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271.
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273.
根据海洋重力测量的实际情况,结合AIRSEA SystemⅡ的结构特点,对仪器在测量中受到测量船摇动的影响进行分析,认为影响仪器观测精度的干扰因素有三类:垂直加速度、横摇与纵摇、交叉耦合效应。并对这三种干扰因素进行分析,给出了减弱干扰影响的措施,这些措施能使海洋重力测量外业获取更高的观测精度。 相似文献
274.
275.
The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) has been used to investigate the extra-area effects of silver iodide (AgI) seeding on stratiform clouds performed at the supercooled layer.A bulk two-moment microphysical scheme and the new software package for silver iodide are incorporated in MM5.Extra conservation equations are applied to trace the seeding agent,which is transported along the flow field and interacts with the supercooled cloud fields.In this study,the model was run using three nested grids,with 3.3 km × 3.3 km horizontal resolution in the finest grid.The model results showed that seeding with AgI at the 5 to 15℃ levels had microphysical effects on the simulated clouds and that the simulation produced a longer-lasting seeding effect because of the transport of the seeding agent by upper-level winds.Most of the AgI particles acted as deposition nuclei,and the deposition nucleation process contributed mostly to additional cloud ice formation in this study.The results showed that more precipitation results from seeded than unseeded case,and the precipitation was redistributed downwind of the target.Augmented precipitation (varying from 5% to 25% downwind) was confined in space to within 250 km of the seeding target and in time to the 3-h period after initial seeding. 相似文献
276.
R. Dimitrova Jean-François Sini K. Richards M. Schatzmann M. Weeks E. Perez García C. Borrego 《Boundary-Layer Meteorology》2009,131(2):223-243
Micrometeorological conditions in the vicinity of urban buildings strongly influence the requirements that are imposed on
building heating and cooling. The goal of the present study, carried out within the Advance Tools for Rational Energy Use
towards Sustainability (ATREUS) European research network, is the evaluation of the wind field around buildings with walls
heated by solar radiation. Two computational fluid dynamics (CFD) codes were validated against extensive wind-tunnel observations
to assess the influence of thermal effects on model performance. The code selected from this validation was used to simulate
the wind and temperature fields for a summer day in a specific region of the city of Lisbon. For this study, the meteorological
data produced by a non-hydrostatic mesoscale atmospheric model (MM5) were used as boundary conditions for a CFD code, which
was further applied to analyze the effects of local roughness elements and thermodynamic conditions on the air flow around
buildings. The CFD modelling can also provide the inflow parameters for a Heating, Ventilation and Air Conditioning (HVAC)
system, used to evaluate the building energy budgets and to predict performance of the air-conditioning system. The main finding
of the present three-dimensional analyses is that thermal forcing associated with the heating of buildings can significantly
modify local properties of the air flow. 相似文献
277.
Heping LIU 《大气科学进展》2009,26(1):9-16
Corrections of density effects resulting from air-parcel expansion/compression are
important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems
are used. To account for these effects, mean vertical velocity and perturbation of the density
of dry air are two critical parameters in treating those physical processes responsible for
density variations. Based on various underlying assumptions, different studies have obtained
different formulas for the mean vertical velocity and perturbation of the density of dry air,
leading to a number of approaches to correct density effects. In this study, we re-examine
physical processes related to different assumptions that are made to formulate the density
effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist
air flux in the surface layer, used for treating density variations, and their implications
for correcting density effects. It is found that physical processes in relation to the assumption
of a zero dry air flux account for the influence of dry air expansion/compression on density
variations. Meanwhile, physical processes in relation to the assumption of a zero moist air
flux account for the influence of moist air expansion/compression on density variations. In
this study, we also re-examine mixing ratio issues. Our results indicate that the assumption
of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the
assumption of a zero moist air flux favors the use of the mixing ratio relative to the total
moist air. Additionally, we compare different formula for the mean vertical velocity, generated
by air-parcel expansion/compression, and for density effect corrections using eddy covariance
data measured over three boreal ecosystems. 相似文献
278.
G. Lombardi V. Zitelli S. Ortolani 《Monthly notices of the Royal Astronomical Society》2009,399(2):783-793
The new extremely large telescope projects need accurate evaluation of the candidate sites. In this paper, we present the astroclimatological comparison between the Paranal Observatory, located on the coast of the Atacama Desert (Chile), and the Observatorio del Roque de Los Muchachos (ORM), located in La Palma (Canary Islands). We apply a statistical analysis using long-term data bases from Paranal and Carlsberg Automatic Meridian Circle (CAMC) weather stations. The monthly, seasonal and annual averages of the main synoptical parameters in the two sites are computed. We compare the long-term trends in order to understand the main differences between the two sites. Significant differences between the two analysed sites have been found. Temperature has increasing trends in both observatories with somewhat higher evidence at the ORM. Seasonal variations of pressure at Paranal have been highly decreasing since 1989, and we do not see the same phenomenon at the ORM. The two sites are dominated by high pressure. In cold seasons, relative humidity (RH) is lower than 60 per cent at CAMC and 15 per cent at Paranal. In warm seasons, RH is lower than 40 per cent at CAMC and 20 per cent at Paranal. The analysis of the dew point has shown better conditions at Paranal with respect to CAMC in winter, autumn and spring before 2001, while the two sites are becoming similar afterwards. Winds at the ORM are subject to pronounced local variations. 相似文献
279.
R. W. Wilson T. Butterley M. Sarazin 《Monthly notices of the Royal Astronomical Society》2009,399(4):2129-2138
An instrument for monitoring of the vertical profile of atmospheric optical turbulence strength, employing the Slope Detection and Ranging (SLODAR) double star technique applied to a small telescope, has been developed by Durham University and the European South Observatory. The system has been deployed at the Cerro Paranal observatory in Chile for statistical characterization of the site. The instrument is configured to sample the turbulence at altitudes below 1.5 km with a vertical resolution of approximately 170 m. The system also functions as a general-purpose seeing monitor, measuring the integrated optical turbulence strength for the whole atmosphere, and hence the seeing width. We give technical details of the prototype and present data to characterize its performance. Comparisons with contemporaneous measurements from a differential image motion monitor (DIMM) and a multi-aperture scintillation sensor (MASS) are discussed. Statistical results for the optical turbulence profile at the Paranal site are presented. We find that, in the median case, 49 per cent of the total optical turbulence strength is associated with the surface layer (below 100 m), 35 per cent with the 'free atmosphere' (above 1500 m) and 16 per cent with the intermediate altitudes (100–1500 m). 相似文献
280.
Peter Foukal Luca Bertello William C. Livingston Alexei A. Pevtsov Jagdev Singh Andrey G. Tlatov Roger K. Ulrich 《Solar physics》2009,255(2):229-238
Spectroheliograms and disk-integrated flux monitoring in the strong resonance line of Ca ii (K line) provide the longest record of chromospheric magnetic plages. We compare recent reductions of the Ca ii K spectroheliograms obtained since 1907 at the Kodaikanal, Mt. Wilson, and US National Solar Observatories. Certain differences
between the individual plage indices appear to be caused mainly by differences in the spectral passbands used. Our main finding
is that the indices show remarkably consistent behavior on the multidecadal time scales of greatest interest to global warming
studies. The reconstruction of solar ultraviolet flux variation from these indices differs significantly from the 20th-century
global temperature record. This difference is consistent with other findings that, although solar UV irradiance variation
may affect climate through influence on precipitation and storm tracks, its significance in global temperature remains elusive. 相似文献