区域GPS气象网站点合理布设的几点依据

区域GPS气象网反演的可降水量资料（GPS／PWV）对提高灾害性天气的监测和预报能力，改进数值天气预报精度已显示出广阔的应用前景，我国许多省市相继计划建设区域的GPS气象网。在区域GPS气象网中如何科学合理地布设GPS站就成了大家关注的问题。结合长江三角洲地区GPS气象网的情况，从长江三角洲地区的水汽通道，PWV分布的气候统计、GPS反演PWV资料的有效半径和在数值天气预报中资料同化的最大影响半径等4个方面，讨论了区域GPS网站点的分布和间距的几点依据：重点沿区域的水汽通道和强对流天气主要路径上布站，经向（南北向）的站点密度应大于纬向密度，站点的最大间距小于60km才能使反演的PwV的有效代表性和对数值预报的影响覆盖整个区域。 距     

GPS-derived precipitable water vapour and its comparison with MODIS data for Almora, Central Himalaya, India

The present study is an attempt to analyse the precipitable water vapour (PWV) derived from Global Positioning System (GPS) and observed meteorological data over Almora, Central Himalayan Region. The PWV values derived using GPS study is compared with the corresponding moderate resolution imaging spectro-radiometer (MODIS) data. The statistical analysis reveals a positive correlation between both methods. Moderate resolution imaging spectroradiometer near-infrared (MODIS NIR) clear column water vapour product shows a higher correlation (R ² = 90–93 %) with GPS-derived precipitable water vapour on annual scale as compared to the seasonal scale (R ² = 62–87 %). MODIS is found to be overestimating in NIR clear column where the magnitude of bias and RMSE show systematic changes from season to season. Monsoon is an important phenomenon in the Indian weather context and holds significant importance in Central Himalayan ecosystem. The monthly and seasonal variation in precipitable water vapour is related with monsoon onset in the region. Diurnal variations in precipitable water vapour are studied with other meteorological data over Almora during dry and wet season. The precipitable water vapour had minimum value in the morning, increases in the afternoon to evening and again decreases to the midnight in both the dry and wet seasons. These results suggest that diurnal variation of water vapour is caused by the transport of water vapour by thermally induced local circulation.     

Observed changes in relative humidity and dew point temperature in coastal regions of Iran

The analysis of trends in hydroclimatic parameters and assessment of their statistical significance have recently received a great concern to clarify whether or not there is an obvious climate change. In the current study, parametric linear regression and nonparametric Mann?CKendall tests were applied for detecting annual and seasonal trends in the relative humidity (RH) and dew point temperature (T _dew) time series at ten coastal weather stations in Iran during 1966?C2005. The serial structure of the data was considered, and the significant serial correlations were eliminated using the trend-free pre-whitening method. The results showed that annual RH increased by 1.03 and 0.28?%/decade at the northern and southern coastal regions of the country, respectively, while annual T _dew increased by 0.29 and 0.15°C per decade at the northern and southern regions, respectively. The significant trends were frequent in the T _dew series, but they were observed only at 2 out of the 50 RH series. The results showed that the difference between the results of the parametric and nonparametric tests was small, although the parametric test detected larger significant trends in the RH and T _dew time series. Furthermore, the differences between the results of the trend tests were not related to the normality of the statistical distribution.     

Multifractal analysis of 1-min summer rainfall time series from a monsoonal watershed in eastern China

Multifractal analysis can provide parameters associated with different scales of rainfall, which may be useful for setting up parsimonious downscaling models of rainfall, or for revealing climate-specific properties. Time series of rain rate with 1-min resolution collected from ten stations over a monsoon watershed in eastern China were used to study the multifractal properties. The power spectra estimated by fast Fourier transform (FFT) and discrete Haar wavelet transform (DWT) showed three scaling regimes: the sub-hourly scaling regime with β?≈?1.2, the scaling regime from 1 h to 1 day with β close to 0.6, and the low-frequency spectra plateau with β?≈?0.1. From the hyperbolic tails of exceeding probability distributions, the estimated values of parameter q _c are in 2–2.5, which were consistent with the critical order of K(q) curves. The statistical moments display two main scaling regimes: the high-frequency regime from 3 min to 5 days and the scaling regime beyond 5 days. The scales of 5–10 days seem a transitional regime. The reason that the regimes, revealed by the power spectra, disagree with the statistical moments may be that both FFT and DWT power spectra have limited abilities of analyzing low-frequency scaling but are sensitive to the properties in high-frequency scales. The H values estimated for the regime of sub-hourly scales are larger than 0.4, and the values for the regime 1 h–1 day are close to 0.1. For the low-frequency scales beyond 1 day, negative H is obtained by DWT power spectra. The parameters of universal multifractal models were also estimated. The values of α for the scaling range of 1 min–5 days are 0.486?±?0.047, and for the low-frequency scaling range, its values are 0.808?±?0.323. For the high- and low-frequency scaling ranges, the values of C ₁ are 0.5 and 0.169, respectively, which is different from the values for daily rainfall series collected at the same rain gages.     

轨道误差对近实时GPS遥感水汽的影响研究

利用GPS技术近实时探测水汽对于气象预报、气候研究具有重要的应用价值，而近实时探测需要使用GPS卫星的预报星历，预报星历的误差会直接影响到实时水汽探测的精度。利用从IGS资料处理中心下载的精密预报星历和最终星历，对2000年北京GPS水汽试验中的资料进行了解算，并结合探空资料计算的水汽进行了分析。结果表明：以探空为标准，使用精密预报星历计算的水汽总量均方根误差为0．31cm，最终星历为0．30cm，二者差别不大，为0．01cm，证明使用精密预报星历可以满足近实时探测水汽的要求。     

华北一次强降水过程的分阶段对比分析

利用GPS可降水量、多普勒天气雷达和地面加密自动站等高时空分辨率资料,对2011年6月23-24日发生在京津冀的强降水天气过程的不同阶段进行了对比分析.结果表明:(1)第一阶段降水为时间短、强度大的积状云对流降水;GPS可降水量的峰值与强降水对应,在降水之前6h左右会有GPS可降水量峰值出现;在空间分布上,高值中心的演变表现为东移南压趋势.(2)第二阶段降水表现为持续时间较长的系统性降水;雷达回波以大面积层状云降水回波为主;此阶段的GPS可降水量长时间维持在高值阶段,空间分布上GPS可降水量等值线“南高北低”并逐渐南压,西部GPS可降水量明显偏高.(3)在液态水与气态水对比上,雷达VIL随时间的变化不连续,而GPS可降水量表现为连续性演变,二者的峰值或高值对应较好,二者均可反映降水出现时间和降水性质,其中雷达VIL大值与降水出现时段吻合得好,而GPS可降水量的大小和演变趋势可以提前预示降水的出现时间和降水性质,对降水天气预报有指示意义.     

地基GPS/PWV在降水过程中的突变与缓变性特征

用江苏省2009-2011年57个地基GPS/MET监测网获取的逐时大气可降水量(PWV)和同期降水及JMA(Japan Meteorological Agency)再分析资料,探讨了PWV的日际和逐时变化与不同时间尺度和强度的降水间的关系。结果表明:PWV日际变化与降水日变化具有显著相似的形态特征和演变趋势,两者存在较为一致的同步性,总体呈单峰分布,强降水集中期对应着PWV最大时段;PWV在入梅和梅汛期内强降水过程中存在明显突变现象,并提炼了以GPS/PWV突变事件为依据的入梅和梅雨期暴雨预报指标;在不同强度的降水过程中,PWV值域局限在一个特定量值区间,其中20 mm/h以下各级强度降水对应PWV区别明显,GPS/PWV值对应的特定量值随降水强度增大而增大,但20 mm/h以上的各级强降水对应PWV特定量值区别较小;在短时强降水的预报中,除充分的水汽条件外,其强度将取决于天气系统对周边水汽的辐合能力和将入流水汽抬升而成云致雨的动力条件;降水发生前存在水汽的连续、缓变蓄积过程,蓄积过程至少可推前12 h。     

GPS遥感大气可降水量在暴雨天气过程分析中的应用

利用北京市气象局地基GPS监测试验网遥感大气可降水量（PWV）数据，分析2004年汛期暴雨天气过程PWV的变化特征及其与降雨量、降雨强度的关系；通过分析地面、高空的位势高度场、风场，以及比湿外水汽通量Q及水汽通量散度AQ等物理量诊断场分布，研究天气系统与大尺度水汽输送、辐合的关系，大尺度水汽输送、辐合与PWV变化的关系；探讨GPS遥感大气水汽资料在预报强降雨天气过程中的应用。得出：PWV的增长方式受当地天气系统的支配和制约，对于明显降雨过程，当地面、高空天气系统有利于暖湿空气的输送时，在北京附近形成等湿度线密集区，PWV逐渐增长（降雨开始前的13-24h）的趋势；当地面、高空有辐合系统东移或生成，或有中小尺度天气系统影响时，PWV显著增长（降雨开始前的3～4h）；当PWV大于某阈值后出现较强降雨，PWV值及增量的大小与降雨量的大小没有明显的关系。     

Evaluating persistence and identifying trends and abrupt changes in monthly and annual rainfalls of a semi-arid region in Western India

In this study, 43-year (1965–2007) monthly and annual rainfall time series of ten rainfall stations in a semi-arid region of western India are analyzed by adopting three tests for testing normality and by applying autoregressive technique for exploring persistence. Gradual trends are identified by three tests, and their magnitudes are assessed by the Sen’s slope estimator. Also, abrupt changes are detected by using four tests and they are further confirmed by two tests. Box-whisker plots revealed that the rainfalls of June and September are right skewed for all the stations. The annual rainfalls of Bhinder, Dhariawad, and Gogunda stations are found considerably right skewed. The normality tests indicated that the rainfall of July does not deviate from the normal distribution at all the stations. However, the annual rainfall is found non-normal at five stations. The monthly rainfalls of June, July, and August have persistence respectively at three (Mavli, Salumber, and Sarada), two (Kherwara and Sarada), and one (Mavli) stations, whereas the annual rainfall has persistence at Girwa and Mavli stations. Significantly increasing trend is detected at Mavli in the rainfall of July and in the annual rainfall (p value?>?0.05), while the negative trend in August rainfall at Dhariawad is found significant (p value?>?0.10). This study revealed that the presence of serial correlation does not affect the performance of the Mann-Kendall test. Mean values of trend magnitudes for the rainfalls of June, July, August, and September are 0.3, 0.8, ?0.4, and 0.4 mm year^?1, respectively, and the overall mean value for the annual rainfall is 0.9 mm year^?1. It is found that the standard normal homogeneity test and the Pettitt test are biased towards the end of the series to locate a change point. Conversely, the Bayesian test has a tendency to look for a change point in the beginning of time series. Confirmed abrupt changes in the rainfall time series are found in the year 2003 (Bhinder) in June; years 1974 (Mavli) and 1989 (Dhariawad and Salumber) in July; years 1972 (Sarada), 1990 (Dhariawad), and 2003 (Mavli) in August; years 1977 (Dhariawad), 1991 (Sarada), and 2004 (Kotra) in September; and in the year 1972 (Mavli and Sarada stations) in the annual series. It is emphasized that the significantly increasing trend of rainfall may have linkages with climate change and/or variability. Finally, this study recommends use of multiple statistical tests for analyzing hydrologic time series in order to ensure reliable decisions.     

Modeling monthly mean air temperature for Brazil

Air temperature is one of the main weather variables influencing agriculture around the world. Its availability, however, is a concern, mainly in Brazil where the weather stations are more concentrated on the coastal regions of the country. Therefore, the present study had as an objective to develop models for estimating monthly and annual mean air temperature for the Brazilian territory using multiple regression and geographic information system techniques. Temperature data from 2,400 stations distributed across the Brazilian territory were used, 1,800 to develop the equations and 600 for validating them, as well as their geographical coordinates and altitude as independent variables for the models. A total of 39 models were developed, relating the dependent variables maximum, mean, and minimum air temperatures (monthly and annual) to the independent variables latitude, longitude, altitude, and their combinations. All regression models were statistically significant (α?≤?0.01). The monthly and annual temperature models presented determination coefficients between 0.54 and 0.96. We obtained an overall spatial correlation higher than 0.9 between the models proposed and the 16 major models already published for some Brazilian regions, considering a total of 3.67?×?10⁸?pixels evaluated. Our national temperature models are recommended to predict air temperature in all Brazilian territories.     

云南地基GPS观测大气可降水量变化特征

利用2007年云南地基GPS站点观测资料,分析GPS反演的大气可降水量(PWV)变化特征,并用探空、实际降水量资料和GPS反演结果进行比较。结果表明:GPS/PWV能反映云南降水的季节变化特征,海拔较低的测站普遍比同期海拔较高的测站测得的GPS/PWV值高;GPS/PWV值与探空得到的大气水汽总量随时间演变趋势基本一致,其相关系数均达0.89;GPS/PWV变化周期和实际降水发生的周期基本相同,降水大多为GPS/PWV值连续增加达到峰值(或从峰值开始下降)后开始;GPS/PWV上升幅度较大或位于高位可作为连续性强降水过程出现的预报指标,但使用GPS/PWV峰值作预报指标时,还应考虑季节因素。     

华西秋雨天气过程中GPS遥感水汽总量演变特征

利用成都地区地基GPS观测网2007年9-11月的观测数据, 结合自动气象站资料计算出30 min间隔GPS遥感的大气水汽总量(GPS-PWV)。将成都地区秋季降雨分为阵性降雨和连续性降雨(秋绵雨), 结合其他气象要素资料, 分析了GPS-PWV变化与成都秋雨之间的关系。结果表明:高值的水汽总量是产生降水的必要条件; 不同的降水过程, GPS-PWV的变化幅度、极值水平和持续时间存在明显差异。水汽的增长、上升运动的增强和温度的减少是造成阵性降水的主要原因; 而秋绵雨过程中, 水汽的增长和地面露点温度差与降水过程有较好的对应关系。     

Long-term changes in heat and moisture related to corn production on the Canadian Prairies

Long-term (approximately 80?years) daily climate records at 12 weather stations across the agricultural production region of the Canadian Prairies were assessed to evaluate trends in seasonal heat units and moisture characteristics for corn (Zea mays). Crop water demand (CWD) and crop water deficit were modelled at each station. Growing season accumulation of these as well as corn heat units (CHU) and rainfall were tested for long-term trends using linear regression. Significant positive trends in CHU were present in the southernmost stations while the northern stations displayed no trend or significant negative trends. Growing season precipitation showed a significant increase on average and most stations showed a positive trend but only one station showed a significant positive trend. CWD declined at most stations with significant negative trends at seven stations. Crop water deficient also declined with significant negative trends at six stations. The spatial variation in these results and those reported in other studies in the region underscores the difficulty involved in forecasting future trends in agroclimatic conditions.     

Detection of a katabatic wind event with GPS meteorology measurements at Scott Base Antarctica

A katabatic wind event which dramatically affects the polar climate has been detected using GPS meteorology measurements. GPS-derived precipitable water vapor (GPS PWV) variability and its relation to a katabatic event at Scott Base station, Antarctica was investigated. The investigations using the data gathered from 21 to 30 November of 2002. They showed that the water vapor profile exhibited an irregular pattern with a maximum PWV of 7.38?mm (~6?mm on average). This event was strongly influenced by relative humidity than by wind speed activity. The dominant wind flow during this period was from the North to Northeast (blowing from the Ross Sea) with a mean speed of 3.79?ms^?1. The PWV increased when the temperature was between ?15 and ?11°C. During the katabatic event identified between 21:30 UT of 28 November and 18:40 UT on 29 November, the wind blew from the Southeast to South direction (from the Ross Ice Shelf) with a maximum speed of 10.92?ms^?1. The PWV increased ~1.0?mm (23%) from the mean value accompanied by severe wind had pronounced effect on GPS observations.     

A composite analysis of diurnal cycle of GPS precipitable water vapor in central Japan during Calm Summer Days

Summary The diurnal variations of water vapor in central Japan were investigated with GPS-derived precipitable water (PWV) and surface meteorological data as classified to three kinds of locations. Twenty-five clear days in central Japan in August 2000 were investigated to clarify the role of water vapor in the nocturnal maximum in the diurnal cycle of convective rainfall. The diurnal variations of PWV and some meteorological factors were composite during the selected days at 6 stations. The PWV shows a clear diurnal cycle with the amplitude of 3.4 mm to 8.8 mm and changes little during the period from the morning to noon. The daily amplitude of PWV is the largest in basin and smallest in plain although mean of PWV keeps high value in plain. A typical feature of the diurnal variation in central Japan is a maximum appearing in the evening. The time of maximum is from 1800 LST to 2000 LST, and minima appears at noon nearly in mountainous area and basin, while in early morning in plain. The diurnal maximum of PWV appears earlier in mountainous region than in plain. A diurnal cycle of specific humidity can be observed in all locations, and the amplitude in mountainous region is especially large compared with that in basin and plain. It is important to notice that there are remarkable differences in specific humidity among the six stations. The results suggest that the diurnal variation of PWV seems to be strongly affected by the local thermal circulations generated by the topography around these stations. The moisture transport causes the differences in phase of the diurnal cycle of PWV between different locations as well as the phase difference in precipitation. A very clear diurnal variation in surface air temperature is similar to that of solar radiation, with a minimum in the morning and a maximum in early afternoon. Maximum of surface wind speed are corresponded to peak of precipitation very well. It can be concluded that the amplitude of solar radiation increases with altitude as opposed to the situation of PWV generally. The precipitation observed frequently in the evening also shows a similar diurnal variation to that of the PWV, indicating the peak of precipitation appearing in late afternoon or in the evening over central Japan. Meanwhile the PWV reaches its nocturnal maximum. There is a good relationship between the diurnal cycle of observed precipitation and that of the PWV. Authors’ addressess: Guoping Li, Department of Atmospheric Sciences, Chengdu University of Information Technology, #3 Section 3, Ren Min Nan Road, Chengdu, Sichuan 610041, P.R. China; Dingfa Huang, Department of Surveying Engineering, Southwest Jiaotong University, Chengdu, China; Fujio Kimura, Tomonori Sato, Institute of Geoscience, University of Tsukuba, Tsukuba, Japan.     

GPS遥感大气可降水量在大连地区3次降水过程中的应用

利用大连市气象局地基GPS/MET观测网大气可降水量（PWV）数据,分析2011年大连瓦房店、庄河和长海地区降水天气过程PWV的变化特征及其与降水量和降水强度的关系,在此基础上通过分析物理量场和天气系统,探讨大尺度水汽输送、辐合与PWV变化的关系及GPS在暴雨天气中的应用。结果表明：PWV的增长方式受当地天气系统的支配和制约,对一次明显的降水过程,从开始至结束PWV的变化与降水量有明显的相关性。当有水汽由南向北输送时,PWV在降水开始前逐渐增长,当地面及高空有大范围的水汽辐合且高空比湿值大于10 g·kg^-1时,PWV显著增长（降水开始前4-5 h）,主要降水时段与PWV峰值相对应,同时PWV的增幅大小与降水强度有明显的关系。     

Effects of climate change on annual streamflow using climate elasticity in Poyang Lake Basin, China

Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration (PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year^?1, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1–16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by ?10.2 to ?2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed.     

Precipitable water vapor estimation in India from GPS-derived zenith delays using radiosonde data

One of the most recent applications of global positioning system (GPS) is the estimation of precipitable water vapor (PWV). It requires proper modeling to extract PWV from zenith wet delay (ZWD). The existing global models take no account of latitudinal and seasonal variation of meteorological parameters in the atmosphere. In fact, they ignore the atmospheric conditions at a specific location. Therefore, site-specific PWV models have been developed for five stations spread over the Indian subcontinent, using 3-year (2006–2008) radiosonde data from each of these stations. Furthermore, a similar regional PWV model is also developed for the Indian region. The purpose of the developed site-specific as well as regional model was to convert ZWDs into PWV without using surface meteorological parameters. It has been found that the developed regional and site-specific PWV models show about mm-level accuracy in estimating PWV using derived ZWD from radiosonde as input. The developed site-specific, regional models were also used to extract PWV from GPS-derived ZWD at Bangalore and New Delhi. The accuracy of the developed site-specific and regional model is of the same level. The PWV accuracy obtained with the developed regional model is about 6.28, 6.6 mm in comparison to radiosonde PWV at Bangalore and New Delhi, respectively.     

南四湖湖面大风预警系统的应用

为弥补采用传统预报方法漏报由中小尺度天气系统所产生的南四湖湖面大风的缺陷,充分利用南四湖周围加密自动气象观测站和常规地面自动气象观测站10 min加密观测资料,采用资料实时提取分析、绘制彩色等值线图、图像发布到网站、满足大风预设条件时声音报警等方法,实现了对南四湖周围大风分布进行实时监控,进一步提高湖面大风精细化预报预警准确率。试用表明,该系统人机界面好,移植性强,运行稳定,漏报率低,可在短时临近大风预警预报中发挥作用。     

Indirect determination of broadband turbidity coefficients over Egypt

Long-term data from diffuse and global irradiances were used to calculate direct beam irradiance which was used to determine three atmospheric turbidity coefficients (Linke T _L , Ångström β and Unsworth–Monteith δ _a ) at seven sites in Egypt in the period from 1981 to 2000. Seven study sites (Barrani, Matruh, Arish, Cairo, Asyut, Aswan and Kharga) have been divided into three categories: Mediterranean climate (MC), desert Nile climate (DNC) and urban climate (UC, Cairo). The indirect method (i.e., global irradiance minus diffuse irradiance) used here allows to estimate the turbidity coefficients with an RMSE% ≤20 % (for β, δ _a and T _L ) and ~30 % (for β) if compared with those estimated by direct beam irradiance and sunphotometeric data, respectively. Monthly averages of T _L , β and δ _a show seasonal variations with mainly maxima in spring at all stations, due to Khamsin depressions coming from Sahara. Secondary maxima is observed in summer and autumn at DNC and MC (Barrani and Arish) stations in summer due to dust haze which prevails during that season and at UC (Cairo) in autumn, due to the northern extension of the Sudan monsoon trough, which is accompanied by small-scale depressions with dust particles. The mean annual values of β, δ _a , and T _L (0.216, 0.314, and 4.6, respectively) are larger in Cairo than at MC stations (0.146, 0.216, and 3.8, respectively) and DNC stations (0.153, 0.227, and 3.8, respectively). Both El-Chichon and Mt. Pinatubo eruptions were examined for all records data at MC, UC and DNC stations. The overburden caused by Mt. Pinatubo’s eruption was larger than El-Chichon’s eruption and overburden for β, and T _L at DNC stations (0.06, and 0.58 units, respectively) was more pronounced than that at MC (0.02, and 0.26, respectively) and UC (0.05 and 0.52 units, respectively) stations. The annual variations in wind speed and turbidity parameters show high values for both low and high wind speed at all stations. The wind directions have a clear effect on atmospheric turbidity, and consequently, largest turbidities occur when the wind carries aerosols from the main particle sources, such as industrial particle sources around Cairo or to some extent from the Sahara surrounding all study stations.