This paper presents the first multi-model ensemble of 10-year, “convection-permitting” kilometer-scale regional climate model (RCM) scenario simulations downscaled from selected CMIP5 GCM projections for historical and end of century time slices. The technique is to first downscale the CMIP5 GCM projections to an intermediate 12–15 km resolution grid using RCMs, and then use these fields to downscale further to the kilometer scale. The aim of the paper is to provide an overview of the representation of the precipitation characteristics and their projected changes over the greater Alpine domain within a Coordinated Regional Climate Downscaling Experiment Flagship Pilot Study and the European Climate Prediction system project, tasked with investigating convective processes at the kilometer scale. An ensemble of 12 simulations performed by different research groups around Europe is analyzed. The simulations are evaluated through comparison with high resolution observations while the complementary ensemble of 12 km resolution driving models is used as a benchmark to evaluate the added value of the convection-permitting ensemble. The results show that the kilometer-scale ensemble is able to improve the representation of fine scale details of mean daily, wet-day/hour frequency, wet-day/hour intensity and heavy precipitation on a seasonal scale, reducing uncertainty over some regions. It also improves the representation of the summer diurnal cycle, showing more realistic onset and peak of convection. The kilometer-scale ensemble refines and enhances the projected patterns of change from the coarser resolution simulations and even modifies the sign of the precipitation intensity change and heavy precipitation over some regions. The convection permitting simulations also show larger changes for all indices over the diurnal cycle, also suggesting a change in the duration of convection over some regions. A larger positive change of frequency of heavy to severe precipitation is found. The results are encouraging towards the use of convection-permitting model ensembles to produce robust assessments of the local impacts of future climate change.
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Large sudden wind-direction shifts and submeso variability under nocturnal conditions are examined using a micrometeorological network of stations in north-western Victoria, Australia. The network was located in an area with mostly homogeneous and flat terrain. We have investigated the main characteristics of the horizontal propagation of events causing the wind-direction shift and not addressed in previous studies. The submeso motions at the study site exhibit behaviour typical of flat terrain, such as the lower relative mesovelocity scale and smaller cross-wind variances than that for complex terrain. The distribution of wind-direction shifts shows that there is a small but persistent preference for counter-clockwise rotation, occurring for 55% of the time. Large wind-direction shifts tend to be associated with a sharp decrease in air temperature (74% of the time), which is associated with rising motion of cold air, followed by an increase in turbulent mixing. The horizontal propagation of events was analyzed using the cross-correlation function method. There is no preferred mean wind direction associated with the events nor is there any relationship between the mean wind and propagation directions. The latter indicates that the events are most likely not local flow perturbations advected by the mean flow but are rather features of generally unknown origin. This needs to be taken into account when developing parametrizations of the stable boundary layer in numerical models. 相似文献
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Efficient testing of earthquake forecasting models 总被引：1，自引：0，他引：1
David A. Rhoades Danijel Schorlemmer Matthew C. Gerstenberger Annemarie Christophersen J. Douglas Zechar Masajiro Imoto 《Acta Geophysica》2011,59(4):728-747
Computationally efficient alternatives are proposed to the likelihood-based tests employed by the Collaboratory for the Study
of Earthquake Predictability for assessing the performance of earthquake likelihood models in the earthquake forecast testing
centers. For the conditional L-test, which tests the consistency of the earthquake catalogue with a model, an exact test using convolutions of distributions
is available when the number of earthquakes in the test period is small, and the central limit theorem provides an approximate
test when the number of earthquakes is large. Similar methods are available for the R-test, which compares the likelihoods of two competing models. However, the R-test, like the N-test and L-test, is fundamentally a test of consistency of data with a model. We propose an alternative test, based on the classical
paired t-test, to more directly compare the likelihoods of two models. Although approximate and predicated on a normality assumption,
this new T-test is not computer-intensive, is easier to interpret than the R-test, and becomes increasingly dependable as the number of earthquakes increases. 相似文献
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Along-Coast Features of Bora-Related Turbulence 总被引：1，自引：1，他引：0
?eljko Ve?enaj Danijel Belu?i? Vanda Grubi?i? Branko Grisogono 《Boundary-Layer Meteorology》2012,143(3):527-545
The along-coast, offshore turbulence structure of the Bora flow that occurred on 7 November 1999 during the Mesoscale Alpine Programme (MAP) Intensive Observation Period 15 is examined. In this analysis we employ the aircraft and dropsonde data obtained over the Adriatic Sea, where the turbulence structure is determined by estimating turbulent kinetic energy (TKE) and its dissipation rate along the flight legs. The turbulence characteristics of Bora in the lee of the Dinaric Alps is greatly influenced by the mesoscale Bora flow structure over the Adriatic Sea, which in the cross-wind direction features an interchange of jets and wakes related to mountain gaps and peaks. In order to establish the origin of turbulence, the Weather Research and Forecasting—Advanced Research WRF (WRF-ARW) numerical model is used and its results are compared to the measurements. All five TKE-prediction parametrization schemes available in the model show reasonable agreement with the measured values. Since these parametrization schemes do not have horizontal advection included, they suggest that the along-flight structure of the Bora turbulence is principally generated by the local vertical wind shear. Further evidence is needed to support this hypothesis. 相似文献
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Pichelli Emanuela Coppola Erika Sobolowski Stefan Ban Nikolina Giorgi Filippo Stocchi Paolo Alias Antoinette Belu&#;i&#; Danijel Berthou Segolene Caillaud Cecile Cardoso Rita M. Chan Steven Christensen Ole B&#;ssing Dobler Andreas de Vries Hylke Goergen Klaus Kendon Elizabeth J. Keuler Klaus Lenderink Geert Lorenz Torge Mishra Aditya N. Panitz Hans-Juergen Sch&#;r Christoph Soares Pedro M. M. Truhetz Heimo Vergara-Temprado Jesus 《Climate Dynamics》2021,56(11):3581-3602
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统计地震学长期使用的两个幂律关系式为:描述地震频度-震级关系的古登堡-里克特(Gutenberg-Richter)关系式[1]和描绘主震后余震随时间衰减速率特征的大森-宇津(Omori-Utsu)定律[2]。最近,地震频度-震级关系斜率(b值)与断裂模式的相关性研究确定了应力对b值的影响[3]。在此,我们以类似的方式根据主震的断裂模式对余震序列进行研究。我们发现逆冲型主震的幂律余震衰减速率起始前的延时(c值)一般比正断层型地震的短,走滑型地震的c值则处于二者之间。对断裂模式的这些类似依赖关系表明两个基本幂律都受应力状态控制。只有2%的余震有已知震源机制解。因此,c值和b值是两个独立的估算值,它们可作为推断应力场的新方法来使用,目前应力场依然难以直接测定。 相似文献
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A Lagrangian stochastic particle model driven by observed winds from a network of 13 sonic anemometers is used to simulate
the transport of contaminates due to meandering of the mean wind vector and diffusion by turbulence. The turbulence and the
meandering motions are extracted from the observed velocity variances using a variable averaging window width. Such partitioning
enables determination of the separate contributions from turbulence and meandering to the total dispersion. The turbulence
is described by a Markov Chain Monte Carlo process based on the Langevin equation using the observed turbulence variances.
The meandering motions, not the turbulence, are primarily responsible for the 1-h averaged horizontal dispersion as measured
by the travel time dependence of the particle position variances. As a result, the 1-h averaged horizontal concentration patterns
are often characterized by streaks and multi-modal distributions. Time series of concentration at a fixed location are highly
nonstationary even when the 1-h averaged spatial distribution is close to Gaussian. The results show that meandering dominates
the travel-time dependence of the horizontal dispersion under all atmospheric conditions: weak and strong winds, and unstable
and stable stratification. 相似文献
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Nicolas Deichmann Manfred Baer Jochen Braunmiller Cécile Cornou Donat Fäh Domenico Giardini Monika Gisler Sarah Huber Stephan Husen Philipp Kästli Urs Kradolfer Martin Mai Silvio Maraini Ivo Oprsal Thomas Schler Danijel Schorlemmer Stefan Wiemer Jochen Wössner Adrian Wyss 《Eclogae Geologicae Helvetiae》2004,97(3):447-458
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