1. 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

2. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20052 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)

3. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20053 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)

4. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20054 Earths Radiation Balance Outgoing Longwave Radiation OLR Incoming Shortwave Radiation Sun Earth

5. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20055 Earths Radiation Balance Wavelength [μm] λE λ [normalized] (Wallace und Hobbs, `Atmospheric Science', Academic Press, 1977.) Radiative equilibrium temperature: -18°C Global mean surface temperature: +15°C 34 K natural greenhouse effect

6. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20056 Clear-Sky OLR Spectrum Water vapor and CO 2 are the most important greenhouse gases.

7. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20057 But what about Clouds?

8. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20058 OLR-Spectrum with Cirrus Single scattering calculation. Ice water content 0.01 g/m 3 (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)

9. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 20059 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)

10. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200510 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)

11. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200511 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 CO 2 (Ramanathan et al., Science, 243, 1989). How will the net effect change for a changing surface temperature? No good answer at the moment.

12. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200512 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).

13. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200513 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.)

14. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200514 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)

15. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200515 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)

16. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200516 Aircraft Campaign Locations (Heymsfield and McFarquhar [2002].)

17. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200517 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].)

18. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200518 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,...)

19. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200519 ESA Earth Explorers CIWSIR current call (Adapted from R. Münzenmayer, EADS Astrium GmbH) Humidity Clouds

20. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200520 EarthCARE Cloud 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

21. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200521 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)

22. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200522 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)

23. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200523 Cirrus Measurement with Microwave Sensors ARTS Simulation (CIWSIR Mission Proposal) (Buehler et al., CIWSIR Mission Proposal, 2005, simulation by Sreerekha Ravi)

24. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200524 Frequency Dependence of Ice Signal (Figure: Sreerekha T. R., IWP = 80 g/m 2, randomly oriented cylindrical ice particles, aspect ratio 4, r = 100 µm)

25. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200525 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)

26. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200526

27. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200527 190 GHz664 GHz (ARTS Simulation: Sreerekha T.R.)

28. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200528 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).

29. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200529 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)

30. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200530 CIWSIR Channels (Buehler et al., CIWSIR Mission Proposal, 2005, figure by Viju O. John)

31. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200531 The CIWSIR Instrument (Antenna diameter: 30 cm Picture: Mark Jarrett)

32. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200532 The CIWSIR Instrument Mission 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.

33. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200533 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.

34. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200534 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)

35. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200535 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)

36. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200536 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)

37. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200537 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)

38. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200538 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!

39. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200539 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)

40. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200540 Summary and Outlook Cirrus 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.

41. Stefan Buehler, COST 723 UTLS Summerschool, Cargese, Oct. 3-15, 200541 Thanks for your attention. Questions?...