takuya kawabata, yoshinori shoji, hiromu … kawabata, yoshinori shoji, hiromu seko and kazuo saito...

Takuya KAWABATA, Yoshinori SHOJI,

Hiromu SEKO and Kazuo SAITO

Meteorological Research Institute

Japan Meteorological Agency

Kawabata, T., Y. Shoji, H. Seko, and K. Saito, 2013: A numerical study on a mesoscale convective system over a subtropical island with 4D-Var assimilation of GPS slant total delays. J. Meteor. Soc. Japan, 91, 705-721.

Observe Cumulonimbus

Water vapor and wind

convergence at low levels

GPS:

Water Vapor in all area

Doppler Radar:

Wind, Water substances

inside clouds

Clear air echoes: Wind

Doppler Lidar:

Wind outside clouds

Cumulonimbus

Horizontal:10-20 km

Lifetime: 1 h

Innovative observations

Assimilation techniques

ISDA 2012

in Offenbach

Kawabata et al., 2014: Impact of Doppler

Wind Lidar Assimilation on a Heavy

Rainfall Forecast at a Meso-beta Scale,

Mon. Wea. Rev., (under review).

Reflectivity, radial

velocity

GPS-PWV

+Doppler lidar

Reflectivity,

radial velocity

GPS-PWV MCS

~30km

NHM-4DVAR (Kawabata et al. 2007; 2011; 2013; 2014)

Model

Forward model : JMANHM with full physics

(JMA operational meso-scale nonhydrostatic model)

Adjoint model ：Dynamical core

Cloud microphysical process

(warm rain; w/o parameterization)

Observation

Doppler radial wind, radar reflectivity,

GPS precipitable water vapor,

GPS slant delay, zenith delay,

Doppler wind lidar, RASS,

wind profiler, surface wind, surface temperature, surface pressure

Horizontal resolution

2 km

GEONET (GNSS Earth Observation Network System)

http://terras.gsi.go.jp/gps/gps-based_control_station.html

•Installed by the Geospatial

Information Authority of Japan

• Number: 1,200 points

•Density: 20 km^2

GPS-derived observations

measure delay by

the atmosphere

and water vapor

Precipitable

water vapor

mapping

Zenith delay

Ps & Temp

Precipitable water vapor (PWV):

vertically accumulated water vapor

・Only water vapor

・Only zenith direction

Zenith total delay (ZTD):

vertically accumulated delay of radio waves

・water vapor, pressure, temperature

・Only zenith direction

Slant total delay (STD):

accumulated delay along the path of radio waves

・water vapor, pressure, temperature

・slant direction to GPS satellites

ma

ny info

rma

tio

n

Are slant delay data advantageous to PWV and ZTD?

Three kinds of observations

derived by ground based GPS

ea

sy to

assim

ilate

Widely used

Challenging!

Why storm scale?

Zenith delay

High resolution

Similar impact Different!

Coarse resolution

𝑛 − 1 × 106 = 𝐾1 𝑃𝑑

𝑇 + 𝐾2

𝑃𝑣𝑇 + 𝐾3

𝑃𝑣𝑇2

Observation operator

∆L= [𝑛(𝑠)− 1]𝑑𝑠 + [S− G]𝐿

(a) Refractive index

Pd : Partial pressure of dry air, Pv : Partial pressure

of water vapor, T : Temperature, K1, K2, K3：Constants

(b) Integrate along the slant path

G : Distance between the GPS satellite and the

receiver.

S : Real length of propagation root of radio wave.

Assumption : S = G

(c) Assumption Amount of delay becomes ZERO at the height of 100 km

over the model top with exponential reduction.

Model top

100km

exponential

reduction

=Obs

Single observation assimilation experiment

• Assimilation of 3 STDs, 1 PWV, or 1 ZTD

• 10-min assimilation window

• Observations at 0, 5, 10 min

Slant paths projected in the model space

ZTD,

PWV

STD

STD

STD

Analysis increments

Vertical cross sections along path III Water vapor Potential temperature

PWV

ZTD

STD

• PWV and ZTD are Almost same

• Larger magnitude of the

increment of PT in ZTD

• Largest magnitude of the

increments in STD

• Widely distribute

Analysis increments of PWV

elliptical and almost axisymmetric reflects the distribution

of the slant paths.

Naha heavy rainfall 19. Aug. 2009

Norh-

easterly

wind

JMA Radar

1030-1500 JST (every 30 min)

1-h accumulated rainfall (mm)

Rainband

20x100km

Slant delay observations

Cold color: small delay

-> dry, low pressure

-> high level

GPS receivers

100 km

Warm color: large delay

-> humid, high pressure

-> low level

2009.08.18 1100 1200 1300 1400 JST

assimilation

forecast

Observation:

• Precipitable water vapor every 10-min (PWV)

• Zenith total delay every 10-min (ZTD)

• Slant total delay every 10-min (STD)

Assimilation Experiment

Result NODA

PWV ZTD

STD Obs 12 JST 13 JST

Analysis increment (assimilation minus NODA)

STD ZTD

θ

Water

vapor

South North

A

B

A B

• Warm and humid

• Unstable

Horizontal distributions at 225 m

STD NODA

• Wider distribution

of warm and

humid air

θ

Water

vapor

Summary

• Slant total delay is useful data for predicting small scale

MCS, particularly for a storm scale assimilation system.

• ZTD has larger impact in temperature field than PWV has,

but its magnitude is small.

• STD assimilation has large impacts particularly at low levels,

because many slant paths exist in a narrow area above the

observation site.

• The STD assimilation influences the initiation and intensity

of the rainband forecast, through the improvement of

environmental field in the model.

Thank you!

Danke schöen!

Kawabata, T., Y. Shoji, H. Seko, and K. Saito, 2013: A numerical study on a mesoscale convective system over a subtropical island with 4D-Var assimilation of GPS slant total delays. J. Meteor. Soc. Japan, 91, 705-721.