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Selected Research Projects |
| DRI Faculty: | John Hallett (PI), Matt Bailey |
| Title: | An Aircraft Study of the Characterization and Evolution of Supercooled and Mixed Phase Clouds |
| Sponsor(s): | National Science Foundation |
| Objectives-Results: | In late 2003, DRI investigators participated in the AIRS II project, the purpose of which was to study aircraft icing conditions over the eastern Great Lakes region and southern Ontario. The project was a collaborative effort involving staff and instrumentation from DRI, the National Center for Atmospheric Research (NCAR), Colorado State University, Purdue, U. Illinois, Oregon State University – Corvalis, NASA, and the Meteorological Service of Canada. The U.S. portion of the study was performed using the NCAR C-130 and NASA’s twin otter aircraft which were based at the NASA Glenn Research Center in Cleveland Ohio. Cloud liquid water and ice water content were measured with two new instruments developed at DRI, the large and small “T-probe”. Video images of ice crystals were obtained with the DRI Standard format and Large Format Cloudscopes. The mission was a success and resulted in an extensive set of data which is currently under analysis. |
| DRI Faculty: | James G. Hudson (PI) |
| Title: | Development of a Cylindrical Cloud Condensation Nuclei (CCN) Spectrometer |
| Sponsor(s): | National Science Foundation |
| Objectives-Results: | After years of laboratory and field experience with the two DRI CCN spectrometers it was decided that cylindrical geometry might have advantages over the rectangular geometry. But before the new instrument was designed, several improvements were made to the present instruments. These improvements proved separately that they should be incorporated into the new instrument. They showed that the new instrument would need to be divided into only two sections in order to provide complete CCN spectra. The new instrument is a double cylinder that is split transversely into two unequal sectors. The smaller sector will have a smaller sample flow rate to cover the higher range of cloud supersaturations. The larger sector will have a higher sample flow rate that will cover the lower supersaturation range because these particles are much less numerous. The design of the new CCN spectrometer has been completed, and some assembly has begun. |
| DRI Faculty: | Douglas Lowenthal (PI), Barbara Zielinska (Co-PI) (PI) |
| Title: | Advanced IMPROVE Studies |
| Sponsor(s): | EPRI |
| Collaborator(s) | Don Collins (Texas A&M University); Jon Allen (Arizona State University |
| Objectives-Results: | The Advanced IMPROVE Studies program is being conducted at U.S. National Parks to address outstanding scientific issues related to the U.S. EPA Regional Haze Rule (RHR). The goal of the RHR is to attain background visibility conditions in U.S. national parks by 2064. Progress in attaining background visibility under the RHR is monitored by following light extinction estimated from IMPROVE filter sample concentrations using a modification of the “IMPROVE” equation. While the revised IMPROVE equation represents an improvement over the old protocol, there are several issues which need to be addressed before the end of the current 5-year RHR assessment period: 1) the assumption that ammonium sulfate hygroscopic growth is represented by the hysteresis branch may over-estimate the amount of water and thus light extinction attributed to sulfates and nitrates and under-estimate the contribution from organics; 2) the assumption that organics are not hygroscopic has been retained although there is considerable evidence that organics absorb water as a function of RH; 3) the assumption that the organic mass to organic carbon (OCM/OC) ratio is 1.8 also derives from limited experimental evidence from the Park Service. The higher this number, the more light scattering attributed to organics; 4) concentration-varying chemical scattering efficiencies depend on a direct relationship between particle size and concentration. An experiment was conducted at Great Smoky Mountains National Park during summer, 2002. Preliminary results suggest that organics absorb water significantly as a function of RH, that the aerosol is rarely deliquescent, and that the dry size of oxygenated organics increases with concentration. |
| DRI Faculty: | David Mitchell (PI), Steve Chai |
| Title: | Implementing Ice Cloud Microphysics and Radiation Schemes into the Community Atmospheric Model (CAM) |
| Sponsor(s): | National Science Foundation |
| Collaborator(s): | Phil Rasch (NCAR) |
| Objectives-Results: | This project demonstrates the impact of the ice particle size distribution (PSD) on simulations of future climate (i.e. Global Climate Model, or GCM, simulations), and the potential for PSD modification through indirect aerosol effects. During two 3-month visits to the National Center for Atmospheric Research (NCAR), the modified anomalous diffraction approximation (MADA), two new PSD schemes for tropical and mid-latitude cirrus clouds, and a new ice particle fall velocity scheme were incorporated into the Community Atmospheric Model (CAM), part of the Community Climate Systems Model (CCSM) developed at NCAR. The initial results from 1-year simulations were surprising. If one uses only one cirrus cloud PSD scheme, either the tropical anvil scheme or the mid-latitude scheme, to represent all cirrus clouds globally in the CAM, the predicted cloud forcing on climate, the in-cloud heating rates, and the upper tropospheric temperatures are considerably different. For example, the annual mean temperature in the tropical upper troposphere was 3 deg. C higher using the tropical PSD scheme. This may point the way towards solving a longstanding problem common to many GCMs, which is the cold bias that occurs in this region of the atmosphere.
Drawing from in-cloud measurements and the results from a cloud parcel model developed at DRI, it can be argued that the small ice crystal mode of the PSD results from the evaporation-freezing of cloud or haze droplets, and is thus susceptible to changes in aerosol particle concentrations. Since the GCM sensitivity to the PSD is due primarily to the small mode, it follows that anything substantially affecting the small crystal mode will affect the GCM response to cirrus clouds. Thus, it appears that changes in aerosol particle concentration may potentially affect the role of cirrus clouds in climate simuations. |