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311.
312.
云粒子谱演化研究中的一些问题 总被引:22,自引:5,他引:17
简略介绍了描述云中水凝物粒子群尺度谱演变的方法:谱函数方法和分档方法,并给出了分档模式实例。讨论了谱参数本身以及在应用中应注意的问题。分析了两类方法的对比研究的结果指出,一些重要的云降水物理过程,如粒子类型间的转化,涉及粒子运动状态和人工播撒的效应等过程,应当用分档方法来处理。 相似文献
313.
Conceptual model of the evolution of groundwater quality at the wet zone in Sri Lanka 总被引:2,自引:1,他引:1
The evolution of groundwater quality at a wet zone in Sri Lanka was made clear using field investigation, chemical and isotopic
analyses methods. In the wet zone, the concentrations of major ions and electrical conductivity (EC) in the groundwater are
low with small seasonal change. Except for sodium, silica and chloride, the EC and other major ion concentrations increase
along the groundwater flow direction. The contributions of bicarbonate and calcium ions to the increase in EC are the largest
among the major ions. The groundwater quality shows calcium-bicarbonate type, the initial stage of the Chebotarev series.
There is a seasonal change in isotopic composition. The isotopically lighter groundwater was found at the valley bottom in
the rainy season. Under the very heavy precipitation conditions, the slope of the regression line between δD and δ18O and deuterium excess for groundwater are close to 8 and 10, respectively. In other cases, the slopes of the regression lines
and deuterium excess are, less than 8 and 10, respectively.
Received: 5 August 1998 · Accepted: 19 October 1998 相似文献
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318.
During uplift of the Tibetan plateau and surrounding ranges, tectonic processes have interacted with climatic change and with local random effects (such as landslides) to determine the development of the major river systems of Asia. Rivers draining northward from the Pamir syntaxis have three distinctive patterns that are controlled by different tectonic and climatic regimes. West of the Pamir, the rivers have moderate but irregular gradients and drain northwards to disappear into arid depressions. Relatively steady uplift of the Hindu Kush in northern Afghanistan allowed rivers to cut across the rising ranges, modified by the shear along the Harirud fault zone, local faulting, and by increasing rain-shadow effects from the rising Makran. In the transition to the Pamir the rivers have steeper but more even gradients suggesting more even flow and downcutting during uplift, possibly related to larger glacial sources. In the central Pamir, only one antecedent river, the Pyandzh appears to have kept its northward course with compression and uplift of the indenter, and its course strangely corresponds with a major geophysical boundary (a distorted subducted slab) but not a geological boundary: the other rivers are subsequent rivers developed along deformation fronts during development and northward displacements of the Pamir structural units. The above areas have sources north of the Cretaceous Karakorum–South Pamir Andean margin. On the eastern flank of the Pamir, in the Kunlun and northern Tibetan plateau, the rivers rise similarly north of the Cretaceous Andean margin of southern Tibet, but then flow with low gradients across the plateau, before cutting and plunging steeply down across the Kunlun to disappear into the arid Tarim. These steep profiles are the result of late Neogene uplift of the northern Tibetan plateau and Kunlun possibly modified by glacial diversion and river capture. The drainage history of the Pamir indenter can be reconstructed by restoring the gross movements of the plates and the tectonic displacements, uplift, and erosion of individual tectonic units. Most important changes in drainage took place in the last 10 million years, late Miocene to Quaternary times, as the Pamir syntaxis developed. 相似文献
319.
We analyze velocity fields of the Great Red Spot (GRS) and Oval BA that were previously extracted from Cassini, Galileo, and Hubble Space Telescope images (Asay-Davis, X.S., Marcus, P.S., Wong, M., de Pater, I. [2009]. Icarus 203, 164-188). Our analyses use reduced-parameter models in which the GRS, Oval BA, and surrounding zonal (east-west) flows are assumed to have piece-wise-constant potential vorticity (PV), but with finite-sized transition regions between the pieces of constant PV rather than sharp steps. The shapes of the regions of constant PV are computed such that the flow is a steady, equilibrium solution of the 2D quasigeostrophic equations when viewed in a frame translating uniformly in the east-west direction. All parameter values of the models, including the magnitudes of the PV, areas of the regions with constant PV, locations of the transition regions, widths of the transition regions, and the value of the Rossby deformation radius, are found with a genetic algorithm such that the velocity produced by the equilibrium solution is a “best-fit” to the observed velocity fields. A Monte Carlo method is used to estimate the uncertainties in the best-fit parameter values.The best-fit results show that there were significant changes (greater than the uncertainties) in the PV of the GRS between Galileo in 1996 and Hubble in 2006. In particular, the shape of the PV anomaly of the GRS became rounder, and the area of the PV anomaly of the GRS decreased by 18%, although the magnitudes of PV in the anomaly remained constant. In contrast, neither the area nor the magnitude of the PV anomaly of the Oval BA changed from 2000, when its cloud cover was white, to 2006, when its cloud cover was red. The best-fit results also show that the areas of the PV anomalies of the GRS and of the Oval BA are smaller than the areas of their corresponding cloud covers at all times. Using the best-fit values of the Rossby deformation radius, we show that the Brunt-Väisälä frequency is 15% larger at 33°S than at 23°S. As expected (Marcus, 1993), the best-fit results show that the PV of the zonal flow has “jumps” at the latitudes of the maxima of the eastward-going jet streams. However, a surprising result is that a large “jump” in the PV of the zonal flow occurs at the location of a maximum of the westward going jet stream neighboring the GRS. Another surprise is that the jumps in the PV of the zonal flow do not all have the same sign, which implies that there is not a monotonic “staircase” of zonal PV from north to south as was anticipated (
[Marcus, 1993] and [McIntyre, 2008]). 相似文献
320.
大气长波的发展和演变影响着大气的可预报性,并对提高天气预报和气候预测水平有重要的意义.在影响大气长波演变的因子中,除波与波非线性相互作用外,基流的作用也非常重要.本文利用非均匀基本场下Rossby波运动方程,通过数值求解,分析了基本场结构和初始场对Rossby波演变的影响,揭示了纬向非均匀基本场对长波调整的作用.研究结果表明:基流纬向非均匀时,线性Rossby波也会出现长波调整现象,基流随纬向变化是长波发生调整的又一个重要机制;大气长波调整对波动的初始振幅不敏感,但基本场振幅影响着长波调整能否出现和出现的时间;基本场纬向平均西风基流的大小除影响波动传播的速度和方向外,还影响长波调整出现的时间和规律;长波调整的出现还与基本场和初始场的结构有关,不同基本场时,波动是否发生调整、向高波数还是向低波数调整都决定于基本场结构,相同基本场时,不同初始结构的波动也有着不同的演变过程. 相似文献