1. NASA CMAI WorkshopApril 20-21, 2006 Modeling Studies of Aerosol-Cold Cloud Interactions Sonia M. Kreidenweis and Paul J. DeMott Department of Atmospheric Science Colorado State University

2. NASA CMAI WorkshopApril 20-21, 2006 Motivation Aerosol indirect effects on climate –Includes effects on mixed and ice phase clouds… but these are poorly understood [IPCC TAR] For warm clouds, and homogeneous freezing processes, aerosol effects depend on size distribution, number concentration, composition –Probably true for ice formation at warmer temperatures Models will need to move toward representation of aerosol sources, sinks, and key characteristics

3. NASA CMAI WorkshopApril 20-21, 2006 Assessing ice nuclei (IN) concentrations, their variability, their sources, and their role in cloud ice formation Measurement of IN in the field and in the lab Evidence for relation of IN to ice in clouds IN variability in atmosphere? Why? Does it matter? Improve representation of cold cloud formation in climate models

4. NASA CMAI WorkshopApril 20-21, 2006 What ice nucleation mechanisms do we measure? Yes Yes/maybe No, but… Aerosols nucleate ice by varied mechanisms, most depending on T, some on RH as well No instrument yet capable of measuring all mechanisms What can a CFDC measure?

5. NASA CMAI WorkshopApril 20-21, 2006 What can be improved in models? Newer and more observations of IN now available to revisit prior parameterizations Also clear that IN must be prognostic –evidence that ice doesn’t form in depleted air masses Certain aerosol types (dust, metallic particles) and certain sizes appear to be more active IN

6. NASA CMAI WorkshopApril 20-21, 2006 What can be improved in models? For solution droplets, the theory of Koop et al. (2000) predicts that homogeneous freezing occurs at a defined a w (T) We have developed methods for converting hygroscopic growth data into solution water activity data (example below is for levoglucosan, a compound in wood smoke) –Already applied to prediction of CCN activity If models carry soluble particle type, and information on hygroscopicity, homogeneous freezing can be predicted

7. NASA CMAI WorkshopApril 20-21, 2006 Proposed Work 1.Build parcel models for aerosol-cloud interactions a.Begin with Feingold et al. (1998) aerosol-warm cloud model and Young (1974) model b.Modifications to include the ice phase, incorporating our lab and field data c.Run as adiabatic parcel or from saved histories 2.Develop parameterizations for CRMs and GCMs to replace saturation-adjustment schemes a.Implement and test through CMAI structure 3.Make models available through web interface

8. NASA CMAI WorkshopApril 20-21, 2006 Seeking correlation of IN with larger aerosol using a variety of data sets r 2 = 0.7526

9. NASA CMAI WorkshopApril 20-21, 2006 Examining cumulative distribution of [IN] and sampling conditions in many projects Increasing dust particle impacts MPACE: Arctic Fall FIRE-ACE: Arctic Spring INSPECT-2: Western U.S. Spring CRYSTAL-FACE: Florida July

10. NASA CMAI WorkshopApril 20-21, 2006 Parcel Model Each parcel initialized with thermodynamic fields and aerosol size distributions, composition, hygroscopicity, ice forming characteristics (onset conditions [T, RH] for homogeneous freezing and for heterogeneous freezing, if applicable) LES simulation of marine stratus Run ensemble of parcels using trajectories & analyze for cloud particle characteristics

11. NASA CMAI WorkshopApril 20-21, 2006 Sample interface

12. NASA CMAI WorkshopApril 20-21, 2006 Specific “framework” activities Implement and test parameterization ideas across the whole range of models We contribute one model type to the investigation encompassing multiple model types As suggested in the White Paper, analyze results to make link to larger-scale models more explicit Help define observational tests for comparing process representation at all scales Threshold conditions for glaciation; precip onset? Mean particle size, IWC CloudSat / CALIPSO

13. NASA CMAI WorkshopApril 20-21, 2006 Specific “support” elements to be used Any trajectory data generated by other investigators Datasets produced for observational tests of model physics and performance Liaison team support for optimization of parameterizations

14. NASA CMAI WorkshopApril 20-21, 2006 Extra

15. NASA CMAI WorkshopApril 20-21, 2006 How do we measure IN and interpret the data?

16. NASA CMAI WorkshopApril 20-21, 2006 In deeper and mostly ice phase clouds: Secondary ice formation or sampling issue? Closest correspondence between ice and IN from CVI residuals occurs only in upper region Nov. 19, 2003

17. NASA CMAI WorkshopApril 20-21, 2006 Some cases for IN = primary initial ice formation: studies in/around orographic wave clouds (WAVEICE, CO-WY, Wyoming King Air, March 2000) (Rogers and DeMott, 2002 AMS Conf. Cloud Phys.) IN

18. NASA CMAI WorkshopApril 20-21, 2006 Some evidence that presence or absence of ice in clouds is linked to the availability of ice nuclei (AIRS-2, Ontario/Quebec, NCAR C-130, Nov. 2003) IN by CFDC from CVI cloud particle residuals CFDC processing temperature approximately equal to cloud temperature

19. NASA CMAI WorkshopApril 20-21, 2006 Great difficulty assigning true ice crystal concentrations based on particle probe data

20. NASA CMAI WorkshopApril 20-21, 2006 Measuring ice nuclei: Continuous flow diffusion chamber (CFDC) OPC 0.31.5 mm aerosol Activated IN

21. NASA CMAI WorkshopApril 20-21, 2006 heated inlet (ambient sample) Interior tubing and transfer to other aerosol instruments CVI inlet (residual particles from evaporated cloud particles) Sampling involves inlets and their potential effects on the nuclei we are trying to measure CFDC CCN

22. NASA CMAI WorkshopApril 20-21, 2006 Future plans – PACDEX with HIAPER aircraft (April-May 2007) Goal: Dust-pollution effects on clouds and radiation following from near-source across ocean. Includes IN measurements.

23. NASA CMAI WorkshopApril 20-21, 2006 Future opportunity – ICE-L (Ice in Clouds Experiment – Layer clouds) with NCAR C-130 aircraft (March-April 2007) Altostratus/altocumuli Wave clouds Goal: Identify ice formation mechanisms in clouds, Includes aerosol, IN, CCN measurements. International Ice Nucleation Workshop: AIDA cloud chamber facility (Karlsruhe, Germany), Summer or Fall 2007, Several new instruments

24. NASA CMAI WorkshopApril 20-21, 2006 IN variability in atmosphere? Why? Does it matter?

25. NASA CMAI WorkshopApril 20-21, 2006 IN relations to aerosols have been explored during sampling periods at mountaintop laboratory SPL: Storm Peak Laboratory, 3.2km MSL, Steamboat Springs, CO INSPECT (Ice Nuclei Spectroscopy) I,II – Fall 2001, Spring 2004

26. NASA CMAI WorkshopApril 20-21, 2006 IN relation to dust particles is clear, which may explain IN-aerosol size relation (most times!) Timeline of global aerosol model dust mass concentration, measured aerosol volume, and IMPROVE dust mass concentration (April to May 2004) Timeline of IN concentration and aerosol particle concentration in the 300 to 700 nm size range. Heavy pollution event NAAPS model results courtesy of Doug Westphal, NRL, Monterrey). µg m -3 µm 3 cm -3 µg m -3 Per std liter cm -3

27. NASA CMAI WorkshopApril 20-21, 2006 Relation apparent between larger aerosol and IN from mixed-phase cloud residual particles Nov. 19, 2003 Appear related Appear not related

28. NASA CMAI WorkshopApril 20-21, 2006 A case for IN impacting Arctic cloudiness during a dust- poor scenario: M-PACE (October 2004) Prenni et al. (2006) Observed cloudiness Cloud model (RAMS) with “global” IN allowed to “deplete” North Slope Alaska IN measured “Global” IN function often assumed (Meyers et al.) Cloud modeled with observed IN allowed to “deplete” Knowing IN concentrations was critical to predicting cloud presence, phase, liquid water path, and surface net infrared radiation. Allowing the nuclei to be redistributed and used up was also very important.