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1.
An improved retrieval method, which uses the solution with a Gaussian constraint as the initial state variables for the Kalman Filtering (KF) method, was developed to retrieve the wet refractivity profiles from slant wet delays (SWD) extracted by the double-differenced (DD) GPS method. The accuracy of the GPS-derived SWDs is also tested in this study against the measurements of a water vapor radiometer (WVR) and a weather model. It is concluded that the GPS-derived SWDs have similar accuracy to those measured with WVR and are much higher in quality than those derived from the weather model used. The developed method is used to retrieve the 3D wet refractivity distribution in the Hong Kong region. The retrieved profiles agree well with the radiosonde observations, with a difference of about 4 mm km-1 in the low levels. The accurate profiles obtained with this method are applicable in a number of meteorological applications. 相似文献
2.
Summary The increasing use of weather radar quantitative precipitation estimates, particularly in automatic applications such as operational
hydrometeorological modelling or assimilation in numerical weather prediction (NWP) models, has promoted the development of
quality control procedures on radar data.
Anomalous propagation (AP) of the radar beam due to deviation from the standard refractivity vertical profile, is one of the
factors that may affect seriously the quality of radar observations because of the increase in quantity and intensity of non-precipitating
clutter echoes and consequent contamination of the estimated rainfall field. Another undesired effect of AP is the change
in the expected radar echo height, which may be relevant when correcting for beam blockage in radar rainfall estimation in
complex terrain. The aim of this paper is to study the use of NWP mesoscale forecasts to predict and monitor AP events.
A nested 15-km grid resolution version of the MASS model has been used to retrieve refractivity profiles in the coastal area
of Barcelona, near a weather radar and a radiosonde station. Using the refractivity profiles two different magnitudes were
computed: the vertical refractivity profile of the lowest 1000 m layer and a ducting index which describes the existence and
intensity of the most super-refractive layer contained in the lowest 3-km layer. A comparison between model forecasts and
radiosonde diagnostics during a six-month period showed that the model tended to underestimate the degree of super-refraction,
with a bias of 4 km−1 and RMSE of 11 km−1 in the 1-km vertical refractivity gradient. Further analysis of the data showed that a combination of previous observations
and forecasts allowed to produce modified forecasts improving the original direct model output, decreasing substantially the
bias, reducing the RMSE by 20% and improving the skill by 40%, beating also radiosonde observations persistence. 相似文献
3.
Iran enjoys a variety of climatological conditions. Moreover, numerical weather prediction (NWP) models are not assimilated with the meteorological data in Iran, the country suffering from poor spatial and temporal resolution of radiosonde measurements. These facts make modeling of troposphere impossible using the measurements and NWP. On the other hand, the global positioning system (GPS) has been emerged as a valuable tool for modeling and remote sensing of Earth’s atmosphere. This research is the first attempt to address the tropospheric wet refractivity modeling by GPS measurements in Iran. Changes of topography in the study area are taken into account. As a leading work, virtual reference stations (VRS) are used to fix the rank deficiency of the problem. The model space resolution matrix is used to achieve the optimum spatial resolution of the tomographic model and the optimum number of VRS stations. The accuracy of the developed model (KNTU1) is investigated by deploying radiosonde measurements. 相似文献
4.
Jihyun Ha Kwan-Dong Park Kihoon Kim Yeon-Hee Kim 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(3):233-241
In studies of weather changes and, especially, in enhancing the performance of rainfall prediction, it is important to measure the water vapor distribution in the atmosphere. We estimated atmospheric water vapor profiles for fourteen days, including periods of severe weather conditions, by processing ground-based Global Positioning System (GPS) measurements and compared our results with microwave radiometer (MWR) and radiosonde (RAOB) observations. As a result, we found that the standard deviation (STD) of wet refractivity profiles between GPS with MWR was smaller than the STD between RAOB and MWR refractivities; the average STD was 9.3 mm km?1. In particular, we found that GPS-based wet refractivities detected inversion layers close to those from MWR when the observed GPS satellites were well distributed in the azimuth and elevation angle directions. When the satellite geometry was better, the mean error of GPS wet refractivities with respect to MWR was reduced to 0.4 from 3.2 mm km?1 for altitudes lower than 3 km. In some cases, however, the precision of GPS refractivities are lower than that of RAOB ones relative to MWR results. 相似文献
5.
Precipitable Water (PW) derived from Global Positioning System (GPS)
measurements and numerical weather prediction (NWP) model analysis data were
compared to further evaluate the efficacy of applying GPS-derived PW to the
NWP model. The spatial and temporal variations of GPS-derived PW during a
rainfall event were also examined.
GPS-derived PW measurements show good agreement with the behavior of water
vapor at a high spatial resolution during the analysis period. Temporal
anomalies of GPS-derived PW moving along with the front are successfully
detected by the GPS array. Large positive anomalies of GPS-derived PW are
indicated immediately before a rainfall event, and the intensity of these
positive anomalies do not seem to decrease significantly as the
precipitation system passes. These results indicate that the Korean GPS
network may have great potential as a PW sensor over the Korean Peninsula.
In contrast with GPS-derived PW, NWP-derived PW shows negative biases. These
biases appear to stem mainly from the differences between modeled and actual
GPS site elevations, as GPS sites were generally located at elevations lower
than those employed by the NWP model. However, there still exists a
discernable dry bias after a PW correction is applied to NWP-derived PW.
GPS-derived PW better reflects the spatial and temporal moisture variations
of precipitation systems, as compared to NWP-derived PW. These results
provide entirely new information for improving the regional NWP system,
since GPS-derived PW produced with data from the Korean GPS network may be
incorporated into the NWP model to improve rainfall forecasts. 相似文献
6.
Precipitable water vapor estimation in India from GPS-derived zenith delays using radiosonde data 总被引：1，自引：0，他引：1
Dinesh Singh Jayanta Kumar Ghosh Deepak Kashyap 《Meteorology and Atmospheric Physics》2014,123(3-4):209-220
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. 相似文献
7.
为了进一步提高GRAPES_Meso的分析和预报效果,该文在GRAPES_Meso三维变分同化系统中建立了同化GNSS/RO反演的大气资料的观测算子,实现了对GNSS/RO反演的大气资料的同化应用,并通过2013年7月1个月的同化和预报试验分析了GNSS/RO反演大气资料对GRAPES_Meso模式系统分析和预报的影响。结果表明:增加了GNSS/RO反演大气资料的同化后,GRAPES_Meso位势高度场的分析误差明显减小,平均分析误差减小约8%,预报误差略有减小,平均预报误差减小约1%;湿度场的分析误差和预报误差变化不明显,常规观测资料稀少的青藏高原地区的降水预报技巧有所提高,小雨到大雨的ETS (equitable threat score) 评分提高约0.01,对全国及其他分区的降水预报技巧总体上有正效果。 相似文献
8.
COSMIC是一个由6颗低轨卫星组成的用于天气、气候和电离层观测的空基GPS星座观测系统, 从2006年9月开始每天可提供覆盖全球的约2000~3000个掩星点, 掩星过程可提供从40 km高空到近地面的大气温、压、湿的廓线资料。为了有效利用这些资料, 以探空资料为基准, 对2007年1-10月我国及邻近区域的COSMIC掩星资料进行精度、可用性和全天候性的检验。结果表明: COSMIC反演的温度和折射率的精度很高, 水汽压的精度相对较差。与NCEP/NCAR再分析资料相比, 折射率和湿度廓线有更高精度。 相似文献
9.
In recent years, radio occultation (RO) technology making
use of global positioning system (GPS) signals has been exploited to
obtain profiles of atmospheric parameters in the neutral atmosphere.
In this paper, the RO refractivity profiles obtained from the
Constellation Observing System for Meteorology, Ionosphere and
Climate (COSMIC) mission are statistically compared with the
observations of 38 radiosonde stations provided by the Australian
Bureau of Meteorology during the period from 15 July 2006 through 15
July 2007. Different collocation criteria are compared at first, and
COSMIC RO soundings that occur within 3 hours and 300 km of
radiosonde measurements are used for the final statistical
comparison. The overall results show that the agreements between the
COSMIC refractivity profiles and the radiosonde soundings from the
38 stations are very good at 0--30 km altitude, with mean absolute
relative refractivity deviations of less than 0.5%. Latitudinal
comparisons indicate that there are negative refractivity deviations
in the lower troposphere over the low latitude and middle latitude
regions and large standard deviations exist in the lower troposphere
of low latitude regions, which can reach up to ~6%. The
comparisons of COSMIC RO refractivity profiles and radiosonde
observations for 3 polar stations in four different seasons indicate
that the accuracy of GPS RO profiles is better in the Austral summer
and autumn than in the Austral spring and winter during the year
from September 2006 to August 2007. 相似文献
10.
In the present reported study, the vertical distributions of local atmospheric refractivity were retrieved from ground- based GPS observations at low elevation angles. An improved optimization method was implemented at altitudes of 0-10 km to search for a best-fit refractivity profile that resulted in atmospheric delays most similar to the delays calculated from the observations. A ray-tracing model was used to simulate neutral atmospheric delays corresponding to a given refractivity profile. We initially performed a ＂theoretical retrieval＂, in which no observation data were involved, to verify the optimization method. A statistical relative error of this ＂theoretical retrieval＂ （-2% to 2%） indicated that such a retrieval is effective. In a practical retrieval, observations were obtained using a dual-frequency GPS receiver, and its initial value was provided by CIRA86aQ_UoG data. The statistical relative errors of the practical retrieval range from -3% to 5% were compared with co-located radiosonde measurements, Results clearly revealed diurnal variations in local refractivity prc,files, The results also suggest that the general vertical distribution of refractivity can be derived with a high temporal resolution. However, further study is needed to describe the vertical refractivity gradient clearly. 相似文献
11.
利用GPS的倾斜路径观测暴雨过程中的水汽空间分布 总被引：1，自引：0，他引：1
介绍了地基全球定位系统 (GPS) 沿倾斜路径方向观测水汽总量 (SWV) 的原理和方法; 不同时间和不同地点的GPS SWV与微波辐射计反演的SWV符合较好, 误差在3 mm左右, 表明GPS可以较高的精度探测SWV.计算了区域GPS观测网在一次暴雨过程中不同空间方位上的水汽观测结果, 为消除不同路径对SWV的影响, 把SWV转化为天顶方向的值VSWV; 分析了同一GPS站点对不同卫星方向VSWV的变化情况, 以及不同GPS站点对同一个卫星方向VSWV的关系.结果表明, 区域GPS观测网中倾斜路径观测可较好地探测不同方位上水汽的分布和变化; SWV相对于天顶方向的大气水汽总量PW而言, 能更好地代表真实大气水汽分布; 在探空或卫星观测等传统观测手段无法探测的情况下, GPS SWV数据可提供中小尺度暴雨结构中水汽分布和变化状况等有用信息. 相似文献
12.
The impact of Global Positioning System data on the prediction of an extratropical cyclone: an observing system simulation experiment 总被引：1，自引：0，他引：1
In this paper, we report a series of observing system simulation experiments that we conducted to assess the potential impact of Global Positioning System/meteorology (GPS/MET) refractivity data on short-range numerical weather prediction. We first conducted a control experiment using the Penn State/NCAR mesoscale model MM5 at 90-km resolution on an extratropical cyclone known as the ERICA (Experiment on Rapidly Intensifying Cyclones over the Atlantic) IOP 4 storm. The results from the control experiment were then used to simulate GPS/MET refractivity observations with different spatial resolution and measurement characteristics. The simulated refractivity observations were assimilated into an 180-km model during a 6-h period, which was followed by a 48-h forecast integration. Key findings can be summarized as follows:
- • The assimilation of refractivity data at the 180-km resolution can recover important atmospheric structures in temperature and moisture fields both in the upper and lower troposphere, and, through the internal model dynamical processes, also the wind fields. The assimilation of refractivity data led to a considerably more accurate prediction of the cyclone.
- • Distributing the refractivity randomly in space and applying a line averaging did not alter the results significantly, while reducing the spatial resolution from 180 km to 360 km produced a moderately degraded result. Even at the 360-km resolution, the GPS-type refractivity data still have a notable positive impact on cyclone prediction.
- • Restricting the refractivity data to altitude 3 km and above considerably degraded its impact on cyclone prediction. This degradation was greater than the combined effects of distributing the refractivity data randomly, performing line averaging, and reducing the resolution to 360 km.
13.
WANG Xiaoying WANG Xianliang DAI Ziqiang KE Fuyang CAO Yunchang WANG Feifei and SONG Lianchun 《大气科学进展》2014,31(2):355-362
This paper presents a novel approach for assessing the precision of the wet refractivity field using BDS （BeiDou navigation satellite system） simulations only,GPS,and BDS＋GPS for the Shenzhen and Hongkong GNSS network.The simulations are carried out by adding artificial noise to a real observation dataset.Instead of using the δ and σ parameters computed from slant wet delay,as in previous studies,we employ the Bias and RMS parameters,computed from the tomography results of total voxels,in order to obtain a more direct and comprehensive evaluation of the precision of the refractivity field determination.The results show that：（1） the precision of tropospheric wet refractivity estimated using BDS alone （only 9 satellites used） is basically comparable to that of GPS; （2） BDS＋GPS （as of current operation） may not be able to significantly improve the data＇s spatial density for the application of refractivity tomography; and （3） any slight increase in the precision of refractivity tomography,particularly in the lower atmosphere,bears great significance for any applications dependent on the Chinese operational meteorological service. 相似文献
14.
Study on Retrieving Three-Dimensional Wind Using Simulated Dual-Doppler Radar Data in the Cartesian Space 
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下载免费PDF全文 1. Introduction Armijo (1969) proposed the three-dimensional wind retrieved equations using multiple-Doppler weather radar network in Cartesian space. There are many sources of error for recovering 3D wind using these equations. These factors include advection and turbulence in the weather system, the error of the empirical relationship between the radar reflectivity factor and the terminal fall velocity of the precipita- tion particle, integrating the air mass continuity equa- tion (problem … 相似文献
15.
从新一代天气雷达径向速度资料中反演出可靠的三维风场对提高新一代天气雷达的应用水平有重要的作用，将雷达直接观测的径向速度转换成台站预报员更为熟悉的风场结构，对识别中小尺度信息有很大帮助。为此该文对4DVAR同化技术在风场业务反演中应用的可能性进行了探讨，利用广州、济南新一代多普勒天气雷达观测资料，从是否加入云模式湿过程以及迭代次数、计算时间、背景场、初始场、分辨率和反演区域等方面对干模式的4DVAR系统进行了讨论，并从风场结构、均方根差别等方面对反演结果进行分析。多种试验表明，干模式的4DVAR系统与湿的云模式反演结果差异不大。模式的初始场和背景场对反演结果具有较高的敏感性，利用前一时次的反演结果作为背景场迭代15～20次的干模式结果可以很好地在业务上试运行，对台站预报员提高中小尺度天气预报的准确率有着很重要的作用。 相似文献
16.
Links Between Weather Phenomena and Characteristics of Refractivity Measured by Precipitation Radar 总被引：1，自引：1，他引：0
Lucas Besson Chiraz Boudjabi Olivier Caumont Jacques Parent du Chatelet 《Boundary-Layer Meteorology》2012,143(1):77-95
Refractivity depends on meteorological parameters such as temperature and water vapour pressure and can be measured using
a weather radar. A realistic atmospheric simulation from the Meso-NH numerical model is used in order to describe and establish
the relation between refractivity and the dynamic and thermodynamic phenomena responsible for the development and propagation
of convection. These investigations lead to discussion of the complementarity between the refractivity and the convective
available potential energy. The relation observed between the refractivity signal and the meteorological parameters calls
the refractivity measurement into question, since it is based on phase differentiation with time and space and can be degraded
by phase aliasing problems. These aliasing problems increase with the radar frequency (perceptible in the S-band, serious
in the C-band, and more serious in the X-band) and also with the integration range and sampling time. Thus, a statistical
approach permits us to simulate the possibility of measuring the refractivity with operational radar during convective events.
A typical case in the south-east region of France is selected to simulate measurements by radar (S-band, C-band, X-band) in
convective systems, in order to evaluate the measurement feasibility, particularly in terms of phase ambiguity, related to
temporal and spatial sampling, of a future implementation of the refractivity measurement over the French operational radar
network. This numerical statistical approach is completed with a similar study using in-situ measurements performed at the
Trappes station. The seasonal and diurnal dependencies of aliasing are investigated, leading to clarification of the impact
of the turbulent fluxes on the refractivity measurement. 相似文献
17.
一种新的COSMIC大气折射率资料观测误差估计方法及在GRAPES全球三维变分同化中的应用 总被引：1，自引：0，他引：1
观测误差协方差是变分同化系统中决定分析及预报效果的关键参数之一,观测误差的估计精度直接影响变分同化分析和预报效果。分析了新息增量法(H-L法)估计全球定位系统无线电掩星这类观测点不固定资料的观测误差的适用条件,并利用1年的气象、电离层及气候星座观测系统(COSMIC)折射率资料,针对局地观测算子,估计了COSMIC折射率在南、北半球高、中、低6个纬度带四季的观测误差,分析了COSMIC折射率观测误差的纬度、高度和季节变化的特点,并将估计的折射率观测误差应用于GRAPES(Global/Regional Assimilation and Prediction Enhanced System)三维变分同化系统。结果表明,折射率观测误差随高度和纬度有明显变化;在中、高纬度带,折射率观测误差有显著的季节变化:夏季折射率的观测误差约为冬季2倍,春、秋两季折射率误差具有较好的南北对称性,冬、夏两季折射率观测误差南、北半球差异较大。与GRAPES原来使用的全球平均单一的折射率观测误差相比,在GRAPES全球三维变分同化系统中使用本研究估计的较高精度的随纬度变化的COSMIC折射率观测误差能够提高GRAPES全球变分同化系统的预报水平。 相似文献
18.
利用中国气象局大气探测试验基地的L波段探空数据和微波辐射计观测数据,采用MonoRTM辐射传输模型作为正演亮温模型,BP (back propagation) 神经网络作为反演工具,在由亮温反演大气湿度廓线的过程中,添加与样本匹配的云底高度和云厚度信息,建立新的反演模型,使新反演模型得到的反演湿度廓线和未添加云信息的反演湿度廓线分别与探空数据进行对比,获取两种反演方法各高度层的均方根误差,分析云信息对反演大气湿度廓线的影响。对比结果表明:未添加云信息时,测试样本的反演湿度廓线与探空廓线的相关系数平均值为0.685,而添加云信息后,相关系数平均值为0.805。相比未添加云信息的反演廓线,添加云信息之后多数高度层的均方根误差均有不同程度减小,而在有云以上高度层表现尤为明显。 相似文献
19.
In this paper, a simple relationship is employed to investigate the relative impacts on the movement and landfall of tropical cyclone in the Bay of Bengal region when wet component of atmospheric refractivity of different tropospheric levels is used as an input. Four tropical cyclones during pre-monsoon and post-monsoon season over the Bay of Bengal region were selected for the study. The radiosonde/radiowind data of coastal stations, namely Kolkata (Dumdum), Agartala, Bhubaneswar, Visakhapatnam, Machlipatnam, Chennai and Karaikal, were collected for the period of the cyclones under study. The wet component of atmospheric refractivity of different standard levels was plotted against time for the stations for every cyclone. The study suggests that the cyclone moves towards and crosses near the station having a relatively steeper increase in the wet component of atmospheric refractivity up to mid-tropical level. A possible explanation is also presented. 相似文献
20.
新发展了一种湿Q矢量释用技术:利用松弛法迭代求解以非地转干Q矢量散度为强迫项的方程得到垂直运动场ω 1, 然后由ω 1计算湿Q矢量散度场, 接着再利用松弛法迭代求解以湿Q矢量散度场为强迫项的ω方程得到垂直运动ω 2, 最后由ω 2结合水汽条件进行降水量计算, 得到湿Q矢量释用降水场。结合一次典型的江淮梅雨锋暴雨过程研究表明, 湿Q矢量释用降水场对同期观测降水场水平分布特征、极端降水强度都具有一定的反映能力, 反映出湿Q矢量释用技术具备实际应用的可行性和一定合理性。将此释用技术应用于华东区域数值预报模式 (基于MM5 V3.6而建立, 以下简称MM5) 产品, 得到湿Q矢量释用定量降水预报 (QPF) 场, 其独立于模式本身输出的QPF场, 但与模式QPF场具有相同的时空分辨率。针对2004年6—8月汛期华东地区一次梅雨锋降水过程和一次登陆台风降水过程, 结合实况雨量资料, 比较分析了湿Q矢量释用QPF场和MM5模式QPF场对实际观测降水场的反映能力, 结果表明, 前者对有无降水、10.0 mm/24 h以上明显降水的反映能力明显优于后者。进一步进行预报统计检验表明, 湿Q矢量释用预报有无降水、小雨及10.0 mm/24 h以上降水的TS评分、正确率都明显高于MM5模式, 而漏报率、空报率则是前者明显低于后者。这也充分反映出湿Q矢量释用技术应用于QPF研究的有效性。最后, 探讨了数值预报产品释用技术对数值预报模式性能的依赖性, 并指出未来对湿Q矢量释用技术进一步改进的方向及其广泛应用前景。 相似文献