Cirrus cloud evolution and radiative characteristics

By

Sardar AL-Jumur

SupervisorSteven Dobbie

Aims and objectives Study the lifetime and evolution of

tropical thin cirrus formed on glassy and non-glassy particles.

Address the following question and find a reasonable answer:

Do we need glassy particles to justify TTL Cirrus cloud observation with:

Synoptic scaleGravity wave (GW)The impact of thin and sub-visual cirrus

cloud on earth’s radiation balance.

Cirrus cloud -definition Detached clouds in the form of white, delicate filaments, white or mostly white patches with fibrous appearance or silky sheen or both. Cirrus cloud forms below -300 C

Tropical tropopause layer (TTL)the tropical transition layer

between the troposphere and the stratosphere.

10-18km height and < 215 K.

Glassy aerosols

Droplets rich in organic material, ubiquitous in the TTL, may become glassy (amorphous, non-crystalline solid) under TTL conditions.

The glass transition temperature (Tg) is the temperature below which the viscosity of a liquid reaches such extreme values that it becomes a brittle solid .

Why do we care about tropical cirrus cloud?In general cirrus cloud often covers more than

70% of the globe with a high frequency in the tropics.

There is uncertainty about the microphysics and radiative properties of cirrus and the role of cirrus cloud in radiation budget and earth’s climate

It plays an important role in regulating the water budget of the atmosphere.

(Whlie et al, 1994)

The frequency of light cirrus (τ < 0.7)over land and ocean

TTL Cirrus observation Very low ice number density (0.005-0.2) cm-3 has

been observed frequently in TTL at temperatures below 205 K (Kramer, 2009).

High in cloud relative humidity (RHi).

Report an Nice range of 0.002 – 0.19 cm-3 at 188 to 198K from 2.4 h of observation time in subvisible cirrus during the CR-AVE field campaign Lawson et al. (2008).

Flight measurement showed ice concentration as low as (0.001-0.07) cm-3 with mean ice crystal size (1-20 μm) during (CRAVE) IN 2006.

Input parameters in addition to the AIDA chamber data for the 1-dimensional Advanced Particle Simulation Code(APSCm) used for the model runs

185 190 195

16.6

16.8

17.0

17.2

17.4

17.6

17.8

18.0

80 90 100 0 20 40 60 80 100 0 1 2 3 4

Alti

tude

/ km

Temperature / K Pressure / mBar RHi (%)

H2O mixing ratio

/ ppm

Murray et al,2010

0 100 200 300 400100

110

120

130

140

150

160

0 100 200 300 400

0.01

0.1

1HOM, 0.76 K hr-1

3.8 K hr-1

3.8 K hr-1

2.5 K hr-1

1.26 K hr-1

0.25 K hr-1

0.76 K hr-1

0.50 K hr-1

HOM, 0.76 K hr-1

% RHi

Time / minutes

0.25 K hr-10.50 K hr-1

0.76 K hr-1 1.26 K hr-1

2.5 K hr-1

N ice

/ cm

-3

Time / minutes

Mea

sure

d N ice

Hetrogeneous nucleation on glassy particles (50% glassy particles) and homogeneous freezing on liquid particles (100 % liquid particles) with deposition coefficient of water vapour on ice α=0.5.

APSC run’s result of the ice number concentration for two vertical profile of temperature the initial Rhi=120%, α=1.0. (Non-glassy case).

0 1 2 3 4 5 6 7 8 9 10 111E-4

1E-3

0.01

0.1

1

ice n

umbe

r (cm-3

)

updraft (cm/sec)

T0+5 T0

In order to have a realistic cirrus scenarios and not just perform an academic exercise, we used observations of gravity waves and vary the key unknown parameters of this problem ( glassy particles concentration, deposition coefficient and cooling rates, amplitude and frequency of gravity wave) in order to explore the possible range of cirrus changes induced by such changes in aerosol and dynamical properties.

Gravity waves (GW)

Exists every were in the atmosphere .Transfer the energy from lower to upper

atmosphere.Recent studies show that GWs in the upper

troposphere and lower stratosphere were found to considerably influence the

formation of high and cold cirrus clouds (Jensen et

al., 2001; Jensen and Pfister, 2004; Haag and Kärcher, , 2004; Jensen et al., 2005).

Why do we care about GW

Gravity waves sourcesJets streams FrontsConvectionOrographyWind shearetc

The corresponding of amplitude and time period and its efficiency to nucleate ice in different mechanisms: heterogeneous and homogeneous RHi = 100% and aerosols number 100 cm -3 , 300 cm -3. Deposition coefficient α=(0.5 )

Time period(sec)Amplitude(cm/sec)

900 1200 1500

20 - - -

50 - glassy (equilibrium) glassy (equilibrium)

90 glassy (equilibrium) glassy(equilibrium) glassy/non-glassy (pulse decay)

100 glassy (equilibrium) glassy/non-glassy glassy/non-glassy(pulse decay)

gravity waves of amplitude 50 cm/sec and time period 1200 sec , T+5,RHi=100%,IN=50cm-3 (dynamic equilibriume).

0 100 200 300 400 5000.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

RHi

time (min)

glassy case

0 100 200 300 400 500194.0

194.2

194.4

194.6

194.8

195.0

195.2

195.4

tem

p (K

)

time (min)

glassy case

0 100 200 300 400 500

0.000

0.005

0.010

0.015

0.020

0.025

Nice

(cm

-3)

time (min)

glassy case

0 100 200 300 400 500-1

0

1

2

3

4

5

6

7

8

R(um

)

time (min)

glassy case

gravity waves of amplitude 50 cm/sec and time period 1500 sec , T+5,RHi=100%,IN=50cm-3 (dynamic equilibriume).

0 100 200 300 400 5000.8

0.9

1.0

1.1

1.2

1.3

1.4

RHi

time (min)

galssy case

0 100 200 300 400 500193.6

193.8

194.0

194.2

194.4

194.6

194.8

195.0

195.2

195.4

195.6

tem

p (K

)

time (min)

glassy case

0 100 200 300 400 500

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Nice

(cm

-3)

time (min)

glassy case

0 100 200 300 400 500

0

1

2

3

4

5

6

7

R (u

m)

time (min)

glassy case

gravity wave with amplitude 90 cm/sec and time period 1500 ,RHi=100%,T+5, IN=50 cm-3 (pulse decay).

0 100 200 300 400 500 6000.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

RHi

time (min)

glassy case

0 100 200 300 400 500 600

192.5

193.0

193.5

194.0

194.5

195.0

195.5

time (min)

tem

p (K

)

glassy case

0 100 200 300 400 500 600

0

10

20

30

40

50

60

time (min)

Nice

(mc-3

)

glassy case

0 100 200 300 400 500 600-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

time (min)

R(um

)

glassy case

imposed a set of seven single gravity waves on constant uplift of 3cm/sec with RH=100%,T+5, glassy particles =50cm-3 , deposition coefficient α =0.5.

0 100 200 300 400 5000.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

RHi

time (minutes)

glassy case

0 100 200 300 400 500

0.00

0.01

0.02

0.03

0.04

0.05

Nice

(cm-3

)

time (minutes)

gassy case

imposed a set of seven single gravity waves on constant uplift of 3cm/sec with RH=100%,T=T+5,liquid particles =100 cm-3, deposition coefficient α =0.5.

0 100 200 300 400 5000.6

0.8

1.0

1.2

1.4

1.6

RHi

time (min)

Non-glassy

0 100 200 300 400 500

0

5

10

15

20

Nice

time (min)

Non-glassy

Jensen&Pfister,2004

imposed waves (kelvin+RGR+IG) on synoptic cooling scale with glassy particles at 150 altitude, other conditions as the same as fig the data has been taken from Jensen & pfister(2004).

0 100 200 300

1.0

1.1

1.2

1.3

1.4RH

%

time (min)

glassy case

0 100 200 300

0.00

0.02

0.04

0.06

Nice

time (min)

glass case

0 50 100 150 200 250 300

0

2

4

6

8

10

R(um

)

time(min)

glassy case

Model runs with glassy and non-glassy particles for a wide range of α

50 100 150 200 250 300 350 4001E-3

0.01

0.1

1

100 200 300 400

ice n

umbe

r den

sity

(cm

-3)

time (min)

hom_d=1

het_d1

het_d0.06

het_d0.1het_0.2

The radiative heating and forcing of cirrus cloud have been performed by using 1D – radiative transfer model (Jiangnan code) through calculating the net impact of cirrus on both solar and IR.

56

54

52

50

48

46

44

42

40

38

36

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.256

54

52

50

48

46

44

42

40

38

36

P (M

B)

solar heating rate (K/DAY)

glassy z=60

Non glassyz=60clear sky

-1 0 1 2 3 4 5 6 7 8 956

54

52

50

48

46

44

42

40

38

36

P (M

B)

IR heating rate (K/DAY)

clear sky glassy Non- glassy

-1 0 1 2 3 4 5 6 7 8 9 10-1 0 1 2 3 4 5 6 7 8 9 1056

54

52

50

48

46

44

42

40

38

36

P (M

B)

net heating rate (K/DAY)

clear sky glassy non-glassy

The maximum radiative heating of cirrus forming on glassy and liquid particle compared to clear sky for for T+5, IN=50cm-3, aerosols=100cm-3, cloud fraction=100%. Updraft=3 cm/sec.α=0.5

The maximum radiative heating of cirrus forming on glassy particle by superimposed gravity wave on synoptic scale for T+5, IN=50cm-3, total aerosols=100cm-3, cloud fraction=100%.(glassy case)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.256

54

52

50

48

46

44

42

40

38

36

P (M

B)

solar heating rate (K/DAY)

GW+constant uplift

-1 0 1 2 3 4 5 6 7 8 956

54

52

50

48

46

44

42

40

38

36

P (M

B)

IR heating rate (K/DAY)

GW+constant uplift

-1 0 1 2 3 4 5 6 7 8 9 1056

54

52

50

48

46

44

42

40

38

36

P (M

B)

net heating rate (K/DAY)

GW+constant uplift

The impact of deposition factor on cirrus microphysics and radiative properties.

0 100 200 300 400 5001E-3

0.01

0.1

ice n

umbe

r den

sity

(cm

-3)

time (min)

updraft= 3 cm/secdeposition=1

updraft = 3 cm/sec deposition =0.5

0 100 200 300 400 5000

1

2

3

4

5

6

7

8updraft = 3 cm/sec deposition =1

mea

n ice

effe

ctive

radi

us (u

m)

time (min)

updraft = 3 cm/sec deposition =0.5

The net flux at the top of the atmosphere (TOA) can be found by using following concept:

Cir,s=Fclir,s- Fov

ir,s Fcl

ir,s the upward flux of infrared or solar for clear sky.

Fovir,s flux of upward infrared or solar for

cloudy sky.Then, the net radiative forcing of cirrus cloud

for solar and IR radiation computed from:C = Cir + CS

(Qiang and Liou, 1993)

-20 0 20 40 60 80 100 120 140 160 180

0

1

2

3

4

5

6

netfl

ux (w

/m2)

time (min)

0.1 glassy

Non glassy

TOA 50 % glassy

-20 0 20 40 60 80 100 120 140 160 180-6

-5

-4

-3

-2

-1

0

netfl

ux (w

/m2)

time (min)

50% glassy

SRF

Non glassy

0.1 glassy

-20 0 20 40 60 80 100 120 140 160 180-0.0050.0000.0050.0100.0150.0200.0250.0300.0350.0400.0450.0500.0550.060

opt

ical d

epth

( tau

)

time (min)

0.1 glassy

50 % glassy

Non - glassy

The variation of optical depth with time for homogenous nucleation (liquid particle), heterogeneous particles (glassy particles) and with 10% glassy particles.α =0.5

Conclusion Run the model with glassy particles show an agreement with TTL

cirrus observation with both constant uplift and gravity waves. Homogeneous freezing with weak updraft could show

observation with specific deposition coefficient. Higher amplitude gravity waves produce higher ice number

densities and smaller crystals. Higher frequency gravity wave produces higher ice number

densities and smaller crystals. The small scale gravity waves have the potential to produce ice

with glassy particles within the range of observation in TTL. (dynamical equilibrium)

Cirrus cloud forming on glassy particles shows dynamic equilibrium up to amplitude of 90 cm/sec and frequency (1200s)-1 of gravity wave.

Cirrus cloud forming on glassy and non glassy particles shows pulse decay with vertical velocity(the amplitude of gravity wave) with 90 and 100 cm/sec and frequency (1500s)-1

Thank you very much