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1.
Both observational and numerical studies suggest that the Eurasian winter snow cover has a strong influence on the subsequent
summer monsoon in Asia. An updated version of the ARPEGE climate model of Météo-France, including a simple but physically-based
snow parameterization, is used to test the impact of an increased snow mass prescribed at the beginning of March on the simulated
summer monsoon circulation and rainfall. The large-scale features of the Asian monsoon are reproduced in a realistic way in
the control integration, which is a necessary premise of such a sensitivity test. In the heavy snow cover experiment, the
anomalous persistence of the winter snow pack delays the springtime continental heating. This weakens the thermal low over
northern India and Persia as well as the southwesterly winds over the monsoon area. There is also a significant decrease in
the rainfall over western India and Bengal-Burma, which usually represent the centers of maximum precipitation. Radiative,
turbulence transfer and hydrological processes seem to be involved in the snow-monsoon relationship. The changes in the monsoon
precipitation are strongly related to changes in the atmospheric circulation and are not reinforced by a local evaporation/convection
feedback in our experiment.
Received: 17 May 1995 / Accepted: 27 November 1995 相似文献
2.
H. Douville 《Climate Dynamics》1998,14(3):151-172
Global soil moisture data of high quality and resolution are not available by direct observation, but are useful as boundary
and initial conditions in comprehensive climate models. In the framework of the GSWP (Global Soil Wetness Project), the ISBA
land-surface scheme of Météo-France has been forced with meteorological observations and analyses in order to study the feasibility
of producing a global soil wetness climatology at a 1°×1° horizontal resolution. A control experiment has been performed from
January 1987 to December 1988, using the ISLSCP Initiative I boundary conditions. The annual mean, the standard deviation
and the normalised annual harmonic of the hydrologic fields have been computed from the 1987 monthly results. The global maps
which are presented summarise the surface hydrologic budget and its annual cycle. The soil wetness index and snow cover distributions
have been compared respectively to the results of the ECMWF reanalysis and to satellite and in situ observations. The simulated
runoff has been validated against a river flow climatology, suggesting a possible underestimation over some large river basins.
Besides the control run, other simulations have been performed in order to study the sensitivity of the hydrologic budget
to changes in the surface parameters, the precipitation forcing and the runoff scheme. Such modifications have a significant
impact on the partition of total precipitation into evaporation and runoff. The sensitivity of the results suggests that soil
moisture remains one of the most difficult climatological parameters to model and that any computed soil wetness climatology
must be considered with great caution.
Received: 3 January 1997 / Accepted: 19 August 1987 相似文献
3.
This paper is dedicated to the analysis of winter cold spells over Western Europe in the simulations of the 5th phase of the Coupled Model Intercomparison Project (CMIP5). Both model biases and responses in a warming climate are discussed using historical simulations and the 8.5 W/m2 Representative Concentration Pathway (RCP8.5) scenario, respectively on the 1979–2008 and 2070–2099 periods. A percentile-based index (10th percentile of daily minimum temperature, Q10) with duration and spatial extent criteria is used to define cold spells. Related diagnostics (intensity, duration, extent, and severity as a combination of the former three statistics) of 13 models are compared to observations and suggest that models biases on severity are mainly due to the intensity parameter rather than to duration and extent. Some hypotheses are proposed to explain these biases, that involve large-scale dynamics and/or radiative fluxes related to clouds. Evolution of cold spells characteristics by the end of the century is then discussed by comparing RCP8.5 and historical simulations. In line with the projected rise of mean temperature, “present-climate” cold spells (computed with the 1979–2008 10th percentile, Q10P) are projected to be much less frequent and, except in one model, less severe. When cold spells are defined from the future 10th percentile threshold (“future-climate” cold spells, Q10F), all models simulate a decrease of their intensity linearly related to the seasonal mean warming. Some insights are given to explain the inter-model diversity in the magnitude of the cold spells response. In particular, the snow-albedo feedback is suggested to play an important role, while for some models changes in large-scale dynamics are also not negligible. 相似文献
4.
The impact of global warming on the warmest and coldest days of the annual cycle is explored according to an A2 scenario simulated
by the CNRM-CM3 climate model in the framework of the IPCC AR4 intercomparison. Given the multi-model spread in IPCC projections,
a validation strategy is proposed using the NCEP/NCAR reanalysis. Validation of the late twentieth century model climatology
shows that warm and cold model events are slightly too long and infrequent. Although interannual trends in the warm (cold)
day occurrence were positive (negative) only for six (three) of the nine considered sub-continental regions, simulated model
trends are always positive (negative). This different behaviour suggests that simulated non-anthropogenic decadal variability
is small relative to anthropogenic trends. Large-scale synoptic processes associated with European regional warm and cold
peaks are also described and validated. Regional cold peaks are better reproduced than warm peaks, whose intensity accuracy
is limited by other physical variables. Positive (negative) winter anomalies of sea and land surface temperature lead to summers
with severe (weak) temperatures. These inter-annual anomalies are generated by a persistent pressure dipole over Europe. Regarding
climate change, warm (cold) events will become more (less) frequent and longer (shorter). The number of warm days will largely
rise and the number of cold days will dramatically decrease. The intensity of warm days will be particularly pronounced over
Europe, given the projected summer drying in this region. However, according to the limited skill of the CNRM model, these
results must be considered with caution. 相似文献
5.
Relative contribution of soil moisture and snow mass to seasonal climate predictability: a pilot study 总被引：1，自引：1，他引：0
Hervé Douville 《Climate Dynamics》2010,34(6):797-818
Land surface hydrology (LSH) is a potential source of long-range atmospheric predictability that has received less attention
than sea surface temperature (SST). In this study, we carry out ensemble atmospheric simulations driven by observed or climatological
SST in which the LSH is either interactive or nudged towards a global monthly re-analysis. The main objective is to evaluate
the impact of soil moisture or snow mass anomalies on seasonal climate variability and predictability over the 1986–1995 period.
We first analyse the annual cycle of zonal mean potential (perfect model approach) and effective (simulated vs. observed climate)
predictability in order to identify the seasons and latitudes where land surface initialization is potentially relevant. Results
highlight the influence of soil moisture boundary conditions in the summer mid-latitudes and the role of snow boundary conditions
in the northern high latitudes. Then, we focus on the Eurasian continent and we contrast seasons with opposite land surface
anomalies. In addition to the nudged experiments, we conduct ensembles of seasonal hindcasts in which the relaxation is switched
off at the end of spring or winter in order to evaluate the impact of soil moisture or snow mass initialization. LSH appears
as an effective source of surface air temperature and precipitation predictability over Eurasia (as well as North America),
at least as important as SST in spring and summer. Cloud feedbacks and large-scale dynamics contribute to amplify the regional
temperature response, which is however, mainly found at the lowest model levels and only represents a small fraction of the
observed variability in the upper troposphere. 相似文献
6.
Petra Döll Hervé Douville Andreas Güntner Hannes Müller Schmied Yoshihide Wada 《Surveys in Geophysics》2016,37(2):195-221
Quantification of spatially and temporally resolved water flows and water storage variations for all land areas of the globe is required to assess water resources, water scarcity and flood hazards, and to understand the Earth system. This quantification is done with the help of global hydrological models (GHMs). What are the challenges and prospects in the development and application of GHMs? Seven important challenges are presented. (1) Data scarcity makes quantification of human water use difficult even though significant progress has been achieved in the last decade. (2) Uncertainty of meteorological input data strongly affects model outputs. (3) The reaction of vegetation to changing climate and CO2 concentrations is uncertain and not taken into account in most GHMs that serve to estimate climate change impacts. (4) Reasons for discrepant responses of GHMs to changing climate have yet to be identified. (5) More accurate estimates of monthly time series of water availability and use are needed to provide good indicators of water scarcity. (6) Integration of gradient-based groundwater modelling into GHMs is necessary for a better simulation of groundwater–surface water interactions and capillary rise. (7) Detection and attribution of human interference with freshwater systems by using GHMs are constrained by data of insufficient quality but also GHM uncertainty itself. Regarding prospects for progress, we propose to decrease the uncertainty of GHM output by making better use of in situ and remotely sensed observations of output variables such as river discharge or total water storage variations by multi-criteria validation, calibration or data assimilation. Finally, we present an initiative that works towards the vision of hyperresolution global hydrological modelling where GHM outputs would be provided at a 1-km resolution with reasonable accuracy. 相似文献
7.
Cécile Gautheron Nicolas Espurt Jocelyn Barbarand Martin Roddaz Patrice Baby Stéphane Brusset Laurent Tassan‐Got Eric Douville 《Basin Research》2013,25(4):419-435
Although the structure of the central Peruvian Subandean zone is well defined, the timing of thrust‐related exhumation and Cenozoic sedimentation remain poorly constrained. In this study, we report new apatite (U–Th)/He (AHe) and fission track (AFT) ages from thrust‐belt and foreland strata along three published balanced cross sections. AHe data from the northern, thick‐skinned domain (i.e. Shira Mountain, Otishi Cordillera and Ucayali Basin) show young AHe ages (ranging from 2.6 ± 0.2 to 13.1 ± 0.8 Ma) compared with AFT ages (ranging from 101 ± 5 to 133 ± 11 Ma). In the southern Camisea Basin, where deformation is mainly thin‐skinned, AHe and AFT ages have been both reset and show young cooling ages (3.7 ± 0.8 Ma and 8 ± 2 Ma respectively). Using low‐temperature thermochronology data and the latest fission track annealing and He diffusion codes, the thermal history of the study area has been reconstructed using inverse modelling. This history includes two steps of erosion: Early Cretaceous and late Neogene, but only Neogene sedimentation and exhumation varies in the different sectors of the study area. From a methodological point of view, large AHe data dispersion point to the need for refinement of AHe damage and annealing models. The influence of grain chemistry on damage annealing, multiple age components and the possibility of fission tracks as traps for He need further consideration. For the central Peruvian Subandes, AHe and AFT ages combined with balanced cross sections emphasize the dominant control of Paleozoic inheritance rather than climate on Cenozoic infilling and exhumation histories. Finally, our data provide the first field example of how thick‐skinned thrust‐related deformation and exhumation in the Subandes can be directly dated through AHe thermochronology. 相似文献
8.
In the framework of the Global Soil Wetness Project (GSWP), the ISBA land-surface scheme of the ARPEGE atmospheric general circulation model has been forced with meteorological observations and analyses in order to produce a two-year (1987–1988) soil moisture climatology at a 1°×1° horizontal resolution. This climatology is model dependent, but it is the climatology that the ARPEGE model would produce if its precipitation and radiative fluxes were perfectly simulated. In the present study, ensembles of seasonal simulations (March to September) have been performed for 1987 and 1988, in which the total soil water content simulated by ARPEGE is relaxed towards the GSWP climatology. The results indicate that the relaxation has a positive impact on both the model's climatology and the simulated interannual variability, thereby confirming the utility of the GSWP soil moisture data for prescribing initial or boundary conditions in comprehensive climate and numerical weather prediction models. They also demonstrate the relevance of soil moisture for achieving realistic simulations of the Northern Hemisphere summer climate. In order to get closer to the framework of seasonal predictions, additional experiments have been performed in which GSWP is only used for initialising soil moisture at the beginning of the summer season (the relaxation towards GSWP is removed on 1st June). The results show a limited improvement of the interannual variability, compared to the simulations initialised from the ARPEGE climatology. However, some regional patterns of the precipitation differences between 1987 and 1988 are better captured, suggesting that seasonal predictions can benefit from a better initialisation of soil moisture. 相似文献
9.
Influence of the Eurasian snow cover on the Indian summer monsoon variability in observed climatologies and CMIP3 simulations 总被引：3，自引：1，他引：2
The present study is aimed at revisiting the possible influence of the winter/spring Eurasian snow cover on the subsequent Indian summer precipitation using several statistical tools including a maximum covariance analysis. The snow–monsoon relationship is explored using both satellite observations of snow cover and in situ measurements of snow depth, but also a subset of global coupled ocean–atmosphere simulations from the phase 3 of the Coupled Model Intercomparison Project (CMIP3) database. In keeping with former studies, the observations suggest a link between an east–west snow dipole over Eurasia and the Indian summer monsoon precipitation. However, our results indicate that this relationship is neither statistically significant nor stationary over the last 40 years. Moreover, the strongest signal appears over eastern Eurasia and is not consistent with the Blanford hypothesis whereby more snow should lead to a weaker monsoon. The twentieth century CMIP3 simulations provide longer timeseries to look for robust snow–monsoon relationships. The maximum covariance analysis indicates that some models do show an apparent influence of the Eurasian snow cover on the Indian summer monsoon precipitation, but the patterns are not the same as in the observations. Moreover, the apparent snow–monsoon relationship generally denotes a too strong El Niño-Southern Oscillation teleconnection with both winter snow cover and summer monsoon rainfall rather than a direct influence of the Eurasian snow cover on the Indian monsoon. 相似文献
10.
Seasonal climate forecasts mainly rely on the atmospheric sensitivity to its lower boundary conditions and on their own predictability.
Besides sea surface temperature (SST), soil moisture (SM) may be an additional source of climate predictability particularly
during boreal summer in the mid-latitudes. In this work, we investigate the role of SM initial conditions on near-surface
climate predictability during ten boreal summer seasons using three complementary ensembles of AMIP-type simulations performed
with the Arpège-Climat atmospheric general circulation model. First we have conducted an assessment of the SM predictability
itself through a comparison of simple empirical SM models with Arpège-Climat. The statistical and dynamical models reveal
similar SM prediction skill patterns but the Arpège-Climat reaches higher scores suggesting that it is at least suitable to
explore the influence of SM initialization on atmospheric predictability. Then we evaluate the relationships between SM predictability
and some near surface atmospheric predictability. While SM initialization obviously improves the predictability of land surface
evaporation, it has no systematic influence on the precipitation and near surface temperature skills. Nevertheless, the summer
hindcast skill is clearly improved during specific years and over certain regions (mainly north America and eastern Europe
in the Arpège-Climat model), when and where the SM forcing is sufficiently widespread and strong. In this case, a significant
impact is also found on the occurrence of heat waves and heavy rains, whose predictability at the seasonal timescale is a
crucial challenge for years to come. 相似文献