To identify important factors for supercell tornadogenesis, 33-member ensemble forecasts of the tornado that struck city Tsukuba, Japan, on 6 May 2012 were conducted using a mesoscale numerical model with 50-m horizontal grid. Based forecasts, sources rotation simulated tornadoes and relationship between tornadogenesis environmental processes near analyzed. Circulation analyses near-surface, tornadolike vortices in several members showed could be frictionally generated surface. However,...

A tornadic supercell and associated low-level mesocyclone (LMC) observed on the Kanto Plain, Japan, 6 May 2012 were predicted with a nonhydrostatic mesoscale model horizontal resolution of 350 m through assimilation surface meteorological data (horizontal wind, temperature, relative humidity) high spatial density C-band Doppler radar (radial velocity rainwater estimated from reflectivity specific differential phase) local ensemble transform Kalman filter. With both data, strong LMC was...

Flows in a cylindrical tank over rotating bottom are investigated by laboratory experiments. Despite the axisymmetry of experimental setup, various anisotropic phenomena observed. The slow rotation disk induces circular flow according to axisymmetric environment, but polygonal vortices form under faster rotation. Between these two vortex states, undergoes transition with clear hysteresis during which elliptical shape assumed is retained when subsequently slowed rates that previously...

Experiments simulating intense vortices associated with tornadoes that occurred on 6 May 2012 the Kanto Plain, Japan, were performed a nested local ensemble transform Kalman filter (LETKF) system. Intense reproduced by downscale experiments 12-member in which initial conditions obtained from LETKF system analyses. The successfully generated three regions similar to observed vortices, whereas only one tornado was deterministic forecast. vorticity of strongest tornado, southernmost region, 10...

This study hybridizes the background error covariance (BEC) of hourly atmospheric three-dimensional variational data assimilation (3DVar) in Local Analysis (LA) operated at Japan Meteorological Agency using flow-dependent BEC derived from singular vector-based Mesoscale Ensemble Prediction System (MEPS) and static BEC. The impact introducing hybrid into 3DVar is examined, along with its sensitivities to various factors like ensemble size that augmented by lagged forecasts, weight given...

We conducted observation system simulation experiments (OSSE) to investigate the effects of water vapor vertical profiles observed by Raman lidar (RL) on forecasts heavy precipitation in Hiroshima, Japan, August 19, 2014 using a local ensemble transform Kalman filter. employed result similar reality as nature-run (NR) and performed two OSSEs. In first experiment (DaQv), conventional data mixing ratio air (qv) estimated from NR were assimilated. second (CNTL), only DaQv, we assumed that RL...

Abstract Strong gusty winds in a weak maritime extratropical cyclone (EC) over the Tsushima Strait southwestern Sea of Japan capsized several fishing boats on 1 September 2015. A C-band Doppler radar recorded spiral-shaped reflectivity pattern associated with convective system and velocity vortex diameter 30 km [meso- β -scale (MBV)] near location wreck. high-resolution numerical simulation horizontal grid interval 50 m successfully reproduced precipitation MBV tornado-like strong vortices...

Abstract The mechanism of tropical cyclogenesis due to the breakdown intertropical convergence zone (ITCZ breakdown) and structure associated vortices are studied by numerical experiments using a nonhydrostatic mesoscale model. First, an idealized experiment, in which simple initial state without external disturbances is assumed, performed cumulus parameterization. A zonally uniform forcing high sea surface temperature (SST) imposed generate ITCZ-like structure. This “ITCZ” starts undulate...

Abstract To improve short‐term rainfall forecasts through direct assimilation of radar reflectivity, atmospheric variables associated with should be modified based on their correlation reflectivity. However, it is difficult to estimate such correlations. The ensemble Kalman filter can the by means forecasts, although estimation limited when forecast at least one member analysis points. assimilate reflectivity effectively even points which no forecast, we suggest adding perturbations, are...

In data assimilation for weather forecast, ensemble Kalman filter assumes linearity of the observation operator and Gaussianity probability distribution function (PDF) to explicitly solve analysis.As a method avoiding errors based on these assumptions, we describe four-dimensional ensemble-based variational (4D-EnVAR) with localization.This formulation differs from that local transform (4D-LETKF) only in two points: (1) not assuming and(2) calculating it globally.Using single-observation...

Intertropical convergence zone (ITCZ) occasionally breaks down to simultaneously form several tropical cyclones mainly due barotropic instability of the zonal flow. This process is called ITCZ breakdown and thought be one mechanisms for a cyclogenesis in central eastern Pacific. In present paper, an idealized numerical simulation performed by non-hydrostatic meso-scale model on f-plane at 10°N, detailed energy budget analysis associated genesis made first time. A sea surface temperature...

This study demonstrates the advantages of scale- and variable-dependent localization (SDL VDL) on three-dimensional ensemble variational data assimilation hourly-updated high-resolution regional forecast system, Rapid Refresh Forecast System (RRFS). SDL VDL apply different radii for each spatial scale variable, respectively, by extended control vectors. Single-observation tests cycling experiments with RRFS indicated that can enlarge radius without increasing sampling error caused small size...

The theory of axisymmetric flow in a cylindrical container with rotating bottom, as described Part I, is validated against the results previous and our own laboratory experiments. First, deformation water surface derived using velocity distribution obtained by theory. form classified into three regimes, rotation rates transitions between these regimes are determined. parameters predicted from this compared measured experiments also data experimental studies. predicts well, but slight...

The ensemble-based tangent linear model (ETLM), which evolves the static background error covariance (BEC) in time data assimilation window, is beneficial for improving analysis and avoids need developing forecast its adjoint as four-dimensional variational (4DVar). This study proposes to apply filtered ETLM (FETLM), composed of ensemble perturbations at limited slots localized with a quasi-Gaussian filter way that calculation inverse matrix. Tests Lorenz (1996) showed FETLM evolved BEC...

This study applies a multigrid beta filter (MGBF) for covariance localization in ensemble-variational (EnVar) data assimilation instead of the conventional recursive (RF) to achieve faster computation large number processors. The parallelization efficiency MGBF is higher than that RF because all-to-all communication change computational region each processor not necessary. However, MGBF-based additionally requires horizontal variable exchange between processors; its cost proportional grid...

Abstract This study demonstrates the advantages of scale‐ and variable‐dependent localization (SDL VDL) on three‐dimensional ensemble variational data assimilation hourly‐updated high‐resolution regional forecast system, Rapid Refresh Forecast System (RRFS). SDL VDL apply different radii for each spatial scale variable, respectively, by extended control vectors. Single‐observation tests cycling experiments with RRFS indicated that can enlarge radius without increasing sampling error caused...

Abstract The complex relationships between rainfall amounts and their causes require further clarification through analytical research. This study utilizes ensemble‐based singular value decomposition (ESVD) analysis that decomposes the cross‐covariance matrix datasets related to atmospheric states hydrometeors. ESVD is applied “Heavy Rain Event of July 2018 in Japan.” initial 301‐member ensemble forecasts are created using a local transform Kalman filter, obtained by regional nonhydrostatic...

Ensemble forecasts with 101 members, including one ensemble mean, using Kalman filter analysis were performed to understand the atmospheric conditions favorable for development of a meso-β-scale vortex (MBV) that caused shipwrecks as result sudden gusty winds in southwestern part Sea Japan on 1 September 2015. A composite was conducted reveal differences structure MBV and around between strongest 8 (STRG) weakest 10 (WEAK) members. Two ten members developed much earlier than other excluded...