Mission and Goals

The mission of ATD's Surface and Sounding Systems Facility (SSSF) is to provide surface-based in-situ and sounding measurements, and associated data-processing and analysis software, in support of atmospheric research. The Facility also engages in related scientific research to maintain a leadership role in the development and operation of state-of-the-art measurement systems. SSSF engages in the following major activities:

• Operation of advanced surface and upsonde/dropsonde direct-sensing systems and ground-based microwave and acoustic profiling systems to support field research of atmospheric scientists.
• Development of new in-situ and remote surface, profiling, and sounding systems in cooperation with other ATD groups, NCAR divisions, universities, NOAA and other government agencies.
• Development of new data-telemetry systems to support ATD’s field-data communication needs.
• Development of operational and analytical techniques for optimum use of field facilities, including techniques for sensor calibration, instrument deployment, data collection, and data analysis, and transfer of these techniques to the atmospheric sciences community.
• Scientific research and engineering development to support, demonstrate, and advance these capabilities.
• Support of university educational programs by providing state-of-the-art observing systems for student training, and by providing lectures upon request pertaining to meteorological instrumentation and observational research.

The traditional emphasis of the Facility has been on supporting mesoscale and boundary-layer experiments in keeping with national scientific priorities for research in atmospheric chemistry, mesoscale precipitation systems, cumulus convection, boundary-layer processes, and air-surface interaction. Recent emphasis has also included process study experiments relevant to climate change studies. SSSF has focused significant resources over the past year on numerous requests for field measurements. SSSF attempts first to satisfy all approved community requests for field support. Next in priority is to optimize the use of remaining facility resources to develop new observing systems and improve existing systems to meet the field-support requirements of major experimental programs of national interest, such as the U.S. Global Change Research Program (GCRP) and the U. S. Weather Research Program (USWRP).

Field Support Activities

NASA WindRad Program. NASA/JPL has developed a microwave radiometer with the capability to measure surface winds over the ocean. This project was a test of the radiometer’s performance in this application. SSSF deployed a dropsonde system on a NASA P-3 flying out of Wallops Island, VA to provide independent wind measurements for calibration and verification of the radiometer data. Because the GPS dropsonde system was not available during this time period, a dual Lightweight Loran Digital Dropsonde (L2D2) system was used by SSSF.

Project Juneau. NCAR/RAP investigators requested the use of one of SSSF’s ISS wind profilers at a site near the Juneau, Alaska airport. SSSF personnel set up the system, optimized its operation in order to reduce ground clutter, and monitored the data in Boulder remotely during the project. Another leased profiler (from Radian Corporation) was installed in another area near the airport. RAP is using the profiler and anemometer data from several key mountain-top instruments to better understand the turbulence generated by high-wind events and to develop an operational system for better prediction and warning of turbulence events. This system consists of turbulence-detecting algorithms and a turbulence display system for the Juneau Area Weather System (JAWS). Data from the two profilers were taken from mid-December 1996 through April 1997. Several suitable turbulent wind events occurred during that time period.

Fronts and Atlantic Storm-Track Experiment (FASTEX). This program was conducted over the North Atlantic during January - February 1997. SSSF supported both the airborne and the surface portions of FASTEX. The newly developed NCAR GPS dropsonde was used on two NOAA aircraft (the G-IV and a WP-3D (16K)) as well as on an NCAR-leased Lear 36 aircraft. A total of 750 GPS sondes were dropped during the experiment, primarily by the G-IV and the Lear 36. The measurements are being used to study either objective target areas (sensitive areas where small analysis errors will amplify most rapidly), or subjective target areas (flow structures associated with the early development stages of cyclogenesis). SSSF also provided Integrated Sounding Systems (ISS) on board two of the research ships, as well as operators for those systems. One ISS was installed on the French R.V. Le Suroit and the other was installed on the U.S. R.V. Knorr. When possible, the FASTEX ships were positioned near dynamically sensitive structures, such as surface fronts and upper jet streams (185K). The two ISS systems provided radiosonde profiles and wind-profiler, Radio-Acoustic Sounding System (RASS), and in-situ surface atmospheric measurements to document atmospheric boundary-layer structure and to help characterize surface fluxes on both sides of the surface fronts. 

Airborne Measurements of Oceanic Wind-Vector Fields Over the Labrador Sea Using Passive Polarimetric Radiometry (LABSEA). The LABSEA experiment was a test of the Georgia Tech scanning polarimetric microwave radiometer and its ability to measure ocean surface winds. The radiometer was flown on the NASA DC-8 in January 1997 over a site in the Labrador Sea that contained a moored instrument platform. The moored platform collected various data including wind speed and direction, air and water temperatures, barometric pressure, and directional wave spectra. The original request for dropsondes was for the use of the LOD2 Omega system but in further conversations with the PI it was determined that near-surface wind measurements were critical to the experiment. The near-surface winds measured by Omega are not very highly resolved because of the long smoothing interval (240 sec) required for the noisy Omega data. SSSF was able to put together a two-channel GPS dropsonde system for use on this project that provided the necessary boundary-layer wind measurements with high resolution and accuracy.

Tropical Ocean Climate Study (TOCS). SSSF also participated in the TOCS experiment on board the R.V. Kaiyo (17K) from 26 January to 1 March 1997. The ship is operated by the Japan Marine Science and Technology Center (JAMSTEC). This cruise took place in the tropical western Pacific in association with servicing of the ocean research buoys in that region. The research vessel was instrumented for atmospheric measurements with the Staring Aerosol Backscatter Lidar (SABL) made available from ATD/RSF, a 915-MHz wind profiler/RASS belonging to the NOAA Environmental Technology Laboratory (ETL), a surface meteorological station with an enhanced surface radiation measurement package deployed by Brookhaven National Laboratory (BNL), and a radiosonde system provided by JAMSTEC. During this cruise, SSSF staff aided in the deployment of the SABL system, the wind profiler, and RASS, and also operated a tethered sounding system. The tethered system used either radiosonde balloons or kites depending upon the wind speed. The cruise was designed to study the diurnal cycle of clouds, precipitation, and surface radiation; to characterize the low-level moisture in order to assist the correction of soundings taken during the TOGA COARE project; and to better understand atmospheric-oceanic interactions. The timing of the cruise was such that it took place during the start of the 1997 El Nino, so a truly unique data set was collected. Research is underway through collaborations between NCAR, JAMSTEC, and BNL.

Cooperative Atmosphere Surface Exchange Study (CASES-97). SSSF deployed Flux-PAM and ASTER systems at eight sites and CLASS stations at three sites in support of this first experiment to take advantage of the newly instrumented CASES facility. For the CASES program, the Walnut River watershed in south-central Kansas was instrumented to collect a dataset to assist in understanding the total water budget over the watershed. The CASES-97 experiment focused on characterizing the atmospheric boundary layer and its interactions with the surface in this region. The sensible and latent heat-flux measurements by the PAM and ASTER systems were central to this goal. PAM and ASTER were merged for the first time in this program. This allowed high-rate data to be saved at two of the sites. The CLASS soundings also were important for characterizing the thermodynamic structure of the boundary layer. These data will be shared with the PIs of the JETEX experiment, which utilized three ISSs and ran concurrently over a wider region.

Low-Level Jet Experiment (JETEX-97). SSSF supplied three ISSs in support of this experiment, which took place during the month of May 1997. The JETEX program was conducted in conjunction with CASES. JETEX was a study of the nocturnal low-level jet (LLJ), which plays an important role in the development and evolution of mesoscale convective systems over the U.S. Great Plains. The LLJ is believed to supply warm, moist air and promote mesoscale convergence, essential factors for the development of mesoscale convective systems. Past studies of the dynamics of the LLJ have been hindered by the lack of high-resolution wind-profile data at the altitudes where the LLJ occurs. The first range gate on the ISS 915-MHz wind profilers is located at 60 m, and therefore high-resolution data were obtained below and through the core of the LLJ.

Radar and Aircraft Cloud Electrification Studies (RACES). SSSF supported the RACES project by providing its Mobile CLASS system with an operator during the period 29 May – 8 July 1997. The project was located in the Greeley, CO area in the vicinity of the CSU-CHILL Doppler radar site. The RACES project is a study to determine the correlation between positive cloud-to-ground lightning flashes from High Plains thunderstorms and the formation of large hail in the storms. The Mobile CLASS system provided vertical-profile data of winds, temperature, humidity, and pressure to characterize atmospheric conditions in the vicinity of the storms, plus the ability to take the sounding to the thunderstorm environment rather than have to wait for a storm to come over the sounding site.

Hurricane Ocean Winds (HOW). This project was a continuation of the November 1996 NASA WindRad project that SSSF supported earlier in the year. The objectives of HOW were similar to those of the earlier project, which were to test and calibrate the newly developed NASA/JPL ocean surface-wind-measuring microwave radiometer. SSSF supported this project with its new GPS dropsonde system to provide high-resolution boundary-layer winds for comparison with the radiometer measurements. The PI had hoped to be able to test the radiometer in several hurricanes, but measurements could be made only in the one storm (Linda) that occurred during the field program.

Surface Heat Budget of the Arctic (SHEBA). Four PAM-III (224K) (Portable Automated Mesonet) stations and a GPS CLASS system were deployed in fall 1997 in support of this 13-month field program to study the surface heat budget of the Arctic ice pack. The field site (199K) is a camp placed on the drifting ice in the Beaufort Sea north of Alaska, and the PAM-III stations were placed at sites chosen to sample the diversity of local ice and snow conditions. In addition to the standard meteorological measurements of wind, pressure, temperature, and humidity, the PAM-III stations are measuring turbulent fluxes of momentum and heat, incoming and outgoing fluxes of long-wave and short-wave radiation, and the surface heat flux at the snow/ice boundary. The data are telemetered in real-time to the project field base located on a Canadian ice-breaker research ship (132K) frozen into the pack ice for the duration of the project. The PAM stations were heavily modified prior to their deployment to produce electrical power with propane thermoelectric generators and to warm the electronics by housing them with the generators. Other special modifications include the use of GPS receivers and electronic compasses to continuously monitor station location and orientation, as well as to provide accurate time-keeping.

Development Activities

Colorado University Flux Facility (CUFF). This development, a collaboration with the Department of Environmental Population and Organismic Biology at the University of Colorado, has been undertaken to to produce an instrument that can obtain long-term surface-flux measurements of biologically important species. The design of CUFF drew heavily upon that of SSSF’s ASTER facility, and thus is compatible with that system. CUFF is to be deployed on a new tower located at Niwot Ridge. The basic components of the system have been successfully field-tested during field programs at Oak Ridge and at the Duke Forest Reserve to measure isoprene and carbon-dioxide fluxes.

Dual-Wavelength Net Radiometer. Tony Delany and Steven Semmer have developed an advanced net radiometer to increase the accuracy of single-instrument measurements of surface radiation flux. Conventional net radiometers make separate determinations of short-wave and long-wave incoming and outgoing radiation which are subsequently differenced, resulting in loss of accuracy. The new system increases accuracy by making differential net short-wave and long-wave radiation determinations. The system was designed to utilize numerically controlled machining techniques to substantially reduce manufacturing costs. Other advanced features include data acquisition and manipulation capabilities and integrated ventilation and leveling. The fabrication of this system is awaiting approval of ARM funding.

Infrared Water Vapor Sensor. Steven Oncley, Steven Semmer, Chuck Frush (ATD/RSF), and Wim Kohsiek (KNMI, The Netherlands) have constructed a prototype, low-power, infrared humidity sensor for flux measurements. A project goal is sensor operation at less than 2 W of electrical power, which has now been achieved. Although the signal level is as expected, the signal noise in the prototype is too high. Work on both the mechanical stability and electronic noise immunity is continuing.

Integrated Surface Radiation Measurement System. Tony Delany and Steven Semmer have developed an integrated system to measure surface radiation flux. The system employs commercially available Eppley and Kipp/Zonen pyranometers and pyrgeometers, modified to ensure proper ventilation and mounted on a leveling platform. A custom computer algorithm provides appropriate corrections for dome heating and sensitivity of the pyrgeometer to short-wave radiation. The new system has been used with the ASTER facility and with the newly deployed PAM-III surface-flux facility for the Flatland and CASES field programs, enabling accurate determination of the radiative surface energy budget. Variants of the system have also been fabricated for deployment as part of the international GEWEX Asian Monsoon Experiment (GAME) program in Asia. The system will be undergoing further development to improve its versatility. Currently it is deployed in the Arctic as part of the SHEBA program.

Multiple Antenna Profiling Radar (MAPR). MAPR uses newly developed spaced-antenna techniques to measure vertical profiles of wind velocity through the lower troposphere. The goal of MAPR is to obtain better accuracy and much higher time resolution than conventional wind profilers. The latter measure winds through the Doppler technique, using multiple beam directions. Measurements from MAPR are being compared directly with those from Doppler systems. Several techniques for analyzing spaced-antenna signals, based upon new theoretical concepts, are being tested with MAPR. To improve signal quality, a larger antenna and a more powerful transmitter are being considered. Software upgrades are being incorporated to allow operation under a UNIX (multi-tasking) operating system, and to shift wind computation from a post-processing step to a real-time process.

Ozone Sensor Development. A collaborative project with DLR (Germany) has led to the development of a small, low-powered, lightweight, inexpensive, fast ozone sensor suitable for dropsonde use. The prototype sensor is 7 cm in diameter and 18 cm long, and can be fabricated for a cost of approximately $500. The sensor has not yet been mass-produced for dropsonde use, but the prototype sensor has been used for tower-based fast-ozone measurements. During the Flatlands-96 field program the sensor was deployed as part of the PAM-III surface-flux facility, and ozone fluxes were determined. Ozone concentrations measured with this new sensor were comparable to those obtained with sophisticated instruments using gas-phase chemiluminescense. Further development of this new sensor is being pursued to determine if an undesirable sensitivity to moisture may be alleviated by the use of a different chemiluminescent target material.

Portable Automated Mesonet III (PAM-III). Three additional PAM-III (Flux-PAM) surface meteorological stations were constructed in early 1997, allowing the deployment of a network of six PAM-III stations to support the CASES field program in April – May 1997. A particular highlight of this field program was the concurrent instrumentation of two additional CASES field sites, using components of the ASTER facility, to also measure fluxes of ozone and carbon dioxide and to meet the investigators' request for archival of high-rate turbulence data for detailed post-project analysis. In preparation for the simultaneous deployment of these formerly separate facilities, the PAM and ASTER data communications, display, and archival software were completely integrated so that the two are now essentially a single, unified field facility. A second Flux-PAM station has also been completed for use by the Japanese National Committee for the GAME program, and three additional stations will be constructed for GAME in late 1997. Over the past year, testing and development also has continued to refine and quantify the performance of standard meteorological as well as flux-measuring sensors. Particular effort has been devoted to the measurement of water-vapor fluxes. This has involved continued evaluation and development of the bandpass covariance technique, as well as the prototype development of a low-cost, fast-response, infrared-absorption hygrometer.

Real-time Data Communications System for Field Projects. Real-time transmission and distribution of data sets has become a standard SSSF procedure over the past year. Increased availability (in the field) of communication service vendors (e.g., Internet Service Providers), and greater convexity at the PIs’ home institutions have allowed SSSF to route data products directly from the field observing system to the participating scientists. Data sets are also routinely monitored in Boulder by SSSF staff. A stable and consistent interface to the Global Telecommunications System (GTS) has been established, which allows SSSF to place WMO-formatted messages on the GTS as needed. This GTS gateway system was implemented and first used in the FASTEX project, and was easily configured for use in the current SHEBA experiment. Prior to this, access to the GTS by SSSF had been difficult.

Relaxed Eddy Accumulator (REA). Using the original SSSF instrument as a basis, David Bowling (University of Colorado) and Tony Delany (SSSF) designed and constructed a new REA by using the latest version of the PAM-III sensor board, plus PC-based software prepared by Bowling in cooperation with SSSF engineers. The REA was deployed at the Oak Ridge deciduous forest site and successfully measured isoprene fluxes. A more advanced REA has now been fabricated to determine carbon and oxygen isotope ratios associated with the surface fluxes of carbon dioxide and water over forests, to investigate the isotopic signatures of plant metabolic activities.

Scientific Data Management System. A prototype of the ATD Informational Retrieval System (AIRS) went through several iterations over the past year, with significant redesign carried out based on experience gained with SSSF data sets. A final version of AIRS was completed near the end of FY 1997. This version benefited significantly from the inclusion of the diverse types of data products created by SSSF observing systems. AIRS will now be evaluated in order to better understand database architecture, performance, and suitability issues relating to scientific data management within ATD.

Wind-Profiler Antenna Test Range. A basic antenna test range has been constructed at NCAR’s Marshall field site. Built cooperatively by researchers from SSSF, several NOAA labs, and Radian Corporation, the range is being used to test clutter-screen technology for lower atmospheric wind profilers. Signal contamination by moving clutter can limit the ability of these profilers to make accurate measurements, especially at the lowest altitudes, and a variety of clutter-screen designs and edge treatments for existing clutter screens have been proposed to address this problem. Because most clutter comes from diffraction over a clutter screen towards the horizon, the range measures the relative radiation pattern at low elevation angles, and can test various screens and edge-treatment combinations. Tests to date have shown a redistribution of the near-horizon radiated energy to different elevation angles. An optimum configuration is still being sought.

Wind-Profiler Real-Time Software Development. The MAPR real-time control software reached a milestone near the end of the year, with the completion of UNIX-based multi-tasking software for system operation and real-time data processing. The new software is able to collect time series, compute power spectra, and save data products in final format. Implementation of real-time processing algorithms, which could include the calculation of correlation functions, structure functions, and cospectra, will begin shortly. The new software system is more easily maintained and more flexible than the previous DOS-based version.

Research Activities

Boreal Ecosystem-Atmosphere Study (BOREAS). Analysis of data obtained using the NCAR/NSF Electra during the BOREAS field program in 1994 is nearing completion. Steven Oncley, along with Don Lenschow (NCAR/MMM), Teresa Campos (ATD/RAF), Ken Davis (University of Minnesota), and Jakob Mann (RISOE, Denmark), found that the area of lakes in the boreal forest is quite important in determining the net surface fluxes of heat, water, carbon dioxide, and ozone over regional scales. The variation of conifer species within the forest did not have a major affect on the surface fluxes, although the change from deciduous to conifer trees was significant. These results will be published in a special BOREAS issue of the Journal of Geophysical Research.

Integrated Data Assimilation and Sounding System (IDASS). Supported by the DOE ARM program, the IDASS seeks to develop improved measurement and data-assimilation strategies. The IDASS development program, led by David Parsons, includes the MAPR development program, the TOCS field deployment, and a joint ATD-MMM data-assimilation task. The data-assimilation effort focuses on real-data tests of the variational and nudging assimilation strategies incorporated into the NCAR/Pennsylvania State mesoscale model (MM5). The current assimilation work includes testing the accuracy of the Newtonian nudging technique during a ten-day field experiment conducted at the ARM/CART site. For this test, the operational data were supplemented by a network of ISS and rawinsonde stations, and the variational assimilation system was used to test the impact of assimilating GPS water-vapor measurements.

Lidars in Flat Terrain (Lift). Detailed examination and analysis of the LIFT dataset began during FY 1997. Three lidars were deployed at LIFT, a backscatter lidar (SABL), a Doppler lidar (HRDL), and an ozone DIAL. In addition, two ISS and three Flux-PAM stations were deployed for a companion field study, Flatland Observatory Project II. The resulting dataset is being used to investigate boundary-layer turbulence, shallow nocturnal low-level jets, and entrainment through the boundary-layer top. Stephen Cohn (SSSF), Shane Mayor (now at the University of Wisconsin), and Christian Grund and Robert Banta (NOAA/NCAR joint optical remote sensing group) are participating in this analysis.

Spaced-Antenna Theoretical Development. Theoretical developments associated with the MAPR profiler continued during FY 1997. These include estimation of the precision of spaced-antenna and Doppler-beam-swinging wind measurements, derivation of turbulence variables, and testing of a generalized theory treating measurements in the presence of horizontally anisotropic refractive-index irregularities. Data from the BLX-96 experiment are being used in these tests. Stephen Cohn (SSSF) is collaborating in this work with Chris Holloway (NTIA/ITS), Richard Doviak (NOAA/NSSL), and Richard Lataitis (NOAA/ETL).

Tropical Ocean - Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). Six Integrated Sounding Systems were deployed during the TOGA COARE program. Through the use of data from these and other observing systems, David Parsons is investigating several topics. One project is a study of the mechanism causing extremely dry air to occur in the middle troposphere over the equatorial warm pool. In this study it was found that the dry air had origins in the mid-latitude westerlies and was advected equatorward in association with mid-latitude baroclinic waves. A paper on these findings has been submitted to the Journal of the Atmospheric Sciences by Parsons and Yoneyama (JAMSTEC). Parsons is also investigating the impact of this dry-air intrusion on the atmosphere-ocean system over the warm pool. One finding was that the dry air was moistened over the tropics by relatively shallow convective clouds associated with an evening maximum in precipitation. The mechanism for the latter appears to involve the diurnal cycle of latent and sensible heat fluxes, the diurnal interplay of long-wave radiational loss, and the absorption of solar energy by water vapor in the clear air. A manuscipt on these results has been prepared by Parsons, Yoneyama, and Redelsperger (CNRM) for submission to the Quarterly Journal of the Royal Meteorological Society.

U.S. Weather Research Program (USWRP). Under USWRP support, David Parsons is collaborating with researchers in NCAR/MMM (Bill Kuo, Jimy Dudhia, and Yong-run Guo) to study one option for improving the model prediction of the vertical profile of water vapor and subsequent prediction of convection. The improvement of the treatment of water vapor is one of the core goals of the USWRP. The work initially is using the variational version of the MM5 mesoscale model, with four test cases selected from the ARM GPS experiment, to determine the impact of assimilating GPS measurements of column-integrated water vapor into the model. Thus far the assimilation technique has improved the model prediction of integrated water vapor and convection, but has only modest impact on the vertical profile of water vapor. Additional data, beginning with surface measurements of water vapor and measurements from wind profilers, are being included to see if further improvements are realized.

Natural Emissions of Oxidants Precursors - Validation of Techniques and Assessment (NOVA-96). This field program, conducted in the Tidewater region of North Carolina, was designed to study techniques for measuring fluxes of nitrogen oxides. Measurements were made using both micrometeorological and enclosure techniques over cropland having a well-established vegetation canopy. It was discovered that the enclosure techniques overestimated the net emission to the free atmosphere when compared with surface-layer measurements by eddy correlation. The investigators believe this is due to redeposition of the nitrogen oxides onto the plant surfaces. Results from the data analysis will be reported at the fall 1997 AGU meeting.