支持向量机方法在南京太阳总辐射推算中的应用          下载免费PDF全文

杨光  谭言科  吴凡 《大气科学学报》2017,40(5):708-714

利用1981、1996和2001年逐日南京站太阳总辐射和日照时数观测资料,建立了基于支持向量机(support vector machine,SVM)方法的太阳总辐射推算模型,预测了1982、1997和2002年的太阳总辐射,并把推算结果和采用线性的气候学方法所得到的推算结果分别与实测值进行对比。采用线性方法得到的1982、1997和2002年的太阳总辐射预测值与实测值间基于1:1线的决定系数(R~2)分别为0.800、0.859和0.838,均方根误差(RMSE)分别为3.250、2.649和2.925 MJ·m~(-2)·d~(-1)。采用SVM方法得到的1982、1997和2002年的R~2分别为0.894、0.938和0.936,RMSE分别为2.353、1.726和1.804 MJ·m~(-2)·d~(-1)。SVM方法得到的太阳总辐射预测值与实测值之间的误差较小,预测精度高于线性方法,更适用于实际太阳总辐射的计算。  相似文献   

UV-B辐射增强对不同品种花生结荚期生理特性日变化的影响     

韩艳  鲁建立  韩晨光  胡程达  崔荣华 《南京气象学院学报》2018,10(2):218-224

以3个花生品种（开农49号、64号和69号）为材料,通过大田模拟试验,研究UV-B辐射增强对花生结荚期叶片的净光合速率（P_n）、气孔导度（G_s）、胞间CO₂浓度（C_i）、蒸腾速率（T_r）和水分利用效率（E_wu）日变化的影响,为筛选高产、抗旱、抗UV-B辐射花生品种提供依据.UV-B辐射设2个水平即自然光（CK,1.5 kJ·m^-2）和UV-B增强20%（T,1.8 kJ·m^-2）.结果表明,UV-B辐射增强明显抑制花生的光合作用和蒸腾作用,与对照相比,UV-B增强条件下,开农49号、64号和69号P_n日均值分别降低19.4%、27.8%、24.7%;G_s日均值降低26.7%、42.9%、28.6%;C_i日均值降低27.2%、20.4%、23.1%;T_r日均值降低17.8%、23.3%、25.1%;E_wu日均值降低16.6%、23.2%、23.9%.UV-B辐射增强对3个品种生长都具有抑制效应,但品种间存在一定的敏感性差异,其中开农49号最不敏感,因此,开农49号在抗UV-B辐射方面比其他2个品种具有更大的优势.  相似文献   

Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake   总被引：1，自引：0，他引：1  

Yichen Yang  Yongwei Wang  Zhen Zhang  Wei Wang  Xia Ren  Yaqi Gao  Shoudong Liu  Xuhui Lee 《Acta Meteorologica Sinica》2018,32(2):219-232

Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here, the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient, the maximum of which exceeds 5°C m^–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s^–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer.  相似文献   

Vulnerabilities of macrophytes distribution due to climate change     

Hossain  Kaizar  Yadav  Sarita  Quaik  Shlrene  Pant  Gaurav  Maruthi  A. Y.  Ismail  Norli 《Theoretical and Applied Climatology》2017,129(3-4):1123-1132

Theoretical and Applied Climatology - The rise in the earth’s surface and water temperature is part of the effect of climatic change that has been observed for the last decade. The rates of...  相似文献   

South-north dipolar pattern around mid-1990s in Korean summer rainfall variability     

《Dynamics of Atmospheres and Oceans》2017

From the time series of rainfall in summer (June, July and August) in South and North Koreas for recent 28 years (1981–2008), rainfall has significantly increased in South Korea while it has significantly decreased in North Korea since 1996. In particular, the decreasing trend of summer rainfall in North Korea was more conspicuous during the second Changma (late August – mid-September). This characteristic was also found in the south-north dipolar pattern based on 1996 by empirical orthogonal function analysis using summer rainfall observed in all weather observation stations in South and North Korea.The decreasing rainfall trend in North Korea was found to be associated with the weakening of convection by anomalous northeasterlies from anomalous anticyclone centered on around Baikal Lake during summer. On the other hand, the increasing rainfall trend of South Korea was associated with the strengthened anomalous cyclone in the southern region of China, which in turn strengthened anomalous southwesterlies.  相似文献   

Model of wind accretion in extrinsic AGB stars under conservation of total angular momentum     

《Chinese Astronomy and Astrophysics》1999,23(2):189-194

The equations of wind accretion and variation of orbital parameters are rederived under conservation of total (rather than tangential) angular momentum, and applied to extrinsic AGB stars. These equations, together with nucleosynthesis in intrinsic AGB stars, are used to calculate heavy element overabundance for the scenario of successive pulses and mixing. The results show that wind accretion pertains when the orbital period is longer than 1300 d or 1600 d according as the initial mass of the Ba star is 2.5 M_⊙ or 1.3 M_⊙, while cataclysmic variables will result if the period is shorter than 600 d in either case. The results are advantageous for interpreting a) the observations on the overabundance and orbital parameters, b) the observed lower limit of 600 d in the period of extrinsic S stars, and c) the observed fact that the mean eccentricity of Ba stars is greater than the mean eccentricities of extrinsic S stars and CH stars.  相似文献   

Assessment of global TEC mapping using a three-dimensional electron density model     

《Journal of Atmospheric and Solar》1999,61(16):1227-1236

Dual-frequency transmissions from the Global Positioning System satellites can be used to measure and map ionospheric total electron content (TEC) on global scales. Using data exclusively from ground-based GPS networks, global ionosphere mapping has been successfully applied using either two- or three-dimensional techniques. Two-dimensional TEC maps retrieve a horizontally-varying distribution of total electron content, assuming a fixed vertical electron density profile. In three-dimensional mapping, both the horizontal and vertical distribution density are adjusted to fit the data. We describe a three-dimensional TEC mapping algorithm that uses three independent constant-density slabs stacked vertically to model the electron density, and compare with a more conventional two-dimensional approach using a single slab. One apparent benefit of the new method is reduction in a level error of the TEC maps, which decreased by 1.7 TECU using the three-dimensional retrieval on simulated data (1 TEC Unit corresponds to 10¹⁶ electrons/m²). Another benefit of the multilayer approach is improved slant TEC modeling. Using actual data from an equatorial site at Cocos Islands (96.8E, 12.2 S), three slab modeling improved estimates of slant TEC by a factor of 2 for elevation angles between 10 and 20° (9 versus 4.4 TECU, root-mean-square). However, the global structure of the vertical TEC retrievals we analyzed did not improve using three-dimensional modeling. This may be due to a critical approximation shared by both techniques that TEC persists unchanged at a given local time. This assumption is required to produce global maps from observations acquired from widely scattered ground receivers. Further improving the retrieval of global TEC structure with ground-based data probably requires improved dynamical models of TEC behavior. New data available from GPS receivers in low Earth orbit is also promising.  相似文献   

中国比辐射率空间分布特征分析   总被引：1，自引：0，他引：1  

姚镇海  邱新法  施国萍  张喜亮 《干旱区地理》2015,38(6):1234-1240

使用2003-2013年MOD/MYD11C3地表比辐射率光谱数据、MOD/MYD13C2植被指数光谱数据,合成全国各月地表比辐射率、NDVI(Normalized Difference Vegetation Index)。基于DEM数据分析比辐射率与NDVI随海拔、坡向的变化规律。结果表明:(1)比辐射率低值段(0.960~0.970)主要分布在我国西北荒漠地区,面积比例全年变化不显著,代表了干燥裸土下低比辐射率的特征;中值段(0.970~0.975)分布于我国大部分植被覆盖地区,面积比例夏高冬低,代表植被覆盖下混合像元的中比辐射率特征;高值段(0.975~0.980)位于我国部分高海拔和高纬度地区,面积比例冬高夏低,代表冰雪与植被混合像元的高比辐射率特征。(2)比辐射率与NDVI随坡向变化呈明显的"双峰双谷"分布。东南坡、西坡为峰值,最大值位于东南坡;南坡、北坡为谷值,最小值位于北坡。两者变化一致性很高。受不同坡向太阳方位角下的地形敏感性与植被覆盖综合影响,比辐射率表现出随坡向的峰谷变化规律。(3)随海拔升高,比辐射率呈垂直地带性变化。存在3个下降区:250 m~1250 m、2500 m~3000 m和4750 m~6000 m;3个上升区:1250 m~2500 m、3000 m~4750 m和6000 m~6500 m。这与NDVI随海拔变化特征类似,反映垂直下垫面植被变化对比辐射率空间分布的影响。  相似文献   

Simulation of Nitrous Oxide Emission and Mineralized Nitrogen under Different Straw Retention Conditions Using a Denitrification–Decomposition Model          下载免费PDF全文

Can Chen  Deli Chen  Shu Kee Lam 《洁净——土壤、空气、水》2015,43(4):577-583

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Modeling the low-latitude ionospheric electron density and plasma turbulence in the November 2004 storm period     

J.M. Retterer  Ronald Ilma  M.C. Kelley  Jorge L. Chau  C.E. Valladares  L.C. Gentile  K. Groves 《Journal of Atmospheric and Solar》2010,72(4):350-357

The storm period of 8–12 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence responsible for radio scintillation within it, using the AFRL low-latitude ambient/turbulent ionospheric model and the storm-time model features described in the companion paper [Retterer, J.M., Kelley, M.C., 2009. Solar-wind drivers for low-latitude ionospheric models during geomagnetic storms. J. Atmos. Solar-Terr. Phys., this issue]. The model plasma densities show very good agreement with the densities measured by the Jicamarca ISR as well as with the total electron content (TEC) measured by the Boston College South American chain of GPS receivers. The detection by the radar of coherent returns from plasma turbulence match well the times of predicted ionospheric instability. The predicted geographic extent of the occurrence of equatorial plasma bubbles was matched by DMSP satellite observations and our forecasts of scintillation strength were validated with measurements of S4 at Ancon and Antofagasta by stations of the AFRL SCINDA network.  相似文献