The present paper is a radar analysis on the mesoscale convective system (MCS), which evolved as a straight line wind across western Romania in the afternoon of the September17th. This convective ...storm has developed in a SV-NE oriented baro-cline area, extending from the Italian Peninsula, over Serbia, Hungary, Poland and Ukraine. The temperature gradient was over 15 degrees, and the tropospheric jet was parallel to this baro-cline. Large wind velocities were present throughout the troposphere column, which means that the shear force had high values throughout the tropospheric column, but concentrated to 500 hPa (approximately 5500 m) and in the low layers below 700 hPa (approximately 3000 m), saturation deficit was high on the western border of Romania. All these elements initiated and organized the thermo-dynamic convection towards a severe structure. The storm was initiated by the strong descending of the convective meso-scale system that evolved over the northwest of the Balkan Peninsula (Croatia and Bosnia).
The heat-driven plain–plateau circulation producing strong summertime winds in Yerevan has been examined. The study indicates that the formation of plain–plateau circulation over the Armenian ...Highland is the combined product of large-scale and local circulations. There is significant enhancement of the westerly subtropical jet over the study region, Caspian Sea and further to the east in the upper troposphere in days with severe wind gusts in Yerevan. Further, the influence of major monsoon systems (Indian and African) on the plain–plateau circulation over the Armenian Highland is considered in this study. Both observations and ERA-Interim reanalysis data show the existence of intense heat source over the southeastern and southern parts of the Armenian Highland which produces an extra daytime warming exceeding 2.1 °C on average at the ground surface during days with severe gusts in Yerevan. This warm center is maintained through 700 hPa level and it disappears in the middle and upper troposphere. The plateau atmospheric boundary layer can extend beyond 4,000 m above mean sea level (up to the middle troposphere) during the afternoon. By contrast, exposed mountain ranges stretching along the Black and Caspian seas are characterized by significant negative temperature differences. It should be noted that ERA-Interim reanalysis data strongly underestimate the significant negative differences in mean daytime temperatures over northeastern, southeastern parts of Armenia and over Sevan Lake basin found in observed data. The results suggest intensification of the plain–plateau circulation over the Armenian Highland induced by recent surface warming over the study region. Temperature projections over the study region for the twenty-first century show that the enhancement of the plain–plateau circulation can be expected under future climate conditions.
Increasing land use intensity in the Xilingol Steppe has changed a former dust deposition area into a vulnerable area against wind erosion. Overgrazing caused large-scale soil degradation and ...destruction. The use as cropping land affects only a small area, but especially these parts of the steppe are extremely endangered. Strong winds, bare soil surface and high soil erodibility caused extreme wind erosion in April and May 2006 on a 147 ha fallow cropping field. The size and thickness of the deposited material in a sediment fan was measured to calculate the volume and the mass of the relocated material. The average thickness, the total size and the volume of the sediment fan were 11 mm, 257 ha and 27,600 m super(3), respectively. Comparison of the grain size distributions of soil and sediment material showed that up to 45,900 m super(3) of surface soil material were moved by wind and up to 18,300 m super(3), largely of the clay and silt fractions, were removed by dust emission. The average erosion rate from the cropped field was between 323 and 340 t ha super(-1), which was equivalent to 30 mm of the upper soil surface. The average dust production at the field amounted up to 136 t ha super(-1). Croplands are thought to contribute considerably to the total dust production and soil degradation in the temperate grasslands of Inner Mongolia. The sediment fan consisted predominantly of sand. This accumulation of coarse particles at the surface of the cropping and grassland locally degraded soil quality.
We examined fine litterfall fluctuations on a seasonal and annual scale for 14 years (1992-2005) in a 1.2-ha plot in an old-growth lucidophyllous (evergreen broad-leaved) forest within the Aya ...Research Site, southwestern Japan. The average total litterfall input was 6.32 Mg ha⁻¹, of which leaf litter accounted for 60% of the total. Two high-impact typhoons struck the study area in 1993 (T9313) and 2004 (T0416) during the observation period; however, the subsequent pattern of litterfall after disturbance was different between the two typhoons. T9313 disturbance caused a reduction of biomass (ca. 10% of basal area (BA)) and a sharp decrease in litterfall input following a massive input in 1993. On the other hand, T0416 caused a minor decline in litterfall input, accompanied by a relatively small reduction of BA (5.2% of the 2001 BA). In spite of large fluctuations, litterfall input increased year by year after the T9313 disturbance. In 2000, 7 years after T9313, leaf input showed no significant differences and recorded more than 90% of pre-T9313 levels. Re-leafing from typhoon survivors may play an important role in the recovery of litterfall input in this forest. This study demonstrated how one high-impact typhoon can alter the temporal fluctuations in fine litterfall in lucidophyllous forest ecosystems.
A brief overview of severe wind/hail storms over Bulgaria in the last 5 years (1997–2001) is presented. Synoptic and thermodynamic analyses of 27 cases during 1999–2001 (April–September) were ...performed. Among others, two events during this period produced extremely damaging winds. The first of them was associated with a tornado close to the Mediterranean coast on 15 May 1999 and has been already described in the literature.
This paper illustrates the role of synoptic scale factors for generation of a second severe windstorm (that occurred near the Bulgarian capital Sofia on 22 May 2001) by using numerical model analysis fields. On the large scale, the circulation pattern was associated with a deformation middle-tropospheric field over the North Atlantic, Western Europe and Mediterranean. A zone of convergence in temperature and mass fields was formed over the Balkans, where there was an interleaving of warm, moist Mediterranean air advected in association with a warm front and cold dry air coming from the northwest in the eastern flank of an upper-level ridge. This synoptic circulation pattern produced deep convection along the boundary between the polar and subtropical high-level frontal systems. It is shown that synoptic- and meso-scale elements of the development may be revealed or confirmed by radiosounding data as well as by satellite and radar imagery. Data from the upper-air sounding of Sofia at 1200 UTC (available up to 650 hPa level) and other proximity soundings were processed and analysed. The obtained results show very high values of atmospheric instability indices (the energy of instability
E
i=3785 J/kg, TT=59 °C,
Z
(ULC)=12.6 km). The updraft was up to 21.9 m/s and the difference of the wind velocity between 300- and 700-hPa levels was up to 12 m/s. Cloud water content reached up to 12.9 g/kg.
Stably stratified flows past a two-dimensional hill in a channel of finite depth are analyzed numerically by using a Direct Numerical Simulation (DNS) with a third-order upwind difference scheme at ...Re=2000. To simulate the flow around the hill with high accuracy, a collocated grid in curvilinear coordinates is employed. Attention is focused on the occurrence of local severe winds which are induced downstream of the hill. A strong wind area with a wind speed greater than 1.29-2.21, which represents a ratio of the local streamwise wind speed to the uniform approaching one of U=1 in the non-dimensional unit, is caused by the downward flow in.the lee wave motion and is located near the first trough behind the hill. A few factors which have an effect on the generation of local severe winds are also discussed.
Resumo Para estimar a magnitude e frequência dos vendavais no Paraná foram analisadas as rajadas de 26 estações meteorológicas. Integrou-se os procedimentos de identificação de regiões homogêneas, ...utilizando o método dos componentes principais, e de análise de frequência regional, pois as séries disponíveis são muito curtas para aplicação dos métodos convencionais. Diagnosticou-se cinco regiões homogêneas: Litoral, Centro, Meio-Oeste, Oeste e Norte. Esses resultados produziram coerência geográfica, pois as estações agrupadas são vizinhas entre si e estão em locais com relevo e continentalidade semelhantes. A distribuição mais adequada para a análise de frequência regional foi a de Wakeby, cujos quantis regionais estimados exibiram elevada coerência com as diferenças espaciais diagnosticadas na estatística descritiva. Para o tempo de recorrência de 50 anos a região composta pelas estações de Cascavel e Toledo apresentou os ventos mais severos, com velocidades de 41,9 e 44,8 ms-1, respectivamente. As demais regiões produziram ventos de 35,3 a 39,7 ms-1 no Oeste, 28,8 a 38,2 ms-1 na região Central, 26,4 a 36,6 ms-1 no Norte e 21,4 a 30,6 ms-1 no Litoral. Os resultados obtidos são inovadores pois se estimaram probabilidades de ocorrências de ventos extremos usando séries de observações muito curtas, embora de boa qualidade e resolução temporal.
Abstract Gusts from 26 meteorological stations at Paraná (Brazil) were analyzed to estimate their magnitude and frequency. This analysis integrated the homogeneous regions identification, using the principal components analysis, and regional frequency analysis, since the available dataset were too short to apply conventional methods. Similar data patterns were identified in five regions: Coast, Central, Mid-West, West and North. This results were geographical consistent, because the stations are at contiguous sites and located at regions with similar characteristics of relief and coast distance. The Wakeby distribution was selected as the most adequate for the regional frequency analysis. The regional quantiles estimated by the adjusted distribution were coherent with the spatial differences verified in the descriptive statistic. For a given return period of 50 years, the region composed by Cascavel and Toledo stations showed the most severe winds, with 41,9 and 44,8 ms-1, respectively. In the West winds vary from 35,3 to 39,7 ms-1, in the Central from 28,8 to 38,2 ms-1, in the North from 26,4 to 36,6 ms-1 and in the Coast from 21,4 to 30,6 ms-1. The results of this study are innovator since the wind probabilities were estimated using a short dataset, however with good quality and temporal resolution.
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