干冷空气入侵台风"海棠"残余低压引发的华北地区大暴雨分析

利用地面逐小时观测资料、NCEP/NCAR (1°×1°)再分析资料、FY-2F卫星加密观测(6 min分辨率)的云顶亮温(TBB)和常规观测资料,对1710号台风"海棠"残余低压北上与冷空气结合导致华北东部大暴雨天气过程进行分析。结果表明:(1)该华北东部大暴雨过程分为两个主要时段,2017年8月1日23时—2日20时(北京时)华北东南部暴雨,由台风残余低压产生,8月2日20时—3日11时华北东北部暴雨,是由减弱变性的台风环流与西风槽东移带来的干冷空气结合进而导致新生气旋和低涡产生引起。(2) 8月2日20时,台风与冷空气逐渐结合,干冷空气从对流层中高层进入变性台风北部,造成位涡下传,进而导致对流层低层形成低涡、地面形成新生气旋,同时激发出中尺度对流系统,系统稳定发展并缓慢向东北方向移动,导致持续近5 h的短时强降雨。(3)暴雨水汽来源主要有两部分,一是台风本身携带来的由南风输送的水汽,二是来自黄渤海由东风输送的水汽,二者结合后从对流层低层将水汽带至华北东北部,且在燕山前形成了水汽强辐合,为该暴雨过程大提供充足的水汽条件。     

1991年北半球夏季风及江淮流域降雨量的低频振荡

根据１９９１年５－８月江淮特大暴雨资料，使用功率谱和带通滤波结合的方法，研究了１９９１年夏季风和江淮梅雨的准周期振荡，探索季风对异常梅雨的影响。分析指出，１９９１年北半球夏季风活动，江淮流域湿度场和降雨量变化均存在显著的准２４天周期振荡，夏季风的周期振荡，主要表现在西南季风（东南季风不明显），它的位相比降雨量提前２－４左右，其振幅大小较好地反映了降雨量的大小。     

参考大气在中期天气预报和气候模拟中的应用

本文概述了根据应用参考大气概念提出的参考大气谱模式计算格式（或称静力扣除法）在国内外一些气象机构的中期天气预报、后处理和四维同化、以及气候模拟中的应用。计算表明，这种参考大气谱模式计算格式，能有效的减少截谱误差，明显地改进中期天气预报和气候模拟。     

北京城郊近地层湍流实验观测

本文利用两台FA-11超声风速温度仪于1992年3月到４月间在北京325 m气象观测塔47 m和120 m两个高度观测到的风速三个正交分量以及声虚温的湍流脉动资料，计算和分析了北京城郊粗糙下垫面近地层湍流特征量及其日变化，无量纲垂直速度和声虚温的方差随稳定度的变化，风速分量和温度的归一化湍流能谱以及动量和热通量的互谱及其随稳定度的变化。并且与平坦均一下垫面近地层湍流观测的结果进行了对比。     

测雨效率方程及其应用

本文提出了雷达测雨效率的理论方程,用实际雷达观测资料对它进行了验证,提出了它的一些应用。     

Impacts of strong El Niño on summertime near-surface ozone over China

The influences of strong El Niño events (1997/98 and 2015/16) on summertime near-surface ozone (O₃) concentrations over China are investigated using the GEOS-Chem model. The results show that near-surface O₃ concentrations increased by a maximum of 6 ppb (parts per billion) during the summer of the developing phase of the 1997/98 El Niño in northeastern China, mainly due to the increased chemical production related to the hot and dry conditions. Besides, the O₃ concentration increased by 3 ppb during the developing summer of both the 1997/98 and 2015/16 El Niño in southern China. It was linked to the weakened prevailing monsoon winds, which led to the accumulation of O₃ in southern China. In contrast, in the summer of the decaying phase of the two El Niño events, O₃ concentrations decreased over many regions of China when the El Niño reversed to the cooling phase. This highlights that El Niño plays an important role in modulating near-surface O₃ concentrations over China.摘要利用全球大气化学三维模式 (GEOS-Chem) 模拟研究两次强厄尔尼诺事件 (1997/98和2015/16) 对中国夏季近地面臭氧 (O₃₎ 浓度的影响. 结果表明1997/98年厄尔尼诺事件发展期夏季中国东北区域O₃浓度升高, 最大值超过6ppb, 这主要归因于高温晴朗低湿等气象因素导致O₃化学生成升高. 此外, 两次厄尔尼诺事件发展期夏季O₃浓度在中国南部均增加了3ppb, 这与盛行季风减弱导致中国南方O₃局地积累有关. 相反, 在两次强厄尔尼诺衰减期夏季, 中国大部分地区O₃浓度下降伴随着海温模态转变为拉尼娜事件. 这表明厄尔尼诺在调节中国近地面O₃浓度中发挥着重要作用.     

A Machine Learning-based Cloud Detection Algorithm for the Himawari-8 Spectral Image

Cloud Masking is one of the most essential products for satellite remote sensing and downstream applications. This study develops machine learning-based (ML-based) cloud detection algorithms using spectral observations for the Advanced Himawari Imager (AHI) onboard the Himawari-8 geostationary satellite. Collocated active observations from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) are used to provide reference labels for model development and validation. We introduce both daytime and nighttime algorithms that differ according to whether solar band observations are included, and the artificial neural network (ANN) and random forest (RF) techniques are adopted for comparison. To eliminate the influences of surface conditions on cloud detection, we introduce three models with different treatments of the surface. Instead of developing independent ML-based algorithms, we add surface variables in a binary way that enhances the ML-based algorithm accuracy by ~5%. Validated against CALIOP observations, we find that our daytime RF-based algorithm outperforms the AHI operational algorithm by improving the accuracy of cloudy pixel detection by ~5%, while at the same time, reducing misjudgment by ~3%. The nighttime model with only infrared observations is also slightly better than the AHI operational product but may tend to overestimate cloudy pixels. Overall, our ML-based algorithms can serve as a reliable method to provide cloud mask results for both daytime and nighttime AHI observations. We furthermore suggest treating the surface with a set of independent variables for future ML-based algorithm development.     

Climate Warming Mitigation from Nationally Determined Contributions

Individual countries are requested to submit nationally determined contributions(NDCs) to alleviate global warming in the Paris Agreement. However, the global climate effects and regional contributions are not explicitly considered in the countries’ decision-making process. In this study, we evaluate the global temperature slowdown of the NDC scenario(?T =0.6°C) and attribute the global temperature slowdown to certain regions of the world with a compact earth system model.Considering reductions ...     

Fengyun-4 Geostationary Satellite-Based Solar Energy Nowcasting System and Its Application in North China

Surface solar irradiance (SSI) nowcasting (0–3 h) is an effective way to overcome the intermittency of solar energy and to ensure the safe operation of grid-connected solar power plants. In this study, an SSI estimate and nowcasting system was established using the near-infrared channel of Fengyun-4A (FY-4A) geostationary satellite. The system is composed of two key components: The first is a hybrid SSI estimation method combining a physical clear-sky model and an empirical cloudy-sky model. The second component is the SSI nowcasting model, the core of which is the derivation of the cloud motion vector (CMV) using the block-matching method. The goal of simultaneous estimation and nowcasting of global horizontal irradiance (GHI) and direct normal irradiance (DNI) is fulfilled. The system was evaluated under different sky conditions using SSI measurements at Xianghe, a radiation station in the North China Plain. The results show that the accuracy of GHI estimation is higher than that of DNI estimation, with a normalized root-mean-square error (nRMSE) of 22.4% relative to 45.4%. The nRMSE of forecasting GHI and DNI at 30–180 min ahead varied within 25.1%–30.8% and 48.1%–53.4%, respectively. The discrepancy of SSI estimation depends on cloud occurrence frequency and shows a seasonal pattern, being lower in spring–summer and higher in autumn–winter. The FY-4A has great potential in supporting SSI nowcasting, which promotes the development of photovoltaic energy and the reduction of carbon emissions in China. The system can be improved further if calibration of the empirical method is improved.