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61.
东南亚夏季风中断、过渡与活跃期的区域能量学研究 总被引:2,自引:0,他引:2
对两次季风演变过程的能量学研究表明,季风演变具有鲜明的阶段性能量学特征。中断期,积云加热小,两个转换函数值很小;过渡期,积云加热增强明显,两个转换函数值迅速加大,边界输送作用也明显朝有利方向变化,同时,纬向平均气流变为向季风供应扰动动能;活跃期,大尺度加热变得重要,积云加热维持,两个转换函数也保持大的正值。分析表明,印度季风东传对东南亚季风活跃的触发作用是重要的,但季风活跃的维持则主要依靠区域内部能量学过程。 相似文献
62.
63.
青藏高原地区地气系统太阳辐射能收支的研究 总被引:7,自引:0,他引:7
本文利用1982年8月—1983年7月Nimbus-7的月平均行星反射率资料和根据卫星资料得到的地面总辐射、地表反射率的估算结果,分析了青藏高原地区地气系统(大气顶)的太阳辐射能收支和地表、大气对太阳辐射吸收的时空变化特征,给出了表征太阳辐射能收支的一些基本参数,讨论了以行星反射率为基本参数表征大气、地表对太阳辐射吸收的参数化方法。分析表明:过渡季节5月份的行星反射率极小值的出现对青藏高原地区太阳辐射能收支有重要调节作用;全年平均而言,青藏高原地区被地气系统反射和被大气、地表吸收的太阳辐射的比例为37:18:45。 相似文献
64.
Field measurements of NO and NO2 emissions from soils have been performed in Finthen near Mainz (F.R.G.) and in Utrera near Seville (Spain). The applied method employed a flow box coupled with a chemiluminescent NO
x
detector allowing the determination of minimum flux rates of 2 g N m-2 h-1 for NO and 3 g m-2 h-1 for NO2.The NO and NO2 flux rates were found to be strongly dependent on soil surface temperatures and showed strong daily variations with maximum values during the early afternoon and minimum values during the early morning. Between the daily variation patterns of NO and NO2, there was a time lag of about 2 h which seem to be due to the different physico-chemical properties of NO and NO2. The apparent activation energy of NO emission calculated from the Arrhenius equation ranged between 44 and 103 kJ per mole. The NO and NO2 emission rates were positively correlated with soil moisture in the upper soil layer.The measurements carried out in August in Finthen clearly indicate the establishment of NO and NO2 equilibrium mixing ratios which appeared to be on the order of 20 ppbv for NO and 10 ppbv for NO2. The soil acted as a net sink for ambient air NO and NO2 mixing ratios higher than the equilibrium values and a net source for NO and NO2 mixing ratios lower than the equilibrium values. This behaviour as well as the observation of equilibrium mixing ratios clearly indicate that NO and NO2 are formed and destroyed concurrently in the soil.Average flux rates measured on bare unfertilized soils were about 10 g N m-2 h-1 for NO2 and 8 g N m-2 h-1 for NO. The NO and NO2 flux rates were significantly reduced on plant covered soil plots. In some cases, the flux rates of both gases became negative indicating that the vegetation may act as a sink for atmospheric NO and NO2.Application of mineral fertilizers increased the NO and NO2 emission rates. Highest emission rates were observed for urea followed by NH4Cl, NH4NO3 and NaNO3. The fertilizer loss rates ranged from 0.1% for NaNO3 to 5.4% for urea. Vegetation cover substantially reduced the fertilizer loss rate.The total NO
x
emission from soil is estimated to be 11 Tg N yr-1. This figure is an upper limit and includes the emission of 7 Tg N yr-1 from natural unfertilized soils, 2 Tg N yr-1 from fertilized soils as well as 2 Tg N yr-1 from animal excreta. Despite its speculative character, this estimation indicates that NO
x
emission by soil is important for tropospheric chemistry especially in remote areas where the NO
x
production by other sources is comparatively small. 相似文献
65.
P. J. Fraser R. A. Rasmussen J. W. Creffield J. R. French M. A. K. Khalil 《Journal of Atmospheric Chemistry》1986,4(3):295-310
New CH4 emission data from a number of Northern and Southern Hemispheric, tropical and temperate termites, are reported, which indicate that the annual global CH4 source due to termites is probably less than 15 Tg. The major uncertainties in this estimate are identified and found to be substantial. Nevertheless, our results suggest that termites probably account for less than 5% of global CH4 emissions. 相似文献
66.
67.
Further Studies Of Atmospheric Turbulence In Layers Near The Surface: Scaling The Tke Budget Above The Roughness Sublayer 总被引:2,自引:0,他引:2
The second of two experimental studies of the TKE budget conducted on sites of different roughness is described, and results are compared. The first took place within a shallow layer above a small field of mostly bare, cultivated soil; the second was carried out above a roughness sublayer of significant depth on an extensive plain of tall dry grass. Budget terms observed in the second study were scaled with a modified u which compensated for effects of an unusually large stress gradient and ensured that the m functions would be collinear. By showing that the modification becomes negligible in smaller gradients, it is demonstrated that in normal conditions, budgets observed above significant roughness sublayers should be normalized by scaling in terms of the unreduced Reynolds stress at the sublayer's upper surface. This procedure is shown to be consistent with the expectation that TKE budgets in layers near the surface all scale in fundamentally the same way.Other findings include: (1) the fact that most m functions previously reported are not quite collinear is attributed to a type of overspeeding known to affect three-cup anemometers; (2) revised m functions, collinear and largely free of the effects of overspeeding, are determined from a well-established characteristic of the linear m relation for the stable case; (3) data that define collinear m functions can also be represented with single hyperbolic curves; (4) dissipation is found to be 10 to 15% too small to balance total TKE production in unstable and neutral conditions and to decrease with increasing z/L in thestable regime; and (5) new relations for based on the observed behaviour of the dissipation deficit provide an improved closure for the set of equations that express the budget terms as functions of m and z/L. 相似文献
68.
A three year monitoring programme of gully‐head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully‐head erosion on the low‐angled alluvio‐lacustrine Njemps Flats in semi‐arid Baringo District, Kenya. This paper discusses the factors controlling the large observed spatial and temporal variation in gully‐head retreat rates, ranging from 0 to 15 m a?1. The selected gullies differed in planform and in runoff‐contributing catchment area but soil material and land use were similar. The data were analysed at event and annual timescales. The results show that at annual timescale rainfall amount appears to be a good indicator of gully‐head retreat, while at storm‐event timescale rainfall distribution has to be taken into account. A model is proposed, including only rainfall (P) and the number of dry days (DD) between storms: which explains 56 per cent of the variation in retreat rate of the single‐headed gully of Lam1. A detailed sediment budget has been established for Lam1 and its runoff‐contributing area (RCA). By measuring sediment input from the RCA, the sediment output by channelized flow and linear retreat of the gully head for nine storms, it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period (DD) between storms. Sediment input from the RCA was usually the largest component for the smaller storms. The erosion of the gully head occurred as a direct effect of runoff falling over the edge (GHwaterfall) and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation (GHmass/storage). The latter component (GHmass/storage) was usually much larger that the former (GHwaterfall). The sediment output from the gully was strongly related to the runoff volume while the linear retreat, because of its complex behaviour, was not. Overall, the results show that the annual retreat is the optimal timescale to predict retreat patterns. More detailed knowledge about relevant processes and interactions is necessary if gully‐head erosion is to be included in event‐based soil erosion models. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
69.
A simple, well-constrained simulation of solute increases in a downgradient direction was used in the shallow unconfined aquifer
of eastern Abu Dhabi Emirate (United Arab Emirates). The simulation indicates that the observed exponential increase in solute
concentrations results from a combination of upward transport of solutes from underlying mudstones and evaporites, and groundwater
losses by evaporation. Groundwater recharge and discharge flux in unconfined regional aquifers in arid regions commonly are
difficult to estimate because there are few constraints on the flux of water lost or gained from the system. Total dissolved
solids (TDS) and deuterium isotopes (δ2H) in groundwater are used to constrain estimated fluxes to the shallow aquifer of eastern Abu Dhabi Emirate. Vertical upward
transport of solutes from underlying mudstones and evaporites accounts for solute increases along approximately the first
80 km of the simulated flow path, but a combination of upward solute transport and evaporation is necessary to explain observed
solute concentrations beyond 80 km. Mobilization and transport of solutes in the unsaturated zone by recharging precipitation
is not a significant factor.
Résumé Une simulation simple et bien contrainte de l’augmentation des solutés dans la direction de l’écoulement a été réalisée sur l’aquifère phréatique et libre de l’Est de l’émirat d’Abu Dhabi (émirats Arabes Unis). La simulation indique que l’augmentation observée de solutés, de forme exponentielle, est le produit de la combinaison du transport ascendant de solutés provenant des mudstones et des évaporites sous-jacents, et de l’évaporation des eaux souterraines. La recharge des eaux souterraines et les flux de vidange dans les aquifères régionaux libres des régions arides sont habituellement difficiles à estimer du fait du peu de contraintes agissant sur la perte ou le gain d’eau dans le système. La charge dissoute totale (TDS, en anglais) et les isotopes deutérium (δ2H) des eaux souterraines sont utilisés pour contraindre l’estimation des flux en direction de l’aquifère phréatique de l’Est de l’émirat d’Abu Dhabi. Le transport vertical ascendant des solutés à partir des mudstones et des évaporites fait parti des processus qui concentrent les solutés approximativement le long des 80 premiers kilomètres du trajet des écoulements simulés, mais une combinaison du transport ascendant des solutés et de l’évaporation est nécessaire pour expliquer les concentrations observées en soluté au delà des 80 km. La mobilisation et le transport des solutés par les précipitations efficaces dans la zone non saturée ne représentent pas des facteurs significatifs.
Resumen Se utilizó una simulación simple y muy restringida, de incrementos de soluto en la dirección del flujo, en el acuífero libre poco profundo del Emirato oriental de Abu Dhabi, (Emiratos árabes Unidos). La simulación indica que el aumento exponencial observado en las concentraciones del soluto, resulta de una combinación de transporte ascendente de solutos desde las evaporitas y lodolitas subyacentes, y por pérdidas del agua subterránea por evaporación. Los flujos de recarga y descarga de agua subterránea, en los acuíferos libres regionales en regiones áridas, normalmente son difíciles estimar, porque hay algunas restricciones en el flujo de agua perdido o ganado por el sistema. Los sólidos disueltos totales (TDS) y los isótopos de deuterio (δ2H) en el agua subterránea, se usan para forzar los flujos estimados hacia el acuífero poco profundo del Emirato oriental de Abu Dhabi. El transporte ascendente vertical de solutos desde las lodolitas y evaporitas subyacentes, involucra los aumentos del soluto a lo largo de aproximadamente los primeros 80 Km. de la dirección de flujo simulada, pero es necesaria una combinación de transporte ascendente del soluto y la evaporación para explicar las concentraciones del soluto observadas más allá de 80 Km. La movilización y transporte de solutos en la zona no saturada, por recarga debida a precipitación, no es un factor significante.相似文献
70.
The effects of climate change on the groundwater systems in the Grote-Nete catchment, Belgium, covering an area of 525 km2, is modeled using wet (greenhouse), cold or NATCC (North Atlantic Thermohaline Circulation Change) and dry climate scenarios. Low, central and high estimates of temperature changes are adopted for wet scenarios. Seasonal and annual water balance components including groundwater recharge are simulated using the WetSpass model, while mean annual groundwater elevations and discharge are simulated with a steady-state MODFLOW groundwater model. WetSpass results for the wet scenarios show that wet winters and drier summers are expected relative to the present situation. MODFLOW results for wet high scenario show groundwater levels increase by as much as 79 cm, which could affect the distribution and species richness of meadows. Results obtained for cold scenarios depict drier winters and wetter summers relative to the present. The dry scenarios predict dry conditions for the whole year. There is no recharge during the summer, which is mainly attributed to high evapotranspiration rates by forests and low precipitation. Average annual groundwater levels drop by 0.5 m, with maximum of 3.1 m on the eastern part of the Campine Plateau. This could endanger aquatic ecosystem, shrubs, and crop production. 相似文献