Ekaterina Batchvarova, NIMH, Sofia – NATO-ATC-MTTP 1-10 August 2007 Surface exchange and boundary-layer parametrisations in MM5 and WRF and the European

Ekaterina Batchvarova, NIMH, Sofia – NATO-ATC-MTTP 1-10 August 2007

Surface exchange and boundary-layer

parametrisations in MM5 and WRF and the European

collaboration on enhancing meso-scale meteorological

modelling capabilities for air pollution and dispersion

applications

Ekaterina Batchvarova, NIMH, Sofia, Bulgaria


OUTLINE:

The ABL

Limits of applicability of the parameterisations used in mesoscale models:urban areasaggregation within a grid cell in nonhonogeneous areas

stable conditions very low wind speeds


Two-way coupling WRF/CFD through MCEL (Model Coupling Environmental Library)

Fei Chen et al, Integrated Urban Modeling System for the Community WRF Model: Current Status and Future Plan, Workshop on Model Urbanization Strategy, Exeter, UK. 3-4 May 2007

WRF-Noah/UCM coupled model forecast

Down-Scale

Up- Scale

Coupling

CFD-Urban:Hi-Res Urban Model

CFD-Urban: T&D

The height of the atmospheric boundarylayer (ABL)

Top of mixing layer

Top of mixing layer


The urban boundary-layer height

Florence

Berlin


COST 728 Action “Enhancing Meso-Scale Meteorological Modelling Capabilities For Air Pollution And Dispersion Applications”

COST Action 732 “Quality Assurance and Improvement of Micro-Scale Meteorological Models”

Why is the ABL height important?

Acts as a lid for air pollution (air pollution concentration, atmospheric chemistry)

Scaling parameter for turbulence (wind turbine load and design, dispersion of air pollution)

Scaling parametre for the wind profile (wind energy as example)

Influences the formation of clouds and ship trails

Influences propagation of radar and microwave signals

and many more……


Wind profiles over flat terrain

U:Urban R:residential

measurements 250 meter tall mast in Hamburg, Germany


0 20 40 60w ind-speed/ustar10 (d im ensionless)

10

20

50

200

Hei

ght

(m)

without accounting for the m ixing height

10 20 30 40 50 60 70wind-speed/ustar10 (dim ensionless)

10

100

20

50

200

He

igh

t (m

)M ixing heightaccounted for

The ABL height influences the wind profile above 50 m (above the surface layer)

without ABL height

with ABL height

What is it and how does it look?

Schematic structure of the growing convective boundary layer. The surface in this case is more humid than the free atmosphere which is

typical for vegetated areas.

The derivation is based on the equation for heat conservation and the budget equation for turbulent kinetic energy:

Heat flux at the top of the mixed layer:

Strength of the inversion:

Heating rate of the mixed layer:

Heat conservation:

h

w

h

w

dt

d hs

ml

)()(

,

dt

dhw h )(

mldt

d

dt

dh

dt

d

Idealized (zero-order model) of the mixed-layer

Model for the mixed-layer height

Parameterized budget for turbulent kinetic energy:

Turbulent kinetic energy budget:

,

dt

dh

hTg

Cu

hTg

BuwAw sh

2*

3*)()(

where lhs represent consumption of potential and kinetic energy by the entrainment process

3** )()( Buhw

T

gAwCuhw

T

gseh

the rhs represents productionof turbulent kinetic turbulent energyby heat flux and wind shear

Solving for the heat flux at the inversion reads:

Batchvarova and Gryning, 1991: BLM

hLBhA

LBAh

2)21(

It is possible to derive an analytical solution for , but it is unattractive for applied use.

An approximation to the analytical solution is suggested

with the correct asymptotic limits for neutral and convective conditions

Solid line the analytical solution, dashed line its approximation

Applying these expressions and the approximation for Δ a differential equation for the height of the internal boundary layer, h, can be derived:

III

s

s

ww

dt

dh

LBhATg

Cu

LBhA

h )(

)1(2)21(

2*

2

The spin-up term (III) dominates the growth of the shallow boundary layerFurther growth makes the contribution of of mechanical turbulence (II)increasingly important until the boundary layer reaches a height of about -1.4L, where convective turbulence (I) takes over the controlof the growth process.

I II

Batchvarova and Gryning, 1991: BLM

s

s

ww

y

hv

x

hu

t

h

LBhATg

Cu

LBhA

h )(

)1(2)21(

2*

2

Coastal area – Internal Boundary Layer

Gryning and Batchvarova, 1990: QJRMS

2.03.3

31

ERih

h

2)(

)(

dtdh

hTgRiE

Entrainment Richardson number:

Entrainment zone depth:

When the ABL isgrowing fast, (morning)the entrainment zone canbe 60% of it. Later in the day it becomes smaller, empirical limit is 20% of the ABL height

Model for the entrainment zoneAnd First order ABL model

The entrainment zone depth estimated from Sodar measurements close to Berlin, Germany. The dashed line represent the parameterisation suggested by Gryning and Batchvarova (1994). The figures indicate the number of cases in each class, and the error bars the standard deviation.

Simulations of the height of the internal boundary layer over land

460 480 500 520 540 560

UT M -E AS T (km )

5400

5420

5440

5460

5480

5500

UT

M-N

OR

TH

(km

)

U rban

A gricu ltu ra l

Park s

Bogs

W ater

Mounta ins

The Vancouver cases

Tethersonde measurements

and model simulations of the mixing height inCentral Vancouver

(Sunset site)

Leg

1

Leg

2

Leg

3

L ang ley-C ent ral

Sun set

H arris-R o ad

460 480 500 520 540 560

UT M -E AST (km)

5400

5420

5440

5460

5480

5500

UT

M-N

OR

TH

(km

)

5400 5420 5440 5460U TM -N O R TH (km )

0

500

1000

INT

ER

NA

L B

OU

ND

AR

Y-L

AY

ER

HE

IGH

T (

m)

0

500

1000

Flight leg 3

F light leg 1

C V

Pacific-93Air-plane measurements by a downlooking lidar.

Flight legs (full lines), there are 3 legs

Dashed line, model simulationsFull line lidar measurements

Intensive network (filled circles) of wind

measurements

6 7 8 9 10

P OTE N T IA L T E MP E R A TU R E (oC )

0

200

400

600

800

1000

HE

IGH

T (

m)

1 No ve mb e r 1 9 9 809:00 G M T

15:00 G M T

24:00 G M T

Christiansø

Modelled andmeasured marine boundarylayer height

Radiosoundings

Mixing height estimated by the HIRLAM model (weather prediction)

26 O

ct

28 O

ct

30 O

ct

1 N

ov

3 N

ov

0

400

800

1200

1600

2000

BO

UN

DA

RY

-LA

YE

R H

EIG

HT

Ri-

VH

(m

)

26 O

ct

28 O

ct

30 O

ct

1 N

ov

3 N

ov

0

400

800

1200

1600

2000

BO

UN

DA

RY

-LA

YE

R H

EIG

HT

Ri-

S (

m)

Boundary-layer heights over Christiansø during the extensive observation period, estimated from profiles of wind and temperature from the HIRLAM model, are shown by thin lines. The left panel shows the results using the Richardson number suggested by Sørensen, the right panel when using the Richardson number in Vogelezang and Holtslag. Bullets show the measurements. The thick line illustrates a running mean over 9 points.

))()()((

))()((22 zvzus

szzgRi

v

vvB

.

2*

22 ))()(())()(()(

))()((

ubsvzvsuzus

szzgRi

v

vvB

The critical Richardson number method:

Sørensen (1998) Vogelezang and Holtslag (1996)

The urban boundary layer

on top: ABL heightthen: the blended layerred: internal boundary layergreen: inertial sublayerblue: roughness sublayer

Highly simplified

cw

b Lu

l2

2

24Ekaterina Batchvarova, NIMH, Sofia – NATO-ATC-MTTP 1-10 August 2007

Representativeness of Measurements in urban areas

25Ekaterina Batchvarova, NIMH, Sofia – NATO-ATC-MTTP 1-10 August 2007

The height of the roughess sublayer

0 0 .4 0 .8 1 .2 1 .6 2 2 .4

M e asu rem e n ts o f w a t 4 0 m h e ig h t [m s-1 ]

0

0 .4

0 .8

1 .2

1 .6

2

2 .4

Par

amet

risa

tion

of w

fro

m 4

0 m

hei

ght [

ms-

1 ]

S o f ia

The level of 40 m is within the inertial sublayer

Under convective conditions, Above the roughness sublayer in urban areas similarity theory and dispersion models are valid – hence the Mesoscale Meteorological and Air Pollution Models are applicable. If the first sigma-level is high enough, it can be used. The 2 m and 10 m values (derived via MO Similarity relations) from the first model level are not true.


Different measurement techniques register different parameters, hence correspond to different definitions of ABL (inversion in pot. Temperature is derived from radiosoundings, cloud base is detected by ceilometers, layers of accumulated aerosols are detected by sodars and lidars


Aggregation

Land-use Northern Germany, 1km resolution

Sub-grid-scale land-use within one gridbox

Eva

po

rati

on

Parameterization of sub- grid- scale land- use

urban areas vs. rural areas:• Distinct heterogeneity (gardens next to

buildings)

• Sealed surfaces

• Reduced evaporation

• Lower wind speeds

? Which parameterization?

? Modif y rural ones for urban areas?

Sylvia Bohnenstengel(1,2), K. Heinke Schlünzen(2), (1)Max-Planck I nstitute for Meteorology, Hamburg, (2) Meteorological I nstitute, University of Hamburg


Two-way coupling WRF/CFD through MCEL (Model Coupling Environmental Library)

Fei Chen et al, Integrated Urban Modeling System for the Community WRF Model: Current Status and Future Plan, Workshop on Model Urbanization Strategy, Exeter, UK. 3-4 May 2007

WRF-Noah/UCM coupled model forecast

Down-Scale

Up- Scale

Coupling

CFD-Urban:Hi-Res Urban Model

CFD-Urban: T&D

Documents

Ekaterina Batchvarova, NIMH, Sofia – NATO-ATC-MTTP 1-10 August 2007 Surface exchange and boundary-layer parametrisations in MM5 and WRF and the European