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Li W.,Yunnan University | Li C.,Meteorological Observatory of Yunnan Province | Yang L.,Yunnan University | Li M.,Guangxi University | Liu X.,Yunnan University
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering

In order to evaluate the farmland environmental quality for the edible agricultural product accurately and improve the edible agricultural product security. Agricultural environment of Jianshui county in Yunnan province was kept monitoring for consecutive years, six web-spatial databases were developed by WebGIS and database technology, including agricultural basic database, agrometeorology database, soil property database, atmospheric pollutant database, soil pollutant database, and irrigation water pollutant database. According to China national standard, farmland environmental quality evaluation standards for edible agricultural products, an evaluation model was developed to evaluate the environmental quality of atmosphere, soil, and irrigation water for edible agricultural product farmland. With the six databases and the evaluation model, an information service system based on WebGIS was developed by the tools SupMapGIS and Visual Studio 2005. The system can be used for the telematic of agricultural environment, spatial analysis of pollutant information, the evaluation of single pollutant in atmosphere, soil and irrigation water, and comprehensive evaluation of farmland environmental quality. This study can provide references for development of Decision Support System of non-pollution agricultural product planting and agricultural regionalization and decision-making in non-pollution agricultural production. Source

Li H.,Yunnan University | Wang M.,Yunnan Institute of Meteorology | Xue J.,Chinese Academy of Meteorological Sciences | Qi M.,Meteorological Observatory of Yunnan Province
Acta Meteorologica Sinica

Statistical tests and error analysis of cloud drift winds (CDWs) from the FY-2C satellite were made by using radiosonde observations. According to the error characteristics of the CDW, a bias correction using the thermal wind theory was applied in the data quality control. The CDW data were then assimilated into the GRAPES-meso model via the GRAPES-3DVar. A torrential rain event that occurred in northwestern China during 1-2 July 2005 was simulated. The results indicate that the CDW data were mainly distributed above 500 hPa and the largest amount of data were at 250 hPa. The CDW data below 500 hPa had errors in both the wind direction and wind speed, and the distribution of the errors was irregular, so these data were discarded. The CDW data above 500 hPa had smaller errors, which presented a Gaussian distribution, so these data were adopted. With the assimilation of the CDW data, the southwest airfl{ligature}ow near the torrential rain area became stronger in the initial wind fl{ligature}eld, which intensifl{ligature}ed the moisture transport and water vapor fl{ligature}ux convergence, and -nally improved the accuracy of the 24-h forecast of the torrential rain in both rain intensity and rain areal coverage. Source

Xie Y.,Yunnan University | Wu J.,Yunnan University | Liu X.,Meteorological Observatory of Yunnan Province | Zhang T.,Yunnan Weather Modification Center | And 3 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics

The characteristics of cloud-to-ground (CG) lightning for nine hailstorms in Yunnan province of China are analyzed statistically. It is determined that the hailstorms were found to present dominant negative CG lightning flashes at any given stage. One specific hailstorm occurring on July 16, 2006, is analyzed in detail by using the data from a CG lightning location network and Doppler radar. This severe hailstorm, which exhibited strong vertical development with cloud tops reaching 15.9 km, produced hailstones as large as 15 mm and had a lifespan of 3 h and 12 min. The total CG lightning within the hailstorm showed high levels of activity with flash rates of up to 79 fl/5 min. The analysis of the storm cell's lifecycle shows similar trends between the CG lightning flash rates and radar-derived parameters. Cloud-to-ground flashes tended to initiate within the cloud region with reflectivity of more than 30 dBZ at the -10 °C isotherm height. A distinct increase in CG flash rate is shown during the rapid development stages of hailstorms. The CG lightning jump pattern appears to be an effective tool for short-term forecasting of possible occurrences of severe weather. © 2015 Elsevier Ltd. Source

Xie Y.,Yunnan University | Wu J.,Yunnan University | Zhang T.,Meteorological Observatory of Yunnan Province | Liu X.,Meteorological Observatory of Yunnan Province
2014 International Conference on Lightning Protection, ICLP 2014

A thunderstorm that developed over the central Lower Latitude Plateau of China on 16 July 2006 is analyzed in detail using the data from a CG lightning location network and Doppler radar. This severe thunderstorm produced hailstones as large as 15 mm and had a lifetime of 3 h and 20 min. The thunderstorm exhibited strong vertical development with cloud top reaching 15.9km. The CG parameters considered are the flash rate, the flash polarity, the multiplicity, and the peak current. The thunderstorm produced especially low positive CG proportions associated with negative CGs with high values of peak current and multiplicity.This second part is mostly centered on the detailed analysis of the CG lightning behavior, its relationship with radar-derived storm parameters, and CG lightning correlation with hazardous weather. The analysis of the storm cells life cycle has showed similar trends between the CG lighting flash rates and radar-derived parameters like the area of reflectivity above 30 dBZ at the -10°C isotherm height. There is a distinct increase in CG flash rate during the rapid development stage of hailstorms. The CG lightning "jump" pattern seems more robust to forecast in a short-term basis the possible occurrence of severe weather. © 2014 IEEE. Source

Xie Y.,Meteorological Observatory of Yunnan Province | Xu K.,Meteorological Science Institute of Yunnan Province | Zhang T.,Meteorological Observatory of Yunnan Province | Liu X.,Meteorological Observatory of Yunnan Province
Atmospheric Research

The characteristics of cloud-to-ground (CG) lightning in Yunnan province, based on the data recorded by the Yunnan Lightning Detection Network (YNLDN), are presented. The data, more than 2.09million CG flashes, cover the entirety of Yunnan province and were recorded from 2006 to 2010. The spatial analyses (total and positive flash density, the percentage of positive flashes, negative and positive peak currents) were done with a resolution of 20km. The average spatial distribution shows a maximum (3.8flasheskm-2yr-1) over the central Yunnan province and Jinsha river associated with topography and cold air mass passage. The mean monthly variation shows a maximum CG lightning between May and October (94%) and minimum values in December and January. High values (0.15flasheskm-2yr-1) for positive CG lightning density are observed in Red river basin. The monthly distribution of positive flashes shows a main maximum in April (19%) and a secondary maximum in July and August (17%), suggesting that positive flashes tend to occur earlier in the year than total flashes. The mean annual percentage of positive flashes has lower values at 3% in the central parts of the province. The percentage of positive CG flashes changes over the year from 2% in August to 49% in January. The monthly variation of median peak current for the negative first-stroke for each month varies only slightly from 27kA. The monthly variation of the median peak current for positive first-stroke, however, has a maximum in winter and the minimum occurs in May. The mean diurnal cycle for the negative CG lightning flashes peaks between 1600 and 1700 LT (11.37%) and shows a minimum between 0900 and 1000 LT (0.23%). The diurnal variation of positive flashes, in turn, shows a maximum around 0100-0200 LT, with a secondary peak at 1800 LT. This variation is associated with local mesoscale circulation, which has an obvious nocturnal feature. © 2013 Elsevier B.V. Source

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