共查询到20条相似文献，搜索用时 31 毫秒
1.
Gilles Tedeschi Alexander M. J. van Eijk Jacques Piazzola Jolanta T. Kusmierczyk-Michulec 《Boundary-Layer Meteorology》2017,163(2):327-350
Sea-salt aerosol concentrations in the coastal zone are assessed with the numerical aerosol-transport model MACMod that applies separate aerosol source functions for open ocean and the surf zone near the sea–land transition. Numerical simulations of the aerosol concentration as a function of offshore distance from the surf zone compare favourably with experimental data obtained during a surf-zone aerosol experiment in Duck, North Carolina in autumn 2007. Based on numerical simulations, the effect of variations in aerosol production (source strength) and transport conditions (wind speed, air–sea temperature difference), we show that the surf-zone aerosols are replaced by aerosols generated over the open ocean as the airmass advects out to sea. The contribution from the surf-generated aerosol is significant during high wind speeds and high wave events, and is significant up to 30 km away from the production zone. At low wind speeds, the oceanic component dominates, except within 1–5 km of the surf zone. Similar results are obtained for onshore flow, where no further sea-salt aerosol production occurs as the airmass advects out over land. The oceanic aerosols that are well-mixed throughout the boundary layer are then more efficiently transported inland than are the surf-generated aerosols, which are confined to the first few tens of metres above the surface, and are therefore also more susceptible to the type of surface (trees or grass) that determines the deposition velocity. 相似文献
2.
SIMULTANEOUS DETERMINATION OF AEROSOL SIZE DISTRIBUTION AND REFRACTIVE INDEX AND SURFACE ALBEDO FROM RADIANCE－PART I: THEORY 总被引：5，自引：0，他引：5
Analyzing in detail the dependence of sky radiance on aerosol optical property and surface albedo, we present a new method for simultaneous determination of aerosol size distribution, its wavelength-dependent refractive index and surface albedo. The aerosol scattering phase function near 10o, its weighted phase function near 40o introduced in this paper, which can be inferred from sky radiance data, and the radiance near 90o are respectively used in retrieving the real part of refractive index, its imaginary part and surface albedo. Results in numerical experiments are satisfactory under different given conditions. 相似文献
3.
An Improved Atmospheric Vector Radiative Transfer Model Incorporating Rough Ocean Boundaries 
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下载免费PDF全文 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
4.
From the mid 1960s to the present, the normalized radar cross-section (NRCS) of the ocean has been measured using airborne radars operating over a frequency range of 0.4 to 14 GHz. Analyses of these data have shown that the NRCS was proportional to the ocean surface wind speed raised to some power, but the values of the exponent remained in dispute. This paper extends previous work and uses these NRCS measurements to demonstrate that to the first order, the NRCS is a function of only the friction velocity at the ocean's surface. Further analyses characterize the dependence of the NRCS on radar variables such as frequency, incidence angle, polarization, etc. Finally, recommendations are made for using Ku-band radars at large incidence angles for remote sensing of the wind friction velocity vector. 相似文献
5.
大气气溶胶的垂直非均一对向上亮度和卫星遥感地表反射率的效应 总被引：1，自引：0，他引：1
均一模式和两层模式是两个忽略气溶胶垂直非均一、并广泛用于卫星遥感的辐射模式。通过两个模式的数值模拟，分析了气溶胶的垂直非均一对向上天空亮度和卫星遥感地面反射率的效应。数值模拟选用了２４个有代表性的气溶胶模式。对于具有强分子散射的卫星短波通道，由于分子和气溶胶散射性的明显不同，应用均一和两层模式计算的向上亮度往往存在较大误差。对长波通道，如果气溶胶的光学特性随高度变化不大，该亮度误差较小，但如果存在不同散射相函数和一次散射反照率的气溶胶层，该误差仍可能较大。对于干净的大气，由均一和两层模式计算的亮度误差可分别高达３１．４％和３１．５％，而对于混浊的大气，该误差可分别高达６７．８％和５９．２％。该亮度误差可以引起地表反射率解存在大的不确定性，特别是对于短波通道和强吸收的气溶胶。对于包含强吸收气溶胶的混浊大气，均一和两层模式不适合于大气订正应用。 相似文献
6.
In this paper, the characteristics of eastern Asian dust storm are examined with emphasis on the satellite measurements of aerosol optical thickness. The reflectivity of solar radiation from the earth’s atmosphere depends on the optical thickness. The satellite measurement of radiance of sunlight, scattered by the earth and its atmosphere, is used to derive the properties of aerosol on oceanic surfaces. This paper involves the following: (1) investigation of the measurement of dust storm over the oceanic surface by GMS satellite; (2) investigation of the measurement of dust storm over the land surface by ground-based instruments such as actinometer, lidar, etc.; (3) for comparison, de-riving an atmospheric aerosol size distribution over the oceanic surface of calm weather through measurements of NOAA satellite; and (4) the weather process and its mass load of eastern Asian dust storm. 相似文献
7.
Various algorithms have recently been developed in order to retrieve the aerosol optical thickness (AOT) at continental scales. However, they are, to some extent, subject to large uncertainties resulting from some necessary physical assumptions on land surface anisotropy and level of brightness. In fact, disentangling aerosol and surface signals contained in the top of atmosphere (TOA) radiance received at the satellite level are a matter of difficulty because a single sensor itself cannot gather all required spatial, temporal, spectral and angular information. In particular, each instrument yields limited scanning configuration due to its platform's orbital characteristics. In this regard, a synergetic approach is presented which merges Advanced Along-Track Scanning Radiometer (AATSR) TOA radiances and the MODerate resolution Imaging Spectroradiometer (MODIS) Bi-directional Reflectance Distribution Function (BRDF)/Albedo Model Parameters Product for the retrieval of AOT at 0.55, 0.66, and 0.87 µm wavelengths over non-Lambertian land surface at a 5 km spatial resolution. In this approach, BRDF products serve to assess the surface reflectance in the AATSR geometry as a boundary layer. The peculiarity of the approach is that no specific assumption is required about the spectral characteristics of land surface, thus allowing for a quantitative retrieval of aerosol particles over any arbitrary land unit in virtue of combining forward and nadir AATSR observations. We obtain on average differences within 0.1τ compared to in situ AErosol RObotic NETwork (AERONET) measurements and 36 retrievals corresponding to 27 January, 12 February, 16 March, 28 May, 26 June, and 21 July 2006, respectively, over the city of Beijing in China. Pearson's correlation coefficient is 0.94 and 0.96 for nadir and forward AATSR, respectively. These suggest that AOT retrieval over land is indeed feasible by taking benefit of the validated MODIS BRDF. Besides, the first results indicate that the AATSR retrievals might be used to evaluate the spectral behaviour of the AOT. 相似文献
8.
Summary Sky luminance and spectral radiance has been characterised at Neumayer, Antarctica for selected situations during the austral
summer 2003/04. Luminance has also been measured at Boulder, Colorado, USA in June 2003. The high reflectivity of the surface
(albedo) in Antarctica, reaching values up to 100% in the ultraviolet (UV) and visible part of the solar spectrum due to snow
cover, modifies the radiation field considerably when compared to mid-latitudes. A dependence of luminance and spectral radiance
on solar zenith angle (SZA) and surface albedo has been identified. For snow and cloudless sky, the horizon luminance exceeds
the zenith luminance by as much as a factor of 8.2 and 7.6 for a SZA of 86° and 48°, respectively. In contrast, over grass
this factor amounts to 4.9 for a SZA of 86° and a factor of only 1.4 for a SZA of 48°. Thus, a snow surface with high albedo
can enhance horizon brightening compared to grass by a factor of 1.7 for low sun at a SZA of 86° and by a factor of 5 for
high sun at a SZA of 48°. For cloudy cases, zenith luminance and radiance exceed the cloudless value by a factor of 10 due
to multiple scattering between the cloud base and high albedo surface. Measurements of spectral radiance show increased horizon
brightening for increasing wavelengths and generally confirm the findings for luminance. Good agreement with model results
is found for some cases; however there are also large deviations between measured and modelled values especially in the infrared.
These deviations can only partly be explained by measurement uncertainties; to completely resolve the differences between
model and measurement further studies need to be performed, which will require an improvement of modelling the spectral radiance.
From the present study it can be concluded that a change in albedo conditions, which is predicted as a consequence of climate
change, will significantly change the radiation conditions in polar regions as well. 相似文献
9.
Numerous factors can influence the radiative transfer simulation of hyper-spectral ultraviolet satellite observation,including the radiative transfer scheme, gaseous absorption coefficients, Rayleigh scattering scheme, surface reflectance, aerosol scattering, band center wavelength shifts of sensor, and accuracy of input profiles. In this study, a Unified Linearized Vector Radiative Transfer Model(UNL-VRTM) is used to understand the influences of various factors on the top of atmosphere(TOA) normalized radiance in the ultraviolet(UV) region. A benchmark test for Rayleigh scattering is first performed to verify the UNL-VRTM accuracy, showing that the model performances agree well with earlier peer-reviewed results. Sensitivity experiments show that a scalar radiative transfer approximation considering only ozone and a constant surface reflectance within the UV region may cause significant errors to the TOA normalized radiance. A comparison of the Ozone Mapping and Profiler Suite(OMPS) radiances between simulations and observations shows that the surface reflectance strongly influences the accuracy for the wavelengths larger than 340 nm. Thus, using the surface reflectivity at 331 nm as a proxy for simulating the whole OMPS hyperspectral ultraviolet radiances is problematic. The impact of rotational Raman scattering on TOA radiance can be simulated through using SCIATRAN, which can also reduce the difference between measurements and simulations to some extent. Overall, the differences between OMPS simulations and observations can be less than 3% for the entire wavelengths. The bias is nearly constant across the cross-track direction. 相似文献
10.
Summary The diffuse sky radiation component in the ultraviolet wavelengths is often at least 50% of the global irradiance under clear skies, and is the dominant component of ultraviolet global radiation under translucent overcast skies. The distribution of sky radiance was measured in a rural area and modeled for wavelength bands of ultraviolet-B (UVB, 280–320 nm) and ultraviolet-A (UVA, 320–400 nm). Sky radiance measurements were made during the summer of 1993 over a wide range of solar zenith angles using radiance sensors mounted on a hand-operated hemispherical rotation mount. UVB irradiance measurements were also made during each scan. Since the ratio of measured irradiance under overcast skies and that predicted for clear skies was not correlated with cloud base height, opaque cloud fraction, or solar zenith angle, it was concluded that the scattering from the clouds dominated the global irradiance, and this scattering was relatively unaffected by the scattering off opaque clouds in the translucent atmosphere.Analysis of the translucent overcast sky UVA and UVB radiance measurements using a semi-empirical distribution model showed that the spectral influences on multiple scattering, single scattering, and horizon brightening components of the distributions agreed with basic atmospheric radiation theory. The best model used solar zenith, the sky zenith, and the scattering angle with resultant coefficient of determination values of 0.62 and 0.25 for the UVA and UVB respectively. The developed equations can be applied directly to the diffuse sky irradiance on the horizontal to provide radiance distributions for the sky.With 6 Figures 相似文献
11.
A Modeling Study of the Effects of Direct Radiative Forcing
Due to Carbonaceous Aerosol on the Climate in East Asia 总被引：6，自引：0，他引：6
The study investigated the effects of global direct radiative forcing due to carbonaceous
aerosol on the climate in East Asia, using the CAM3 developed by NCAR. The results showed that
carbonaceous aerosols cause negative forcing at the top of the atmosphere (TOA) and surface under
clear sky conditions, but positive forcing at the TOA and weak negative forcing at the surface under
all sky conditions. Hence, clouds could change the sign of the direct radiative forcing at the TOA,
and weaken the forcing at the surface. Carbonaceous aerosols have distinct effects on the summer
climate in East Asia. In southern China and India, it caused the surface temperature to increase,
but the total cloud cover and precipitation to decrease. However, the opposite effects are caused
for most of northern China and Bangladesh. Given the changes in temperature, vertical velocity,
and surface streamflow caused by carbonaceous aerosol in this simulation, carbonaceous aerosol
could also induce summer precipitation to decrease in southern China but increase in northern China. 相似文献
12.
13.
The Kuroshio Extension region is characterized by energetic oceanic mesoscale and frontal variability that alters the air–sea fluxes that can influence large-scale climate variability in the North Pacific. We investigate this mesoscale air-sea coupling using a regional eddy-resolving coupled ocean–atmosphere (OA) model that downscales the observed large-scale climate variability from 2001 to 2007. The model simulates many aspects of the observed seasonal cycle of OA coupling strength for both momentum and turbulent heat fluxes. We introduce a new modeling approach to study the scale-dependence of two well-known mechanisms for the surface wind response to mesoscale sea surface temperatures (SSTs), namely, the ‘vertical mixing mechanism’ (VMM) and the ‘pressure adjustment mechanism’ (PAM). We compare the fully coupled model to the same model with an online, 2-D spatial smoother applied to remove the mesoscale SST field felt by the atmosphere. Both VMM and PAM are found to be active during the strong wintertime peak seen in the coupling strength in both the model and observations. For VMM, large-scale SST gradients surprisingly generate coupling between downwind SST gradient and wind stress divergence that is often stronger than the coupling on the mesoscale, indicating their joint importance in OA interaction in this region. In contrast, VMM coupling between crosswind SST gradient and wind stress curl occurs only on the mesoscale, and not over large-scale SST gradients, indicating the essential role of the ocean mesocale. For PAM, the model results indicate that coupling between the Laplacian of sea level pressure and surface wind convergence occurs for both mesoscale and large-scale processes, but inclusion of the mesoscale roughly doubles the coupling strength. Coupling between latent heat flux and SST is found to be significant throughout the entire seasonal cycle in both fully coupled mode and large-scale coupled mode, with peak coupling during winter months. The atmospheric response to the oceanic mesoscale SST is also studied by comparing the fully coupled run to an uncoupled atmospheric model forced with smoothed SST prescribed from the coupled run. Precipitation anomalies are found to be forced by surface wind convergence patterns that are driven by mesoscale SST gradients, indicating the importance of the ocean forcing the atmosphere at this scale. 相似文献
14.
使用RegCM3-dust区域气候模式,单向嵌套MIROC3．2-hires全球模式输出结果,在IPCCA1B温室气体排放情景下,对中国及东亚地区进行了当代（1991年-2000年）和未来（2091年-2100年）水平分辨率为50km的气候以及沙尘气溶胶数值模拟试验。结果表明,模式对中国地区地面气温、降水和东亚沙尘气溶胶空间分布模拟较好。未来东亚沙尘气溶胶年平均起沙通量增加2％,其中12月-3月由于地表积雪量的减少而增加,4月-11月由于10m风速的减小而减少,不同强度的强起沙事件同样12月-3月增加,4月-11月减少。年平均沙尘气溶胶柱含量增加14％,其中3月-5月和8月略减少,其它月份增加。沙尘气溶胶引起地面（SRF）负辐射强迫和沙尘源区大气顶（TOA）正辐射强迫、下游地区TOA负辐射强迫,受沙尘气溶胶辐射强迫的影响,地面起沙通量和柱含量减少。 相似文献
15.
国际Argo(Array for Real-time Geostrophic Oceanography)计划的实施,提供了前所未有的全球深海大洋0～2000 m水深范围内的海水温度和盐度观测资料,在大气和海洋科研业务中应用这一全新的资料,是深入认识大气和海洋变异、提高我国气候预测、海洋监测分析和预报能力的一个关键所在.通过开发非线性温—盐协调同化方案和利用同化高度计资料来调整模式的温度和盐度场,建立了可同化包括Argo等多种海洋观测资料的全球海洋资料变分同化系统,提高了对全球海洋的监测分析能力.实现了海洋资料同化系统与全球海气耦合模式的耦合,显著提高了短期气候预测水平.利用Argo资料改进了海洋动力模式中的物理过程参数化方案,有效提高了海洋模式对真实大洋的模拟能力和对厄尔尼诺/拉尼娜的预测能力.开发了利用Argo浮标漂流轨迹推算全球海洋表层和中层流的方法,提高了推算的全球表层流、中层流资料质量,有效弥补了洋流观测的匮乏. 相似文献
16.
采用1948—2014年NCEP/NCAR大气再分析资料以及延伸重建海温资料,基于大气海洋间不同的主导关系对冬季北太平洋大范围海温异常进行分类,探究其相应的海气结构特征。结果表明:1)大气影响海洋的个例多于海洋影响大气的个例,即在冬季北太平洋大气强迫海洋占主要地位,但也存在海洋对大气的反馈作用。2)对于大气影响海洋而言,SST(Sea Surface Temperature)暖异常区上空主要伴随着东北—西南走向的相当正压高低压异常(东北高西南低),对应东南风异常以及显著的深厚暖异常,表现出相当正压暖/脊结构,冷异常情况与此相反。SST异常为净热通量异常与风速异常共同作用引起。3)对于海洋影响大气而言,在SST暖异常区上空西部为南北向高低压异常(北高南低),东部为低压异常,对应偏东风异常。在SST冷异常区上空为偶极型的南北向高低压异常(南高北低),对应偏西风异常;位势高度异常表现出相当正压结构且较大气影响海洋时相对偏弱,大气暖(冷)温度异常比较浅薄且主要局限于对流层低层。4)海洋温度结构异常主要表现为,在大气影响海洋时海温异常由表层下传,海洋影响大气时为上下一致的温度异常。 相似文献
17.
Abstract Cloudless‐sky solar fluxes calculated by the radiative transfer algorithm used in the Canadian Climate Centre's general circulation climate model are compared with measurements of upwelling radiation at the top of the atmosphere (TOA) and downwelling radiation at the surface. The 12‐layer model partitions the solar spectrum into two broad wavebands (0.25–0.68 and 0.68–4.00 μm). The comparison utilized TOA fluxes estimated from Nimbus‐ 7 measurements and measured downwelling fluxes at the surface for Kalgoorlie, West Australia, and downwelling fluxes at the surface for Woodbridge, Ontario. Model estimates and measurements agreed to within experimental error for most solar zenith angles. Estimates improved, especially at Woodbridge, when aerosol effects were included. The mean bias error was less than 4% for surface irradiance and less than 6% for upwelling TOA irradiance, which produces a TOA albedo error of about 0.01. 相似文献
18.
19.
用EVAP方法反演冷流暴雪的风场及检验 总被引：2，自引：0，他引：2
EVAP(Extended VAP)雷达反演方法是在忽略空气垂直运动速度而考虑云雨粒子下落速度影响的条件下,导出从雷达多仰角多普勒速度资料产生不同高度上的水平径向速度计算公式,然后利用VAP方法来反演出等高面上的二维水平风场.利用烟台多普勒天气雷达资料,采用EVAP方法反演了2005年12月山东半岛两个风场背景条件和暴雪落区均有明显差异的冷流暴雪个例水平风场.将雷达实测的径向速度、反射率因子插值到各等高面上,并与反演的同等高面风场叠加显示,以此分析反演的风场是否与原始雷达数据相符.此外,还与地面自动站风场、高空风场等实测资料进行对比,综合检验反演结果的合理性和可靠性,并进一步分析了冷流暴雪的中尺度风场结构.结果表明,反演风场与实测资料相符;EVAP方法对强风和弱风的冷流暴雪个例都可反演出不同高度的中尺度风场结构,反演的西南风与东北风、西北风与东北风之间的切变线和强回波带相对应,揭示了暴雪产生的动力机制,说明EVAP方法对不同风场条件的暴雪中尺度系统都有一定的反演能力.高时空分辨率的EVAP反演风场弥补了天气图上仅能分析出山东半岛西北风的缺憾,且反演过程中一个体扫的计算时间不足1 min,因此EVAP反演的中尺度风场信息适合在冷流降雪的短时临近预报业务中应用. 相似文献
20.
为探讨黄海海洋涡旋的三维结构特征、能量输送与转换及影响机制,对黄海海域典型台风海洋气旋与近海海湾反气旋式涡旋个例进行数值模拟和时空诊断分析。采用FVCOM(Finite Volume Community Ocean Model)区域海洋数值模式精细化描述台风海洋涡旋与近海海洋中小尺度涡旋系统。对涡旋能量传输特征模拟显示,气旋式和反气旋式海洋涡旋中,非对称强流区动能能量下传比涡旋中心部位的强度更强,维持时间更长,下传深度更深。反气旋式海洋涡旋因Ekman流动形成的向中心辐合作用,造成此类差异更显著。气旋涡的动能主要来源于台风的近海面风应力动能和海洋涡旋有效位能的转换,反气旋涡旋区域风动力偏弱,其动能强度维持在低位,其涡旋增强伴随着有效位能的增加。环境因子影响机制从风浪,底摩擦和地形三方面讨论。结果显示:耦合波浪模块后,台风强风应力和风浪的综合作用扩大台风海洋涡旋尺度,并增强涡旋环流强度,同时对相邻的反气旋涡有压缩和减弱作用。风浪效应对台风海洋涡旋有正贡献。强台风过程表层环流响应台风应力而浅水地形和底摩擦强烈影响涡旋下层,造成台风海洋涡旋结构在垂直方向上偏移,并影响到下层环流速度减小,流向与表层相反。在海洋气旋涡和反气旋涡的显著辐散区,其混合层下方有温盐要素的涌升对应,辐合区有温盐要素的下沉对应;同时海底地形的升降也造成温盐强迫上升与下降,其强度与地形起伏尺度成正比,较环流系统作用更强。 相似文献