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Mean Wind Speed (mean + wind_speed)

Distribution by Scientific Domains

Earth and Environmental Science	70%

Selected Abstracts

Climate Variability in Regions of Amphibian Declines

CONSERVATION BIOLOGY, Issue 4 2001
Michael A. Alexander
The reanalysis system merges observations from airplanes, land stations, satellites, ships, and weather balloons with output from a weather-forecast model to create global fields of atmospheric variables. Station data consisted of temperature and precipitation measured with thermometers and rain gauges at fixed locations. Temperatures were near normal in Colorado when the amphibian declines occurred in the 1970s, whereas in Central America temperatures were warmer than normal, especially during the dry season. The station data from Puerto Rico and Australia indicated that temperatures were above normal during the period of amphibian declines, but reanalysis did not show such a clear temperature signal. Although declines occurred while the temperature and precipitation anomalies in some of the regions were large and of extended duration, the anomalies were not beyond the range of normal variability. Thus, unusual climate, as measured by regional estimates of temperature and precipitation, is unlikely to be the direct cause of amphibian declines, but it may have indirectly contributed to them. Previous researchers have noted that the declines appear to have propagated from northwest to southeast from Costa Rica to Panama and from southeast to northwest in Queensland, Australia. Wind has the potential to transport pathogens that cause amphibian mortality. The mean direction of the near-surface winds tended to parallel the path of amphibian declines from July,October in Central America and from May,July in Australia. The wind direction was highly variable, however, and the propagation rate of amphibian declines was much slower than the mean wind speed. In addition, the most likely pathogen is a chytrid fungus that does not produce desiccation-resistant spores. Thus, if wind is involved in the propagation of amphibian declines, it is through a complex set of processes. Resumen: Exploramos la relación entre las declinaciones de anfibios y las variaciones climáticas en Colorado, E.U.A., Puerto Rico, Costa Rica/Panamá y Queensland, Australia por medio de dos fuentes de información: resultados "sistema de reanálisis" del Centro Nacional de Predicción Ambiental y datos de estaciones área-promedio. El sistema de reanálisis combina observaciones de aeroplanos, estaciones terrestres, satélites, barcos y globos climatológicos, con resultados de un modelo de predicción climatológica para crear campos globales de variables atmosféricas. Los datos de estaciones fueron de temperatura y precipitación medidos con termómetros y pluviómetros en localidades fijas. Las temperaturas fueron casi normales en Colorado cuando ocurrieron las declinaciones en la década de 1970, mientras que las temperaturas en Centro América fueron mayores a lo normal, especialmente durante la época de sequía. Los datos de estaciones en Puerto Rico y Australia indicaron que la temperatura fue mayor a la normal durante el período de declinación de anfibios, pero un nuevo análisis no mostró una señal de temperatura tan clara. Aunque las declinaciones ocurrieron mientras las anomalías de temperatura y precipitación fueron grandes y de duración prolongada en algunas de las regiones, las anomalías no rebasaron el rango de variabilidad normal. Por lo tanto, es poco probable que el clima inusual, medido por estimaciones regionales de temperatura y precipitación, sea la causa directa de las declinaciones de anfibios, pero pudo haber contribuido indirectamente a ellas. Investigaciones previas notan que las declinaciones parecen haberse propagado de noroeste a sureste de Costa Rica a Panamá y de sureste a noreste en Queensland, Australia. El viento tiene el potencial de transportar patógenos que causan mortalidad de anfibios. La dirección promedio de los vientos superficiales tendió a ser paralela al camino de las declinaciones de anfibios de julio a octubre en Centro América y de mayo a julio en Australia. Sin embargo, la dirección del viento fue altamente variable y la tasa de propagación de declinaciones de anfibios fue mucho más lenta que la velocidad promedio del viento. Adicionalmente, el patógeno más probable es un hongo quítrido que no produce esporas resistentes a la desecación. Por tanto, si el viento está implicado en la propagación de declinaciones de anfibios, lo es por medio de un complejo conjunto de procesos. [source]

Time series analysis of wind speed with time-varying turbulence

ENVIRONMETRICS, Issue 2 2006
Bradley T. Ewing
Abstract The characterization of the time series properties of wind speed, in terms of the mean and variance, is important and relevant to both engineers and businesses. This research investigates the first and second moments of the Texas Tech WERFL wind speed data utilizing the ARMA-GARCH-in-mean framework. The methodology allows the conditional variance to depend on the size of past shocks (i.e. gusts) in the series. Results have important implications for wind energy production as well as for the operational and financial hedging strategies of companies exposed to wind-related risk. The findings can be summarized as follows: (i) mean wind speeds measured at different heights above ground exhibit persistence and are highly dependent on immediate past wind speed values; (ii) regardless of the height at which the data were collected, wind speed exhibits time-varying variance; (iii) persistence in conditional variance increases with height at which the data were collected; (iv) there is strong evidence that conditional volatility is positively correlated with mean wind speed while the magnitude of this relationship declines with height. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Species interaction and response to wind speed alter the impact of projected temperature change in a montane ecosystem

JOURNAL OF VEGETATION SCIENCE, Issue 4 2010
Dafydd Crabtree
Abstract Question: How does an improved understanding of species interactions, combined with an additional ecological variable (wind speed), alter the projected vegetation response to variation in altitudinal temperature? Location: Cairngorm Mountains, Scotland. Methods: Montane heathland vegetation was sampled from 144 plots (432 quadrats) comprising eight altitudinal transects. Ordination by partial DCA and path analysis was used to confirm: (1) the effect of wind speed and altitude (, temperature) on vegetation structure, i.e. canopy height and cover of bare ground, and (2) the control of arctic/alpine macrolichen occurrence by vegetation structure. Nested regression analysis was used to project the response of vegetation structure and lichen occurrence to temperature change scenarios with and without a step-wise change in future wind speed. Results: Warming trends shifted vegetation zones upwards, with a subsequent loss of suitable habitat for arctic/alpine lichens. However, incorporating wind speed as an additional explanatory variable had an important modifying effect on the vegetation response to temperature: decreasing wind speed exaggerates the effects of increased temperature and vice versa. Our models suggest that for the wind-driven heath examined, a 20% increase in mean wind speed may negate the effect of increased temperature on vegetation structure, resulting in no net change in lichen occurrence. Conclusions: We caution that an improved understanding of species interactions in vegetation response models may force the consideration of locally variable environmental parameters (e.g. wind speed), bringing into question the predicted vegetation response based on standard projections of temperature change along altitudinal gradients. [source]

Threshold wind velocity as an index of soil susceptibility to wind erosion under variable climatic conditions

LAND DEGRADATION AND DEVELOPMENT, Issue 1 2009
Laura A. de Oro
Abstract Wind erosion starts when the threshold wind velocity (µt) is exceeded. We evaluated the sensitivity of µt to determine the wind erosion susceptibility of soils under variable climatic conditions. Three years field data were used to calculate µt by means of the equation µt,=,, - , ,,1 (,), where , is the mean wind speed (m,s,1), , the , standard deviation (m,s,1), , the saltation activity and , the standard normal distribution function of ,. Saltation activity was measured with a piezoelectric sensor (Sensit). Results showed that , of the whole studied period (3·41 m,s,1) was lower than µt (7·53,m,s,1), therefore, wind erosion was produced mainly by wind gusts. The µt values ordered in the sequence: Winter (6·10 m,s,1),<,Spring (8·22,m,s,1),=,Summer (8·28,m,s,1),<,Autumn (26·48,m,s,1). Higher µt values were related to higher air humidity and lower wind speeds and temperatures. The µt values did not agree with the erosion amounts of each season, which ordered as follows: Summer (12·88,t ha,1),>,Spring (3·11,t ha,1),=,Winter (0·17,t ha,1),=,Autumn (no erosion). Low µt and erosion amounts of Winter were produced by a scarce number of gusts during eroding storms. We concluded that µt is useful as an index of soil susceptibility to wind erosion of different climatic periods. The use of a unique µt value in wind erosion prediction models can lead to erroneous wind erosion calculations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The influence of background wind direction on the roadside turbulent velocity field within a complex urban street

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 635 2008
R. J. Smalley
Abstract The turbulent velocity field within a complex urban street in the city of York, United Kingdom was measured over a one-month period, with data coverage over a wide range of background wind directions, ,ref (where ,ref = 0° is relative to the street axis, and angles increasing clockwise). Within the street, a persistent mean-flow cross-street circulation exists for 15° ,,ref < 165° in addition to possible flow convergence for 240° ,,ref < 300° . The magnitude of the in-street normalised turbulent kinetic energy (TKE) is dependent on the type of predominant in-street mean-flow structures. During conditions that correspond to mean-flow cross-street circulation, the TKE is approximately twice the magnitude on the windward side compared with the leeward side. For nearly all wind directions, and on both sides of the street, the TKE is approximately constant with height for 0.4 < z/H < 0.8. There is evidence that the in-street TKE increases with background TKE when other meteorological influences are relatively constant. For background wind directions free from mean flow convergence, the least variability in the sector-averaged turbulence data occurs when the TKE is normalised by the in-street mean wind speed, rather than the background wind speed. The two-point cross-correlation of the vertical-velocity component fluctuations on the windward side is at least 0.6 between the mid and upper anemometers. The two-point cross-correlation between cross-street (same height) vertical-velocity component fluctuations is negative and non-negligible during mean-flow circulation, which indicates possible cross-street coherence in the turbulent velocity field. The turbulent Reynolds stress anisotropy tensor, which provides an indication of the level of TKE redistribution between the components, and the overall level of turbulence anisotropy, is discussed with reference to the mean-flow structures within the street. Copyright © 2008 Royal Meteorological Society [source]

Air,sea exchanges in the equatorial area from the EQUALANT99 dataset: Bulk parametrizations of turbulent fluxes corrected for airflow distortion

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 610 2005
A. Brut
Abstract Turbulent fluxes of momentum, sensible heat and water vapour were calculated using both the eddy covariance (EC) and the inertial dissipation (ID) methods applied to data collected on board the research vessel La Thalassa during 40 days of the EQUALANT99 oceanographic campaign. The aim of this experiment was to establish accurate parametrizations of air,sea fluxes for the equatorial Atlantic area from a large dataset. However, the accuracy of turbulent fluxes measured aboard ships is strongly affected by the distortion of airflow patterns generated by obstacles such as the ship and mast. For the EQUALANT99 experiment, the effects of airflow distortion were estimated using physical simulations in a water channel. To reproduce the conditions of the campaign, a neutral boundary layer was simulated in the water channel and a detailed model of the ship La Thalassa was built. Correction coefficients for the mean wind speed were evaluated from these physical simulations. They show a dependence on both the azimuth angle of the flow (i.e. the horizontal direction of the flow with respect to the ship's longitudinal axis) and the angle of incidence of the wind. The correction for airflow distortion was applied to the measured wind speed and also included in the flux computation using the ID method. Compared with earlier studies which applied a single correction per flux sample, it appears that our results for the corrected transfer coefficients present greater dependence on neutral wind speed than the previous parametrizations; the method also shows encouraging results, with a decrease in the scatter of the transfer coefficients parametrization. However, the distortion could not be corrected for in the fluxes calculated using the EC method, because this technique integrates a wide range of turbulence scales for which the airflow distortion cannot be simulated in a water channel. Fluxes computed using the ID and EC methods are presented and compared in order to determine which method, in the configuration of the EQUALANT99 experiment, provides the best resulting transfer coefficients. According to the results, fluxes of momentum and latent heat computed by ID were better for deriving the drag and humidity coefficients. The EC method seemed better adapted to calculate sensible-heat fluxes than the ID method, although a high scatter remained on the Stanton neutral number. Copyright © 2005 Royal Meteorological Society [source]

Time series analysis of wind speed with time-varying turbulence

The surface winds of Sweden during 1999,2000

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2006
Christine Achberger
Abstract This study aims at increasing our understanding of the regional wind climate in Sweden. Spatial and temporal patterns of the surface winds are presented for the years 1999,2000. Annual mean wind speeds range between 2 and 5 m/s with high values at exposed mountainous sites and on islands off the coast. Combining wind speed and direction into mean wind velocities shows that flow conditions are stronger and more coherent in space in southern Sweden than in central and northern Sweden. The spatial scale, defined as the distance between stations when the correlation for wind speed drops to ,0.37, was determined by pairwise correlations between all possible station pairs. Scales range from 38 to 530 km for wind speed and from 40 to 830 km for wind direction depending on the region. They tend to be smaller in central and northern Sweden, where the more pronounced relief has a larger influence on the local wind conditions. The strength and the timing of the annual and diurnal wind speed cycle have been estimated for each station. Amplitudes of the annual cycle are greater at exposed sites and correlate generally well with annual mean wind speeds. Monthly mean wind speeds peak in winter in southern Sweden, but peak in other seasons in the remaining regions. In winter, weaker pressure gradients over northern Sweden and surface-near temperature inversions contribute to weaker surface winds. Diurnal cycles vary in strength between summer and winter. Compared to the last normal climate period (1961,1990), 1999,2000 is characterized by the increased occurrence of westerly and southerly geostrophic flow. Copyright © 2005 Royal Meteorological Society. [source]

Antarctic climate change during the last 50 years

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2005
John Turner
Abstract An erratum has been published for this article in International Journal of Climatology 25 (8) 2005, 1147,1148. The Reference Antarctic Data for Environmental Research (READER) project data set of monthly mean Antarctic near-surface temperature, mean sea-level pressure (MSLP) and wind speed has been used to investigate trends in these quantities over the last 50 years for 19 stations with long records. Eleven of these had warming trends and seven had cooling trends in their annual data (one station had too little data to allow an annual trend to be computed), indicating the spatial complexity of change that has occurred across the Antarctic in recent decades. The Antarctic Peninsula has experienced a major warming over the last 50 years, with temperatures at Faraday/Vernadsky station having increased at a rate of 0.56 °C decade,1 over the year and 1.09 °C decade,1 during the winter; both figures are statistically significant at less than the 5% level. Overlapping 30 year trends of annual mean temperatures indicate that, at all but two of the 10 coastal stations for which trends could be computed back to 1961, the warming trend was greater (or the cooling trend less) during the 1961,90 period compared with 1971,2000. All the continental stations for which MSLP data were available show negative trends in the annual mean pressures over the full length of their records, which we attribute to the trend in recent decades towards the Southern Hemisphere annular mode (SAM) being in its high-index state. Except for Halley, where the trends are constant, the MSLP trends for all stations on the Antarctic continent for 1971,2000 were more negative than for 1961,90. All but two of the coastal stations have recorded increasing mean wind speeds over recent decades, which is also consistent with the change in the nature of the SAM. Copyright © 2005 Royal Meteorological Society [source]

Long-term trends in near-surface flow over the Baltic

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2003
S. C. Pryor
Abstract We report an analysis of trends in 850 hPa wind speed, as manifest in the NCEP,NCAR reanalysis fields, over the Baltic region during the latter half of the 20th century. The results indicate that annual mean wind speeds over the Baltic significantly increased over the period 1953,99 with the majority of the increase being associated with increases in the upper quartile of the wind speed distribution. Accordingly, much of the change is focused on the winter season. The trends in annual and seasonal mean wind speeds are greatest in relative and absolute sense in the southwest of the Baltic basin, where they are in excess of 0.25 m s,1 per decade for the annual mean. The extremes of the wind-speed distribution also increased by up to 5 m s,1 over the study period for the wind speed with a 50 year return period, again with the largest magnitude changes in the southwestern Baltic. These changes in wind speed are strongly linked to changes in the synoptic-scale circulation. The majority of the increase in wintertime wind speeds is attributable to an increase in westerly anticyclonic, westerly cyclonic and northwesterly cyclonic circulation types as manifest in the Grosswetterlagen catalogue, which are in turn related to the recent prevalence of the positive phase of the North Atlantic oscillation. Copyright © 2003 Royal Meteorological Society [source]