共查询到20条相似文献，搜索用时 31 毫秒
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N. R. Dalezios M. V. Sioutas T. S. Karacostas 《Meteorology and Atmospheric Physics》1991,45(1-2):101-111
Summary Hailpads are used to provide quantitative hailfall measurements in several hail experiments and hail suppression operations around the world. The dented hailpads record the time-integrated size distribution and concentration of hailfall. In the five-year Greek National Hail Suppression Program (GNHSP) hailpad data have been used to estimate the global (impact) energy of hailswaths for the evaluation of the GNHSP.In this paper a systematic hailpad calibration procedure is developed applicable to operational programs. To meet this objective a calibration experiment has been conducted consisting of several tests to: consider differences between pad types; to examine the effects of ultra violet-light on hailpads for varying periods of time; to investigate the effect of painting and inking of the hailpad surfaces; to consider the effect of analyst's variability, loose hailpad stands, and bouneing; and to develop calibration eqqations. The concluded results seem to justify the design and performance of the hailpad calibration procedure.With 9 Figures 相似文献
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Abstract The purpose of this study was to measure, with the help of a sensor measuring the impact of hailstones, the physical characteristics of hailfalls point‐by‐point, and to extend these measurements to a larger surrounding area. The results of calibrations and data‐handling methods, applying to a type of hailpad used in France and in Switzerland, are presented. The sources of error due to the pad, to the natural variability of the hailfalls and to the integration of the data over area are then reviewed. 相似文献
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Alexis B. Long 《大气与海洋》2013,51(1):35-48
Abstract Hail and rain data collected in the National Hail Research Experiment's 1976 dense precipitation network have proved useful in defining the requirements of hail measuring networks. It is shown, at least for the hailstorm of 22 June 1976, that the primary maxima and minima of the spatial distribution of hail mass are revealed by a hailpad spacing of about 4 km, and that increasing detail obtains with smaller spacings until with spacings of 0.4 to 0.8 km finer scale features with dimensions of 1–3 km become defined. Monte‐Carlo and conventional statistical analysis show that the confidence limits on the errer in estimating the true hail mass for a storm increase approximately linearly with the mean spacing of hailpads. For the hailfall of 22 June 1976, there is 90% confidence that the true hail mass is estimated within ± 10% for a hailpad spacing of 1.7 km. Estimates of hail kinetic energy and number of hailstones of this accuracy require that hailpads be approximately 10–20% closer or farther apart, respectively. There is no simple numerical relation between the densities of hailpad and wedge raingauge networks covering the same area such that, if satisfied, the networks would then provide estimates of hail mass and total precipitation of the same accuracy for any storm. There is considerable daily variation in the size of hailswaths and in the spatial distribution of hail mass within them, pointing to the need for a climatological study of these aspects of hailfall to assess properly the requirements that a hail network must meet in a given region. 相似文献
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自动气象站是由各要素的传感器和数据采集器组成的。随着时间的推移, 各传感器和数据采集器的测量误差将会发生漂移。为确保各要素观测数据的准确、可靠并具有可比性, 定期开展自动气象站的检定和校准是非常重要的。通过检定将各要素系统误差控制在允许范围内, 并对检定结果进行不确定度分析, 是考察检定结果可信程度的重要步骤。本文依据自动气象站检定规程及JJF1059-1999《测量不确定度评定与表示》的要求, 并根据检定数据, 进行自动气象站的各要素检定结果的不确定度分析, 对自动气象站检定结果可信度评估具有指导意义。 相似文献
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The ANELFA scale for hailfall intensity is proposed on the model of the 6-class Fujita scale for tornadoes. It is based on more than three thousand point hailfalls measured by hailpads over a 16-year period in France. The class number of a hailfall is determined by the integer value of the largest measured hailstone diameter in cm, or by equivalence with current objects: A0 to A5 for pea, grape, pigeon's egg, walnut, hen's egg, orange. The class number is followed by a plus or minus sign if the ground is significantly more or less than half-covered by hailstones respectively. When the scale is applied to the ANELFA data, a log-normal distribution is found for the class distribution, allowing the frequency determination of the upper class ever observed until now at the hailpad stations. 相似文献
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L. Haimberger B. Ahrens F. Hamelbeck M. Hantel 《Meteorology and Atmospheric Physics》2001,77(1-4):167-184
Summary Diagnostic time-mean budgets of energy and water are evaluated in many atmospheric process studies. The errors of budget-derived
quantities like sub-gridscale fluxes or diabatic heating are governed by the errors of the budgets. Here we consider 3D-budgets
on the meso-β scale over Europe. They are compiled from analyses of state quantities available from forecast centres.
In the present study we found that the mandatory 6 hours sampling interval between synoptic observations is the main error
source for routine time-mean budgets. The errors have been quantified (i) by first sampling forecast data of the German Europamodell every 5 minutes and averaging them over 12 hours (reference budget), and (ii) by sampling the same data only every 6 hours and averaging these also over 12 hours (routine budget). With this method we find that routine budgets in single atmospheric meso-β scale columns show relative random errors
of typically 200% and systematic errors of up to 20%, exclusively due to undersampling. Thus routine budgets, if applied to
specific days at individual locations, cannot be expected to yield useful results, except perhaps for cases with extremely
strong signal. Compositing over several hundreds of columns with similar weather reduces the random budget error down to about
50%; this seems to be the best one can achieve for routine budgets. The systematic error of some budget quantities is caused
by a correlation between the time of occurence of certain processes (mainly convection) and the sampling times. While this
error cannot be reduced through compositing, we find that it can be crudely estimated by using different time averaging methods.
As application for this method we determine sub-gridscale budget quantities over the BALTEX catchment (August-September 1995)
for an ensemble of convectively active and an ensemble of rain-active columns. For the ensemble mean profiles we find, in
terms of the diagnosed sub-gridscale test quantities diabatic heating and vertical moist enthalpy flux divergence, that their
accuracy is sufficient to detect statistically significant differences between both ensembles. The diabatic heating is about
the same for both ensembles, while the flux divergence in the convective ensemble is about three times as large as in the
rain ensemble.
Received November 7, 2001 Revised April 4, 2001 相似文献
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通过对CTL713C数字化天气雷达回波标定原理和方法的阐述,从雷达参数的测量、A/D变换及视频积分处理、测试仪器的稳定性及精确度等几方面因素对造成雷达回波强度标定误差进行了分析,分别得出几种情况下可能出现的误差值,对测试环境与人为可能造成的回波强度标定误差进行了说明。给出雷达回波强度标定结果准确性的检验方法,并对雷达回波强度标定工作中的关键问题进行了总结。 相似文献
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利用可模拟冰雹尺度的三维冰雹分档对流云模式,研究了2014年7月16日北京一次大冰雹的形成过程。此次冰雹天气过程的地面降雹最大尺度为7 cm,对流有效位能为1785.3 J·kg-1,具有上干下湿的大气层结条件。数值模拟的冰雹云顶高度达13 km,与雷达观测比较一致,模拟的最大上升气流达30 m·s-1。由于风切变较大,冰雹云出现明显倾斜垂直结构,使冰雹云持续时间较长。此次大冰雹形成的微物理过程具有明显特点,冰雹云中-35~-10℃层存在含量达12~16 g·kg-1的高过冷雨水累积区,冰雹胚胎主要通过受到冰晶接触扰动的过冷雨滴冻结产生,其产生率量级达10-2 g·kg-1·s-1,冰雹增长过程主要依靠雹胚撞冻过冷云水,其增长率的量级与冰雹胚胎产生率的量级一致。 相似文献
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Dario Camuffo 《Climatic change》2002,53(1-3):297-329
Calibration and instrumental errors of early thermometers are analysed. The first concepts, the development of scientific ideas, the main problems linked to the construction of early thermometers and the calibration are considered in order to evaluate errors. The operating principle of the `constant-volume' air thermometer is presented andits limits are discussed. The theory shows that for an ideal Amontons' thermometer, only one calibration point is sufficient from which the other can be calculated; it is therefore possible to determine the difference from an ideal instrument. A comparison is made between calibrations and instruments made by G. Amontons (1699), G. Poleni (Venice, 1709; Padova 1725), and J.H. Lambert (1779). Amontons' thermometer needs to be integrated with a barometric reading; an important error arises from the different density of mercury during calibration and usage. The calibration was made in winter and at the upper point the thermometer was at 100 ° C, while the barometer remained near 0 ° C. However, field observations were made with both instruments at the same temperature and this caused an error that in the cold season is negligible, but in the hot season reaches 1 ° C. Problems connected with the calibration and scale linearity are discussed in view of the beliefs of the time and the operative methodologies used in early meteorology. Emphasis is given to comparability of different instruments, thermometric scales and calibration methodologies used in Padova in the 18th century for Amontons' Poleni's, Fahrenheit's, Réaumur's and Delisle's thermometers. The instrument supports and the incision of the scale were subject to expand or contract depending on temperature or humidity changes, and this was a source of error that can be corrected with the help of observed or estimated data. Problems linked to the construction of thermometers have been evaluated, as well as the linearity of displacements of the thermometric liquid, or the drift due to ageing and transformation of the thermometric liquid, the glass or the support. All these errors have been evaluated and some of them have been found negligible, but some are of the order of 0.5 ° C. The quantitative resultsobtained here can also be usefully applied to correct and validate other long series. 相似文献
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Laura Lpez Jos Luis Marcos Jos Luis Snchez Amaya Castro Roberto Fraile 《Atmospheric Research》2001,56(1-4)
A study has been carried out in León (in the northwest of the Iberian Peninsula) on atmospheric convection during summer periods, by analyzing the values of the Convective Available Potential Energy (CAPE) around 07:00 UTC. The project analyzed the data provided by a network of voluntary observers, a hailpad network, and a meteorological station on a sample of 224 days. The CAPE values found were not high: they never reached 2000 J/kg, not even on hail days, i.e. on days with high convective activity. These values are much lower than the ones measured in convective situations in tropical regions, but they are within the usual values found in Europe. The same happens with the wet bulb potential temperature measured in León. The frequency distribution of the CAPE values shows a clear prevalence of very low or zero values. The group of days with the lowest CAPE value is that which included days with no storm. The mean value increases on storm days, and it is even higher for the days with recorded hailfalls. All these differences are significantly marked. Nevertheless, the differences across the years are not significant enough to be able to speak of an influence of the climatic change on the CAPE. The correlation of the CAPE with some of the variables previously used for hail forecasts was analyzed, and the correlation found was higher for the lifted index. The possible use of the CAPE as a thunderstorm and hailstorm forecasting method was considered. The results were encouraging, especially for hail forecasting, although the CAPE should not be used as the only variable, but combined with other parameters. Moreover, the relationships between the CAPE and the wet bulb potential temperature and between the CAPE and the physical parameters of the hailstones were also analyzed. A relationship was observed with the parameters of the hailstone size distribution. Nonetheless, these results are provisional, and they should be confirmed by analyzing a more representative sample. With a more detailed analysis of these and other relationships, the present forecast model used by the Laboratory for Atmospheric Physics at the University of León is expected to be greatly improved by including the CAPE in this model. 相似文献
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Initial condition and model errors both contribute to the loss of atmospheric predictability. However, it remains debatable which type of error has the larger impact on the prediction lead time of specific states. In this study, we perform a theoretical study to investigate the relative effects of initial condition and model errors on local prediction lead time of given states in the Lorenz model. Using the backward nonlinear local Lyapunov exponent method, the prediction lead time,also called local backward predictability limit(LBPL), of given states induced by the two types of errors can be quantitatively estimated. Results show that the structure of the Lorenz attractor leads to a layered distribution of LBPLs of states. On an individual circular orbit, the LBPLs are roughly the same, whereas they are different on different orbits. The spatial distributions of LBPLs show that the relative effects of initial condition and model errors on local backward predictability depend on the locations of given states on the dynamical trajectory and the error magnitudes. When the error magnitude is fixed, the differences between the LBPLs vary with the locations of given states. The larger differences are mainly located on the inner trajectories of regimes. When the error magnitudes are different, the dissimilarities in LBPLs are diverse for the same given state. 相似文献
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Summary Errors produced by a nonlinear predictive scheme contain information about both the observations and the prediction system.
Therefore, its error history would be expected to contribute to increasing the skill of the predictions if it is included
in the forecast. In this study an error recycling procedure is developed for tropical cyclone track prediction. Errors are
defined here as differences between the model forecast and the best track position. Error histories are incorporated into
a nonlinear analogue, or simplex, forecast scheme and applied to tropical cyclone track prediction, using the archives of
observed position data associated with the forecast errors. Various forecast experiments of the cyclone tracks are performed:
standard simplex predictions using observed positions only; simplex predictions improved by error forecasts based on libraries
of both observations and the recycled forecast errors; and, finally, predictions that include NWP-model forecasts and their
errors as predictors. The resulting gains in skill of predictions out to 72 hours ahead are found to be substantial.
Received August 12, 1999 Revised November 5, 1999 相似文献
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【目的】为进一步探索C波段双偏振雷达参数指标的本地化运用。【方法】利用习水C波段双偏振雷达资料、地面自动站资料、探空资料,对2022年3月16日发生在黔北的一次冰雹天气过程成因以及双偏振雷达回波特征进行分析。【结果】（1）此次强对流天气发生在500 hPa前倾槽前、低层低涡切变东南侧,中低空急流的北侧及地面低压倒槽内,同时午后升温及中高层干冷平流入侵,使得层结更趋于上干冷下暖湿的不稳定层结,冷锋前沿的地面辐合线为过程提供了触发机制。（2）过程由多单体风暴引发,最大反射率因子达65 dBz,40 mm冰雹出现了三体散射,剖面图中出现了悬垂结构和有界弱回波区,低层观测到辐合速度对。（3）对比30 mm和40 mm的冰雹双偏振参数发现：融化层以上冰雹ZDR在-1~0.2 dB,CC值在0.90~0.99之间,KDP均为0;从融化层以下,30 mm冰雹CC值在0.70~0.90,40 mm冰雹CC值在0.80~0.97,两者有所区别,ZDR也有明显增加,在0~4 dB之间;由于融化层以下大雨滴的混合,KDP在0~3.1 °·km-1之间。（4）大冰雹偏振参数出现明显ZDR柱、KDP柱,CC谷,CC图中出现明显的非均匀波束充塞,ZDR和CC图中有明显的三体散射现象。【结论】该文仅是对一次多单体天气过程个例的偏振参数特征粗略分析,未来仍需分析更多个例用以完善C波段双偏振天气雷达在强对流天气中各种偏振参数的标准,为实际业务提供更精准的参考。 相似文献
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太阳辐射测量标准仅采取定期参加国际比对的溯源方法不能完全满足质量保证的要求。只有联合国际比对和期间核查的控制方法,才能确保测量标准的测量不确定度持续控制在误差允许范围之内。我国太阳辐射测量标准与世界辐射测量基准 (WRR) 比对结果的不确定度为0.17%,满足世界气象组织 (WMO) 要求,并达到世界先进水平。为了保证在两次国际周期比对间隔之间的准确可靠,并保证其处于良好置信度的校准状态,定期对测量标准的重复性和稳定性进行期间核查, 以图形记忆方式对太阳辐射测量标准的测量过程进行连续和长期的统计控制。通过期间核查,保证了太阳辐射测量标准的重复性不大于0.1%,年稳定性小于0.25%,未超出控制界限且分布呈随机状态,保证了测量过程处于稳定受控状态,满足建标要求。 相似文献
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In this work, the hailstone size distributions at the ground in the plain of Friuli-Venezia Giulia are presented, as revealed through a network of polystyrene pads (hailpads), managed by volunteers, which has been active since 1988. The aim of this work is to highlight possible differences in the diurnal and seasonal behavior of hail at the ground, both from Friuli-Venezia Giulia and other countries, in order to improve the knowledge of this meteorological phenomenon.In the comparison between different countries, differences are found between the yearly size distributions of Friuli-Venezia Giulia and those of North-East Colorado, measured during the National Hail Research Experiment (NHRE). The size distributions obtained in South West France and in Friuli-Venezia Giulia are quite similar and they are slightly different from those of the Grossversuch experiment.In the comparison between different periods of the year, relevant differences are found between April and May and the other months. In particular, thunderstorms are less efficient in producing big hailstones during the former months. The most prolific month in producing hailstones is June, followed by September. This feature is interpreted as due to a form of synergy between the frequency of the synoptic forcing of storms and the amount of available energy at the ground.Analyzing the size distributions at different times of the day, the greatest differences are found in the intervals [00–06] and [06–12] in local time (respectively, [22–04] and [04–10] in UTC). These differences cannot be ascribed to the melting of the hailstones during their fall. 相似文献
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风廓线雷达返回信号功率定标通常通过返回信号信噪比和系统噪声功率的估算得到。该方法存在着噪声电平的确定、外部噪声等不确定性因素,影响了定标的精度。采用信号源分别对接收机和信号处理器进行定量测试,进而对雷达系统进行定标,是另一种可行的办法,该文利用这种方法对CFL-03风廓线雷达进行了定标,并利用该雷达在东莞2009年7月和8月探测资料与广州S波段天气雷达和地面雨量计资料进行比较。结果表明:用该定标方法得到的回波强度与天气雷达回波强度和地面雨量计资料估算的回波强度基本一致,平均标准差在1 dB左右,表明这种定标方法是可行的。 相似文献
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Summary A sun photometer fitted with 9 narrowband interference filters from 368 nm to 1024 nm was used to determine the aerosol optical depth at 8 measuring stations in Europe. Of the 9 filters, 4 were not included in the standard equipment of the sun photometer. Given the temporal instabilities of the calibration factors of these 4 filters, meaningful results for the aerosol optical depth can be achieved only if calibration and measurements follow each other closely. Calibration was performed using the Langley plot method. For wavelengths < 500 nm, the measured aerosol optical depths were compared with the results of a high resolution spectrometer. Broadband aerosol optical depths, centred at 427 nm, were determined with an actinometer and were also used for comparison. Generally, there was good agreement of the results. To characterize the aerosol optical depths, the Ångström parameters and were used. The individual measuring stations showed a clustered distribution of and values.With 6 Figures 相似文献