检索结果-内蒙古大学图书馆

Conference on Laser Communication and Propagation through the Atmosphere and Oceans

作者： Perlot, Nicolas Moll, Florian Inst Commun & Nav DLR D-82234 Wessling Germany

ISBN: (纸本)9780819492340

We consider n independent disruptive channels with random availability periods and make use of channel diversity to maintain a link as often as possible. This situation arises when an optical link is to be maintained between a spacecraft and n ground stations affected by cloud coverage. Statistical independence between the stations and equal (un) availability duration distributions are assumed. Based on a given single-station (un) availability duration distribution, we derive analytically the network (un) availability duration distributions. Also derived is the distribution of the station operation duration within a network. Derived expressions allow evaluating the increase of the continuous operation duration of a station and the decrease of the network unavailability durations.

关键词： MIMO channel diversity selection combining random link duration free-space optical communications cloud coverage

来源：评论

学校读者我要写书评

暂无评论

Relation between the atmospheric characteristics in the antarctic regions and the space weather factors

引用

GEOMAGNETISM AND AERONOMY 2008年第4期48卷 536-541页

作者： Vovk, V. Ya. Egorova, L. V. Troshichev, O. A. Russian Acad Sci Arctic & Antarctic Res Inst St Petersburg 199397 Russia

Considerable variations in the cloud cover level and air temperature, related to the variations in GCRs and IMF, have been revealed based on an analysis of the meteorological and aerological data obtained at Vostok station from 1974 to 1994. It has been found out that the cloud cover at Vostok decreased, on average, by 35% a day after powerful Forbush decreases in GCRs following a considerable increase in the southward IMF component. In the years of solar activity minimum, when the variations in SCRs and GCRs are insignificant, the cloudiness and surface temperature increase on a day of B-z minimum and decrease on a day of maximum as compared to the average level. On days of B-z minimum, the air temperature rises at altitudes of h = 3.5-7 km, remains almost unchanged at an altitude of h = 8 km, and slightly decreases at higher altitudes. An increase in cloudiness at altitudes below 8 km causes warming, probably due to the greenhouse effect, because the temperature of the Earth's surface decreases.

关键词： GALACTIC COSMIC-RAYS SOLAR-ACTIVITY POSSIBLE CONNECTIONS FORBUSH-DECREASES cloud coverage EL-NINO CLIMATE WIND TEMPERATURE VARIABILITY

来源：评论

学校读者我要写书评

暂无评论

Reliability of a small power system using solar power and hydro

引用

ELECTRIC POWER SYSTEMS RESEARCH 2005年第1期74卷 119-127页

作者： Ehnberg, SGJ Bollen, MHJ Chalmers Univ Technol Dept Elect Power Engn S-41296 Gothenburg Sweden STRI AB Ludvika Sweden

This paper studies the availability of the electricity supply when the sources consist of a combination of solar energy and a small hydro installation. Instead of flow-of-river, a small reservoir is used. By not using the hydro energy during sunny periods, the natural flow-of-river fills up the reservoir for later use. A model for global solar radiation is proposed with an astronomical part (deterministic) and a meteorological part (stochastic). The meteorological part is based on a Markov model of the cloud coverage. The solar model does not require solar radiation measurements, just cloud observations. A case study has been performed for Timbuktu (16.75degreesN, 0.07degreesW) in which generation availability is simulated for four different cases: solar power only;solar power with storage;solar and hydro power and solar and hydro, power with storage. To be able to use exclusively renewable energy sources, a combination of sources is needed to secure the reliability of the supply. Using solar cells in combination with a small reservoir is favorable. Even with a weak flow the affect of the flow on the day time reliability is minor, but great benefits can be found for reliability during low load hours (night time). (C) 2004 Elsevier B.V. All rights reserved.

关键词： solar power power system reliability renewable energy cloud coverage hydro power

来源：评论

学校读者我要写书评

暂无评论

Simulation of global solar radiation based on cloud observations

引用

SOLAR ENERGY 2005年第2期78卷 157-162页

作者： Ehnberg, JSG Bollen, MHJ Chalmers Univ Technol Dept Elect Power Engn SE-41296 Gothenburg Sweden

A stochastic model for simulating global solar radiation on a horizontal surface has been developed for use in power systems reliability calculations. The importance of an appropriate model for global solar radiation has increased with the increased use of photovoltaic power generation. The global solar radiation shows not only regular yearly and daily variations but also a random behaviour. The yearly and daily variations can be described in a deterministic way while the random behaviour has a high correlation with the state of the atmosphere. The astronomic effects can easily be described mathematical with only some minor simplifications but the atmospheric effects are more complicated to describe. The transmittivity of solar radiation in the atmosphere depends on various factors, e.g. humidity, air pressure and cloud type. By using cloud observations as input for the simulations, the local meteorological conditions can be accounted for. The model is usable for any geographical location if cloud observations are available at the location or at locations with similar climatological conditions. This is especially useful for development countries where long-term solar radiation measurement can be hard to obtain. cloud observations can be performed without any expensive equipment and have been a standard parameter for many years throughout the world. Standard observations are done according to the Oktas-scale. It is the interval between observations that sets the resolution of the simulation: the observations are normally only every hour or every third hour. The model can easily be combined with cloud coverage simulations, has been proposed, for a more general model. For some calculations higher resolution may be needed. This can be obtained by including a stochastic model for the short-term variations and simple model has been proposed. Errors and limitations of the model are estimated and discussed. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： solar power Markov model cloud coverage

来源：评论

学校读者我要写书评

暂无评论

Simulation of global solar radiation based on cloud observations

Simulation of global solar radiation based on cloud observat...

引用

World Congress of the International-Solar-Energy-Society

作者： Ehnberg, JSG Bollen, MHJ Chalmers Univ Technol Dept Elect Power Engn SE-41296 Gothenburg Sweden

关键词： solar power Markov model cloud coverage

来源：评论

学校读者我要写书评

暂无评论

Affordable lidar for atmospheric aerosol and cloud studies

Affordable lidar for atmospheric aerosol and cloud studies

引用

2nd Conference on Lidar Remote Sensing for Industry and Environment Monitoring

作者： Münkel, C Leiterer, U Dier, HD Vaisala Impulsphys GmbH D-22869 Schenefeld Germany

ISBN: (纸本)0819441988

The Vaisala ceilometer LD-40 "Tropopauser" is a compact eye-safe lidar measuring continuously under all possible climatic conditions and scanning the atmosphere up to a height of 13000 m. It uses laser diodes with 855 nm wavelength that are pulsed at an average frequency of 4000 Hz. The distance of the system's range bins is 7.5 in. Its main purpose is reporting cloud base heights and vertical visibility for aviation safety purposes. This paper focuses on the additional parameters this affordable lidar is able to report due to its advanced technical properties. These parameters include kind of precipitation detected, presence and distance of cirrus, extinction coefficients within clouds, vertical profiles of planetary boundary layer backscatter power, and a comparison of cloud coverage detected by a ceilometer with values obtained with a total cloud coverage scanner. Comparison instruments include regular radiosonde soundings performed at the Meteorological Observatory Lindenberg of the German Weather Service.

关键词： lidar ceilometer precipitation cirrus clouds extinction profile planetary boundary layer cloud coverage

来源：评论

学校读者我要写书评

暂无评论

Does the earth have an adaptive infrared iris?

引用

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 2001年第3期82卷 417-432页

作者： Lindzen, RS Chou, MD Hou, AY MIT Dept Earth Atmospher & Planetary Sci Cambridge MA 02139 USA NASA Goddard Space Flight Ctr Atmospheres Lab Greenbelt MD 20771 USA

Observations and analyses of water vapor and clouds in the Tropics over the past decade show that the boundary between regions of high and low free-tropospheric relative humidity is sharp, and that upper-level cirrus and high free-tropospheric relative humidity tend to coincide. Most current studies of atmospheric climate feedbacks have focused on such quantities as clear sky humidity, average humidity, or differences between regions of high and low humidity, but the data suggest that another possible feedback might consist of changes in the relative areas of high and low humidity and cloudiness. Motivated by the observed relation between cloudiness (above the trade wind boundary layer) and high humidity, cloud data for the eastern part of the western Pacific from the Japanese Geostationary Meteorological Satellite-5 (which provides high spatial and temporal resolution) have been analyzed, and it has been found that the area of cirrus cloud coverage normalized by a measure of the area of cumulus coverage decreases about 22% per degree Celsius increase in the surface temperature of the cloudy region. A number of possible interpretations of this result are examined and a plausible one is found to be that cirrus detrainment from cumulus convection diminishes with increasing temperature. The implications of such an effect for climate are examined using a simple two-dimensional radiative-convective model. The calculations show that such a change in the Tropics could lead to a negative feedback in the global climate, with a feedback factor of about -1.1, which if correct, would more than cancel all the positive feedbacks in the more sensitive current climate models. Even if regions of high humidity were not coupled to cloudiness, the feedback factor due to the clouds alone would still amount to about -0.45, which would cancel model water vapor feedback in almost all models. This new mechanism would, in effect, constitute an adaptive infrared iris that opens and closes in

关键词： .cloudy feedbacks surface temperature Cirrus cloudiness cloud data detrainment Cumulus Convection high humidity cloud coverage per degree Celsius

来源：评论

学校读者我要写书评

暂无评论

Radiative transfer code: Application to the calculation of PAR

引用

PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND PLANETARY SCIENCES 2000年第4期109卷 407-413页

作者： Emmanuel, D Phillipe, D Malik, C Lab Interdisciplinaire Sci Environm F-62930 Wimereux France

The production of carbon in the ocean, the so-called primary production, depends on various physicobiological parameters: the biomass and nutrient amounts in oceans, the salinity and temperature of the water and the light available in the water column. We focus on the visible spectrum of the solar radiation defined as the Photosynthetically Active Radiation (PAR). We developed a model (Chami et al, 1997) to simulate the behavior of the solar beam in the atmosphere and the ocean. We first describe the theoretical basis of the code and the method we used to solve the radiative transfer equation (RTE): the successive orders of scattering (SO), The second part deals with a sensitivity study of the PAR just above and below the sea surface for various atmospheric conditions. In a cloudy sky, we computed a ratio between vector fluxes just above the sea surface and spherical fluxes just beneath the sea surface. When the optical thickness of the cloud increases this ratio remains constant and around 1.29. This parameter is convenient to convert vector flux at the sea surface as retrieved from satellite to PAR. Subsequently, we show how solar radiation as vector flux rather than PAR leads to an underestimate of the primary production up to 40% for extreme cases.

关键词： PAR cloud coverage primary productivity

来源：评论

学校读者我要写书评

暂无评论

cloud coverage ASPECTS OF THE ALBEDO EFFECT

引用

CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY 1993年第3期57卷 493-508页

作者： Vokrouhlicky, David Sehnal, Ladislav Charles Univ Astron Inst Prague 15000 5 Czech Republic Acad Sci Czech Republ Inst Astron CS-25165 Ondrejov Czech Republic

We discuss some details of the cloud coverage aspects of the albedo effect-the pressure of the radiation reflected by the Earth-on the motion of an artificial satellite. We focus on modeling of the Earth's surface reflection and propagation of the radiation through the atmosphere. We adopt analytical models of these phenomena from radiative transfer theory, in contrast to earlier approaches, based on the fitting of satellite photometry data. We perform several computations based on the accepted models for the ERS-1 and MACEK satellites to test the hierarchy of importance of the effects investigated. In the case of the MACEK mission (which carried a precision accelerometer on board) this information might be essential when interpreting the data.

关键词： Satellites radiation mechanisms Earth atmosphere albedo effect cloud coverage

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：