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doppler radar Data Assimilation with a Local SVD-En3DVar Method

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Acta meteorologica Sinica 2012年第6期26卷 717-734页

作者：徐道生邵爱梅邱崇践 Key Laboratory for Semi-Arid Climate Change of the Ministry of Education Key Laboratory of Arid Climate Change and Disaster Reduction of Gansu Province College of Atmospheric Sciences Lanzhou University State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences

An observation localization scheme is introduced into an ensemble-based three-dimensional variational （3DVar） assimilation method based on the singular value decomposition technique （SVD-En3DVar） to im- prove assimilation skill. A point-by-point analysis technique is adopted in which the weight of each obser- vation decreases with increasing distance between the analysis point and the observation point. A set of numerical experiments, in which simulated doppler radar data are assimilated into the Weather Research and Forecasting （WRF） model, is designed to test the scheme. The results are compared with those ob- tained using the original global and local patch schemes in SVD-En3DVar, neither of which includes this type of observation localization. The observation localization scheme not only eliminates spurious analysis increments in areas of missing data, but also avoids the discontinuous analysis fields that arise from the local patch scheme. The new scheme provides better analysis fields and a more reasonable short-range rainfall forecast than the original schemes. Additional forecast experiments that assimilate real data from i0 radars indicate that the short-term precipitation forecast skill can be improved by assimilating radar data and the observation localization scheme provides a better forecast than the other two schemes.

关键词： doppler radar ensemble data assimilation 3DVar (three-dimensional variational) method,SVD (singular value decomposition) localization

Kinematic Features of a Bow Echo in Southern China Observed with doppler radar

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Advances in Atmospheric Sciences 2013年第6期30卷 1535-1548页

作者：彭新东张人禾王红艳 State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences

A bow echo is a type of mesoscale convective phenomenon that often induces extreme weather and appears with strong reflectivity on radar images. A strong bow echo that developed from a supercell was observed over Foshan City in southern China on 17 April 2011. The intense gusty winds and showers caused huge losses of property and severely affected human lives. This paper presents an analysis of this strong meso- n-scale convective system based on doppler radar observations. The isolated bow echo exhibited a horizontal scale of about 80 km in terms of reflectivity above 40 dBZ, and a life span of 8 hours. The system originated from the merging of a couple of weakly organized cells in a shear line, and developed into an arch shape as it moved through the shear zone. Sufficient surface moisture supply ensured the convective instability and development of the bow echo. The low-altitude winds retrieved from single doppler radar observations showed an obvious rear-inflow jet along the notch area. Different from the conventional definition, no book- end anticyclone was observed throughout the life cycle. Very strong slantwise updrafts and downdrafts were recognizable from the retrieved winds, even though the spatial scale of the bow echo was small. Strong winds and induced damage on the surface are considered to have been caused by the mid-level rear-inflow jet and intense convective downdrafts.

关键词： bow echo kinematic features doppler radar wind retrieval

Improvement of the Integrating Velocity-Azimuth Process Single-doppler radar Wind-Retrieval Method

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Acta meteorologica Sinica 2010年第6期24卷 721-731页

作者：梁旭东 Institute of Urban Meteorology China Meteorological Administration

Among the single-doppler radar wind analysis methods,the velocity-azimuth display（VAD）,velocityazimuth process（VAP）,and uniform wind（UW） methods are widely used because of their simplicity.A general form of the VAD,VAP,and UW methods is the integrating VAP（IVAP） method,which is based on the azimuth uniform-wind *** this study,the IVAP method is improved by applying the method along natural coordinates. The natural coordinates can be chosen to ensure that the tangential and radial winds are uniform,thereby ensuring the validity of the basic assumption that underlies the IVAP *** winds at each point of the natural coordinates are retrieved on the osculating circle,in which the IVAP method is employed. The results of the experiments show that retrieval of the wind field using single-doppler radar data depends not only on the retrieval technique,but also on the characteristic pattern of the wind *** we know the characteristic pattern of the wind field,we can retrieve the wind field using the IVAP method in the chosen natural coordinates,with higher precision.

关键词： doppler radar wind-retrieval method IVAP

An Integrating VAP Method for Single-doppler radar Wind Retrieval

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Acta meteorologica Sinica 2009年第2期23卷 166-174页

作者：梁旭东王斌 Laboratory of Typhoon Forecast Technique Shanghai Typhoon Institute of CMA LASG Institute of Atmospheric PhysicsChinese Academy of Sciences

Some traditional methods, such as the velocity-azimuth display （VAD） and the velocity-azimuth processing （VAP）, have been widely used to retrieve the 3-D wind field from single-doppler radar data because of their relative conceptual and practical simplicity. The advantage of VAD is that it is not affected by small-scale perturbations of the radial wind along the azimuth, to which the VAP method is very sensitive. Nevertheless, the spatial resolution of the VAD method is very poor compared to the VAP method. We show, in this study, that these two retrieval methods are actually related with each other and they are two special applications of a retrieval function based on the azimuthal uniform-wind assumption for a given azimuthal interval [01,02]. When using this retrieval function to retrieve wind fields, the azimuthal interval used in retrieval can be adjusted according to the requirement of smoothness or resolution. The larger （smaller） the azimuthal interval is, the coarser （finer） the horizontal resolution of retrieved wind field is, and the more insensitive （sensitive） the retrieval method is to small-scale perturbations. Because the full information within the azimuthal interval [01,02], instead of the information at two terminal points only, i.e., azimuths 01 and 02, is used to retrieve the wind fields, this method is referred to as the integrating VAP （IVAP） method, wherein the horizontal wind field is retrieved by using the doppler velocity over the part of circumference, delimited by the given azimuthal interval times the scan radius. By contrast, the VAP method uses only the velocities at two terminal points of the given azimuthal interval. Therefore, the IVAP method has a filtering function, and the filtering rate can be controlled by adjusting the azimuthal interval. The filter such as that used in the pre-processing of the VAP method is no longer necessary for the IVAP method. When the retrieval azimuthal interval is as large as a whole circumference,

关键词： doppler radar wind retrieval integrating velocity-azimuth processing (IVAP) velocity-azimuth display (VAD)

The WRF 3DVar System Combined with Physical Initialization for Assimilation of doppler radar Data

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Acta meteorologica Sinica 2009年第2期23卷 129-139页

作者：杨毅邱崇践龚建东黄静 Key Laboratory of Semi-Arid Climate Change of the Ministry of Education College of Atmospheric SciencesLanzhou University National Meteorological Center of China

The three-dimensional variational data assimilation （3DVar） system of the Weather Research and Forecasting （WRF） model （WRF-Var） is further developed with a physical initialization （PI） procedure to assimilate doppler radar radial velocity and reflectivity observations. In this updated 3DVar system, specific humidity, cloud water content, and vertical velocity are first derived from reflectivity with PI, then the model fields of specific humidity and cloud water content are replaced with the modified ones, and finally, the estimated vertical velocity is added to the cost-function of the existing WRF-Var （version 2.0） as a new observation type, and radial velocity observations are assimilated directly by the method afforded by WRF-Var. The new assimilation scheme is tested with a heavy convective precipitation event in the middle reaches of Yangtze River on 19 June 2002 and a Meiyu front torrential rain event in the Huaihe River Basin on 5 July 2003. Assimilation results show that the increments of analyzed variables correspond well with the horizontal distribution of the observed reflectivity. There are positive increments of cloud water content, specific humidity, and vertical velocity in echo region and negative increments of vertical velocity in echo-free region where the increments of horizontal winds present a clockwise transition. Results of forecast experiments show that the effects of adjusting cloud water content or vertical velocity directly with PI on forecast are not obvious. Adjusting specific humidity shows better performance in forecasting the precipitation than directly adjusting cloud water content or vertical velocity. Significant improvement in predicting precipitation as well as in reducing the model＇s spin-up time are achieved when radial velocity and reflectivity observations are assimilated with the new scheme.

关键词： 3DVar physical initialization assimilation doppler radar

QUALITY CONTROL OF SINGLE doppler radar DATA AND RETRIEVAL OF HORIZONTAL WIND FOR A LANDING TYPHOON

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Journal of Tropical Meteorology 2008年第2期14卷 165-167页

作者：刘淑媛闫丽凤孙健 Air Force Meteorological Center Yantai Weather Bureau Chinese Academy of Meteorological Sciences/State key Laboratory of Severe Weather

The removal of noise and velocity ambiguity and retrieval and verification of horizontal wind field is a prerequisite to make the best and fullest use of doppler radar measurements. This approach was applied to the doppler radar data collected during August 2005 for a landing typhoon Matsa (0509) in Yantai, Shangdong Province, and the verified result shows that the quality control for this dataset was successful. The horizontal wind field was retrieved and then verified by studying the characteristics of the radar radial velocity and large-scale wind field and the vertical cross section of the radial velocity determined with the typhoon center as the circle center and comparing it with satellite imagery. The results show that the meso- and small-scale systems in Matsa and its horizontal and vertical structure could be clearly retrieved using the dataset collected by single doppler radar, and a shear or a convergence was corresponding with a band of severe storm around Matsa. At the same time, the retrieved wind field from single doppler radar is proved to be a reliable and high-resolution dataset in analyzing the inner meso-scale structure of Matsa. It is also proved that the method for removing the velocity ambiguity could be an effective approach for preliminary quality control of the doppler radar data, and the VAP method could also be a reasonable solution for the analysis of mesoscale wind field.

关键词： doppler radar horizontal wind retrieval velocity ambiguity landing typhoon

RETRIEVAL OF HORIZONTAL WIND PERTURBATION FIELDS FROM SIMULATED SINGLE doppler radar OBSERVATIONS

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Acta meteorologica Sinica 1994年第1期8卷 89-108页

作者：顾松山 I.Zawadzki S.Laroche Nanjing Institute of Meteorology Nanjing 210044 Departement de physique Universite du Quebec a Montreal CanadaH3P 3P8

The application of the single doppler radar dataset analysis is usually confined to the assumption that the actual wind is linearly distributed or uniform *** some dynamic features of convective weather,a conceptual model of moderate complexity is constructed,wherewith a horizontal wind perturbation field is retrieved directly from the single doppler radar *** numerical experiments are based on a 3-D cloud model-generated convective cell,whose radial velocity component is taken as the radar observations that are put into the closed equations based on the conceptual model to retrieve the horizontal wind perturbation *** the initial field is properly treated,the retrieval equation is solved in terms of the 2-D FFT technique and the sensitivity to noise is examined. Finally,contrast analysis is done of the retrieved and the cloud model output wind fields,indicating the usefulness of the approach proposed in this paper.

关键词： doppler radar FFT technique retrieval wind field

Dynamical and Microphysical Retrieval from Simulated doppler radar Observations Using the 4DVAR Assimilation Technique

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Acta meteorologica Sinica 2005年第2期19卷 160-173页

作者：许小永刘黎平郑国光 Chinese Academy of Meteorological Sciences Beijing 100081 China Meteorological Administration Beijing 100081

Based on a cloud model and the four-dimensional variational (4DVAR) dataassimilation method developed by Sun and Crook (1997), simulated experiments of dynamical andmicrophysical retrieval from doppler radar data were performed. The 4DVAR data assimilationtechnique was applied to a cloud scale model with a warm rain parameterization scheme. The 3D wind,thermodynamical, and microphysieal fields were determined by minimizing a cost function, defined bythe difference between both radar observed radial velocities and reflectivities and their modelpredictions. The adjoint of the numerical model was used to provide the gradient of the costfunction with respect to the control variables. Experiments have demonstrated that the 4DVARassimilation method is able to retrieve the detailed structure of wind, thermodynamics, andmicrophysics by using either dual-doppler or single-doppler information. The quality of retrievaldepends strongly on the magnitude of constraint with respect to the variables. Retrieving thetemperature field, cloud water and water vapor is more difficult than the recovery of the wind fieldand rainwater. Accurate thermodynamic retrieval requires a longer assimilation period. Theinclusion of a background term, even mean fields from a single sounding, helped reduce the retrievalerrors. Less accurate velocity fields were obtained when single-doppler data were used. It wasfound that the retrieved velocity is sensitive to the location of the retrieval domain relative tothe radars while the other fields have very little changes. Two radar volumetric scans are generallyadequate for providing the evolution, although the use of additional volumes improves theretrieval. As the amount of the observations decreases, the performance of the retrieval isdegraded. However, the missing observations can be compensated by adding a background term to thecost function. The technique is robust to random errors in radial velocity and calibration errors inreflectivity. The boundary

关键词： doppler radar 4DVAR assimilation retrieval cost function

ERROR COMPARISON OF WIND FIELD RETRIEVAL FROM SINGLE AND DUAL-doppler radar OBSERVATIONS

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Acta meteorologica Sinica 1994年第3期8卷 337-345页

作者：陶祖钰 National Laboratory for Severe Storm Research Department of GeophysicsPeking UniversityBeijing 100871

The error distributions of the wind fields retrieved from single and dual-doppler radar observations are given in this *** results indicate that the error of dual-doppler retrieval depends on the position in the scan region of the dual-doppler *** error of single-doppler retrieval by using velocity azimuth processing(VAP)technique de- pends on the angle between the directions of wind and the radar ***,the winds retrieved from single Doppl- er radar are close to those retrieved from dual-doppler ***,the error distribution of the single-doppler retrieval is different from the dual-doppler *** simulate the retrievals of single doppler observation by the use of the output wind data from a 3-D numerical model of severe *** comparison of the simulated single-and dual-doppler retrievals shows that the VAP may be a suitable technique for the operational analysis of mesoscale wind *** can also be used as a supplement to wind field retrieval in the field experiment.

关键词： doppler radar wind field retrieval velocity azimuth processing(VAP)technique