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OBS 15: New Satellite Sensors to study Cirrus Clouds in the sub-mm Spectral Range. COST 723 UTLS Summerschool Cargese, Corsica, Oct. 3-15, 2005 Stefan A. Buehler Institute of Environmental Physics University of Bremen www.sat.uni-bremen.de. Overview. - PowerPoint PPT Presentation
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COST 723 UTLS Summerschool
Cargese, Corsica, Oct. 3-15, 2005
Stefan A. Buehler
Institute of Environmental Physics
University of Bremen
www.sat.uni-bremen.de
OBS 15: New Satellite Sensors to study Cirrus Clouds
in the sub-mm Spectral Range
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
2
Overview
Ice clouds in the earths radiation balance
Existing ice cloud observations
Observing ice clouds in the sub-mm spectral range
Summary and outlook
(Picture by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
3
Overview
Ice clouds in the earths radiation balance
Existing ice cloud observations
Observing ice clouds in the sub-mm spectral range
Summary and outlook
(Picture by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
4
Earths Radiation Balance
Outgoing Longwave Radiation OLR
Incoming Shortwave
RadiationSun
Earth
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
5
Earths Radiation Balance
Wavelength [μm]
λEλ
[nor
mal
ized
]
(Wallace und Hobbs, `Atmospheric Science', Academic Press, 1977.)
Radiative equilibrium temperature: -18°C
Global mean surface temperature: +15°C
34 K natural greenhouse effect
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
6
Clear-Sky OLR Spectrum
Water vapor and CO2 are the most important greenhouse gases.
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
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But what about Clouds?
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
8
OLR-Spectrum with Cirrus
Single scattering calculation.
Ice water content 0.01 g/m3 (contrail-cirrus), altitude 6-7 km.
Cloud reduces OLR.
Not the whole story: Clouds are active in the shortwave and in the longwave.
(Calculation: Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
9
The Role of Cirrus Clouds: Shortwave
Cirrus clouds reflect sunlight and thus increase the planetary albedo.
(AVHRR, Channel 1, 580-680nm, 25.1.2002, 13:30 UTC, Data Source: Met Office / Dundee Receiving Station)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
10
The Role of Cirrus Clouds: Longwave
Cirrus clouds are radiatively cold and thus reduce the OLR.
Attention: grayscale is normally reversed for IR images so that clouds look white.
(AVHRR, Channel 4, 10.3-11.3μm, 25.1.2002, 13:30 UTC, Data source: Met Office / Dundee Receiving Station)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
11
The Net Effect of Cirrus Clouds
For high and optically thin clouds the longwave warming effect dominates.
For lower and optically thicker clouds the shortwave cooling effect dominates.
Global net effect of all clouds is cooling. Magnitude: 4 times double CO2 (Ramanathan et al., Science, 243, 1989).
How will the net effect change for a changing surface temperature?
No good answer at the moment.
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
12
Cirrus Particle Sizes and Shapes
(Miloshevich et al., J. Atmos. Oceanic. Tech., 2001)
Many different particle types (compare lecture by Klaus Gierens)
For cirrus clouds the net effect depends on the size (and shape) of the ice particles.
Feedback direction unclear. (Stephens et al., J. Atmos. Sci., 47(14), 1742-1754, 1990).
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
13
Ice Clouds in Weather Prediction Models
In models: Ice Water Content (IWC)(compare lecture by Francois Bouttier)
(Met Office, UK, mesoscale model, Image: Sreerekha T.R.)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
14
Ice Clouds in Climate Models
Climatology of zonal, annual mean IWP from various models in the IPCC AR4 data archive shows difference up to an order of magnitude.
Delta-IWP after a CO2 doubling shows also vast differences.
IWP observations are needed to resolve model differences.
(Figure by Brian Soden, University of Miami)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
15
Overview
Ice clouds in the earths radiation balance
Existing ice cloud observations
Observing ice clouds in the sub-mm spectral range
Summary and outlook
(Picture by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
16
Aircraft Campaign Locations
(Heymsfield and McFarquhar [2002].)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
17
Particle Size
Larger size for warmer temperature, but
Large natural variability
Overall:
Large instrumentation Inhomogeneity
Need global satellite data to validate GCMs
(Heymsfield and McFarquhar [2002].)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
18
Existing Satellite Observations
Cloud emission (IR radiometry):Retrieval of ice water path (IWP) and size (D) only for thin (semitransparent) ice clouds(ATSR-2, HIRS, Meteosat, ...)
Solar reflectance (UV/Vis):Retrieval of D and gross habit classification for particles near cloud top(POLDER, Meteosat, ...)
Cloud transmission (mm-wave):Retrieval of IWP only for thick (deep convective) ice clouds(AMSU-B, SSM-T2, ...)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
19
ESA Earth Explorers
CIWSIR
current
call(Adapted from R. Münzenmayer, EADS Astrium GmbH)
Humidity
Clouds
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
20
EarthCARECloud Profiling Radar (CPR)at 94 GHz (similar to the CPR on CLOUDSAT)
Lidar (ATLID) at 355 nm (UV)
+ other instruments
Spots of < 1 km diameter
High vertical resolution (CPR < 400 m, ATLID < 100 m)
aerosol and cloud profiles plus radiation fluxes
Point samples along flight track
IWC from CPR to factor of 2 with assumptions on size distribution
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
21
Overview
Ice clouds in the earths radiation balance
Existing ice cloud observations
Observing ice clouds in the sub-mm spectral range
Summary and outlook
(Picture by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
22
Cirrus Measurement with Microwave Sensors
Ice cloud reduces the brightness temperature, as a part of the upwelling radiation is scattered away.
Compared to the IR, the measurement „sees“ the inside of the cloud, not just the top.
Sensitivity is strongly frequency dependent.
(Buehler et al., CIWSIR Mission Proposal, 2005, Figure by Oliver Lemke)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
23
Cirrus Measurement with Microwave Sensors
ARTS Simulation
(CIWSIR Mission Proposal)
(Buehler et al., CIWSIR Mission Proposal, 2005,
simulation by Sreerekha Ravi)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
24
Frequency Dependence of Ice Signal
(Figure: Sreerekha T. R., IWP = 80 g/m2, randomly oriented cylindrical ice particles, aspect ratio 4, r = 100 µm)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
25
Influence of Cirrus Clouds on AMSU-B
Strong ice clouds are detectable at AMSU frequencies (183±7 GHz)
(25.1.2002, 1330 UTC
Figure: Sreerekha Ravi)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
26
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
27
190 GHz 664 GHz
(ARTS Simulation: Sreerekha T.R.)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
28
New Cirrus Sensors
Strong Cirrus clouds have an important influence on AMSU-B measurements near 183 GHz, but
to determine the ice water content of weaker clouds (and ice particle size/shape) we need more channels at higher frequencies.
NASA proposal SIRICE (PI Steve Ackerman).
ESA Opportunity Mission Proposal CIWSIR (Cloud Ice Water Sub-millimeter Imaging Radiometer).
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
29
Different Particle Sizes
Different frequencies sample different parts of the size distribution
IR sees only smallest particles, radar only largest particles (compare lecture by Geraint Vaughan)
(Buehler et al., CIWSIR Mission Proposal, 2005, simulation by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
30
CIWSIR Channels
(Buehler et al., CIWSIR Mission Proposal, 2005, figure by Viju O. John)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
31
The CIWSIR Instrument
(Antenna diameter: 30 cmPicture: Mark Jarrett)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
32
satellite orbit
swath width
flight direction
SSP
footprints
fore-view
aft-view
45°flightdirection
fore-view
aft-view
view from the top
The CIWSIR InstrumentMission proposal to ESA for current explorer call.
Conical scanner.
Goal: Ice water path and effective ice particle size with 15 km horizontal resolution and 25% accuracy.
Preparation: Aircraft campaigns with sub-mm receivers and simultaneous in-situ measurements.
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
33
Retrieval by Bayesian Interpolation
Compare lecture by Francois Bouttier.
Create training dataset that covers the atmospheric variability (atmospheric states plus simulated radiances).
Bayes’ theorem quantifies the notion that if the measurement looks similar then the underlying state is likely to be also similar.
Retrieved IWP is the mean of all IWP in the training dataset, weighted with the “closeness” of the simulated radiances to the measured radiances.
For Gaussian statistics same result as 1D-Var.
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
34
Performance Estimate
IWP and D median errors mostly below 25 %
IR radiances complement sub-mm channels
Requirement for CIWSIR to fly tandem with Metop (AVHRR/3, IASI)
Co-registration facilitated by high AVHRR spatial resolution
(Buehler et al., CIWSIR Mission Proposal, 2005, simulation by Frank Evans)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
35
Odin Data
There are no meteorological sub-mm sensors (yet)
Odin SMR is a stratospheric chemistry instrument with a band at 502 GHz
Choose measurements with low tangent altitude
Ice clouds clearly visible(Tangent altitude 6 km, arbitrary simulation, IWP not fitted,Source: Patrick Eriksson)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
36
Ice Clouds in Odin sub-mm Data
(Ice column above 10.5 km. Top: Odin-SMR Retrieval fall 2002. Bottom: ECHAM autumn average. Source: Patrick Eriksson)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
37
Simulated Polarization Signal in MLS Data
R2(V): 200.5 GHz
R3(H): 230 GHz
Similar absorption in both channels
Observe difference in cloud signal between channels
(Emde, 2005)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
38
EOS-MLS Data
Simulation MLS Measurement
Davis et al. [2005] found effective aspect ratio of 1.2±0.2
Not to be confused with the large aspect ratios of individual particles!
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
39
Overview
Ice clouds in the earths radiation balance
Existing ice cloud observations
Observing ice clouds in the sub-mm spectral range
Summary and outlook
(Picture by Claudia Emde)
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
40
Summary and OutlookCirrus clouds play a crucial role in the earths climate due to their strong interaction with shortwave and longwave radiation.
Climate models and NWP models include cloud ice water content (IWC). There are large variations between models.
Global IWC or ice water path (IWP) data are urgently needed for validation.
IWC can not be directly measured with existing satellite sensors.
CLOUDSAT and EarthCARE will be a big steps towards a better understanding of cloud processes and cirrus climatology, but will not provide daily accurate global IWP data.
A sensor in the sub-mm, combined with existing IR data, can measure IWP directly.
SIRICE (NASA) and CIWSIR (ESA) proposals.
Aircraft campaigns are needed to validate retrieval algorithms.
Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 2005
41
Thanks for your attention.Questions?
...