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
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