• Title, Summary, Keyword: thunderstorms

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Risk assessment of transmission line structures under severe thunderstorms

  • Li, C.Q.
    • Structural Engineering and Mechanics
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    • v.6 no.7
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    • pp.773-784
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    • 1998
  • To assess the collapse risk of transmission line structures subject to natural hazards, it is important to identify what hazard may cause the structural collapse. In Australia and many other countries, a large proportion of failures of transmission line structures are caused by severe thunderstorms. Because the wind loads generated by thunderstorms are not only random but time-variant as well, a time-dependent structural reliability approach for the risk assessment of transmission line structures is essential. However, a lack of appropriate stochastic models for thunderstorm winds usually makes this kind of analysis impossible. The intention of the paper is to propose a stochastic model that could realistically and accurately simulate wind loading due to severe thunderstorms. With the proposed thunderstorm model, the collapse risk of transmission line structures under severe thunderstorms is assessed numerically based on the computed failure probability of the structure.

Emerging issues and new frameworks for wind loading on structures in mixed climates

  • Solari, Giovanni
    • Wind and Structures
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    • v.19 no.3
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    • pp.295-320
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    • 2014
  • Starting from an overview on the research on thunderstorms in the last forty years, this paper provides a general discussion on some emerging issues and new frameworks for wind loading on structures in mixed climates. Omitting for sake of simplicity tropical cyclones and tornadoes, three main aspects are pointed out. The first concerns the separation and classification of different intense wind events into extra-tropical depressions, thunderstorms and gust fronts, with the aim of improving the interpretation of the phenomena of engineering interest, the probabilistic analysis of the maximum wind velocity, the determination of the wind-induced response and the safety format for structures. The second deals with the use of the response spectrum technique, not only as a potentially efficient tool for calculating the structural response to thunderstorms, but also as a mean for revisiting the whole wind-excited response in a more general and comprehensive framework. The third involves the statistical analysis of extreme wind velocities in mixed climates, pointing out some shortcomings of the approaches currently used for evaluating wind loading on structures and depicting a new scenario for a more rational scheme aiming to pursue structural safety. The paper is set in the spirit of mostly simplified analyses and mainly qualitative remarks, in order to capture the conceptual aspects of the problems dealt with and put on the table ideas open to discussion and further developments.

Wind velocity field during thunderstorms

  • Ponte, Jacinto Jr.;Riera, Jorge D.
    • Wind and Structures
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    • v.10 no.3
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    • pp.287-300
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    • 2007
  • Wind action is a factor of fundamental importance in the structural design of light or slender constructions. Codes for structural design usually assume that the incident mean wind velocity is parallel to the ground, which constitutes a valid simplification for frequent winds caused by meteorological phenomena such as Extratropical Storms (EPS) or Tropical Storms. Wind effects due to other phenomena, such as thunderstorms, and its combination with EPS winds in so-called squall lines, are simply neglected. In this paper a model that describes the three-dimensional wind velocity field originated from a downburst in a thunderstorm (TS) is proposed. The model is based on a semi empirical representation of an axially-symmetrical flow line pattern that describes a stationary field, modulated by a function that accounts for the evolution of the wind velocity with time. The model allows the generation of a spatially and temporally variable velocity field, which also includes a fluctuating component of the velocity. All parameters employed in the model are related to meteorological variables, which are susceptible of statistical assessment. A background wind is also considered, in order to account for the translational velocity of the thunderstorm, normally due to local wind conditions. When the translation of the TS is caused by an EPS, a squall line is produced, causing the highest wind velocities associated with TS events. The resulting vertical velocity profiles were also studied and compared with existing models, such as the profiles proposed by Vicroy, et al. (1992) and Wood and Kwok (1998). The present model predicts horizontal velocity profiles that depend on the distance to the storm center, effect not considered by previous models, although the various proposals are globally compatible. The model can be applied in any region of interest, once the relevant meteorological variables are known, to simulate the excitation due to TS winds in the design of transmission lines, long-span crossings, cable-stayed bridges, towers or similar structures.

Noise Phobia-Induced Relative Polycythemia in a Dog (개에서 소리공포증에 의해 발생한 상대적 적혈구증가증 증례)

  • Kang, Min-Hee;Park, Hee-Myung
    • Journal of Veterinary Clinics
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    • v.29 no.6
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    • pp.494-497
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    • 2012
  • A 6-year-old castrated male Miniature Pinscher dog was referred due to shaking, panting and inappropriate elimination during thunderstorms. The dog had noise phobia after a car accident two years ago. The intensity of the fear of noise, especially with thunderstorms, worsened during the past 3 months (thunderstorm season). Physical examination revealed hyperthermia, tachypnea (panting), mild tachycardia, and an elevated systolic blood pressure. Laboratory examination revealed mild polycythemia with a lower oxygen pressure and saturation. Based on the history, physical examination, and laboratory tests, the dog was diagnosed as a noise phobia concurrent with relative polycythemia. Treatment was initiated with behavior modification with desensitization, counter-conditioning, and medication. Music therapy was also used and appeared to be beneficial. Clinical signs including polycythemia are improved. This case indicates that relative polycythemia can be occurred by chronic mental stress, such as noise phobia in a dog.

Characteristics of thunderstorms relevant to the wind loading of structures

  • Solari, Giovanni;Burlando, Massimiliano;De Gaetano, Patrizia;Repetto, Maria Pia
    • Wind and Structures
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    • v.20 no.6
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    • pp.763-791
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    • 2015
  • "Wind and Ports" is a European project that has been carried out since 2009 to handle wind forecast in port areas through an integrated system made up of an extensive in-situ wind monitoring network, the numerical simulation of wind fields, the statistical analysis of wind climate, and algorithms for medium-term (1-3 days) and short term (0.5-2 hours) wind forecasting. The in-situ wind monitoring network, currently made up of 22 ultrasonic anemometers, provides a unique opportunity for detecting high resolution thunderstorm records and studying their dominant characteristics relevant to wind engineering with special concern for wind actions on structures. In such a framework, the wind velocity of thunderstorms is firstly decomposed into the sum of a slowly-varying mean part plus a residual fluctuation dealt with as a non-stationary random process. The fluctuation, in turn, is expressed as the product of its slowly-varying standard deviation by a reduced turbulence component dealt with as a rapidly-varying stationary Gaussian random process with zero mean and unit standard deviation. The extraction of the mean part of the wind velocity is carried out through a moving average filter, and the effect of the moving average period on the statistical properties of the decomposed signals is evaluated. Among other aspects, special attention is given to the thunderstorm duration, the turbulence intensity, the power spectral density and the integral length scale. Some noteworthy wind velocity ratios that play a crucial role in the thunderstorm loading and response of structures are also analyzed.

Near-ground wind and its characterization for engineering applications

  • Crandell, Jay H.;Farkas, William;Lyons, James M.;Freeborne, William
    • Wind and Structures
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    • v.3 no.3
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    • pp.143-158
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    • 2000
  • This report presents the findings of a one-year monitoring effort to empirically characterize and evaluate the nature of near-ground winds for structural engineering purposes. The current wind engineering practice in the United States does not explicitly consider certain important near-ground wind characteristics in typical rough terrain conditions and the possible effect on efficient design of low-rise structures, such as homes and other light-frame buildings that comprise most of the building population. Therefore, near ground wind data was collected for the purpose of comparing actual near-ground wind characteristics to the current U.S. wind engineering practice. The study provides data depicting variability of wind speeds, wind velocity profiles for a major thunderstorm event and a northeaster, and the influence of thunderstorms on annual extreme wind speeds at various heights above ground in a typical rough environment. Data showing the decrease in the power law exponent with increasing wind speed is also presented. It is demonstrated that near-ground wind speeds (i.e., less than 10 m above ground) are likely to be over-estimated in the current design practice by as much as 20 percent which may result in wind load over-estimate of about 50% for low-rise buildings in typical rough terrain. The importance of thunderstorm wind profiles on determination of design wind speeds and building loads (particularly for buildings substantially taller than 10 m) is also discussed. Recommendations are given for possible improvements to the current design practice in the United States with respect to low-rise buildings in rough terrain and for the need to study the impact of thunderstorm gust profile shapes on extreme value wind speed estimates and building loads.

A Study on the Characteristics of Convective Activities related to Atmospheric Stability Index and Thunderstorms over the Naro Space Center (나로우주센터 상공의 대기 안정도지수 및 뇌운관련 대류활동 특성 연구)

  • Kim, Hong-Il;Choi, Eun-Ho;Seo, Seong-Gyu
    • Journal of Environmental Science International
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    • v.28 no.12
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    • pp.1133-1145
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    • 2019
  • Successful launch requires state-of-the-art launch vehicle technology and constant test operations, However, the meteorological threat to the launch vehicle flight trajectory is also an important factor for launch success. Atmospheric stability above the Naro Space Center at the this time is very important, especially because the initial flight operation can determine the success of the launch. Moreover, during the flight of launch vehicle with rapid pressure and thrust into the atmosphere, convection activity in the atmosphere may create environmental conditions that cause severe weather threats such as thunderstorms. Hence, studies of atmospheric instability characteristics over the Naro Space Center are a necessary part of successful launch missions. Therefore, the main aims of this study were to (1) verify the atmospheric stability index and convection activity characteristics over the Naro Space Center using radiosonde data observed from 2007 to 2018 by the Naro Space Center, (2) analyze changes in the atmospheric stability index according to monthly and seasonal changes, and (3) assess how the calculated atmospheric stability index is related to actual thunderstorm occurrence using statistical analysis. Additionally, we aimed to investigate the atmospheric characteristics above the Naro Space Center through the distribution chart of the atmospheric stability index during summer, when convection activity is highest. Finally, we assessed the relationship between lightning occurrence and unstable atmospheric conditions, through predictability analysis performed using the lightning observation data of the Korea Meteorological Administration.

Characteristics of Atmospheric Stability Index of Airmass thunderstorm day at Busan (부산지역 기단성 뇌우 발생일의 대기안정도지수 특성)

  • Jeon, Byung Il
    • Journal of Wetlands Research
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    • v.5 no.1
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    • pp.29-40
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    • 2003
  • This study was performed to research the relation between airmass thunderstorm and stability index with 12 years meteorological data(1990~2001) at Busan. Also We used the analysed stability indices from University of Wyoming to consider airmass thunderstorm. The frequency of thunderstorm occurrence during 12 years was 156 days(annual mean 13days). The airmass thunderstorm frequency was 14 days, most of those occurrence were summertime(59%). And occurrence hour of airmass thunderstorm was distributed from 1300LST to 2100LST broadly. The highest forecast index for airmass thunderstorm at Busan was K index, the lowest forecast index was SWEAT index. The forecasting of thunderstorms is based primary on the concepts of conditional instability, convective instability, and forced lifting of air near the surface. Instability is a critical factor in severe weather development. Severe weather stability indices can be a useful tool when applied correctly to a given convective weather situation.

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Protection for Telecommunications Equipment from Lightning -to Provide service with Higher Reliability - (낙뢰로부터 통신장치를 보호하는 방법 -보다 고신뢰 서비스 제공을 위하여 -)

  • 조규심
    • Journal of the Korean Professional Engineers Association
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    • v.29 no.3
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    • pp.87-93
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    • 1996
  • Lightening is a phenomenon in which electric charges accumulated in the air due to a strong ascending air current are instantly discharged. As the air current rises, the steam in the air turns into hail and grows to a certain size. Thunderclouds brought together by the ascending air current when the earth's surface is heated by strong summer sunlight produce what are called heat thunderstorms. Compared to transistors and IC's that operate at several volts, lightening induces voltages of from several 100 to several 10,000 volts and sometimes causes great damage, such as destroying equipment or delaying communication. The following describes the cause of lighting damage and basic idea behind countermeasures against such damage.

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GROUND OBSERVATIONS OF SPRITES AND OTHER TLES IN TAIWAN

  • WANG YUN-CHING;HSU RUE-RON;SU HAN-TZONG;CHEN ALFRED BING-CHIH;LEE YI-JEN;KUO CHENG-LING;TSAY WEAN-SHUN;CHANG CHAN-KAO;WANG SHI-CHUN;LEE LOU-CHUANG;LIU TIE-YUE
    • Journal of The Korean Astronomical Society
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    • v.38 no.2
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    • pp.299-302
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    • 2005
  • Sprites, elves and blue jets are collectively denominated as the upper atmospheric transient luminous events (TLEs). They are recently discovered optical flashes between active thunderstorms and the ionosphere. In this report, a brief introduction to the most important characteristics of TLEs is given. Since 2001, scientists from the National Cheng Kung University have been performing yearly summer campaigns from various locations in Taiwan. The main achievements of their yearly campaign are presented.