首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Summary The influence of agricultural management on the CO2 budget of a typical subalpine grassland was investigated at the Swiss CARBOMONT site at Rigi-Seebodenalp (1025m a.s.l.) in Central Switzerland. Eddy covariance flux measurements obtained during the first growing season from the mid of spring until the first snow fall (17 Mai to 25 September 2002) are reported. With respect to the 10-year average 1992–2001, we found that this growing season had started 10 days earlier than normal, but was close to average temperature with above-normal precipitation (100–255% depending on month). Using a footprint model we found that a simple approach using wind direction sectors was adequate to classify our CO2 fluxes as being controlled by either meadow or pasture. Two significantly different light response curves could be determined: one for periods with external interventions (grass cutting, cattle grazing) and the other for periods without external interventions. Other than this, meadow and pasture were similar, with a net carbon gain of –128±17g Cm–2 on the undisturbed meadow, and a net carbon loss of 79±17g Cm–2 on the managed meadow, and 270±24g Cm–2 on the pasture during 131 days of the growing season, respectively. The grass cut in June reduced the gross CO2 uptake of the meadow by 50±2% until regrowth of the vegetation. Cattle grazing reduced gross uptake over the whole vegetation period (37±2%), but left respiration at a similar level as observed in the meadow.  相似文献   

2.
Summary Regional climate model (RegCM2) and sulfur transport model (NJUADMS) were combined to simulate the distribution of anthropogenic sulfate aerosol burden over China, where a look up table method was applied to illustrate sulfate formation from SO2-oxidation. Direct radiative forcing of sulfate aerosol was further estimated using the scheme suggested by Charlson et al (1991). Investigations show that the annual average total sulfate column over mainland China is 2.01mg/m2 with high value in East and Central areas (more than 7mg/m2). The annual average direct radiative forcing of China is about –0.85W/m2. The forcing can reach –7W/m2 in Central and East China during the winter season. Total sulfate column shows significant seasonal variations with winter maximum-summer minimum in the Southern part of China and spring maximum-autumn minimum in the northern part of China. Strong seasonal cycles of direct radiative forcing are also found due to the influence of total sulfate column, cloud, relative humidity and the reflectivity of underlying surfaceReceived May 16, 2001; accepted August 5, 2002 Published online: May 8, 2003  相似文献   

3.
Summary This paper reports on a small-scale pilot experiment held early in the dry season near Darwin, Australia, in which fine-scale observations of several prescribed fires were made using infrared digital video. Infrared imaging is used routinely to locate fires as infrared radiation suffers little attenuation as it propagates through the smoke that normally obscures visible imagery. However, until now, little use has been made of digital video imagery in analyzing the convective-scale structure of prescribed (or wild) fires. The advantage of digital video imagery is that the individual frames can be objectively analyzed to determine the convective motion in the plane viewed by the camera. The infrared imagery shows mostly rising plumes, much like convective clouds. The flow is highly convective, and the vertical transport of heat is confined to relatively narrow thermals. The updrafts range from a few ms–1 to around 15ms–1. A numerical model is used to simulate one of the prescribed fires at very high-resolution. For the most part, the model predictions compare well to the observations. The model produces plumes that are around 7m high, and spaced around 5m apart, which is similar to that observed. The model correctly predicts the mean rate of spread of the fire to be 1.3ms–1. Perhaps the most serious limitations to using infrared observations of the type presented here are the difficulties in interpreting precisely the relationship between the observed infrared temperature field and the air temperature calculated by the model, and the exact connection between the infrared camera derived flow field and that calculated by the model.  相似文献   

4.
Summary A simple parameterization for the estimation of turbulent kinetic energy (TKE) and momentum flux profiles under near-neutral stratification based on sodar measurements of the vertical velocity variance has been tested using data from the LINEX-2000 experiment. Measurements included operation of a phased-array Doppler sodar DSDPA.90 and of a sonic anemometer USA-1 mounted at a meteorological tower at a height of 90m. Good agreement has been found between the TKE and momentum flux values derived from the sonic and sodar data (with correlation coefficients r>0.90 and a slope of the regression lines of about 1.01.1) suggesting the possible use of sodar measurements of w 2 to derive turbulence parameter profiles above the tower range.  相似文献   

5.
Summary The relative strength of the stabilizing effect of buoyancy and the destabilizing effect of velocity shear in a stratified shear flow, such as a stable atmospheric boundary layer, is measured by the gradient Richardson number, Rig. The boundary layer static stability, as described by the buoyancy frequency, N, can be calculated from the virtual potential temperature gradient derived from RASS temperature profiles. The mean wind profiles from a sodar can be used to calculate the mean vertical velocity shear. In combination these profilers are potentially a powerful tool for the remotely sensing the dynamic stability of the boundary layer. However, experience shows that the combinations of two experimentally derived quantities, like N and shear, may give highly variable results. On the other hand, a simple sensitivity analysis shows that reasonable estimates of Rig are achievable over a range of conditions in the stable nocturnal boundary layer. To test this conclusion, high spatial and temporal resolution temperature and velocity soundings were obtained above 50m in the stable nocturnal boundary layer using a 920MHz continuous wave Radio Acoustic Sounding System (RASS) and 1.875kHz and 5.00kHz Doppler sodars. Examples of the evolution of Rig are presented from 24 hours of observations of the boundary layer in Canberra, on the tablelands in south- eastern Australia. Most of the boundary layer had Rig between 0.1 and 1. Thus, it was marginally dynamically stable, even with the gradient Richardson number calculated from finite differences over a vertical interval of 68m. A comparison of the results from the two sodars showed that the velocity shear increased significantly when the vertical differencing interval was decreased from 68m to 20m.  相似文献   

6.
Summary ¶Global, diffuse, and horizontal direct (beam) irradiances have been evaluated for 13 stations in Germany where the time series vary between 11 and 48 years. Global irradiance has decreased significantly at two stations and increased at four stations. The mean trend in global is an increase of 1.94Wm–2 or 1.83% per decade. Diffuse irradiance has decreased at five stations, with a mean reduction of 2.44Wm–2 or 3.46% per decade, while horizontal direct irradiance has increased an average of 4.86Wm–2 or 10.40% per decade at five stations. Increases in global and direct are most common at stations in the southwest region of Germany, decreases in global were observed in the southeast, and there was an absence of spatial homogeneity in the diffuse trends. Spatial variability in irradiance over Germany is higher in the direct component compared to variability in global and diffuse.Trend analyses of concomitant time series of radiation, bright sunshine duration, and modeled estimates of Ångströms turbidity coefficient suggest that long-term decreases in aerosols are the most likely cause of increases in global irradiance observed at Mannheim, Norderney, and Trier; decreases in diffuse at Hohenpeissenberg, Kassel, Mannheim, and Trier; and increases in direct irradiance at Bocholt, Kassel, Mannheim, and Trier. An increase in sunshine duration at Freiburg likely contributed to an increase in global and direct irradiance observed at that station.  相似文献   

7.
Summary A variety of programmes and field experiments were carried out in order to develop and evaluate models of transport and diffusion of pollutants in complex terrain areas. As part of this programme, in this study, we have focused our interest on analyzing the basic features of different flow fields and thermal structures developed in a complex area and their relation to air pollution problems. The area is located in the province of Barcelona (in the northeast of Spain) close to a wide industrial zone, thus a pollutant flux could affect this region. In order to carry out the main purpose of this study we have analysed data from a Doppler Sodar (FAS 64) and a network of near surface meteorological and air quality stations. In addition, different dynamical simulations given by a numerical mesoscale model (MM5) are also analyzed. The results show that the main flow fields and thermal structures generated in this area are: sea breeze, slope drainage winds, channelling winds created by terrain constrictions and cool-air accumulation in low-lying regions. This last structure, developed specially in winter time, gives rise to stagnant cold air masses and strong thermic inversions, with average lapse rate of –4 degrees on 100m, which contribute to increase air pollution concentration, especially SO2. Hourly and daily averaged SO2 concentration can be higher than 350 and 138µgm–3 respectively. In addition, as La Plana is located not far from the Mediterranean Sea, during summertime the sea breeze arrives into this zone via its southern entrance, thereby reaching the whole area. The arrival of the sea breeze in to La Plana, which advects pollutants from the nearby industrial area, is the main cause of some of these pollutants, especially ozone and its precursors, attaining high concentrations during afternoon hours. The contribution of the sea breeze is variable, but could represent between a 25% to a 30% of its total value.  相似文献   

8.
Summary This study assessed the climatic suitability for the expansion of Solenopsis invicta Buren (red imported fire ant) in Oklahoma under the present climate and with a doubling of atmospheric CO2 using three general circulation models (GCMs) (GFDL R30, OSU, UKMO). Oklahoma was chosen as the geographical focus because it has a dense network of meteorological stations and lies on the edge of the current biogeographic range of S. invicta. Meteorological data were spatially referenced with model data in GIS to produce a series of images of selected suitability indicators: (1) mean annual precipitation >510mm; (2) less than seven consecutive days with mean air temperature <1.1C; and (3) mean winter air temperature >9.4C. These indicator images were combined to produce suitability maps for the potential range of S. invicta. Under current climatic conditions, roughly three-quarters of Oklahoma is suitable for potential invasion by S. invicta. The GFDL R30, OSU, and UKMO show that the area suitable for colonization increases by approximately 26, 26, and 36%, respectively. In terms of actual land area, the increase with a warmer, wetter climate ranges from 35,300km2 to 47,600km2. The destructiveness of S. invicta on human livelihood necessitates a better understanding of the future expansion of the species for an uncertain future climate.  相似文献   

9.
Summary The purpose of this study is to better understand the dynamical and microphysical processes within Arctic clouds, which occurred in April 1998 over the Surface Heat Budget of the Arctic Ocean (SHEBA) ship during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment Arctic Cloud Experiment (FIRE.ACE). The observations from the four cases in the present study were collected by instruments mounted onboard the National Research Council (NRC) Convair, as well as, the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) satellite, the SHEBA surface based NOAA Doppler radar (35GHz, Ka-Band), and the NOAA depolarization lidar (0.523µm) measurements. The aircraft observations were collected at 32Hz (3-m scale). The Meteorological Services of Canada (MSC) lidar (1.064µm) was operated onboard the Convair-580. The AVHRR observations, representing a 5-km horizontal resolution, were used to estimate particle size, phase, and optical thickness. Constant altitude flight legs were made at about 100m over the ocean surface. Vertical air velocity (w), reflectivity and Doppler velocity, and backscatter and depolarization ratio values were used to define the size of the important dynamical structures. Ice crystal number concentration (Ni), ice water content (IWC), droplet number concentration (Nd), liquid water content (LWC) and characteristic particle size and shape were summarized for each case. The effective radius (reff) values for liquid clouds obtained from in-situ and AVHRR observations were found comparable. The large variability in IWC can be due to undetected ice crystals at small size ranges. Mixed phased conditions in the AVHRR retrievals complicated the comparisons with in-situ data. Ni was found to be directly related to the history of the air-parcel dynamics e.g., w. The variability and differences in the parameters obtained from various platforms can be attributed to their instrumental capabilities, resolution, as well as the cloud development.  相似文献   

10.
Summary A zonally averaged global energy balance model with feedback mechanisms was constructed to simulate (i) the poleward limits of ITCZ over the continent and over the ocean and (ii) a simple monsoon system as a result of differential heating between the continent and the ocean. Three numerical experiments were performed with lower boundary as (1) global continent, (2) global ocean and (3) continent-ocean, with freezing latitudes near the poles. Over the continent, midlatitude deserts were found and the ITCZ migrates 25° north and south with seasons. Over a global swamp ocean results do not show migration of ITCZ with time but once the ocean currents are introduced the ITCZ migrates 5° north and south with seasons. It was found that the seasonal migration of ITCZ strongly depends on the meridional distribution of the surface temperature. It was also found that continent influences the location of the oceanic ITCZ. In the tropics northward progression of quasi-periodic oscillations called events are found during the pre- and post-monsoon periods with a period of 8 to 15 days. This result is consistent with the observed quasi-periodic oscillations in the tropical region. Northward propagation of the surface temperature perturbation appears to cause changes in the sensible heat flux which in turn causes perturbations in vertical velocity and latent heat flux fields.List of Symbols vertical average - 0 zonal average - vertical mean of the zonal average - 0s zonal average at the surface - 0a zonal average at 500 mb level - latitude We now define the various symbols used in the model rate of atmospheric heating due to convective cloud formation (K/sec) - dp/dt (N/m2/sec) - density - potential temperature (K) - rate of rotation of the earth (rad/sec) - empirical constant - humidity mixing ratio - * saturated humidity mixing ratio - opacity of the atmosphere - 1,2 factors for downward and upward effective black body long wave radiation from the atmosphere - Stefan-Boltzmann constant - emissivity of the surface - D subsurface temperature (K) - a specific volume - 0xs ,0ys eastward and northward components of surface frictional stress - * vertical velocity at the top of the boundary layer (N/m2/sec) - P Thickness of the boundary layer (mb) - nondimensional function of pressure - P pressure - P a pressure of the model atmosphere (N/m2) - P s pressure at the surface (N/m2) - t time (sec) - U eastward wind speed (m/sec) - V northward wind speed (m/sec) - surface water availability - T absolute temperature (K) - heat addition due to water phase changes - g acceleration due to gravity (m2/sec) - a radius of the earth (m) - R gas constant for dry air (J/Kg/K) - C p specific heat of air at constant pressure (J/Kg/K) - k R/C p - L latent heat of condensation (J/Kg) - f coriolis parameter (rad/sec) - H s H 0s (1) +H 0s (2) +H 0s (3) +H 0s (4) +H 0s (5) (J/m2/Sec)=sum of the rates of vertical heat fluxes per unit surface area, directed toward the surface - H a H 0a (1) +H 0a (2) +H 0a (3) +H 0a (4) (J/m2/Sec)=sum of the rates of heat additions to the atmospheric column per unit horizontal area by all processes - H 0s (1) ,H 0a (1) heat flux due to short wave radiation - H 0s (2) ,H 0a (2) heat flux due to long wave radiation - H 0s (3) ,H 0a (3) heat flux due to small scale convection - H 0s (4) heat flux due to evaporation - H 0a (4) heat flux due to condensation - H 0s (5) heat flux due to subsurface conduction and convection - e * saturation vapor pressure - R solar constant (W/m2) - r a albedo of the atmosphere - r s albedo of the surface - b 2 empirical constant (J/m2/sec) - c 2 empirical constant (J/m2/sec) - e 2 nondimensional empirical constant - f 2 empirical constant (J/m2/sec) - factor proportional to the conductive capacity of the surface medium - a s constant used in Sellers model - b s positive constant of proportionality used in the Sellers model (kg m2/J/sec2) - K HT coefficient for eddy diffusivity of heat (m2/sec) - K HE exchange coefficient for water vapor (m2/sec) - h depth of the water column (m) - z height (m) - V 0ws meridional component of surface current (m/sec) - n cloud amount - G 0,n long wave radiation form the atmosphere for cloud amount n (W/m2) - B 0 long wave radiation from the surface (W/m2) - S 0,n short wave radiation from the atmosphere for cloud amount n (W/m2) - A n albedo factor for a cloud amount n - R f1 large scale rainfall (mm/day) - R f2 small scale rainfall (mm/day) With 22 Figures  相似文献   

11.
Summary In order to quantify the effects of temperature and soil water content on soil respiration, during June and July 2002 CO2 soil efflux was measured with a closed chamber (non-steady state, flow through) system in the field. The amount of CO2 emission was highly dependent on the land-use in the observation area, which consisted of meadow soil and brownfield. The CO2 emission from the brownfield ranged from 0.9 to 5.5µmol CO2 m–2s–1, and that for meadow soil from 1.1 to 12.6µmol CO2 m–2s–1. Soil respiration, as a function of soil temperature (Tsoil), relative soil water content (RSWC), soil pH, and the soil carbon/nitrogen ratio (C/N), was analysed by a modified closed non-linear regression model. Between 63% and 81% of the variation of soil CO2 emission could be explained with changes of Tsoil, RSWC, pH, and C/N for the individual chambers on the brownfield.Subsequent analysis involved a comparison of the soil chamber results with eddy covariance (EC) measurements of one week, and included a footprint analysis to account for the influence of the different land use types on the measurements. For this, EC data (143 measurements after quality check) were restricted to those originating from the brownfield area with more than 90% of the flux. For a second comparison, the net ecosystem exchange (NEE) was calculated for different parts of the meadow using the SVAT model PROXEL. Together with the respiration from the brownfield, a weighted average of model NEE was produced using the flux contribution determined by the footprint model. Acceptable agreement (r2=0.69) was found between the modelled data and individual EC measurements, except during situations where the performance of the footprint model was disturbed by internal boundary layer effects.  相似文献   

12.
Summary The evolving modes of the sea-surface temperature (SST) in the Tropical Atlantic on the short interannual (IA) timescale were obtained by performing the extended empirical orthogonal function (EEOF) analyses on this variable separately for the 106-year (1871–1976) and 20-year (1881–1900; 1901–1920; 1921–1940; 1941–1960) periods. The equatorial and inter-hemispheric patterns manifest in the first EEOF mode of each analysis as part of the short IA evolution of the SST anomalies in the Tropical Atlantic. Another outstanding feature of the first EEOF mode of each analysis concerns the propagations of the SST anomalies in the meridional direction within the 20°N–20°S band and in the zonal direction in the sector 40°W–20°W. For all analyses, the SST anomalies propagate northward from the equator to 15°N and southward from 20°N to 15°N, with the same sign anomalies merging approximately at 15°N. On the other hand, the SST anomalies propagate westward in the sector 40°W–20°W with a propagation rate close to that of the phase speed of the fastest baroclinic Rossby wave in the ocean. So, the observed propagations of the SST anomalies in the 20°N–20°S band might result from the combined effect of the surface oceanic currents in this band and the baroclinic Rossby waves in the ocean.  相似文献   

13.
Summary The first GCM climate change projections to include dynamic vegetation and an interactive carbon cycle produced a very significant amplification of global warming over the 21st century. Under the IS92a business as usual emissions scenario CO2 concentrations reached about 980ppmv by 2100, which is about 280ppmv higher than when these feedbacks were ignored. The major contribution to the increased CO2 arose from reductions in soil carbon because global warming is assumed to accelerate respiration. However, there was also a lesser contribution from an alarming loss of the Amazonian rainforest. This paper describes the phenomenon of Amazonian forest dieback under elevated CO2 in the Hadley Centre climate-carbon cycle model.  相似文献   

14.
Summary The Earths local fair-weather electric field is significantly affected by small ions present in the atmosphere. These ions are typically smaller than 0.001µm and occur in concentrations from 500 to 600cm–3 in air. Attachment to larger aerosol particles may severely decrease the mobility of these atmospheric ions resulting in an increased local electric field. The number concentration of environmental aerosol particles in the size range 0.1 to 5.0µm was measured with two automatic laser scattering particle counters. The Earths electric field was monitored with an electric fieldmeter. Measurements were made in clean air and in an environment highly polluted by wood smoke. The electric field was found to be positively correlated to the aerosol number concentration. During one 24-hour period of measurement, the electric field increased from 180 to about 280Vm–1 as the number concentration of aerosols larger than 0.1µm increased from about 2000 to 9000cm–3. The number concentrations of aerosols larger than 0.1 and 0.3µm were both found to be positively correlated with the Earths electric field with correlation coefficients of 70% and 61%, respectively.Present address: School of Physical Sciences, Queensland University of Technology, Brisbane 4001, Australia.  相似文献   

15.
Effect of finite sampling on atmospheric spectra   总被引：2，自引：0，他引：2  
The effect of a finite averaging time on variances is well known, but its effect on power spectra is less clearly understood. We present numerical solutions for the spectral distortion arising from sampling over a finite time interval T and show that the commonly used filter function (1 – sinc2f T), valid for variances, is a reasonable approximation for power spectra only when T 10 m , where f is the cyclic frequency, and m is the dominant time scale of the process. Our results exhibit an increasingly steeper low-frequency roll-off as T decreases relative to m , indicating that the measured spectrum is subject to a greater suppression of the lower frequencies (f > 1/T) than predicted by (1 – sinc2f T). This suppression is, in a sense, compensated by an overestimation of spectral estimates in the frequency range f 1/T.  相似文献   

16.
Summary ¶In order to better understand land-atmosphere interactions and increase the predictability of climate models, it is important to investigate the role of forest representation in climate modeling. Corresponding to the big-leaf model commonly employed in land surface schemes to represent the effects of a forest, a so called big-tree model, which uses multi-layer vegetation to represent the vertical canopy heterogeneity, was introduced and incorporated into the National Center for Atmospheric Research (NCAR) regional climate model RegCM2, to make the vegetation model more physically based. Using this augmented RegCM2 and station data for China during 1991 Meiyu season, we performed 10 experiments to investigate the effects of the application of the big-tree model on the summer monsoon climate.With the big-tree model incorporated into the regional climate model, some climate characteristics, e.g. the 3-month-mean surface temperature, circulation, and precipitation, are significantly and systematically changed over the model domain, and the change of the characteristics differs depending on the area. Due to the better representation of the shading effect in the big-tree model, the temperature of the lower layer atmosphere above the plant canopy is increased, which further influences the 850hPa temperature. In addition, there are significant decreases in the mean latent heat fluxes (within 20–30W/m2) in the three areas of the model domain.The application of the big-tree model influences not only the simulated climate of the forested area, but also that of the whole model domain, and its impact is greater on the lower atmosphere than on the upper atmosphere. The simulated rainfall and surface temperature deviate from the originally simulated result and are (or seem to be) closer to the observations, which implies that an appropriate representation of the big-tree model may improve the simulation of the summer monsoon climate.We also find that the simulated climate is sensitive to some big-tree parameter values and schemes, such as the shape, height, zero-plane displacement height and mixing-length scheme. The simulated local/grid differences may be very large although the simulated areal-average differences may be much lower. The area-average differences in the monthly-mean surface temperature and heat fluxes can amount to 0.5°C and 4W/m2, respectively, which correspond to maximum local/grid differences of 3.0°C and 40W/m2 respectively. It seems that the simulated climate is most sensitive to the parameter of the zero-plane displacement among the parameters studied.  相似文献   

17.
Summary A 1290MHz wind profiler (Radian Lap-3000), at present one of three operational wind profilers in Austria, is operated at Vienna airport. In spite of quality assurance procedures as consensus averaging included in the data evaluation process from profiler raw data, some spurious peaks of wind speed and unrealistic changes of the wind vector in time or height occur in the wind measurements. This is especially true for sampling intervals of only 5 minutes which are used to resolve the temporal evolution of summer thunderstorms and frontal passages. Averaging periods of only a few minutes are rather the lower limit apt for wind profiler observations and result in a low data availability of 28%, whereas about 55% of data (relative to the maximum height range according to the parameter setting) are available for 10 to 30 minutes profiles.Approaches to a posteriori quality control using checks for automatic error detection are proposed and tested on a one and a half year data-set: Flagging data when the three-dimensional wind divergence exceeds a predefined limit (0.5s–1) is in most cases successful in combination with thresholds for wind speed (2 times the median of the daily data-set) or wind shear (0.2s–1).The wind profiler data is compared to wind profiles from the next radiosonde station where soundings are launched 4 times a day at Hohe Warte, approx. 20km northwest, at the hill-side of the Viennese Woods. Deviations of about 1m s–1 in wind speed are found between the observations of the two systems. Differences between the wind profiles within the boundary layer can be explained by local differences in the wind regime observed at the airport and the radiosounding – blocking effects of the Viennese Woods during south-easterly flow. Comparing the profiler data to radiosoundings on a monthly basis gives a tool to monitor the profiler performance.  相似文献   

18.
Summary Trends of monthly air temperature extremes were investigated in five meteorological stations of the Grand-Duchy of Luxembourg during the period 1949–1998. The application of an innovative homogenization method based on the concept of relative homogeneity to climatic time series allows identifying multiple break points, as well as correcting data series in an objective and robust statistical way. The rise of maximum temperature (Tmax) has occurred at a rate of 1.5 times that of the minimum temperature (Tmin) in winter (+1.4°C versus +0.9°C) and summer (+1.4°C versus +0.8°C). No trend in temperature extremes was found in autumn, while spring was affected by a small warming (+0.3°C) of Tmin and no change in Tmax resulting in a decrease of the diurnal temperature range (DTR) (–0.3°C). In spring, a strong positive linear relationship between Tmin warming and local terrain slope could be found. Comparison to new-gridded large-scale climatologies indicates generally close agreement to temperature trends during the 1949–1998 period, while a lower local warming was observed in summer during the post-1975 period following the changing-point year of atmospheric circulation over North-western Europe. This study shows that the question of data homogeneity is not trivial and should receive careful attention before quantifying historical temperature trends and identifying their spatial patterns at regional scale.  相似文献   

19.
Summary In addition to global solar radiationE g , the hourly diffuse componentE d incident on a horizontal surface has been measured from February 1993 to January 1995 at a meteorological station in tropical West Africa. The measured diffuse solar irradiance data was corrected for shadow band effects. The monthly mean diurnal variations of diffuse solar irradiance obtained for identical months in the two years have been compared and found to be generally consistent. The corresponding monthly mean hourly values ofE d for identical months in 1993 and 1994 agreed to within 9% while yielding correlation coefficients greater than 0.960. In addition, the monthly mean daily totals ofE d for identical months were found to agree mostly to within 6% and showed virtually the same annual variations in both years. The monthly mean daily total values of diffuse solar radiation for most months in the two years ranged between 7.94 MJm–2d–1 and 10.50 MJm–2d–1. The monthly mean of daily hourly maximum values ofE d obtained for identical months in the two years have been discussed in relation to the dominant atmospheric conditions during these months. The results been presented here have been compared with those of some investigators within and outside the Africa region.With 8 Figures  相似文献   

20.
Summary ¶The 0°C isotherm height, a parameter needed for the estimation of attenuation of microwave and millimetre wave for earth-space communication, has been estimated for different stations spread over India. The variations of 0°C isotherm height for different seasons over these stations are presented. Attenuations of radio wave due to rain at frequencies 10GHz and above have also been estimated for few stations using the 0°C isotherm height so derived. The results are useful for radio systems designers.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号