Correlations between microphysical properties
of large-scale semi-transparent cirrus
(from TOVS)
and the state of the atmosphere
(from ECMWF ERA-40)
Gaby Rädel
Claudia Stubenrauch, Fadoua Eddounia
Laboratoire de Météorologie Dynamique
Ecole Polytechnique, France
Gaby Rädel
ITSC-13, November 2003
1
Effective ice crystal size (De) and IWP retrieval
of semi-transparent cirrus
based on: spectral difference of cirrus emissivities at 11-8 µm
Observations:
NOAA10 1987 – 1991, 60°N – 60°S , θv< 25°
large-scale cirrus: 1°x1° overcast, pcld<440 hPa
3R radiative transfer
Tcld < 263K,TBmeas(8µm), TBmeas(11µm), Tcld, Tsurf
εsurf(SARB), closest TIGR H2O/T profiles
(ε8µm,ε11µm)
Method: simulate ε(λ,De,IWP,θ)
hom. cloud, βabs(De),<ω0(De)>,<g(De)>
planar polycrystals (mod. ADA)
bimodal size distribution
Gaby Rädel
radiative transfer
(Streamer (J.Key))
vary De, IWP
ITSC-13, November 2003
ε(λ,De,IWP,θ)
2
De and IWP retrieval (cont.)
produce look-up tables: De = f(ε8µm,ε11µm), IWP = f (De,ε11µm)
ε11
ε11−ε8
ε11
for
De
0.3 < ε11µm < 0.85
0.7 < τVIS < 3.8
sensitivity up to De ≤ 80µm
Gaby Rädel
IWP
ITSC-13, November 2003
IWP
3
Sensitivity study on ice crystal size retrieval
Rädel et al., J. Geophys. Res., May 2003
NOAA10 global average : <De> = 55µm
<IWP>= 30 g/m2
possible errors:
Overestimation of De: thin Ci with underlying water cloud
partial cover of thick Ci
different crystal shapes, e.g.
hexagonal columns instead of polycrystals
Underestimation of De: vertical heterogeneity, i.e.:
increasing De with cloud depth
broader size distribution
Gaby Rädel
ITSC-13, November 2003
4
Evaluation of TOVS cloud height with LITE
(newest LITE inversion by L. Sauvage)
796 TOVS low clouds
560 LITE single- 236 multi-layer
495 TOVS high clouds
161 LITE single- 334 multi-layer
heterogenous
scenes
very thin LITE high
clouds
zTOVS – 0.5(ztop+zbase)LITE (km)
single layer: |∆z|<1 km: 70%
peak at 0
zTOVS – 0.5(ztop+zbase)LITE (km)
|∆z| < 2 km : 60 %
peak at –0.5 km
Pcld(TOVS) ≈ pcld(mid-cloud)
better agreement for low large-scale cirrus clouds
LITE:
ztop-zbase:
Gaby Rädel
low clouds
1.3 km
high clouds
2.7 km
ITSC-13, November 2003
5
Regional and seasonal variations of De and IWP
TOVS NOAA10 3-year averages
Nε
IWP
30
70
65
25
20
60
55
win
spg
sum
aut
15
win
De
65
eff. Diameter (micron)
35
IWP (g/m2)
eff. emissivity (%)
75
NH ocean
60
NH land
55
trop. Ocean
trop. Land
50
SH ocean
45
SH land
40
NH z=2km
trop. z=2km
35
SH z=2km
spg
sum
aut
30
win
spg
sum
aut
Nε(SHm) > Nε(NHm) > Nε(trop)
NH land: Nε(sum) < Nε(win)
IWP(trop) > IWP(NHm) > IWP(SHm)
land: IWP(midsum) > IWP(midwin)
De(trop) > De(NHm) > De(SHm)
land: De(midsum) > De(midwin)
Gaby Rädel
ITSC-13, November 2003
6
De and IWP as function of cloud temperature
De90
Large-scale semi-transparent cirrus 60°N –60°S
55
7,5
80
22,5
37,5
IWP
all
different IWP
45
60
IWP (g/m2)
De (micron)
70
50
40
30
35
25
20
10
200
different De
15
32,5
210
220
230
240
250
260
270
5
200
210
Gaby Rädel
220
62,5
230
240
82,5
250
all
260
270
Tcld (K)
Tcld (K)
cold cirrus:
47,5
De depends more on IWP than on Tcld
IWP increases with Tcld
ITSC-13, November 2003
7
Regional dependence for thin and thick Cirrus
thin cirrus
90
midlatitudes
80
thick cirrus midlatitudes thin cirrus
55
midlatitudes
all
52,5
50
40
60
IWP (g/m2)
60
50
40
30
30
20
20
45
35
25
220
230
240
250
260
10
200
270
210
220
Tcld (K)
90
250
80
70
70
60
50
40
30
tropics
5
200
->Tcld
tropics55
260
270
210
220
230
240
250
260
5
200
270
50
40
220
230
tropics
62,5
47,5
240
all
82,5
270
->Tcld
250
260
Tcld (K)
55
tropics
all
82,5
45
45
60
210
Tcld (K)
32,5
IWP (g/m2)
tropics
80
35
25
35
25
30
20
210
220
230
240
7,5
250
Tcld (K)
260
270
10
200
15
15
20
all
37,5
22,5
7,5
10
200
240
Tcld (K)
De (micron)
De (micron)
90
230
62,5
47,5
32,5
IWP (g/m2)
210
25
all
37,5
22,5
7,5
35
15
15
10
200
thick cirrus IWP
midlatitudes
all
82,5
45
70
De (micron)
De (micron)
37,5
22,5
7,5
62,5
47,5
32,5
80
70
55
midlatitudes
IWP (g/m2)
De90
210
37,5
22,5
220
230
240
Tcld (K)
all
52,5
250
260
270
->Tcld
5
200
210
220
230
240
250
260
270
5
200
210
62,5
47,5
32,5
220
230
different behaviour in midlatitudes and tropics
thick Ci in tropics: De and IWP do not depend strongly on T,
almost no scatter due to different IWP or De
Gaby Rädel
Tcld (K)
ITSC-13, November 2003
240
Tcld (K)
all
82,5
->Tcld
250
260
8
270
Atmospheric properties accompanying large-scale cirrus
ERA-40 ECMWF reanalyses:
¾humidity, U, V and W for 23 pressure levels
¾Every 6 hours, 1.125° x 1.125° spatial resolution
Co-location with TOVS observations: (1989, 1990)
Water vapour (cm) Horizontal wind (m/s)
Frequency of situations with
strong
strong
mean
RMS
mean
RMS
updraft
no wind
downdraft
NH midlatitude summer
3.0
1.2
14.5
10.9
9%
38%
3%
NH midlatitude winter
1.4
0.8
26.1
15.8
13%
29%
7%
tropics
5.0
0.9
7.6
6.0
7%
44%
0.1%
SH midlatitude summer
2.3
1.0
23.4
13.8
6%
42%
4%
SH midlatitude winter
1.5
0.8
22.3
15.2
10%
34%
4%
tropics: largest water vapour, smallest winds
midlat. winter: strongest winds
SH: horizontal winds always strong
most large-scale semi-transparent cirrus in situations with no vertical wind
Gaby Rädel
ITSC-13, November 2003
9
De and IWP as function of humidity and wind
Large-scale semi-transparent cirrus 60 N – 60 S, Tcld < 233K
Stubenrauch et
al. 2003,
submitted to
Atmos.Res.
De and IWP increase with water vapour
De 12 µm smaller in case of strong winds
IWP 10 gm-2 larger in case of strong vertical updraft
Gaby Rädel
ITSC-13, November 2003
10
Regional distributions of De and IWP as
function of humidity and wind
dry, strong updraft
dry, strong hor. wind
De
humid, strong updraft
humid, strong hor. wind
IWP
De larger in case with no winds than strong winds
humid tropics: IWP larger in case of strong w than strong u+v
Gaby Rädel
ITSC-13, November 2003
11
Cirrus horizontal extent
determine horizontal extent of cirrus clouds (ε > 0.3):
a. empty boxes are filled with ‘most likely’ information on cirrus type
b. simple clustering algorithm groups adjacent boxes containing
), cirrus (0.95>ε>0.5
)
deep convection (ε>0.95
or thin cirrus (0.5>ε>0.3
)
Examples: 18/07/1989
and
30/12/1989
7h30 PM
very thin Ci
clear sky
mid and low
clouds
thin Ci
Ci
deep conv.
Gaby Rädel
ITSC-13, November 2003
12
Cirrus horizontal extent
cirrus clusters: largest in tropics
smallest in ML summer
De as fct. of distance to convective centre:
De small if very close to convective centre
and in smaller clusters -> dynamics?
(1 box = 100 x 100 km)
small clusters (<20boxes)
large clusters (>500boxes)
Gaby Rädel
ITSC-13, November 2003
13
Conclusions and Outlook
™ Large-scale semi-transparent cirrus: <De>=55µm <IWP>=30g/m2
™ IWP increases with Tcld
™ TOVS Path-B & ECMWF reanalyses Æ
De and IWP increase with atmospheric water vapour,
increase depends on vertical updraft, hor. wind,
formation processes?
™ Study De as function of cirrus size and location to
convective center for different dynamic situations
™ Find parameterizations IWP =f (q,w,T), De=f (IWP,q,w,u+v,T)
using also cluster information
Gaby Rädel
ITSC-13, November 2003
14