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Beijing, China

Yang X.H.,Zhejiang University | Huang J.F.,Zhejiang University | Wu Y.P.,Meteorological | Wang J.W.,Meteorological | And 3 more authors.
Science China Life Sciences | Year: 2011

Hyperspectral reflectance (350-2500 nm) measurements were made over two experimental rice fields containing two cultivars treated with three levels of nitrogen application. Four different transformations of the reflectance data were analyzed for their capability to predict rice biophysical parameters, comprising leaf area index (LAI; m2 green leaf area m-2 soil) and green leaf chlorophyll density (GLCD; mg chlorophyll m-2 soil), using stepwise multiple regression (SMR) models and support vector machines (SVMs). Four transformations of the rice canopy data were made, comprising reflectances (R), first-order derivative reflectances (D1), second-order derivative reflectances (D2), and logarithm transformation of reflectances (LOG). The polynomial kernel (POLY) of the SVM using R was the best model to predict rice LAI, with a root mean square error (RMSE) of 1.0496 LAI units. The analysis of variance kernel of SVM using LOG was the best model to predict rice GLCD, with an RMSE of 523.0741 mg m-2. The SVM approach was not only superior to SMR models for predicting the rice biophysical parameters, but also provided a useful exploratory and predictive tool for analyzing different transformations of reflectance data. © 2011 The Author(s). Source

Yong H.,Meteorological | Chong-yin L.,PLA University of Science and Technology | Chong-yin L.,CAS Institute of Atmospheric Physics | Ying W.,Meteorological
Journal of Tropical Meteorology | Year: 2012

Based on analyses of the relationship between Pacific Meridional Mode (PMM) and number of tropical cyclones (TCs) activity over the western North Pacific, the impacts of the PMM on Tc activity over the western North Pacific are studied using numerical simulations with an Atmospheric General Circulation Model (CAM3) of National Center for Atmospheric Research (of USA). The result shows that the PMM has impacts on the large-scale generating environment of TCs, thus affecting their number and strength. The numerical simulations using the NCAR CAM3 indicate that with the inclusion of the forcing from sea surface temperature (SST) of the PMM, there appears a decreased magnitude of the vertical zonal wind shear, large proportion of relative humidity, anomalous westerly wind at low levels and anomalous easterly wind at high levels, in association with anomalous cyclonic circulation at low levels and anomalous anti-cyclonic circulation at high levels over the tropical western Pacific. Thus, the PMM provides favorable environment for the typhoon genesis. In the sensitivity experiment, TCs have larger strength, lower SST at the center, stronger tangential wind at 850 hPa and intensified warm cores at high levels. In this paper, the simulation results are similar to that in the data analyses, which reveals the important impact of the PMM on TC activity over the western North Pacific. Source

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