| 1. |
- Chen, Deliang, 1961, et al.
(författare)
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Spatial Interpolation of Daily Precipitation in China : 1951-2005
- 2010
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 27:6, s. 1221-1232
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Tidskriftsartikel (refereegranskat)abstract
- Climate research relies heavily on good quality instrumental data; for modeling efforts gridded data are needed. So far, relatively little effort has been made to create gridded climate data for China. This is especially true for high-resolution daily data. This work, focuses on identifying an accurate method to produce gridded daily precipitation in China based on the observed data at 753 stations for the period 1951-2005. Five interpolation methods, including ordinary nearest neighbor, local polynomial, radial basis function, inverse distance weighting, and ordinary kriging, have been used and compared. Cross-validation shows that the ordinary kriging based on seasonal semi-variograms gives the best performance, closely followed by the inverse distance weighting with a power of 2. Finally the ordinary kriging is chosen to interpolate the station data to a 18 kmx 18 km grid system covering the whole country. Precipitation for each 0.5A degrees x 0.5A degrees latitude-longitude block is then obtained by averaging the values at the grid nodes within the block. Owing to the higher station density in the eastern part of the country, the interpolation errors are much smaller than those in the west (west of 100A degrees E). Excluding 145 stations in the western region, the daily, monthly, and annual relative mean absolute errors of the interpolation for the remaining 608 stations are 74%, 29%, and 16%, respectively. The interpolated daily precipitation has been made available on the internet for the scientific community.
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| 2. |
- Fan, Lijun, et al.
(författare)
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Statistical downscaling of summer temperature extremes in northern China
- 2013
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 30:4, s. 1085-1095
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Tidskriftsartikel (refereegranskat)abstract
- Two approaches of statistical downscaling were applied to indices of temperature extremes based on percentiles of daily maximum and minimum temperature observations at Beijing station in summer during 1960-2008. One was to downscale daily maximum and minimum temperatures by using EOF analysis and stepwise linear regression at first, then to calculate the indices of extremes; the other was to directly downscale the percentile-based indices by using seasonal large-scale temperature and geo-potential height records. The cross-validation results showed that the latter approach has a better performance than the former. Then, the latter approach was applied to 48 meteorological stations in northern China. The cross-validation results for all 48 stations showed close correlation between the percentile-based indices and the seasonal large-scale variables. Finally, future scenarios of indices of temperature extremes in northern China were projected by applying the statistical downscaling to Hadley Centre Coupled Model Version 3 (HadCM3) simulations under the Representative Concentration Pathways 4.5 (RCP 4.5) scenario of the Fifth Coupled Model Inter-comparison Project (CMIP5). The results showed that the 90th percentile of daily maximum temperatures will increase by about 1.5A degrees C, and the 10th of daily minimum temperatures will increase by about 2A degrees C during the period 2011-35 relative to 1980-99.
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| 3. |
- Fu, J., et al.
(författare)
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Trends in graded precipitation in China from 1961 to 2000
- 2008
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Ingår i: Advances in atmospheric Sciences. - : Springer Science and Business Media LLC. - 1861-9533 .- 0256-1530. ; 25:2, s. 267-278
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Tidskriftsartikel (refereegranskat)abstract
- Daily precipitation rates observed at 576 stations in China from 1961 to 2000 were classified into six grades of intensity, including trace (no amount), slight (<= 1 mm d(-1)), small, large, heavy, and very heavy. The last four grades together constitute the so called effective precipitation (> 1 mm d(-)1). The spatial distribution and temporal trend of the graded precipitation days are examined. A decreasing trend in trace precipitation days is observed for the whole of China, except at several sites in the south of the middle section of the Yangtze River, while a decreasing trend in slight precipitation days only appears in eastern China. The decreasing trend and interannual variability of trace precipitation days is consistent with the warming trend and corresponding temperature variability in China for the same period, indicating a possible role played by increased surface air temperature in cloud formation processes. For the effective precipitation days, a decreasing trend is observed along the Yellow River valley and for the middle reaches of the Yangtze River and Southwest China, while an increasing trend is found for Xinjiang, the eastern Tibetan Plateau, Northeast China and Southeast China. The decreasing trend of effective precipitation days for the middle-lower Yellow River valley and the increasing trend for the lower Yangtze River valley are most likely linked to anomalous monsoon circulation in East China. The most important contributor to the trend in effective precipitation depends upon the region concerned.
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| 4. |
- Hua, Chen, et al.
(författare)
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Downscaling GCMs using the Smooth Support Vector Machine method to predict daily precipitation in the Hanjiang Basin
- 2010
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 27:2, s. 274-284
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Tidskriftsartikel (refereegranskat)abstract
- General circulation models (GCMs) are often used in assessing the impact of climate change at global and continental scales. However, the climatic factors simulated by GCMs are inconsistent at comparatively smaller scales, such as individual river basins. In this study, a statistical downscaling approach based on the Smooth Support Vector Machine (SSVM) method was constructed to predict daily precipitation of the changed climate in the Hanjiang Basin. NCEP/NCAR reanalysis data were used to establish the statistical relationship between the larger scale climate predictors and observed precipitation. The relationship obtained was used to project future precipitation from two GCMs (CGCM2 and HadCM3) for the A2 emission scenario. The results obtained using SSVM were compared with those from an artificial neural network (ANN). The comparisons showed that SSVM is suitable for conducting climate impact studies as a statistical downscaling tool in this region. The temporal trends projected by SSVM based on the A2 emission scenario for CGCM2 and HadCM3 were for rainfall to decrease during the period 2011-2040 in the upper basin and to increase after 2071 in the whole of Hanjiang Basin.
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| 5. |
- Lai, Hui-Wen, et al.
(författare)
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Modeling Arctic Boundary Layer Cloud Streets at Grey-zone Resolutions
- 2020
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 37:1, s. 42-56
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Tidskriftsartikel (refereegranskat)abstract
- To better understand how model resolution affects the formation of Arctic boundary layer clouds, we investigated the influence of grid spacing on simulating cloud streets that occurred near Utqiagvik (formerly Barrow), Alaska, on 2 May 2013 and were observed by MODIS (the Moderate Resolution Imaging Spectroradiometer). The Weather Research and Forecasting model was used to simulate the clouds using nested domains with increasingly fine resolution ranging from a horizontal grid spacing of 27 km in the boundary-layer-parameterized mesoscale domain to a grid spacing of 0.111 km in the large-eddy-permitting domain. We investigated the model-simulated mesoscale environment, horizontal and vertical cloud structures, boundary layer stability, and cloud properties, all of which were subsequently used to interpret the observed roll-cloud case. Increasing model resolution led to a transition from a more buoyant boundary layer to a more shear-driven turbulent boundary layer. The clouds were stratiform-like in the mesoscale domain, but as the model resolution increased, roll-like structures, aligned along the wind field, appeared with ever smaller wavelengths. A stronger vertical water vapor gradient occurred above the cloud layers with decreasing grid spacing. With fixed model grid spacing at 0.333 km, changing the model configuration from a boundary layer parameterization to a large-eddy-permitting scheme produced a more shear-driven and less unstable environment, a stronger vertical water vapor gradient below the cloud layers, and the wavelengths of the rolls decreased slightly. In this study, only the large-eddy-permitting simulation with gird spacing of 0.111 km was sufficient to model the observed roll clouds.
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| 6. |
- Li, Hanying, et al.
(författare)
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Understanding Interannual Variations of the Local Rainy Season over the Southwest Indian Ocean
- 2021
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 38:11, s. 1852-1862
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Tidskriftsartikel (refereegranskat)abstract
- Located at the southern boundary of the tropical rainfall belt within the South Africa monsoon regime, Rodrigues Island, ∼2500 km east of East Africa, is ideally located to investigate climatic changes over the southwest Indian Ocean (SWIO). In this study, we investigate the climatic controls of its modern interannual rainfall variability in terms of teleconnection and local effects. We find that increased rainfall over the SWIO tends to occur in association with anomalously warm (cold) SSTs over the equatorial central Pacific (Maritime Continent), resembling the central Pacific El Niño, closely linked with the Victoria mode in the North Pacific. Our analyses show that the low-level convergence induced by warm SST over the equatorial central Pacific leads to anomalous low-level divergence over the Maritime Continent and convergence over a large area surrounding the Rodrigues Island, which leads to increased rainfall over the SWIO during the rainy season. Meanwhile, the excited Rossby wave along the tropical Indian Ocean transports more water vapor from the tropical convergence zone into the SWIO via intensified northwest wind. Furthermore, positive feedback induced by the Rossby wave response to the increased rainfall in the region contributes to the large interannual variations over the SWIO.
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| 7. |
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| 8. |
- Mei, H., et al.
(författare)
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A Global Spectral Element Model for Poisson Equations and Advective Flow over a Sphere
- 2016
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 33:3, s. 377-390
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Tidskriftsartikel (refereegranskat)abstract
- A global spherical Fourier-Legendre spectral element method is proposed to solve Poisson equations and advective flow over a sphere. In the meridional direction, Legendre polynomials are used and the region is divided into several elements. In order to avoid coordinate singularities at the north and south poles in the meridional direction, Legendre-Gauss-Radau points are chosen at the elements involving the two poles. Fourier polynomials are applied in the zonal direction for its periodicity, with only one element. Then, the partial differential equations are solved on the longitude-latitude meshes without coordinate transformation between spherical and Cartesian coordinates. For verification of the proposed method, a few Poisson equations and advective flows are tested. Firstly, the method is found to be valid for test cases with smooth solution. The results of the Poisson equations demonstrate that the present method exhibits high accuracy and exponential convergence. Highprecision solutions are also obtained with near negligible numerical diffusion during the time evolution for advective flow with smooth shape. Secondly, the results of advective flow with non-smooth shape and deformational flow are also shown to be reasonable and effective. As a result, the present method is proved to be capable of solving flow through different types of elements, and thereby a desirable method with reliability and high accuracy for solving partial differential equations over a sphere.
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| 9. |
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| 10. |
- Wang, Jianfeng, 1984-, et al.
(författare)
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A Hybrid Statistical-Dynamical Downscaling of Air Temperature over Scandinavia Using the WRF Model
- 2020
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Ingår i: Advances in Atmospheric Sciences. - : Springer. - 0256-1530 .- 1861-9533. ; 37:1, s. 57-74
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Tidskriftsartikel (refereegranskat)abstract
- An accurate simulation of air temperature at local scales is crucial for the vast majority of weather and climate applications. In this work, a hybrid statistical–dynamical downscaling method and a high-resolution dynamical-only downscaling method are applied to daily mean, minimum and maximum air temperatures to investigate the quality of localscale estimates produced by downscaling. These two downscaling approaches are evaluated using station observation data obtained from the Finnish Meteorological Institute over a near-coastal region of western Finland. The dynamical downscaling is performed with the Weather Research and Forecasting (WRF) model, and the statistical downscaling method implemented is the Cumulative Distribution Function-transform (CDF-t). The CDF-t is trained using 20 years of WRF-downscaled Climate Forecast System Reanalysis data over the region at a 3-km spatial resolution for the central month of each season. The performance of the two methods is assessed qualitatively, by inspection of quantile-quantile plots, and quantitatively, through the Cramer-von Mises, mean absolute error, and root-mean-square error diagnostics. The hybrid approach is found to provide significantly more skillful forecasts of the observed daily mean and maximum air temperatures than those of the dynamical-only downscaling (for all seasons). The hybrid method proves to be less computationally expensive, and also to give more skillful temperature forecasts (at least for the Finnish near-coastal region).
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