Evaluation of Satisfaction Survey of Decision-Making Meteorological Services in Shaanxi Province, China in 2017

In China, decision-making meteorological services provide meteorological information for the production organization, disaster prevention and mitigation by the CPC committee, government, military leaders and decision-making departments at all levels, as well as scientific decision-making in the areas of rational development and utilization of climate resources and environmental protection. In order to understand the user’s satisfaction with the decision-making meteorological service, the Shaanxi Provincial Meteorological Bureau conducted a statistical survey, and the results showed that: 1) In 2017, the satisfaction level of provincial-level decision-making meteorological services in Shaanxi, China was 92.77%. Among them, the satisfaction index of “Ministry Department Service Personnel Professional Image and Service Awareness” was 94.12%, and the “Weather Forecast Warning Accuracy” satisfaction index was 90.18%. 2) Decision-making users have become an important channel for obtaining meteorological information through meteorological websites, televisions, mobile phone text messages, APP mobile applications, broadcasting, and Meteorological Information Express. Rainstorms, floods, high temperature heat, cold winds, hail, precipitation, and lightning are still the main concerns of decision-makers. 3) The focus on haze and UV intensity is 15% and 8% higher than that of 2016. The next 1 - 3 days weather forecast and 0 - 6 hours short-term forecast are still the most valuable forecast products for decision-making users. Compared with 2016, the next 1 - 3 days weather forecast, future 0 - 6 hours forecast, traffic meteorology, precipitation probability, and air quality forecast increase by 1% to 14% in the year of 2017.

Analysis of a Regional Rainstorm Process in South Shaanxi during July 17-18,2010

Based on conventional high-altitude aerial and ground data, regional intensive rainfall data, Doppler weather radar and satellite cloud data, the occurrence and development process of a regional rainstorm in South Shaanxi during July 17 -18, 2010 was discussed deeply. The results showed that the occurrence and development of the mesoscale weather system resulted in the heavy storm directly besides favorable large-scale background, and the the occurrence and development of the system had strong local and sudden characters. In addition, heavily concentrated wa- ter vapor in the troposphere at low and middle altitudes as well as existence of unstable conditions of convection might be favorable to the develop- ment of the system, while dynamic action of terrain, ground weak cold front and disturbance of the low-level jet stream might trigger the occurrence and development of the system.

Simulation of Change Trend of Drought in Shaanxi Province in Future Based on PRECIS Model

[Objective] The aim was to predict the change trend of drought in Shaanxi Province in future. [Method] Based on the regional climate model PRECIS from Hadley Climate Center, British Meteorological Bureau, taking precipitation anomaly percentage as assessment index, the change trend of drought in Shaanxi Province in reference years (1971-1990) was simulated, and the change trend of drought in Shaanxi Province from 2071 to 2100 was predicted. [Result] The simulated value of drought frequency in reference years could simulate the distribution of drought well, namely drought frequency was high in the north and low in the south; annual mean frequency of drought above second grade decreased gradually from north to south in future, and it was the highest in northern Shaanxi (above 4 times) and lowest in southern Shaanxi (below 2.5 times); drought frequency in future went down in northern Shaanxi from southern Yulin to Yan’an, eastern Guanzhong (including Weibei) and the west of southern Shaanxi, while it went up in the north of northern Shaanxi, Qinling Mountains and Shangluo region in western Guanzhong. [Conclusion] The study could provide theoretical references for the research on the change trend of drought in Shaanxi Province in future.

Assessment of ECMWF’s Precipitation Forecasting Performance for China from 2017 to 2022

This study used the China Meteorological Administration(CMA)three-source fusion gridded precipitation analysis data as a reference to evaluate the precipitation forecast performance of the European Centre for Medium-Range Weather Forecasts(ECMWF)model for China from 2017 to 2022.The main conclusions are as follows.The precipitation forecast capability of the ECMWF model for China has gradually improved from 2017 to 2022.Various scores such as bias,equitable threat score(ETS),and Fractions Skill Score(FSS)showed improvements for different categories of precipitation.The bias of light rain forecasts overall adjusted towards smaller values,and the increase in forecast scores was greater in the warm season than in the cold season.The ETS for torrential rain more intense categories significantly increased,although there were large fluctuations in bias across different months.The model exhibited higher precipitation bias in most areas of North China,indicating overprediction,while it showed lower bias in South China,indicating underprediction.The ETSs indicate that the model performed better in forecasting precipitation in the northeastern part of China without the influence of climatic background conditions.Comparison of the differences between the first period and the second period of the forecast shows that the precipitation amplitude in the ECMWF forecast shifted from slight underestimation to overestimation compared to that of CMPAS05,reducing the likelihood of missing extreme precipitation events.The improvement in ETS is mainly due to the reduction in bias and false alarm rates and,more importantly,an increase in the hit rate.From 2017 to 2022,the area coverage error of model precipitation forecast relative to observations showed a decreasing trend at different scales,while the FSS showed an increasing trend,with the highest FSS observed in 2021.The ETS followed a parabolic trend with increasing neighborhood radius,with the better ETS neighborhood radius generally being larger for moderate rain and heavy rain compared with light rain and torrential rain events.

Analysis of Abnormal Temperature Change in Guanzhong Plain in the North of Qingling Mountains

In this study, we analyzed the changes of houdy temperature in some regions of Guanzhong Plain in the north of Qingling Mountains on December 4, 2012. The results show that daily variation of temperature was abnormal in some regions of Guanzhong Plain on December 4, 2012, and medium fog and haze inhibited the increase of air temperature in the urban area of Xi＇an in the morning of December 4, so that air temperature went up slowly during the day of December 4. The sinking of the northwest cold air before arriving Guanzhong Plain as well as atmospheric com- pression warming effect caused by Qinling terrain blocking were the main reasons for the abnormal increase of temperature in some areas of Guanzhong Plain. Compared with surrounding districts and counties, urban heat island effect was more obvious in the urban area of Xi＇an.

Irregular Information of the Rainstorm in a Continuous Rainy Weather

[Objective] The research aimed to analyze irregular information of the local rainstorm process (during 5-6 September,2009) in autumn continuous rainy weather in north Shaanxi. [Method] Based on V-3θ chart, routine observation data provided by Micaps system, satellite cloud chart and data at 100 automatic meteorological stations of Shaanxi, for rainstorm process in autumn continuous rainy weather in north Shaanxi during 4-10 September, 2009, by using structure analysis method, irregular information in local rainstorm weather was analyzed. [Result] In whole precipitation process, atmospheric structure in rainstorm zone presented obvious evolution process. Before precipitation, typical atmospheric structure information of the sudden convective weather appeared. Obvious ultra-low temperature structure appeared at 200 hPa, and consistent clockwise rotation flow was at vertical wind field. Meanwhile, water vapor was sufficient, and unstable energy existed at low layer. Structure characteristic of the convective strong precipitation appeared by advancing for 12h. As precipitation weakened, unstable energy was released, and ultra-low temperature disappeared. [Conclusion] The research provided some thoughts for the forecast of such weather process.

Quantifying the Response Strength of the Southern Stratospheric Polar Vortex to Indian Ocean Warming in Austral Summer

A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.However,a significant difference exists in the modeled strengths,particularly in the stratosphere,with those in three of the AGCMs （CCM3,CAM3,and GFS） being four to five times as strong as those in the two other models （GFDL AM2,ECHAM5）.As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic,but also for projecting its future trend.This issue is addressed in the present study through comparing the models＇ climatological mean states and intrinsic variability,particularly those influencing tropospheric signals to propagate upward and reach the stratosphere.The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference.Based on a comparison with observations,it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5,rather than the strong one simulated by the three other models （CCM3,CAM3 and GFS）.In particular,IOW during the past 50 years may have dynamically induced a 1.0℃ warming in the polar lower stratosphere （～100 hPa）,which canceled a fraction of radiative cooling due to ozone depletion.

Spatiotemporal characteristics of ultraviolet solar radiation in China

UV radiation plays an important role in climate change and photochemical reactions,and in Ecosystem Research.In this study,the authors presented study results of China’s National Basic Research Program Study on the climatic characteristics and reconstruction method of UV radiation in China.The spatiotemporal variation of UV radiation in China has been discussed,and then an effcient modeling method has been established to obtain history UV radiation data to analyse the variation trends of UV radiation in China.Finally,the influence of aerosol,cloud,ozone,and water vapor on UV radiation has been discussed.

Inversion of Urban Heat Island Effect in Xi'an City

[Objective] The study aims at conducting the inversion of urban heat island effect in Xi＇an City. [Method] Based on the United States Landsat-7 ETM~ and TM data in different phases, the spatial distribution and changing trends of urban heat island effect in Xi＇an City were ana- lyzed, and some corresponding measures to relieve the heat island effect in Xran were put forward according to its spatial distribution and intensity changes. [ Result] Urban heat island effect was very obvious in Xi＇an City, that is, surface temperature of urban areas was distinctly higher than that of surrounding suburban areas, and the high-temperature region was akin to an island with a clear boundary. As the enlarging of Xi＇an City, the areas subjected to heat island effect expended toward the south and north especially. In addition, heat island effect of Lantian District became more prominent, so it should be paid more attention to. We suggest that some measures like improving urban vegetation coverage, reasonably planing urban buildings, reducing the discharge of man-made heat, preventing and controlling atmospheric pollution should be adopted to control urban heat island effect of Xi＇an City effectively. [ Concision] The study could offer theoretical references for the control of urban heat island effect and the im- provement of ecological environment in Xi＇an City.

Application of the Attenuation Correction Technology in C-band Radar Precipitation Estimation

[ Objective] The research aimed to study application of the attenuation correction technology in C-band radar precipitation estimation. [ Method~ Based on CINRAD-CB radar data in Shaanxi, we conducted the attenuation correction experiment by using iteration method and Kufa method respectively. Moreover, we conducted application expedment of the Kufa attenuation correction method in the quantitative precipitation esti- mation. [ Result~ Attenuation correction technology could compensate for attenuation problem of the echo at the distant range. Calculation result of the iteration method finally tended to that of the Kufa method. Moreover, iteration method spent more time. Therefore, Kufa attenuation correction technology was more suitable for business operation. When strong echo was near radar, generated attenuation was more obvious, and application value of the attenuation correction was bigger. Attenuation correction technology was used for quantitative precipitation estimation, which was favor- able for improving accuracy of the precipitation estimation. But we should conduct detailed planning on calculation scheme of the precipitation esti- mation because that different calculation schemes had great influences on accuracy of the quantitative precipitation estimation. [ Cendusien] This research provided a basis for improving accuracy of the quantitative precipitation estimation in Shaanxi. Key words Attenuation correction

Characteristic Analysis of Short Time Heavy Rain in Yulin, China

National Centers for Environment Prediction (NCEP) reanalysis data, automatic observation data, FY-2E satellite data and Doppler radar data are used to analyze a short-time local heavy rain in Yulin city, Shaanxi, China on August 7, 2018. The result shows that the strong convective weather occurred in peripheral subtropical high over west pacific, being caused by short wave disturbance, and surface convergence lines with positive pressure variation are corresponding to areas of short-time heavy precipitation. The degree of temperature change in cold pool caused by thunderstorm may decide the intensity of a short-time rainfall, and local topography plays an important role in extreme precipitation. Local water vapour accumulation and water vapour flux convergence in the middle and lower layers support adequate moisture condition in the process. Moving direction and development direction of mesocale convective cloud are in a line to develop the train effect, leading to local short-time heavy rain in Yulin city, Shaanxi, China.