共查询到20条相似文献，搜索用时 31 毫秒
1.
A TKE-dissipation model for the atmospheric boundary layer 总被引：1，自引：0，他引：1
Anders Andrén 《Boundary-Layer Meteorology》1991,56(3):207-221
The dissipation, , of turbulent kinetic energy (TKE) is a key parameter in atmospheric boundary-layer (ABL) models. Besides being a sink for momentum, it is often used together with the TKE to define an internal turbulence time scale for closure relations. A prognostic formulation for the dissipation of TKE is formulated, based on isotropic tensor modeling methods. The formulation is coupled to a level 2.5 second-order closure model and evaluated against measurements taken in horizontally homogeneous conditions, as well as against a tailored length-scale formulation. A formulation suitable for convective as well as neutral and stable ABLs is suggested.On leave from Department of Meteorology, Uppsala University, P.O. Box 516, S-751 20 Uppsala, Sweden.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
2.
L. Mahrt R. C. Heald D. H. Lenschow B. B. Stankov IB Troen 《Boundary-Layer Meteorology》1979,17(2):247-264
In an effort to describe the basic vertical structure of the nocturnal boundary layer, observations from four experiments are analyzed. During the night, the depth of significant cooling appears to increase with time while the depth of the turbulence and height of the low level wind maximum tend to remain constant or decrease with time. Since the inversion layer extends above the low level wind maximum and shear is small in the region of the low level jet, the Richardson number reaches a maximum at the jet level and then decreases again with height. As a result, turbulence is observed to be a minimum at the height of the low level wind maximum and then increases again above this height.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Part of this work was performed while a visiting scientist at Oregon State University. 相似文献
3.
Relationship of surface heat flux to microscale temperature variations: Application to boreas 总被引：1，自引：0，他引：1
The surface heat flux is normally parameterized in terms of the difference between the air temperature and the surface radiative temperature, or equivalently, the temperature computed from the surface energy balance. In this note, the relationship between the heat flux and the air-surface temperature difference is shown to be sensitive to the microscale variability of the surface radiation temperature caused by differences between the well-ventilated tree tops and less ventilated ground surface. This conclusion is based on surface and aircraft data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS). For this case, the heat flux cannot be predicted by adjusting the thermal roughness height. As an alternative, the aerodynamic temperature can be related to a weighted average of the surface radtation temperature analogous to application of a simple canopy model. Here, the total heat flux is the sum of the heat fluxes from each individual surface type weighted by the area-fractional coverage.Part of this work was carried out in the Dept. of Earth and Atmospheric Sciences, St. Louis University and the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research.Part of this work was carried out in the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research. 相似文献
4.
A workshop on the stable planetary boundary layer (PBL) was held on 21–24 October, 1997 at Lövånger, a small town about 80 km north of Umeå, Sweden. Thirty-five scientists representing eight countries participated in the meeting, which was arranged by the U.S. Army Research Office, the Swedish Defence Research Establishment, the U.S. National Oceanic and Atmospheric Administration's Air Resources Laboratory, and the Meteorology Department of Uppsala University. Topics addressed included the very stable boundary layer, gravity wave/turbulence interactions, modeling the stable boundary layer, future observations and new measurement techniques, the role of condensation (fog) and radiative flux divergence, and atmospheric diffusion. Invited papers appear in this special issue. Workshop discussions, informal presentations, and specific recommendations are summarized. Workshop participants and organizers are presented in Appendix A. 相似文献
5.
对流尺度集合预报是研究飑线等强对流天气的新方向。当前对飑线系统结构的研究主要采用卫星和雷达资料结合高分辨率确定性预报的方法,而本文从集合预报技术的角度分析飑线结构特征。针对2014年7月30日中国江淮地区的一次强飑线过程,利用WRF模式开展了对流尺度集合预报试验,采用概率匹配平均法对集合预报结果进行综合处理,重点考察集合预报对飑线结构特征的模拟能力。结果表明:对流尺度集合预报能够模拟出飑线系统的基本结构特征。集合平均和概率匹配平均法相比控制预报而言,对飑线回波、热力场、动力场和微物理量场结构有明显的改善作用。同时模拟出了飑线系统近地面冷池和环境垂直风切变的相互作用,与RKW理论相一致。概率匹配平均法在回波强度上较集合平均更接近实况,应用于对流尺度集合预报研究极端天气事件具有指示意义。 相似文献
6.
Analysis of high frequency (20 Hz) turbulence data collected from low level flights by the National Center for Atmospheric Research (NCAR) Electra aircraft over the central Arabian Sea on 20 and 24 June, 1979 as part of MONEX 79 indicates the influence of the Somali Jet on boundary-layer turbulence. Different stages of monsoon development were evident on the two observation days from mean boundary-layer profiles. However, turbulence statistics of wind speed components and temperature in the monsoon boundary layer for both days are generally greater than those observed in laboratory experiments or tropical and trade wind boundary layers in which a strong jet was not present. Analysis of high frequency wind, temperature and humidity data was made to obtain fluxes of momentum and heat. Magnitudes of the sensible and latent heat fluxes are three to five times larger than the values observed over the monsoon boundary layer over the Bay of Bengal. The turbulent kinetic energy budget over the Arabian Sea for 24 June indicates the importance of buoyancy, and to a lesser extent shear as the dominant term. Dissipation serves as the primary sink term. 相似文献
7.
《中国气象科学研究院年报》2005,(1):40-41
世界气象组织秘书长雅罗2005年11月访问气科院大气成分中心；美国马里兰大学气象系的张大林教授被邀请任灾害天气国家重点实验室海外主任；中国气象科学研究院与上海市气象局局院合作签字仪式；局、院、青海省领导参观大气成分观测与服务中心；中国气象科学研究院灾害天气国家重点实验室首届学术年会. 相似文献
8.
A Heavy Sea Fog Event over the Yellow Sea in March 2005： Analysis and Numerical Modeling 总被引：36，自引：0，他引：36
In this paper, a heavy sea fog episode that occurred over the Yellow Sea on 9 March 2005 is investigated. The sea fog patch, with a spatial scale of several hundred kilometers at its mature stage, reduced visibility along the Shandong Peninsula coast to 100 m or much less at some sites. Satellite images, surface observations and soundings at islands and coasts, and analyses from the Japan Meteorology Agency （JMA） axe used to describe and analyze this event. The analysis indicates that this sea fog can be categorized as advection cooling fog. The main features of this sea fog including fog area and its movement axe reasonably reproduced by the Fifth-generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model （MM5）. Model results suggest that the formation and evolution of this event can be outlined as： （1） southerly warm/moist advection of low-level air resulted in a strong sea-surface-based inversion with a thickness of about 600 m; （2） when the inversion moved from the warmer East Sea to the colder Yellow Sea, a thermal internal boundary layer （TIBL） gradually formed at the base of the inversion while the sea fog grew in response to cooling and moistening by turbulence mixing; （3） the sea fog developed as the TIBL moved northward and （4） strong northerly cold and dry wind destroyed the TIBL and dissipated the sea fog. The principal findings of this study axe that sea fog forms in response to relatively persistent southerly waxm/moist wind and a cold sea surface, and that turbulence mixing by wind shear is the primary mechanism for the cooling and moistening the marine layer. In addition, the study of sensitivity experiments indicates that deterministic numerical modeling offers a promising approach to the prediction of sea fog over the Yellow Sea but it may be more efficient to consider ensemble numerical modeling because of the extreme sensitivity to model input. 相似文献
9.
With Doppler radar data from Shantou and Xiamen and the National Centers for Environmental
Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, the
characteristics of a short-term heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied.
Doppler radar data indicates that during the period from 1800 to 1900 May 17, the azimuthal phases of the
positive and negative radial wind maximums are asymmetric around the core radius of the typhoon, i.e.,
the radial wind on the left side of the track is anomalously larger than that on the right side. Studies show
that this is induced by the intrusion of cold air (northeasterly wind), which is primarily located at the
mid-lower layers, lower than 4 km; this is due to the intruding cold air that forces the atmosphere to uplift,
enhancing the release of instability energy, which triggers the heavy precipitation. During the late stage of
the cold air activity, the typhoon is rapidly weakened. Consistent with the radar-observed intrusion of cold
air, the NCEP/NCAR reanalysis of wind data also shows that there are obvious large scalar wind values at
the mid-lower layers (approximately 1–3 km) to the left of the typhoon center (1800 May 17), and in all
regions—except those affected by the intruding cold air—the wind speeds on the right side of the track
remain larger than those on the left side. Furthermore, the Rankine model results confirm that
northeasterly cold air is introduced to the typhoon at the mid-lower layers to the left of the track.
Calculations also point out that there exists a frontal zone with high θse that tilts from southeast to
northwest with height and the super heavy rainstorm occurring in the south of Fujian province lies just near
the frontal zone. 相似文献
10.
Variations in Guangzhou’s aerosol optical characteristics and their possible causes are studied against the large-scale background of South China Sea summer monsoons(SCSSM) using aerosol data derived from Panyu Atmospheric Composition Watch Station in Guangzhou and the National Centers for Environmental Prediction/National Center for Atmospheric Research(USA). The data is reanalyzed to develop a composite analysis and perform physical diagnoses. Analysis of the results shows that aerosol extinction in Guangzhou first increases then decreases during the active period of a SCSSM, with variations in the stratification of the planetary boundary layer(PBL) and environmental winds playing important roles in affecting Guangzhou’s aerosol optical characteristics. Regional diabatic heating and anomalous cyclonic circulations excited by monsoon convection induce environmental wind anomalies that significantly modify the stratification of the PBL. 相似文献
11.
Numerical Experiment Research of a Marine Fog Event in the Pearl River Estuary Region 总被引：4，自引：0，他引：4
FAN Qi WANG Anyu FAN Shaoji LI Jiangnan WU Dui LEONG Ka Cheng 《Acta Meteorologica Sinica》2005,19(2):231-240
A marine fog event that occurred near the Pearl River Estuary region on 26 March 2002 was investigated with the fifth-generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5). The results of numerical experiment are very consistent with the surface observations, especially in the processes of marine fog formation and evolution. Besides, a series of sensitivity numerical experiments were performed by varying the distribution of landuse type and the turbulence exchange process. It is shown that the marine fog forms along the coastal line. Tests have indicated that when the distribution of landuse type is modified, the regions where the marine fog can intrude into are obviously different. The turbulence process in the model is important for fog formation and evolution. If the influence of turbulence process is ignored in numerical simulation experiment, the simulated maximum of the cloud liquid water content and the height of fog top will be decreased greatly. 相似文献
12.
Kim-Chiu Chow Lin Su Jimmy C. H. Fung Hui Ma Alexis K. H. Lau 《Meteorology and Atmospheric Physics》2014,126(3-4):119-138
The mesoscale model WRF-Chem was used to simulate a severe dust storm event that occurred in March 2010. The storm affected a vast area of East Asia, including the south China region and Hong Kong. This southern region is rarely affected by dust weather. The performance of the WRF-Chem was evaluated by observational data such as the National Center for Atmospheric Research reanalysis data for atmospheric circulation, PM10 concentration from various ground stations, and satellite images of Moderate Resolution Imaging Spectroradiometer and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. The dependence of the model’s performance on certain important parameterizations was examined in this study. For this particular dust storm event, the model results suggest that the simulation is not very sensitive to certain key physical parameterizations such as threshold wind speed of dust emission and the choice of land surface model. In general, the WRF-Chem is capable of capturing the key physical processes for this severe dust event. The analysis of the dust transport fluxes suggests that the dust transport to the south China region is mainly from the north, although there is a mountainous region in the northern part of the south China region. 相似文献
13.
利用欧洲中期天气预报中心(ECMWF)提供的1979-2016年ERA-Interim再分析资料分析了青藏高原(下称高原)夏季云水含量及其水汽输送情况。结果表明:高原夏季云水含量占全年48%,东南向西北减少。影响高原云水含量的水汽通道有印度洋通道、南海通道、孟加拉湾北部及伊朗西部通道(依次简称通道1、2、3、4)。高原云水含量和各水汽通道强度均有明显年际变化。云水含量年际变化与通道2,4基本一致。云水含量与各水汽通道强度均呈增加趋势。通道1偏强时,来自印度洋北部和南海的异常水汽在孟加拉湾交汇向高原输送,主要使高原西北部云水含量增多。通道2偏强时,南海、中南半岛的异常偏南通量及孟加拉湾北部的异常西南通量向高原东南部输送更多水汽。通道3偏强时,西风带水汽和来自印度洋水汽更多输送到高原,主要使高原东北部云水含量偏多。通道4偏强时,来自南海-孟加拉湾南部的水汽向高原异常输送,使高原中部、东南部云水含量偏多。此外,西太平洋副热带高压(下称副高)偏西南偏强时,水汽通道2、4强度偏强,有利于水汽向高原输送。 相似文献
14.
This study revises Weare’s latent heat parameterization scheme and conducts an associated
theoretic analysis. The revised Weare’s scheme is found to present potentially better results than Zebiak’s
scheme. The Zebiak-Cane coupled ocean-atmosphere model, initialized by the National Centers for
Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis of
wind stress anomaly at 925 hPa, is referred to as the ZCW coupled model. The atmosphere models of the
ZCW coupled model that use Zebiak’s scheme and the revised Weare’s scheme are referred to as the
ZCW0 and ZCWN atmosphere models, respectively. The coupled ocean-atmosphere models that use
Zebiak’s scheme and the revised Weare’s scheme are referred to as the ZCW0and ZCWN coupled models,
respectively. The simulations between the ZCW0 and ZCWN atmosphere models and between the ZCW0
and ZCWN coupled models are analyzed. The results include: (1) The evolution of heat, meridional wind
and divergence anomalies simulated by similar ZCW0 and ZCWN atmosphere models, although the
magnitudes of the former are larger than those of the latter; (2) The prediction skill of the Ni?o3 index
from 1982 to 1999 by the ZCWN coupled model shows improvement compared with those by the ZCW0
coupled model; (3) The analysis of El Ni?o events in 1982/1983, 1986/1987, and 1997/1998 and La Ni?a
events in 1984/1985, 1988/1989, and 1998/2000 suggests that the ZCWN coupled model is better than the
ZCW0 coupled model in predicting warm event evolution and cold event generation. The results also show
the disadvantage of the ZCWN coupled model for predicting El Ni?o 相似文献
15.
The Kolmogorov constants for CO2, wind velocity, air temperature, and humidity fluctuations were evaluated from measurements made over soybean and grain sorghum fields and found to be 0.78 ± 0.11, 0.49 ± 0.08, 0.70 ± 0.15, and 0.99 ± 0.16, respectively. These results are consistent with recent observations reported in the literature.Published as Paper No. 7255, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Regional Research Project 11-33 and Nebraska Agricultural Experiment Station Project 27-003.Associate Professor and Post Doctoral Research Associate, respectively, Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE, U.S.A., 68583-0728. 相似文献
16.
Nirmala D. Desouza Baby Simon Muhammad S. Qureshi 《Meteorology and Atmospheric Physics》2011,114(3-4):107-121
The evolutionary characteristics of a dust storm over Oman on 2 February 2008 were studied by analyzing the weather associated with it. The National Center for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis wind flow pattern at 1,000?hPa showed a clockwise and outward wind flow pattern over the study region, a manifestation of a high-pressure cold air mass. In addition, ground truth observations for surface temperature and surface winds showed cold northerly winds until the early morning of 2 February 2008. A strong wind shear resulted from differences in wind speed between warm air and trapped cold air. This vertical wind shear enhanced instability. Furthermore, the weakening of the inversion in the lower troposphere and the formation of a mixed layer due to transfer of horizontal momentum from upper air towards the surface led to strong surface winds. These strong winds lifted a large amount of dust particles off the ground, resulting in the dust event of 2 February 2008. 相似文献
17.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
18.
Stephen H. Schneider 《Climatic change》1993,23(1):vi-vii
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
19.
Stephen H. Schneider 《Climatic change》1991,19(4):v-vi
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
Analysis of the mean wind, equivalent potential temperature and virtual potential temperature profiles observed by the National Center for Atmospheric Research (NCAR) Electra aircraft and obtained from dropwindsondes and ship-launched radiosondes were made in conjunction with synoptic observations to study the structure of the monsoon boundary layer over the Arabian Sea during MONEX 79. Comparison of mean profiles indicates the monsoon boundary layer to be much different from the trade wind boundary layer. Results confirm the existence of a boundary-layer jet known as East African or Somali Jet. Regions of multiple cloud layers at roughly the height of the capping inversion layer were associated with the jet. Regions in which a more well-mixed layer was observed showed a jet structure depressed in height. A free-jet surface-layer model appears to describe the mean wind structure of this jet observed during the present study and by others. An approximate balance of forces was found in the monsoon boundary layer between friction, advective acceleration, Coriolis and pressure gradient forces. Friction and advective acceleration terms were significant in the lower levels of the boundary layer. Forces in a typical trade wind boundary layer were found to be approximately one order of magnitude smaller than those observed in the monsoon boundary layer. 相似文献