance of the typhoon and result in its intensity loss near the landfall. It is the cloud microphysical processes that strengthen and create the outer spiral rainbands, which then increase the local convergence away from the typhoon center and prevent more moisture and energy transport to the inner core of the typhoon. The developed outer rainbands are supposed to bring dry and cold air mass from the middle troposphere to the planetary boundary layer (PBL). The other branch of the cold airflow comes from the evaporation of rain water itself in the PBL while the droplets are falling. Thus, the cut-off of the warm and moist air to the inner core and the invasion of cold and dry air to the eyewall region are expected to bring about the intensity reduction of the modeled typhoon. Therefore, the deepening and maintenance of Typhoon Rananim during its landing are better simulated through the reduction of these two kinds of model errors.     

Formation of the anomalous summer precipitation in east China in 2010 and 1998: A comparison of the impacts of two kinds of El Niño

In the summers of 1998 and 2010, severe floods occurred in the middle and lower reaches of the Yangtze River. Although an El Niño event took place preceding each of the summer floods, significant differences between the two summer floods and the two El Niño events were identified. The 1997/98 El Niño is a conventional one with strongest warming in the central-eastern Pacific, whereas the 2009/10 event is an El Niño Modoki with strongest warming in the central Pacific. In this study, summer rainfall anomalies (SRA) in the two years were first compared based on the rainfall data at 160 stations in mainland China, and a significant difference in SRA was found. To understand the underlying mechanism for the difference, the atmospheric circulation systems, particularly the western North Pacific anticyclone (WNPAC), the western Pacific subtropical high (WPSH), and the low-level air flows, were compared in the two years by using the NCEP/NCAR reanalysis data. The results display that the WNPAC was stronger in 2010 than in 1998, along with a northwestward shift, causing weakened southwesterly from the Bay of Bengal to the South China Sea but intensified southerly in eastern China. This resulted in less water vapor transport from the tropical Indian Ocean and the South China Sea but more from the subtropical western Pacific to East Asia. Subsequently, the rainband in 2010 shifted northward. The difference in the WNPAC was caused by the anomalous ascending motion associated with the warming location in the two El Niño events. Furthermore, the role of tropical sea surface temperature (SST) in modulating these differences was investigated by conducting sensitivity experiments using GFDL AM2.1 (Geophysical Fluid Dynamics Laboratory Atmospheric Model). Two experiments were performed, one with the observed monthly SST and the other with June SST persisting through the whole summer. The results suggest that the model well reproduced the primary differences in the atmospheric circulation systems in the two years. It is found that the difference in El Niño events has shaped the rainfall patterns in the two years of 1998 and 2010. At last, the case of 2010 was compared with the composite of historical El Niño Modoki events, and the results indicate that the impact of El Niño Modoki varies from case to case and is more complicated than previously revealed.     

风廓线雷达资料在暴雨天气过程特征分析中的应用

为了研究风廓线雷达在暴雨天气过程预报中的作用,对2008年6月1日至6月2日云南大理发生的一次暴雨过程进行研究。结果表明,降水前三维风的脉动变化较大,水平风在垂直方向上存在风速切变,最大探测高度明显升高;降水期间可以对降水性质进行判断;降水期间功率谱密度出现双峰谱,能测出垂直气流速度及下降粒子速度,通过这样的分析,便于开展更深层次的降水物理过程研究。     

WRF模式三维变分中背景误差协方差估计

利用WRF模式2008年5-10月逐日预报结果,通过NMC方法进行背景误差协方差(B)估计.给出其结构特征,进行单点数值试验,并利用不同B进行1个月的数值模拟试验,检验模拟降水效果.结果表明:通过单点数值试验验证估算的B结构合理.不同的B,资料同化过程差别较大,应用重新统计的B,同化效率更高,目标函数收敛更稳定.模式模...     

Composition and major sources of organic compounds in urban aerosols

Total suspended particles (TSP), collected during June 2002 to July 2003 in Guangzhou, a typical economically developed city in South China, were analyzed for the organic compound compositions using gas chromatography–mass spectrometry (GC/MS). Over 140 organic compounds were detected in the aerosols and grouped into different classes including n-alkanes, hopanoids, polycyclic aromatic hydrocarbons, alkanols, fatty acids, dicarboxylic acids excluding oxalic acid, polyols/polyacids, lignin products, phytosterols, phthalates and water-soluble sugars. The total amounts of the identified organic compounds including unresolved complex mixture (UCM) ranged from 3112 ng/m³ in spring to 5116 ng/m³ in winter, comprising on seasonal average 2.8% of TSP. Primary organic compounds peaked in winter although there are no heating systems burning fuels in Guangzhou. The highest saccharide levels occurred in fall due to agricultural activities. This study demonstrated that utilization of fossil fuels, biomass burning, soil resuspension and plastic/refuse burning are the major contributors to the identified organic compounds in the urban atmosphere of South China.     

The effects of past climate change on the northern limits of maize planting in Northeast China

Northeast China (NEC) is one of the major agricultural production areas in China and also an obvious region of climate warming. We were motivated to investigate the impacts of climate warming on the northern limits of maize planting. Additionally, we wanted to assess how spatial shifts in the cropping system impact the maize yields in NEC. To understand these impacts, we used the daily average air temperature data in 72 weather stations and regional experiment yield data from Jilin Province. Averaged across NEC, the annual air temperature increased by 0.38 °C per decade. The annual accumulated temperature above 10 °C (AAT10) followed a similar trend, increased 66 °C d per decade from 1961 to 2007, which caused a northward expansion of the northern limits of maize. The warming enabled early-maturing maize hybrids to be sown in the northern areas of Heilongjiang Province where it was not suitable for growing maize before the warming. In the southern areas of Heilongjiang Province and the eastern areas of Jilin Province, the early-maturing maize hybrids could be replaced by the middle-maturing hybrids with a longer growing season. The maize in the northern areas of Liaoning Province was expected to change from middle-maturing to late-maturing hybrids. Changing the hybrids led to increase the maize yield. When the early-maturing hybrids were replaced by middle-maturing hybrids in Jilin Province, the maize yields would increase by 9.8 %. Similarly, maize yields would increase by 7.1 % when the middle-maturing hybrids were replaced by late-maturing hybrids.