Radar reflectivity data assimilation method based on background‐dependent hydrometeor retrieval: Comparison with direct assimilation for real cases

Abstract A radar reflectivity data assimilation scheme was developed within the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) three-dimensional variational data assimilation (3DVAR) system. The model total water mixing ratio was used as a control variable. A warm-rain process, its linear, and its adjoint were incorporated into the system to partition the moisture and hydrometeor increments. The observation operator for radar reflectivity was developed and incorporated into the 3DVAR. With a single reflectivity observation, the multivariate structures of the analysis increments that included cloud water and rainwater mixing ratio increments were examined. Using the onshore Doppler radar data from Jindo, South Korea, the capability of the radar reflectivity assimilation for the landfalling Typhoon Rusa (2002) was assessed. Verifications of inland quantitative precipitation forecasting (QPF) of Typhoon Rusa (2002) showed positive impacts of assimilating radar reflectivity data on the short-range QPF.

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AVALIAÇÃO DO WRF-4DVAR EM UM CASO DE EVENTO SEVERO NO RIO GRANDE DO SUL

Ciência e Natura ◽

10.5902/2179460x18698 ◽

2016 ◽

Vol 38 (2) ◽

pp. 1077

Author(s):

Luana Ribeiro Macedo ◽

João Luiz Martins Basso ◽

Yoshihiro Yamasaki

Keyword(s):

Data Assimilation ◽

Meteorological Data ◽

Rio Grande ◽

Real Data ◽

Radar Reflectivity ◽

Rio Grande Do Sul ◽

Mesoscale System ◽

Accumulated Rainfall ◽

Reflectivity Data ◽

The Impact

The WRF mesoscale system 4DVAR data assimilation technique have been used with the purpose of evaluating the impact of the meteorological data assimilation on the numeric time prognosis over the Rio Grande do Sul state. It has been done utilizing the surface and altitude data. The consistency analysis has been done evaluating the numerical prognosis exploring the differences between the analysis with and without data assimilation. The produced prognosis results have been compared spatially using the TRMM satellite data as well as the Canguçu radar reflectivity data. The accumulated rainfall has been validated and compared spatially with the TRMM data for the time period of 12 hours comprehended between October 29th and 30th of 2014. It was possible to realize that as well as the WRF, the WRFVAR overestimated the rainfall values. The radar reflectivity field without data assimilation for October 30th at 06:00UTC detected most accurately the reflectivity centers over the state. On the other hand this field with data assimilation did not present good skill. The temperature field analyses reveal that the 4DVAR assimilation system contributes, one way or another, presenting a little improvement for some points compared to the real data.

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Operational Implementation of the 1D+3D-Var Assimilation Method of Radar Reflectivity Data in the AROME Model

Monthly Weather Review ◽

10.1175/mwr-d-13-00230.1 ◽

2014 ◽

Vol 142 (5) ◽

pp. 1852-1873 ◽

Cited By ~ 68

Author(s):

Eric Wattrelot ◽

Olivier Caumont ◽

Jean-François Mahfouf

Keyword(s):

Relative Humidity ◽

Data Assimilation ◽

Three Dimensional ◽

Radar Reflectivity ◽

Precipitation Forecast ◽

Limited Area ◽

Short Term ◽

Background Error ◽

Reflectivity Data

AbstractThis paper presents results from radar reflectivity data assimilation experiments with the nonhydrostatic limited-area model Application of Research to Operations at Mesoscale (AROME) in an operational context. A one-dimensional (1D) Bayesian retrieval of relative humidity profiles followed by a three-dimensional variational data assimilation (3D-Var) technique is adopted. Several preprocessing procedures of raw reflectivity data are presented and the use of the nonrainy signal in the assimilation is widely discussed and illustrated. This two-step methodology allows the authors to build up a screening procedure that takes into account the evaluation of the results from the 1D Bayesian retrieval. In particular, the 1D retrieval is checked by comparing a pseudoanalyzed reflectivity to the observed reflectivity. Additionally, a physical consistency between the reflectivity innovations and the 1D relative humidity increments is imposed before assimilating relative humidity pseudo-observations with other observations. This allows the authors to counteract the difficulty of the current 3D-Var system to correct strong differences between model and observed clouds from the crude specification of background-error covariances. Assimilation experiments of radar reflectivity data in a preoperational configuration are first performed over a 1-month period. Positive impacts on short-term precipitation forecast scores are systematically found. The evaluation shows improvements on the analysis and also on objective conventional forecast scores, in particular for the model wind field up to 12 h. A case study for a specific precipitating system demonstrates the capacity of the method for improving significantly short-term forecasts of organized convection.

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Mesoscale Resolution Radar Data Assimilation Experiments with the Harmonie Model

Remote Sensing ◽

10.3390/rs10091453 ◽

2018 ◽

Vol 10 (9) ◽

pp. 1453 ◽

Cited By ~ 3

Author(s):

Serguei Ivanov ◽

Silas Michaelides ◽

Igor Ruban

Keyword(s):

Data Assimilation ◽

Weather Prediction ◽

Precipitable Water ◽

Original Data ◽

Radar Data ◽

Numerical Weather Prediction Model ◽

Radar Reflectivity ◽

Horizontal Structure ◽

Cell Patterns ◽

Reflectivity Data

This study presents a pre-processing approach adopted for the radar reflectivity data assimilation and results of simulations with the Harmonie numerical weather prediction model. The proposed method creates a 3D regular grid in which a horizontal size of meshes coincides with the horizontal model resolution. This minimizes the representative error associated with the discrepancy between resolutions of informational sources. After such preprocessing, horizontal structure functions and their gradients for radar reflectivity maintain the sizes and shapes of precipitation patterns similar to those of the original data. The method shows an improvement of precipitation prediction within the radar location area in both the rain rates and spatial pattern presentation. It redistributes precipitable water with smoothed values over the common domain since the control runs show, among several sub-domains with increased and decreased values, correspondingly. It also reproduces the mesoscale belts and cell patterns of sizes from a few to ten kilometers in precipitation fields. With the assimilation of radar data, the model simulates larger water content in the middle troposphere within the layer from 1 km to 6 km with major variations at 2.5 km to 3 km. It also reproduces the mesoscale belt and cell patterns of precipitation fields.

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Representation of model error in convective scale data assimilation

10.5194/egusphere-egu2020-11232 ◽

2020 ◽

Author(s):

Tijana Janjic ◽

Yuefei Zeng ◽

Alberto de Lozar ◽

Yvonne Ruckstuhl ◽

Ulrich Blahak ◽

...

Keyword(s):

Data Assimilation ◽

Additive Noise ◽

Model Error ◽

Ensemble Member ◽

Radar Reflectivity ◽

Model Errors ◽

Estimation Of Parameters ◽

Convective Scale ◽

Reflectivity Data ◽

Scale Data

<p>Model error is one of major contributors to forecast uncertainty. In addition, statistical representations of possible model errors substantially affect the data assimilation results. We investigate variety of methods of taking into account model error in ensemble based convective scale data assimilation. This is done using the operational convection-permitting COSMO model and data assimilation system KENDA of German weather service, for a two-week convective period in May 2016 over Germany. Conventional and radar reflectivity observations are assimilated hourly by the LETKF. For example, to take into account the model error due to unresolved scales and processes, we use the additive noise with samples coming from the difference between high-resolution model run and low-resolution experiment. We compare this technique for assimilation of radar reflectivity data to other methods such as RTPS, warm bubble initialization, stochastic boundary layer perturbation and estimation of parameters. To further improve on additive noise technique, which consists of perturbing each ensemble member with a sample from a given distribution, we propose a more flexible approach in which the model error samples are treated as additional synthetic ensemble members that are used in the update step of data assimilation but are not forecasted. In this way, the rank of the model error covariance matrix can be chosen independently of the ensemble. This altered additive noise method is analyzed as well.</p>

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Experiments on the radar reflectivity data assimilation in the WRF-ARW model

Russian Meteorology and Hydrology ◽

10.3103/s1068373912030016 ◽

2012 ◽

Vol 37 (3) ◽

pp. 149-158 ◽

Cited By ~ 2

Author(s):

N. F. Vel’tishchev ◽

V. D. Zhupanov

Keyword(s):

Data Assimilation ◽

Radar Reflectivity ◽

Arw Model ◽

Reflectivity Data

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A Cloud-Resolving 4DVAR Assimilation Experiment for a Local Heavy Rainfall Event in the Tokyo Metropolitan Area

Monthly Weather Review ◽

10.1175/2011mwr3428.1 ◽

2011 ◽

Vol 139 (6) ◽

pp. 1911-1931 ◽

Cited By ~ 44

Author(s):

Takuya Kawabata ◽

Tohru Kuroda ◽

Hiromu Seko ◽

Kazuo Saito

Keyword(s):

Data Assimilation ◽

Metropolitan Area ◽

Heavy Rainfall ◽

Rainfall Event ◽

Radar Reflectivity ◽

Heavy Rainfall Event ◽

Convective System ◽

Single Observation ◽

Assimilation Experiment ◽

Reflectivity Data

Abstract A cloud-resolving nonhydrostatic four-dimensional variational data assimilation system (NHM-4DVAR) was modified to directly assimilate radar reflectivity and applied to a data assimilation experiment using actual observations of a heavy rainfall event. Modifications included development of an adjoint model of the warm rain process, extension of control variables, and development of an observation operator for radar reflectivity. The responses of the modified NHM-4DVAR were confirmed by single-observation assimilation experiments for an isolated deep convection, using pseudo-observations of rainwater at the initial and end times of the data assimilation window. The results showed that the intensity of convection could be adjusted by assimilating appropriate observations of rainwater near the convection and that undesirable convection could be suppressed by assimilating small or no reflectivity. An assimilation experiment using actual observations of a local heavy rainfall in the Tokyo, Japan, metropolitan area was conducted with a horizontal resolution of 2 km. Precipitable water vapor derived from global positioning system data was assimilated at 5-min intervals within 30-min assimilation windows, and surface and wind profiler data were assimilated at 10-min intervals. Doppler radial wind and radar-reflectivity data below the elevation angle of 5.4° were assimilated at 1-min intervals. The 4DVAR assimilation reproduced a line-shaped rainband with a shape and intensity consistent with the observation. Assimilation of radar-reflectivity data intensified the rainband and suppressed false convection. The simulated rainband lasted for 1 h in the extended forecast and then gradually decayed. Sustaining the low-level convergence produced by northerly winds in the western part of the rainband was key to prolonging the predictability of the convective system.

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X-Net-Based Radar Data Assimilation Study over the Seoul Metropolitan Area

Remote Sensing ◽

10.3390/rs12050893 ◽

2020 ◽

Vol 12 (5) ◽

pp. 893 ◽

Cited By ~ 1

Author(s):

Ji-Won Lee ◽

Ki-Hong Min ◽

Young-Hee Lee ◽

GyuWon Lee

Keyword(s):

Data Assimilation ◽

Radial Velocity ◽

Metropolitan Area ◽

Numerical Data ◽

Radar Data ◽

Radar Reflectivity ◽

Model Verification ◽

Seoul Metropolitan Area ◽

X Band ◽

Reflectivity Data

This study investigates the ability of the high-resolution Weather Research and Forecasting (WRF) model to simulate summer precipitation with assimilation of X-band radar network data (X-Net) over the Seoul metropolitan area. Numerical data assimilation (DA) experiments with X-Net (S- and X-band Doppler radar) radial velocity and reflectivity data for three events of convective systems along the Changma front are conducted. In addition to the conventional assimilation of radar data, which focuses on assimilating the radial velocity and reflectivity of precipitation echoes, this study assimilates null-echoes and analyzes the effect of null-echo data assimilation on short-term quantitative precipitation forecasting (QPF). A null-echo is defined as a region with non-precipitation echoes within the radar observation range. The model removes excessive humidity and four types of hydrometeors (wet and dry snow, graupel, and rain) based on the radar reflectivity by using a three-dimensional variational (3D-Var) data assimilation technique within the WRFDA system. Some procedures for preprocessing radar reflectivity data and using null-echoes in this assimilation are discussed. Numerical experiments with conventional radar DA over-predicted the precipitation. However, experiments with additional null-echo information removed excessive water vapor and hydrometeors and suppressed erroneous model precipitation. The results of statistical model verification showed improvements in the analysis and objective forecast scores, reducing the amount of over-predicted precipitation. An analysis of a contoured frequency by altitude diagram (CFAD) and time–height cross-sections showed that increased hydrometeors throughout the data assimilation period enhanced precipitation formation, and reflectivity under the melting layer was simulated similarly to the observations during the peak precipitation times. In addition, overestimated hydrometeors were reduced through null-echo data assimilation.

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