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An Idealized Numerical Simulation of Meso- -scale Low on the Baiu Front. Hirotaka Tagami 1 , Hiroshi Niino 2 1: Advance Soft corporation 2:Ocean Research Institute, Univ of Tokyo. 1:Introduction and Purpose 2:Setting 3:Result 4:Conclusion. An example of Meso- -Low (MAL).

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an idealized numerical simulation of meso scale low on the baiu front

An Idealized Numerical Simulation of Meso--scale Low on the Baiu Front

Hirotaka Tagami1, Hiroshi Niino2

1: Advance Soft corporation

2:Ocean Research Institute, Univ of Tokyo

1:Introduction and Purpose

2:Setting

3:Result

4:Conclusion

an example of meso low mal
An example of Meso--Low (MAL)

18UTC 4th July 2005

Weather map

GMS IR image

●Only a few hPa lower than the environment.

●Active Cloud Cluster accompanies.

MAL on the Baiu Front (BF)

often causes torrential rain in the Baiu season.

past studies on the structure and dynamics of mal
Past studies on the structure and dynamics of MAL

Vertical structure with sonde data Yoshizumi (1977)

Vertical structure

400

  • Cold air to the east of trough
  • Trough tilts eastward with height
  • (Ninomiya and Akiyama,1971, Akiyama1990b)
  • Warm core above the low
  • Meridionally different

500

600

700

800

900

1000

0 500km

Shade; potential temperature anomaly (θ’)

(blue; negative, red; positive)

Contour; geopotential anomaly

Theoretical study for vertical structure

Adiabatic coolingassociated with updraft

enforced by diabatic heating

(Yanase and Niino, 2004)

problems
Problems

Analytical Study:

 Mechanism of 3-dimensional structure

 Developing process (Energy budget).

 The environment of MALsis different from case to case.

Theoretical Study:

 Meridionally uniform environment

 Crudely parameterized convective heating

 Non-linear effects

Purposes

  • Obtainment of realistic environment for the BF
  • Idealized numerical simulationwithout cumulus

convective parameterization

  • General structure and developing process
  • (Sensitivity to the baroclinicity)
model and setting
Model and Setting
  • The anelastic equation system (for energy budget analysis) ofMeteorological Research Institute / Numerical Prediction Division Non-Hydrostatic Model (Saito et al. 2000; NHM) is modified.
  • Zonal BC:cyclic
  • Meridional and Vertical BC:free slip
  • 500x500x36(dx=dy=5km,dz=500m)
  • Cloud Physic:Cold rain scheme (Lin et al. 1983)
  • No cumulus convective parameterization
  • Newtonian cooling (e-folding time = 5hour) is applied to the deviation of zonal mean of u,v,w, θ.
  • f-plane at 32.5゜N

 Anomaly : deviation from zonal mean.

 Horizontal smoothing over 100km square is applied to the model result.

design of environment field

km

km

  • 726 casesdistinctBF are selected between 1958 and 2002
  • 8-day low-pass filter
  • Superposed while keeping the south edge of BF
  • Geostrophic zonal wind
  • Distribution at 125°E is given uniformly in the x-direction
  • qv is modified with modification of RH (≦95%)
  • Thermal wind valanced weak vortex(diameter :1000km height : 6km, max velocity : 2m/s)
Design of Environment Field

Meridionally vertical section of Basic Field

for control run (CNTL)

Temperature (contour; every 5K),

zonal wind(larger than 10m/s, shadowed every 5m/s)

Relative Humidity[%]

z

y

↑:south edge of BF

result of cntl
Result of CNTL

vertical integration of

condensational water [10-1g]

& surface pressure [hPa] (2hPa)

GMS IR image 00UTC 21 June 2001

& SLP of RANAL

·Round shaped Cloud Cluster appears in SE quadrant

·Cloud zone such as cold front

(trailing portion, Ninomiya et al. 1988)

horizontal structure
Horizontal Structure

u’ and v’ & updraft (shaded) at T=60hr

z=1km

[km]

Center of LLJ

[m/s]

[km]

y

[m/h]

x

In the low-level ;

 Horizontal trough is oriented in SW-NE at north side of the LLJ.

Barotropic energy conversion can occur.

vertical structure
Vertical Structure

contour:P’(every 0.2hPa), shadow:positive ’[K]

(meridionally averaged over 100km through the center)

T=60hourの

at the center

T=60hourの

150km north from the center

[km]

[km]

z

[km]

[km]

x

slightly or westward tilting of the trough

 Pressure trough tilts eastward

 Cold anomaly to the east

Meridionally different vertical structure

heat budget analysis around mal

Distribution of each terms, averaged 25-30hr

Interval is each 0.1K/hr in (a)~(d), 0.5K/hr in (e)、(f)

x=0 : Center of Low

Heat Budget Analysis around MAL

(b)zonal advection

(a)tendency

 Negative tendency

( c ) meridional advection

(d) (e) + (f)

 Cold areais induced by sum of adiabatic cooling and latent heat.

(e)vertical advection

(f)condensational heating

 Cold area depends on the adiabatic cooling.

z

x

Condensational heating induces warm core at middle- or upper-level

→updraft is enforced

developing process energy budget

K→K’ is mainly barotropic conversion,

and about 1/4 of the increase of K’,

Energy Diagram between 50 and 60hr.

Normalized with EKE.

Dimension is [10-6s-1].

Developing Process -energy budget-

Mean

Available

Potential

Energy

Mean

Kinetic

Energty

Eddy

Kinetic

Energy

(EKE)

Eddy Available

Potential Energy

(EPE)

Loading with

precipitation

Condensational heating

Developing mainly depends on P’→K’

P’ mainly depends on Q, and P→P’ is much small.

conclusion
Conclusion
  • Several observational features is well reproduced under an idealized environment without cumulus parameterization.

(warm core, shape of cloud cluster, trailing portion)

  • A vertical trough of MAL tilts eastward with heihgt, because adiabatic cooling induces cold area in low-level to the east of low.
  • The vertical structure is meridionally different.

(Because of the difference of contribution of adiabatic cooling.)

  • The development mainly depends on EPE induced by condensational heating.
vertical structure1

contour:P’(every 0.2hPa), shadow:positive ’[K]

(meridionally averaged over 100km through the center)

Vertical Structure

T=60hourの

at the center

T=60hourの

150km north from the center

[km]

[km]

z

[km]

[km]

x

slightly or westward tilting of the trough

 Pressure trough tilts eastward

 Cold anomaly to the east

Meridionally different vertical structure

contour:P’(every 0.05hPa), shadow:positive ’[K]

When condensation is not concidered,

[km]

Vertical trough tilts westward with height.

[km]

developing process energy budget1

K→K’ is mainly barotropic conversion,

and about 1/4 of the increase of K’,

Developing Process -energy budget-

Energy Diagram between 50 and 60hr.

Normalized with TKE.

Dimension is [10-6s-1].

Tendency of EKE

averagedover whole region

[J m-3]

Mean

Available

Potential

Energy

Mean

Kinetic

Energty

Eddy

Kinetic

Energy

(EKE)

Eddy Available

Potential Energy

(EPE)

[hour]

Loading with

precipitation

Condensational heating

Developing mainly depends on P’→K’

P’ mainly depends on Q, and P→P’ is much small.

sensitivity to the baroclinicity
Sensitivity to the Baroclinicity

Environmental U and T of

CNTL and B15

CNTL

Environment:

●Baroclinicity is as same as 1.5 times of one of CNTL

●qv becomes small amount in north side

●Wind velocity becomes large

B15

overview
Overview

Vertical integration of condensational water [10-1g] and

SLP[hPa] at 70hr.

B15

CNTL

y

x

●Cloud Cluster exists to the east of low.

horizontal structure1
Horizontal Structure

u’,v’ and w at z=3km at 60hr.

CNTL

B15

Center

of Jet

[m/s]

[m/s]

[m/h]

[m/h]

●Horizontal structure changed

Because of vertical shear becomes strong.

vertical structure2
Vertical Structure

P’ (contour, 0.2hPa) and positive θ’(shadowed) at70hr

CNTL

B15

Z [km]

Y [km]

●Vertical trough still tilts eastward with increasing height

slide21

Energetics

Budget of Eddy Kinetic Energy :

[K,K’]y

[K,K’]z

redistributio

[P’,K’]

dissipation

Budget of Eddy Available Potential Energy :

[P,P’]

[K’,P’]

[Q,P’]

Ek=ρ0(u’2+v’2+w’2)/2, Ep=αθ’2/2

V : velocity (vector), p:pressure, Cs : sound velocity, Q : condensational heating

q : condensational water

Ek : Eddy Kinetic Energy, Ep: Eddy Available Potential Energy

( ̄): zonal mean,

( )’ : deviation from zonal mean

res: residual terms、diff : diffusion

difference of developing process

Tendency of EKE[J m-3] averaged over whole region

Difference of Developing Process

Developing rate becomes small because qv becomes small amount

Energy Diagram between 50-60hour

CNTL

B15

●Contribution of Q becomes weak

●Effect of Basic Field becomes strong

●mainly depends on Q

mechanism of trailing portion 1
Mechanism of Trailing Portion 1

Mixing ratio of water vapor [g/kg] at z=0.5km

dry air advection from above

large gradient of qv

mechanism of trailing portion 2
Mechanism of Trailing Portion 2

Each Terms of Front Genesis

at 19hr

  • Condensation
  • Divergence
  • Deformation
  • Tilting Term

Deformation and Tilting are

much strong!!

Mechanism:

1:dry air advection from above

with down draft

2:deformation and tilting strengthen