• Wind and Structures
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• v.15 no.2
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• pp.87-109
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• 2012

A substantial part of South Africa is subject to more than one strong wind source. The effect of that on extreme winds is that higher quantiles are usually estimated with a mixed strong wind climate estimation method, compared to the traditional Gumbel approach based on a single population. The differences in the estimated quantiles between the two methods depend on the values of the Gumbel distribution parameters for the different strong wind mechanisms involved. Cluster analysis of the distribution parameters provides a characterization of the effect of the relative differences in their values, and therefore the dominance of the different strong wind mechanisms. For gusts, cold fronts tend to dominate over the coastal and high-lying areas, while other mechanisms, especially thunderstorms, are dominant over the lower-lying areas in the interior. For the hourly mean wind speeds cold fronts are dominant in the south-west, south and east of the country. On the West Coast the ridging of the Atlantic Ocean high-pressure system dominate in the south, while the presence of a deep trough or coastal low pressure system is the main strong wind mechanism in the north. In the central interior cold fronts tend to share their influence almost equally with other synoptic-scale mechanisms.

• 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.

• Steel and Composite Structures
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• v.52 no.4
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• pp.461-473
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• 2024

This study focuses on the reliability of a transmission line under wind excitation and evaluates the failure probability using explicit data resources. The data-driven framework for calculating the failure probability of a transmission line subjected to wind loading is presented, and a probabilistic method for estimating the yearly extreme wind speeds in each wind direction is provided to compensate for the incompleteness of meteorological data. Meteorological data from the Xuwen National Weather Station are used to analyze the distribution characteristics of wind speed and wind direction, fitted with the generalized extreme value distribution. Then, the most vulnerable tower is identified to obtain the fragility curves in all wind directions based on uncertainty analysis. Finally, the failure probabilities are calculated based on the presented method. The simulation results reveal that the failure probability of the employed tower increases over time and that the joint probability distribution of the wind speed and wind direction must be considered to avoid overestimating the failure probability. Additionally, the mixed wind climates (synoptic wind and typhoon) have great influence on the estimation of structural failure probability and should be considered.

• Wind and Structures
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• v.15 no.2
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• pp.111-129
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• 2012

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 sypnoptic events. Wind effects due to other phenomena, such as thunderstorm downbursts, are simply neglected. In this paper, results of recent and ongoing research on this topic in Brazil are presented. The model of the three-dimensional wind velocity field originated from a downburst in a thunderstorm (TS), proposed by Ponte and Riera for engineering applications, is first described. This model allows the generation of a spatially and temporally variable velocity field, which also includes a fluctuating component of the velocity. All parameters are related to meteorological variables, which are susceptible of statistical assessment. An application of the model in the simulation of the wind climate in a region sujected to both EPS and TS winds is discussed next. It is shown that, once the relevant meteorological variables are known, the simulation of the wind excitation for purposes of design of transmission lines, long-span crossings and similar structures is feasible. Complementing the theoretical studies, wind velocity records during a recent TS event in southern Brazil are presented and preliminary conclusions on the validity of the proposed models discussed.

• Wind and Structures
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• v.8 no.4
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• pp.269-281
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• 2005

The paper describes the work of the IAWE Working Group WGF - Extreme Wind Prediction and Zoning, one of the international codification working groups set up in 2000. The topics covered are: the international database of extreme winds, quality assurance and data quality, averaging times, return periods, probability distributions and fitting methods, mixed wind climates, directionality effects, the influence of orography, rare events and simulation methods, long-term climate change, and zoning and mapping. Recommendations are given to promote the future alignment of international codes and standards for wind loading.

• Fisheries and Aquatic Sciences
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• v.10 no.3
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• pp.150-158
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• 2007

Data on squid catches, water temperature, and climatic factors collected for the Northwest and subtropical North Pacific were analyzed to examine the influence of oceanic and climatic conditions in spawning grounds on catches of Japanese common squid, Todarodes pacificus, in the East (Japan) Sea. The main spawning ground was divided into four sub-areas: the South Sea of Korea (R1), the southern waters off Jeju, Korea (R2), the southwestern part of Kyushu, Japan (R3), and the northern part of Okinawa, Japan (R4). Interannual and decadal fluctuations in water temperatures correlated well with squid catches in the East/Japan Sea. In particular, water temperatures at a depth of 50 to 100 m in sub-areas R3 and R4 showed higher correlation coefficients (0.54 to 0.59, p<0.01) in relation to squid catches in the East/Japan Sea than for R1 and R2, which had correlation coefficients of 0.40 or less (p>0.05). Air temperature and wind velocity fluctuations in each sub-area are correlated with water temperature fluctuations and were closely connected with variations in the surface mixed layers. Water, air temperatures and wind velocities at the main spawning grounds are linked to the Southern Oscillation Index (SOI) with higher signals in the ca. 2-4-year band. Strong changes in a specific band and phase occurred around 1976/77 and 1986/87, coincident with changes in squid catches.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.183-183
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• 2017

Pan evaporation (Epan) is an important indicator of water and energy balance. Despite global warming, decreasing annual Epan has been reported across different continents over last decades, which is claimed as pan evaporation paradox. However, such trend is not necessarily found in seasonal data because the level of contributions on Epan vary among meteorological components. This study investigates long-term trend in seasonal pan evaporation from 1908 to 2016 across South Korea. Meteorological variables including air temperature (Tair), wind speed (U), vapor pressure deficit (VPD), and solar radiation (Rs) are selected to quantify the effects of individual contributing factor to Epan. We found overall decreasing trend in Epan, which agrees with earlier studies. However, mixed tendencies between seasons due to variation of dominant factor contributing Epan were found. We also evaluated the reference evapotranspiration based on Penman-Monteith method and compared this with Epan to better understand the physics behind the evaporation paradox.

• Proceedings of the KSRS Conference
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• v.1
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• pp.21-24
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• 2006

Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the NINO3 domain ($150-90^{\circ}W$, $5^{\circ}N-5^{\circ}S$) are studied using an ocean data assimilation product that covers the period of 1993 to 2003. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed mostly by Ekman current advecting large-scale temperature anomalies though the southern boundary of the domain. Unlike many previous studies, we explicitly evaluate the subsurface processes that consist of vertical mixing and entrainment. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to temporal change in ML depth is negligible comparing to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in wind-driven upwelling and temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Ni? cooling events. When the advective tendencies are evaluated by spatially averaging the conventional local advective tendencies of temperature, the apparent effects of currents with spatial scales smaller than the domain (such as TIWs) become very important as they redistribute heat within the NINO3 domain. However, such internal redistribution of heat does not represent external processes that control the domain-averaged MLT.

• Atmosphere
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• v.15 no.2
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• pp.75-90
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• 2005

This study examines the impacts of land cover changes on the East Asia summer monsoon with the National Center for Atmospheric Research Regional Climate Model (NCAR RegCM2), coupled with Biosphere Atmosphere Transfer Scheme (BATS). To assess the goals, two types of land cover maps were used in the simulation of summer climate. One type was NCAR land cover map (CTL) and the other was current land cover map derived from satellite data (land cover: LCV). Warm and cold surface temperature biases of $1-3^{\circ}C$ occurred over central China and Mongolia in CTL. The model produced excessive precipitation over northern land area but less over southern ocean of the model domain. Changes of biophysical parameters, such as albedo, minimum stomatal resistance and roughness length, due to the land cover changes resulted in the alteration of land-atmosphere interactions. Latent heat flux and wind speed in LCV increased noticeably over central China where deciduous broad leaf trees have been replaced by mixed farm and irrigated crop. As a result, the systematic warm biases over central China were greatly reduced in LCV. Strong cooling of central China decreased pressure gradient between East Asian continent and Pacific Ocean. The decreased pressure gradient suppressed the northward transport of moisture from south China and South China Sea. These changes reduced not only the excessive precipitation over north China and Mongolia but also less precipitation over south China. However, the land cover changes increased the precipitation over the Korean Peninsula and the Japan Islands, especially in July and August.

• Atmosphere
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• v.27 no.2
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• pp.225-233
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• 2017

Korea has recently suffered from severe hazes, largely being long-range transported from China but frequently mixed with domestic pollution. It is important to identify the origin of the frequently-occurring hazes, which is however hard to clearly determine in a quantitative term. In this regard, we suggest a possible classification procedure of various hazes into long-range transported haze (LH), Yellow Sand (YS), and urban haze (UH), based on mass loading of fine particles, time lag of PM mass concentrations between two sites aligned with dominant wind direction, backward trajectory of air mass, and the mass ratio of PM2.5 to PM10. The analysis sites are Seoul (SL) and Baengnyeongdo (BN), which are distant about 200 km from each other in the west to east direction. Aerosol concentrations at BN are overall lower than those of SL, indicative of BN being a background site for SL. We found distinct time lag of PM2.5 and PM10 concentrations between BN and SL in case of both LH and YS, but the intensity of YS being stronger than LH. Time scale (e-folding time scale) of LH appears to be longer and more variable than YS, which implies that LH covers much larger spatial scale. In addition, we found linear and significant correlations between ${\tau}_a$ obtained from sunphotometer and ${\tau}_{cal}$ calculated from surface aerosol scattering coefficient for LH episodes, relative to few correlation between those for YS, which might be associated with transported height of YS being much higher than LH. Therefore surface PM concentrations for the YS period are thought to be not representative for vertical integrated amount of aerosol loadings, probably by virtue of decoupled structure of aerosol vertical distribution. Improvement of various hazes classification based on the current result would provide the public as well as researchers with more accurate information of LH, UH, and YS, in terms of temporal scale, size, vertical distribution of aerosols, etc.