In order to study the transport characteristics of air pollution in Linfen City, based on the hourly air quality index (AQI) data in Linfen City from the Ministry of Ecology and Environment from 2016 to 2017, the six-hour reanalysis data and the global data assimilation system (GDAS) data with a horizontal resolution of 1°×1° from the National Centers for Environmental Prediction (NCEP), the influence of topography and weather situation on air pollution during the 24 pollution processes in Linfen City was analyzed by using backward trajectory clustering analysis of HYSPLIT4 (hybrid single-particle lagrangian integrated trajectory) model. The results are as follows: (1) The sea-level circulation situation during the 24 pollution processes mainly included the following six types: front of Mongolian high pressure bottom type, front of low pressure type, rear of North China high pressure type, front of invert trough near the Hetao area type, uniform pressure field and low pressure belt type. (2) The 24 h and 60 h backward trajectory can represent the impact of topography conditions and weather conditions on pollution in Linfen City, respectively. (3) The 24 h backward trajectories show that the air flow can sink and transport pollutants along the leeward slope of the Lüliang Mountain. The pollution in Linfen City was formed from inverted “concave” shape terrain opening to the south and the southwest wind near the ground. The air flow can also return to Linfen City after touching the surrounding mountains. Among them, the transportation along the subsidence of the Lüliang Mountain from the northwest direction was main. (4) The 60 hour backward trajectories show that the air flow transporting pollutants met with the easterly or southerly airflow under the influence of the weather situation, and then turned back to Linfen City. The pollutant particles hygroscopic grew with the increase of humidity caused by southwesterly or easterly wind. The topography and weather situation have an impact on the transport route of air pollution in Linfen City.

The 40 summer maize varieties passing the certification were selected, variety comparison field trials were carried out at Xunxian located in northern Henan, Xuchang located in central Henan, and Fangcheng located in southern Henan. The high-yield and high-efficiency comprehensive evaluation index of summer maize varieties was constructed to carry out a comprehensive evaluation of the adaptability of summer maize varieties in three ecological regions from aspects of high and stable yield and climate resource utilization efficiency. The results show that the full growth period length of summer maize varieties was shortest at Fangcheng, with an average value of 108 days, and it was longest at Xunxian, with an average value of 111 days. The difference of the full growth period length of summer maize varieties ranged from 12 to 16 days in three ecological regions, and the full growth period length was correlated significantly with the flowering and grain period. The average yield of summer maize varieties at Fancheng was highest, while it was lowest at Xuchang, and yield difference between two ecological regions passed the 0.05 significance test. The highest utilization rates of light, temperature, water were at Fangcheng. The light and temperature utilization rate was higher at Xunxian than at Xuchang, but the water use efficiency was lowest at Xunxian. According to the ranking of high-yield and high-efficiency evaluation comprehensive index of summer maize varieties, 11 high-yield and high-efficiency summer maize varieties were selected including Weike 702, Qingyu 9, Xindan 68, Denghai 605, Dafeng 30, Zhengdan 1002, Fengdecunyu 10, Jundan 29, Zhengdan 538, Huaichuan 39 and SK1098.

 Based on NCEP/NCAR reanalysis data and observation data from radar, sounding station and ground-encrypted observations, the reason why the precipitation center of the northward NO.10 typhoon “Ambi” moved from its right front side to left front side and the precipitation intensity increased significantly  were analyzed. The results are as follows: (1) The 500 hPa western Pacific subtropical high ridge line on 24 July 2018 extended abnormally northward, and the southerly air flow on its west side provided favorable circulation conditions for the typhoon moving northward. At the same time, the stability of the upper warm ridge prevented the eastward movement of the west trough, and enabled the “Ambi” to maintain a complete warm core structure when it moved northward to 40°N. (2) At 08:00 BST on July 24, the southwest jet on 200 hPa strengthened, the divergence and the ascending motion both enhanced on the right side of southwest jet entrance area, and the latent heat of condensation released, which further strengthened the low-altitude convergence and the ascending motion on the north side of “Ambi” and promoted the precipitation enhancement. (3) At 08:00 BST on July 24, the northeastern wind speed on 925 hPa in the northwestern part of the “Ambi” reduced to 4 m·s-1, while the easterly jet in the northestern part of the “Ambi” increased to 25 m·s-1, which caused the convergence center moving westward and the precipitation center moving westward. (4) The water vapor transport mainly concentrated below 850 hPa. The net inflow of water vapor transport was mainly from input of zonal wind from the eastern boundary of the precipitation area. Compared with 20:00 BST on July 23, net input of water vapor in the latitudinal direction increased by 3 times at 08:00 BST on 24. (5) On night of  July 23, “Ambi” carring warm and humid airflow moved northward, and temperature and dew point in the northwest side of the typhoon center gradually declined due to radiation cooling and weak cold air infiltration, but temperature and dew point on the southeast side were still high, which caused northwest-southeast temperature and dew point gradient. The corresponding mesoscale rain belt made the precipitation center move to the left front of the moving path.

Based on precipitation observation information and NCEP reanalysis data during 1981-2018, the causes of abnormal precipitation in spring sowing period in northern Hubei Province were analyzed by using synthetic diagnostics and atmospheric energy spectrum methods. The results show that in abnormally less precipitation years, the subtropical high was weaker and its position was southerly, and the polar vortex was weaker too. The perturbation kinetic energy over mid-latitude was weak in meridional direction, while the zonal transfer position was southerly, and the angular momentum transferred obviously to the south, the energy exchange between north and south was weak. Thus the intersection of cold and warm air was not obvious over the north of Hubei, and it was divergent in the lower troposphere, which was not conducive to the frontogenesis. In abnormally more precipitation years, both the subtropical high and polar vortex were stronger, the plateau trough was more actively. The perturbation kinetic energy over mid-latitude was stronger in meridional direction, while the zonal transfer position was northerly，the angular momentum transferred obviously and the energy exchanged frequently between the south and north. Thus the intersection of cold and warm air was obvious over the north of Hubei, it was convergence in the lower troposphere, which was conducive to the frontogenesis.

The fifth generation PSU /NCAR’s non - hydrostatic mesoscalemodel ( MM5 ) is app lied to simulatemeteorological fields of the dustweather affecting Beijing in North China on 21March 2001. The results show the model is capable for simulating and p redicting spatial and temporal variations of dustweather in Northern China. Low - p ressure system and its vertical structure of high - level divergence and low - level convergence resulted in strong updraft causing dust emission, and strong wind was dynamic condition for transmission of sand dust. The trajectorymodel is app lied to simulate the air particle trajectory, which commendably reflects source area and transmission trajectory of sand dust. The p redicted area of dust storms is in good agreementwith those ofmeteorological observation and satellite images. The software is p rogrammed to demonstrate dynamic p rocess of the meteorological fields.

Based on the fifth generation PSU /NCAR’s non - hydrostatic mesoscale model (MM5) and comp rehensive air qualitymodel with extensions (CAMx, a 3 - D Eulerian regional air qualitymodel) a air quality simulation system has been comp leted, which is app lied to simulate sandstorm transmission affecting Beijing in North China in sp ring 2001. The results show the system is capable for simulating and p redicting sandstorm transmission and concentration distribution in North China. Significant correlation was found between simulation value of TSP and L idar observation, which confidence levelwas above 99%. The contribution rate ofMongolia, Inner Mongolia and Hebei to dust concentration in Beijing are 30% - 50% , 30% - 60% and under 29% , respectively.