A high-quality monthly pan evaporation dataset for Australia

A high-quality monthly pan evaporation dataset of 60 stations has been developed for monitoring long-term pan evaporation trends over Australia. The quality control process involved examination of historical station metadata together with an objective test comparing candidate series with neighboring stations. Identified points of discontinuity were located, including installations of bird guards, site relocations and changes in exposure. Appropriate inhomogeneity adjustments have been applied using established methods to produce the first homogeneous pan evaporation dataset for Australia. Analysis of these data reveals that Australian annual mean pan-evaporation shows large interannual variability with no trend over the 1970–2005 period. Previous studies using unadjusted data have shown a decline in pan evaporation, highlighting the importance of checking data for homogeneity before drawing conclusions about long-term trends. A strong inverse correlation is evident between all-Australian means of pan evaporation and rainfall, while a moderate positive correlation is found between pan evaporation and mean temperature. The positive correlations between mean temperature and pan evaporation that exist on the interannual time scales are not reflected in the long-term trends, highlighting that the mechanisms that are responsible for variations on the short and longer time scales are different. This result cautions against the expectation that large changes in potential evaporation are a natural consequence of global warming.     

Comparison of satellite and ship observations for total cloud amount

The data series of monthly clouldiness over global ocean from COADS was compared with that of from satellite Nimbus-7 during April 1979 to March 1985. The correspondence between them is good. Both the two methods of observation can provide useful information of the distribution of cloudiness and the two data sets can be mutually complementary.     

A seasonal scale analysis correlating total cloud amount anomalies with ENSO over the tropical Pacific

The seasonal patterns of total cloud amount (TCA) responsible for El Ni?o/La Ni?a-Southern Oscillation (ENSO) Sea Surface Temperature (SST) anomalies were investigated using the ISCCP-D2 cloud and NOAA OI.v2 SST datasets for the period of July 1983 to June 2008. The results show three main ENSO-sensitive regions obtained by spatial overlapping of seasonal correlations, two in the western tropical Pacific and one in the central tropical Pacific. These regions were named WTP1, WTP2, and CTP. In all three regions, except the JJA (June?CAugust) WTP2, the TCA changes were significantly correlated with the Ni?o 3.4 anomalies during the four seasons (December?CJanuary?CFebruary (DJF), March?CApril?CMay, JJA, and September?COctober?CNovember (SON)). Remarkable differences in the seasonal variability of TCA were observed in these regions. In the WTP1, the DJF TCA always remained the highest value among the four seasons in all years. In the WTP2, the maximum TCA occurred during JJA in most years. In the CTP, the extreme value of TCA was mainly observed in DJF or SON near the peak time of ENSO. Seasonal cross-correlation analyses also showed significant relations between TCA and Ni?o 3.4 SST in these regions, which may be helpful for forecasting the evolution of ENSO.     

Estimation of monthly sums of total solar radiation at snow-free surface from cloud observations

An empirical formula is proposed for calculating monthly sums of total solar radiation at the snow-free surface from cloud observations and empirical parameters characterizing the optical properties of different cloud layers.     

全球地面降水月值历史数据集研制

全球降水历史数据是开展气候、水循环等研究的基础。收集整理全球12个数据源降水历史月值资料,通过站号、站名甄别不同数据源中相同台站,对344个通过相关系数、一致率、均值t检验、方差F检验的台站多源资料进行拼接,尽可能多地融合各套数据产品优势,最终形成全球降水历史月值数据集(CMA Global PrecipitationV1.0, CGP)。数据集重点解决当前国际数据产品在东亚地区站点稀少、同时应用多套数据应用门槛较高等问题。数据集收录3.1万个台站共计1.87×107组月降水记录, 4152个台站序列长度达百年。与美国大气海洋局(NOAA)的全球降水数据集(GHCN-M V2.0)对比,CGP新增1万个站点、0.5×107组有效观测记录和1030条百年序列,其中141条百年序列通过多源整合技术获取。CGP的站点和数据量优势主要体现在东亚、东欧、西伯利亚等站点稀疏地区。基于CGP分析的全球降水时空特征与国际同类产品的结果较一致。新增的数据虽然没有改变全球降水分布的总体特征,但对区域性的百年降水变化检测有一定影响。基于CGP的全球降水百年序列结果显示,20世纪前半叶全球降水量偏小,近20年是1900年以来全球降水量最大的时期,各纬度带、各个国家或地区的降水长期变化趋势呈现显著的差异。      

A comparison of MODIS-derived cloud amount with visual surface observations

Two main sources for global cloud climatologies are visual surface observations and observations made by spaceborne sensors. Satellite observations compared with surface data show in most cases differences ranging from − 15% up to − 1%, depending on sensor and observation conditions. These differences are partially controlled by sensors' cloud detection capabilities — a higher number of spectral bands and higher spatial resolution are believed to allow discrimination of clouds from land/ocean/snow background. A Moderate-Resolution Imaging Spectroradiometer (MODIS) produces images of the atmosphere in 36 spectral bands with a spatial resolution of 250–1000 m, thus having a capacity for cloud detection far more advanced than other operating sensors. In this study, instantaneous MODIS cloud observations were compared with surface data for Poland for January (winter) and July (summer) 2004. It was found that MODIS observed 4.38% greater cloud amount in summer conditions and 7.28% in winter conditions. Differences were greater at night (7–8%) than in daytime (0.5–7%) and correlations ranged between 0.577 (winter night) and 0.843 (winter day, summer day and night).     

Gaussian components of cloud amount frequency distributions

Summary Interannual variability of meteorological conditions produces cloud amount sequences that statistically cannot be regarded as samples from the same population. Consequently in order to treat cloud amount distributions the traditional methods of mathematical statistics are useless. In this paper a method is presented that enables to approximate the cloud amount histograms by means of mixtures of Gaussian components. When a component can be found that is common to the histograms of different years, it may be regarded as a characteristic of a quasistationary cloudiness regime that is induced by stable meteorological conditions above the respective target area during the given period.The procedure to separate a cloud amount frequency distribution into Gaussian components is demonstrated on the basis of an example of March–May cloudiness analysis in the mid-ocean regions of the belt 0°–13.5° S. The monthly mean cloud amount data in the (500 km)² squares have been determined from Nimbus-7 short-wave albedo measurements in 1979–1986. It has been demonstrated that even in the years that are not affected by the El Niño event the interannual variability of the autumn cloud amount histograms is essential at the 95% significance level. But separating the frequency distributions into Gaussian components, a part can be found that is common to all the autumns and, thus, may be regarded as a characteristic of the contemporary climate.With 6 Figures     

用卫星资料反演臭氧总含量的初步试验

本文介绍了一个用TIROS—N/NOAA卫星携带的高分辨率红外辐射探测器-2型(简称HIRS/2)测量的辐射值计算臭氧总含量的物理模式.根据该物理模式我们得到了中国上空的臭氧总含量分布图.文中给出了实时卫星资料反演的臭氧总含量与北京、昆明两站的常规探测臭氧总含量的分析比较.比较结果表明:反演的臭氧总含量精度可优于3％.文中还揭示:臭氧总含量的低值和高值区通常分别与500hPa高度场的高压中心和低压中心相对应.     

Assessment of GEWEX/SRB version 3.0 monthly global radiation dataset over China

NASA/GEWEX (National Aeronautics and Space Administration/Global Energy and Water Cycle Experiment) Surface Radiation Budget (SRB) has released its latest radiation dataset, version 3.0. We examine the accuracy of the monthly mean global radiation in China using surface-observed radiation (SOR) data at 42 stations during the period 1984?C2004. Overall comparison shows a general overestimation of satellite retrieval radiation data with a bias of 14.6?W?m^?2 and a root mean square error of 25.9?W?m^?2. Differences at individual stations suggested satellite data are consistently higher than surface measurements over eastern China (110°E), but occasional underestimation occurs in Western China, especially Southwest China. Intra-annual variation analysis indicates that SRB satellite radiation can capture the annual cycle well. For trend of global radiations, there are evident discrepancies between satellite retrievals and surface measurements for both the entire period and segmental terms. For the entire period from 1984 to 2004, most stations show a positive trend based on surface measurements, while the majority of collocated pixels show a negative trend. Segmental trends demonstrated that the principal difference occurred during the first period of 1981?C1994. After 1994, the two datasets change similarly. Therefore, trend analysis in terms of detecting global dimming/brightening remains very difficult as surface measurements and satellite products do not agree yet. In addition, some proposals are made towards better understanding of the bias of satellite products and to improve further the satellite retrieval algorithm with better representation of both cloud and aerosol properties.     

Simultaneous statistical modeling of monthly precipitation amount at several observational points

Demonstrated is the possibility of the group modeling of the series of monthly precipitation amount using the method of canonical expansion. Used are the algorithms and software computing programs developed as applied to the statistical models of the monthly and annual river runoff. The model of canonical expansion preserves all statistical characteristics of initial series.     

降水时间随机性对月总降水量的影响

降水量在时间分布上呈现较大的随机性,极端降水事件尤为如此。受此影响,月初(月末) 1～5 d之内的累积降水量很可能会超过当月总降水量的50%乃至更多。对1961—2017年中国2 400多站点资料统计分析结果发现,月初(月末) 1～5 d累积降水量对当月总降水量显著影响事件的出现频次,在季节和空间分布上都有鲜明特征。主要包括:1)月初累积降水量对秋冬季中各月的总降水量影响更大,月末累积降水量对1—4月的月总降水量影响较大。2)受月初累积降水量的影响,显著站点数在某些年份的某些月份出现极大值;受单次事件显著影响的站点数占全国总站点数的30%～50%,此即对应着一次全国大范围的极端降水事件。3)受月初(月末)累积降水量显著影响的站点空间分布随季节变化呈现出明显空间集聚特征。     

层状云增雨催化剂用量的估算

通过人工影响天气原理的分析,从过冷水量的平衡关系．分析了作业时机与部位;从过冷水量、冰面与水面饱和水汽密度差、固相雨胚、催化剂扩散等方面,在国内外的观测事实与数值模拟结果的基础上,估算了催化剂的用量与播撒速率,对实际工作有一定的参考意义。但是,所得的结果是初步的．还存在许多方面的不确定性,有待进一步完善。     

On the relation between cloud cover amount and sunshine duration

Summary The total cloud cover is deduced from measurements of monthly mean averages of the percent of possible sunshine duration at three locations in Egypt, Cairo, Bahtim and Sedi-Barrani stations during the period 1987–1995. This sunshine-derived total cloud cover (C_s) is compared to conventional ground-based observations of total cloud covers (C_g) made by meteorological observers. A linear relationship between the two estimates is calculated, and the difference between the two estimates as a function of C_s and C_g is fitted with a least-squares linear equation. It is found that on the average the sunshine-derived values of total cloud cover are about 7% lower than the corresponding ground-based estimated of total cloud cover. Both of these parameters are mainly used in solar radiation models and the error sources are mainly depending upon the way to describe sky cover.     

基于FY-2G产品的江西省总云量最小二乘法建模与分析

使用2016年1月至2018年12月FY-2G卫星逐小时总云量产品和江西省26个测站的地面总云量观测资料,分析了两者在江西地区相关性的时空分布特征。结果表明:江西地区卫星总云量和地面观测总云量在数值和演变趋势上一致性较好,两者的总体相关系数超过0.60,但空间分布不均匀,大型水体(鄱阳湖和柘林湖)附近相关系数较低,低于0.45,江西省南部地区相关系数也不高,低于0.50。两者的相关系数在时间上也分布不均,其中14时的相关系数最高。此外,基于FY-2G卫星总云量产品和最小二乘法采用分段建模的方式,构建了江西省地面观测云的回归模型,且模拟的地面总云量在数值和演变趋势上更加接近观测的地面云量。     

关于帕斯奎尔稳定度类别的云量判别及入射太阳辐射量判别方法的研究

本文给出了有云天空入射太阳辐射量计算式,将Pasquill稳定度类别的Turner(或Gordon)判别法与Smith判别法直接联系了起来。说明按有效云量即总云量与低云量之和的一半所判别的太阳辐射强度指数,将使Turner方法更简单、准确。     

南海及周边地区云量分布及低云量与南海海温的关系

利用国际卫星云气候计划提供的月平均云气候资料集,分析了南海及周边地区云量的分布特征,并进一步研究了低云量与南海海温的关系。结果表明:(1)南海及周边地区总云量分布存在显著的季节性差异特征。(2)低云主要分布在南海海区,中云为华南地区,而高云则主要位于靠近赤道区域。(3)低云受海表温度影响较大,而中高云则主要与强对流相对应。低云主要分布于南海海表冷水中心南侧的暖水区内的温度梯度区,其高值区分布与海表温度梯度分布基本一致,海表温度梯度的大小与高值中心的低云量成正比。(4)低云量高值中心位置与水平海温梯度区两侧基本一致,高温暖水受西边界强迫上升在海表层辐合,有利于低云的生成。