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1.
The effects of an air-temperature inversion in the atmosphere and a seawater density jump in the ocean on the structure of the atmospheric and oceanic boundary layers are studied by use of a coupled model. The numerical model consists of a closed system of equations for velocities, turbulent kinetic energy, turbulent exchange coefficient, local turbulent length scale, and stratification expressions for both air and sea boundary layers. The effects of the temperature inversion and the density jump are incorporated into the equations of turbulent kinetic energy of the atmosphere and ocean by a parameterization. A series of numerical experiments was conducted to determine the effects of various strengths of the inversion layer and surface heat fluxes in the atmosphere and of the density-jump layer in the ocean on the structure of the interacting boundary layers.The numerical results show that the temperature inversion in the atmosphere and density jump in the ocean have strong influences on turbulent structure [especially on the turbulent exchange coefficient (TEC) and turbulent kinetic energy (TKE)] and on air-sea interaction characteristics. Maxima of TKE and TEC strongly decrease with increasing strength of the inversion layer, and they disappear for strong inversions in the atmosphere. Certain strengths (density differences between the upper and the lower layers) of the density-jump layer in the ocean (2 0.1 g/cm3) produce double maxima in TEC-profiles and TKE-profiles in the ocean. The magnitudes of air-sea interaction characteristics such as geostrophic drag coefficient, and surface drift current increase with increasing strength of the density-jump layer in the ocean. The density-jump layer plays the role of a barrier that limits vertical mixing in the ocean. The numerical results agree well with available observed data and accepted quantitive understanding of the influences of a temperature inversion layer and a density-jump layer on the interacting atmospheric and oceanic boundary layers.  相似文献   

2.
对非球形冰晶94 GHz云雷达后向散射和衰减的研究   总被引：1，自引：0，他引：1  
针对94 GHz毫米波云雷达的数据处理,基于离散偶极子近似法(DDA)计算了几种非球形冰晶的后向散射及衰减效率,探讨了不同冰云模型下冰云的雷达反射率因子(Z_e)和衰减系数(k)及冰水含量(IWC,记作W)的关系。结果表明:(1)形状对冰晶的散射及衰减效率与粒子大小有关。(2)在实际的冰云中,将六角形冰晶和椭圆冰晶看做同体积的球形粒子将低估其衰减和后向散射。将聚合物冰晶看做等体积球形,将高估其后向散射及衰减,子弹花冰晶的后向散射与同体积的球形相比有减小也有增大,但是衰减比同体积球形的小。(3)冰云模型对Z_e-k、Z_e-W关系具有较大影响,假设滴谱相同的条件下,得到了具体冰云模型下对应Z_e-k、Z_e-W关系的系数。这些探讨为我国W波段云雷达的数据处理提供了参考。  相似文献   

3.
Summary A short historical review and an analysis of the current status of both theoretical and experimental studies of long-range sound propagation in the atmosphere are given. Basic results are given on the atmospheric fine-layered structure that significantly affects the infrasonic pulse propagation and scattering in the lower and middle atmosphere. The effect of time variations (seasonal changes, tides, and both planetary and internal gravity waves) in the effective acoustic speed profile on the characteristics of infrasonic signals from different pulsed sources is discussed. The results of the studies of partial reflection (scattering) of low-frequency acoustic pulses from the fine-layered inhomogeneities of the middle atmosphere are presented. The results of the corresponding theoretical studies are also given. The potentialities of the method of long-range acoustic sounding of large-scale anisotropic turbulence in the middle atmosphere are discussed. The problems of infrasonic monitoring of nuclear low-energy explosions are also considered.  相似文献   

4.
Summary The broadband solar absorptivity concept is employed to parameterize the aerosol absorption effect. The solar radiation model developed by Liou and his associates was modified to incorporate the parameterization of solar radiative transfer in an aerosol layer. Comparison of the results from this method with other schemes exhibits close agreement. A Sahara dust storm case was also chosen to test the performance of the present model, and the computed heating rate profiles agree well with calculations based on optical properties derived from observations for both clear and dust cases. In general, enhanced heating due to aerosol absorption of solar flux occurs particularly in the lower troposphere (below 5 km). The heating rate is independent of the scattering partition factor (), but the planetary albedo increases with . Further study shows that the aerosol heating is sensitive to the surface albedo (r s ) and to the cosine of the solar zenith angle (µ 0). The decrease inr s and/or increase inµ 0 lower the solar heating rate, the planetary albedo and the atmospheric absorptivity, but raise the surface absorptivity due to reduced multiple reflection between the atmosphere and surface.With 9 Figures  相似文献   

5.
The major components of the marine boundary layer biogeochemical sulfur cycle were measured simultaneously onshore and off the coast of Washington State, U.S.A. during May 1987. Seawater dimethylsulfide (DMS) concentrations on the continental shelf were strongly influenced by coastal upwelling. Concentration further offshore were typical of summer values (2.2 nmol/L) at this latitude. Although seawater DMS concentrations were high on the biologically productive continental shelf (2–12 nmol/L), this region had no measurable effect on atmospheric DMS concentrations. Atmospheric DMS concentrations (0.1–12 nmol/m3), however, were extremely dependent upon wind speed and boundary layer height. Although there appeared to be an appreciable input of non-sea-salt sulfate to the marine boundary layer from the free troposphere, the local flux of DMS from the ocean to the atmosphere was sufficient to balance the remainder of the sulfur budget.  相似文献   

6.
The three-dimensional nonlinear quasi-geostrophic potential vorticity equation is reduced to a linear form in the stream function in spherical coordinates for the permanent wave solutions consisting of zonal wavenumbers from 0 to n and rn vertical components with a given degree n. This equation is solved by treating the coefficient of the Coriolis parameter square in the equation as the eigenvalue both for sinusoidal and hyperbolic variations in vertical direction. It is found that these solutions can represent the observed long term flow patterns at the surface and aloft over the globe closely. In addition, the sinusoidal vertical solutions with large eigenvalue G are trapped in low latitude, and the scales of these trapped modes are longer than 10 deg. lat. even for the top layer of the ocean and hence they are much larger than that given by the equatorial β-plane solutions. Therefore such baroclinic disturb-ances in the ocean can easily interact with those in the atmosphere.Solutions of the shallow water potential vorticity equation are treated in a similar manner but with the effective depth H = RT / g taken as limited within a small range for the atmosphere.The propagation of the flow energy of the wave packet consisting of more than one degree is found to be along the great circle around the globe both for barotropic and for baroclinic flows in the atmosphere.  相似文献   

7.
 Decadal time scale climate variability in the North Pacific has implications for climate both locally and over North America. A crucial question is the degree to which this variability arises from coupled ocean/atmosphere interactions over the North Pacific that involve ocean dynamics, as opposed to either purely thermodynamic effects of the oceanic mixed layer integrating in situ the stochastic atmospheric forcing, or the teleconnected response to tropical variability. The part of the variability that is coming from local coupled ocean/atmosphere interactions involving ocean dynamics is potentially predictable by an ocean/atmosphere general circulation model (O/A GCM), and such predictions could (depending on the achievable lead time) have distinct societal benefits. This question is examined using the results of fully coupled O/A GCMs, as well as targeted numerical experiments with stand-alone ocean and atmosphere models individually. It is found that coupled ocean/atmosphere interactions that involve ocean dynamics are important to determining the strength and frequency of a decadal-time scale peak in the spectra of several oceanic variables in the Kuroshio extension region off Japan. Local stochastic atmospheric heat flux forcing, integrated by the oceanic mixed layer into a red spectrum, provides a noise background from which the signal must be extracted. Although teleconnected ENSO responses influence the North Pacific in the 2–7 years/cycle frequency band, it is shown that some decadal-time scale processes in the North Pacific proceed without ENSO. Likewise, although the effects of stochastic atmospheric forcing on ocean dynamics are discernible, a feedback path from the ocean to the atmosphere is suggested by the results. Received: 23 January 2000 / Accepted: 10 January 2001  相似文献   

8.
Because the atmosphere and ocean are interacting systems, it is inappropriate to specify sea surface temperature when dealing with the atmosphere, or atmospheric anemometer level temperature and moisture when dealing with the ocean. All of these quantities should be determined interactively in terms of the external forcing: the solar constant.In the tropics, it is shown that the (cumulus) convective processes may be described by a one-dimensional cloud model. The near-surface ocean may similarly be described by a one-dimensional mixed-layer model. The coupling is achieved through a sea surface flux budget combined with the flux parameterizations implied by Monin-Obukhov similarity theory.The coupled one-dimensional atmosphere-ocean model is applied to the equilibrium situation in which all temperatures reach a steady state. Since the ocean, lacking an internal heating or cooling mechanism, can only be heated or cooled through sensibleheat fluxes through the sea surface, in equilibrium these fluxes must vanish. The atmosphere, however, maintains a stable lapse rate by balancing cumulonimbus heating against net radiative cooling. All water precipitated from cumulonimbus clouds must have evaporated from sea surface. It is shown that this equilibrium system is closed and determinable solely in terms of the solar constant.For various values of the solar constant, the sea surface temperature, the flux of latent and sensible heat from the surface, the height of the tropopause, mixed layer, and trade inversion layer, and generally, the entire vertical structure of the tropical atmosphere and near-surface ocean can be determined. The equilibrium sea surface temperature is shown to be relatively insensitive to changes in the solar constant, additional solar flux being compensated mainly by additional evaporation. Finally, the usefulness and limitations of the model are pointed out.  相似文献   

9.
Summary ?Analysis of available data shows that the duration of the glacial/interglacial cycle is determined by the time for the ocean to go through one major temperature cycle. At the start of an interglacial period, clear skies with consequent release of CO2 from the ocean, warms the atmosphere, which in turn eventually warms the ocean to its maximum. Cloudy skies then cause the climate (land and air temperature) to cool and the CO2 to be reabsorbed to start glaciation preliminaries. The albedo feedback effect of the glacial ice, a relatively warm ocean, which produces enhanced cloud cover, and the increased solubility of CO2 in cold seawater ensure a long period of glaciation. Glacial periods end when pack ice spreads out on the ocean cooling it until reduced cloud cover once again allows the Sun’s heat, unreflected by cloud cover, to melt the ice and release CO2 back into the atmosphere. Received May 22, 2002; accepted June 20, 2002  相似文献   

10.
Using the Differential Absorption Lidar (DIAL) technique, two types of approaches, namely, reflection from retroreflector/topographic target and backscatter from atmosphere, are available for studying remotely the atmos-pheric NO2 concentration. The Argon ion lidar system at the Indian Institute of Tropical Meteorology (IITM), Pune, India has been used for the measurements by following both the path-averaged and range-resolved ap-proaches. For the former, a topographic target (hill) is used for determining path-averaged surface concentration. In the latter, spectral properties of atmospheric attenuation is used for making range-resolved measurements in the sur-face layer. The results of the observations collected by following both approaches are presented. The average surface NO2 concentration was found to vary between 0.01 and 0.105 ppm and the range-resolved measurements exhibited higher values suggesting treatment of the lidar data for scattering and extinction effects due to atmospheric aerosols and air molecules, and atmospheric turbulence. Certain modifications that arc suggested to the experimental set-up, data acquisition and analysis to improve the measurements are briefly described.  相似文献   

11.
The ocean heat transport into the Arctic and the heat budget of the Barents Sea are analyzed in an ensemble of historical and future climate simulations performed with the global coupled climate model EC-Earth. The zonally integrated northward heat flux in the ocean at 70°N is strongly enhanced and compensates for a reduction of its atmospheric counterpart in the twenty first century. Although an increase in the northward heat transport occurs through all of Fram Strait, Canadian Archipelago, Bering Strait and Barents Sea Opening, it is the latter which dominates the increase in ocean heat transport into the Arctic. Increased temperature of the northward transported Atlantic water masses are the main reason for the enhancement of the ocean heat transport. The natural variability in the heat transport into the Barents Sea is caused to the same extent by variations in temperature and volume transport. Large ocean heat transports lead to reduced ice and higher atmospheric temperature in the Barents Sea area and are related to the positive phase of the North Atlantic Oscillation. The net ocean heat transport into the Barents Sea grows until about year 2050. Thereafter, both heat and volume fluxes out of the Barents Sea through the section between Franz Josef Land and Novaya Zemlya are strongly enhanced and compensate for all further increase in the inflow through the Barents Sea Opening. Most of the heat transported by the ocean into the Barents Sea is passed to the atmosphere and contributes to warming of the atmosphere and Arctic temperature amplification. Latent and sensible heat fluxes are enhanced. Net surface long-wave and solar radiation are enhanced upward and downward, respectively and are almost compensating each other. We find that the changes in the surface heat fluxes are mainly caused by the vanishing sea ice in the twenty first century. The increasing ocean heat transport leads to enhanced bottom ice melt and to an extension of the area with bottom ice melt further northward. However, no indication for a substantial impact of the increased heat transport on ice melt in the Central Arctic is found. Most of the heat that is not passed to the atmosphere in the Barents Sea is stored in the Arctic intermediate layer of Atlantic water, which is increasingly pronounced in the twenty first century.  相似文献   

12.
A 1D model, including a time variation of eddy viscosity and mixed layer depth, is applied to study Ekman spirals. It simulates a weak velocity in the atmosphere but a jet in the upper oceanic mixed layer during daytime; and a strong velocity in the atmosphere but a weak, uniform velocity in the ocean at night. The mean spirals in both atmosphere and ocean are close to the average spirals at midday and midnight, they are not flat as suggested by previous studies but consistent with the observations of Polton et al (2013). Our results also show shorter length scale for magnitude decay than for rotation of mean velocity as observed in the ocean, which comes from the combined effects of the diurnal variation of PBL and the Coriolis force. The latter becomes more important away from the surface. In the upper oceanic mixed layer, the mean velocity mainly comes from the strong jets in the late afternoon and early evening. Near and below the depth of Ekman depth, the weak velocities change with time and cancel out each other if averaged timing is longer than the inertia period. It results in diminishing of magnitude of the mean velocity, but the amplitude of individual parcel oscillating can still be quite large near the Ekman depth. Meanwhile, the change of velocity angle from the surface is near or less than 90 degree. Hence, shorter length scale for magnitude decay than for rotation of the mean velocity is not controlled by viscosity alone. Meanwhile, the model does not need two viscosities as suggested previously.The results also show that either the diurnal variation of surface stress or eddy viscosity alone can create a diurnal oscillation of velocity in the ocean. The interactions between PBL force and the Coriolis force can create a weak instability in the atmosphere and ocean at 30° and 90°. This weak instability may explain the observed nocturnal LLJ near 30 °N on the lee of the Rocky Mountains and the intensification of mesoscale circulation simulated by Sun and Wu (1992).  相似文献   

13.
应用含湍流频散效应的近地面层的运动方程求解了不同层结下的风速廓线，着重分析了湍流频散效应对近地面层平稳运动的影响。分析指出：湍流的频散效应对经典的幂律廓线一对数修正，该修正在不稳定层结时比稳定层时明显；利用相似理论也得到了该常数。  相似文献   

14.
The radiative transfer model (RT3), a vector radiative transfer (VRT) scheme in a plane-parallel atmosphere, was bounded by a rough ocean surface in this study. The boundary problem was solved using a Fourier series decomposition of the radiation field as a function of the azimuth. For the case of a rough ocean surface, the decomposition was obtained by developing both the Fresnel reflection matrix and the probability distribution of the water facet orientation as Fourier series. The effect of shadowing by ocean surface waves was also considered in the boundary condition. The VRT model can compute the intensity and degree of polarization of the light at the top of the atmosphere (TOA), the ocean surface, and any level of the atmosphere in the ocean-atmosphere system. The results obtained by our model are in good agreement with those computed by Ahmad’s model. The simulated results showed that the shadow effects of wave facets on the intensity and the degree of polarization are negligible except at the ocean surface near the grazing angle, possibly because we did not consider the effect of white caps.  相似文献   

15.
C2-C6 Nonmethane hydrocarbon (NMHC) concentrations in the atmospheric boundary layer and in surface seawater were simultaneously measured during an oceanographic cruise in the intertropical Indian Ocean. NMHC were found to be mainly C2-C4 alkenes and C2-C3 alkanes. Their concentrations ranged from 1 to 30×10–9 l/l in the seawater and 0.1 to 15 ppbv in the atmosphere. Seawater appeared to be a source because the C2-C6 NMHC were supersaturated with respect to the atmosphere by 2 or 3 orders of magnitude.After a selection of the pure marine atmospheric samples, performed with the help of stable and radioactive continental tracers, we found an identical composition in NMHC of surface air and seawater. This observation enabled us to establish that the gas transfer between sea and air occurred according to nonsteady state processes, and that the fluxes cannot be deduced only from atmospheric measurements. An order of magnitude value of the oceanic source for the different NMHC is however derived from the comparison of their sea water concentrations to that of propane and an independent evluation of the marine source of this last compound.  相似文献   

16.
A similarity theory is developed to describe diffusion of a cloud of passive material in a neutral barotropic steady-state boundary layer of the Earth's atmosphere. It is suggested that a characteristic length scale U */f is relevant in the diffusion process when the diffusing cloud mixes well into the depth of the boundary layer. For an atmosphere having an effective upper bound for vertical spread, an expression for the trajectory of the centroid of the diffusing cloud is derived. The theoretically computed vertical spread is compared with experimental data on diffusion of tracer cloud over rough (urban) and smooth terrains.  相似文献   

17.
During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground.  相似文献   

18.
A cloud-ocean planetary boundary layer (OPBL) feedback mechanism is presented and tested in this paper. Water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective clouds under a conditionally unstable lapse rate. The variable cloud cover and rainfall may have positive and negative feedback with the ocean mixed layer temperature and salinity structure. The coupling of the simplified Kuo’s (1965) cumulus cloud model to the Kraus-Turner’s (1967) ocean mixed layer model shows the existence of this feedback mechanism. The theory also predicts the generation of low frequency oscillation in the atmosphere and oceans.  相似文献   

19.
The commonly reported temperature coefficient of P. the equilibrium partial pressure of CO2, is (P/T) A,C ,which is about 15 ppm/°C, or 5% of the atmospheric partial pressure of CO2. This coefficient, however, applies only to deep water, not to surface water which can exchange CO2 with the atmosphere. The coefficient (P/T) A,C ,, where designates constancy of the sum of atmospheric and surface-ocean CO2, is the appropriate value for air-sea exchange. Numerical values are mass-dependent because the depth of the exchanging ocean layer must be specified. For a 100-m surface layer, the value is ca. 1.5 ppm/°C, or 0.5% of ambient CO2. Editor's Note:In view of the interdisciplinary importance of the carbon dioxide-climate problem, this note on seawater chemistry should be of interest to specialists beyond the discipline of ocean chemistry.  相似文献   

20.
Summary ?We have investigated the effects of shear and sharp gradients in static stability and demonstrated how a mountain wave and its associated surface winds can be strongly influenced. Linear theory for two-dimensional, nonrotating stratified flow over an isolated mountain ridge with positive shear and constant static stability shows that the horizontal wind speeds on both the lee and upslope surfaces are suppressed by positive shear. The critical F(=U/Nh where U is the basic wind speed, N the Brunt-Vaisala frequency, and h the mountain height) for the occurrence of wave breaking decreases when the strength of the positive shear increases, while the location for the wave-induced critical level is higher in cases with larger positive shear. The linear theory is then verified by a series of systematic nonlinear numerical experiments. Four different flow regimes are found for positive shear flow over a two-dimensional mountain. The values of critical F which separate the flow regimes are lower when the strength of the positive shear is larger. The location of stagnation aloft from numerical simulations is found to be quite consistent with those predicted by linear theory. We calculate the strongest horizontal wind speed on the lee surface (U max), the smallest horizontal wind speed on the upslope surface (U min), the reflection (Ref), and the transmission (Tran) coefficients for different combinations of the stability ratio between the upper and lower layers (i.e. and z 1 (interface height) in a two-layer atmosphere from linear analytical solutions. Both Ref and Tran are found to be functions of log() but not the interface height (z 1). Ref is larger when is much different from 1, no matter whether it is larger or smaller than 1. However, Tran decreases when log() increases and approaches 0 when log() is large. The magnitude of the largest U max (smallest U min) increases (decreases) as the absolute value of log() increases. It is found that the largest U max occurs when the nondimensional z 1 is near for cases with a less stable upper layer or when z 1 is near for cases with a more stable upper layer. These results are confirmed by nonlinear numerical simulations. We find that linear theory is very useful in qualitative analysis of the possibility of high-drag state for different stability profiles. The location of stagnation aloft in a two-layer atmosphere from numerical simulations agrees very well with those predicted by linear theory. The above findings are applied to investigate the Boulder severe downslope windstorm of 11 January 1972. We find that the windstorm cannot develop if the near mountain-top inversion is located at a higher altitude (e.g.,  km). However, if there exists a less stable layer right below the tropopause, the windstorm can develop in the absence of a low-level inversion. These results indicate the importance of partial reflection due to the structured atmosphere in influencing the possibility of severe downslope windstorms, although partial reflection may not be the responsible mechanism for the generation of windstorms. Received September 25, 1999/Revised February 9, 2000  相似文献   

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