Cirrus cloud evolution and radiative
characteristics
By
Sardar AL-Jumur
Supervisor
Steven 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 scale
 Gravity 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.

The frequency of light cirrus (τ < 0.7)over land and ocean
(Whlie et al, 1994)
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
18.0
Altitude / km
17.8
17.6
17.4
17.2
17.0
16.8
16.6
185
190
195 80
Temperature / K
90
100
Pressure / mBar
0 20 40 60 80 100 0
RHi (%)
1
2
3
H2O mixing ratio
/ ppm
4
Murray et al,2010
1
160
HOM, 0.76 K hr
-1
3.8 K hr
Measured Nice
0.1
-1
150
-1
2.5 K hr
2.5 K hr
-1
-1
1.26 K hr
-1
0.76 K hr
-1
0.50 K hr
0.25 K hr
140
-1
-1
1.26 K hr
-1
0.76 K hr
-1
0.50 K hr
-1
0.25 K hr
-1
130
% RHi
Nice / cm
-3
3.8 K hr
HOM, 0.76 K hr
-1
120
0.01
110
0
100 200 300 400 0
Time / minutes
100
200
300
400
100
Time / minutes
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).
T0+5
T0
1
-3
ice number (cm )
0.1
0.01
1E-3
1E-4
0
1
2
3
4
5
6
7
updraft (cm/sec)
8
9
10
11
Gravity waves (GW)

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.
Why do we care about 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).
Gravity waves sources
Jets streams
 Fronts
 Convection
 Orography
 Wind shear
 etc

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)
Time period(sec)
Amplitude(cm/sec)
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 )
1.30
glassy case
195.4
glassy case
1.25
195.2
1.20
195.0
temp (K)
RHi
1.15
1.10
1.05
194.8
194.6
1.00
194.4
0.95
194.2
0.90
194.0
0.85
0
100
200
300
time (min)
0.025
400
0
500
100
300
time (min)
8
glassy case
200
400
500
glassy case
7
0.020
6
5
R(um)
-3
Nice (cm )
0.015
0.010
4
3
2
0.005
1
0
0.000
-1
0
100
200
time (min)
300
400
500
0
100
200
300
400
500
time (min)
gravity waves of amplitude 50 cm/sec and time period 1200 sec ,
T+5,RHi=100%,IN=50cm-3 (dynamic equilibriume).
glassy case
galssy case
1.4
195.6
195.4
1.3
195.2
195.0
temp (K)
RHi
1.2
1.1
194.8
194.6
194.4
1.0
194.2
194.0
0.9
193.8
0.8
193.6
0
100
200
300
400
500
0
100
time (min)
200
300
400
500
time (min)
glassy case
glassy case
7
0.06
6
0.05
5
0.04
R (um)
-3
Nice (cm )
4
0.03
3
0.02
2
0.01
1
0
0.00
0
100
200
time (min)
300
400
500
0
100
200
300
400
time (min)
gravity waves of amplitude 50 cm/sec and time period 1500 sec ,
T+5,RHi=100%,IN=50cm-3 (dynamic equilibriume).
500
glassy case
glassy case
1.7
195.5
1.6
195.0
1.5
194.5
temp (K)
RHi
1.4
1.3
1.2
194.0
193.5
1.1
1.0
193.0
0.9
192.5
0.8
0
100
200
300
400
500
time (min)
600
0
100
200
300
400
500
time (min)
glassy case
60
600
glassy case
2.0
1.8
50
1.6
1.4
40
R(um)
-3
Nice (mc )
1.2
30
20
1.0
0.8
0.6
0.4
10
0.2
0.0
0
-0.2
0
100
200
300
400
time (min)
500
600
0
100
200
300
time (min)
400
500
600
gravity wave with amplitude 90 cm/sec and time period 1500
,RHi=100%,T+5, IN=50 cm-3 (pulse decay).
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.
glassy case
gassy case
1.35
0.05
1.30
0.04
1.25
0.03
-3
Nice (cm )
RHi
1.20
1.15
1.10
0.02
1.05
0.01
1.00
0.95
0.00
0.90
0
100
200
300
time (minutes)
400
500
0
100
200
300
time (minutes)
400
500
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.
Non-glassy
Non-glassy
1.6
20
15
1.2
Nice
RHi
1.4
10
1.0
5
0.8
0
0.6
0
100
200
time (min)
300
400
500
0
100
200
time (min)
300
400
500
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).
glassy case
glass case
1.4
0.06
1.3
Nice
0.02
1.1
0.00
1.0
0
100
200
300
0
time (min)
glassy case
10
8
6
R(um)
RH%
0.04
1.2
4
2
0
0
50
100
150
time(min)
200
250
300
100
time (min)
200
300
Model runs with glassy and non-glassy
particles for a wide range of α
hom_d=1
het_d0.06
-3
ice number density (cm)
1
het_d0.1
het_0.2
0.1
het_d1
0.01
1E-3
50
100
150
200
250
time (min)
300
350
400

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.
36
36
38
38
40
40
44
46
Non- glassy
glassy
clear sky
44
P (MB)
glassy z=60
46
48
48
50
50
52
52
54
54
56
56
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
1.2
0
1
2
3
4
5
6
7
8
9
IR heating rate (K/DAY)
solar heating rate (K/DAY)
36
38
40
42
P (MB)
P (MB)
42
Non glassyz=60
clear sky
42
non-glassy
glassy
clear sky
44
46
48
50
52
54
56
-1
0
1
2
3
4
5
6
7
8
9
10
net heating rate (K/DAY)
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
GW+constant uplift
36
36
38
38
40
40
42
42
44
P (MB)
44
46
48
50
46
48
50
52
52
54
54
56
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
56
1.2
-1
solar heating rate (K/DAY)
0
1
2
3
4
5
6
7
8
9
IR heating rate (K/DAY)
GW+constant uplift
36
38
40
42
44
P (MB)
P (MB)
GW+constant uplift
46
48
50
52
54
56
-1
0
1
2
3
4
5
6
7
8
9
10
net heating rate (K/DAY)
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)
The impact of deposition factor on cirrus microphysics and
radiative properties.
updraft= 3 cm/sec
deposition=1
0.1
8
mean ice effective radius (um)
-3
ice number density (cm)
updraft = 3 cm/sec
deposition =0.5
0.01
updraft = 3 cm/sec
deposition =1
7
6
5
4
updraft = 3 cm/sec
deposition =0.5
3
2
1
1E-3
0
100
200
time
(min) 300
400
500
0
0
100
200
time (min)
300
400
500
(Qiang and Liou, 1993)






The net flux at the top of the atmosphere (TOA)
can be found by using following concept:
Cir,s=Fclir,s- Fovir,s
Fclir,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
The variation of optical depth with time for homogenous nucleation (liquid
particle), heterogeneous particles (glassy particles) and with 10% glassy
particles.α =0.5
SRF
6
50 % glassy
TOA
0.1 glassy
5
0.1 glassy
-1
Non glassy
netflux (w/m2)
4
3
2
-2
50% glassy
-3
Non glassy
-4
1
-5
0
-6
-20
0
20
40
60
80
100
120
140
160
180
-20
0
20
40
time (min)
60
80
100
time (min)
0.060
0.055
0.050
Non - glassy
0.045
optical depth( tau)
netflux (w/m2)
0
0.040
0.035
0.030
0.025
50 % glassy
0.020
0.015
0.010
0.005
0.1 glassy
0.000
-0.005
-20
0
20
40
60
80
100
time (min)
120
140
160
180
120
140
160
180
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