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Hu W.,University of Saskatchewan | Hu W.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Shao M.A.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Hou M.T.,China Meteorological Administration Training Center | And 2 more authors.
Journal of Hydrology | Year: 2013

Quick and accurate estimates of spatial mean volumetric soil water content (θ) are essential for validating remotely-sensed soil water content and water budget analyses. The objective of this study was to test and validate a methodology that utilizes measured θ from the Most Time Stable Locations (MTSLs) to estimate mean θ in an adjacent or distant area while negating the impact of variability in soil, vegetation and topographic properties. Soil water content measured by a neutron probe at depths of 0.1, 0.2, 0.4, 0.6 and 0.8. m in Laoyemanqu watershed on the Chinese Loess Plateau was used to test our methodology. This method predicts mean θ of one area with measured θ at the MTSL from another area. Estimation errors depend on size of the study areas, number of measurement times in the target area and soil depth. A more accurate estimation of mean θ was found when using larger areas and deeper soils. Our method was also validated by predicting mean θ of a larger watershed (Liudaogou watershed) using the θ measurement at the MTSL at Laoyemanqu watershed. The proposed method has great potential for soil water upscaling with socio-economic, environmental and geo-political values. © 2013 Elsevier B.V.

Hu Y.,CAS Institute of Atmospheric Physics | Hu Y.,China Meteorological Administration Training Center | Dong W.,Beijing Normal University | He Y.,National Climate Center
Journal of Geophysical Research: Atmospheres | Year: 2010

The "observation minus reanalysis" (OMR) method is used to estimate the impact of land surface forcings on surface temperature by computing the difference of trends between the observations and reanalysis data set. The basis of this method is that if observed surface temperature, moisture, and wind over land are not used in reanalysis, the reanalysis data set should not be sensitive to urbanization and other land use change. In this study, the OMR method is used to estimate the impacts of land surface change on surface temperature trends during the period from 1979 to 2008 in eastern China, and the difference time series of extreme temperature indices between the observations and the reanalysis data sets is also analyzed. The OMR trends of annual cold (warm) nights exhibit generally decrease (increase), it means that land surface change is likely to enhance the decreasing (increasing) trends of annual cold (warm) nights. The decreasing (increasing) OMR trends of annual cold (warm) days is found in semiarid region in northern China, while the increasing (decreasing) of cold (warm) days occurs in eastern agricultural area. For eastern China as a whole, the land surface change impact may explain about one third of the observed increase for the annual warm nights and nearly half of the observed decrease for the annual cold nights, and the impacts on the annual cold days and warm days are relatively small. The land surface change may reduce the diurnal temperature range significantly. The impact of land surface forcings on extreme temperature demonstrates obviously annual variation. Copyright © 2010 by the American Geophysical Union.

Sun J.,CAS Institute of Atmospheric Physics | Wang H.,CAS Institute of Atmospheric Physics | Yuan W.,China Meteorological Administration Training Center
Journal of the Meteorological Society of Japan | Year: 2010

The relationship between the boreal spring (or the austral autumn) Antarctic Oscillation (AAO) (March-April) and the West African summer monsoon (WASM) (June-September) is analyzed based on NCEP/NCAR reanalysis data. The results show that the linkage of the boreal spring AAO to the WASM exhibits decadal-scale variations: a strong connection between the two appears over the period 1985-2006 and a weak connection over the period 1970-1984. Further analysis indicates that such an unstable relationship between the two results from the modulation by ENSO events to a large extent. A possible mechanism for the impacts of the boreal spring AAO on the WASM is also discussed. The variability of the boreal spring tropical South Atlantic sea surface temperature (SST) appears to serve as a bridge linking these two systems. The boreal spring AAO produces an anomalous SST over the tropical South Atlantic by exciting an equatorward Rossby wave train over the western Southern Hemisphere (SH). This AAO-related SST anomaly modulates the meridional gradient of moist static energy (MSE) between the Sahel and the Guinea-tropical Atlantic region in the boreal spring. The MSE gradient is of paramount importance for the changes from spring to summer in the West African monsoon because its relaxation along the seasonal cycle is linked to the northward excursion of the WASM system into the African continent. Therefore, an anomalous AAO-related MSE gradient can lead to anomalous Sahel rainfall in the early summer. When this rainfall occurs over the Sahel, the local positive soil moisture-rainfall feedback plays a crucial role in sustaining and prolonging this rainfall anomaly throughout the whole summer. © 2010, Meteorological Society of Japan.

Yang P.,China Meteorological Administration Training Center | Ren G.,National Climate Center | Liu W.,Institute of Urban Meteorology
Journal of Applied Meteorology and Climatology | Year: 2013

An hourly dataset of automatic weather stations over Beijing Municipality in China is developed and is employed to analyze the spatial and temporal characteristics of urban heat island intensity (UHII) over the built-up areas.Atotal of 56 stations that are located in the built-up areas [inside the 6th Ring Road (RR)] are considered to be urban sites, and 8 stations in the suburban belts surrounding the built-up areas are taken as reference sites. The reference stations are selected by using a remote sensing method. The urban sites are further divided into three areas on the basis of the city RRs. It is found that the largest UHII generally takes place inside the 4th RR and that the smallest ones occur in the outer belts of the built-up areas, between the 5th RR and the 6th RR, with the areas near the northern and southern 6th RR experiencing the weakest UHI phenomena. On a seasonal basis, the strongest UHII generally occurs in winter and weak UHII is dominantly observed in summer and spring. The UHII diurnal variations for each of the urban areas are characterized by a steadily strong UHII stage from 2100 local solar time (LST) to 0600 LST and a steadily weak UHII stage from 1100 to 1600 LST, with the periods 0600-1100 LST and 1600-2100 LST experiencing a swift decline and rise, respectively. UHII diurnal variation is seen throughout the year, but the steadily strong UHII stage at night is longer (shorter) and the steadily weak UHII stage during the day is shorter (longer) during winter and autumn (summer and spring). © 2013 American Meteorological Society.

Chen Z.,China Meteorological Administration Training Center | Yang G.,China University of Geosciences
Natural Hazards | Year: 2013

This paper examines the characteristics of historical meteorological hazards and associated natural-anthropogenic variations in China, with specific attention given to the meteorological drought hazards occurring at very high frequency and affecting social-economic development in North China. Owing to an increasing awareness of meteorological droughts in this area, the aim of this contribution is to provide a comprehensive overview of meteorological droughts in North China by reviewing the meteorological references and their intrinsic linkages with climatic, geological, and anthropogenic controls. Our study highlights the region-wide meteorological droughts with a rather clear recurrence of 30 and 100 years, totally indicating Shanxi and Shandong being the predominated area suffering from extreme meteorological droughts. The spatial and temporal distribution of meteorological drought hazards in this region is considered to be a function of climatic, topographic, hydrological, and anthropogenic characteristics. In view of the wide distribution and linkage with geo-hazards and changes of dynasties, the meteorological drought hazard is one of the key issues for long-term social-economic harmonization. This study can be expected to prioritize drought mitigation measures and ensure regional sustainable development in North China. © 2012 Springer Science+Business Media B.V.

Yang G.,China University of Geosciences | Zhang C.L.,Tongji University | Zhang C.L.,University of Georgia | Xie S.,Wuhan University | And 4 more authors.
Organic Geochemistry | Year: 2013

Suspended particulate matter (SPM) was collected above and below the Three Gorges Dam (TGD) on the Yangtze River in May, July and December 2009, respectively, for a study of the spatial and temporal variation in glycerol dialkyl glycerol tetraethers (GDGTs) in the riverine system. The branched GDGTs (bGDGTs) were > 0.6ng/l and isoprenoid GDGTs (iGDGTs) > 0.3ng/l in most SPM samples in May and July, whereas, iGDGTs were on average about 10× more abundant than bGDGTs in December. The results suggest that the abundance of bGDGTs and iGDGTs in the Yangtze River at the TGD varied seasonally, which might be affected by soil runoff and in situ production. Despite these effects, the TEX86-inferred temperature derived from SPM reflected the measured river surface water temperature in the sampling months, suggesting that planktonic Thaumarchaeota might actively make iGDGTs in the river water near the TGD throughout the year. The bGDGT-derived CBT/MBT temperature from the SPM was not significantly different among the three seasons and the values together averaged 15.2±0.7°C, close to the annual mean air temperature (16.9°C) in the region near the TGD. However, the bGDGT-derived pHCBT values were close to the water pH and slightly higher than the pH of the local soil. These results suggest that the sources of bGDGTs in the river water are complicated and that bGDGTs may not solely derive from the local soil runoff. Nevertheless, our study highlights the potential of using TEX86 and MBT/CBT proxies for a better understanding of the source and mechanism of GDGT production in riverine systems increasingly affected by the construction of dams. © 2012 Elsevier Ltd.

Zhao J.,China Meteorological Administration Training Center | Zou X.,Florida State University | Zou X.,Nanjing University of Information Science and Technology | Weng F.,National Oceanic and Atmospheric Administration
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

A detection of radio-frequency interference (RFI) in the space-borne microwave radiometer data is difficult under snow and sea ice-covered conditions. The existing methods such as a spectral difference technique or a principal component analysis (PCA) of RFI indices produce many false RFI signals near the boundary of Greenland and Antarctic ice sheets. In this paper, a double PCA (DPCA) method is developed for RFI detection over Greenland and Antarctic regions. It is shown that the new DPCA method is effective in detecting RFI signals in the C- and X-band radiometer channels of WindSat while removing the false RFI signals over Greenland and Antarctic. It also worked well in other snow-free or snow-rich regions such as winter data over the United States. The proposed DPCA can be applied to satellite radiometer data orbit-by-orbit or granule-by-granule and is thus applicable in an operational environment for fast processing and data dissemination. © 1980-2012 IEEE.

Zou X.,Florida State University | Zhao J.,China Meteorological Administration Training Center | Weng F.,National Oceanic and Atmospheric Administration | Qin Z.,Florida State University | Qin Z.,Nanjing University of Information Science and Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2012

The MicroWave Radiation Imager (MWRI) onboard the FengYun (FY)-3B satellite has five frequencies at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz, each having dual channels at vertical and horizontal polarization states, respectively. It is found that radio-frequency interference (RFI) is present in MWRI data over land. The RFI signals are, in general, detectable from a spectral difference method and a principal component analysis (PCA) method. In particular, the PCA method is applied to derive RFI signals from natural radiations by using the characteristics of natural radiation measurements having all-channel correlations. In the area where data have a higher projection onto the first principle component (PC) mode, RFI is, in general, present. However, both the spectral and PCA methods cannot detect RFI reliably over frozen grounds and scattering surfaces, where the brightness temperature difference between 10.65 and 18.7 GHz is large. Thus, detection is improved through the use of normalized PCA. The new RFI detection algorithm is now working reliably for MWRI applications. It is found that RFI at 10.65 GHz distributes widely over Europe and Japan, and is less popular over the United States and China. © 2012 IEEE.

Duan W.,CAS Institute of Atmospheric Physics | Zhao P.,CAS Institute of Atmospheric Physics | Zhao P.,China Meteorological Administration Training Center
Climate Dynamics | Year: 2015

The nonlinear forcing singular vector (NFSV) approach is used to identify the most disturbing tendency error of the Zebiak–Cane model associated with El Niño predictions, which is most potential for yielding aggressively large prediction errors of El Niño events. The results show that only one NFSV exists for each of the predictions for the predetermined model El Niño events. These NFSVs cause the largest prediction error for the corresponding El Niño event in perfect initial condition scenario. It is found that the NFSVs often present large-scale zonal dipolar structures and are insensitive to the intensities of El Niño events, but are dependent on the prediction periods. In particular, the NFSVs associated with the predictions crossing through the growth phase of El Niño tend to exhibit a zonal dipolar pattern with positive anomalies in the equatorial central-western Pacific and negative anomalies in the equatorial eastern Pacific (denoted as “NFSV1”). Meanwhile, those associated with the predictions through the decaying phase of El Niño are inclined to present another zonal dipolar pattern (denoted as “NFSV2”), which is almost opposite to the NFSV1. Similarly, the linear forcing singular vectors (FSVs), which are computed based on the tangent linear model, can also be classified into two types “FSV1” and “FSV2”. We find that both FSV1 and NFSV1 often cause negative prediction errors for Niño-3 SSTA of the El Niño events, while the FSV2 and NFSV2 usually yield positive prediction errors. However, due to the effect of nonlinearities, the NFSVs usually have the western pole of the zonal dipolar pattern much farther west, and covering much broader region. The nonlinearities have a suppression effect on the growth of the prediction errors caused by the FSVs and the particular structure of the NFSVs tends to reduce such suppression effect of nonlinearities, finally making the NFSV-type tendency error yield much large prediction error for Niño-3 SSTA of El Niño events. The NFSVs, compared to the FSVs, are more applicable in describing the most disturbing tendency error of the Zebiak–Cane model since they consider the effect of nonlinearities. The NFSV-type tendency errors may provide information concerning the sensitive areas where the model errors are much more likely to yield large prediction errors for El Niño events. If the simulation skills of the states in the sensitive areas can be improved, the ENSO forecast skill may in turn be greatly increased. © 2014, The Author(s).

Sun J.,CAS Institute of Atmospheric Physics | Sun J.,Chinese Academy of Sciences | Wang H.,CAS Institute of Atmospheric Physics | Wang H.,Chinese Academy of Sciences | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010

The statistical spatial-temporal features of the intense snowfall event (ISE) in China are investigated over the period of 1962-2000. The results indicate that eastern China, northern Xinjiang, the eastern Tibetan plateau, and northeastern China are four key regions for the ISE, with more frequency and strong variability. Annual cycle analysis shows the ISE exhibits a unimodal distribution with maximum frequency at winter months for eastern China, a bimodal distribution with maximum frequency at early winter and spring months for northern Xinjiang and northeastern China, and a bimodal distribution with maximum frequency at autumn and spring months for the eastern Tibetan plateau. Linear trend analysis indicates that in the last 39 years, the ISE exhibits a decreasing trend for eastern China and an increasing trend for northern Xinjiang and the eastern Tibetan plateau. The linear trend of the ISE is weak over northeastern China. Based on the simulations of the most recent and comprehensive climate models in the 20th century run, the performance of the current climate models in simulating the Chinese ISE is investigated. The results indicate that, of the 20 models, there are four models that can reasonably reproduce the spatial-temporal features of the Chinese ISE. Based on these four models' simulation for the 21st century under A1B and A2 scenarios, the future variability of the Chinese ISE is projected. It is found that global warming will cause the ISE frequency over southern China to decrease, while the ISE over northern China will initially increase and then decrease. Copyright 2010 by the American Geophysical Union.

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