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排序方式: 共有4668条查询结果,搜索用时 265 毫秒
941.
G. Chen D. Davis J. Crawford B. Heikes D. O'Sullivan M. Lee F. Eisele L. Mauldin D. Tanner J. Collins J. Barrick B. Anderson D. Blake J. Bradshaw S. Sandholm M. Carroll G. Albercook A. Clarke 《Journal of Atmospheric Chemistry》2001,38(3):317-344
Reported are the results from a comparison of OH,H2O2CH3OOH, and O3 observationswithmodel predictions based on current HOx–CH4reaction mechanisms. The field observations are thoserecorded during the NASA GTE field program, PEM-Tropics A. The major focus ofthis paper is on thosedata generated on the NASA P-3B aircraft during a mission flown in the marineboundary layer (MBL) nearChristmas Island, a site located in the central equatorial Pacific (i.e.,2° N, 157° W). Taking advantage of thestability of the southeastern trade-winds, an air parcel was sampled in aLagrangian mode over a significantfraction of a solar day. Analyses of these data revealed excellent agreementbetween model simulated andobserved OH. In addition, the model simulations reproduced the major featuresin the observed diurnalprofiles of H2O2 and CH3OOH. In the case ofO3, the model captured the key observational feature whichinvolved an early morning maximum. An examination of the MBL HOxbudget indicated that the O(1D) + H2Oreaction is the major source of HOx while the major sinks involveboth physical and chemical processes involving the peroxide species,H2O2 and CH3OOH. Overall, the generally goodagreement between modeland observations suggests that our current understanding ofHOx–CH4 chemistry in the tropical MBL isquite good; however, there remains a need to critically examine this chemistrywhen both CH2O and HO2are added to the species measured. 相似文献
942.
Cao Shuyang Akira Nishi Kimitaka Hirano Shigehira Ozono Hiromori Miyagi Hiromori Kikugawa Yuji Matsuda Yasuo Wakasugi 《Boundary-Layer Meteorology》2001,101(1):61-76
An actively controlled wind tunnel equipped with multiple fansand airfoils has been developed, mainly for the purpose of reproducing the atmospheric boundary layer (ABL) for wind engineering applications. Various fluctuating flows can be achieved in this wind tunnel by altering the input data of the fans and airfoils through computer control. In this study, the ABL is physically simulated in this wind tunnel, and particular attention ispaid to the simulation of the profile of Reynolds stress. The method of generating the fluctuating flow and the experimental results of reproducing the ABL are presented. As the results show, the spatial distribution of Reynolds stress is satisfactorily simulated, and the profiles of other statisticalturbulent parameters, such as mean velocity, turbulent intensity, integral scale and power spectrum are successfully reproduced simultaneously. 相似文献
943.
C. Warneke R. Holzinger A. Hansel A. Jordan W. Lindinger U. Pöschl J. Williams P. Hoor H. Fischer P. J. Crutzen H. A. Scheeren J. Lelieveld 《Journal of Atmospheric Chemistry》2001,38(2):167-185
Airborne measurements of volatile organic compounds (VOC) were performed overthe tropical rainforest in Surinam (0–12 km altitude,2°–7° N, 54°–58° W) using the proton transferreaction mass spectrometry (PTR-MS) technique, which allows online monitoringof compounds like isoprene, its oxidation products methyl vinyl ketone,methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, andseveral other organic compounds. Isoprene volume mixing ratios (VMR) variedfrom below the detection limit at the highest altitudes to about 7 nmol/molin the planetary boundary layer shortly before sunset. Correlations betweenisoprene and its product compounds were made for different times of day andaltitudes, with the isoprene-hydroperoxides showing the highest correlation.Model calculated mixing ratios of the isoprene oxidation products using adetailed hydrocarbon oxidation mechanism, as well as the intercomparisonmeasurement with air samples collected during the flights in canisters andlater analysed with a GC-FID, showed good agreement with the PTR-MSmeasurements, in particular at the higher mixing ratios.Low OH concentrations in the range of 1–3 × 105molecules cm-3 averaged over 24 hours were calculated due to lossof OH and HO2 in the isoprene oxidation chain, thereby stronglyenhancing the lifetime of gases in the forest boundary layer. 相似文献
944.
Ulrich C. E. ZANKE Prof Institute of Hydraulic Engineering University of Technology Darmstadt Germany 《国际泥沙研究》2001,16(1)
l PROBLEMS AND AlMSSediments may be transported close to the bed, rolling and sliding, as we1l as susPended in the flow. Forvarious reasons the theoretical treatment of the bed-load problem has been exceptionally difficult. Noanalytical solution had been fOund uP to now, beginning with Du Buat (l786), Huebbe (l86l) and DuBoys (I 879). Since the aPProach of Du Boys numerous new attemPts have been catried out, mostly of anempirical nature. Consequently they are not generally valid an… 相似文献
945.
MODELING OF THE HIGH CONCENTRATION LAYER OF COHESIVE SEDIMENT UNDER THE ACTION OF WAVES AND CURRENTS
Qinghe ZHANG Yongsheng WU Jijian LIANand Pingxing DING School of Civil Engineering Tianjin University Tianjin China Dept. Hydraulic Engineering Tsinghua University Beijing China State Key Lab. of Estuarine Co 《国际泥沙研究》2001,16(2)
MODELING OF THE HIGH CONCENTRATION LAYEROF COIIESIVE SEDMNT UNDER Tus ACTIONOF WAVES AND CURRENTSQinghe ZHANG', Yongsheng WU', Jiian LIAN1 and Pingxing DING3Abstract:High concenhation layer of cohesive sediment frequenhy occurs in muddy estUaries and coastalzones, and causes raPid siltation of the waterways. A one dimensional vertical coupled modeldescribing the interactions betWeen waves, currentS and suspended cohesive sediment is develoPed inthe pre… 相似文献
946.
947.
本文设计了一冠层(CL)和大气边界层(ABL)之间物质和动量交换的耦合模式,并对CL内风速、物质随高度分布和日变化作了数值模拟.结果表明,由大尺度扩散引起冠层低层的第二个风速极大和多极值的浓度分布,CL内湍流通量和物质浓度随高度减小而迅速降低,以及CL动量减小对浓度分布的重要影响,模式都能很好地描述,模拟结果与观测事实有好的一致性.利用浓度和温度廓线相似假设,导出了质量汇的经验关系. 相似文献
948.
Based on the HEIFE 1988 and 1990 pilot observations,an analysis on the turbulence structure of Gobi surfacelayer,mainly on the similarity formulations of wind and temperature variances,the spectra and cospectracharacteristics,is presented.The phenomenon of downward water vapor flux over Gobi desert in daytime is confirmedin both observations,this and the well-known‘oasis effect’are two sides of a local mesoscale circulation. 相似文献
949.
G. W. Harris D. Klemp T. Zenker J. P. Burrows B. Mathieu 《Journal of Atmospheric Chemistry》1992,15(3-4):315-326
Measurements of NO2, HCHO, and H2O2 were made by the highly specific method of mid infra-red absorption spectroscopy using tunable diode lasers (TDLAS) during the 1988 Polarstern expedition. The TDLAS data are compared to those obtained during the cruise using less direct methods. Southern Hemisphere NO2 levels suggest nett photochemical destruction of O3 in the boundary layer. Northern Hemisphere HCHO averaged 0.47±0.2 ppbv; the HCHO measurements are used in a simple calculation to estimate OH noontime maxima of 3–6×106 cm-3. 相似文献
950.
伍荣生 《Acta Meteorologica Sinica》1991,(1)
It is convenient to use σ-coordinates to discuss the dynamic effect of orography and the flow inEkman boundary layer.In this paper,the theory of mixing length is generalized to the σ-coordinate system.Then the governing equations,describing the motion in the boundary layer over the mountain regions arederived.The features of flow in the boundary layer,especially the effects of Ekman pumping,are discussed indetails.It is pointed out that there are three factors affecting the vertical motion at the top of the boun-dary layer:(1)vorticity distribution in the boundary layer,which is directly related to the divergence andconvergence of air flow caused by friction,(2)the upslope or downslope motion of flow over the mountainslopes,and(3)the mutual effect of orography and friction induced by the ageostrophic component climbing up-ward or downward in the boundary layer over mountain regions. 相似文献