Sodar Detected Top-Down Convection in a Nocturnal Cloud-Topped Boundary Layer: A Case Study     

P. Martano  D. Cava  G. Mastrantonio  S. Argentini  A. Viola 《Boundary-Layer Meteorology》2005,115(1):85-103

Nocturnal convection, originating in a well-mixed marine cloud-topped boundary layer, advected onshore, was observed using a Doppler sodar on the Tyrrhenian coast in Italy. The horizontal and vertical dimensions of the downdrafts were evaluated. The oscillation frequency triggered by the downdrafts at the inversion layer, derived from the harmonic analysis of the sodar measured vertical velocity (w), is compared with the Brunt-Vaisala frequency, obtained from the rawinsonde temperature profile. A similarity function for the ²_w vertical profile was used to fit the sodar experimental data and to retrieve the depth of the mixing layer and the sensible heat flux at the top of the cloud layer. The results are in agreement with the convection layer depth observed in the sodar echoes facsimile record, and with the energy budget evaluated at the top of the cloud layer using the rawinsonde profiles.  相似文献   

青海省岩石地层单位概要   总被引：1，自引：0，他引：1  

Reseach group of stratigraphic multiple division  correlation  Qinghai Province 《青海国土经略》1995,(1)

分三个部分对青海省岩石地层单位进行概要介绍。第一部分是建议采用的岩石地层单位(包括顺序号、单位名称、代号、地质年代、资料卡片号与现在定义);第二部分是建议采用的岩石地层单位名称索引(一)、(二);第三部分是建议不采用的地层单位名称。为方便读者查找,文前附有编辑说明。  相似文献   

Geometry and growth of sill complexes: insights using 3D seismic from the North Rockall Trough   总被引：1，自引：0，他引：1  

K.?ThomsonEmail author  D.?Hutton 《Bulletin of Volcanology》2004,66(4):364-375

Doleritic sill complexes, which are an important component of volcanic continental margins, can be imaged using 3D seismic reflection data. This allows unprecedented access to the complete 3D geometry of the bodies and an opportunity to test classic sill emplacement models. The doleritic sills associated with basaltic volcanism in the North Rockall Trough occur in two forms. Radially symmetrical sill complexes consist of a saucer-like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined, commonly ragged, outer rim. Bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano. With an elongate, concave upwards, trough-like geometry bilaterally symmetrical sills climb away from the magma source from which they originate. Both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge, producing hybrid sill complexes. Radial sill complexes consist of a series of radiating primary flow units. With dimensions up to 3 km, each primary flow unit rises from the inner saucer and is fed by primary magma tube. Primary flow units contain secondary flow units with dimensions up to 2 km, each being fed by a secondary magma tube branching from the primary magma tube. Secondary flow units in turn are composed of 100-m scale tertiary flow units. A similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes, with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex. This branching flow pattern, as well as the interaction between flow units of varying orders, provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger. The data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer, grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature. These features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening. The branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex, suggesting that the general features of the laccolith emplacement model also apply.Editorial responsibility: J. Stix  相似文献   

Palaeogeography and tectonic structure of allochthonous units in the German part of the Rheno-Hercynian Belt (Central European Variscides)     

H.?HuckriedeEmail author  K.?Wemmer  H.?Ahrendt 《International Journal of Earth Sciences》2004,93(3):414-431

New information on palaeogeography, orogenic evolution, tectonic structure, and boundaries of allochthonous units in the Rheno-Hercynian Belt is based on provenance analyses of clastic sediments and field studies. ⁴⁰K/⁴⁰Ar dating of detrital muscovites proved to be a particularly useful method because Cadomian, Caledonian and Early Variscan provenances of detrital material can be distinguished. Cadomian muscovite cooling ages are restricted to allochthonous units whereas Caledonian ages dominate within par-autochthonous and shortly displaced allochthonous units. The largest and uppermost preserved nappe, the Gießen-Harz Nappe, is derived from an oceanic flysch basin, which was not reached by Caledonian detritus. The other allochthonous units form a duplex-like structure sandwiched between the Gießen-Harz Nappe and par-autochthonous units at its base. The thick and heterogeneous roof- and floor-thrusts of this structure were previously often misinterpreted as olistostromes. The northern margin of allochthonous units is the steeply dipping Hörre-Gommern Zone. It consists of three sub-units derived from deep-water areas between the shelf at the southern margin of the Old Red Sandstone Continent and an oceanic basin to the south. The southeastern part of the duplex-structure (Harzgerode Zone) shows close affinities to Armorican terranes.  相似文献   

辨析“气候变暖”     

刘秀铭  李志忠  雷培文  赵国永  姜修洋  陈秀玲  陈家胜  朱芸  吕镔  雷国良  李平原  靳建辉  陈渠 《福建地理》2012,(1):1-11

近年来人们对＂气候变暖＂及其机制的争论达到了前所未有的程度,这可能是因为气候变化不再是单纯研究大气变化规律的科学,而变成一门与＂减排方案＂和＂征收碳税＂有关的政治与经济问题相联系,与国家经济利益有关的崭新课题.＂气候变暖＂既与利益有关,就会难免偏离公正,偏离纯理论科学.本研究对国内外＂气候变暖＂最新动态进行回顾分析,得出以下认识和结论.1）过去百年城市发展,极大地影响了器测温度数据,如果没有对＂热岛效应＂进行矫正,无疑高估了过去百年全球升温的幅度;2）过去百年全球有所变暖是事实,但不同学者增温估算不一致.不仅升温幅度不确定,而且人类和自然因素对升温贡献各占多少也不确定;如果考虑到城市发展对增温估算的影响,过去百年增温应当比0.4℃更低,远没有达到历史上次级波动的变化范围.3）尽管过去百年地球有所变暖,但在万年轨道尺度上,现在地球处于变冷的大趋势过程中.对现在气候变暖更合理解释,是属于变冷大趋势中的次级变暖波动;4）不论过去还是现在,大气CO2浓度变化总是落后于温度变化,即总是温度驱动着CO2变化,而不是CO2浓度驱动地球增温.  相似文献   

北京市1996-2007年住宅空调致冷耗能影响因素分析   总被引：1，自引：0，他引：1       下载免费PDF全文

陈莉  李帅  方修琦  陈坤 《气候变化研究进展》2009,5(4):231-236

 采用气象资料和经济统计资料,以北京市为例,分析了城镇住宅空调致冷耗能的影响因素。结果显示：在一定建筑设计标准下,直接影响城镇住宅空调致冷耗能的因子主要有降温强度、城镇人口数、人均住宅建筑面积和城镇家庭空调器拥有比例。总的来说,由于目前中国城市化进程的加速,城镇人口、人均住宅建筑面积、城镇空调器拥有比例在不断增加,因此,无论气候变暖或变冷,各地空调致冷耗能不可避免地在增加。在上述因子中,气候是目前为止唯一可能起到降低能耗作用的因子。对于城市化较快的北京市,由于城镇家庭空调器拥有比例的快速增长,城镇家庭空调器拥有比例这一因子对空调致冷耗能增量的贡献率普遍最大。  相似文献   

Increased Tibetan Plateau Snow Depth：An Indicator of the Connection between Enhanced Winter NAO and Late-Spring Tropospheric Cooling over East Asia   总被引：4，自引：1，他引：3  

XIN Xiaoge  ZHOU Tianjun  YU Rucong 《大气科学进展》2010,27(4):788-794

The authors present evidence to suggest that variations in the snow depth over the Tibetan Plateau (TP) are connected with changes of North Atlantic Oscillation (NAO) in winter (JFM). During the positive phase of NAO, the Asian subtropical westerly jet intensifies and the India-Myanmar trough deepens. Both of these processes enhance ascending motion over the TP. The intensified upward motion, together with strengthened southerlies upstream of the India-Myanmar trough, favors stronger snowfall over the TP, which is associated with East Asian tropospheric cooling in the subsequent late spring (April--May). Hence, the decadal increase of winter snow depth over the TP after the late 1970s is proposed to be an indicator of the connection between the enhanced winter NAO and late spring tropospheric cooling over East Asia.  相似文献   

The Effects of Line-Wing Cutoff in LBL Integration on Radiation Calculations          下载免费PDF全文

ZHANG Hu  SHI Guangyu  LIU Yi 《Acta Meteorologica Sinica》2008,22(2):248-255

There are three basic methods in radiative transfer calculations, i.e., line-by-line (LBL) integration, correlated k-distribution method, and band model. The LBL integration is the most accurate of all, in which, there are two quadrature algorithms named in this paper as integration by lines and by sampling "points when calculating atmospheric transmittance in the considered wavenumber region. Because the LBL integration is the most expensive of all, it is necessary and important to save calculation time but increase calculation speed when it is put into use in the daily operation in atmospheric remote sensing and atmospheric sounding. A simplified LBL method is given in this paper on the basis of integration by lines, which increases computational speed greatly with keeping the same accuracy. Then, we discuss the effects of different cutoff schemes on atmospheric absorption coefficient, transmittance, and cooling rate under both of accurate and simplified LBL methods in detail. There are four cutoff schemes described in this paper, i.e., CUTOFFs 1, 2, 3, and 4. It is shown by this numerical study that the way to cut off spectral line-wing has a great effect on the accuracy and speed of radiative calculations. The relative errors of the calculated absorption coefficients for CUTOFF 2 are the largest under different pressures, while for CUTOFF 1, they are less than 2% at most of sampling points and for CUTOFFs 3 or 4, they are ahnost less than 5% in the calculated spectral region, however, the calculation time is reduced greatly. We find in this study that the transmittance in the lower atmosphere is not sensitive to different LBL methods and different cutoff schemes. Whereas for the higher atmosphere, the differences of transmittance results between CUTOFF 2 and each of other three cutoff schemes are the biggest of all no matter for the accurate LBL or for the simplified LBL integrations. By comparison, the best and optimized cutoff scheme is given in this paper finally.  相似文献   

Radiative Processes in the Stable Boundary Layer: Part I. Radiative Aspects   总被引：1，自引：0，他引：1  

J. M. Edwards 《Boundary-Layer Meteorology》2009,132(2):349-350

The structure of the radiatively dominated stable boundary layer is analysed using idealized calculations at high vertical and spectral resolution. The temperature profile of a nocturnal radiative boundary layer, developing after the evening transition, is found to be well described in terms of radiative cooling to the surface, although radiative exchanges within the atmosphere become increasingly important with time. The treatment of non-black surfaces is discussed in some detail and it is shown that the effect of reducing the surface emissivity is to decrease rather than to increase the radiative cooling rate in the surface layer. It is also argued that an accurate assessment of the impact of non-black surfaces requires careful attention to the spectral and directional characteristics of the surface emissivity. A polar nocturnal boundary layer, developing above snow-covered ground, is simulated and found to reach a slowly evolving state characterized by a strong radiative divergence near the surface that is comparable to observed values. Radiative boundary layers are characterized by large temperature gradients near the surface. An erratum to this article can be found at  相似文献   

Observable consequences of kinetic and thermal AGN feedback in elliptical galaxies and galaxy clusters     

Edward C. D. Pope 《Monthly notices of the Royal Astronomical Society》2009,395(4):2317-2325

We have constructed an analytical model of active galactic nuclei (AGN) feedback and studied its implications for elliptical galaxies and galaxy clusters. The results show that momentum injection above a critical value will eject material from low-mass elliptical galaxies, and leads to an X-ray luminosity, L _X, that is  ∝σ⁸⁻¹⁰  , depending on the AGN fuelling mechanism, where σ is the velocity dispersion of the hot gas. This result agrees well with both observations and semi-analytic models. In more massive ellipticals and clusters, AGN outflows quickly become buoyancy dominated. This necessarily means that heating by a central cluster AGN redistributes the intracluster medium (ICM) such that the mass of hot gas, within the cooling radius, should be  ∝ L _X(< r _cool)/[ g ( r _cool)σ]  , where   g ( r _cool)  is the gravitational acceleration at the cooling radius. This prediction is confirmed using observations of seven clusters. The same mechanism also defines a critical ICM cooling time of  ∼0.5 Gyr  , which is in reasonable agreement with recent observations showing that star formation and AGN activity are triggered below a universal cooling time threshold.  相似文献