Japan Meteorological Agency Nonhydrostatic Model Research Articles

Ensemble flood simulation for a small dam catchment in Japan using nonhydrostatic model rainfalls – Part 2: Flood forecasting using 1600-member 4D-EnVar-predicted rainfalls

Abstract. This paper is a continuation of the authors' previous paper (Part 1) on the feasibility of ensemble flood forecasting for a small dam catchment (Kasahori dam; approx. 70 km2) in Niigata, Japan, using a distributed rainfall–runoff model and rainfall ensemble forecasts. The ensemble forecasts were given by an advanced four-dimensional, variational-ensemble assimilation system using the Japan Meteorological Agency nonhydrostatic model (4D-EnVar-NHM). A noteworthy feature of this system was the use of a very large number of ensemble members (1600), which yielded a significant improvement in the rainfall forecast compared to Part 1. The ensemble flood forecasting using the 1600 rainfalls succeeded in indicating the necessity of emergency flood operation with the occurrence probability and enough lead time (e.g., 12 h) with regard to an extreme event. A new method for dynamical selection of the best ensemble member based on the Bayesian reasoning with different evaluation periods is proposed. As the result, it is recognized that the selection based on Nash–Sutcliffe efficiency (NSE) does not provide an exact discharge forecast with several hours lead time, but it can provide some trend in the near future.

Observational operators for dual polarimetric radars in variational data assimilation systems (PolRad VAR v1.0)

Abstract. We implemented two observational operators for dual polarimetric radars in two variational data assimilation systems: WRF Var, the Weather Research and Forecasting Model variational data assimilation system, and NHM-4DVAR, the nonhydrostatic variational data assimilation system for the Japan Meteorological Agency nonhydrostatic model. The operators consist of a space interpolator, two types of variable converters, and their linearized and transposed (adjoint) operators. The space interpolator takes account of the effects of radar-beam broadening in both the vertical and horizontal directions and climatological beam bending. The first variable converter emulates polarimetric parameters with model prognostic variables and includes attenuation effects, and the second one derives rainwater content from the observed polarimetric parameter (specific differential phase). We developed linearized and adjoint operators for the space interpolator and variable converters and then assessed whether the linearity of the linearized operators and the accuracy of the adjoint operators were good enough for implementation in variational systems. The results of a simple assimilation experiment showed good agreement between assimilation results and observations with respect to reflectivity and specific differential phase but not with respect to differential reflectivity.

Ensemble flood simulation for a small dam catchment in Japan using 10 and 2 km resolution nonhydrostatic model rainfalls

Abstract. This paper presents a study on short-term ensemble flood forecasting specifically for small dam catchments in Japan. Numerical ensemble simulations of rainfall from the Japan Meteorological Agency nonhydrostatic model (JMA-NHM) are used as the input data to a rainfall–runoff model for predicting river discharge into a dam. The ensemble weather simulations use a conventional 10 km and a high-resolution 2 km spatial resolutions. A distributed rainfall–runoff model is constructed for the Kasahori dam catchment (approx. 70 km2) and applied with the ensemble rainfalls. The results show that the hourly maximum and cumulative catchment-average rainfalls of the 2 km resolution JMA-NHM ensemble simulation are more appropriate than the 10 km resolution rainfalls. All the simulated inflows based on the 2 and 10 km rainfalls become larger than the flood discharge of 140 m3 s−1, a threshold value for flood control. The inflows with the 10 km resolution ensemble rainfall are all considerably smaller than the observations, while at least one simulated discharge out of 11 ensemble members with the 2 km resolution rainfalls reproduces the first peak of the inflow at the Kasahori dam with similar amplitude to observations, although there are spatiotemporal lags between simulation and observation. To take positional lags into account of the ensemble discharge simulation, the rainfall distribution in each ensemble member is shifted so that the catchment-averaged cumulative rainfall of the Kasahori dam maximizes. The runoff simulation with the position-shifted rainfalls shows much better results than the original ensemble discharge simulations.

Regional variability in the impacts of future land use on summertime temperatures in Kanto region, the Japanese megacity

Summer high temperatures affecting urban areas pose a significant problem to human health. The Japanese megacity, Tokyo Metropolitan Area (TMA) in Kanto region, where significant urban shrinkage is expected to occur in the coming decades, is also vulnerable to such temperature issues. We investigated the impacts arising from changes in land use on future maximum surface air temperature (Tsmax) at the regional scale in Kanto region. For our numerical experiments, we introduced surface parameters (i.e., albedo, evapotranspiration coefficient, and heat capacity) into the Japan Meteorological Agency Non-Hydrostatic Model (JMANHM), used for operational weather forecasts in Japan. The impacts were estimated regarding several urban planning scenarios, in which the micro scale afforestation in TMA was considered, i.e., compact-city, dispersed-city, and active afforestation. The obtained results indicated that the afforestation might decrease Tsmax, and active afforestation within a compact-city scenario was the most effective for reducing Tsmax in Kanto region. Our findings also revealed a relatively smaller afforestation impact on Tsmax values in the coastal areas (e.g., Kanagawa) than those affecting inland regions (e.g., Saitama and Tokyo). In coastal areas located upwind of Kanto region, only local afforestation affected Tsmax. On the other hand, in inland zones, located on the downwind side of Kanto region, afforestation in both local and upwind areas contributed to a decrease in Tsmax. Consequently, the impacts of afforestation were larger in inland areas.

Ensemble Kalman Filter data assimilation and storm surge experiments of tropical cyclone Nargis

Data assimilation experiments on Myanmar tropical cyclone (TC), Nargis, using the Local Ensemble Transform Kalman Filter (LETKF) method and the Japan Meteorological Agency (JMA) non-hydrostatic model (NHM) were performed to examine the impact of LETKF on analysis performance in real cases. Although the LETKF control experiment using NHM as its driving model (NHM–LETKF) produced a weak vortex, the subsequent 3-day forecast predicted Nargis’ track and intensity better than downscaling from JMA's global analysis. Some strategies to further improve the final analysis were considered. They were sea surface temperature (SST) perturbations and assimilation of TC advisories. To address SST uncertainty, SST analyses issued by operational forecast centres were used in the assimilation window. The use of a fixed source of SST analysis for each ensemble member was more effective in practice. SST perturbations were found to have slightly positive impact on the track forecasts. Assimilation of TC advisories could have a positive impact with a reasonable choice of its free parameters. However, the TC track forecasts exhibited northward displacements, when the observation error of intensities was underestimated in assimilation of TC advisories. The use of assimilation of TC advisories was considered in the final NHM–LETKF by choosing an appropriate set of free parameters. The extended forecast based on the final analysis provided meteorological forcings for a storm surge simulation using the Princeton Ocean Model. Probabilistic forecasts of the water levels at Irrawaddy and Yangon significantly improved the results in the previous studies.

Forecasting a Large Number of Tropical Cyclone Intensities around Japan Using a High-Resolution Atmosphere–Ocean Coupled Model

Abstract This work quantifies the benefits of using a high-resolution atmosphere–ocean coupled model in tropical cyclone (TC) intensity forecasts in the vicinity of Japan. To do so, a large number of high-resolution calculations were performed by running the Japan Meteorological Agency (JMA) nonhydrostatic atmospheric mesoscale model (AMSM) and atmosphere–ocean coupled mesoscale model (CMSM). A total of 281 3-day forecasts were compiled for 34 TCs from April 2009 to September 2012 for each model. The performance of these models is compared with the JMA global atmospheric spectral model (GSM) that is used for the operational TC intensity guidance. The TC intensities are better predicted by CMSM than the other models. The improvement rates in CMSM relative to GSM and AMSM generally increase with increasing forecast time (FT). CMSM is better than GSM and AMSM by 27.4% and 21.3% at FT = 48 h in terms of minimum sea level pressure, respectively. Regarding the maximum wind speed, CMSM is better than GSM and AMSM by 12.8% and 19.5% at FT = 48 h, respectively. This is due to smaller initial intensity errors and sea surface cooling consistent with in situ observations that suppress erroneous TC intensification. Thus, a high-resolution coupled model is promising for TC intensity prediction in the area surrounding Japan, where most of the TCs are in a decay stage. In contrast, coupling to the upper-ocean model yields only a negligible difference in the TC track forecast skill on average.

A Theoretical Study on the Spontaneous Radiation of Inertia–Gravity Waves Using the Renormalization Group Method. Part II: Verification of the Theoretical Equations by Numerical Simulation

Abstract The renormalization group equations (RGEs) describing spontaneous inertia–gravity wave (GW) radiation from part of a balanced flow through a quasi resonance that were derived in a companion paper by Yasuda et al. are validated through numerical simulations of the vortex dipole using the Japan Meteorological Agency nonhydrostatic model (JMA-NHM). The RGEs are integrated for two vortical flow fields: the first is the initial condition that does not contain GWs used for the JMA-NHM simulations, and the second is the simulated thirtieth-day field by the JMA-NHM. The theoretically obtained GW distributions in both RGE integrations are consistent with the numerical simulations using the JMA-NHM. This result supports the validity of the RGE theory. GW radiation in the dipole is physically interpreted either as the mountain-wave-like mechanism proposed by McIntyre or as the velocity-variation mechanism proposed by Viúdez. The shear of the large-scale flow likely determines which mechanism is dominant. In addition, the distribution of GW momentum fluxes is examined based on the JMA-NHM simulation data. The GWs propagating upward from the jet have negative momentum fluxes, while those propagating downward have positive ones. The magnitude of momentum fluxes is approximately proportional to the sixth power of the Rossby number between 0.15 and 0.4.

Cloud-Resolving 4D-Var Assimilation of Doppler Wind Lidar Data on a Meso-Gamma-Scale Convective System

Abstract The authors evaluated the effects of assimilating three-dimensional Doppler wind lidar (DWL) data on the forecast of the heavy rainfall event of 5 July 2010 in Japan, produced by an isolated mesoscale convective system (MCS) at a meso-gamma scale in a system consisting of only warm rain clouds. Several impact experiments using the nonhydrostatic four-dimensional variational data assimilation system (NHM-4DVAR) and the Japan Meteorological Agency nonhydrostatic model with a 2-km horizontal grid spacing were conducted in which 1) no observations were assimilated (NODA), 2) radar reflectivity and radial velocity determined by Doppler radar and precipitable water vapor determined by GPS satellite observations were assimilated (CTL), and 3) radial velocity determined by DWL were added to the CTL experiment (LDR) and five data denial and two observational error sensitivity experiments. Although both NODA and CTL simulated an MCS, only LDR captured the intensity, location, and horizontal scale of the observed MCS. Assimilating DWL data improved the wind direction and speed of low-level airflows, thus improving the accuracy of the simulated water vapor flux. The examination of the impacts of specific assimilations and assigned observation errors showed that assimilation of all data types is important for forecasting intense MCSs. The investigation of the MCS structure showed that large amounts of water vapor were supplied to the rainfall event by southerly flow. A midlevel inversion layer led to the production of exclusively liquid water particles in the MCS, and in combination with the humid airflow into the MCS, this inversion layer may be another important factor in its development.

An Ensemble Downscaling Prediction Experiment for Medium-Range Forecast of the Daily Mean Surface Temperature Distribution over Northeastern Japan during Summer

To assess medium-range forecasts of detailed spatial distributions of the daily mean temperature, an ensemble downscaling forecast experiment was conducted using the Japan Meteorological Agency (JMA) nonhydrostatic model (NHM) with horizontal resolutions of 25 km and 5 km. Special attention was paid to the anomalously cool summers over northeastern Japan caused by northeasterly winds called Yamase. The results are validated against the daily mean surface temperatures observed by the Automated Meteorological Data Acquisition System (AMeDAS) in the study area. Ensemble mean downscaling forecasts can successfully extract reliable signals with information about local circulations. The ensemble mean forecasts reduce the root mean square errors of the daily mean surface temperature by 15 % compared to single downscaling forecasts. The ensemble spreads also indicate the possibility of making probabilistic predictions that consider the effects of local circulations in addition to large-scale motions. The ensemble downscaling forecasts have 80 % larger spreads than the global forecasts with the JMA global spectral model at a resolution TL159L60 and approach the theoretical value. An empirical orthogonal function (EOF) analysis indicates that the predictability depends on the EOF modes. The predictable periods are 8 days for the homogeneous mode over northeastern Japan, 5 days for the Yamase mode (east-west mode), and 2 days for the north-south mode. The dynamical downscaling can properly predict the amplitudes of the EOF modes. In particular, the dynamical downscaling can predict 90 % of the Yamase mode, as compared to 20 % prediction of the global model for the same mode.

Influence of Land Cover Change on Regional Water Cycles in Eastern Siberia

AbstractThis study evaluated the effect of recent eastern Siberian land surface changes, such as water surface expansion, on water-energy fluxes and precipitation and focused on land surface parameters using a three-dimensional atmospheric model [the Japan Meteorological Agency Nonhydrostatic model (JMA-NHM)]. Five parameters were set (viz., surface albedo, evaporative efficiency, roughness length, heat capacity, and thermal conductivity), and a response of evaporation and precipitation was evaluated. Increased precipitation corresponded to 75% of the increased evaporation on interparameter average, indicating strong land–atmosphere coupling. Water-energy flux and precipitation responses to water surface expansion were evaluated by two methods: JMA-NHM and the parameter sensitivity method. The latter method used a linear combination of parameter sensitivity on the fluxes and precipitation and parameter changes with land surface change. JMA-NHM demonstrated an increase in evaporation and precipitation and a decrease in downward shortwave radiation with low-level cloud increases. The parameter sensitivity method gave the same order as JMA-NHM in the estimation. This method has minimal calculation cost; thus, water-energy flux and precipitation response with further water surface expansion and decreases in forest area were simulated, producing various land surface data. The enhancement of the precipitation response to evaporation was weak for further water surface expansion in the largely expanded water surface area; however, the ratio increased dramatically for the small water surface expanding area, indicating intense water cycle enhancement at the beginning of water surface expansion. Although grassland formation from forest has minimal impact, if incoming downward shortwave radiation were to increase because of the disappearance of the forest shading effect and the water surface formed by permafrost melting, the water cycle would be enhanced intensely.

中小河川流域における豪雨・洪水のアンサンブル予測

This paper deliberates an ensemble flood forecasting method using high-resolution ensemble rainfalls. The authors use numerical ensemble rainfalls simulated by the Japan Meteorological Agency – Nonhydrostatic Model (JMA-NHM) with a 2-km resolution as inputs to a distributed rainfall-runoff/flood inundation (DRR/FI) model. The feasibility study of the ensemble river water-stage and flood inundation depth prediction to be used for the operational forecast is carried out with DRR/FI and ensemble rainfalls. The 2-km spatial resolution of the ensemble rainfalls by JMA-NHM has a potential to be used for even small Japanese river basins such as the Sayogawa River basin (191 km2), the application site in the paper. The paper presents the ensemble simulations of the 2011flood by Typhoon No.12 in the basin. The result shows that the water stage at a given point in the Sayogawa River exceeds the evacuation call level in some ensemble members. This indicates the possibility that the ensemble flood forecasting can be used as the additional information for the evacuation call.

A Numerical Study on a Mesoscale Convective System over a Subtropical Island with 4D-Var Assimilation of GPS Slant Total Delays

A method to assimilate slant total delays derived from global positioning system (GPS) data using the fourdimensional variational data assimilation technique was developed and applied to a line-shaped, local heavy rainfall event that formed on 19 August 2009 over Okinawa Island, Japan. First, to identify the primary factors affecting rainband initiation, we performed impact tests using the Japan Meteorological Agency non-hydrostatic model (JMANHM) with 5-km horizontal grid spacing. Simulations in which the orography of Okinawa was removed successfully reproduced the rainband over southern Okinawa, which showed that the primary factor leading to rainband initiation was land surface heating. However, the timing of rainband initiation in these experiments was delayed, and the rainfall intensities were weaker than those observed. To reduce these discrepancies, we first conducted a high-resolution numerical experiment using JMANHM with 2km horizontal grid spacing (NODA) followed by data assimilation experiments with GPS observations (i.e., GPS zenith total delay (GPS-ZTD), GPS precipitable water vapor (GPS-PWV), and GPS slant total delay (GPS-STD)) at the same resolution. As a result, increasing the horizontal resolution improved the simulation of the rainfall intensity. Generally, compared with NODA, the assimilations of GPS-ZTD and GPS-PWV are known to slightly improve the timing of the subsequent rainband initiation. However, the GPS-STD assimilation significantly improved the water vapor and temperature fields over a wide area and yielded a clearly improved forecast in terms of both rainfall timing and intensity.

Airport Terrain-Induced Turbulence Simulations Integrated with Weather Prediction Data

The wind environment at an airport is affected by terrain features. In Japan, Shonai Airport is known to frequently have wind shear over the runway due to the turbulence induced by the neighboring hills in winter. In this study, large eddy simulation (LES) is performed to investigate the turbulence around Shonai Airport. The initial and boundary conditions are given according to the weather prediction data by the Japan Meteorological Agency non-hydrostatic model (JMANHM). These data are downscaled and transferred to LES domains, which consider actual terrain features as the boundary conditions on the ground, using the two-way nesting method. The present simulations indicate that terrain features may have a significant influence on the turbulence appearing in flight paths; i.e., aircraft safety may depend on wind direction. In addition, it is shown that the present simulation method can predict the turbulence induced by terrain features based on good agreement of results with the turbulence actually observed using a Doppler radar.

Evaluation of Cloud Microphysics in JMA-NHM Simulations Using Bin or Bulk Microphysical Schemes through Comparison with Cloud Radar Observations

AbstractNumerical weather prediction (NWP) simulations using the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborne W-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separately for an intercomparative study. A radar product simulator that is compatible with both microphysics schemes is developed to enable a direct comparison between simulation and observation with respect to the equivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). In general, the bin model simulation shows better agreement with the observed data than the bulk model simulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves the result of the bin model simulation. The results indicate that there are substantial uncertainties in the mass–size and size–terminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snow aloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominance of snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows that a correction for the fall velocity of hydrometeors considering a change of particle size should be introduced even in single-moment bulk cloud microphysics.

Tephra Fall Simulation for the Eruptions at Mt. Shinmoe-dake during 26-27 January 2011 with JMANHM

The tephra fall caused by the eruptions at Mt. Shinmoe-dake during 26 to 27 January 2011 is simulated with Japan Meteorological Agency Non-Hydrostatic Model. The model has been improved so as to involve the tephra transport and sedimentation with four aerosol classes representing different sizes of tephra particles. The total mixing ratio and number concentration are prognosed with the advection, diffusion, and source and sink terms for each class. The simulated result on the distribution of tephra deposit shows a good agreement with observation.

A Square Prism Urban Canopy Scheme for the NHM and Its Evaluation on Summer Conditions in the Tokyo Metropolitan Area, Japan

AbstractA single-layered square prism urban canopy (SPUC) scheme for the Japan Meteorological Agency nonhydrostatic model (NHM) was developed. This scheme considers the urban canopy layer with square prism–shaped buildings. The basic concept of this scheme is similar to those of the conventional energy balance models for an urban canyon structure. The scheme presented here differs slightly from them in its representation of the bulk resistance circuit and some treatments of radiation processes, however, as well as by considering the water reservoir on building surfaces. A comparison between the SPUC scheme and the existing slab scheme of the NHM was made on summer days in the Tokyo metropolitan area. The SPUC run more accurately reproduced the expected behavior of the urban canopy effect than did the slab run. The effective albedo was smaller in the SPUC run than in the slab run (the upward shortwave radiation of the SPUC run was smaller than that of the slab run). The forecast heat fluxes in the SPUC run, however, showed worse performances. Adequate parameter settings (especially concerning latent heat fluxes) are needed in the SPUC run. The mean bias errors of the surface air temperature during nighttime were less negative and slightly improved in the SPUC run than in the slab run.

Data assimilation experiments of precipitable water vapour using the LETKF system: intense rainfall event over Japan 28 July 2008

We performed data assimilation experiments using data from an intense rainfall event in western Japan on 28 July 2008 with the Local Ensemble Transform Kalman Filter (LETKF) and analysed fields of the mesoscale four-dimensional variational assimilation (4DVAR) system of the Japan Meteorological Agency (JMA). We supplemented conventional observation data with precipitable water vapour (PWV) data derived from the Global Positioning System (GPS) Earth Observation Network of the Geospatial Information Authority of Japan. Because the LETKF system assimilates fewer data than the 4DVAR system, ensemble mean fields of the LETKF cycle experiment were replaced with analysed fields from the 4DVAR system each day at 12 UTC. PWV values were converted to relative humidity profiles for assimilation by the LETKF. The addition of PWV data tended to increase low-level water vapour and improve the precipitation forecast. We attempted to reproduce the intense rainfall band using downscale forecast experiments with the JMA non-hydrostatic model (JMANHM) with grid spacings of 5 and 1.6 km. The experiment with 5-km resolution generated a rainfall band in western Japan that was not reproduced using conventional data, although the rainfall was smaller than observations. The experiment with 1.6-km resolution faithfully reproduced the observed band of intense rainfall.

Dependence of Model-Simulated Heavy Rainfall on the Horizontal Resolution during the Jakarta Flood Event in January-February 2007

Time-lagged ensemble downscaling experiments with Japan Meteorological Agency-Nonhydrostatic model are performed to study the dependence of heavy precipitation simulated by the model on the horizontal resolution for five days during late January to early February 2007, when the Jakarta Flood event occurred. The model runs with horizontal resolutions of 2, 4, and 5 km downscaled from the model runs with a 20-km resolution demonstrate the ability to reproduce a region of strong convective activity to the north of Java Island during the event. Daily meridional propagation of enhanced precipitation signals is simulated in the model runs with 2- and 4-km resolutions.Cumulative distribution functions of precipitation rate in the model are analyzed for four different regions: ocean, northern coast, mountain, and southern coast. The northern coast region shows the highest contribution of heavy precipitation compared to other regions for all the experiments as well as for satellite-based precipitation estimates. The statistics on the frequency of heavy precipitation show that the diurnal variation of heavy precipitation produced by the model with a 2-km resolution agrees well with that of satellite-based precipitation estimates.

Comparison of initial perturbation methods for the mesoscale ensemble prediction system of the Meteorological Research Institute for the WWRP Beijing 2008 Olympics Research and Development Project (B08RDP)

Different initial perturbation methods for the mesoscale ensemble prediction were compared by the Meteorological Research Institute (MRI) as a part of the intercomparison of mesoscale ensemble prediction systems (EPSs) of the WorldWeather Research Programme (WWRP) Beijing 2008 Olympics Research and Development Project (B08RDP).Five initial perturbation methods for mesoscale ensemble prediction were developed for B08RDP and compared at MRI: (1) a downscaling method of the Japan Meteorological Agency (JMA)’s operational one-week EPS (WEP), (2) a targeted global model singular vector (GSV) method, (3) a mesoscale model singular vector (MSV) method based on the adjoint model of the JMA non-hydrostatic model (NHM), (4) a mesoscale breeding growing mode (MBD) method based on the NHM forecast and (5) a local ensemble transform (LET) method based on the local ensemble transform Kalman filter (LETKF) using NHM. These perturbation methods were applied to the preliminary experiments of the B08RDP Tier-1 mesoscale ensemble prediction with a horizontal resolution of 15 km. To make the comparison easier, the same horizontal resolution (40 km) was employed for the three mesoscale model-based initial perturbation methods (MSV, MBD and LET).The GSV method completely outperformed the WEP method, confirming the advantage of targeting in mesoscale EPS. The GSV method generally performed well with regard to root mean square errors of the ensemble mean, large growth rates of ensemble spreads throughout the 36-h forecast period, and high detection rates and high Brier skill scores (BSSs) for weak rains. On the other hand, the mesoscale model-based initial perturbation methods showed good detection rates and BSSs for intense rains. The MSV method showed a rapid growth in the ensemble spread of precipitation up to a forecast time of 6 h, which suggests suitability of the mesoscale SV for short-range EPSs, but the initial large growth of the perturbation did not last long. The performance of the MBD method was good for ensemble prediction of intense rain with a relatively small computing cost. The LET method showed similar characteristics to the MBD method, but the spread and growth rate were slightly smaller and the relative operating characteristic area skill score and BSS did not surpass those of MBD. These characteristic features of the five methods were confirmed by checking the evolution of the total energy norms and their growth rates.Characteristics of the initial perturbations obtained by four methods (GSV, MSV, MBD and LET) were examined for the case of a synoptic low-pressure system passing over eastern China. With GSV and MSV, the regions of large spread were near the low-pressure system, but with MSV, the distribution was more concentrated on the mesoscale disturbance. On the other hand, large-spread areas were observed southwest of the disturbance in MBD and LET. The horizontal pattern of LET perturbation was similar to that of MBD, but the amplitude of the LET perturbation reflected the observation density.

Development of Air-Sea Bulk Transfer Coefficients and Roughness Lengths in JMA Non-hydrostatic Model and Application in Prediction of an Intense Tropical Cyclone

A new parameterization scheme of air-sea momentum flux, heat flux and moisture flux is introduced into the Japan Meteorological Agency Non-Hydrostatic Model (JMA-NHM, Saito et al. 2006). The new formulation describes the saturation properties of bulk transfer coefficients of momentum, heat and moisture under high winds regime (> 30 m s-1). It also considers the effect of sea-wave drag in the roughness length. The proposed parameterization is applied to simulate an intense tropical cyclone Hagupit (0814). The impact of the new scheme on the tropical cyclone prediction is found in the increase of maximum surface wind speed and decrease of central pressure. Improvements in the forecasts of distribution of high wind areas and precipitation are obtained. This may help to improve the model predicted wind-pressure relationship for intense tropical cyclones.