共查询到20条相似文献，搜索用时 772 毫秒
1.
R. Singh P. C. Joshi C. M. Kishtawal P. K. Pal 《Meteorology and Atmospheric Physics》2006,94(1-4):1-10
Summary A new methodology for deriving daily averages of near surface specific humidity (Q
a
) is developed. Remotely sensed parameters, total water vapor (W), boundary-layer water vapor (W
b
), and sea-surface temperature (SST) are used to derive Q
a
. Genetic algorithm (GA) is used to find the empirical function relating the input (W, W
b
, and SST) and output (Q
a
) parameters. The input data consist of 2 years (1999–2000) of daily W, W
b
, from SSM/I (Special Sensor Microwave Imager), and SST data from AVHRR (Advanced Very High Resolution Radiometer). COADS
(Comprehensive Ocean Atmospheric Data Set) observations of Q
a
are used to develop and evaluate the new methodology.
The performance of the algorithm is measured with COADS observations, which are not used in the development phase. The global
mean rms error for daily averages Q
a
is 1.5 ± 0.40 g/kg. Slightly higher discrepancies between Q
a
derived from the new method and COADS observations are found over the Northwestern Pacific, North Atlantic oceans and Arabian
Sea. This method improves upon the humidity retrieval of Liu (1986), Schulz et al (1993), and Chou et al (1997). 相似文献
2.
利用Nimbus-7行星反射率观测资料估算青藏高原地区的总辐射 总被引：10，自引：1，他引：10
本文利用1982年8月—1983年7月期间Nimbus-7行星反射率的月平均资料用“物理模式方法(Raschke and Preuss,1979)”估算了青藏高原及其邻近地区月平均地面总辐射的分布。得到的结果较好地反映了纬度、海拔与云量三个主要因子对总辐射分布的支配作用。根据高原及其邻近地区23个测站的资料,对总辐射的计算值与观测值进行了比较。统计分析表明,相关系数f=0.90,标准误差RMS=27w/m~2,平均绝对误差ABS=21w/m~2(相当于有效平均总辐射的11.7％)。文中还对误差来源和敏感性问题进行了讨论。 相似文献
3.
The Multi frequency Scanning Microwave Radiometer (MSMR) onboard Oceasat-1 was used to develop a retrieval method fornear-surface specific humidity by means of multivariate regressiontechnique. The MSMR measures the microwaveradiances in 8 channels at the frequencies of 6.6, 10.7, 18 and 21 GHzfor both vertical and horizontal polarizations. Regression coefficients were derived using the ship reports of the Comprehensive Ocean-Atmosphere Data Set (COADS) for the months of July, October and December, in 1999. Daily near-surface specific humidity data from COADS in 2° × 2° latitude/longitude bins and collocated brightness temperature data from MSMR were used to derive the coefficients. The derived coefficients werevalidated with humidity given in COADS.A linear relationship is established to determine the near-surface specifichumidity from MSMR brightness temperature (Tb) with an rms error of 1.2 g kg-1 for individual situations and an rms errorof 0.84 g kg-1 for monthly time scales over global oceans.The retrieval algorithm is validonly for the open sea regions. 相似文献
4.
Surface-level moisture transport over the Indian Ocean has been computed using NOAA/HIRS data for the years 1980, 1981 and 1984. The global relation between monthly mean surface-level humidity and precipitable water (Liu, 1986) has been applied for the computation of surface-level humidity using monthly mean satellite-derived water vapour. The monthly mean surface wind fields over the Indian ocean provided by Florida State University have been used for the surface-level moisture flux computations. Our analysis indicates net positive surface-level moisture flux divergence over the Arabian Sea and negative moisture flux divergence over the Bay of Bengal. It has also been found that evaporation over the Arabian Sea is a variable quantity and forms a significant part of the net moisture budget over the Arabian Sea. The relative contribution of cross-equatorial flux and evaporation from the Arabian Sea has been studied for all three years. 相似文献
5.
X. Yin 《Theoretical and Applied Climatology》1999,64(1-2):61-68
Summary Bright sunshine duration (BSD) is of singular importance for estimating solar irradiance, and its data base is small in comparison.
This paper reports a generic algorithm that captures global variation in monthly BSD data in relation to temperature, precipitation
and geographic location. The algorithm depicts BSD in terms of reduction from daylength as a negative exponential function
of standard station pressure, with the exponential reduction rate as proportional to the product of a series of multiplicative
functions reflective of global generalities and regional idiosyncrasies. The algorithm is parameterized by regression fitting
to monthly climate normal data for 729 stations worldwide. It accounts statistically for 85% of the variance in the BSD data,
with a root mean square error of 1.0 hr, or 15% of the data mean. The data fitting tends to be least robust for tropical humid
climates or for tropical and subtropical monsoonal Asia. The spatially-based algorithm projects with a reasonable accuracy
5-yr sequential monthly BSD data for five stations representative of the climate regimes in the conterminous United States:
the absolute error is within ±1.5 hr for 70% to 93% of the 60 monthly mean BSD values for each of the stations.
Received April 22, 1999 相似文献
6.
Soil temperature is a meteorological data directly affecting the formation and development of plants of all kinds. Soil temperatures are usually estimated with various models including the artificial neural networks (ANNs), adaptive neuro-fuzzy inference system (ANFIS), and multiple linear regression (MLR) models. Soil temperatures along with other climate data are recorded by the Turkish State Meteorological Service (MGM) at specific locations all over Turkey. Soil temperatures are commonly measured at 5-, 10-, 20-, 50-, and 100-cm depths below the soil surface. In this study, the soil temperature data in monthly units measured at 261 stations in Turkey having records of at least 20 years were used to develop relevant models. Different input combinations were tested in the ANN and ANFIS models to estimate soil temperatures, and the best combination of significant explanatory variables turns out to be monthly minimum and maximum air temperatures, calendar month number, depth of soil, and monthly precipitation. Next, three standard error terms (mean absolute error (MAE, °C), root mean squared error (RMSE, °C), and determination coefficient (R 2)) were employed to check the reliability of the test data results obtained through the ANN, ANFIS, and MLR models. ANFIS (RMSE 1.99; MAE 1.09; R 2 0.98) is found to outperform both ANN and MLR (RMSE 5.80, 8.89; MAE 1.89, 2.36; R 2 0.93, 0.91) in estimating soil temperature in Turkey.
相似文献7.
Summary The annual and monthly mean diurnal variations of the diffuse fraction of global solar irradiance arriving on the ground
at a tropical station in Sub-Sahel Africa is here been reported. The monthly mean hourly values of the diffuse fraction (K
d
) for such clear-sky months as February, March and November at this location, which approach a minimum at about local noon,
are observed to lie generally below 0.50 during the period from 11:00 to 15:00 hrs (LST). Consequently, solar concentrators
utilising parabolic mirrors are expected to have high performance during these months in this region. Like the mainly-cloudy
and wet months (June to August) in which monthly mean hourly values of K
d
higher than 0.62 have been recorded, the corresponding diffuse fraction for dust-haze months (mostly December and January)
with high turbidity coefficients were generally above 0.50. Monthly mean hourly values of K
d
for less cloudy months (April, May, September and October) ranged between 0.48 and 0.77 during the period from 11:00 to 15:00 hrs
(LST). The effects of atmospheric dust-haze, clouds and albedo on the monthly mean diurnal variation of the diffuse fraction
has been discussed. Also reported are the characteristic values of K
d
for sets of months with relatively similar atmospheric and sky conditions at this location. The annual variations of the
monthly mean daily values of K
d
which exhibit strong seasonal dependence showed a peak in August for both years. Except for the months of February and March,
the monthly mean daily totals of K
d
exhibited similar annual marches during both years. The major discrepancy in the values of the monthly mean daily totals
of K
d
in both years were recorded in the months of February, November and December, with the corresponding K
d
values for these months in both years agreeing only to within 32.9% in February, 15.4% in November and 16.2% in December.
Apart from the aforementioned months, the corresponding monthly mean daily totals of K
d
for the remaining nine months in both years agreed mostly to within less than 8.4%. The least monthly mean daily ratios of
K
d
were obtained in the relatively clear month of November for both years being 0.43 in 1993 and 0.49 in 1994. On an annual
average, the diffuse component was found to constitute 59.6% of the global solar irradiance arriving on the ground at this
region in 1993 and 60.9% in 1994. The results been reported here have been compared with a few others emanating from other
tropical stations.
Received February 5, 1998 Revised May 12, 1998 相似文献
8.
FY-3系列卫星星载IRAS仪器设有26个通道,其中20个通道用于探测地球大气在红外波段的热辐射,通道辐射率代表了地球大气系统在大气顶的向外辐射光谱信息,与总波段的射出长波辐射（OLR）通量相关性高。该文基于逐线辐射传输模式计算软件LBLRTM对全球2521条大气廓线的大气顶射出辐射率模拟数据,计算了每条廓线的OLR和FY-3B/IRAS,FY-3C/IRAS通道辐射率,用统计回归方法建立了利用IRAS的多通道辐射率计算OLR的非线性理论回归模式;应用模式和FY-3B/IRAS,FY-3C/IRAS的L1级数据,处理得到2016年4月1-30日的全球日平均、月平均OLR格点产品。与Aqua/CERES,Terra/CERES仪器宽波段观测OLR产品对比表明:对于水平分辨率为1°×1°的全球月平均OLR格点产品,均方根误差为2.22 W·m-2,相关系数为0.9982 W·m-2,平均偏差为-0.2 W·m-2,表明FY-3/IRAS仪器定标及反演模式均达到较高水平。文中还回顾了历史上不同气象卫星的多种OLR反演算法模式,并对不同模式精度进行了比较。 相似文献
9.
Analyzed are the anomalies of monthly mean values of surface pressure over Eurasia in winter seasons of 1901–2010. It is noted
that the centers of large monthly positive pressure anomalies (16–24 hPa) are usually located within the 60°–70°N latitude
zone. The Siberian high is well developed but the pressure anomalies in its center amount to 3–8 hPa only. The large monthly
pressure anomalies at the isobaric surface of 500 hPa in the first natural synoptic area are mainly accompanied by the E-type of circulation (according to G.Ya. Vangengeim). The number of days with the western (W) type of circulation is extremely small and is practically absent when the anomalies in the center exceed 20 hPa (blocking
process). The time periods of increase (decrease) in the annual number of days with W-circulation are well agreed with the periods of the Earth rotation acceleration (deceleration). The positive pressure anomalies
were four or five times more frequent in the periods of the Earth angular velocity decrease: in 1933–1972 and after 2004. 相似文献
10.
In this study,the clear sky hourly global and net solar irradiances at the surface determined using SUNFLUX,a simple parameterization scheme,for three stations(Gaize,Naqu,and Lhasa) on the Tibetan Plateau were evaluated against observation data.Our modeled results agree well with observations.The correlation coefficients between modeled and observed values were > 0.99 for all three stations.The relative error of modeled results,in average was < 7%,and the root-mean-square variance was < 27 W m 2.The solar irradiances in the radiation model were slightly overestimated compared with observation data;there were at least two likely causes.First,the radiative effects of aerosols were not included in the radiation model.Second,solar irradiances determined by thermopile pyranometers include a thermal offset error that causes solar radiation to be slightly underestimated.The solar radiation absorbed by the ozone and water vapor was estimated.The results show that monthly mean solar radiation absorbed by the ozone is < 2% of the global solar radiation(< 14 W m 2).Solar radiation absorbed by water vapor is stronger in summer than in winter.The maximum amount of monthly mean solar radiation absorbed by water vapor can be up to 13% of the global solar radiation(95 W m 2).This indicates that water vapor measurements with high precision are very important for precise determination of solar radiation. 相似文献
11.
J. Mubiru E. J. K. B. Banda F. D’Ujanga T. Senyonga 《Theoretical and Applied Climatology》2007,87(1-4):179-184
Summary Solar radiation incident on the Earth’s surface is a determining factor of climate on Earth, hence having a proper solar radiation
database is crucial in understanding climate processes in the Earth’s atmosphere. Solar radiation data may be used in the
development of insolation maps, analysis of crop growth and in the simulation of solar systems. Unfortunately, measured solar
radiation data may not be available in locations where it is most needed. An alternative to obtaining observed data is to
estimate it using an appropriate solar radiation model. The purpose of this study is to assess the performance of thirteen
global solar radiation empirical formulations, in Kampala, Uganda, located in an African Equatorial region. The best performing
formulations were determined using the ranking method. The mean bias error, root mean square error and t-statistic value were calculated and utilized in the ranking process. Results have shown that the formulation:
is ranked the highest and therefore is the recommended empirical equation for the estimation of the monthly mean global solar
irradiation in Kampala, Uganda and in other African Equatorial locations with similar climate and terrain. 相似文献
12.
Ren Li Lin Zhao Tonghua Wu Yongjian Ding Yufei Xin Defu Zou Yao Xiao Yongliang Jiao Yanhui Qin Linchan Sun 《Theoretical and Applied Climatology》2013,113(3-4):573-583
Global solar radiation is of great significance to the balance of ground surface radiation, the energy exchange between the Earth’s surface and atmosphere, and the development of weather and climate systems in various regions. In this study, the monthly global radiation recorded at 23 stations over the Qinghai–Tibetan Plateau (QTP) was utilized to estimate global solar radiation (Q) from sunshine duration and to obtain improved fits to the variation coefficients of the monthly Angström–Prescott model (APM). The modeling results were evaluated by calculating the statistical errors, including mean bias error, mean absolute error, root mean square error, and mean relative error. We demonstrate that the monthly Q values can be predicted accurately by APM over the QTP. We also assess the variations of Q values at 116 meteorological stations by APM over the QTP during 1961–2000. The analysis shows that the annual mean sunshine duration amounted to more than 3,000 h over the whole plateau, implying promising prospects for economic applications of solar energy. During the past 40 years, the mean global solar radiation has been relatively high in the western QTP, extending northward to the Inner Mongolian Plateau. Although its decadal variations in the QTP and surrounding regions were inconsistent, the anomaly values of global solar radiation were generally positive during the 1960s and 1970s, indicating that the QTP’s global solar radiation has increased during those periods. The anomaly values were negative during the 1980s and 1990s, showing that the plateau’s global solar radiation has decreased during those periods. Global solar radiation over the QTP is negatively proportional to latitude but positively proportional to altitude and relative sunshine duration. Three factors, the sunshine duration, latitude, and altitude, exert great influence on global surface radiation, of which sunshine duration is most significant. A high-variation-coefficient zone of global solar radiation occurred in the western part of the QTP but, on average, the variation coefficient of the plateau’s global solar radiation was only 0.031, suggesting that the variation in global radiation was relatively stable over the whole QTP. 相似文献
13.
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
14.
Summary Convection, a sub-gridscale process, is coupled to the gridscale motions via the averaged budget equations. In this study atmospheric convection is represented by the vertical eddy flux of equivalent temperature, referred to asconvective flux. It is demonstrated with a thermodynamic diagnostic model for an atmospheric column (DIAMOD) that the convective flux can, with tolerable error, be diagnosed from daily global gridscale analyses. These yield the gridscale budget of equivalent temperature. The budget is the observable quantity, it is in balance with the unobservable convective flux. We reproduce the known result that in convectively active atmospheric columns the budget is negative in lower and positive in upper layers. The corresponding vertical mean slope of the budget controls the convective strength; the slope is strongly negative for deep convection.In the global mean column the convective flux converges upward throughout the entire atmosphere. In actual convective situations, however, the flux diverges in lower layers, reaches highest intensity somewhere between 700–500 hPa and converges in the upper atmosphere. We find maximum fluxes around 600 W/m2 in individual tropical columns and extreme fluxes exceeding 1000 W/m2 in midlatitude columns. In the monthly mean however, the convective flux is clearly larger in the tropics; it also reaches to significantly higher levels in the tropics than in midlatitudes. While these qualitative results are invariant against using both routine analysis and reanalysis data from different sources (ECMWF and NCEP) our results change quantitatively when changing the data sources. We attribute this effect to differences in the sub-gridscale parameterization implicit in the objective data assimilation of the weather centres which are not completely removed by the incoming observation data in the final analyses.With 12 Figures 相似文献
15.
Summary The diurnal variation of the Earth Radiation Budget and its components require for sparsely temporal sampling a high amount of modeling for the derivation of precise daily averages. In the present study the time integration errors of the regional monthly averages of the Earth Radiation Budget Experiment (Barkstrom, 1984) are estimated for April 1985. For this error assessment we made use of data of the European geostationary satellite Meteosat 2 which narrowbanded measurements have been converted to reasonable estimates of broad-band radiation fluxes. Based on this data set the measurements of the ERBE satellites, ERBS, NOAA 9, and NOAA 10 are simulated. For the time integration the ERBE time integration models are used.The mean error for the regional monthly average of the net radiation flux varies between — 3 and + 5 W/m2 for the combination of all three satellites. The largest contribution to this uncertainty is given by the time integration of the shortwave fluxes. A new approach for the time integration procedure is presented which is based on the Maximum Entropy spectral analysis of temporal high resolution data sets as provided by geostationary satellites.This study closes with the estimation of the final error for ERBE regional monthly averages of the net radiation flux, which includes the uncertainties of the instruments, the inversion process and the time integration process. These errors lie between 11.1 W/m2 for single NOAA 9 products and 7.8 W/m2 for the combination of all three satellites. With that the Earth Radiation Budget Experiment fulfills the required accuracy.With 12 Figures 相似文献
16.
V. Bădescu 《Theoretical and Applied Climatology》1991,44(3-4):187-200
Summary This paper analyses the accuracy of three simple relationships of cloud shade (CS) to point cloudiness (PC). 1740 pairs of monthly average values (CS, PC) from twenty-nine weather stations of Romania were used. The following statistical indicators of accuracy were used: the mean bias error, the mean absolute error and the root mean square error. Also, a bootstraping technique provided a general way to evaluate the confidence and significance associated with each of the statistical indicators of accuracy. The paper deals with the accuracy of the empirical relationships when applied in other areas and time intervals than the ones where the relations were determined.With 10 Figures 相似文献
17.
Nine profiles of the temperature structure parameter C
T
2
and the standard deviation of vertical velocity fluctuations (
w) in the convective boundary layer (CBL) were obtained with a monostatic Doppler sodar during the second intensive field campaign of the First ISLSCP Field Experiment in 1987. The results were analyzed by using local similarity theory. Local similarity curves depend on four parameters: the height of the mixed layer (z
i
), the depth of the interfacial layer (), and the temperature fluxes at the top of the mixed layer (Q
i
) and the surface (Q
o). Values of these parameters were inferred from sodar data by using the similarity curve for C
T
2
and observations at three points in its profile. The effects of entrainment processes on the profiles of C
T
2
and
wnear the top of the CBL appeared to be described well by local similarity theory. Inferred estimates of surface temperature flux, however, were underestimated in comparison to fluxes measured by eddy correlation. The measured values of
wappeared to be slightly smaller than estimates based on available parmeterizations. These discrepancies might have been caused by experimental error or, more likely, by the distortion of turbulence structure above the site by flow over the nonuniform terrain at the observation site. 相似文献
18.
《大气与海洋》2013,51(3):203-215
Abstract The forecast skill of the Canadian Meteorological Centre (CMC) operational global forecast/analysis system is assessed as a function of scale for the traditional forecast variable of 500‐hPa geopotential height using results from January 2002. These results are compared to an earlier analysis of forecasts from the European Centre for Medium‐range Weather Forecasts (ECMWF) which indicated unexpectedly enhanced skill at high wavenumbers (small scales) especially in the mean forecast component identified with local topographical structures. The global rms error for the CMC forecasts is dominated by the transient component compared to the mean and continues to grow with time during the six days of the forecast. Geographically the transient error grows most rapidly in middle and high latitude regions of large natural variability. The relative error behaves differently and grows most rapidly initially in tropical regions and is inferred to exhibit both climatological and flow‐dependent error growth. In terms of spherical harmonic two‐dimensional wavenumber n, low wavenumber (large scale) 500‐hPa geopotential height structures are dominated by the mean component but beyond wavenumber 10 to 15 the transient component dominates and exhibits an approximately n–5 spectral slope consistent with a quasi‐two dimensional turbulence enstrophy cascading subrange. Error grows slowly for the large scales dominated by mean climatological structures but these are not of interest for daily weather forecasting. Transient error grows rapidly at small scales and penetrates toward larger scales with time in keeping with the expected predictability behaviour. An expression of the form f(n, τ) = 1 – e–τ/τp(n) is fitted to the growth of relative error as a function of wavenumber and forecast range and gives a scale dependent predictability timescale for the transient component that varies as τp ? n?3/2, although the generality of the relationship is not known. The mean component at intermediate/high wavenumbers exhibits an apparent region of enhanced skill in the CMC system apparently connected to the topography. The result supports the possibility that some small‐scale mean flow structures, although containing only a minor amount of variance, are maintained in the face of errors in other scales. The results do not support the level of enhanced skill found in an earlier analysis of ECMWF results suggesting them to be an artefact of the analysis/forecast system in use at the time. 相似文献
19.
Analytical solutions for the Ekman layer 总被引：1，自引：0，他引：1
John Miles 《Boundary-Layer Meteorology》1994,67(1-2):1-10
The PBL equation that governs the transition from the constant-stress surface layer to the geostrophic wind in a neutrally stratified atmosphere for which the eddy viscosityK(z) is assumed to vary smoothly from the surface-layer value U
*z (0.4,U
*=friction velocity,z=elevation) to the geostrophic asymptoteK
GU
*d forzd is solved through an expansion in fd/U
*1 (f=Coriolis parameter). The resulting solution is separated into Ekman's constant-K solution an inner component that reduces to the classical logarithmic form forzd and isO() relative to the Ekman component forzd. The approximationKU
*d is supported by the solution of Nee and Kovasznay's phenomenological transport equation forK(z), which yieldsK–U
*d exp(–z/d), where is an empirical constant for which observation implies, 1. The parametersA andB in Kazanskii and Monin's similarity relation forG/U
* (G=geostrophic velocity) are determined as functions of . The predicted values ofG/U
* and the turning angle are in agreement with the observed values for the Leipzig wind profile. The predicted value ofB based on the assumption of asymptotically constantK is 4.5, while that based on the Nee-Kovasznay model is 5.1; these compare with the observed value of 4.7 for the Leipzig profile. A thermal wind correction, an asymptotic solution for arbitraryK(z) and 1, and an exact (unrestricted ) solution forK(z)=U
*d[1–exp(–z/d)] are developed in appendices. 相似文献
20.
利用水平面太阳直接辐射日曝辐量反演大气气溶胶光学厚度的方法研究 总被引：3，自引：1，他引：2
本文发展了一个从宽带水平面太阳直接辐射日曝辐量 (总辐射与散射辐射日曝辐量之差) 反演光谱大气气溶胶光学厚度的方法, 包括建立一个 “等效” 的瞬时太阳天顶角模型, 并提出了一个基于气溶胶标高的云影响甄别方法。对该反演方法的数值模拟和误差分析表明: “等效” 瞬时太阳天顶角模型的不稳定性引起的光学厚度反演误差平均为3.66％; 光学厚度日变化对一段较长时间的平均光学厚度的影响不显著; 订正造成的散射辐射误差≤20％时, 光学厚度平均偏差≤4％。通过与AERONET产品的比对验证表明: 本文发展的光学厚度反演方法和云影响甄别方法都是有效的; 晴空反演的0.75 μm光学厚度与AERONET的相关系数超过0.95, 平均误差约0.02; 云甄别方法计算的季节和年平均光学厚度与AERONET具有较好的一致性。 相似文献