From andrew at ucar.edu Fri Nov 10 16:33:02 2006 From: andrew at ucar.edu (Andrew Gettelman) Date: Fri Nov 10 16:32:50 2006 Subject: [Microphysics] CAM Microphysics Update Message-ID: Greetings, It has been about a year since we met in Boulder to discuss microphysics in global models. This is a brief update on our progress and plans, and a request for assistance again. In the last several months, we have managed to get a new 2 moment microphysics scheme running in the global model with prescribed aerosols. This is thanks largely to the efforts of Hugh Morrison and Steve Ghan. I should note that this is just a candidate scheme for the next model release and is still in a preliminary stage. Other extensions to the scheme or other schemes are still possible. We would like to solicit your help in evaluating the resulting simulations. In particular, we are struggling with even basic questions of whether cloud particle sizes and number concentrations are reasonable. We are interested in collecting your thoughts on the best way to diagnose the simulations, and data sets/diagnostics for comparison. The model is global, so we can output fields for comparison with data taken anywhere (in situ) or everywhere (satellites). If you would be interested in looking at the simulations or comparisons to detailed models or observations, please let me know, and we would be happy to discuss the best way to compare the simulations. If you have questions about the simulations or the paramterization, please let me know. We expect to have a draft description of the scheme available in the next few months. Snapshots of some results are available at: http://www.cgd.ucar.edu/cms/andrew/diag/micro_diag_nmicro1.38.pdf These plots show PDFs of ice and liquid effective radius (EFF) and number concentration (NC), maps of the same (zonal means and at a level) and some zonal mean plots of the subgrid vertical velocity (WSUB) and the CCN at 1% supersaturation (CCN6). General diagnostics of the simulation are available at: http://www.cgd.ucar.edu/cms/andrew/diag/index.html#microphys against observations or against the base case model. We are currently evaluating the effect of changing aerosol mass in the simulations and hope to present this at AGU. Thanks again for your help. Please feel free to contact me with questions. Regards, Andrew -- o__ __ Dr. Andrew Gettelman andrew@ucar.edu _,>/'_ -- http://www.cgd.ucar.edu/cms/andrew/ +1.303.497.1887 (_) \(_)-- National Center For Atmospheric Research 1850 Table Mesa Dr, Boulder, CO, USA 80305 From ejensen at sky.arc.nasa.gov Sat Nov 11 08:36:07 2006 From: ejensen at sky.arc.nasa.gov (Eric Jensen) Date: Sat Nov 11 08:36:21 2006 Subject: [Microphysics] CAM Microphysics Update In-Reply-To: References: Message-ID: Andrew, The ice effective radius and number concentration plots indicate that you typically have large concentrations of small (~20-30 microns) ice crystals. I assume that the CAM ice cloud parameterization is based on FSSP measurements. However, I (and much of the cirrus community) have become convinced that the large concentrations of small crystals indicated by FSSP (and other in situ instruments such as CAPS) are predominantly artifacts of shattering at the instrument inlets. There are several lines of evidence for this conclusion: 1. Physical plausibility. The in situ measurements indicate large concentrations of small crystals throughout cirrus clouds (including anvil cirrus). The existence of small crystals in the upper parts of the cloud and near nucleation zones makes sense, but it doesn't make sense to have lots of small crystals in the precipitation zone near cloud base. You could argue that they are produced by crystal-crystal collisions, but an inlet plowing through the cloud at 200 m/s is a much better candidate for shattering crystals. 2. Isaac and Korolev have taken high-speed videos of instrument inlets on aircraft flying through cirrus. You see large crystals come into the frame and literally explode at the inlets producing large numbers of small crystals, many of which get swept into the instrument. 3. Small-crystal (20-40 microns) concentration is extremely well correlated with large-crystal surface area or mass (r=0.95). The only plausible explanation for this correlation is shattering at the inlets. It also suggests that the small crystal concentration is dominated by this effect. 4. During the CRAVE mission, the shroud in front of the CAPS CAS component was removed. The result was that in anvil cirrus, small ice concentrations were orders of magnitude lower than we've seen in previous missions. Also, the small-large correlation disappeared. 5. Comparisons with remote sensing measurements. Jay Mace has done retrievals of 2-mode ice crystal size distributions based on Raman lidar and radar measurements. He finds that the inferred concentrations of small crystals are orders of magnitude lower than those indicated by the in situ measurements. Peter Pilewskie get's similar results with his solar spectral flux measurements. Upcoming missions, including Heymsfield's ICE experiment and TC4, will include open-path instruments for which the shattering effect should be minimized. We will also include the standard CAPS instrument such that we can quantify the shattering effect and evaluate previous measurements. The small crystal issue is very important because if you take the FSSP/CAPS measurements at face value, then the small crystals dominate the extinction. And, of course, getting the crystal size wrong will affect the vertical redistribution of water in the atmosphere. I'm working on a paper discussing some of these issues, and I'd be happy to send it to you once it is in presentable form. I hope this message doesn't start a firestorm. -Eric On Fri, 10 Nov 2006, Andrew Gettelman wrote: > Greetings, > > It has been about a year since we met in Boulder to discuss > microphysics in global models. This is a brief update on our progress > and plans, and a request for assistance again. > > In the last several months, we have managed to get a new 2 moment > microphysics scheme running in the global model with prescribed > aerosols. This is thanks largely to the efforts of Hugh Morrison and > Steve Ghan. I should note that this is just a candidate scheme for > the next model release and is still in a preliminary stage. Other > extensions to the scheme or other schemes are still possible. > > We would like to solicit your help in evaluating the resulting > simulations. In particular, we are struggling with even basic > questions of whether cloud particle sizes and number concentrations > are reasonable. We are interested in collecting your thoughts on the > best way to diagnose the simulations, and data sets/diagnostics for > comparison. The model is global, so we can output fields for > comparison with data taken anywhere (in situ) or everywhere > (satellites). > > If you would be interested in looking at the simulations or > comparisons to detailed models or observations, please let me know, > and we would be happy to discuss the best way to compare the > simulations. > > If you have questions about the simulations or the paramterization, > please let me know. We expect to have a draft description of the > scheme available in the next few months. > > Snapshots of some results are available at: > http://www.cgd.ucar.edu/cms/andrew/diag/micro_diag_nmicro1.38.pdf > > These plots show PDFs of ice and liquid effective radius (EFF) and > number concentration (NC), maps of the same (zonal means and at a > level) and some zonal mean plots of the subgrid vertical velocity > (WSUB) and the CCN at 1% supersaturation (CCN6). > > General diagnostics of the simulation are available at: > http://www.cgd.ucar.edu/cms/andrew/diag/index.html#microphys > against observations or against the base case model. > > We are currently evaluating the effect of changing aerosol mass in > the simulations and hope to present this at AGU. > > Thanks again for your help. Please feel free to contact me with > questions. > > Regards, > > Andrew > > > -- > o__ __ Dr. Andrew Gettelman andrew@ucar.edu > _,>/'_ -- http://www.cgd.ucar.edu/cms/andrew/ +1.303.497.1887 > (_) \(_)-- National Center For Atmospheric Research > 1850 Table Mesa Dr, Boulder, CO, USA 80305 > > > > _______________________________________________ > Microphysics mailing list > Microphysics@mailhub.cgd.ucar.edu > http://www.cgd.ucar.edu/mailman/listinfo/microphysics > ---------------------------------------------------------------- Eric Jensen office (temp) 303-492-3290 NASA Ames Research Center Cell 415-710-3064 Mail Stop 245-4 Fax 650-604-3625 Moffett Field, CA 94035 eric.j.jensen@nasa.gov ----------------------------------------------------------------