In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar(DPR) suitable over the Tibetan Plateau(TP) was proposed by analyzing Global Precipitation Measurement(GPM) DPR Level-2...In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar(DPR) suitable over the Tibetan Plateau(TP) was proposed by analyzing Global Precipitation Measurement(GPM) DPR Level-2 data in summer from 2014 to 2020. It was found that the DPR rain type classification algorithm(simply called DPR algorithm) has mis-identification problems in two aspects in summer TP. In the new algorithm of rain type classification in summer TP,four rain types are classified by using new thresholds, such as the maximum reflectivity factor, the difference between the maximum reflectivity factor and the background maximum reflectivity factor, and the echo top height. In the threshold of the maximum reflectivity factors, 30 d BZ and 18 d BZ are both thresholds to separate strong convective precipitation, weak convective precipitation and weak precipitation. The results illustrate obvious differences of radar reflectivity factor and vertical velocity among the three rain types in summer TP, such as the reflectivity factor of most strong convective precipitation distributes from 15 d BZ to near 35 d BZ from 4 km to 13 km, and increases almost linearly with the decrease in height. For most weak convective precipitation, the reflectivity factor distributes from 15 d BZ to 28 d BZ with the height from 4 km to 9 km. For weak precipitation, the reflectivity factor mainly distributes in range of 15–25 d BZ with height within 4–10 km. It is also shows that weak precipitation is the dominant rain type in summer TP, accounting for 40%–80%,followed by weak convective precipitation(25%–40%), and strong convective precipitation has the least proportion(less than 30%).展开更多
An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insula...An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain.展开更多
Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce ra...Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce rain or mixed precipitation. It is beneficial for meteorologists to better understand the commonly used 5400 and 1300 GPM line to better forecast rain versus snow events. Other studies have looked into the use of the 5400 GPM (540 dm) line but none have assessed the validity of this boundary with respect to weather type characterization at Albany. This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events. The mean daily 500, 850, 925 and 1000 mb heights and weather type frequency of the Spatial Synoptic Classification between November and March of 1980 - 2012 are analyzed. Results indicate that the standard vertical boundaries are inaccurate indicators of a rain versus snow event in Albany. More reasonable rain-snow cut offs for the 1000 - 500 and 1000 - 850 mb thicknesses are 5222 and 1262 GPM. For the 1000 - 925 mb level, 606 GPM is a helpful aid of identifying the rain-snow boundary. Further scrutinizing by weather type indicates that the rain-snow boundary also varies depending on what air mass/weather type is present on a given day. For instance, when the most prominent weather type is observed over Albany (Dry Polar), at the 1000 - 850 mb and 1000 - 500 mb layers, a boundary of 1242 GPM and 5152 GPM is found to be most representative. Results indicate only for the rarest of winter weather types observed over Albany, Moist Tropical, are the standard cut offs useful. Determining the reliability of this precipitation indicator at a specific station, like Albany, could enable meteorologists in other regions of the country to draw parallels between weather type, precipitation, and thickness in their forecast zones.展开更多
Summer Precipitation in Eastern China was closely related to the global sea surface temperature field. In this paper, the impact of the main sea surface temperature anomaly on flood season precipitation in China’s Hu...Summer Precipitation in Eastern China was closely related to the global sea surface temperature field. In this paper, the impact of the main sea surface temperature anomaly on flood season precipitation in China’s Huanghuai and Jianghuai regions is examined as an external forcing factor for short-term climate prediction. Through analysis of global sea surface temperature anomalies and regional anomalies in Huanghuai and Jianghuai, a significant effect related to the main area, the North Pacific region, and the Nino3 corresponding index calculation is found. Various key areas are examined for their relevance, and finally, the mechanism of summer precipitation in two key zones, China’s Huanghuai and Jianghuai regions, is briefly discussed. The main implication is the prediction of season precipitation based on the external forcing signal of sea surface temperature anomaly in China’s Huanghuai and Jianghuai regions.展开更多
[Objective] The research aimed to review the research progresses and the research achievements of plum rain in China.[Method] By using the precipitation,the sunshine data in the related observatories during 1961-2009 ...[Objective] The research aimed to review the research progresses and the research achievements of plum rain in China.[Method] By using the precipitation,the sunshine data in the related observatories during 1961-2009 and the daily height field data of NCEP/DOE2 in 1996,which were provided by the National Meteorological Information Center,the prior researches about the plum rain in China were reviewed from the division of plum rain,the range of plum rain area and the space distribution.[Result] The formulation of an objective,unified plum rain division standard needed the further research and discussion,which provided the basis for the determination of plum rain range in China.In the division of plum rain period,when the sunshine duration parameter was considered,the division of plum rain period could be more reliable.The climatic mean result showed that the plum rain phenomenon still existed in the southwest part of Hubei Province where was in the west of Yichang,and the plum rain range could extend westward a longitude.In the northwest part of the traditional plum rain area,the plum rain phenomenon wasn’t significant,and it didn’t belong to the plum rain range in China.Spring rain and the plum rain in central Hunan,central Jiangxi and central south of Zhejiang should be differentiated by the objective and unified plum rain standard.[Conclusion] Chinese scholars still had some controversies about the typing of plum rain in Jiang-Huai.The selections of suitable analytical method and region had the important effects on the plum rain typing.展开更多
运用我国2016-2018年三个冬半年(10月至次年3月)地面2515个站的天气现象观测资料,对ECMWF(European Centre for Medium-Range Weather Forecasts)的降水相态预报产品(PTYPE)(分为雨、雨夹雪、雪和冻雨四类)进行了系统性的检验评估,包括...运用我国2016-2018年三个冬半年(10月至次年3月)地面2515个站的天气现象观测资料,对ECMWF(European Centre for Medium-Range Weather Forecasts)的降水相态预报产品(PTYPE)(分为雨、雨夹雪、雪和冻雨四类)进行了系统性的检验评估,包括细网格确定性模式预报产品和集合预报系统概率预报产品。结果显示,ECMWF的确定性预报产品对四类降水相态的正确率普遍达到90%以上,对降雨和降雪的TS评分也较高,冻雨次之,雨夹雪的TS评分较低,预报能力有限。确定性模式对我国雨雪分界线的预报,普遍存在短期位置略偏南、中期随时效延长越来越偏北的误差特点,且对雨夹雪的预报范围明显偏小,对冻雨的预报范围明显偏大。集合预报系统从概率的角度一定程度上弥补了确定性模式的上述误差。对概率预报的检验结果显示,集合预报系统降雨概率普遍偏低,降雪概率短期偏高、中期偏低,而雨夹雪和冻雨概率普遍偏低,但是都有一定的预报技巧。集合预报系统相对于确定性模式的优势,降雨体现在较小花费损失比事件的预报上,降雪体现在较大花费损失比事件的预报上。对雨夹雪和冻雨,相对于确定性模式,集合预报系统体现出了显著的优势,尤其是冻雨,集合预报系统的优势更加明显。展开更多
基金funded by the National Natural Science Foundation of China project (Grant Nos.42275140, 42230612, 91837310, 92037000)the Second Tibetan Plateau Scientific Expedition and Research (STEP) program(Grant No. 2019QZKK0104)。
文摘In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar(DPR) suitable over the Tibetan Plateau(TP) was proposed by analyzing Global Precipitation Measurement(GPM) DPR Level-2 data in summer from 2014 to 2020. It was found that the DPR rain type classification algorithm(simply called DPR algorithm) has mis-identification problems in two aspects in summer TP. In the new algorithm of rain type classification in summer TP,four rain types are classified by using new thresholds, such as the maximum reflectivity factor, the difference between the maximum reflectivity factor and the background maximum reflectivity factor, and the echo top height. In the threshold of the maximum reflectivity factors, 30 d BZ and 18 d BZ are both thresholds to separate strong convective precipitation, weak convective precipitation and weak precipitation. The results illustrate obvious differences of radar reflectivity factor and vertical velocity among the three rain types in summer TP, such as the reflectivity factor of most strong convective precipitation distributes from 15 d BZ to near 35 d BZ from 4 km to 13 km, and increases almost linearly with the decrease in height. For most weak convective precipitation, the reflectivity factor distributes from 15 d BZ to 28 d BZ with the height from 4 km to 9 km. For weak precipitation, the reflectivity factor mainly distributes in range of 15–25 d BZ with height within 4–10 km. It is also shows that weak precipitation is the dominant rain type in summer TP, accounting for 40%–80%,followed by weak convective precipitation(25%–40%), and strong convective precipitation has the least proportion(less than 30%).
文摘An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain.
文摘Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce rain or mixed precipitation. It is beneficial for meteorologists to better understand the commonly used 5400 and 1300 GPM line to better forecast rain versus snow events. Other studies have looked into the use of the 5400 GPM (540 dm) line but none have assessed the validity of this boundary with respect to weather type characterization at Albany. This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events. The mean daily 500, 850, 925 and 1000 mb heights and weather type frequency of the Spatial Synoptic Classification between November and March of 1980 - 2012 are analyzed. Results indicate that the standard vertical boundaries are inaccurate indicators of a rain versus snow event in Albany. More reasonable rain-snow cut offs for the 1000 - 500 and 1000 - 850 mb thicknesses are 5222 and 1262 GPM. For the 1000 - 925 mb level, 606 GPM is a helpful aid of identifying the rain-snow boundary. Further scrutinizing by weather type indicates that the rain-snow boundary also varies depending on what air mass/weather type is present on a given day. For instance, when the most prominent weather type is observed over Albany (Dry Polar), at the 1000 - 850 mb and 1000 - 500 mb layers, a boundary of 1242 GPM and 5152 GPM is found to be most representative. Results indicate only for the rarest of winter weather types observed over Albany, Moist Tropical, are the standard cut offs useful. Determining the reliability of this precipitation indicator at a specific station, like Albany, could enable meteorologists in other regions of the country to draw parallels between weather type, precipitation, and thickness in their forecast zones.
文摘Summer Precipitation in Eastern China was closely related to the global sea surface temperature field. In this paper, the impact of the main sea surface temperature anomaly on flood season precipitation in China’s Huanghuai and Jianghuai regions is examined as an external forcing factor for short-term climate prediction. Through analysis of global sea surface temperature anomalies and regional anomalies in Huanghuai and Jianghuai, a significant effect related to the main area, the North Pacific region, and the Nino3 corresponding index calculation is found. Various key areas are examined for their relevance, and finally, the mechanism of summer precipitation in two key zones, China’s Huanghuai and Jianghuai regions, is briefly discussed. The main implication is the prediction of season precipitation based on the external forcing signal of sea surface temperature anomaly in China’s Huanghuai and Jianghuai regions.
基金Supported by " Development of Subtropical Monsoon System Monitoring and Diagnosis Technology " of Cooperative Science and Research Item of Shanghai Meteorological Bureau and School in 2009
文摘[Objective] The research aimed to review the research progresses and the research achievements of plum rain in China.[Method] By using the precipitation,the sunshine data in the related observatories during 1961-2009 and the daily height field data of NCEP/DOE2 in 1996,which were provided by the National Meteorological Information Center,the prior researches about the plum rain in China were reviewed from the division of plum rain,the range of plum rain area and the space distribution.[Result] The formulation of an objective,unified plum rain division standard needed the further research and discussion,which provided the basis for the determination of plum rain range in China.In the division of plum rain period,when the sunshine duration parameter was considered,the division of plum rain period could be more reliable.The climatic mean result showed that the plum rain phenomenon still existed in the southwest part of Hubei Province where was in the west of Yichang,and the plum rain range could extend westward a longitude.In the northwest part of the traditional plum rain area,the plum rain phenomenon wasn’t significant,and it didn’t belong to the plum rain range in China.Spring rain and the plum rain in central Hunan,central Jiangxi and central south of Zhejiang should be differentiated by the objective and unified plum rain standard.[Conclusion] Chinese scholars still had some controversies about the typing of plum rain in Jiang-Huai.The selections of suitable analytical method and region had the important effects on the plum rain typing.
文摘运用我国2016-2018年三个冬半年(10月至次年3月)地面2515个站的天气现象观测资料,对ECMWF(European Centre for Medium-Range Weather Forecasts)的降水相态预报产品(PTYPE)(分为雨、雨夹雪、雪和冻雨四类)进行了系统性的检验评估,包括细网格确定性模式预报产品和集合预报系统概率预报产品。结果显示,ECMWF的确定性预报产品对四类降水相态的正确率普遍达到90%以上,对降雨和降雪的TS评分也较高,冻雨次之,雨夹雪的TS评分较低,预报能力有限。确定性模式对我国雨雪分界线的预报,普遍存在短期位置略偏南、中期随时效延长越来越偏北的误差特点,且对雨夹雪的预报范围明显偏小,对冻雨的预报范围明显偏大。集合预报系统从概率的角度一定程度上弥补了确定性模式的上述误差。对概率预报的检验结果显示,集合预报系统降雨概率普遍偏低,降雪概率短期偏高、中期偏低,而雨夹雪和冻雨概率普遍偏低,但是都有一定的预报技巧。集合预报系统相对于确定性模式的优势,降雨体现在较小花费损失比事件的预报上,降雪体现在较大花费损失比事件的预报上。对雨夹雪和冻雨,相对于确定性模式,集合预报系统体现出了显著的优势,尤其是冻雨,集合预报系统的优势更加明显。
