共查询到20条相似文献，搜索用时 15 毫秒
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Energy transfer via resonance in a stratified fluid with a constant Brunt–Väisälä frequency is studied through the Manley–Rowe relation and direct numerical simulations. The objectives of this study are two-fold. One is to determine if there is a limitation on the lengthscale of small-scale waves to which primary energy can be effectively transferred. The other is to study factors affecting the growth of parametric subharmonic instability. Resonantly interacting modes are classified into three groups: local sum modes, quasi-subharmonic modes and remote parametric subharmonic instability modes (characterized by interaction with very small-scale waves). The latter two involve energy transfer from a primary wave to secondary waves with half the frequency. Most energy transfer is through local sum resonant modes and quasi-subharmonic modes. Energy cannot effectively transfer to higher wavenumber modes since dynamical systems are altered as wavenumbers of excited modes increase. In the remote modes, the solution is sinusoidal with high angular frequency and very small energy capacity. As a consequence, these modes are inactive in energy transfer despite their high energy growth rates. Effects of non-uniform white noise amplitude and primary mode propagation angle on the quasi-subharmonic modes are also investigated. Implications for energy transfer in the ocean are discussed. 相似文献
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Laboratory experiments were carried out to investigate the interaction between turbulent line buoyant plumes and sharp density interfaces, with the aim of using the results to interpret oceanic observations pertinent to crack openings in the polar ice-cap (leads). These openings take the form of long narrow channels, and are often modeled as line bouyant plumes. The plumes descend as in a homogenoous fluid, impinge on the density interface, and then spread horizontally as gravity currents. Depending on the Richardson number
, where Δb is the buoyancy jump across the interface, lD is the half-width of the plume before the impingement and q0is the buoyancy flux per unit length of the source, different flow patterns were identified. When Ri < 0.5, the plumes penetrate deep into the bottom layer, deflect horizontally and then spread while showing little vertical rise. When 0.6 < Ri < 5, the penetration is significant, but the fluid bounces back after entraining heavy fluid from the lower layer and then spreads horizontally above the interface as a gravity current. Appreciable mixing between this current and the lower layer was detected when Ri <1. When Ri > 10, the penetration was small and a sharp-nosed gravity current emerged some time after the impact. Measurements were made on the penetration depth, the velocities of the gravity current and the subsurface flow towards the plume, the entrainment rate and other wave parameters. Possible implications of the results for oceanic cases are also discussed. 相似文献
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G.E. Shaw 《Atmospheric Research》1986,20(1)
Measurements in Alaska in sub-polar night conditions have indicated that the size distribution of atmospheric aerosols varies significantly and systematically depending upon the type of air mass. Atmospheric aerosol particles are small and numerous in warm Pacific marine air mass systems and large and sparse in cold, Arctic-derived air mass systems. In a previous paper this was hypothesized to be associated with the progressive loss of the smallest particles by attachment to cloud droplets under the driving influence of thermal Brownian motion. A theory involving two parameters,
(mean particle radius), and n0 (aerosol number concentration) was developed to describe the process. In the previous paper, the relationship
where ν is the Junge power law exponent (ν 3) was derived and has recently been confirmed to acceptable accuracy with the use of a simple experiment which employed diffusive separation. The diffusion experiment has also allowed us to estimate that the fraction of time, φ, that the aerosol-laden polar air masses coexist in the presence of cloud is 0.01 < φ < 0.1. The submicron aerosol particles in Arctic-derived air masses flowing into central Alaska are deduced to have residence times on the order of 10 days. 相似文献
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Ekaterina Batchvarova Xiaoming Cai Sven-Erik Gryning Douw Steyn 《Boundary-Layer Meteorology》1999,90(1):1-20
The purpose of this paper is to test the ability of two quite different models to simulate the combined spatial and temporal variability of the internal boundary layer in an area of complex terrain and coastline during one day. The simple applied slab model of Gryning and Batchvarova, and the Colorado State University Regional Atmospheric Modelling System (CSU-RAMS) are tested by comparison with data gathered during a field study (called Pacific '93) of photochemical pollution in the Lower Fraser Valley of British Columbia, Canada. The data utilised here are drawn from tethered balloon flights, free flying balloon ascents, and downlooking lidar operated from an aircraft flown at roughly 3500 m above sea level. Both models are found to represent the temporal and spatial development of the internal boundary-layer depth over the Lower Fraser Valley very well, and reproduce many of the finer details revealed by the measurements. 相似文献
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R. E. Robson 《Boundary-Layer Meteorology》1987,39(3):207-218
Dispersion from a line source into a stable boundary layer of thickness l is analysed through solution of the diffusion equation assuming an exchange coefficient K(z) (1 – z/l)
2 and wind profiles u(z) z
n, with n = 0,1. Estimates of ground-level concentrations are made by developing analytic formulae where this is possible. A general method of solution using Laplace transformation and Green's function techniques is developed as an alternative to the eigenfunction expansion method discussed previously (Robson, 1983). 相似文献
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Decadal climate predictions with a coupled OAGCM initialized with oceanic reanalyses 总被引：2，自引：1，他引：1
A. Bellucci S. Gualdi S. Masina A. Storto E. Scoccimarro C. Cagnazzo P. Fogli E. Manzini A. Navarra 《Climate Dynamics》2013,40(5-6):1483-1497
We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmosphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using historical radiative forcing conditions for the 1960–2005 period, followed by RCP4.5 scenario settings for the 2006–2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full-value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2–5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturning circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions. 相似文献
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D. Engelbart H. Steinhagen U. Görsdorf J. Neisser H. J. Kirtzel G. Peters 《Meteorology and Atmospheric Physics》1999,71(1-2):61-68
Summary At a special measuring site for boundary-layer studies as well as land-surface processes the Meteorological Observatory Lindenberg
of the German Weather Service (DWD) has recently put into operation a newly-desi gned phased-array SODAR/RASS, which has been
developed by METEK on behalf of the DWD. This system provides the vertical profiles of the three-di mensional wind vector
in the boundary layer on an operational basis and is furthermore suitable for getting information on the profile of virtual
temperature up to about 400 m in height based on the addition of RASS components. The following paper describes both the technique
of this SODAR/RASS and the various modes of operation as well as the different options in managing the system. First evaluations
on the data availability concerning the maximum height coverage will give an impression on the system’s capabilities. Finally,
the accuracy of the derived profiles of winds and temperature will be investigated by means of comparisons of the SODAR/RASS
data with measurements of a six-sonde tethered-balloon system as well as meteorological data of a 99 m tower in the vicinity
of the system.
Received November 27, 1998 Revised April 9, 1999 相似文献
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M. E. S. Silva S. H. Franchito V. Brahmananda Rao 《Theoretical and Applied Climatology》2006,85(1-2):1-18
Summary A coupled biosphere-atmosphere statistical-dynamical model (SDM) is used to study the climatic effects of Amazonian deforestation.
A soil moisture model based on BATS has been incorporated into the SDM in order to study the biogeophysical feedback of change
in surface characteristics to regional climate due to the deforestation. In the control experiment, the mean annual and mean
seasonal climate is well simulated by the model when compared with NCEP/NCAR reanalysis data. In the deforestation experiment,
the evergreen broadleaf trees in the Amazonian region are substituted by short grass. The effects of Amazonian deforestation
on regional climate are analysed taking into account the model simulations for the land portion of the latitude belts comprising
the tropical region. Amazonian deforestation results in regional climate changes such as a decrease in evaporation, precipitation,
available surface net radiation and soil moisture content, and an increase in temperatures and sensible heat flux. The reduction
in transpiration was responsible for the most part of the decrease in total evapotranspiration. The reduction in precipitation
was larger than the decrease in evapotranspiration so that runoff was reduced. The simulation of the diurnal cycle of the
surface temperature shows an increase in temperature during the day and a decrease at night, which is in agreement with observations,
whereas earlier GCM experiments showed an increase both during the day and night. In general, the changes in temperature and
energy fluxes are in good agreement with GCM experiments, showing that the SDM is able to simulate the characteristics of
the tropical climate that are associated with the substitution of forest by pasture areas. 相似文献
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In this research,a novel dual-model system,one-dimensional stratiform cold cloud model(1DSC) coupled to Weather Research and Forecast(WRF) model(WRF-1DSC for short),was employed to investigate the effects of cloud seeding by silver iodide(AgI) on rain enhancement.Driven by changing environmental conditions extracted from the WRF model,WRF-1DSC could be used to assess the cloud seeding effects quantitatively.The employment of WRF-1DSC,in place of a one-dimensional two-moment cloud seeding model applied to a three-dimensional mesoscale cloud-resolving model,was found to result in massive reduction of computational resources.Numerical experiments with WRF-1DSC were conducted for a real stratiform precipitation event observed on 4-5 July 2004,in Northeast China.A good agreement between the observed and modeled cloud system ensured the ability of WRF-1DSC to simulate the observed precipitation process efficiently.Sensitivity tests were performed with different seeding times,locations,and amounts.Experimental results showed that the optimum seeding effect(defined as the percentage of rain enhancement or rain enhancement rate) could be achieved through proper seeding at locations of maximum cloud water content when the updraft was strong.The optimum seeding effect was found to increase by 5.61% when the cloud was seeded at 5.5 km above ground level around 2300 UTC 4 July 2004,with the maximum AgI mixing ratio(X s) equaling 15 ng kg 1.On the other hand,for an overseeded cloud,a significant reduction occurred in the accumulated precipitation(-12.42%) as X s reached 100 ng kg 1.This study demonstrates the potential of WRF1DSC in determining the optimal AgI seeding strategy in practical operations of precipitation enhancement. 相似文献
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California coastal management with a changing climate 总被引：2，自引：0，他引：2
With over 2,000 miles (3,218 km) of ocean and estuarine coastline, California faces significant coastal management challenges
as a result of climate change-induced sea level rise. Under high emission scenarios, recent models predict 1.4 m or more of
sea level rise by 2100, accompanied by increasing storm surges. This article investigates the most important issues facing
coastal managers, explores the policy tools available for adapting to the impacts of climate change, assesses institutional
constraints to adaptation, and identifies priorities for future research and policy action. We find that adaptation tools
exist for dealing with anticipated increases in coastal erosion and flooding, but they involve significant costs and tradeoffs.
In particular, coastal armoring, such as seawalls, can protect developed coastal lands, but destroys beaches and habitat.
Although California already has policies and institutions that aim to balance the competing objectives for coastal development,
management agencies are at the early stages of understanding how to facilitate adaptation. Research priorities to inform coastal
adaptation planning include: (i) inventorying coastal resources to provide a firmer basis for balancing decisions on property
and habitat protection, (ii) identifying opportunities for coastal habitat migration, (iii) assessing the vulnerabilities
of existing and planned coastal infrastructure, and (iv) experimenting with alternatives to armoring as a way of managing
the changing coastline. 相似文献
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Earlier GCM studies have expressed the concern that an enhancement of greenhouse warming might increase the occurrence of summer droughts in mid-latitudes, especially in southern Europe and central North America. This could represent a severe threat for agriculture in the regions concerned, where summer is the main growing season. These predictions must however be considered as uncertain, since most studies featuring enhanced summer dryness in mid-latitudes use very simple representations of the land-surface processes ("bucket" models), despite their key importance for the issue considered. The current study uses a regional climate model including a land-surface scheme of intermediate complexity to investigate the sensitivity of the summer climate to enhanced greenhouse warming over the American Midwest. A surrogate climate change scenario is used for the simulation of a warmer climate. The control runs are driven at the lateral boundaries and the sea surface by reanalysis data and observations, respectively. The warmer climate experiments are forced by a modified set of initial and lateral boundary conditions. The modifications consist of a uniform 3 K temperature increase and an attendant increase of specific humidity (unchanged relative humidity). This strategy maintains a similar dynamical forcing in the warmer climate experiments, thus allowing to investigate thermodynamical impacts of climate change in comparative isolation. The atmospheric CO 2 concentration of the sensitivity experiments is set to four times its pre-industrial value. The simulations are conducted from March 15 to October 1st, for 4 years corresponding to drought (1988), normal (1986, 1990) and flood (1993) conditions. The numerical experiments do not present any great enhancement of summer drying under warmer climatic conditions. First, the overall changes in the hydrological cycle (especially evapotranspiration) are of small magnitude despite the strong forcing applied. Second, precipitation increases in spring lead to higher soil water recharge during this season, compensating for the enhanced soil moisture depletion occurring later in the year. Additional simulations replacing the plant control on transpiration with a bucket-type formulation presented increased soil drying in 1988, the drought year. This suggests that vegetation control on transpiration might play an important part in counteracting an enhancement of summer drying when soil water gets limited. Though further aspects of this issue would need investigating, our results underline the importance of land-surface processes in climate integrations and suggest that the risk of enhanced summer dryness in the region studied might be less acute than previously assumed, provided the North American general circulation does not change markedly with global warming. 相似文献
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通过两要素自动站接收平台(WIMI-1型CGSM智能通信仪)对接收信息的处理,结合天气雷达观测数据,分析两要素自动站运行中的故障,并找出相应的解决对策,以确保两要素自动站的正常运行。 相似文献
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2月,全国平均气温为0.7℃,比常年同期偏高3.5℃,为1951年以来历史同期最高值。全国平均降水量为18.0mm,较常年同期略偏多。月内,我国大部地区气温明显偏高,19个省(市、区)的月平均气温为1951年以来历史同期最高值;华北东部、西北东部、川渝等地的部分地区旱情持续或发展;我国中东部地区出现大雾天气,给春运交通带来不利影响;云南、黑龙江、新疆等地的部分或局部地区遭受雪灾和低温冷冻灾害;南方部分地区出现持续阴雨天气;辽宁、内蒙古、新疆等地的部分地区遭受沙尘和大风天气袭击。1我国大部气温明显偏高,部分地区气温创1951年以来历史同期… 相似文献
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Bruno Bueno Leslie Norford Grégoire Pigeon Rex Britter 《Boundary-Layer Meteorology》2011,140(3):471-489
A scheme that couples a detailed building energy model, EnergyPlus, and an urban canopy model, the Town Energy Balance (TEB), is presented. Both models are well accepted and evaluated within their individual scientific communities. The coupled scheme proposes a more realistic representation of buildings and heating, ventilation and air-conditioning (HVAC) systems, which allows a broader analysis of the two-way interactions between the energy performance of buildings and the urban climate around the buildings. The scheme can be used to evaluate the building energy models that are being developed within the urban climate community. In this study, the coupled scheme is evaluated using measurements conducted over the dense urban centre of Toulouse, France. The comparison includes electricity and natural gas energy consumption of buildings, building façade temperatures, and urban canyon air temperatures. The coupled scheme is then used to analyze the effect of different building and HVAC system configurations on building energy consumption, waste heat released from HVAC systems, and outdoor air temperatures for the case study of Toulouse. Three different energy efficiency strategies are analyzed: shading devices, economizers, and heat recovery. 相似文献
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D. Etling F. Gelhardt U. Schrader F. Brennecke G. Kühn G. Chabert d'Hieres H. Didelle 《Dynamics of Atmospheres and Oceans》2000,31(1-4)
The behaviour of a density current on a sloping bottom in a rotating system is investigated by laboratory experiments. The main result is that the dense bottom outflow induces cyclonic vortices in the upper fluid layer, which are formed periodically and move to the west parallel to coast. Two regimes of vortex formation have been identified. For strong density currents and weak rotation, vortices are formed by stretching of the upper layer near the source as found also in the experiments by Lane-Serff and Baines (1998) [Lane-Serff, G.F., Baines, P.G., 1998. Eddy formation by dense flows on slopes in a rotating fluid. J. Fluid Mech. 363, 229–253]. For weak density currents and strong rotation vortices are due to instability of the bottom plume itself as found in the numerical simulations of Jiang and Garwood (1996) [Jiang, L., Garwood, W. Jr., 1996. Three-dimensional simulations of overflows on continental slopes. J. Phys. Oceanogr. 26, 1224–1233]. 相似文献