Mission and Goals

The mission of the Research Aviation Facility (RAF) is to develop and operate instrumented research aircraft for the atmospheric science community at a level of sophistication and operational complexity not generally available from university-based aircraft.

RAF goals are:

• To operate the research aircraft safely and reliably. Safety is the foremost factor guiding RAF in operation of the NCAR/NSF aircraft fleet.

• To provide research aircraft users with the technical support needed to maximize the scientific effectiveness of RAF aircraft and instrumentation. To accomplish this, RAF staff assist in planning and conducting field experiments; carry out the processing and quality control of RAF data sets; establish instrumentation characteristics and limitations; and, when appropriate, collaborate with investigators in the scientific analysis of project data.

• To track current and future scientific needs of the atmospheric science community, and to acquire and maintain research systems (aircraft, instruments, and data acquisition systems) that utilize current technology to best meet these needs.

WB-57F Development. Work during the first nine months of the fiscal year yielded substantial improvements in airframe, flight systems, and research infrastructure of the WB-57F in preparation for support of its first NSF field study, the Stratosphere-Troposphere Experiments: Radiation, Aerosols, and Ozone (STERAO-A) program. However, experience during aircraft flight tests in the fourth quarter of the year lead first to a change of operations base, and then to grounding of the aircraft pending re-evaluation of the feasibility and cost of safe operations. By the end of FY 96, RAF and ATD were devoting substantial effort to this re-evaluation, while the aircraft remained unavailable for use by requestors. An outline of progress and events through the year follows below.

• An X-ray examination of the structural integrity of wing spars in March 1996 showed evidence of rapidly progressing stress-corrosion cracking in two spar sections of the right wing. To correct this, RAF elected to remove the faulty spar sections and replace them with new spars machined from improved, crack-resistant aluminum alloy. The lengthy replacement operation was completed in mid-June.

• Work on aircraft systems and research infrastructure needed to support STERAO-A proceeded through August 1996. Tasks accomplished include complete replacement of the power distribution infrastructure, installation of an RAF-developed ADS-II data system, installation of a radome gust probe for wind and turbulence measurements, installation of a broad suite of instruments for in situ and state-parameter measurements, near-complete modification of wing pods for instrumentation, provision for user-supplied instrumentation, and other tasks.

• During a test flight on 3 July 1996, the left tip of the 125-foot-wide WB-57F wing struck a runway sign during a normal, centerline landing at JeffCo Airport. This lead to a decision to discontinue use of the 100-foot-wide runways at JeffCo Airport and relocate operations to Denver International Airport (DIA), where runway width is 150 feet. UCAR secured a 12-month lease of hangar space in mid-August, and flight testing resumed at that time from the new DIA base.

• In late August the trim control of the horizontal stabilizer became inoperative in flight at 50,000 feet altitude. This yielded a difficult situation for the pilot until trim control was restored at the warmer temperatures encountered during descent near 20,000 feet altitude. In consideration of this malfunction and the previous history of problems with the flight systems on the aircraft, ATD and RAF grounded the aircraft pending full review of its condition and the feasibility of ensuring the safety of future operations. This grounding precluded provision of support to the STERAO-A program in August and September 1996.

• By fiscal year-end, ATD had taken steps to establish a WB-57F Evaluation Panel with membership from several NCAR Divisions, NOAA Aeronomy Lab, and NSF. RAF, ATD and UCAR technical teams as well as non-NCAR experts and consultants will serve as resources to the Panel as it carries out its charge to determine the full operational and maintenance requirements and costs necessary to operate the WB-57F safely and reliably. The Panel will report its findings to NCAR, NSF, and the NSF Observing Facilities Advisory Panel in April 1997. NCAR and NSF will plan for the future role of the aircraft after consideration of the Panel report.

Electra Upgrades. RAF temporarily removed the Electra from operational status in FY 96 to carry out a mandated five-year recurrent airframe inspection and to upgrade the research infrastructure of the aircraft. The inspection and associated minor repairs confirmed that the airframe is in excellent condition. Upgraded cabin safety features include addition of handholds and provision for secured cabin storage. Improved scientific infrastructure features include the following: installation of an RAF-built ADS-II data system (similar to that on the C-130 and WB-57F aircraft); expansion from three to four workstation areas, and relocation of workstations to better support coordination of ELDORA missions; incorporation of an RSF-built Weather Avoidance Radar Data System to record and display data from the Electra weather avoidance nose radar; provision for multiple displays of ELDORA and nose radar data; and installation of an improved, switchable intercom system throughout the cabin.

Acquisition of C-130 Parts Aircraft. Through cooperation between NSF and NASA management, a Lockheed EC-130Q formerly based at NASA/AMES Research Center has been transferred to NSF for use as a non-flyable parts aircraft supporting the needs of NSF and NASA. Operation of the NCAR/NSF C-130 will benefit substantially from the spare parts available from this surplus aircraft.

Table ATD-1: Summary of Disposition of FY 96 RAF Flight Requests

Aircraft	Number of Projects		Number of Hours			Number of Flights
	Requested	Flown	Requested	Allocated	Flown
C-130	5	2	695	395	396	55
Electra	4	0	349	0	0	0
WB-57F	2	1	130	110	14	3
Total	11	3	1,074	505	410	58

Table ATD-2: Summary of FY 96 Aircraft Use

User	Project	Aircraft	Science*	Research Period	Hours Flown
Huebert (U. Hawaii)	ACE-1	C-130	AC,BL,CP	10/31/95 - 12/22/95	297
Rogers (Scripps)	Coastal Waves	C-130	BL	05/30/96 - 07/02/96	99
Dye et al. (NCAR)	STERAO Test	WB-57F	E,AC	07/15/96 - 09/01/96	14
Total Hours					410

^* AC = Atmospheric Chemistry, E = Evaluation of Instruments, BL = Boundary Layer, MS = Mesoscale Studies, CP = Cloud Physics, R = Radiative Studies

Aerosol Characterization Experiment-1 (ACE-1). The ACE-1 air chemistry/aerosol program utilized the C-130 aircraft during November and December 1996. The program was conducted by an international team of scientists and included operations over a broad area extending to Alaska, the central Pacific, New Zealand, and Tasmania. The program was the most complex atmospheric chemistry deployment ever supported by RAF, requiring integration of fifteen separate experiments on the C-130. As outlined under Research Activities, several members of RAF played a scientific role in the program. Research operations were divided into two parts to address the primary objectives: a "Pole-to-Pole" meridional chemistry profile through the central Pacific, and a study of clean air aerosol generation between southern Australia and Antarctica. Chemical species measured included: various sulfur gases, H₂SO₄ and MSA, NH₃, NO, CO₂, CO, H₂O₂, and O₃. Whole air samples were also collected for hydrocarbon analyses. A total of seven separate aerosol measurements were made ranging from CCN and ultra-fine CN particles through the larger marine sea salts. All aerosol samples were collected using RAF's new Community Aerosol Inlet, which is described under Development Activities. ATD's new Staring Aerosol Backscatter Lidar (SABL, 106Kb) provided maps of aerosol distributions through the lower troposphere during the program.

Coastally Trapped Waves Experiment. The C-130 was deployed to Monterey, California in support of this boundary-layer program during June 1996. The research addressed the dynamics of coastally-trapped waves, the ageostophy of the wind constrained by the coastal mountain range, the interaction of orographically-forced flow with the sea breeze circulation, the offshore variability of the marine boundary layer, and the influence of these features on the development of boundary-layer clouds. The C-130 in situ measurements were used to characterize the along-shore and across-shore turbulent structure of the boundary layer. ATD's SABL lidar provided maps of boundary-layer structure to supplement the in situ measurements.

Counterflow Virtual Impactor (CVI). The CVI samples cloud droplets or ice crystals and evaporates them, allowing the residual nuclei and volatile gases to be measured downstream by various methods. This technique has been used successfully for several years in studies of cloud nucleation, droplet chemistry, and radiative transfer. Recent work has focused on improving the CVI inlet and flow system for better aspiration efficiency and ease of use. A new CVI with a shrouded inlet was built to fly on the NASA DC-8 aircraft during the SUCCESS project. (See Research Activities.) Preliminary results indicate the new design represents a marked improvement. The new features will be incorporated into the NCAR CVI before deployment on future projects.

Airflow Studies. Recently, sophisticated software (STAR-CD) has been acquired and used to model the airflow and particle trajectories around complicated shapes, such as the inlets used for aerosol and cloud water collection. This extends the RAF flow modeling capabilities dramatically. The new code solves the full Navier-Stokes equations, and can accurately simulate transonic and unsteady flow problems. The complicated flow field inside the NCAR counterflow virtual impactor (CVI) has been modeled by Cindy Twohy, in collaboration with Mary Laucks of the University of Washington. The code was also used in designing the C-130 community aerosol inlet and in developing a shroud for the CVI. Two papers detailing the inlet modeling results are expected to be published soon in Aerosol Science and Technology.

Community Aerosol Inlet (CAI). The CAI (20Kb) is a major new instrument developed in a joint project between NCAR/RAF and university researchers. It is designed to be more effective than traditional inlets in collecting aerosol particles during airborne research. This sophisticated inlet system, described in detail in the 1995 Annual Scientific Report, was designed to minimize particle losses due to turbulence and deposition -- a known problem in other inlet systems. The CAI was deployed during the ACE-1 project; the results from this project are still being analyzed. An additional test program will be conducted in spring 1997 for further characterization of the flow field and aspiration efficiency of the CAI.

Radiometer Correction Algorithm. Krista Laursen has developed an algorithm to partially remove the effects of aircraft attitude from hemispheric radiometer data collected on NCAR/NSF research aircraft. The algorithm will soon be added to the RAF's Nimbus data processing package. Krista worked with Judy Curry and Mark Tschudi (University of Colorado) to reprocess data from the Beaufort and Arctic Seas Experiment (BASE) using this algorithm.

Aircraft Information Retrieval System (AIRS). A prototype, beta version of the relational database developed at the RAF to archive a broad range of information about ATD-supported field projects is now in the demonstration phase. Julie Haggerty and Gary Horton lead this effort. The system is based on commercial relational database software and can be accessed through a Motif-based GUI or from external applications, including the World Wide Web. AIRS is designed to streamline the archival and user access of all RAF flight data, as well as other information about the Facility and the projects being conducted. AIRS has also been expanded to include datasets from SSSF platforms and facility request metadata from the ATD Director's Office. It offers a highly flexible way to assimilate multi-dimensional data sets.

Air Chemistry Instrumentation. Greg Kok and Richard Schillawski have been improving the processing methods for data from the CO analyzer. They have also modified the LICOR H₂O/CO₂ sensor. The high-altitude design of the instrument developed at the University of Harvard (Kristie Boering) was adapted for use in the troposphere. Preliminary results from measurements during ACE-1 indicate that these modifications have greatly improved the resolution and sensitivity of the instrument.

Greg Kok continues his collaborative work with Phil Hemberger at Los Alamos National Laboratory (LANL) on an adsorbent trap system for an ion-trap mass-spectrometer analytical system. The results of this work were published in the November 1966 issue of the Journal of the American Society for Mass Spectrometry.

NASA Subsonic Contrails and Clouds Effects Study (SUCCESS). This project focused on studying the microphysical and optical properties of contrails and cirrus clouds. RAF scientists Darrel Baumgardner, Cynthia Twohy, Teresa Campos, Bruce Gandrud, Al Cooper, and Larry Radke participated in SUCCESS by making measurements on the NASA DC-8 with the MASP, CVI, UV hygrometer, and a newly developed CCN counter. Also, in collaboration with Andy Weinheimer and Brian Ridley of NCAR/ACD, Teresa Campos measured in situ nitric oxide, reactive odd nitrogen species, and ozone. The RAF researchers were joined by over a hundred other scientists from universities and government laboratories during April and May 1996 in Salina, Kansas. The measurements made by the RAF scientists were crucial to the goals of SUCCESS. The CVI system measured the ice water content and number concentration of ice crystals in contrails, cirrus, and wave clouds, and was able to measure the very low water content present in many of the contrails (typically only 1-2 mg m^-3 for particles larger than 6 microns diameter). The mean crystal size was observed to decrease and the volatility of the residual particles from the contrail ice was observed to be substantially higher when high-sulfur fuel was used, suggesting additional nucleation on sulfuric acid aerosols. The MASP was the only in situ sensor of aerosol size distributions on the aircraft that obtained measurements in the free air stream. All other instruments required inlets, in which larger aerosols are typically lost by deposition. The MASP provided size distributions and asphericity measurements of aerosol particles, water droplets, and ice crystals from 0.4 - 20 microns in diameter. The NO measurements provided an important indicator of aircraft exhaust encounters and allowed direct quantification of the aircraft NO emissions at cruise altitudes. The ozone measurements proved a useful indicator of air history. Measurable concentrations of particulate NO_y were observed frequently in cirrus clouds.

Aircraft Contrail Studies. In this work, Darrel Baumgardner and Bruce Gandrud are using NCAR/NSF Sabreliner aircraft measurements from the 1989 Contrails project. The data are being evaluated in collaboration with the Aerodyne Corp. for comparison with models of aircraft exhaust and wake formation. This study is funded by the NASA High Speed Research Program to assess the effects of tropospheric aircraft emissions on regional and global climate. This past year's study has culminated in a presentation at the spring 1996 AGU meeting and a Journal of Geophysical Research paper (currently in review) entitled "Thermodynamic and Turbulent Effects of a Jet Contrail." This study compares observed temperature, water vapor, and vertical velocity profiles with predicted profiles from the Aerodyne wake-vortex model. The excellent agreement indicates the model can be successfully applied to study other contrail processes such as particle formation. In a related study, Darrel Baumgardner and Keith Barr installed the MASP on the German DLR Falcon aircraft in March 1996, and participated in a study of the effect of fuel sulfur content on contrail formation. This project involved researchers from the DLR, University of Stockholm, University of Heidelberg, University of Missouri-Rolla, and the University of Mainz. The Falcon was flown closely behind various test aircraft, and measurements were made in their exhaust and contrails.

Stratospheric Aerosols. RAF researchers Darrel Baumgardner, James Dye, and Bruce Gandrud are analyzing measurements from the MASP to better understand the fundamental mechanisms of aerosol production, growth, and transport in the lower stratosphere and upper troposphere. The data were collected when the MASP was flown in the ASHOE/MAESA campaign during March - November 1994, and later in TOTE/VOTE in December 1995 and January-February 1996 (see next paragraph). The research team made measurements of aerosol size, concentration, and refractive index to assess the optical and microphysical properties of the particles in these stratospheric regions. (The surface area of aerosols is a critical parameter in models of stratospheric ozone loss because that is where important heterogeneous chemical reactions occur.) The ability to measure the refractive index of individual particles is a new capability not previously available. The MASP measurements will be used by modelers to better understand the mechanisms of ozone depletion. The above scientists have published a paper in Geophysical Research Letters on refractive index measurements in the lower statosphere and upper troposphere. The results presented in this paper challenge some current theories about the composition of stratospheric aerosols.

Tropical Ozone Transport Experiment and Vortex Ozone Transport Experiment (TOTE/VOTE). This project was flown with NASA's DC-8 aircraft in the tropics around Hawaii and in the Arctic near Fairbanks, Alaska. The purpose was to study the transport of Arctic vortex filaments into the tropics and midlatitudes. RAF researchers Campos, Gandrud, Barr, and Baumgardner participated in this experiment along with many other university and government scientists. Teresa Campos collaborated with NCAR/ACD researchers in measuring in situ nitric oxide, reactive odd nitrogen species, and ozone to determine transport during various experiments. Intercomparison of these measurements with similar measurements made by the NOAA Aeronomy Lab (David Fahey, et al.) on the ER-2 aircraft yielded encouraging results. Latitudinal transects during the mission showed interesting interactions between the troposphere and stratosphere at the subtropical jets, as confirmed by seemingly contradictory measurements of temperature vertical profiles and stratospheric chemical tracers like ozone and nitrous oxide. Comparisons of odd nitrogen and ozone with MASP aerosol measurements (made by Baumgardner, Barr, and Gandrud) in sub-visible cirrus showed interesting correlations that are currently being evaluated.

Joaquin Valley Study. Teresa Campos participated in a third field experiment, in collaboration with Jeff Collett of Colorado State University, to measure gas-phase total peroxides in California's Central Valley. The California Air Resources Board sponsored this study of the interaction between photochemistry and fog. NCAR involvement was limited largely to technology transfer. The addition of vapor-phase peroxide measurements was an important enhancement to the extensive cloud chemical analyses conducted by Collett.

Small Cumulus Microphysics Study (SCMS). Darrel Baumgardner, Al Cooper, and Larry Radke are investigating the formation of precipitation through non-ice processes and the interaction of clouds and aerosols in marine and continental cumulus. These scientists recently presented papers on these topics at the 13th International Conference on Clouds and Precipitation in Zurich, Switzerland. A paper on this research is currently in preparation for a special issue of Atmospheric Research.

Aerosol Characterization Experiment-1 (ACE-1). RAF scientists Greg Kok, Richard Schillawski, Andre Prevot (visitor from Zurich, Switzerland), Krista Laursen, Bruce Morley, and Darrel Baumgardner participated in the ACE-1 project in November and December 1995. Kok, Schillawski, and Prevot made measurements of ozone, carbon monoxide, carbon dioxide, and hydrogen peroxide. Laursen measured spectral radiation with the Multichannel Cloud Radiometer (MCR). Baumgardner used the MASP on the C-130 to measure the microphysical and optical properties of aerosols. Morley made aerosol backscatter measurements from the C-130 with the new NCAR Staring Aerosol Backscatter Lidar (SABL). Laursen and Morley have been working with Lynn Russell (an ASP post-doctoral fellow) and Don Lenschow on wavelet analyses of ACE-1 lidar data in an effort to perform boundary-layer height retrievals for various research flights. Laursen, Baumgardner, and Morley, in collaboration with Tony Clarke of the University of Hawaii, are using a lidar inversion algorithm to derive extinction coefficients for radiative closure studies . Baumgardner is evaluating all the aerosol measurements to investigate the coupling of microphysical and optical properties in the troposphere studied during ACE-1.

Swiss Oxidant Study. Based on analysis of the data from the 1993 Swiss Oxidant Study, Kok and Prevot completed the paper, "The Milan Photo-oxidant Plume". A pollutant plume from the Milan, Italy industrial region that impacts southern Switzerland was clearly identified.

Hong Kong Air Quality Study. Kok's analysis of the data collected in this 1994 study shows that there are three distinct areas of polluted air: polluted background air extending out over the South China Sea, a plume that travels down the Pearl River from the People's Republic of China, and a fresh emissions plume from Hong Kong. A paper entitled "An Airborne Study of Air Quality Around the Hong Kong Territory" has been submitted to the Journal of Geophysical Research.

Lidars in Flat Terrain (LIFT) Project. In July and August 1996 Kok and Schillawski participated in the LIFT project, making fast-response measurements of ozone for eddy-correlation purposes. The LIFT project was designed to test the potential of using lidars for turbulence and chemistry measurements for deriving deposition fluxes of selected chemical species. The project was conducted both at the Boulder Atmospheric Observatory near Erie, Colorado and at the Flatland observing site near Bondville, Illinois.