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1.
We examined the effects of freshwater flow and light availability on phytoplankton biomass and production along the Louisiana continental shelf in the region characterized by persistent spring–summer stratification and widespread summer hypoxia. Data were collected on 7 cruises from 2005 to 2007, and spatially-averaged estimates of phytoplankton and light variables were calculated for the study area using Voronoi polygon normalization. Shelf-wide phytoplankton production ranged from 0.47 to 1.75 mg C m−2 d−1 across the 7 cruises. Shelf-wide average light attenuation (kd) ranged from 0.19–1.01 m−1 and strongly covaried with freshwater discharge from the Mississippi and Atchafalaya Rivers (R2=0.67). Interestingly, we observed that the euphotic zone (as defined by the 1% light depth) extended well below the pycnocline and to the bottom across much of the shelf. Shelf-wide average chlorophyll a (chl a) concentrations ranged from 1.4 to 5.9 mg m−3 and, similar to kd, covaried with river discharge (R2=0.83). Also, chl a concentrations were significantly higher in plume versus non-plume regions of the shelf. When integrated through the water-column, shelf-wide average chl a ranged from 26.3 to 47.6 mg m−2, but did not covary with river discharge, nor were plume versus non-plume averages statistically different. The high integrated chl a in the non-plume waters resulted from frequent sub-pycnocline chl a maxima. Phytoplankton production rates were highest in the vicinity of the Mississippi River bird's foot delta, but as with integrated chl a were not statistically different in plume versus non-plume waters across the rest of the shelf. Based on the vertical distribution of light and chl a, a substantial fraction of phytoplankton production occurred below the pycnocline, averaging from 25% to 50% among cruises. These results suggest that freshwater and nutrient inputs regulate shelf-wide kd and, consequently, the vertical distribution of primary production. The substantial below-pycnocline primary production we observed has not been previously quantified for this region, but has important implications about the formation and persistence of hypoxia on the Louisiana continental shelf. 相似文献
2.
为了研究抚仙湖紫外辐射(UVR)和光合有效辐射(PAR)衰减的时空特征及其与有色可溶性有机物(CDOM)、悬浮物(SS)、浮游植物(叶绿素a表征)等因子的关系,于2014年10月(秋季)、2015年1月(冬季)开展现场调查,结果显示:秋季不同波长(段)的漫射衰减系数Kd(305)、Kd(340)和Kd(PAR)分别为1.27±0.12、0.68±0.11和0.32±0.13 m-1,冬季分别为1.13±0.10、0.63±0.07和0.36±0.07 m-1;秋季CDOM的不同波长吸收系数ag(254)、ag(305)和ag(340)分别为4.09±0.26、1.18±0.09和0.57±0.05 m-1,冬季分别为2.95±0.24、0.61±0.11和0.11±0.07 m-1,秋季ag(254)、ag(305)和ag(340)显著高于冬季;秋季Kd(305)显著大于冬季,这与秋季(雨季)较高的CDOM丰度、浮游植物生物量(及SS浓度)有关.秋季ag(305)/Kd(305)、ag(340)/Kd(340)均显著高于冬季;秋季及秋冬季整体而言,ag(254)与Kd(305)、Kd(340)呈显著正相关,各多元逐步回归方程中均包含ag(254),说明CDOM吸收对UVR的衰减有重要贡献.空间差异方面,秋季北部的ag(254)、Kd(305)和Kd(340)显著高于南部,冬季南北部无明显差异,或与雨旱季北岸河流输入的CDOM和SS的情况有关.此外,浮游植物对UV-B衰减的影响和SS(与CDOM的交互作用)对UV-A衰减的影响更在于季节变化方面,而影响UVR、PAR衰减的各因子的相对贡献有待进一步量化. 相似文献
3.
Pan evaporation modelling and changing attribution analysis on the Tibetan Plateau (1970–2012) 
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下载免费PDF全文 Pan evaporation (Ep) is an important indicator of water and energy and the decline of Ep has been reported in many regions over the last decades. The climate and Ep are dependent on each other. In this study, the temporal trends of Ep and main Ep drivers, namely mean air temperature (Ta), wind speed (u), global solar radiation (Rs), net long‐wave radiation(Rnl) and vapour pressure deficit (D) from 1970 to 2012, were calculated on the basis of 26 meteorological stations on the Tibetan Plateau. The arithmetic average of Ep from 26 stations decreased with the rate of ?11.91 mm a?2; the trends of Rs, Rnl, Ta, u and D were ?1.434 w m?2 decade?1, 0.2511 w m?2 decade?1, 0.3590°C decade?1, ?0.2376 m s?1 decade?1 and 9.523 Pa decade?1, respectively. The diffuse irradiance is an essential parameter to model Ep and quantify the contribution of climatic factors to changing Ep. 60 724 observations of Rs and diffuse solar irradiance (Rd) from seven of the 26 stations were used to develop the correlation between the diffuse fraction (Rd/Rs), and the clearness index (Rs/Ro). On the basis of the estimation of the diffuse component of Rs and climatic data, we modified the PenPan model to estimate Chinese micro‐pan evaporation (Ep) and assess the attribution of Ep dynamics using partial derivatives. The results showed that there was a good agreement between the observed and calculated daily Ep values. The observed decrease in Ep was mostly due to declining wind speed (?13.7 mm a?2) with some contributions from decreasing solar irradiance (?3.1 mm a?2); and the increase of temperature had a large positive effect (4.55 mm a?2) in total whilst the increase of Rnl had insignificant effect (0.35 mm a?2) on Ep rates. The change of Ep is the net result of all the climatic variables. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Ａｌｉｇｎｍｅｎｔｓｉｌｋｗｏｒｍｓａｓｓｅｉｓｍｉｃａｎｉｍａｌａｎｏｍａｌｏｕｓｂｅｈａｖｉｏｒ（ＳＡＡＢ）ａｎｄｅｌｅｃｔｒｏｍａｇｎｅｔｉｃｍｏｄｅｌｏｆａｆａｕｌｔ：ａｔｈｅｏｒｙａｎｄｌａｂｏｒａｔｏｒｙｅｘｐｅｒｉｍｅｎｔＭＯＴＯ... 相似文献
5.
Denitrification is studied in sediments from two areas of the River Butrón which represent different situations with respect to their degree of pollution. Denitrification is analysed by means of the following parameters: maximum denitrification rate (Vmax), Michaelis constant (Km), denitrification rate (v), denitrification constant (kd) and number of denitrifiers. In all the samples analysed denitrification follows a kinetic type Michaelis-Menten with respect to nitrate. Vmax, Km and number of denitrifiers are clearly superior in the polluted area when compared to the cleaner area, indicating an advantage given that denitrification suggests an alternative pathway for breaking down organic matter with low levels of dissolved oxygen. By comparison between Km and natural nitrate concentration values we find that v follows a first order kinetic depending directly on the nitrate concentration. v also presents higher values in the area of the river where the entry of sewage is taking place than in the cleaner area. However, this difference does not have a kinetic origin but rather is given by different nitrate concentrations in their sediments. This is due to the fact that the two areas present similar efficiencies in the elimination of nitrate, which is deduced from the similar values of kd. 相似文献
6.
7.
The MacCullagh equation is of key importance in the study of the Earth. It connects the geometrical and the physical properties of the Earth through the geodynamical shape factor J2. This second zonal geopotential coefficient is closely related to the flattening and to the angular spin velocity of the Earth as well as to its equatorial (A) and polar (C) moments of inertia. Through these moments of inertia the gravitational potential V is connected to the mass density distribution within the Earth.The main target of the present study is to obtain a generalized form of the MacCullagh equation for even orders n ≥ 2 by including the higher order zonal coefficients Jn connected with the higher (n ≥ 2) degree moments of inertia Cn and An. The higher the degree n, the higher is the weight of the near-surface (i.e. shallow) mass density distribution in Jn. The second part of this contribution deals with the temporal variations of Jn, dJn/dt for n ≥ 2. 相似文献
8.
Alice Courvoisier 《地球物理与天体物理流体动力学》2013,107(2):217-243
We look at the large-scale dynamo properties of spatially periodic, time dependent, helical 2D flows of the form u(x, t)?=?(? y ?ψ?(x, y, t), ?? x ?ψ?(x, y, t), ?ψ (x, y, t). These flows act as kinematic fast dynamos and are able to generate a mean magnetic field uniform and constant in the xy-plane but whose direction varies periodically along z with wavenumber k. Using Mean Field Electrodynamics, the generation mechanism can be understood in terms of a k-dependent α-effect, which depends on the magnetic Reynolds number, R m . We calculate this effect for different motions and investigate how its limit as k?→?0 depends on R m and on the properties of the flows such as their spatial structure or correlation time. This work generalises earlier studies based on 2D steady flows to motions with time dependence. 相似文献
9.
The relative abundance of the different picoplankton components (eukaryotic picophytoplankton (Peuk), picocyanobacteria (Pcy) and bacterioplankton), and their relationships with the lake conditions were studied in three types of shallow lakes from the Pampa Plain (Argentina) that differ in their optical properties: clear-vegetated, phytoplankton-turbid and inorganic-turbid. All the selected lakes, but one, are characterized by their different alternative steady state (clear-vegetated and phytoplankton-turbid water phases) following the model proposed by Scheffer et al. (1993).Autotrophic and heterotrophic picoplankton abundances were analyzed seasonally in relation to environmental variables. All the lakes presented high concentrations of total nitrogen (TN) (>229 μg L−1), total phosphorus (TP) (>46 μg L−1) and dissolved organic carbon (DOC) (>13.7 mg L−1). Clear-vegetated lakes were characterized by vertical diffuse PAR (photosynthetic active radiation) attenuation coefficient (kdPAR) lower than 11 m−1, whereas inorganic-turbid lake always showed values higher than 21.1 m−1. The euphotic zone depth (Z1%) was wider in clear-vegetated lakes (40–140 cm) and thinner in the inorganic-turbid (10–20 cm). The phytoplankton-turbid lakes presented a wide range in the values of these variables (kdPAR: 5.2–35.8 m−1; Z1%: 10–90 cm). Phytoplankton chlorophyll-a (Chl-a) strongly differed, ranging from 1.6 to 334.6 μg L−1. Picophytoplankton was mainly represented by phycocianine-rich (PC-rich) Pcy in all cases, dominating over Peuk algae. The total and relative abundances of eukaryotic picophytoplankton, Pcy and bacterioplankton, as well as the size structure of the phytoplankton community differed among the water bodies. In general, clear-vegetated water bodies exhibited similar abiotic characteristics, picophytoplankton/bacterioplankton ratios, and phytoplankton size structure. Contrarily, no clear trend was identified for the group of turbid lakes. The contrasting results obtained for the importance of the picoplankton components in phytoplankton-turbid shallow lakes evidence that the availability of the energetical and nutrient resources cannot be solely considered to predict their relative importance in this type of shallow lake. 相似文献
10.
下行漫衰减系数(K_d)是描述水下光场的重要参数,决定水体真光层深度,影响着浮游藻类初级生产力及其分布特征.基于2008—2013年太湖4次大规模野外试验数据,分析太湖水体漫衰减系数特征及其影响因素,建立适用于多种卫星数据且较高精度的太湖水体490 nm处下行漫衰减系数估算模型.结果表明:无机悬浮物是太湖水体漫衰减系数的主要影响因素;红绿波段比值(674 nm/555 nm)最适合于太湖K_d(490)估算,模型反演精度较高(N=72,R~2=0.72,RMSE=0.89 m~(-1),MAPE=21.58%);利用实测光谱数据,模拟得到MODIS/EOS、OLCI/Sentinel-3、GOCI/COMS和MSI/Sentinel-2等主要传感器波段的信号,构建适用于多种卫星传感器K_d(490)估算的红绿波段模型,建模精度较高(N=72,R~20.7,RMSE0.9 m~(-1),MAPE22.0%),且进行了验证(N=37,R~20.7,RMSE0.9 m~(-1),MAPE22.0%). 相似文献
11.
Evapotranspiration is an important component of the water and energy balance. It is dependent on climate. Precipitation, solar radiation, temperature, humidity, and wind all contribute to the rate of evapotranspiration. In this study, the temporal trends of reference evapotranspiration (ETref) and four main ETref drivers, namely, mean air temperature (Ta), wind speed (u2), net radiation (Rn) and actual vapour pressure (ea) from 1970 to 2009, were calculated based on 75 meteorological stations on the Tibetan Plateau. The results showed that the ETref on the Tibetan Plateau decreased on average by 0.6909 mm a‐1a‐1 from 1970 to 2009. Ta and ea showed an increasing trend, whereas u2 and Rn exhibited a decreasing trend. To explore the underlying causes of the ETref variation, an attribution analysis was performed to quantify the contribution of Ta, u2, Rn and ea, which showed that the changes in u2, Rn and ea produced the negative effect, whereas Ta produced the positive effect on ETref rates. The changes in u2 were found to produce the largest decrease (?0.7 mm) in ETref, followed by ea (?0.4 mm) and Rn (?0.1 mm). Although the significant increase in Ta had a large positive effect (0.51 mm) on ETref rates, changes in the other three variables each reduced ETref rates, resulting in an overall negative trend in ETref. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
12.
During 1986 planktonic primary production and controlling factors were investigated in a small (A0 = 11.8 · 103 m2, Zmax = 11.5 m) meromictic kettle lake (Mittlerer Buchensee). Annual phytoplankton productivity was estimated to ca 120 gC · m–2 · a–1 (1,42 tC · lake–1 · a–1). The marked thermal stratification of the lake led to irregular vertical distributions of chlorophylla concentrations (Chla) and, to a minor extent, of photosynthesis (Az). Between the depths of 0 to 6 m low Chla concentrations (< 7 mg · m–3) and comparatively high background light attenuation (kw = 0,525 m–1, 77% of total attenuation due to gelbstoff and abioseston) was found. As a consequence, light absorption by algae was low (mean value 17,4%) and self-shading was absent.Because of the small seasonal variation of Chla concentrations, no significant correlation between Chla and areal photosynthesis (A) was observed. Only in early summer (June–July) biomass appears to influence the vertical distribution of photosynthesis on a bigger scale. Around 8 m depth, low-light adapted algae and phototrophic bacteria formed dense layers. Due to low ambient irradiances, the contribution of these organisms to total primary productivity was small. Primary production and incident irradiance were significantly correlated with each other (r2 = 0.68). Although the maximum assimilation number (Popt) showed a clear dependence upon water temperature (Q10 = 2.31), the latter was of minor importance to areal photosynthesis. 相似文献
13.
D. Zúñiga F. Alonso-PérezC.G. Castro B. ArbonesF.G. Figueiras 《Continental Shelf Research》2011,31(5):414-424
The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m−2 d−1 and 22 mg chl a m−2 d−1, respectively) and minimum values during winter (22 mg m−2 d−1 and 0.1 mg chl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension. 相似文献
14.
Teruo Yamashita 《Pure and Applied Geophysics》1990,132(3):545-568
The effect of randomly distributed cracks on the attenuation and dispersion ofSH waves is theoretically studied. If earthquake ruptures are caused by sudden coalescence of preexisting cracks, it will be crucial for earthquake prediction to monitor the temporal variation of the crack distribution. Our aim is to investigate how the property of crack distribution is reflected in the attenuation and dispersion of elastic waves.We introduce the stochastic property, in the mathematical analysis, for the distributions of crack location, crack size and crack orientation. The crack size distribution is assumed to be described by a power law probability density (p(a) a
– fora
minaa
max according to recent seismological and experimental knowledge, wherea is a half crack length and the range 13 is assumed. The distribution of crack location is assumed to be homogeneous for the sake of mathematical simplicity, and a low crack density is assumed. The stochastic property of each crack is assumed to be independent of that of the other cracks. We assume two models, that is, the aligned crack model and the randomly oriented crack model, for the distribution of crack orientation. All cracks are assumed to be aligned in the former model. The orientation of each crack is assumed to be random in the latter model, and the homogeneous distribution is assumed for the crack orientation. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.We observe the following features common to both the aligned crack model and the randomly oriented crack model. The attenuation coefficientQ
–1 decays in proportion tok
–1 in the high frequency range and its growth is proportional tok
2 in the low frequency range, wherek is the intrinsic wave number. This asymptotic behavior is parameter-independent, too. The attenuation coefficientQ
–1 has a broader peak as increases and/ora
min/a
max decreases. The nondimensional peak wave numberk
p
a
max at whichQ
–1 takes the peak value is almost independent ofa
min/a
max for =1 and 2 while it considerably depends ona
min/a
max for =3. The phase velocity is almost independent ofk in the rangeka
max<1 and increases monotonically ask increases in the rangeka
max>1. While the magnitude ofQ
–1 and the phase velocity considerably depend on the orientation of the crack in the aligned crack model, the above feature does not depend on the crack orientation.The accumulation of seismological measurements suggests thatQ
–1 ofS waves has a peak at around 0.5 Hz. If this observation is combined with our theoretical results onk
p
a
max, the probable range ofa
max of the crack distribution in the earth can be estimated for =1 or 2. If we assume 4 km/sec as theS wave velocity of the matrix medium,a
max is estimated to range from 2 to 5 km. We cannot estimatea
max in a narrow range for =3. 相似文献
15.
16.
Takesi Nagata 《Pure and Applied Geophysics》1971,89(1):159-177
Summary Effects of mechanical shocks of about 0.5 msec in duration on the remanent magnetization of igneous rocks are experimentally studied. The remanent magnetization acquired by applying a shock (S) in the presence of a magnetic field (H), which is symbolically expressed asJ
R
(H+S Ho), is very large compared with the ordinary isothermal remanent magnetization (IRM) acquired in the same magnetic field.J
R
(H+S Ho) is proportional to the piezo-remanent magnetization,J
R
(H+P+Po Ho).The effect of applyingS in advance of an acquisition of IRM is represented symbolically byJ
R
(S H+ Ho).J
R
(S H+ Ho) can become much larger than the ordinary IRM, and is proportional to the advance effect of pressure on IRM,J
R(P+ P0 H+ H0).The effect of shockS applied on IRM in non-magnetic space is represented by the shock-demagnetization effect,J
R(H+ H0 S), which also is proportional toJ
R(H+ H0 P+ P0).Because, the duration of a shock is very short, a single shock effect cannot achieve the final steady state. The effect ofn-time repeated shocks, is represented byJ
0+J
*(n), whereJ
0 means the immediate effect and J
*(n) represent the resultant effect of repeating, which is of mathematical expression proportional to [1–exp {–(n–1)}].
Zusammenfassung Die Effekte des mechanischen Stosses mit der Dauer von etwa 0.5 ms auf der remanenten Magnetisierung wurden experimentell nachgesucht. Das erworbene Remanenz der Magnetisierung nach dem Stoss (S) unter dem magnetischen Feld (H), das hier symbolisch alsJ R(H+ SH0) bezechnet wird, ist sehr stark im Vergleich mit der normalen isothermischen remanenten Magnetisierung (IRM) unter demselben magnetischen Feld.J R(H+ S H0) ist im Verhältnis zur piezoremanenten Magnetisierung,J R(H+ P+ P0 H0).Der Effekt vom Stoss vor der Erwerbung von IRM wird symbolisch alsJ R(S H+ H0) bezeichnet.J R(S H+ H0) kann viel stärker als die normale IRM werden, im verhältnis zum Effekt des vorausgegebenen Drucks auf IRMJ R(P+ P0 H+ H0).Der Effekt des Stosses auf IRM im Raum ohne magnetisches Feld wird mit dem Stossentmagnetisierungseffekt dargestellt,J R(H+ H0 S), der auch proportional zuJ R(H+ H0 P+ P0) ist.Da die Dauer einzelnen Stosses sehr kurz ist, kann der Effekt des einmaligen Stosses den endgültigen stabilen Zustand nicht erreichen. Der Effekt nachn-maligen wiederholten Stossen wird alsJ 0+J *(n) bezeichnet, wobeiJ 0 den unverzüglichen Effekt bedeutet, und J *(n) beschreibt den resultanten Effekt der Stosswiederholung, dessen mathematische Darstellung proporational zu [1–exp {–(n–1)}] ist.相似文献
17.
Li Jun Yu Qiang Sun Xiaomin Tong Xiaojuan Ren Chuanyou Wang Jing Liu Enmin Zhu Zhilin Yu Guirui 《中国科学D辑(英文版)》2006,49(2):226-240
CO2 flux was measured continuously in a wheat and maize rotation system of North China Plain using the eddy covariance technique to study the characteristic of CO2 exchange and its response to key environmental factors. The results show that nighttime net ecosystem exchange (NEE) varied exponentially with soil temperature. The temperature sensitivities of the ecosystem (Q 10) were 2.94 and 2.49 in years 2002–2003 and 2003–2004, respectively. The response of gross primary productivity (GPP) to photosynthetically active radiation (PAR) in the crop field can be ex-pressed by a rectangular hyperbolic function. Average A max and α for maize were more than those for wheat. The values of α increased positively with leaf area index (LAI) of wheat. Diurnal variations of NEE were significant from March to May and from July to September, but not remarkable in other months. NEE, GPP and ecosystem respiration (R ec) showed significantly seasonal variations in the crop field. The highest mean daily CO2 uptake rate was ?10.20 and ?12.50 gC·m?2?d?1 in 2003 and 2004, for the maize field, respectively, and ?8.19 and ?9.50 gC?m?2·d?1 in 2003 and 2004 for the wheat field, respectively. The maximal CO2 uptake appeared in April or May for wheat and mid-August for maize. During the main growing seasons of winter wheat and summer maize, NEE was controlled by GPP which was chiefly influenced by PAR and LAI. R ec reached its annual maximum in July when R ec and GPP contributed to NEE equally. NEE was dominated by R ec in other months and temperature became a key factor controlling NEE. Total NEE for the wheat field was ?77.6 and ?152.2 gC·m?2·a?1 in years 2002–2003 and 2003–2004, respectively, and ?120.1 and ?165.6 gC·m?2·a?1 in 2003 and 2004 for the maize field, respectively. The cropland of North China Plain was a carbon sink, with annual ?197.6 and ?317.9 gC·m?2·a?1 in years 2002–2003 and 2003–2004, respectively. After considering the carbon in grains, the cropland became a carbon source, which was 340.5 and 107.5 gC·m?2·a?1 in years 2002–2003 and 2003–2004, respectively. Affected by climate and filed managements, inter-annual carbon exchange varied largely in the wheat and maize rotation system of North China Plain. 相似文献
18.
Wei Zhao Zhao‐Liang Li Hua Wu Bo‐Hui Tang Xiaoyu Zhang Xiaoning Song Guoqing Zhou 《水文研究》2013,27(19):2825-2833
Land surface soil moisture (SSM) is an important variable for hydrological, ecological, and meteorological applications. A multi‐linear model has recently been proposed to determine the SSM content from the combined diurnal evolution of both land surface temperature (LST) and net surface shortwave radiation (NSSR) with the parameters TN (the LST mid‐morning rising rate divided by the NSSR rising rate during the same period) and td (the time of daily maximum temperature). However, in addition to the problem that all the coefficients of the multi‐linear model depend on the atmospheric conditions, the model also suffers from the problems of the nonlinearity of TN as a function of the SSM content and the uncertainty of determining the td from the diurnal evolution of the LST. To address these problems, a modified multi‐linear model was developed using the logarithm of TN and normalizing td by the mid‐morning temperature difference instead of using the TN and td. Except for the constant term, the coefficients of all other variables in the modified multi‐linear model proved to be independent of the atmospheric conditions. Using the relevant simulation data, results from the modified multi‐linear model show that the SSM content can be determined with a root mean square error (RMSE) of 0.030m3/m3, provided that the constant term is known or estimated day to day. The validation of the model was conducted using the field measurements at the Langfang site in 2008 in China. A higher correlation is achieved (coefficient of determination: R2 = 0.624, RMSE = 0.107m3/m3) between the measured SSM content and the SSM content estimated using the modified multi‐linear model with the coefficients determined from the simulation data. Another experiment is also conducted to estimate the SSM content using the modified model with the constant term calibrated each day by one‐spot measurements at the site. The estimation result has a relatively larger error (RMSE = 0.125m3/m3). Additionally, the uncertainty of the determination of the coefficients is analysed using the field measurements, and the results indicate that the SSM content obtained using the modified model accurately characterizes the surface soil moisture condition. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
19.
Fikret Inal 《洁净——土壤、空气、水》2010,38(10):897-908
Tropospheric (ground‐level) ozone has adverse effects on human health and environment. In this study, next day's maximum 1‐h average ozone concentrations in Istanbul were predicted using multi‐layer perceptron (MLP) type artificial neural networks (ANNs). Nine meteorological parameters and nine air pollutant concentrations were utilized as inputs. The total 578 datasets were divided into three groups: training, cross‐validation, and testing. When all the 18 inputs were used, the best performance was obtained with a network containing one hidden layer with 24 neurons. The transfer function was hyperbolic tangent. The correlation coefficient (R), mean absolute error (MAE), root mean squared error (RMSE), and index of agreement or Willmott's Index (d2) for the testing data were 0.90, 8.78 µg/m3, 11.15 µg/m3, and 0.95, respectively. Sensitivity analysis has indicated that the persistence information (current day's maximum and average ozone concentrations), NO concentration, average temperature, PM10, maximum temperature, sunshine time, wind direction, and solar radiation were the most important input parameters. The values of R, MAE, RMSE, and d2 did not change considerably for the MLP model using only these nine inputs. The performances of the MLP models were compared with those of regression models (i.e., multiple linear regression and multiple non‐linear regression). It has been found that there was no significant difference between the ANN and regression modeling techniques for the forecasting of ozone concentrations in Istanbul. 相似文献
20.
We present an uncertainty analysis of ecological process parameters and CO2 flux components (R
eco, NEE and gross ecosystem exchange (GEE)) derived from 3 years’ continuous eddy covariance measurements of CO2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to
analyze the random error of CO2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters
and CO2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather
than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters.
Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary
least square method (OLS). (3) The differences between simulated Reco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m−2·a−1), 34.33% (79 g C·m−2·a−1) and 5.4% (92 g C·m−2·a−1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from
a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m−2·a−1), 2.1% (5.7 g C·m−2·a−1), and 0.26% (4.3 g C·m−2·a−1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing
uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the
timescale, the smaller the uncertainty. The relative uncertainties of Reco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale.
Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership
Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No.
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