FY 1997 NCAR Annual Scientific Report - ATD/Research Aviation Facility

Mission and Goals

The mission of ATD's 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; document 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.

Overview of the NCAR/NSF Fleet

The NCAR/NSF fleet provides capability to address a variety of aircraft mission requirements within the atmospheric sciences community. The Lockheed Electra (45K) serves as the platform for the ELDORA Doppler Radar, other remote sensing instruments, the SSSF dropsonde system, and a wide variety of in-situ instruments for application to problems in atmospheric chemistry, the structure and dynamics of weather systems, boundary-layer dynamics and fluxes, cloud and aerosol physics, and other research topics. The Lockheed C-130 (48K) supports science objectives that are similar to those of the Electra, but provides greatly increased range and payload capabilities that are particularly valuable for missions to remote areas or requiring large scientific payloads. The General Dynamics WB-57F high-altitude jet (57K) was placed in stand-down status for FY 1997 to allow NCAR and NSF to fully evaluate the physical condition of the aircraft and the feasibility of future operations (see further discussion below). The aircraft can serve as a platform for the study of radiation, aerosols, chemistry, electrification, dynamics and thermodynamics of the troposphere and lower stratosphere, and other research topics. The Beechcraft Super King Air B200T twin-engine turboprop was sold this year to Airborne Research Australia at Flinders University of South Australia. The Schweitzer 2-32 sailplane remained in stand-down status to facilitate development and operation of higher-priority aircraft.

Aircraft Development Activities

WB-57F Evaluation. In response to a series of operational problems uncovered in FY 1996, ATD set up and convened a WB-57F Evaluation Panel to investigate the following: the current mechanical status of the aircraft; the availability and cost of essential parts and sub-systems; the staffing and funding requirements for safe operations; unresolved operational issues and limitations; and runway/airport characteristics required for safe operation. The Panel members and other specialists who contributed to the study brought a high level of expertise in aviation, airborne science, and program management to the evaluation. The Panel members were drawn from NCAR/UCAR, NOAA's Aeronomy Lab (NOAA/AL), and NSF. The Panel also brought in several experts from NASA with specialized expertise in high-altitude aviation to allow in-depth investigation of specific operational issues. Following its detailed examination, the Panel concluded in its Final Report that the NCAR/NSF WB-57F is fundamentally sound, and that an organization such as NCAR/ATD or NASA's Johnson Space Center (JSC) could operate the aircraft safely and reliably. (JSC currently operates the only other WB-57F that is in flyable condition.) The Panel recommended that NCAR and NSF explore all options for cooperation with JSC to take advantage of the operational expertise and extensive infrastructure already resident there.

Following up on the Panel recommendations and NSF guidance, NCAR initiated detailed discussions with JSC to explore options for operation of the aircraft that take advantage of current JSC expertise and infrastructure and that will be of mutual benefit to both NCAR and JSC. To solve NCAR's short-term need to relocate the aircraft from leased space at Denver International Airport, the aircraft was brought to flyable condition and ferried in August 1997 to available hangar space at JSC in Houston. By FY 1997 year-end, NCAR and JSC had completed initial discussions about an ongoing cooperation to operate the aircraft in the future. If these discussions reach agreement in early FY 1998, and if the necessary funding is available from NSF, the WB-57F would likely resume instrumentation flight tests in the latter half of FY 1998.

High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER). Planning was initiated with NSF/ATM in FY 1997 on the acquisition of a new, high-performance aircraft for the NCAR/NSF fleet. A HIAPER Project Development Plan (PDP) was prepared by ATD and ATM and submitted in late FY 1997 to the National Science Board, which gave it a favorable review. Input from several community workshops during the last two decades has demonstrated a strong scientific need for an aircraft with capabilities that significantly surpass those of the current fleet. Specifically, an aircraft that can carry scientific payloads of up to 7,000 lb, to altitudes of up to 50,000 ft, and over ranges of up to 7,500 miles would allow a number of important new studies into the tropical tropopause region and into remote oceanic and polar areas which are currently inaccessible to investigators.

Current planning indicates that a state-of-the-art, mid-sized, high-performance jet aircraft would provide these capabilities. The aircraft would be modified to support an array of advanced instrumentation, science stations, and communications technologies. Both ATD and the university community would be heavily involved in developing the new instrumentation.

This initiative will likely compete for funding from NSF’s Major Research Equipment (MRE) budget in the FY 1999-2000 time frame. If the necessary funding commitment is obtained, acquisition, modification, and instrumentation of the new aircraft would take approximately four years. Activities in FY 1998 will include more detailed specification of the scientific requirements, analyses of alternatives and costs, and refinement of the PDP.

Field Support and Test Activities

During FY 1997, RAF supported two field projects for university and NCAR PIs with its aircraft, flying 32 missions for a total of 134 flight hours as shown in Table RAF-1. As summarized in Table RAF-2, these FY 1997 field deployments supported studies of frontal and mesoscale dynamics, planetary boundary-layer processes, and air-sea interaction, as well as tests of newly-developed instrumentation. The supported field programs are briefly described below.

Table RAF-1: Summary of Disposition of FY 1997 RAF Flight Requests

Aircraft	Number of Projects		Total Flight Hours			Number of Flights
	Requested	Flown	Requested	Allocated	Flown
C-130	3	1	242	52	52	17
Electra	4	1	314	126	82	15
Total	7	2	556	178	134	32

Table RAF-2: FY 1997 Aircraft Use Summary

User (Affiliation)	Project	Aircraft	Science*	Research Period	Hours Flown
Huebert (U. Hawaii)	CAINE-2	C-130	E	5/14/97 - 6/12/97	52
Testud/Wakimoto (CETP/NCAR)	FASTEX	Electra	MS, BL, AS	1/6/97 - 2/9/97	82
Total Hours					134

^{* AC = Atmospheric Chemistry, AS = Air-Sea
Interaction, BL = Boundary Layer, CP = Cloud Physics, E = Evaluation
of Instrument, MS = Mesoscale Studies, R = Radiative Studies.}

Fronts and Atlantic Storm Track Experiment (FASTEX). In January- February 1997, RAF staff supported the deployment of the NCAR/NSF Electra equipped with the ELDORA Doppler radar and a variety of microphysical probes and other in-situ sensors to study the mesoscale structure of developing cyclones in the North Atlantic ocean and the relationship between cyclone intensification and upstream precursors embedded in the large-scale flow. The Electra and crew were based at Shannon Airport in Shannon, Ireland, along with the NOAA WP-3D (16K) and Gulfstream-IV research aircraft. Other participating research platforms included the U.K. C-130 and U.S. Lear 36 research aircraft, as well as research ships from France, Ukraine, Iceland, and the United States. Scientists from several different countries representing various research institutions and operational weather prediction centers took part in the program.

Seven Electra research flights were carried out under the direction of PIs Roger Wakimoto (UCLA), Jacques Testud (CETP/CNET), and Peter Hildebrand (ATD/RSF). During the second week of February, a crack (371K) developed in a surface plank on the left wing of the Electra, requiring a halt to research flights. A repair team from Zantop, Inc. in Atlanta, Georgia, was dispatched to Shannon to carry out the repairs, which required extensive shoring of the aircraft and several hundred hours of labor. The repair work was successful, but could not be completed in time to return the aircraft to research operations during the FASTEX period.

Community Aerosol Inlet Evaluation (CAINE-2). The development and testing of the C-130 Community Aerosol Inlet (CAI) was brought to a close with the CAINE-2 field program, a collaboration with the University of Hawaii and Denver University, in May-June 1997. The CAI is basically a three-stage diffuser designed to slow incoming air prior to its ingestion into the cabin for distribution to a variety of particle samplers. Hot-wire anemometer mapping carried out during CAINE-2 showed that flow characteristics were uniform across the CAI sampling plane, where seven small inlets draw environmental air and aerosol for distribution to users' instrumentation on board the aircraft. Comparisons with pitot-static measurements confirmed that the flow at the CAI inlet tip was isokinetic under most conditions. Aerosol size-distribution measurements, collected in a marine boundary-layer environment, were used to determine the inlet collection efficiency as a function of particle size. Analysis of these data will continue through FY 1998.

Development Activities

Multichannel Cloud Radiometer (MCR). The MCR is an instrument for measuring spectral radiation in seven bands at visible and near-IR wavelengths. This instrument mounts on the C-130 aircraft in a wing pod, and scans in a plane perpendicular to the aircraft flight track. The MCR is currently being modified and improved to make it available for aircraft operations during the SHEBA project that begin in May 1998. Specific tasks targeted for this effort include replacing many of the existing optical components (filters, dewars, and detectors), re-wiring the instrument, modifying the heating components and controls, re-designing the instrument control box and control cards, and developing MCR data-processing and on-board display software. This development is being led by Krista Laursen with assistance from other RAF and DFS staff.

Radiometric Measurement Corrections and Documentation. RAF staff completed an algorithm to partially remove the effects of aircraft attitude from shortwave radiometer data collected on NCAR/NSF aircraft. This algorithm will be released as a routine data processing component in FY 1998. New documentation of RAF radiometric capabilities was released in a revised version of RAF Bulletin 25, entitled "Passive Broadband and Spectral Radiometric Measurements Available on NCAR/NSF Research Aircraft."

Evaluation and Improvement of Lyman-Alpha Hygrometer. Allen Schanot is leading an RAF effort to reduce measurement error in the Lyman-Alpha instrument, which serves as a critical source of high-rate humidity measurements for turbulent-flux calculations. Work to date has identified two principal measurement problems: temperature-related drift in the calibration of the instrument, and degradation due to wetting of optical components during cloud penetrations. To mitigate the temperature-drift problem, sensor electronics are being moved to inside the skin of the aircraft to reduce exposure to cold ambient temperatures. A new sampling inlet will reduce sensor wetting through improved separation of cloud drops from sample air. Initial testing and evaluation of these modifications to the hygrometer will proceed in FY 1998.

Evaluation of Tunable Diode Laser Hygrometer: The use of tunable diode laser (TDL) technology at near-infrared wavelengths for the measurement of water vapor has recently been advanced by the availability of lasers capable of working in the temperature range attainable with thermo-electric coolers. NASA's Jet Propulsion Laboratory (JPL) has invested heavily is TDL technology for use in the planetary exploration program. Randy May of JPL has developed a highly sensitive TDL hygrometer for measurement of the low water-vapor concentrations found in the stratosphere. Collaboration between JPL and Bruce Gandrud of RAF will lead to tests of a similar instrument for the measurement of the much higher water-vapor concentrations found in the boundary layer and the lower troposphere. May will adapt the TDL system for tropospheric use, and RAF will engineer its integration aboard the NSF/NCAR C-130. Flight tests of the system are planned for FY 1998. JPL and RAF will work together to evaluate the performance of the new instrument.

Evaluation of the UV Hygrometer: Through laboratory tests, Bruce Gandrud has succeeded in verifying the calibration of the ATD UV hygrometer (UVH) down to the 100 ppm_v level. The sensor was also tested aboard the NASA DC-8 aircraft during the SUCCESS program. Comparisons with the cryogenic frost-point hygrometer during these flights showed very good agreement when the UVH is unaffected by in-cloud sensor wetting. Further field tests and intercomparison with the JPL TDL hygrometer are planned for FY 1998.

Research Activities

Research activities by RAF staff in FY 1997 covered a wide range of topics in aerosol physics, cloud physics, radiative transfer, and atmospheric chemistry. Some of these research activities were connected with involvements in new field projects, while others utilized data sets from previous experimental studies.

NASA Subsonic Contrails and Clouds Effects Study (SUCCESS). RAF Scientists Darrel Baumgardner, Cynthia Twohy, Bruce Gandrud, and Larry Radke evaluated measurements they made during the NASA SUCCESS project on the NASA DC-8 with the RAF Multiangle Aerosol Spectrometer Probe (MASP), Counterflow Virtual Impactor (CVI), UV Hygrometer, and a newly developed CCN counter. SUCCESS focused on the study of microphysical and optical properties of contrails and cirrus clouds. Twohy and Gandrud have recently completed a paper on the results of CVI measurements of the total water content and composition of ice crystals. Baumgardner has written another paper that examines the microphysical and optical properties of aerosol and cloud particles in waveclouds and contrails sampled in this project. Both of these papers have been accepted for publication in a special issue of Geophysics Research Letters on SUCCESS.

NASA Photochemistry in the Arctic Stratosphere in the Summer (POLARIS). RAF scientists Darrel Baumgardner and Bruce Gandrud participated in a study of photochemical and heterogeneous chemical processes in the stratosphere over the Arctic during the summer of 1997. This study used the NASA ER-2 high-altitude aircraft instrumented with an extensive array of gas and aerosol sensors as well as a UV spectral radiometer. The NCAR MASP measured the larger aerosols from 0.3 to 40 micrometers in diameter. This program consisted of three segments covering the late spring, early summer, and late summer. Preliminary results indicate that the measurements generally agree reasonably well with the predictions of photochemical models, but significant discrepancies still remain with respect to the chlorine budget.

Small Cumulus Microphysics Study (SCMS). Darrel Baumgardner, Larry Radke, and Graciela Raga (Universidad Nacional Autonoma de Mexico) are investigating the interaction of clouds and radiation. Their research uses measurements of aerosol and cloud droplet size distributions to compute total scattering of visible radiation, which is then compared with results from a MonteCarlo photon-counting model. Preliminary results show that the haze associated with submicron particles on the edges of clouds can significantly increase the effective optical width of clouds. These results were presented at the 1997 meeting of the American Association of Aerosol Research and are being prepared for journal publication.

Aerosol Characterization Experiment - 1 (ACE-1). RAF investigators 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-December 1995. Kok, Schillawski, and Prevot used special instruments to measure ozone, carbon monoxide, carbon dioxide, and hydrogen peroxide. Laursen measured spectral radiation with the MCR. Baumgardner flew the MASP on the C-130 and measured 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). In FY 1997 Laursen and Morley worked with Lynn Russell (Princeton University and former ASP post-doc) and Don Lenschow (NCAR/MMM) on wavelet analyses of ACE-1 lidar data in an effort to retrieve boundary-layer heights for various research flights and time periods of interest to other researchers.

The analysis by Kok and colleagues of CO measurements along the transect portion of the ACE-1 flights shows a clear hemispheric gradient, with the highest concentrations at the most northerly latitudes. High concentrations of CO were also measured between the equator and 20°N. The sources for these elevated mid-latitude concentrations could not be determined. The CO₂ concentrations also show a strong latitudinal gradient, with the highest concentrations in the Northern Hemisphere. Over the South Tasman Sea there was a strong vertical concentration gradient for CO₂, with the lowest concentrations at the ocean surface. Work is underway to derive values for CO₂ flux to the ocean from these data. The hydrogen peroxide data from this study is being analyzed by Andre Prevot of ETH in Zurich, Switzerland, who was a visitor at NCAR during the ACE-1 study.

Baumgardner is investigating the coupling of microphysical and optical properties of the aerosols measured during ACE-1. He presented results of his study at the 1997 conference of the American Association for Aerosol Research that showed the strong dependency of aerosol volume and optical scattering on fluctuations of relative humidity. Papers from both Baumgardner and Kok have been accepted for publication in the special issue of Journal of Geophysical Research on ACE-1.

Hong Kong Air Quality Study. Data analysis was completed on the Hong Kong study, a measurement program made with the NCAR King Air in 1994. Major results of this study have been published this past year in JGR, detailing the gas and aerosol chemistry of the region. Additional analysis has been done on the emissions ratios from the Hong Kong Territory and the People's Republic of China (PRC). This analysis shows that the Hong Kong territory has a very low CO/NO_y emission ratio, approximately 4, due probably to the relatively small number of motor vehicles in that region. The PRC has a much higher emission ratio, about 16. The causes for this high ratio have not been determined. The results of the latter analysis will be published in Atmospheric Environment during 1998.

Cooperative Air Surface Exchange Study (CASES). Greg Kok participated in this NOAA program designed to examine fluxes of heat, moisture, and some chemical species over Eastern Kansas. The measurements of ozone fluxes were made from the NOAA Twin Otter aircraft in collaboration with Bob McMillin and Winston Luke of NOAA. The data will become part of the general CASES archive. A detailed analysis of the ozone fluxes will be made during 1998.

Project Azteca. Preparations are underway for Project Azteca, to measure air quality in Mexico City during November 1997. Greg Kok and Darrel Baumgardner, in collaboration with Graciela Raga (University of Mexico), Sonia Keidenweiss (Colorado State University), and T. Novakov (Lawrence Berkeley Laboratory), are setting up gas, aerosol, and solar radiation measurement systems on a hillside south of Mexico City. The air chemistry measurements will include ozone, nitrogen oxides (NO, NO₂, and NO_y), carbon monoxide, and sulfur dioxide. Aerosol characteristics will be measured with a number of sensors. This experiment is a pilot project to demonstrate the need for comprehensive measurements for better understanding the origins of aerosols and gases in the Mexico City Basin; the microphysical, optical, and chemical composition of aerosols; and the impact of these pollutants on visibility.

NCAR FY97 ASR | ATD FY97 ASR | ATD/SSSF Report