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1.
R. Huth 《Theoretical and Applied Climatology》1999,64(3-4):151-162
Summary The question discussed in this study is how to calculate linear trends in data that are not distributed evenly in time. This
is examined with time series of ten climate elements at a single station, stratified according to a classification based on
daily circulation patterns. Trends are calculated in three different ways: (i) from seasonal means, which is a common approach,
(ii) from means of individual events, the event being defined as a sequence of days classified as one particular type, preceded
and succeeded by another type, and (iii) from individual daily values. The most common method of estimating trend significance,
i.e. the t-test of the Pearson correlation coefficient, has been shown to be applicable to seasonal and event-mean trends for all variables.
For daily trends, the Monte Carlo test should be used instead. The daily, event-mean and seasonal trends differ from each
other considerably for many combinations of climate variable and circulation type. The reason for this difference is identified.
Received December 3, 1998 Revised June 21, 1999 相似文献
2.
Circulation patterns, daily precipitation in Portugal and implications for climate change simulated by the second Hadley Centre GCM 总被引：2，自引：1，他引：1
Based on principal component analysis (PCA) and a k-means clustering algorithm, daily mean sea level pressure (MSLP) fields over the northeastern Atlantic and Western Europe,
simulated by the Hadley Centre's second generation coupled ocean-atmosphere GCM (HADCM2) control run (HADCM2CON), are validated
by comparison with the observed daily MSLP fields. It is clear that HADCM2 reproduces daily MSLP fields and its seasonal variability
over the region very well, despite suffering from some deficiencies, such as the systematic displacement of the atmospheric
centres of action. Four daily circulation patterns, previously identified from the observed daily MSLP fields over the area
and well related to daily precipitation in Portugal, were also well classified from the daily MSLP fields simulated by HADCM2.
The model can also simulate rather successfully the relationships between the four daily circulation patterns and daily precipitation
in southern Portugal. However, compared with observations, daily precipitation intensities simulated by the model are too
weak in southern Portugal. Nevertheless, HADCM2 represents a considerable improvement relative to the UKTR experiment. The
results described here imply that it is doubtful whether regional precipitation scenarios provided by HADCM2 can be directly
applied in impact studies and that a downscaling technique, based on daily circulation patterns, might be successful in reproducing
local and regional precipitation characteristics. Moreover, the four circulation patterns can also be clearly identified in
the two perturbed experiments, one under greenhouse gases forcing only (HADCM2GHG) and the other under additional forcing
of sulphate aerosol (HADCM2SUL), although changes in the frequencies of occurrence of certain circulation patterns are found.
Nevertheless, the observed links between regional precipitation in southern Portugal and large-scale atmospheric circulation
seem likely to hold in the model's perturbed climate. It is therefore credible to use those links to downscale large-scale
atmospheric circulation from GCM simulations to obtain future precipitation scenarios in southern Portugal.
Received: 21 August 1998 / Accepted: 28 May 1999 相似文献
3.
Heat waves and dry spells are analyzed (i) at eightstations in south Moravia (Czech Republic), (ii) inthe control ECHAM3 GCM run at the gridpoint closest tothe study area, and (iii) in the ECHAM3 GCM run fordoubled CO2 concentrations (scenario A) at thesame gridpoint (heat waves only). The GCM outputs arevalidated both against individual station data andareally representative values. In the control run, theheat waves are too long, appear later in the year,peak at higher temperatures and their numbers areunder- (over-) estimated in June and July (in August).The simulated dry spells are too long, and the annualcycle of their occurrence is distorted.Mid-tropospheric circulation, and heat waves and dryspells are linked much less tightly in the controlclimate than in the observed. Since mid-troposphericcirculation is simulated fairly successfully, wesuggest the hypothesis that either the air-masstransformation and local processes are too strong inthe model or the simulated advection is too weak. Inthe scenario A climate, the heat waves become a commonphenomenon: warming of 4.5 °C in summer(difference between scenario A and control climates)induces a five-fold increase in the frequency oftropical days and an immense enhancement of extremityof heat waves. The results of the study underline theneed for (i) a proper validation of the GCM outputbefore a climate impact study is conducted and (ii)translation of large-scale information from GCMs intolocal scales using downscaling and stochasticmodelling techniques in order to reduce GCMs' biases. 相似文献
4.
I. Matyasovszky I. Bogardi A. Bardossy L. Duckstein 《Theoretical and Applied Climatology》1994,50(1-2):1-13
Summary A methodology to estimate the space-time distribution of daily mean temperature under climate change is developed and applied to a central Nebraska case study. The approach is based on the analysis of the Markov properties of atmospheric circulation pattern (CP) types, and a stochastic linkage between daily (here 500hPa) CP types and daily mean temperatures. Historical data and general circulation model (GCM) output of daily CP corresponding to 1 × CO2 and 2 × CO2 scenarios are considered. The relationship between spatially averaged geopotential height of the 500 hPa surface — within each CP type — and daily mean temperature is described by a nonparametric regression technique. Time series of daily mean temperatures corresponding to each of these cases are simulated and their statistical properties are compared. Under the climate of central Nebraska, the space-time response of daily mean temperature to global climate change is variable. In general, a warmer climate appears to cause about 5°C increase in the winter months, a smaller increase in other months with no change in July and August. The sensitivity of the results to the GCM utilized should be considered.On leave from the Department of Meteorology, Eötvós Loránd University, Budapest, Hungary.With 14 Figures 相似文献
5.
The Canadian Centre for Climate Modelling and Analysis global coupled model and its climate 总被引：16，自引：5，他引：11
G. M. Flato G. J. Boer W. G. Lee N. A. McFarlane D. Ramsden M. C. Reader A. J. Weaver 《Climate Dynamics》2000,16(6):451-467
A global, three-dimensional climate model, developed by coupling the CCCma second-generation atmospheric general circulation
model (GCM2) to a version of the GFDL modular ocean model (MOM1), forms the basis for extended simulations of past, current
and projected future climate. The spin-up and coupling procedures are described, as is the resulting climate based on a 200 year
model simulation with constant atmospheric composition and external forcing. The simulated climate is systematically compared
to available observations in terms of mean climate quantities and their spatial patterns, temporal variability, and regional
behavior. Such comparison demonstrates a generally successful reproduction of the broad features of mean climate quantities,
albeit with local discrepancies. Variability is generally well-simulated over land, but somewhat underestimated in the tropical
ocean and the extratropical storm-track regions. The modelled climate state shows only small trends, indicating a reasonable
level of balance at the surface, which is achieved in part by the use of heat and freshwater flux adjustments. The control
simulation provides a basis against which to compare simulated climate change due to historical and projected greenhouse gas
and aerosol forcing as described in companion publications.
Received: 24 September 1998 / Accepted: 8 October 1999 相似文献
6.
Fredrik Wetterhall András Bárdossy Deliang Chen Sven Halldin Chong-yu Xu 《Theoretical and Applied Climatology》2009,96(1-2):95-103
A classification of Swedish weather patterns (SWP) was developed by applying a multi-objective fuzzy-rule-based classification method (MOFRBC) to large-scale-circulation predictors in the context of statistical downscaling of daily precipitation at the station level. The predictor data was mean sea level pressure (MSLP) and geopotential heights at 850 (H850) and 700 hPa (H700) from the NCEP/NCAR reanalysis and from the HadAM3 GCM. The MOFRBC was used to evaluate effects of two future climate scenarios (A2 and B2) on precipitation patterns on two regions in south-central and northern Sweden. The precipitation series were generated with a stochastic, autoregressive model conditioned on SWP. H850 was found to be the optimum predictor for SWP, and SWP could be used instead of local classifications with little information lost. The results in the climate projection indicated an increase in maximum 5-day precipitation and precipitation amount on a wet day for the scenarios A2 and B2 for the period 2070–2100 compared to 1961–1990. The relative increase was largest in the northern region and could be attributed to an increase in the specific humidity rather than to changes in the circulation patterns. 相似文献
7.
A high-resolution tropical Pacific general circulation model (GCM) coupled to a global atmospheric GCM is described in this paper. The atmosphere component is the 5°×4°global general circulation model of the Institute of Atmospheric Physics (IAP) with 9 levels in the vertical direction. The ocean component with a horizontal resolution of 0.5°, is based on a low-resolution model (2°×1°in longitude-latitude).Simulations of the ocean component are first compared with its previous version. Results show that the enhanced ocean horizontal resolution allows an improved ocean state to be simulated; this involves (1) an apparent decrease in errors in the tropical Pacific cold tongue region, which exists in many ocean models,(2) more realistic large-scale flows, and (3) an improved ability to simulate the interannual variability and a reduced root mean square error (RMSE) in a long time integration. In coupling these component models, a monthly "linear-regression" method is employed to correct the model's exchanged flux between the sea and the atmosphere. A 100-year integration conducted with the coupled GCM (CGCM) shows the effectiveness of such a method in reducing climate drift. Results from years 70 to 100 are described.The model produces a reasonably realistic annual cycle of equatorial SST. The large SSTA is confined to the eastern equatorial Pacific with little propagation. Irregular warm and cold events alternate with a broad spectrum of periods between 24 and 50 months, which is very realistic. But the simulated variability is weaker than the observed and is also asymmetric in the sense of the amplitude of the warm and cold events. 相似文献
8.
9.
Climate change that results from increasing levels of greenhouse gases in the atmosphere has the potential to increase temperature and alter rainfall patterns across the boreal forest region of Canada. Daily output from the Canadian Climate Centre coupled general circulation model (GCM) and the Hadley Centre's HadCM3 GCM provided simulated historic climate data and future climate scenarios for the forested area of the province of Ontario, Canada. These models project that in climates of increased greenhouse gases and aerosols, surface air temperatures will increase while seasonal precipitation amounts will remain relatively constant or increase slightly during the forest fire season. These projected changes in weather conditions are used to predict changes in the moisture content of forest fuel, which influences the incidence of people-caused forest fires. Poisson regression analysis methods are used to develop predictive models for the daily number of fires occurring in each of the ecoregions across the forest fire management region of Ontario. This people-caused fire prediction model, combined with GCM data, predicts the total number of people-caused fires in Ontario could increase by approximately 18% by 2020–2040 and50% by the end of the 21st century. 相似文献
10.
Uncertainties in the regional climate models simulations of South-Asian summer monsoon and climate change 总被引：1，自引：0，他引：1
The uncertainties in the regional climate models (RCMs) are evaluated by analyzing the driving global data of ERA40 reanalysis and ECHAM5 general circulation models, and the downscaled data of two RCMs (RegCM4 and PRECIS) over South-Asia for the present day simulation (1971–2000) of South-Asian summer monsoon. The differences between the observational datasets over South-Asia are also analyzed. The spatial and the quantitative analysis over the selected climatic regions of South-Asia for the mean climate and the inter-annual variability of temperature, precipitation and circulation show that the RCMs have systematic biases which are independent from different driving datasets and seems to come from the physics parameterization of the RCMs. The spatial gradients and topographically-induced structure of climate are generally captured and simulated values are within a few degrees of the observed values. The biases in the RCMs are not consistent with the biases in the driving fields and the models show similar spatial patterns after downscaling different global datasets. The annual cycle of temperature and rainfall is well simulated by the RCMs, however the RCMs are not able to capture the inter-annual variability. ECHAM5 is also downscaled for the future (2071–2100) climate under A1B emission scenario. The climate change signal is consistent between ECHAM5 and RCMs. There is warming over all the regions of South-Asia associated with increasing greenhouse gas concentrations and the increase in summer mean surface air temperature by the end of the century ranges from 2.5 to 5 °C, with maximum warming over north western parts of the domain and 30 % increase in rainfall over north eastern India, Bangladesh and Myanmar. 相似文献
11.
An ensemble of seven climate models from the North American Regional Climate Change Assessment Program (NARCCAP) was used to examine uncertainty in simulated runoff changes from a base period (1971–2000) to a future period (2041–2070) for the Churchill River basin, Labrador, Canada. Three approximations for mean annual runoff from each ensemble member were included in the analysis: (i) atmospheric moisture convergence, (ii) the balance between precipitation and evaporation, and (iii) instantaneous runoff output from respective land-surface schemes. Using data imputation (i.e., reconstruction) and variance decomposition it was found that choice of regional climate model (RCM) made the greatest contribution to uncertainty in the climate change signal, whereas the boundary forcing of a general circulation model (GCM) played a smaller, though non-negligible, role. It was also found that choice of runoff approximation made a substantial contribution to uncertainty, falling between the contribution from RCM and GCM choice. The NARCCAP output and imputed data were used to calculate mean and median annual changes and results were presented via probability distribution functions to facilitate decision making. Mean and median increases in runoff for the basin were found to be 11.2% and 8.9%, respectively. 相似文献
12.
Properties of the circulation classification scheme based on the rotated principal component analysis 总被引：3，自引：0，他引：3
Dr. R. Huth 《Meteorology and Atmospheric Physics》1996,59(3-4):217-233
Summary The study addresses some methodological issues of application of principal component analysis (PCA) to the classification of circulation patterns. The obliquely rotated PCA in T-mode (i.e. with time observations corresponding to variables and grid points to realizations) is applied to 500 hPa geopotential heights over Europe and adjacent parts of Atlantic Ocean. The solutions are examined for various numbers of principal components rotated, and for both raw and anomaly data, with the aim to find the way of determining the optimum number of circulation types. This is done, among others, by examining temporal and spatial stability of solutions, their compliance with simple structure requirements, and temporal behaviour of classifications. Some of the solutions that are pre-selected according to the rule based upon the separation between successive eigenvalues prove to perform considerably better than unselected ones; some of them do not. Which pre-selected solutions should be given preference is impossible to decide in advance, without a detailed scrutiny. Nevertheless, even after such a scrutiny is done, more than a single classification are acceptable. The final choice of the optimum solution depends on the aims of the intended study: It should balance the demands on statistical stability of types and on resemblance between types and daily patterns classified with them.With 6 Figures 相似文献
13.
Anji Seth Sara A. Rauscher Suzana J. Camargo Jian-Hua Qian J. S. Pal 《Climate Dynamics》2007,28(5):461-480
To enable downscaling of seasonal prediction and climate change scenarios, long-term baseline regional climatologies which
employ global model forcing are needed for South America. As a first step in this process, this work examines climatological
integrations with a regional climate model using a continental scale domain nested in both reanalysis data and multiple realizations
of an atmospheric general circulation model (GCM). The analysis presents an evaluation of the nested model simulated large
scale circulation, mean annual cycle and interannual variability which is compared against observational estimates and also
with the driving GCM for the Northeast, Amazon, Monsoon and Southeast regions of South America. Results indicate that the
regional climate model simulates the annual cycle of precipitation well in the Northeast region and Monsoon regions; it exhibits
a dry bias during winter (July–September) in the Southeast, and simulates a semi-annual cycle with a dry bias in summer (December–February)
in the Amazon region. There is little difference in the annual cycle between the GCM and renalyses driven simulations, however,
substantial differences are seen in the interannual variability. Despite the biases in the annual cycle, the regional model
captures much of the interannual variability observed in the Northeast, Southeast and Amazon regions. In the Monsoon region,
where remote influences are weak, the regional model improves upon the GCM, though neither show substantial predictability.
We conclude that in regions where remote influences are strong and the global model performs well it is difficult for the
regional model to improve the large scale climatological features, indeed the regional model may degrade the simulation. Where
remote forcing is weak and local processes dominate, there is some potential for the regional model to add value. This, however,
will require improvments in physical parameterizations for high resolution tropical simulations. 相似文献
14.
15.
We report on simulations of present-day climate (1961–1990) and future climate conditions (2071–2100, Special Report on Emissions
Scenario A2) over the Caspian sea basin with a regional climate model (RCM) nested in time-slice general circulation model
(GCM) simulations. We also calculate changes (A2 scenario minus present-day) in Caspian sea level (CSL) in response to changes
in the simulated hydrologic budget of the basin. For the present-day run, both the GCM and RCM show a good performance in
reproducing the water budget of the basin and the magnitude of multi-decadal changes in CSL. Compared to present-day climate,
in the A2 scenario experiment we find an increase in cold season precipitation and an increase in temperature and evaporation,
both over land and over the Caspian sea. We also find a large decrease of CSL in the A2 scenario run compared to the present-day
run. This is due to increased evaporation loss from the basin (particularly over the sea) exceeding increased cold season
precipitation over the basin. Our results suggest that the CSL might undergo large changes under future climate change, leading
to potentially devastating consequences for the economy and environment of the region. 相似文献
16.
Climate scenarios for the Netherlands are constructed by combining information from global and regional climate models employing
a simplified, conceptual framework of three sources (levels) of uncertainty impacting on predictions of the local climate.
In this framework, the first level of uncertainty is determined by the global radiation balance, resulting in a range of the
projected changes in the global mean temperature. On the regional (1,000–5,000 km) scale, the response of the atmospheric
circulation determines the second important level of uncertainty. The third level of uncertainty, acting mainly on a local
scale of 10 (and less) to 1,000 km, is related to the small-scale processes, like for example those acting in atmospheric
convection, clouds and atmospheric meso-scale circulations—processes that play an important role in extreme events which are
highly relevant for society. Global climate models (GCMs) are the main tools to quantify the first two levels of uncertainty,
while high resolution regional climate models (RCMs) are more suitable to quantify the third level.
Along these lines, results of an ensemble of RCMs, driven by only two GCM boundaries and therefore spanning only a rather
narrow range in future climate predictions, are rescaled to obtain a broader uncertainty range. The rescaling is done by first
disentangling the climate change response in the RCM simulations into a part related to the circulation, and a residual part
which is related to the global temperature rise. Second, these responses are rescaled using the range of the predictions of
global temperature change and circulation change from five GCMs. These GCMs have been selected on their ability to simulate
the present-day circulation, in particular over Europe. For the seasonal means, the rescaled RCM results obey the range in
the GCM ensemble using a high and low emission scenario. Thus, the rescaled RCM results are consistent with the GCM results
for the means, while adding information on the small scales and the extremes. The method can be interpreted as a combined
statistical–dynamical downscaling approach, with the statistical relations based on regional model output. 相似文献
17.
Aurore Voldoire Bas Eickhout Michiel Schaeffer Jean-François Royer Fabrice Chauvin 《Climate Dynamics》2007,29(2-3):177-193
To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents
socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3.
In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs)
concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation.
With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with
maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up,
land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence
of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change
is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account
climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of
the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these
effects are relevant mainly for multi-centennial simulations. 相似文献
18.
Peter Siegmund 《Climate Dynamics》1995,11(2):129-140
The generation of available potential energy (APE) in the space-time domain in January and July in a present-day climate simulation with a general circulation model (GCM) is compared with observations. An attempt is made to explain the differences. The generation is computed from the fields of diabatic heating and temperature. The heating is computed with the residual method, using UKMO (United Kingdom Meteorological Office) Unified Model GCM circulation data and ECMWF (European Centre for Medium-Range Weather Forecasts) initialized analyses for the period 1989–1992. The global value of the generation of APE is about 35% larger in the GCM climate than the value computed from the analyses. This is mainly because the generation of transient eddy APE in the GCM is too large, due to the more than 40% too large generation of transient eddy kinetic energy by baro-clinic processes. In most of the extratropics the local contribution to the generation of transient eddy APE in the GCM climate is more than twice as large as the contribution computed from the analyses. A possible qualitative explanation for this difference is presented. 相似文献
19.
A numerical nesting system is developed to simulate wintertime climate of the eastern South Pacific-South America-western
South Atlantic region, and preliminary results are presented. The nesting system consists of a large-scale global atmospheric
general circulation model (GCM) and a regional climate model (RCM). The latter is driven at its boundaries by the GCM. The
particularity of this nesting system is that the GCM itself has a variable horizontal resolution (stretched grid). Our main
purpose is to assess the plausibility of such a technique to improve climate representation over South America. In order to
evaluate how this nesting system represents the main features of the regional circulation, several mean fields have been analyzed.
The global model, despite its relatively low resolution, could simulate reasonably well the more significant large-scale circulation
patterns. The use of the regional model often results in improvements, but not universally. Many of the systematic errors
of the global model are also present in the regional model, although the biases tend to be rectified. Our preliminary results
suggest that nesting technique is a computationally low-cost alternative for simulating regional climate features. However,
additional simulations, parametrizations tuning and further diagnosis are clearly needed to represent local patterns more
precisely.
Received: 18 February 1999 / Accepted: 31 May 2000 相似文献
20.
Filippo Giorgi Linda O. Mearns Christine Shields Larry McDaniel 《Climatic change》1998,40(3-4):457-493
A nested regional climate model is used to generate a scenario of climate change over the MINK region (Missouri, Iowa, Nebraska, Kansas) due to doubling of carbon dioxide concentration (2 × CO2) for use in agricultural impact assessment studies. Five-year long present day (control) and 2 × CO2 simulations are completed at a horizontal grid point spacing of 50 km. Monthly and seasonal precipitation and surface air temperature over the MINK region are reproduced well by the model in the control run, except for an underestimation of both variables during the spring months. The performance of the nested model in the control run is greatly improved compared to a similar experiment performed with a previous version of the nested modeling system by Giorgi et al. (1994). The nested model generally improves the simulation of spatial precipitation patterns compared to the driving general circulation model (GCM), especially during the summer. Seasonal surface warming of 4 to 6 K and seasonal precipitation increases of 6 to 24% are simulated in 2 × CO2 conditions. The control run temperature biases are smaller than the simulated changes in all seasons, while the precipitation biases are of the same order of magnitude as the simulated changes. Although the large scale patterns of change in the driving GCM and nested RegCM model are similar, significant differences between the models, and substantial spatial variability, occur within the MINK region. 相似文献