The Meteorological Research Institute of the Japan Meteorological Agency has developed a cloud-resolving nonhydrostatic 4-dimensional variational assimilation system (NHM-4DVAR) based on the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM), in order to investigate the mechanism of heavy rainfall events induced by mesoscale convective systems (MCSs). The horizontal resolution of the NHM-4DVAR is set to 2 km to resolve MCSs and the length of the assimilation window is 1-hour. The control variables of the NHM-4DVAR are horizontal wind, vertical wind, nonhydrostatic pressure, potential temperature, surface pressure and pseudo relative humidity. Perturbations to the dynamical processes and the advection of water vapor are considered, but these to the other physical processes.　　　 The NHM-4DVAR is applied to the heavy rainfall event observed at Nerima, central part of Tokyo metropolitan area, on 21 July 1999. Doppler radar’s radial wind data (RW), GPS precipitable water vapor data (GPS-PWV) and surface temperature and wind data were assimilated as high temporal and spatial resolution data. The Nerima heavy rainfall is well reproduced in the assimilation and subsequent forecast with respect to time sequence of 10-minute rainfall amount.

Assimilation Experiment of the Heavy Convective Rainfall Eventwith a Cloud Resolving Nonhydrostatic 4 Dimensional Variational Data Assimilation System Takuya Kawabata1 (tkawabat@mri-jma.go.jp), Hiromu Seko1, Tohru Kuroda1, Kyuichiro Tamiya2, Kazuo Saito1, Tadashi Tsuyuki2

Variables Formula

Wind u, v, w

Non-Hydrostatic pressure πU = π - πB

Potential temperature θ

Surface pressure Ps

Pseudo relative humidity qu = q / qsb

Category Specification of JMA-NHM Specifications of the adjoint model

Basic equations Fully compressible with a map factor

O

Prognostic variables Momentums, potential temperature, pressure, kinetic turbulent energy, mixing ratio of water vapor, cloud water, cloud ice, rain, snow and graupel and predict number density of cloud ice, snow and graupel.

Momentums, potential temperature, pressure, mixing ratio of water vapor

Advection term Flux form, second order Second order

Sound waves Vertically implicit, horizontally split and explicit

O

Turbulent closure model Deardorff (1980) level 2.5 X

Cloud microphysics 3 ice bulk microphysics (Ikawa and Saito, 1991)

Advection of water vapor.

Radiation Sugi et al.(1990) X

Surface layer Monin-Obukhov (Sommeria, 1976))Kondo (1975)

X

bs

uq

qq

pCR

p

p

0

z

surfsurfB

dzz

)(

m

100km0

Haneda

Nerima

Narita

Assimilation area and Observation stations: Nerima AMeDAS station (■), the Haneda and the Narita airport Dopplar radars (●) and the GPS-PWV observation stations (Δ).

GPS-PWV1 minute interval

Radial Wind1 minute interval

Surface wind & temperature1 minute interval

0

5

10

15

20

25

30

1510 1520 1530 1540 1550 1600 1610 1620 1630 1640 1650J ST

mm Observation Forecast

0.E+00

5.E+05

1.E+06

2.E+06

2.E+06

3.E+06

3 4 5 7 8 9 11 12 14 15 iterations

Tot

al, R

W

0.E+00

2.E+04

4.E+04

6.E+04

8.E+04

1.E+05

1.E+05

1.E+05

Surf

ace

, G

PS

PW

V

Total RWSurface GPS-PWV

14JST 15JST 16JST 17JST

Assimilation window

3-hour forecast

Time evolution of Nerima heavy rainfall

Formation Develop Mature

Design of the assimilation experiment: Assimilation window, forecast time. Time evolution of Nerima cells are indicated.

Observations and the time interval of the assimilation.

Cost function 10-minute rainfall amount at Nerima

Surface wind field the observation (red arrows) and the analysis (black arrows) at 1440 JST. Color contours show the model orography.

Distribution of PWV the observation (circles) and the analysis (contours) at 1440 JST.

Hourly accumulated rainfall amount

Forecast results

Control variables

Abstract

Model specifications

Design of the assimilation

Assimilation system

Assimilation result Observation and Forecast result

Radar reflectivity (dBZ)

Observations

Nerima heavy rainfall

A

A

A A

A AA

A

B B

B

B

CC

CCC

Symbols of A, B and C denote MCSs.

1448JST 1507JST 1525JST 1545JST

1550JST1530JST1510JST1450JST

Observation Forecast result

First guess

1: Meterological Research Institute

2: Japan Meteorological Agency

KAWABATA et al., An Assimilation and Forecasting Experiment of the Nerima Heavy Rainfall with a Cloud-Resolving Nonhydrostatic 4-Dimensional Variational Data Assimilation System, Journal of the Meteorological Society of Japan (submitted)

No heavy rainfall