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Heavy Precipitation (heavy + precipitation)
Selected AbstractsDifferent methods for modelling the areal infiltration of a grass field under heavy precipitationHYDROLOGICAL PROCESSES, Issue 7 2002Bruno Merz Abstract The areal infiltration behaviour of a grass field is studied using a data set of 78 sprinkler infiltration experiments. The analysis of the experimental data shows a distinct event dependency: once runoff begins, the final infiltration rate increases with increasing rainfall intensity. This behaviour is attributed to the effects of small-scale variability. Increasing rainfall intensity increases the ponded area and therefore the portion of the plot which infiltrates at maximum rate. To describe the areal infiltration behaviour of the grass field the study uses two different model structures and investigates different approaches for consideration of subgrid variability. It is found that the effective parameter approach is not suited for this purpose. A good representation of the observed behaviour is obtained by using a distribution function approach or a parameterization approach. However, it is not clear how the parameters can be derived for these two approaches without a large measurement campaign. The data analysis and the simulations show the great importance of considering the effects of spatial variability for the infiltration process. This may be significant even at a small scale for a comparatively homogeneous area. The consideration of heterogeneity seems to be more important than the choice of the model type. Furthermore, similar results may be obtained with different modelling approaches. Even the relatively detailed data set does not seem to permit a clear model choice. In view of these results it is questionable to use very complex and detailed simulation models given the approximate nature of the problem. Although the principle processes may be well understood there is a lack of models that represent these processes and, more importantly, there is a lack of techniques to measure and parameterize them. Copyright © 2002 John Wiley & Sons, Ltd. [source] The annual cycle of heavy precipitation across the United Kingdom: a model based on extreme value statisticsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2009D. Maraun Abstract The annual cycle of extreme 1-day precipitation events across the UK is investigated by developing a statistical model and fitting it to data from 689 rain gauges. A generalized extreme-value distribution (GEV) is fit to the time series of monthly maxima, across all months of the year simultaneously, by approximating the annual cycles of the location and scale parameters by harmonic functions, while keeping the shape parameter constant throughout the year. We average the shape parameter of neighbouring rain gauges to decrease parameter uncertainties, and also interpolate values of all model parameters to give complete coverage of the UK. The model reveals distinct spatial patterns for the estimated parameters. The annual mean of the location and scale parameter is highly correlated with orography. The annual cycle of the location parameter is strong in the northwest UK (peaking in late autumn or winter) and in East Anglia (where it peaks in late summer), and low in the Midlands. The annual cycle of the scale parameter exhibits a similar pattern with strongest amplitudes in East Anglia. The spatial patterns of the annual cycle phase suggest that they are linked to the dominance of frontal precipitation for generating extreme precipitation in the west and convective precipitation in the southeast of the UK. The shape parameter shows a gradient from positive values in the east to negative values in some areas of the west. We also estimate 10-year and 100-year return levels at each rain gauge, and interpolated across the UK. Copyright © 2008 Royal Meteorological Society [source] Episodes of alpine heavy precipitation with an overlying elongated stratospheric intrusion: a climatologyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2006Olivia Martius Abstract This study discusses the role of stratospheric intrusions (determined as potential vorticity (PV) streamers) as upper-level instigators of heavy precipitation along the Swiss Alpine south side (AS) on a climatological timescale. A climatology of streamers is used compiled on the basis of the ECMWF 40-year re-analysis data set (ERA-40). Days of extreme and heavy precipitation along the Swiss AS are determined from an existing observational Alpine precipitation climatology. For these days, the presence of streamers over western Europe as well as their location and orientation is recorded. On 73% of the extreme precipitation days, a streamer is situated over western Europe. The mean spatial frequency distribution of the streamers on the extreme precipitation days exhibits a structure that resembles in its form and location the ,archetypal heavy precipitation streamer' known from case studies. The frequency maximum is situated over southern England and the west coast of France. The same analysis is applied to three sub-domains (Valais, Grisons, Ticino) along the Swiss AS. Significant differences in the location and the orientation of the streamers for the sub-domains are found. The majority of streamers associated with heavy rain in the western-most sub-domain (Valais) are oriented in a cyclonically-sheared fashion, while for the Ticino the streamers are more anti-cyclonically orientated. Differences for events of increasing severity are analysed by comparing the form, location, amplitude (PV), and persistence of the streamers on extreme and heavy precipitation days. The precipitation distribution is shifted to higher intensities for more persistent streamers. There is no detectable difference found in the form parameters, but the southerly moisture flux into the domain is significantly larger during extreme precipitation days than during heavy precipitation days. Likewise, the seasonal variation in the percentage of streamer-related heavy precipitation, which is highest in autumn (85%), can be related to the seasonal variation of southerly moisture fluxes. Copyright © 2006 Royal Meteorological Society. [source] Diagnostic study of generalized moist potential vorticity in a non-uniformly saturated atmosphere with heavy precipitationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 650 2010Zhaoming Liang Abstract A Meiyu front accompanied by a band of heavy precipitation in East Asia is typically characterized by a much larger moisture gradient than temperature gradient. Many previous studies have suggested use of equivalent potential temperature as a thermodynamic variable under this circumstance. However, dynamic variables coupled with such a thermodynamic variable, e.g. a derived moist potential vorticity (MPV) based on equivalent potential temperature, does not provide useful dynamic insight into these systems. In this study, generalized moist potential vorticity (GMPV) is derived based on a generalized form of potential temperature. Diagnoses of numerical simulations for three typical Meiyu rainfall events show that GMPV provides remarkably accurate tracking of rainfall location, suggesting its potential use as a dynamic tracer for heavy rainfall events such as Meiyu rain bands. Copyright © 2010 Royal Meteorological Society [source] Modification of sediment characteristics during glacial transport in high-alpine catchments: Mount Cook area, New ZealandBOREAS, Issue 4 2004MICHAEL J. HAMBREY The Mount Cook area in the Southern Alps of New Zealand is heavily glacierized with numerous peaks over 3000 m a.s.l. feeding several large valley glaciers. The region is subject to rapid tectonic uplift and heavy precipitation (up to 15 m per year). This paper describes the clast roundness, clast shape and textural characteristics associated with five glaciers (Fox, Franz Josef, Hooker, Mueller and Tasman) in terms of inputs to the glacier system, transport by the glaciers and reworking following glacial deposition. Inputs include rockfall, alluvial fan and avalanche material delivered to the surface of valley glaciers. Basal debris, where observed at the terminus of two glaciers, consists mainly of incorporated fluvial material. Following deposition, reworking is mainly by subglacial and proglacial streams. The dominant facies are (i) boulder gravel with mainly angular clasts on the steep slopes above the glaciers, (ii) sandy boulder gravel, with mainly angular and subangular clasts, forming lateral and end moraines, and (iii) sandy boulder/cobble gravel with mainly subrounded clasts, and sand, which represent glacially transported sediment reworked by braided rivers. Diamicton is rare in the contemporary glacial environment. Since most sediment associated with glaciers in the Southern Alps lacks unambiguous indications of glacial transport, interpretation of similar sediments in the geological record should not necessarily exclude the involvement of glacial processes. [source] Structure Elucidation and Phytotoxicity of Ecdysteroids from Chenopodium albumCHEMISTRY & BIODIVERSITY, Issue 4 2005Marina DellaGreca The leaves of Chenopodium album were infused in H2O/MeOH. The extract treated with cold acetone gave heavy precipitation, which was removed by centrifugation. Solid material was fractionated into acidic and neutral fractions. The acidic material was subjected to different silica-gel column chromatographies, and then it was purified by reversed-phase HPLC to afford four known ecdysteroids and the new 3,,14, -dihydroxy-5, -pregn-7-ene-2,6,20-trione that were characterized by extensive spectroscopic investigation, especially by 1D- and 2D-NMR. Their effects on germination and growth of Lactuca sativa L. have been studied. The results are reported as percentage differences of germination, root elongation and shoot elongation, from the control at concentrations ranging from 10,4 to 10,7,M. [source] | ||||||||||