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High Wind Speeds (high + wind_speed)
Selected AbstractsWind speed measurements and forest damage in Canton Zurich (Central Europe) from 1891 to winter 2007INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2010Tilo Usbeck Abstract The most severe damage to forests in central Europe occurs during winter storms that are caused by Northern Hemispheric mid-latitude cyclones. These winter storms have caused several catastrophic windthrows during the past four decades. Amounts of forest storm damage are believed to be a function of both the size of the forest and the storm intensity. To test this hypothesis, the Zurich region (city and canton) was chosen because long-term climate observation data is available for the region. The relationships between forest attributes, wind speed and forest damage were explored by comparing data on forests and wind speed from 107 winters with forest damage. Storm damage was defined as the proportion of damaged forests with respect to the growing stock. The variables: daily wind run (91 years), daily maximum hourly average wind speed (107 years) and peak gust wind speed (74 years) were homogenized with respect to high wind speed and related to levels of forest damage. High maximum wind speed at the end of the 19th century and at the beginning of the 20th century was followed by low maximum wind speed in the 1940s, 1960s and 1970s. Since then, maximum values have increased. Gusts (extremes of the maximum wind speed) increased from the beginning of the recordings in 1933 and peaked in the early 1990s. Forest damage due to winter storms is best correlated with peak wind speed. Gusts exceeding 40 m/s and resulting in catastrophic windthrow have increased in recent winters. Copyright © 2009 Royal Meteorological Society [source] Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditionsPLANT PATHOLOGY, Issue 5 2003L. Y. Chen This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage (Brassica pekinensis). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r2 of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants. [source] Measurement and data analysis methods for field-scale wind erosion studies and model validation,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2003Ted M. Zobeck Abstract Accurate and reliable methods of measuring windblown sediment are needed to con,rm, validate, and improve erosion models, assess the intensity of aeolian processes and related damage, determine the source of pollutants, and for other applications. This paper outlines important principles to consider in conducting ,eld-scale wind erosion studies and proposes strategies of ,eld data collection for use in model validation and development. Detailed discussions include consideration of ,eld characteristics, sediment sampling, and meteorological stations. The ,eld shape used in ,eld-scale wind erosion research is generally a matter of preference and in many studies may not have practical signi,cance. Maintaining a clear non-erodible boundary is necessary to accurately determine erosion fetch distance. A ,eld length of about 300 m may be needed in many situations to approach transport capacity for saltation ,ux in bare agricultural ,elds. Field surface conditions affect the wind pro,le and other processes such as sediment emission, transport, and deposition and soil erodibility. Knowledge of the temporal variation in surface conditions is necessary to understand aeolian processes. Temporal soil properties that impact aeolian processes include surface roughness, dry aggregate size distribution, dry aggregate stability, and crust characteristics. Use of a portable 2 tall anemometer tower should be considered to quantify variability of friction velocity and aerodynamic roughness caused by surface conditions in ,eld-scale studies. The types of samplers used for sampling aeolian sediment will vary depending upon the type of sediment to be measured. The Big Spring Number Eight (BSNE) and Modi,ed Wilson and Cooke (MWAC) samplers appear to be the most popular for ,eld studies of saltation. Suspension ,ux may be measured with commercially available instruments after modi,cations are made to ensure isokinetic conditions at high wind speeds. Meteorological measurements should include wind speed and direction, air temperature, solar radiation, relative humidity, rain amount, soil temperature and moisture. Careful consideration of the climatic, sediment, and soil surface characteristics observed in future ,eld-scale wind erosion studies will ensure maximum use of the data collected. Copyright © 2003 John Wiley & Sons, Ltd. [source] The impact of non-stationarities in the climate system on the definition of ,a normal wind year': a case study from the BalticINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005S. C. Pryor Abstract Wind speeds over the Baltic significantly increased over the second half of the 20th century (C20th), with the majority of the increase being focused on the upper quartile of the wind speed distribution and in the southwest of the region. These changes have potentially profound implications for the wind energy resource. For example, based on the National Centers for Environmental Prediction,National Center for Atmospheric Research (NCEP,NCAR) reanalysis data it is shown that, owing to this non-stationarity, using the normalization period of 1987,98 to determine the wind resource (as in the Danish wind index) leads to overestimation of the wind energy index (and hence the wind energy resource) in western Denmark relative to 1958,2001 by approximately 10%. To address whether the increased prevalence of high wind speeds at the end of the C20th will be maintained in the future, we provide a first prognosis of annual wind indices from the HadCM3 coupled atmosphere,ocean general circulation model. The results suggest the 21st century (C21st) will be similar to the 1958,2001 period with respect to the wind energy density, but that the northeastern Baltic will exhibit slightly higher wind energy indices over the course of the C21st relative to the latter half of the C20th, whereas the southwest of the Baltic exhibits some evidence of declining wind indices towards the end of the C21st. These changes may indicate a tendency in HadCM3 towards more northerly tracking of mid-latitude cyclones in the future, possibly due to evolution of the North Atlantic oscillation. As a caveat to this finding, it should be noted that the NCEP,NCAR and European Centre for Medium-Range Weather Forecasts reanalysis data sets and HadCM3 simulations, although exhibiting commonalities during the period of overlap, differ quantitatively in terms of the spatial fields and empirical cumulative probability distributions at individual grid cells. Copyright © 2005 Royal Meteorological Society [source] Effects of canopy heterogeneity, seed abscission and inertia on wind-driven dispersal kernels of tree seedsJOURNAL OF ECOLOGY, Issue 4 2008Gil Bohrer Summary 1Understanding seed dispersal by wind and, in particular, long-distance dispersal (LDD) is needed for management of plant populations and communities, especially in response to changes in climate, land use and natural habitats. Numerical models designed to explore complex, nonlinear atmospheric processes are essential tools for understanding the fundamental mechanisms involved in seed dispersal. Yet, thus far, nearly all such models have not explicitly accounted for the spatial heterogeneity that is a typical feature of all ecosystems. 2The recently developed Regional Atmospheric Modelling System (RAMS)-based Forest Large Eddy Simulation (RAFLES) is used here to explore how within-stand canopy heterogeneity impacts LDD. RAFLES resolves microscale canopy heterogeneity such as small gaps and variable tree heights, and it simulates their impacts on turbulence inside and above the canopy in the atmospheric boundary layer (ABL). For that purpose, an Eulerian,Lagrangian module of seed dispersal is added to RAFLES to simulate seed trajectories. 3Particular attention is paid to the sensitivity of statistical attributes of the dispersal kernels (i.e. mean, mode, variance, tail) to key simplifications common to all seed dispersal models, such as horizontal homogeneity in the canopy and flow field, and the tight coupling between air parcel trajectories and seed trajectories (i.e. neglecting seed inertia). These attributes appear to be sensitive to various factors operating at scales ranging from the seed scale to the ABL scale. 4Simulations with RAFLES show that LDD is characterized by a dispersal kernel with a ,tail', asymptotically approaching a power law decay of ,3/2 (mainly occurring for lighter seeds at high wind speeds). This is consistent with asymptotic predictions from analytical models. The wind speed threshold at which seed abscission occurs, set-up to be twice the standard deviation of the vertical wind speed, is shown to affect short-distance dispersal, but has no significant impact on LDD. Ignoring the effects of seed inertia on the seed trajectory calculations has a minor effect on short-distance dispersal and no effect on the probability of seed uplift. Thus, it has no significant impact on LDD. 5Synthesis. Tree-scale canopy heterogeneity affects the turbulence characteristics inside and above the canopy and, consequently, this affects dispersal kernel statistics. A key finding from this study is that ejection is enhanced above the shorter trees of the canopy. Seeds dispersed above shorter trees have a higher probability of experiencing LDD while their short-distance dispersal remains practically the same. At inter-annual time scales, such interactions could affect species composition. [source] | |||||||||||||