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The Aerosol Indirect Effect: Can we measure it? Reinout Boers, KNMI

The Aerosol Indirect Effect: Can we measure it? Reinout Boers, KNMI. Contributions by Juan Acarreta, formerly at KNMI John Gras, CSIRO, Australia Henk Klein Baltink, KNMI Erik v Meijgaard, KNMI Ulrich Loehnert, UMunchen Ela Grzeszczak, IGUWarsaw. Structure of talk.

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The Aerosol Indirect Effect: Can we measure it? Reinout Boers, KNMI

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  1. The Aerosol Indirect Effect: Can we measure it? Reinout Boers, KNMI AIE-Seminar, IMAU, April 2005

  2. Contributions by Juan Acarreta, formerly at KNMI John Gras, CSIRO, Australia Henk Klein Baltink, KNMI Erik v Meijgaard, KNMI Ulrich Loehnert, UMunchen Ela Grzeszczak, IGUWarsaw AIE-Seminar, IMAU, April 2005

  3. Structure of talk 1. What is the Aerosol Indirect Effect? 2. Technique to ‘measure’ it 3. Measurements over the Southern Ocean 4. Measurements at Cabauw and Opportunities AIE-Seminar, IMAU, April 2005

  4. Definition of AIE according to IPPC report Page 307 IPPC 2001: ‘Indirect forcing by aerosols is broadly defined as the overall process by which aerosols perturb the Earth-Atmosphere radiation balance by modulation of cloud albedo and cloud amount’ AIE-Seminar, IMAU, April 2005

  5. Definition of AIE more precise ‘Indirect forcing by aerosols is defined as the change in shortwave radiative energy at the top of the atmosphere caused by aerosols that modulate cloud reflectivity’ AIE-Seminar, IMAU, April 2005

  6. Definition of AIE even more precise ‘Indirect forcing by aerosols is defined as the change in shortwave radiative energy at the top of the atmosphere caused by anthropogenic aerosols that modulate cloud reflectivity’ AIE-Seminar, IMAU, April 2005

  7. Definition of AIE even even more precise ‘Indirect forcing by aerosols is defined as the change in shortwave radiative energy at the top of the atmosphere caused by anthropogenic aerosols that modulate cloud reflectivity since the beginning of the Industrial Revolution’ AIE-Seminar, IMAU, April 2005

  8. In brief……. There is no precise definition that is used by everyone AIE-Seminar, IMAU, April 2005

  9. Earth Radiation Budget F A Cloud albedo A OD 1 OD CDNC Cloud optical depth 2 Warm cloud CDNC / size Precip OD CDNC,h F f,t CDNC CCN Cloud fraction f, Life time t, CDNC, Cloud depth h CCN CCN Mass Aerosol mass Pathways of the AIE for warm clouds Aerosol mass emission Surface AIE-Seminar, IMAU, April 2005

  10. When presented with a time series of cloud albedo, how much of the observed change is due to the AIE? AIE-Seminar, IMAU, April 2005

  11. Cloud optical depth OD CDNC A OD Warm cloud CDNC / size Cloud albedo CDNC CCN F A CCN CCN Mass Earth Radiation Budget Aerosol mass emission Aerosol mass Surface AIE-Seminar, IMAU, April 2005

  12. Optical depth Optical depth is a measure of how much light cloud droplets prevent from passing through an atmospheric column. It is proportional to the total surface area of columnal cloud droplets exposed to the sun light AIE-Seminar, IMAU, April 2005

  13. Effective radius Effective radius is defined as the fraction of the third to the second moment of the size distribution It is proportional to the radius of cloud droplets AIE-Seminar, IMAU, April 2005

  14. For measuring the (1st) Aerosol Indirect Effect over time, cloud droplet concentration N=(SO42-+B)b is the key parameter to monitor How are we going to do that globally?? AIE-Seminar, IMAU, April 2005

  15. Procedure Satellite radiance- ch 1 Satellite radiance- ch 2 Optical depth  Effective radius reff Atmospheric model (single layered cloud) =A1N1/3h5/3, reff=A2N-1/3h2/3 Droplet concentration N Cloud depth h AIE-Seminar, IMAU, April 2005

  16. Australia Tasmania Modis box MODIS Terra L2 data July 2000 – July 2004 AIE-Seminar, IMAU, April 2005

  17. For this region light and temperature dependent DMS emission from the ocean surface is the primary source of nss-sulphates acting as CCN in the marine atmosphere Seasonal Cycle in CCN, N, albedo Low CCN High CCN Sea salt spray Sea salt spray DMS Winter Ocean Surface Summer AIE-Seminar, IMAU, April 2005

  18. Optical thickness Effective radius derived from MODIS L2 Observations 2000-2004 AIE-Seminar, IMAU, April 2005

  19. Retrievals of droplet concentration AIE-Seminar, IMAU, April 2005

  20. Retrieval of cloud depth AIE-Seminar, IMAU, April 2005

  21. Determine the sensitivity of albedo to changes in N, h AIE-Seminar, IMAU, April 2005

  22. Respective contributions to A from N, h, 0 AIE-Seminar, IMAU, April 2005

  23. Conclusion Contribution to albedo change: Changes in 0 60% Changes in N 20% Changes in h 20% Even though the sensitivity to changes in N is double that of the sensitivity to changes in h! AIE-Seminar, IMAU, April 2005

  24. What can we do at Cabauw? 1) Conception of experiment to measure pathways of the AIE 2) Retrieval of cloud droplet concentration AIE-Seminar, IMAU, April 2005

  25. The Aerosol Indirect Effect is primarily a SW radiative boundary layer cloud effect, so requirements are: • Accurate SW radiation measurements at top of atmosphere • A method to attribute the observed radiation to boundary layer cloud and aerosol processes AIE-Seminar, IMAU, April 2005

  26. Linking the measured SW radiation to boundary layer clouds and aerosols Use BL Observations with quantifiable errors Compute Radiation profile Long-term Observations plus occasional IOPS Constrain to SW Surface and SW TOA fluxes AIE-Seminar, IMAU, April 2005

  27. Earth Radiation Budget F A MSG+BSRN Cloud albedo A OD MSG+Surface Remote sensing Cloud optical depth OD CDNC Warm cloud CDNC / size CDNC CCN Tower Measurements CCN CCN Mass Tower+Surface Measurements Aerosol mass Aerosol mass emission Cabauw Surface and Remote Sensing Observations of Aerosol, Clouds and Radiation (CESAR partners KNMI, TUDelft, TNO, ECN, WUR, ESA, RIVM) AIE-Seminar, IMAU, April 2005

  28. Earth Radiation Budget F A Cloud albedo A OD Cloud optical depth OD CDNC Warm cloud CDNC / size CDNC CCN CCN CCN Mass Aerosol mass Aerosol mass emission Combined with Radiative Transfer Calculations AIE-Seminar, IMAU, April 2005

  29. Cabauw Site: The site to do a long-term process study of the Aerosol Indirect Effect AIE-Seminar, IMAU, April 2005

  30. The importance of Cabauw within Netherlands / Europe B) Cabauw is a continental / maritime site. A great variety of air masses come across this region depending on air mass history A) Cabauw is within the centre of the Netherlands / Northwest Europe, therefore it is representative of the Netherlands and of Northwest Europe. C) No orography to confuse you AIE-Seminar, IMAU, April 2005

  31. Backtrajectories originating at an altitude of 500 m at Cabauw,and droplet concentrations for seven days of the Merlin flights in September 2001, 172 cm-3 124 cm-3 Cabauw -1 hour -1 day (24 hours) 157 cm-3 180 cm-3 210 cm-3 270 cm-3 275 cm-3 AIE-Seminar, IMAU, April 2005

  32. An experiment quantifying the Aerosol Indirect Effect should consist of Long-term continuous measurements at a single site to obtain closure of the radiative budget using in situ, ground-based and satellite-based remote sensing observations AND An number of Intensive Observation Periods for combining aircraft in situ studies with ground-based observations AIE-Seminar, IMAU, April 2005

  33. First step: Integrated Profiling (IPT) and Determining cloud microphysics from remote sensing at Cabauw AIE-Seminar, IMAU, April 2005

  34. Integrated Profiling Technique (IPT) (University of Munchen, U. Loehnert)Determining consistency between radiative and physicals properties of the atmospheric column1) Use multiwave length microwave radiometer, radar, lidar to retrieve T, LWC, water vapor profiles2) Make consistent with radiation profiles AIE-Seminar, IMAU, April 2005

  35. Integrated Profiling Technique: How good is this technique in profiling? (Loehnert, v Meijgaard, Klein Baltink, Boers) Use Regional Climate Model (RCM) T, qv, ql profiles to compute Tb’s Ingest Tb’s plus lidar / radar data into IPT procedure Compare IPT against RCM output IPT to compute T, qv, ql profiles AIE-Seminar, IMAU, April 2005

  36. Integrated Profiling Technique: Results for LWP, IWV AIE-Seminar, IMAU, April 2005

  37. Integrated Profiling Technique: Results for T, q proflies AIE-Seminar, IMAU, April 2005

  38. Integrated Profiling Technique: Results for radiative retrievals (preliminary) AIE-Seminar, IMAU, April 2005

  39. Retrieval of cloud droplet concentration (method 1, Klein Baltink / Boers) Retrieve cloud boundaries from radar / lidar Retrieve cloud base extinction from lidar Combine to retrieve N Retrieve liquid water path from microwave radiometer AIE-Seminar, IMAU, April 2005

  40. Retrieval of cloud droplet concentration (method 2, Grzeszczak ) Retrieve cloud boundaries from radar / lidar Retrieve in-cloud reflectivity from radar Combine to retrieve N Retrieve liquid water path from microwave radiometer AIE-Seminar, IMAU, April 2005

  41. Retrieval of cloud droplet concentration (method 3, Dong, Boers, Klein Baltink) Retrieve liquid water path from microwave radiometer Retrieve surface irradiance from pyranometers Combine to retrieve N AIE-Seminar, IMAU, April 2005

  42. Cloud depthAdiabaticityLWPDropletConcentration AIE-Seminar, IMAU, April 2005

  43. Radar retrieval of droplet concentration AIE-Seminar, IMAU, April 2005

  44. Conclusions • It is possible to extract the Aerosol Indirect Effect from albedo observations by monitoring the cloud droplet concentration • Over the Southern Ocean, albedo changes due to the AIE make up 20% of total change. AIE-Seminar, IMAU, April 2005

  45. Conclusions(2) • At Cabauw the AIE will be studied by combining radiative transfer modelling with integrated observations • Procedures to retrieve T, q profiles using IPT are starting to work AIE-Seminar, IMAU, April 2005

  46. Conclusions(3) • Procedures to retrieve droplet concentration from remote sensing observations are becoming mature(!) AIE-Seminar, IMAU, April 2005

  47. Can we now measure the AIE?? Yes………. But …………… AIE-Seminar, IMAU, April 2005

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