Altostratus

Nimbostratus

12

Chimney clouds

						Cb
	Cu hum		Cu med	Cu cong

13

Meso – scale convective complexes (MCC)

14

Chimney cloud formation

p z	E	zE E	Convection level
			(FCL)

zdW	0	0°C
dt
E
Condensation		zk
level (LCL)
		T

Three important levels: lifting condensation level (Zk)
practically coincides with cloud bottoms, zero isotherm level (Z0)
that separates super cooled (upper) part of the cloud water from
non-super cooled (lower) one, free convection level (Zc)
practically coincides with the cloud top.	15

Lifting condensation level

Determination of the lifting condensation level

S 0,622 e

P

;

ln S ln 0,622 ln e ln P

1 dS

1 de

1 dp

In case of adiabatic ascent

S const;

dS

dz e dz

0

S

P dz

dz

1 de

1

dp

dP g

P

g

Using Clausius Clapeyron equation

e dz

P dz

RT

dz

dE

L

dT

de

L

d

L

d

1 dP

E R

T 2

e R

2

Rw

2

P dz

w

w

dz

L

d

1

Pg

d

gRw 2

gRw

9,8 461

6,3 10 6

287 2,5 10

6

2

P RT

Rw

dz

dz

RL

T

RL

16

		gRw		2	6.3 10 6 2
		RL T			T

0 Zk T0 a Zk

According to results of calculation dew point lapse rate in the conditions typical for the atmosphere in the extratropical latitudes, the value of this lapse rate can be adopted with the accuracy of 10% 0,17°/100m =const.

(T

) ( )Z

0

k

T0 0

0

a

Zk С

Zk

T0 0

С

1

1,23

a

0,98

0,17

h. m.

m

Z

k

1,23 T

0

Z

k

123 T

0

0

0

An example

Zk

123 15 9 738 m

Pk P0 13,6 T0 0

T 150 C

0

Zk

1,23 15 9 7,4 h. m.

Tk 1,22 0 0,22T0

0 90 C

17

Free Convection level

		Free convection	W 0
Z3	'dz	level	E E
E g
Z 2

W 0

Z '

dW 0

dt

E g ' dz

Z 2

Z1

Lifting condensation level

18

Level T=0°C determination

p	z	Temperature
		in the cloud

Temperature variation within an ascending particle

ZT 0

T 0°C

19

Entrainment

Ascending particle (thermic) is not

isolated. It exchanges mass, momentum,

heat, moisture etc with ambient air

Thermic

Ascending cloud air is (a) warmer, (b)

saturated; ambient air is not saturated.

In the course of the exchange, the

entrained air make the cloud air

temperature lower ad drier. As result

p

z

some droplets evaporate, that makes the

temperature even more lower, and energy

m

4

R3

of instability decreases.

dm

4

dR

2 dR

3

1 dm

R

2

3

4 R

a

dz

3

dz

dz

T

m dz

20

entrainment index