A hybrid technique for computing the monthly mean net longwave surface radiation over oceanic areas

Summary Global maps of the monthly mean net upward longwave radiation flux at the ocean surface have been obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top-of-the-atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (> 80 W m^–2) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux (< 40 Wm^–2) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover. The technique used in this study relies on GCM simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of the net longwave radiation at the surface over the oceans.With 9 Figures     

Modelling longwave radiation exchange between complex shapes

Modelling longwave radiation exchange between a complex shape and surrounding surfaces requires the specification of view-factors for that shape. View-factors for complex shapes are usually determined either from experimental observations or by direct integration over a geometrical element which is assumed to approximate the complex shape. An alternative, combining both approaches, is to integrate over more than one geometric shape and then to derive weights for those shapes, according to their relative surface areas, from experimental data. Application of the technique is illustrated by the determination of view-factors between a person and the surfaces of a room.     

An approach to the estimation of surface net radiation in mountain areas using remote sensing and digital terrain data

Summary An approach is proposed to estimate the net radiation load at the surface in mountain areas. The components of the radiation balance are derived using a radiative transfer model combined with remotely sensed and digital terrain data. Integrated shortwave (0.28–6.00 µm) and longwave irradiances (3.00–100.00 µm) are computed using a modified version of the Practical Improved Flux Method (PIFM) of Zdunkowski et al. (1982) which makes use of digital topographic data in order to account for slope, aspect, and shading effects. Surface albedo and thermal exitance estimates are obtained using Landsat Thematic Mapper (TM) and digital terrain data combined with the LOWTRAN 7 atmospheric model (Kneizys et al., 1988). LOWTRAN 7 is utilized together with a set of terrain modeling programs to compute direct and diffuse sky irradiance for selected TM bands, and to remove atmospheric effects within the visible, near-infrared, mid-infrared, and thermal infrared bands of Landsat TM. Model testing in the Colorado alpine show a generally good correspondence between estimated values and field measurements obtained over comparable tundra surfaces during several field campaigns. The method is finally used to produce 1) maps of the components of the radiation balance at the time of Landsat TM overflight and 2) maps of daily totals of shortwave irradiance and net shortwave radiation on a typical summer day in the Colorado Rocky Mountains (i.e. including cloud cover effects). The results indicate that the proposed approach is particularly suitable for obtaining estimates of net radiation at the surface from the toposcale to the regional scale.With 6 Figures     

Estimates of effective surface roughness over complex terrain

Turbulence data collected in an area of three-dimensional complex terrain using instruments atteched to the tether cable of a captive balloon together with radiosonde ascents are presented. In addition, data collected using only radiosonde ascents in an area of two-dimensional complex terrain of large slope are also shown. Eddy correlation measurements of the turbulent momentum flux and wind velocity profiles are used to deduce the magnitude of the effective roughness from the drag coefficient and normalised velocity profiles. A relationship connecting the terrain characteristics and the roughness length is compared with the experimental data for both types of terrain plus previous experimental estimates of the roughness length over complex terrain. The formula taken from previous work by Grant and Mason (1990) is found to agree with the data when representing an area of order 100 km².     

Prediction of surface potential temperature over complex terrain

Based on a statistical approach, the surface potential temperature at seven observing stations in complex terrain has been examined. It is shown that the surface potential temperature depends primarily on the rate of change of slope wind and on the geostrophic-level potential temperature.     

长波区间太阳辐射对气候模拟的影响

长波区间的太阳辐射在气候模式中往往被忽略。利用国家气候中心BCC_AGCM2.0.1大气环流模式,采用矩阵算子辐射传输算法,研究了长波区间太阳辐射对气候模式辐射通量和温度模拟结果的影响。结果表明,以ISCCP和CERES辐射资料为标准,考虑长波区间太阳辐射后,长波区间晴空大气地表向下辐射通量平均误差减小2.05 W/m2,均方根误差减少1.29 W/m2;长波区间晴空大气模式顶向上辐射通量平均误差减小0.70 W/m2,均方根误差减小0.21 W/m2;长波区间有云大气地表向下辐射通量平均误差减小1.38 W/m2,均方根误差减小1.03 W/m2;长波区间有云大气模式顶向上辐射通量平均误差减小0.99 W/m2,均方根误差减小0.30 W/m2。以ECMWF再分析资料为标准,考虑长波区间太阳辐射后,赤道地区上对流层—下平流层区域温度的冷偏差得到改善,对流层顶温度平均误差减小0.27 K,均方根误差减小0.25 K。     

Estimation of daytime downward longwave radiation at the surface from satellite and grid point data

Summary A hybrid method is developed for the estimation of the daytime downward longwave radiation flux (DLF) at the surface. The method makes use of the grid point thermodynamic fields at the surface and at the 1000 and 850 hPa levels. The cloud parameters are derived from the infrared and visible image data of the satellite METEOSAT-2. The calculation of the DLF is split into a clear-sky contribution, which is calculated from empirical formulae, and a cloud contribution which depends on cloud amount, cloud base height, and temperature.A sensitivity test to perturbations in the relevant parameters resembles closely the response of a multispectral radiation scheme, however the humidity dependence under clear sky has been identified as a weak point. A comparison of the method using observed input parameters with simultaneous measurements of the DLF yields an RMS error of 12.2 W/m².The method is applied for mapping the DLF over western Europe and the Mediterranean using satellite images for two days near midday and ancillary grid point data obtained during the ALPEX experiment. A comparison with ground measurements of 4 stations in West Germany shows a mean deviation of 3.9 W/m² and an RMS error of 11.6 W/m². The method is a first attempt to estimate the DLF at regional scales from satellite data on the cloud field and grid point analysis data on the thermodynamic field.

---

Zusammenfassung Zur Schätzung des abwärts gerichteten langwelligen Strahlungsflusses (DLF) während des Tages an der Erdoberfläche wird eine Hybridmethode entwickelt. Die Methode verwendet Gitterpunkt-thermodynamische Felder am Boden und auf den 1000 und 850 h Pa-Flächen. Die Wolkenparameter stammen von den Bilddaten im infraroten und sichtbaren Bereich des Satelliten METEOSAT-2. Die Berechnung des DLF teilt sich in einen, aus empirischen Formeln berechneten Beitrag des wolkenlosen Himmels und einen Beitrag durch Wolken, welcher von der Wolkenmenge, von der Höhe der Wolkenbasis und der Temperatur abhängt.Ein Test der Empfindlichkeit auf Störungen in den relevanten Parametern ist der Reaktion eines multispektraligen Strahlungsschemas sehr ähnlich, obwohl die Feuchtigkeitsabhängigkeit unter wolkenlosem Himmel als Schwachpunkt herausgefunden wurde. Ein Vergleich der Methode unter Verwendung beobachteter Inputparameter bei gleichzeitigen Messungen des DLF ergibt einen RMS-Fehler von 12.2 W/m².Diese Methode wird für die Kartierung des DLF über Westeuropa und dem Mittelmeer angewendet. Dazu werden Satellitenbilder von zwei Tagen um Mittag und zusätzliche Gitterpunktdaten, die während des ALPEX-Experiments gewonnen wurden, verwendet. Ein Vergleich mit Bodenmessungen von 4 Stationen in West-deutschland zeigt eine mittlere Abweichung von 3.9 W/m² und einen RMS-Fehler von 11.6 W/m². Diese Methode ist ein erster Versuch, den DLF im regionalen Bereich aus Satellitendaten des Wolkenfeldes und Gitterpunkt-Analysedaten des thermodynamischen Feldes zu schätzen.

---

---

With 10 Figures     

中国地球系统模式对全球地表入射短波辐射和大气逆辐射的模拟效果评估

以云和地球辐射能量系统(CERES)数据集为准,量化了中国地球系统模式对地表入射短波辐射和大气逆辐射时空变化的模拟性能,明确了多模式间模拟结果存在不确定性的区域。结果表明：中国模式均能模拟出北半球地表入射短波辐射和大气逆辐射“夏高冬低”的季节变化特征。陆地上,中国模式对两个辐射分量月均值的模拟结果与CERES相当,在海洋上低于CERES结果。中国模式能模拟出地表入射短波辐射下降、大气逆辐射上升的年际变化趋势。对于2001—2014年均值,中国模式模拟的地表入射短波辐射在海洋和陆地上较CERES分别偏低3.3和3.0 W·m^-2,模拟的大气逆辐射在海洋上与CERES结果相当,在陆地上较CERES低1.3 W·m^-2。除南北纬30°附近之外,中国模式在其他纬度均低估地表入射短波辐射,以热带和北极最为明显。模式对大气逆辐射的模拟偏差呈纬向波动特征,模拟误差大值出现在高大山脉处。中国模式模拟地表入射短波辐射不确定性极大的区域分布在热带雨林和南极洲沿海,模拟大气逆辐射不确定性极大的区域分布在格林兰岛、青藏高原、安第斯山脉和南极洲沿海。     

An improvement in cumulus parameterization by invoking outgoing longwave radiation

Summary The Kuo-type cumulus parameterization and rainfall rate scheme is extended by including the outgoing longwave radiation (OLR), the local time rate of change of OLR, and the horizontal Laplacian of OLR to include the additional source of mesoscale moisture supply. The extended scheme remains simple and efficient. A series of 5-day forecasts of the 1979 monsoon for the tropical belt between the Arabian Sea and the western Pacific Ocean show improvement in the 3-day forecast in the daily accumulated precipitation in both the amount and location. Further RMS error analyses indicate that using OLR and the Laplacian of OLR also produces a significant improvement in a 3-day forecast. Additional tests of the extended scheme for the 1987 and 1988 monsoons produced consistent and characteristic areal rainfall rates in the tropics. The improvement in the OLR model forecasts is attributed to the improved skill of OLR forecast in the forecast model as the RMS errors for 5 consecutive days in the 6 experimental forecasts are smaller than those of the 3 control forecasts.With 12 Figures     

Retrieval of outgoing longwave radiation from COMS narrowband infrared imagery

Hourly outgoing longwave radiation(OLR) from the geostationary satellite Communication Oceanography Meteorological Satellite(COMS) has been retrieved since June 2010. The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels. This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm(OLR12.0using the 12.0 μm channel) and three multiple-channel algorithms(OLR10.8+12.0using the 10.8 and 12.0 μm channels; OLR6.7+10.8using the 6.7 and 10.8 μm channels; and OLR All using the 6.7, 10.8, and 12.0 μm channels). The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth's Radiant Energy System(CERES) over the full COMS field of view [roughly(50°S–50°N, 70°–170°E)] during April 2011.Validation results show that the root-mean-square errors of COMS OLRs are 5–7 W m-2, which indicates good agreement with CERES OLR over the vast domain. OLR6.7+10.8and OLR All have much smaller errors(～ 6 W m-2) than OLR12.0and OLR10.8+12.0(～ 8 W m-2). Moreover, the small errors of OLR6.7+10.8and OLR All are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration. These results indicate a noteworthy role of the6.7 μm water vapor absorption channel in improving the accuracy of the OLRs. The dependence of the accuracy of COMS OLRs on various surface, atmospheric, and observational conditions is also discussed.     

中国东南地区复杂地形下降水概率预报的订正研究

使用TIGGE (the THORPEX interactive grand global ensemble)资料集下欧洲中期天气预报中心(the European Centre for Medium-Range Weather Forecasts, ECMWF)逐日起报的预报时效为24～168 h的日降水量集合预报资料,集合预报共包括51个成员,利用左删失的非齐次Logistic回归方法(left-Censored Non-homogeneous Logistic Regression, CNLR)和标准化的模式后处理方法(Standardized Anomaly Model Output Statistics, SAMOS)对具有复杂地形的中国东南部地区降水预报进行统计后处理。结果表明：采用CNLR方法能够有效改进原始集合预报的平均绝对误差(Mean Absolute Error, MAE)和连续分级概率评分(Continuous Ranked Probability Score, CRPS),提升了降水的定量预报和概率预报的预报技巧。而使用SAMOS方法对数据进行预处理,考虑地形...     

Modeling heavy precipitation in complex terrain

Summary A numerical prediction model is described which uses the full set of prognostic equations on a domain roughly the size of the United States with a 96 km horizontal grid resolution and six sigma-coordinate levels. Within this grid resides a nested domain of approximately 1000×1000 km with 24 km horizontal resolution. In this nested grid only modifications to the wind field by the better resolved terrain are considered on the lowest two sigma levels. The terrain effects necessitate adjustments in the location of these two sigma levels. Adjusted wind fields cause modifications in the mass and moisture divergence fields, hence in precipitation. These modifications are averaged into the appropriate meteorological fields on the larger grid.The algorithms used by our model allow continuous interaction between both grids with high computational efficiency.The relative importance of synoptic forcing and terrain is demonstrated for the cases of the Big Thompson, Colorado, flood of 1976 and the Cheyenne, Wyoming, flood of 1985.With 15 Figures     

The effect of cloud cover on surface net radiation: Simple formulae for use in mesoscale models

The effect of cloud cover on surface net radiation is parameterised into simple formulae, which have been fitted to calculated results from a detailed radiation model for various single-layer cloud types. The detailed model uses cloud optical depth information from satellite data analysis as input. The formulae use functional forms based on some of those reported in the literature. The proposed formulae have been shown to compare well to results from the detailed model for various combinations of cloud at different height levels in the atmosphere. By analysis of optical depth variations throughout the world, the proposed formulae have been shown to be valid for any location, except perhaps near the poles.     

应用HIRS/2仪器资料计算长波辐射通量

辐射收支是影响气候演变的基本因素,而长波辐射通量又是辐射收支的重要组成。由于地气系统红外辐射过程的复杂性,如何利用NOAA系列气象卫星资料精确快速地估计长波辐射通量,迄今还存在问题。本文从遥感方程出发,建立了卫星测得辐射率值和(HIRS/2测得)长波辐射通量的准解析函数关系。利用这种准解析函数和精选的NOAA-10 HIRS/2五个通道辐射率测值,提出了精确快速计算长波辐射通量的方法,并得到验证。     

复杂山地近地层强风特性分析

利用在贵州省西南部复杂山地上获取的近地层梯度风观测资料和三维超声测风仪观测资料,从中筛选出具有该地气候特征的强风样本,利用数量统计和谱分析等方法,计算分析了由于复杂地形影响而导致的局地低层强风的平均和脉动特征.平均风场主要表现在受当地主要特征地形(西北-东南走向的深切峡谷)影响,其全年的主导风向和最大风速出现的方向几乎完全转为沿峡谷走向,即使在符合中性大气层结条件下,风的垂直廓线也完全不满足幂指数分布,风攻角远远大于规范推荐的值,并且不同风向的强风攻角因地形影响其差异可达20°;强风条件下脉动风场的主要特征是:不同风向强风的湍流强度有所不同,在纵、横和垂直方向的湍流强度比值与现行设计规范给出的三维湍流强度比值有明显差异,其中垂直方向的湍流强度显著偏大是突出特征;湍流积分尺度偏大,其中纵向值偏大20%-60%,横向值在某些风向上可偏大3倍以上,垂直方向则普遍较平坦地形偏大一个量级左右;在桥梁结构较为敏感的频域范围内,各风向的湍流谱密度值有显著差异,其中不同风向在纵向上最大差值可达8倍,横向和垂直向可相差6倍,但无论哪个方向的湍流谱密度值均比台风中心要小1-2个量级.