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Wenjuan Zhang, Yijun Zhang, Dong Zheng, and Xiuji Zhou

Abstract

Cloud-to-ground lightning data and storm intensity data (winds and central pressure) for 33 northwest Pacific tropical cyclones were used to analyze lightning distributions during the period of landfall in China. Lightning activities varied enormously from storm to storm with an average flash rate over 500 km of radius from 3 to 3201 flashes per hour, and no obvious relationship between average intensity and average flash rate occurred. The maximum flash density shifted from the eyewall region (0–60 km) to outer rainbands (180–500 km) as the intensity level increased. The average ratio of flash density in the eyewall to outer rainband was highest (1:0.5) for storms with the level of a tropical storm (17.2–24.4 m s−1) and lowest (1:8.6) for severe typhoons (41.5–50.9 m s−1). After storm landfall, flash density in the rainband decreased more rapidly in severe typhoons than in severe tropical storms (24.5–32.6 m s−1) and typhoons, but increased in tropical depressions (10.8–17.1 m s−1) and tropical storms. With the strength of intensity level, lightning in the outer rainband gradually weakened after the storm landfall.

Lightning outbreaks were identified in a consistent manner for all tropical cyclones to inspect the relationship of eyewall flashes to the changes of structure and intensity. Eyewall flash outbreaks were found during the period of intensity change (15% of outbreaks in intensification and 43% in weaken), and the period of maximum intensity (15% of outbreaks) of storms. A new result of this analysis found that 10% of the outbreaks occurred prior to and during periods of storm turning, which is potentially important for the trajectory change forecasting of tropical cyclones.

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Xiuzhong Li, Yijun He, Biao Zhang, and Chenqing Fan

Abstract

In this study, a rotating frequency-modulated continuous wave (FMCW) radar is installed on an aircraft to retrieve the sea wave spectra. Because the aircraft attitude angles produce the incorrect antenna gain used in the radar equation, the incorrect normalized radar cross section (NRCS) of the sea surface will be acquired. To eliminate the effect of the angles, a three-dimensional matrix of the radar antenna gain is constructed by means of coordinate transformation and interpolation, based on a large set of configurations of the aircraft attitude angles (roll, pitch, etc.). With the application of the matrix, the NRCS of the sea surface is corrected and the calculating time is reduced. Then the sea surface mean square slope (MSS) is obtained from the echoes of the airborne wave spectrometer. Considering a weak periodicity of MSS due to low sea state, four images are presented to show the variation of the MSS after aircraft attitude angle correction. The results indicate that the accurate incidence angle of the antenna beam center is critical for retrieving the sea surface MSS, and that the magnitude of the MSS from three cycles of radar echoes can be changed by as much as 40% within 5° of the attitude angles. Furthermore, the MSS becomes more periodic and regular after correction.

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Dong Zheng, Yijun Zhang, Qing Meng, Luwen Chen, and Jianru Dan

Abstract

The first climatological comparison of small-current cloud-to-ground (SCCG; peak current ≤50 kA) and large-current cloud-to-ground (LCCG; peak current >50 kA, >75 kA, and >100 kA) lightning flashes is presented for southern China. The LCCG lightning exhibits an apparent preference to occur over the sea. The percentage of positive LCCG lightning during the nonrainy season was more than twice that during the rainy season, while the percentage of positive SCCG lightning showed small seasonal differences. Positive cloud-to-ground (PCG) lightning was more likely to feature a large peak current than was negative cloud-to-ground (NCG) lightning, especially during the nonrainy season and over land. Distinct geographical differences are found between SCCG and LCCG lightning densities and between their own positive and negative discharges. Furthermore, the percentages of positive lightning from LCCG and SCCG lightning exhibit distinctly different geographical and seasonal (rain and nonrainy season) distributions. The diurnal variations in SCCG and LCCG lightning are clearly different over the sea but similar over land. Diurnal variations in the percentage of positive lightning are functions of the peak current and underlying Earth’s surface. In combination with the University of Utah precipitation feature (PF) dataset, it is revealed that thunderstorms with relatively weak convection and large precipitation areas are more likely to produce the LCCG lightning, and the positive LCCG lightning is well correlated with mesoscale convective systems in the spatial distribution during nonrainy season.

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Biao Zhang, William Perrie, Jun A. Zhang, Eric W. Uhlhorn, and Yijun He

Abstract

This study presents a new approach for retrieving hurricane surface wind vectors utilizing C-band dual-polarization (VV, VH) synthetic aperture radar (SAR) observations. The copolarized geophysical model function [C-band model 5.N (CMOD5.N)] and a new cross-polarized wind speed retrieval model for dual polarization [C-band cross-polarized ocean surface wind retrieval model for dual-polarization SAR (C-2POD)] are employed to construct a cost function. Minimization of the cost function allows optimum estimates for the wind speeds and directions. The wind direction ambiguities are removed using a parametric two-dimensional sea surface inflow angle model. To evaluate the accuracy of the proposed method, two RADARSAT-2 SAR images of Hurricanes Bill and Bertha are analyzed. The retrieved wind speeds and directions are compared with collocated Quick Scatterometer (QuikSCAT) winds, showing good consistency. Results suggest that the proposed method has good potential to retrieve hurricane surface wind vectors from dual-polarization SAR observations.

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Ruiyang Ma, Dong Zheng, Yijun Zhang, Wen Yao, Wenjuan Zhang, and Deqing Cuomu

Abstract

Herein, we compared data on the spatiotemporal distribution of lightning activity obtained from the World Wide Lightning Location Network (WWLLN) with that from the Lightning Imaging Sensor (LIS). The WWLLN and LIS both suggest intense lightning activity over the central and southeastern Tibetan Plateau (TP) during May–September. Meanwhile, the WWLLN indicates relatively weak lightning activity over the northeastern TP, where the LIS suggests very intense lightning activity, and it also indicates a high-density lightning center over the southwestern TP, not suggested by the LIS. Furthermore, the WWLLN lightning peaks in August in terms of monthly variation and in late August in terms of ten-day variation, unlike the corresponding LIS lightning peaks of July and late June, respectively. Other observation data were also introduced into the comparison. The black body temperature (TBB) data from the Fengyun-2E geostationary satellite (as a proxy of deep convection) and thunderstorm day data support the spatial distribution of the WWLLN lightning more. Meanwhile, for seasonal variation, the TBB data is more analogous to the LIS data, while the cloud-to-ground (CG) lightning data from a local CG lightning location system is closer to the WWLLN data. It is speculated that the different WWLLN and LIS observation modes may cause their data to represent different dominant types of lightning, thereby leading to differences in the spatiotemporal distributions of their data. The results may further imply that there exist regional differences and seasonal variations in the electrical properties of thunderstorms over the TP.

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Penglei Fan, Dong Zheng, Yijun Zhang, Shanqiang Gu, Wenjuan Zhang, Wen Yao, Biwu Yan, and Yongbin Xu

Abstract

A systematic evaluation of the performance of the World Wide Lightning Location Network (WWLLN) over the Tibetan Plateau is conducted using data from the Cloud-to-Ground Lightning Location System (CGLLS) developed by the State Grid Corporation of China for 2013–15 and lightning data from the satellite-based Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) for 2014–15. The average spatial location separation magnitudes in the midsouthern Tibetan Plateau (MSTP) region between matched WWLLN and CGLLS strokes and over the whole Tibetan Plateau between matched WWLLN and LIS flashes were 9.97 and 10.93 km, respectively. The detection efficiency (DE) of the WWLLN rose markedly with increasing stroke peak current, and the mean stroke peak currents of positive and negative cloud-to-ground (CG) lightning detected by the WWLLN in the MSTP region were 62.43 and −56.74 kA, respectively. The duration, area, and radiance of the LIS flashes that were also detected by the WWLLN were 1.27, 2.65, and 4.38 times those not detected by the WWLLN. The DE of the WWLLN in the MSTP region was 9.37% for CG lightning and 2.58% for total lightning. Over the Tibetan Plateau, the DE of the WWLLN for total lightning was 2.03%. In the MSTP region, the CG flash data made up 71.98% of all WWLLN flash data. Based on the abovementioned results, the ratio of intracloud (IC) lightning to CG lightning in the MSTP region was estimated to be 4.05.

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Luwen Chen, Yijun Zhang, Weitao Lu, Dong Zheng, Yang Zhang, Shaodong Chen, and Zhihui Huang

Abstract

Performance evaluation for the lightning location system (LLS) of the power grid in Guangdong Province, China, was conducted based on observation data of the triggered lightning flashes obtained in Conghua, Guangzhou, during 2007–11 and natural lightning flashes to tall structures obtained in Guangzhou during 2009–11. The results show that the flash detection efficiency and stroke detection efficiency were about 94% (58/62) and 60% (97/162), respectively. The arithmetic mean and median values for location error were estimated to be about 710 and 489 m, respectively, when more than two reporting sensors were involved in the location retrieval (based on 87 samples). After eliminating one obviously abnormal sample, the absolute percentage errors of peak current estimation were within 0.4%–42%, with arithmetic mean and median values of about 16.3% and 19.1%, respectively (based on 21 samples).

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Jun Yang, Weitao Lyu, Ying Ma, Yijun Zhang, Qingyong Li, Wen Yao, and Tianshu Lu

Abstract

The macroscopic characteristics of clouds in the Tibetan Plateau are crucial to understanding the local climatic conditions and their impact on the global climate and water vapor cycle. In this study, the variations of cloud cover and cloud types are analyzed by using total-sky images of two consecutive years in Shigatse, Tibetan Plateau. The results show that the cloud cover in Shigatse presents a distinct seasonal difference that is characterized by low cloud cover in autumn and winter and high cloud cover in summer and spring. July is the month with the largest cloud coverage, and its average cloud cover exceeds 75%. The probability of clouds in the sky is the lowest in November, with an average cloud cover of less than 20%. The diurnal variations of cloud cover in different months also have considerable differences. Specifically, cloud cover is higher in the afternoon than that in the morning in most months, whereas the cloud cover throughout the day varies little from July to September. The dominant cloud types in different months are also not the same. The proportion of clear sky is large in autumn and winter. Stratiform cloud occupies the highest percentage in March, April, July, and August. The probability of emergence of cirrus is highest in May and June. The Shigatse region has clear rainy and dry seasons, and correlation analysis between precipitation and clouds shows that the largest cumulative precipitation, the highest cloud cover, and the highest proportion of stratiform clouds occur simultaneously in July.

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Yali Luo, Renhe Zhang, Qilin Wan, Bin Wang, Wai Kin Wong, Zhiqun Hu, Ben Jong-Dao Jou, Yanluan Lin, Richard H. Johnson, Chih-Pei Chang, Yuejian Zhu, Xubin Zhang, Hui Wang, Rudi Xia, Juhui Ma, Da-Lin Zhang, Mei Gao, Yijun Zhang, Xi Liu, Yangruixue Chen, Huijun Huang, Xinghua Bao, Zheng Ruan, Zhehu Cui, Zhiyong Meng, Jiaxiang Sun, Mengwen Wu, Hongyan Wang, Xindong Peng, Weimiao Qian, Kun Zhao, and Yanjiao Xiao

Abstract

During the presummer rainy season (April–June), southern China often experiences frequent occurrences of extreme rainfall, leading to severe flooding and inundations. To expedite the efforts in improving the quantitative precipitation forecast (QPF) of the presummer rainy season rainfall, the China Meteorological Administration (CMA) initiated a nationally coordinated research project, namely, the Southern China Monsoon Rainfall Experiment (SCMREX) that was endorsed by the World Meteorological Organization (WMO) as a research and development project (RDP) of the World Weather Research Programme (WWRP). The SCMREX RDP (2013–18) consists of four major components: field campaign, database management, studies on physical mechanisms of heavy rainfall events, and convection-permitting numerical experiments including impact of data assimilation, evaluation/improvement of model physics, and ensemble prediction. The pilot field campaigns were carried out from early May to mid-June of 2013–15. This paper: i) describes the scientific objectives, pilot field campaigns, and data sharing of SCMREX; ii) provides an overview of heavy rainfall events during the SCMREX-2014 intensive observing period; and iii) presents examples of preliminary research results and explains future research opportunities.

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Timothy J. Lang, Stéphane Pédeboy, William Rison, Randall S. Cerveny, Joan Montanyà, Serge Chauzy, Donald R. MacGorman, Ronald L. Holle, Eldo E. Ávila, Yijun Zhang, Gregory Carbin, Edward R. Mansell, Yuriy Kuleshov, Thomas C. Peterson, Manola Brunet, Fatima Driouech, and Daniel S. Krahenbuhl

Abstract

A World Meteorological Organization weather and climate extremes committee has judged that the world’s longest reported distance for a single lightning flash occurred with a horizontal distance of 321 km (199.5 mi) over Oklahoma in 2007, while the world’s longest reported duration for a single lightning flash is an event that lasted continuously for 7.74 s over southern France in 2012. In addition, the committee has unanimously recommended amendment of the AMS Glossary of Meteorology definition of lightning discharge as a “series of electrical processes taking place within 1 s” by removing the phrase “within 1 s” and replacing it with “continuously.” Validation of these new world extremes 1) demonstrates the recent and ongoing dramatic augmentations and improvements to regional lightning detection and measurement networks, 2) provides reinforcement regarding the dangers of lightning, and 3) provides new information for lightning engineering concerns.

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