• The Aerosol Characterization Experiment (ACE-1) was ATD's most challenging field deployment during the year. Led by Barry Huebert of the University of Hawaii, this important Southern Hemisphere study was the first in a series of experiments to characterize the chemical and physical processes controlling atmospheric aerosols and their role in radiative climate forcing. For this first study focusing on naturally occurring background aerosols in the remote marine atmosphere, ATD deployed the C-130 aircraft and three sounding/profiler systems (two shipborne and one ground-based) to Hobart, Tasmania. The C-130 carried a large number of instruments supplied by PIs from eight universities, as well as two newly developed NCAR measurement systems (an advanced multi-user aerosol inlet and a dual-wavelength backscatter lidar). The resulting instrumentation payload of almost 15,000 pounds was the largest ever carried by an NCAR aircraft. The flight program started with a Pacific transect from near the North Pole to near the South Pole, then moved to an extensive series of flights over the Southern Ocean from Hobart. The resulting highly unique dataset is now being intensively analyzed.

  • ATD field-tested its new highly portable, S-band dual-polarimetric Doppler radar (S-Pol) (128Kb), this summer at the Front Range Airport near Denver. S-Pol is NCAR's second dual-polarimetric radar. Its predecessor, CP-2, was expensive to transport and set up because it required the construction of a massive concrete pad at each site. By contrast, S-Pol can be assembled on a base of four seatainers -- the same ones in which it is shipped -- at any stable, accessible site in the world. Not only is S-Pol convenient to ship and assemble, but it sports a much improved antenna. The 28-foot-diameter dish is sturdy in winds up to 50 miles/hour and can be covered with a radome if necessary in more severe weather. A new data processor using modern digital technology further supports S-Pol's advanced status.

  • The results from S-Pol's first field study are noteworthy in that they represent a technological breakthrough in quantitative, remote precipitation measurements. S-Pol's new antenna provides more accurate measurements than CP-2, allowing researchers for the first time to discriminate between different types of precipitation. The radar's dual-polarimetry technology proved its state-of-the-art precision on 12 July 1996 by distinguishing between the large, flat raindrops causing Buffalo Creek to flood, and the relatively round hailstones pounding the eastern prairie. Traditional radar (the National Weather Service's nationwide network, WSR-88D, formerly known as NEXRAD) showed both areas as having similarly heavy rain and/or hail, without distinguishing between the two.

  • The development of the advanced Airborne Vertical Atmospheric Profiling System (AVAPS)/GPS Dropsonde System was close to completion at the end of FY 96. This work has been supported by NOAA and the Deutsche Forschungsanstalt fuer Luft- und Raumfahrt (DLR, Germany). AVAPS has now progressed to the point where all the NOAA data systems (two four-channel systems plus spares for the NOAA G-IV aircraft and two four-channel systems plus spares for the NOAA P-3 aircraft) have been delivered, and the initial flight testing has been completed. Both high-level (45,000-foot-altitude) and low-level (22,000-foot-altitude) drop tests have been completed, including intercomparison tests in which sondes were dropped from both the G-IV and the P-3s. Data taken by the AVAPS system on the G-IV and by a second system installed in a leased Lear 36 aircraft are expected to play a key role in the Fronts and Atlantic Storm Tracks Experiment (FASTEX), scheduled for early 1997. The DLR four-channel AVAPS system is currently being built and will be installed on the DLR Falcon aircraft in March 1997. NCAR has transferred the technology to the public sector by licensing a commercial firm (Vaisala, Inc.) to build future GPS sondes and data systems. This effort is led by Hal Cole and Terry Hock.

  • The Electra aircraft was significantly upgraded during FY 96, with the work carrying over into FY 97. Upgraded cabin safety features include new 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 (WARDS) to record and display data from the Electra nose radar; provision for multiple displays of ELDORA and nose-radar data; and installation of an improved, switchable intercom system throughout the cabin. During this renovation period, RAF also carried out a mandated five-year recurrent airframe inspection. The inspection confirmed that the airframe is in excellent condition, requiring only minor repairs.

  • The Community Aerosol Inlet (CAI) is a major new airborne instrument developed in a joint project by 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, is designed to minimize particle losses due to turbulence and deposition, a known problem in other inlet systems. The CAI was deployed successfully for the first time during the ACE-1 project. A test program will be conducted in spring 1997 to further characterize the flow field and aspiration efficiency of the new instrument.

  • Major efforts on the SOLO data perusal and editing software by Dick Oye, Sherrie Frederick, and Wen-Chau Lee have significantly improved the capabilities of the software. SOLO is now ATD's primary package for comprehensive, window-oriented display, analysis, and editing of radar and lidar data. During FY 96, a number of new features were added to SOLO, including capabilities for flexible data editing, batch editing, time-series displays, supporting a number of new platforms (S-Pol, SABL, 2-micron lidar, etc.), and porting to the Linux operating system. For compatibility purposes, SOLO also translates a variety of data formats during ingest.

  • Another major advance in radar data acquisition and signal processing was made by Eric Loew and Mitch Randall in FY 96 with their extension of the PC-Based Integrated Radar Acquisition System (PIRAQ) to VMEBus applications (VIRAQ). The new VIRAQ radar data acquisition system extends the PIRAQ system with a dual-channel, digital, intermediate-frequency signal processor and a digital signal-processor (DSP). The main difference in the two systems is that the VIRAQ plugs into a VMEBus and has two DSPs, while the PIRAQ requires a conventional personal computer and uses one DSP. These advanced boards were tested successfully as part of the S-Pol radar during the NEXRAD/S-Pol Precipitation Measurement program, and also are used in WARDS.

  • A unique field experiment called Lidars in Flat Terrain (LIFT) was designed and led by visiting ATD scientist Shane Mayor in summer 1996. This program was closely linked with the Flatland Observatory Project II in central Illinois. ATD observing systems used in LIFT included two ISS stations, three Flux-PAM stations, the Staring Aerosol Backscatter Lidar (SABL, 106Kb ), and one enhanced Flux-PAM (66Kb) for ozone flux measurements at one of the ISS sites. Other LIFT instrumentation included NOAA/ETL's 2-micron High-Resolution Doppler Lidar (HRDL, 121Kb), and the Ozone Differential Absorption Lidar (DIAL, 56Kb). LIFT's objective was to study the high-resolution structure of winds, aerosol, and ozone as the daytime boundary layer grows and decays. The data gathered during the four-week experiment will also be used to evaluate lidar and profiler techniques for quantifying fluxes, turbulence, and boundary-layer height. The combined data from the co-located, vertically-pointing, high-resolution lidars are expected to provide an unprecedented look at evolving boundary-layer features.

  • The first dense mesoscale deployment of Global Positioning System (GPS) receivers for meteorological purposes was conducted by ATD during the ARM GPS/Water Vapor Experiment in September 1996. During this program, SSSF operated six newly acquired GPS receivers capable of obtaining a vertically integrated estimate of atmospheric water vapor above the sensor. The effort was a joint project with NOAA/ETL, which also operated a GPS receiver network over this region, and UCAR/UNAVCO, which is processing the data. Other ARM participants operated a variety of remote and in situ water-vapor sensors, co-located with one of the GPS receivers. The goals of this experiment were (1) to gain experience with this instrumentation for future deployments, (2) to assess the ability of the sensors to provide water-vapor measurements with high spatial and temporal resolution, and (3) in collaboration with NCAR/MMM, determine whether these measurements significantly improve the accuracy of predicted water-vapor profiles through use of a variational data-assimilation model.

  • A new collaborative project was initiated in FY 96 between ATD and the German DLR to develop a small, low-powered, lightweight, inexpensive, fast ozone sensor suitable for dropsonde use. In its current state of development, the prototype sensor is housed in a small cylinder, 7 cm in diameter and 18 cm long, meeting the size, weight, power, and cost requirements for dropsonde applications. However, an undesirable sensitivity to humidity needs to be corrected before the ozone sensor will be fully satisfactory. Research into modification of the chemiluminescent target material for this purpose is currently being pursued in Germany. The prototype sensor has already been used for tower-based fast-ozone measurements during LIFT in summer l996.

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