总结了目前最具代表性的3个全球集合预报系统(global ensemble forecast system,GEFS)——美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)、欧洲中期天气预报中心(European Centre for Medium-Range Weathe...总结了目前最具代表性的3个全球集合预报系统(global ensemble forecast system,GEFS)——美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)和加拿大气象中心(Canadian Meteoro-logical Centre,CMC)建成至今的发展概况。由于计算资源的不断扩展,各中心集合预报系统的模式分辨率、集合成员数也随之增加。同时各中心都在不断地致力于发展和完善初始和模式扰动方法,来更好地估计与初值和模式有关的不确定性,促进预报技巧的提高。其中初始扰动方法从最初的奇异向量法(ECMWF)、增殖向量法(NCEP)和观测扰动法(CMC)更新为现在的集合资料同化—奇异向量法(ECMWF)、重新尺度化集合转换法(NCEP)和集合卡尔曼滤波(CMC)。在估计模式不确定性方面,ECMWF和CMC都修订了各自的随机参数化方案和多参数化方案,NCEP最近也在模式中加入了随机全倾向扰动。为提高全球高影响天气预报的准确率,TIGGE计划(the THORPEX interactive grand global ensemble)的提出增进了国际间对多模式、多中心集合预报的合作研究,北美集合预报系统(North American ensemble forecast system,NAEFS)为建立全球多模式集合预报系统提供了业务框架,这都将有助于未来全球交互式业务预报系统的构建。展开更多
Two years of mid-latitude cirrus cloud macrophysical and optical properties over North China are described from Earth-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) satellite measurements. Global cl...Two years of mid-latitude cirrus cloud macrophysical and optical properties over North China are described from Earth-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) satellite measurements. Global cloud climatological studies based on active remote sensing data sets benefit from more accurate resolution of vertical structure and more reliable detection of optically thin layers.The mean values for cirrus cases over North China are 0.19±0.18 for infrared emittance,0.41±0.68 for visible optical depth, 0.26±0.12 for integrated depolarization ratio,and 0.72±0.22 for integrated color ratio.When studied using reasonable assumptions for the relationship between extinction and ice crystal backscatter coefficients,our results show that most of the cirrus clouds profiled using the 0.532μm channel data stream correspond with an optical depth of less than 1.0.The dependence of cirrus cloud properties on cirrus cloud mid-cloud temperature and geometry thickness are generally similar to the results derived from the ground-based lidar, which are mainly impacted by the adiabatic process on the ice cloud content.However,the differences in macrophysical parameter variability indicate the limits of spaceborne-lidar and dissimilarities in regional climate variability and the nature and source of cloud nuclei in different geographical regions.展开更多
Two important questions are addressed in this paper using the Global Ensemble Forecast System （GEFS） from the National Centers for Environmental Prediction （NCEP）： （1） How many ensemble members are needed to be...Two important questions are addressed in this paper using the Global Ensemble Forecast System （GEFS） from the National Centers for Environmental Prediction （NCEP）： （1） How many ensemble members are needed to better represent forecast uncertainties with limited computational resources？ （2） What is tile relative impact on forecast skill of increasing model resolution and ensemble size？ Two-month experiments at T126L28 resolution were used to test the impact of varying the ensemble size from 5 to 80 members at the 500- hPa geopotential height. Results indicate that increasing the ensemble size leads to significant improvements in the performance for all forecast ranges when measured by probabilistic metrics, but these improvements are not significant beyond 20 members for long forecast ranges when measured by deterministic metrics. An ensemble of 20 to 30 members is the most effective configuration of ensemble sizes by quantifying the tradeoff between ensemble performance and the cost of computational resources. Two representative configurations of the GEFS the T126L28 model with 70 members and the T190L28 model with 20 members, which have equivalent computing costs--were compared. Results confirm that, for the NCEP GEFS, increasing the model resolution is more （less） beneficial than increasing the ensemble size for a short （long） forecast range.展开更多
Meteorological data is useful for varied applications and sectors ranging from weather and climate forecasting, landscape planning to disaster management among others. However, the availability of these data requires ...Meteorological data is useful for varied applications and sectors ranging from weather and climate forecasting, landscape planning to disaster management among others. However, the availability of these data requires a good network of manual meteorological stations and other support systems for its collection, recording, processing, archiving, communication and dissemination. In sub-Saharan Africa, such networks are limited due to low investment and capacity. To bridge this gap, the National Meteorological Services in Kenya and few others from African countries have moved to install a number of Automatic Weather Stations (AWSs) in the past decade including a few additions from private institutions and individuals. Although these AWSs have the potential to improve the existing observation network and the early warning systems in the region, the quality and capacity of the data collected from the stations are not well exploited. This is mainly due to low confidence, by data users, in electronically observed data. In this study, we set out to confirm that electronically observed data is of comparable quality to a human observer recorded data, and can thus be used to bridge data gaps at temporal and spatial scales. To assess this potential, we applied the simple Pearson correlation method and other statistical tests and approaches by conducting inter-comparison analysis of weather observations from the manual synoptic station and data from two Automatic Weather Stations (TAHMO and 3D-PAWS) co-located at KMD Headquarters to establish existing consistencies and variances in several weather parameters. Results show there is comparable consistency in most of the weather parameters between the three stations. Strong associations were noted between the TAHMO and manual station data for minimum (r = 0.65) and maximum temperatures (r = 0.86) and the maximum temperature between TAHMO and 3DPAWS (r = 0.56). Similar associations were indicated for surface pressure (r = 0.99) and RH (r > 0.6) with the weakest correlations occurring in wind direction and speed. The Shapiro test for normality assumption indicated that the distribution of several parameters compared between the 3 stations were normally distributed (p > 0.05). We conclude that these findings can be used as a basis for wider use of data sets from Automatic Weather Stations in Kenya and elsewhere. This can inform various applications in weather and climate related decisions.展开更多
Using the velocity fields of 28 GPS sites in China and its contiguous area and International Terrestrial Reference Frame ITRF96, an initial tectonic block motion model of China was established. The model was quite con...Using the velocity fields of 28 GPS sites in China and its contiguous area and International Terrestrial Reference Frame ITRF96, an initial tectonic block motion model of China was established. The model was quite consistent with those obtained from the geologic data. The model could show the sketch of China crustal horizontal motion.展开更多
Central Asia is one of the most vulnerable regions on the planet earth to global climate change, depending on very fragile natural resources. The Soviet legacy has left the five countries （Kazakhstan, Tajikistan, Kyr...Central Asia is one of the most vulnerable regions on the planet earth to global climate change, depending on very fragile natural resources. The Soviet legacy has left the five countries （Kazakhstan, Tajikistan, Kyrgyzstan, Turkmenistan, and Uzbekistan） with a highly integrated system but they are facing great challenges with tensions that hinder regional coordination of food and water resources. With increasing climate variability and warming trend in the region, food and water security issues become even more crucial now and, if not addressed properly, could affect the regional stability. The long-term drivers of these two most critical elements, food and water, are climate change; the immediate and probably more drastic factors affecting the food and water security are land uses driven by institutional change and economic incentives. As a feedback, changes in land use and land cover have directly implications on water uses, food production, and lifestyles of the rural community in the region. Regional and international efforts have been made to holistically understand the cause, extent, rate and societal implications of land use changes in the region. Much of these have been understood, or under investiga- tion by various projects, but solutions or research effort to develop solutions, to these urgent regional issues are lacking. This article, serves as an introduction to the special issue, provides a brief overview of the challenges facing the Central Asian countries and various interna- tional efforts in place that resulted in the publications of this special issue.展开更多
文摘总结了目前最具代表性的3个全球集合预报系统(global ensemble forecast system,GEFS)——美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)和加拿大气象中心(Canadian Meteoro-logical Centre,CMC)建成至今的发展概况。由于计算资源的不断扩展,各中心集合预报系统的模式分辨率、集合成员数也随之增加。同时各中心都在不断地致力于发展和完善初始和模式扰动方法,来更好地估计与初值和模式有关的不确定性,促进预报技巧的提高。其中初始扰动方法从最初的奇异向量法(ECMWF)、增殖向量法(NCEP)和观测扰动法(CMC)更新为现在的集合资料同化—奇异向量法(ECMWF)、重新尺度化集合转换法(NCEP)和集合卡尔曼滤波(CMC)。在估计模式不确定性方面,ECMWF和CMC都修订了各自的随机参数化方案和多参数化方案,NCEP最近也在模式中加入了随机全倾向扰动。为提高全球高影响天气预报的准确率,TIGGE计划(the THORPEX interactive grand global ensemble)的提出增进了国际间对多模式、多中心集合预报的合作研究,北美集合预报系统(North American ensemble forecast system,NAEFS)为建立全球多模式集合预报系统提供了业务框架,这都将有助于未来全球交互式业务预报系统的构建。
基金supported by the National Natural Science Foundation of China(Grant No.40875084)National Natural Science Foundation for Youth Science Foundation of China(Grant No.40705012).
文摘Two years of mid-latitude cirrus cloud macrophysical and optical properties over North China are described from Earth-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) satellite measurements. Global cloud climatological studies based on active remote sensing data sets benefit from more accurate resolution of vertical structure and more reliable detection of optically thin layers.The mean values for cirrus cases over North China are 0.19±0.18 for infrared emittance,0.41±0.68 for visible optical depth, 0.26±0.12 for integrated depolarization ratio,and 0.72±0.22 for integrated color ratio.When studied using reasonable assumptions for the relationship between extinction and ice crystal backscatter coefficients,our results show that most of the cirrus clouds profiled using the 0.532μm channel data stream correspond with an optical depth of less than 1.0.The dependence of cirrus cloud properties on cirrus cloud mid-cloud temperature and geometry thickness are generally similar to the results derived from the ground-based lidar, which are mainly impacted by the adiabatic process on the ice cloud content.However,the differences in macrophysical parameter variability indicate the limits of spaceborne-lidar and dissimilarities in regional climate variability and the nature and source of cloud nuclei in different geographical regions.
文摘Two important questions are addressed in this paper using the Global Ensemble Forecast System （GEFS） from the National Centers for Environmental Prediction （NCEP）： （1） How many ensemble members are needed to better represent forecast uncertainties with limited computational resources？ （2） What is tile relative impact on forecast skill of increasing model resolution and ensemble size？ Two-month experiments at T126L28 resolution were used to test the impact of varying the ensemble size from 5 to 80 members at the 500- hPa geopotential height. Results indicate that increasing the ensemble size leads to significant improvements in the performance for all forecast ranges when measured by probabilistic metrics, but these improvements are not significant beyond 20 members for long forecast ranges when measured by deterministic metrics. An ensemble of 20 to 30 members is the most effective configuration of ensemble sizes by quantifying the tradeoff between ensemble performance and the cost of computational resources. Two representative configurations of the GEFS the T126L28 model with 70 members and the T190L28 model with 20 members, which have equivalent computing costs--were compared. Results confirm that, for the NCEP GEFS, increasing the model resolution is more （less） beneficial than increasing the ensemble size for a short （long） forecast range.
文摘Meteorological data is useful for varied applications and sectors ranging from weather and climate forecasting, landscape planning to disaster management among others. However, the availability of these data requires a good network of manual meteorological stations and other support systems for its collection, recording, processing, archiving, communication and dissemination. In sub-Saharan Africa, such networks are limited due to low investment and capacity. To bridge this gap, the National Meteorological Services in Kenya and few others from African countries have moved to install a number of Automatic Weather Stations (AWSs) in the past decade including a few additions from private institutions and individuals. Although these AWSs have the potential to improve the existing observation network and the early warning systems in the region, the quality and capacity of the data collected from the stations are not well exploited. This is mainly due to low confidence, by data users, in electronically observed data. In this study, we set out to confirm that electronically observed data is of comparable quality to a human observer recorded data, and can thus be used to bridge data gaps at temporal and spatial scales. To assess this potential, we applied the simple Pearson correlation method and other statistical tests and approaches by conducting inter-comparison analysis of weather observations from the manual synoptic station and data from two Automatic Weather Stations (TAHMO and 3D-PAWS) co-located at KMD Headquarters to establish existing consistencies and variances in several weather parameters. Results show there is comparable consistency in most of the weather parameters between the three stations. Strong associations were noted between the TAHMO and manual station data for minimum (r = 0.65) and maximum temperatures (r = 0.86) and the maximum temperature between TAHMO and 3DPAWS (r = 0.56). Similar associations were indicated for surface pressure (r = 0.99) and RH (r > 0.6) with the weakest correlations occurring in wind direction and speed. The Shapiro test for normality assumption indicated that the distribution of several parameters compared between the 3 stations were normally distributed (p > 0.05). We conclude that these findings can be used as a basis for wider use of data sets from Automatic Weather Stations in Kenya and elsewhere. This can inform various applications in weather and climate related decisions.
文摘Using the velocity fields of 28 GPS sites in China and its contiguous area and International Terrestrial Reference Frame ITRF96, an initial tectonic block motion model of China was established. The model was quite consistent with those obtained from the geologic data. The model could show the sketch of China crustal horizontal motion.
文摘Central Asia is one of the most vulnerable regions on the planet earth to global climate change, depending on very fragile natural resources. The Soviet legacy has left the five countries （Kazakhstan, Tajikistan, Kyrgyzstan, Turkmenistan, and Uzbekistan） with a highly integrated system but they are facing great challenges with tensions that hinder regional coordination of food and water resources. With increasing climate variability and warming trend in the region, food and water security issues become even more crucial now and, if not addressed properly, could affect the regional stability. The long-term drivers of these two most critical elements, food and water, are climate change; the immediate and probably more drastic factors affecting the food and water security are land uses driven by institutional change and economic incentives. As a feedback, changes in land use and land cover have directly implications on water uses, food production, and lifestyles of the rural community in the region. Regional and international efforts have been made to holistically understand the cause, extent, rate and societal implications of land use changes in the region. Much of these have been understood, or under investiga- tion by various projects, but solutions or research effort to develop solutions, to these urgent regional issues are lacking. This article, serves as an introduction to the special issue, provides a brief overview of the challenges facing the Central Asian countries and various interna- tional efforts in place that resulted in the publications of this special issue.
