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61.
Summary We use the regional climate model RegCM nested within time-slice atmospheric general circulation model experiments to investigate the possible changes of intense and extreme precipitation over the French Maritime Alps in response to global climate change. This is a region with complex orography where heavy and/or extended precipitation episodes induced catastrophic floods during the last decades. Output from a 30-year simulation of present-day climate (1961–1990) is first analysed and compared with NCEP reanalysed 700 hPa geopotential heights (Z700) and daily precipitation observations from the Alpine Precipitation Climatology (1966–1999). Two simulations under forcing from the A2 and B2 IPCC emission scenarios for the period 2071–2100 are used to investigate projected changes in extreme precipitation for our region of interest. In general, the model overestimates the annual cycle of precipitation. The climate change projections show some increase of precipitation, mostly outside the warm period for the B2 scenario, and some increase in the variability of the annual precipitation totals for the A2 scenario. The model reproduces the main observed patterns of the spatial leading EOFs in the Z700 field over the Atlantic-European domain. The simulated large scale circulation (LSC) variability does not differ significantly from that of the reanalysis data provided the EOFs are computed on the same domain. Two similar clusters of LSC corresponding to heavy precipitation days were identified for both simulated and observed data and their patterns do not change significantly in the climate change scenarios. The analysis of frequency histograms of extreme indices shows that the control simulation systematically underestimates the observed heavy precipitation expressed as the 90th percentile of rainday amounts in all seasons except summer and better reproduces the greatest 5-day precipitation accumulation. The main hydrological changes projected for the Maritime Alps consist of an increase of most intense wet spell precipitation during winters for both scenarios and during autumn for the B2 scenario. Case studies of heavy precipitation events show that the RegCM is capable to reproduce the physical mechanisms responsible for heavy precipitation over our region of interest.  相似文献   
62.
Summary In this paper, we investigate the role that horizontal resolution plays in the simulation of East Asia precipitation. Two sets of numerical experiments are performed using the Regional Climate Model (RegCM2) nested in one-way mode within the CSIRO global coupled atmosphere-ocean model. In the first set we use the actual RegCM2 topography at the selected model resolutions, which are 45, 60, 90, 120, 180, 240 and 360 km. In the second set of the experiments, the same coarse CSIRO model topography is used in all simulations using the different resolutions of the first set. The results demonstrate that the simulation of East Asian precipitation improves as the horizontal resolution is increased. Moreover, it is shown that the simulations using a higher resolution along with the coarse CSIRO topography perform better than the simulations using a coarser model resolution with corresponding model topography. This suggests that over East Asia adequate spatial resolution to resolve the physical and dynamical processes is more important than topography. Lastly, the results indicate that model resolutions of 60 km or higher are needed to accurately simulate the distribution of precipitation over China and East Asia.  相似文献   
63.
Two helium surveys were carried out at Phlegraean Fields in July and September 1983 aiming at locating loci of discontinuities (fractures) in the area on the basis of variations in helium concentrations following the bradyseismic crisis then in progress.  相似文献   
64.
The isotopic composition of neon was measured for seventeen samples of submarine basalt glass from the Mid-Atlantic Ridge between 54° and 73°N. They include the Reykjanes, Kolbeinsey, and Mohns Ridge segments. Neon isotopic anomalies, relative to the atmospheric ratios, exist in both20Ne/22Ne and21Ne/22Ne. A maximum excess20Ne of 7% was measured in two samples from the Reykjanes Ridge. Samples with lower20Ne excesses (six samples with δ20Ne between 2 and 4%) from all three ridge segments, appear to result from mixing of a mantle component with a δ20Ne of 7% and atmospheric neon.21Ne/22Ne ratios are up to 8% above the atmospheric value, with no apparent correlation with the20Ne excesses. The anomalies in20Ne/22Ne are difficult to explain by mass fractionation of an atmospheric reservoir since several of the samples have δ20Ne values greater than could be produced by single-stage fractionation. Most likely, the excess21Ne results from nuclear reactions in the mantle source, although there is no definite correlation between the δ21Ne or the excess21Ne (cm3 STP/g) and the uranium concentration. Large variations in the observed4He/20Ne ratio (40–12,000) remain unexplained at this time.  相似文献   
65.
Summary An analysis of daily climatological data covering the period from 1901 to 1992 for four locations in Switzerland (Zurich, Lugano, Davos, and Säntis) has been made. The study has highlighted the fact that climate change this century is characterized by increases in minimum temperatures of about 2 K, a more modest increase in maximum temperatures (in some instances a decrease of maxima in the latter part of the record), little trend in the precipitation data, and a general decrease of sunshine duration through to the mid 1980s. The interannual variability is generally large, and filtering of the data to remove high-frequency noise shows that the regional climate undergoes a series of fluctuations of between 8 and 20 years' duration. The temperature change over this century is of greater magnitude than the global temperature changes published in the literature, reflecting an amplification of the global signal in the Alpine region; warming has been most intense in the 1940s, followed by the 1980s; the cooling which intervened from the 1950s to the late 1970s was not sufficient to offset the warming in the middle of the century.Pressure statistics have been compiled as a means of providing a link between the regional-scale climatological variables and the synoptic, supra-regional scale. These statistics show that pressure also exhibits a number of decadal-scale fluctuations, with the appearance of a new and anomalous behavior in the 1980s; in this decade, pressure reaches annual average values far higher than at other times this century. The pressure field is well correlated with the North Atlantic Oscillation (NAO) Index for distinct periods of the record (1931–1950 and 1971–1990) and is almost decorrelated from the NAO Index for the other decades of the century; this is indicative of transition from one climatic régime to another, dominated by zonal flow when the correlation with the NAO Index is high. In the 1980s, when zonal flow over the North Atlantic is strong, episodes of persistent, anomalously high pressures (blocking highs) are seen to occur over Switzerland, particularly during the winter season. The difference between the zonal and non-zonal régimes is particularly marked between the decade of the 1950s and that of the 1980s.The impact of this change between the 1950s and the 1980s on a number of climatological variables has been investigated statistically in order to provide an illustration of the manner in which changes in synoptic régimes (i.e., climate change) impacts upon climate characteristics on a regional scale. The analysis shows that temperature, precipitation, snow depth, and sunshine duration are indeed sensitive to large-scale influences; not only can yearly mean changes be quantified, but also seasonal and monthly fluctuations.With 26 Figures  相似文献   
66.
Seismic signals generated by avalanches have been recorded by theavalanche team of the Universitat de Barcelona at theVallée de la Sionne experimental site (Switzerland) since 1998. During these years avalanches of varying size and flowwere recorded by two sensors located at different positions.In the present paper we show the general features of the running spectra of the seismicsignals for the different type of recorded avalanches. Using this method we are able not only to detect avalanches with low amplitude signals but also to distinguishbetween avalanches and other seismic sources (i.e., local earthquakes) which have thesame frequency content but a different frequency evolution.  相似文献   
67.
Impacts of greenhouse effects(2×CO2) on climate change over China as simulated by a regional climate model have been investigated.The model was based on RegCM2 and is nested in one-way mode within a global coupled atmosphere-ocean model(CSIRO R21L9 AOGCM).Two multi-year simulations,the control run with normal CO2 concentration and the sensitivity run with doubled CO2 concentration are conducted. As Part I of the publications,results of control run of the CSIRO,i.e.its simulation of present climate in China,are analyzed briefly.It shows that the model can basically reproduce the surface air temperature and precipitation pattern over China.Therefore,its outputs can be used to drive the regional model. Analysis of control run of RegCM shows that with a high resolution,the model improves the simulations of surface air temperature and precipitation in China as compared to the CSIRO model, especially for the precipitation.The spatial correlation coefficient between simulated and observed annual temperature increased from 0.83 in the CSIRO to 0.92 in the RegCM and for annual precipitation from 0.48 in the CSIRO to 0.65 in the RegCM.A similar improvement in the RegCM compared to the CSIRO was found in all simulated months.The main improvement for surface temperature is that RegCM can simulate the fine scale structure of temperature caused by topography.RegCM greatly improved the spatial distribution of precipitation by eliminating the virtual precipitation center in central China,which was simulated by many other GCMs.The precipitation simulated by RegCM in North and Northwest China is smaller than that by CSIRO, which makes it closer to the observation.  相似文献   
68.
We investigated the dynamics of explosive activity at Mt. Etna between 31 August and 15 December 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active, summit crater. The analysed scoria clasts present large, connected vesicles with complex shapes and smaller, isolated, spherical vesicles, the content of which increases in scoriae from the most explosive events. Gas geochemistry reports CO2/SO2 and SO2/HCl ratios supporting a deep-derived gas phase for fire-fountain activity. By integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of Mt. Etna activity in 2006 were driven by a previously accumulated CO2-rich gas phase but we highlight the lesser role of syn-eruptive vesicle nucleation driven by water exsolution during ascent. We conclude that syn-eruptive vesiculation is a common process in Etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation.  相似文献   
69.
We present an analysis of a high resolution multi-decadal simulation of recent climate (1971–2000) over the Korean Peninsula with a regional climate model (RegCM3) using a one-way double-nested system. Mean climate state as well as frequency and intensity of extreme climate events are investigated at various temporal and spatial scales, with focus on surface air temperature and precipitation. The mother intermediate resolution model domain encompasses the eastern regions of Asia at 60 km grid spacing while the high resolution nested domain covers the Korean Peninsula at 20 km grid spacing. The simulation spans the 30-year period of January 1971 through December 2000, and initial and lateral boundary conditions for the mother domain are provided from ECHO-G fields based on the IPCC SRES B2 scenario. The model shows a good performance in reproducing the climatological and regional characteristics of surface variables, although some persistent biases are present. Main results are as follows: (1) The RegCM3 successfully simulates the fine-scale structure of the temperature field due to topographic forcing but it shows a systematic cold bias mostly due to an underestimate of maximum temperature. (2) The frequency distribution of simulated daily mean temperature agrees well with the observed seasonal and spatial patterns. In the summer season, however, daily variability is underestimated. (3) The RegCM3 simulation adequately captures the seasonal evolution of precipitation associated to the East Asia monsoon. In particular, the simulated winter precipitation is remarkably good, clearly showing typical precipitation patterns that occur on the northwestern areas of Japan during the winter monsoon. Although summer precipitation is underestimated, area-averaged time series of precipitation over Korea show that the RegCM3 agrees better with observations than ECHO-G both in terms of seasonal evolution and precipitation amounts. (4) Heavy rainfall phenomena exceeding 300 mm/day are simulated only at the high resolution of the double nested domain. (5) The model shows a tendency to overestimate the number of precipitation days and to underestimate the precipitation intensities. (6) A CSEOF analysis reveals that the model captures the strength of the annual cycle and the surface warming trend throughout the simulated period.  相似文献   
70.
We analyze ensembles (four realizations) of historical and future climate transient experiments carried out with the coupled atmosphere-ocean general circulation model (AOGCM) of the Hadley Centre for Climate Prediction and Research, version HADCM2, with four scenarios of greenhouse gas (GHG) and sulfate forcing. The analysis focuses on the regional scale, and in particular on 21 regions covering all land areas in the World (except Antarctica). We examine seasonally averaged surface air temperature and precipitation for the historical period of 1961–1990 and the future climate period of 2046–2075. Compared to previous AOGCM simulations, the HADCM2 model shows a good performance in reproducing observed regional averages of summer and winter temperature and precipitation. The model, however, does not reproduce well observed interannual variability. We find that the uncertainty in regional climate change predictions associated with the spread of different realizations in an ensemble (i.e. the uncertainty related to the internal model variability) is relatively low for all scenarios and regions. In particular, this uncertainty is lower than the uncertainty due to inter-scenario variability and (by comparison with previous regional analyses of AOGCMs) with inter-model variability. The climate biases and sensitivities found for different realizations of the same ensemble were similar to the corresponding ensemble averages and the averages associated with individual realizations of the same ensemble did not differ from each other at the 5% confidence level in the vast majority of cases. These results indicate that a relatively small number of realizations (3 or 4) is sufficient to characterize an AOGCM transient climate change prediction at the regional scale. Received: 12 January 1998 / Accepted: 7 July 1999  相似文献   
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