AULA 3

CAMADA LIMITE ATMOSFÉRICA

– PARTE CONVECTIVA

E ESTÁVEL

Sunrise Noon Sunset Sunrise

Residual Layer Residual Layer

Stable (nocturnal) Layer

2000

1500

1000

500

0

Inversion

He

igh

t (m

ete

rs)

Adapted from Introduction to Boundary Layer Meteorology -R.B. Stull, 1988

Convective

Mixed Layer

Stable (nocturnal) Layer

Atmospheric Boundary Layer

Diurnal Variation

ATMOSPHERIC TURBULENCE

•Turbulence due to two effects:

–Atmospheric heating, and resulting convection due to

density gradient

–Mechanical turbulence due to velocity gradient

•The flux Richardson number Rf is the ratio of these

two effects:

•The numerator can be negative, representing a loss

of kinetic energy by buoyancy

stressesshear by

energy kinetic of production

buoyancyby

energy kinetic of production

fR

The Convective Boundary Layer (CBL)

• When turbulence in the atmospheric boundary layer is maintained

largely by buoyant production the boundary layer is said to be in a

convective state

• The source of buoyancy is the upward heat flux originating from the

ground heated by solar radiation.

• Convective turbulence is relatively vigorous and causes rapid

vertical mixing in the atmospheric boundary layer.

Essential processes to be represented in the CBL

(2) Land/surface processes (surface fluxes)

(1) Turbulent mixing (turbulent fluxes)

(3) Entrainment (exchange fluxes)

Estimating the height of the planetary boundary

layer

The stable value cannot be higher than the neutral

The unstable value cannot be less than the

neutral

Inversion layer limitation

Under unstable conditions, the determination of zp is not

critical: a temperature inversion which limits the extent of

vertical mixing is generally present at zi < zp

Convective mixed layer (CML):

Growth

The turbulence (largely the

convectively driven

thermals) mixes (entrains)

down potentially warmer,

usually drier, less turbulent

air down into the mixed

layer

(3) Entrainment

The third essential process is entrainment

Top-down diffusion of an scalar.

Laboratory experiment by Harm Jonker (TUD)

07/03/2010

0

200

400

600

800

1000

298 299 300 301 302 303 304 305 306

T e m p Pot (K)

Alt

itu

de

(m

)

00:09

02:03

04:03

06:03

08:03

10:03

12:03

14:03

16:03

18:03

20:03

22:03

23:51

Sunrise Noon Sunset Sunrise

Residual Layer Residual Layer

Stable (nocturnal) Layer

2000

1500

1000

500

0

Inversion

He

igh

t (m

ete

rs)

Adapted from Introduction to Boundary Layer Meteorology -R.B. Stull, 1988

Convective

Mixed Layer

Stable (nocturnal) Layer

Atmospheric Boundary Layer

Diurnal Variation